Abstrict In regard to an output of an intake flow meter for an internal
combustion engine, a pulsation error can be reduced and dispersion
in correction at the time of correction of response delay (a recovering
of response delay) is reduced. A digital device is used for pre-processing
of a control unit for inputting a flow rate measuring signal. An
output voltage of the flow sensor is converted into a digital value,
the digital value is converted into a flow rate and adds a response
delay. The control unit detects a degree of response delay in reference
to dispersion in a clock signal so as to perform response delay
recovering and reduce dispersion of the response delay.
Claims What is claimed is:
1. A thermal flow meter having a flow rate detecting element for
outputting a non-linear signal in response to a flow rate comprising:
a response delay element for adding a response delay during a process
for processing an output signal of said flow rate detecting element;
and means for transmitting information on this response delay to
the control unit having a response delay recovering function.
2. The thermal flow meter according to claim 1 wherein the response
delay added by said response delay element is a time constant which
is larger than a response delay of said flow rate detecting element
itself.
3. The thermal flow meter according to claim 1 wherein information
on said response delay is a parameter indicating dispersion in response
delay.
4. A control system comprising a thermal flow meter for outputting
a non-linear signal in response to a flow rate; a pre-processing
means for performing a pre-processing for returning an output of
said flow meter to a non-linear output after a linear processing
and a smoothening operation; and a control unit for calculating
an amount of control of a controlled equipment on the basis of said
flow meter that is pre-processed, wherein said pre-processing means
has a function for outputting a parameter indicating a degree of
response delay generated by smoothening an output of said flow meter
to said control unit; and said control unit has a function for correcting
said response delay and a function for reducing a dispersion in
correction of response delay on the basis of said parameter.
5. A control system comprising a thermal flow meter for outputting
a non-linear signal in response to a flow rate; and a control unit
for calculating an amount of control of a controlled equipment on
the basis of said flow meter that is pre-processed, wherein there
is provided a response delay element for adding a response delay
to said output signal at a pre-processing step when an output signal
of said flow meter is inputted to said control unit; and said control
unit has a function for correcting said response delay by using
information on this response delay.
6. The control system according to claim 5 wherein information
on said response delay is a parameter indicating dispersion in response
delay.
7. The control system according to claim 5 wherein whether or
not said output signal is passed through said response delay element
can be selected in response to an instruction from said control
unit or other external units at a pre-processing step when an output
signal of said flow meter is inputted to said control unit.
8. The control system according to claim 5 wherein an output signal
of said flow meter is processed in a digital manner before being
inputted to said control unit, and information on said response
delay is a clock signal used for a digital processing.
9. The control system according to claim 5 wherein an output signal
of said flow meter is a frequency output and processed in a digital
form before being inputted to said control unit, information on
said response delay is a clock signal used for the digital processing,
and this clock signal is overlapped on a frequency of the output
signal of said flow meter and outputted.
10. The control system according to claim 5 wherein an output
signal of said flow meter is a frequency output synchronized with
a reference signal of frequency, processed in a digital form before
being inputted to said control unit, information on said response
delay is a clock signal used for the digital processing and this
clock signal is counted by said reference signal.
11. The control system according to claim 5 wherein a degree of
response speed of the output signal from said flow meter can be
selected in response to a request from said control unit.
12. The control system according to claim 5 wherein a form of
the output signal from said flow meter can be selected in response
to a request from said control unit.
13. The thermal flow meter according to claim 1 wherein said flow
rate detecting element and said response delay element are integrally
formed on a silicon substrate.
14. A flow rate measuring system comprising a thermal flow meter
for outputting a non-linear signal in response to a flow rate and
a plurality of transmittance elements for processing an output signal
of said flow meter and transmitting it to a device related to said
flow meter, wherein said related device has a function for detecting
at least a response delay of said transmittance elements or dispersion
of response delay, and a function for correcting a response delay
of said flow meter using a detected signal concerning this response
delay.
Description BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a thermal flow meter for detecting
a flow rate of fluid such as air and the like and a flow rate measuring
device utilizing the thermal flow meter.
[0003] 2. Background Art
[0004] The thermal air flow meter using a thermo-sensitive resistor
such as a heat generating resistor and a temperature compensating
resistor and the like having a temperature characteristic can directly
detect a mass amount of air, so that this air flow meter is widely
used for measuring a flow rate of intake air for an internal combustion
engine of an automobile and the like. A detected air flow rate signal
is utilized for calculating a fuel injection amount of an electronic
controlled fuel injection device and the like.
[0005] The thermal sensitive type resistor such as a heat generating
resistor or the like of a type in which a platinum wire is wound
around a bobbin and coated with glass has been widely used and in
recent years, a thin film type in which a thin film resistor is
formed on either a ceramic substrate or on a silicon substrate and
a semiconductor type such as a polysilicon have been proposed.
[0006] As a flow rate detecting system, there have been provided
one system in which a heat generating resistor mounted at a flow
path is heated and controlled in such a way that a temperature difference
between it and the temperature compensating resistor may become
a predetermined difference and an electrical current flowing at
the heat generating resistor is directly detected; and the other
system in which temperature detecting resistors are arranged at
both sides of the heat generating resistor and a flow rate is detected
in reference to the temperature difference of the temperature detecting
resistors and the like. Both of them basically utilize a resistive
temperature characteristic which is changed when the thermo-sensitive
resistor heat exchanges with fluid.
[0007] When a flow rate detecting element showing a relative high
response delay in output is used, it is necessary to correct a response
delay by inversely changing a time constant in delay in response.
Such a correction as above for delay in response is carried out
at the sensor side in a step (a pre-processing) performed before
inputting a flow rate detecting signal to a control device (an engine
control unit, for example)(the gazette of Japanese Unexamined Patent
Publication No. 62012/1996 and the gazette of Japanese Unexamined
Patent Publication No. 14418/1999 and the like) and carried out
at the engine control unit (the gazette of Japanese Unexamined Patent
Publication No. 10752/1994 and the gazette of Japanese Unexamined
Patent Publication No. 13789/2003 for example).
[0008] The former is one example of a correction of characteristic
of the flow meter (a sensor) performed through a digital correction,
and the latter is one example of a system used at the engine control
unit for improving a measurement error caused by a response delay
of the sensor. Both of them are used for improving the delay in
response when a sensor showing a high delay in response is utilized.
[0009] In addition, the thermo-sensitive type flow rate sensor
has a non-linear output characteristic and also shows a pulsation
caused by a blow-by gas at the engine and the like. Since they are
causes for producing factors for error of output signal, the gazette
of Japanese Unexamined Patent Publication No. 94620/1999 and the
like have a description about one example in which the output signal
is digitally corrected at the sensor circuit side in a digital manner
and outputted to the engine control unit.
[0010] In the gazette of Japanese Unexamined Patent Publication
No. 821/1987 is described a technology in which when there occurs
a pulsation flow having a high pulsation amplitude of an amount
of intake air and accompanied with a partial inverse flow at a region
of low number of rotation of an engine with 4 cylinders or less
or at a region showing a heavy load operation, the pulsation is
to be corrected because an accuracy is decreased in the prior art
air flow rate device.
[0011] In addition, as a method for decreasing an error in a flow
rate output signal accompanied with a pulsation, the gazette of
Japanese Unexamined Patent Publication No. 316145/1999 and the gazette
of Japanese Unexamined Patent Publication No. 337382/1999 and the
like have a proposal that an error correction is carried as follows
by using either the engine control unit or the controlling microcomputer.
That is, a non-linear sensor output signal is converted into a linear
signal (a flow rate) under application of a map to convert it into
an air flow rate and the like, the pulsation amplitude is reduced
by a filter, then it is changed into a non-linear line again to
cause the amplitude of the final output signal to be reduced and
the error is reduced.
[0012] [Patent Document 1]
[0013] Gazette of Japanese Unexamined Patent Publication No. 62012/1996
[0014] [Patent Document 2]
[0015] Gazette of Japanese Unexamined Patent Publication No. 14418/1999
[0016] [Patent Document 3]
[0017] Gazette of Japanese Unexamined Patent Publication No. 10752/1994
[0018] [Patent Document 4]
[0019] Gazette of Japanese Unexamined Patent Publication No. 13789/2003
[0020] [Patent Document 5]
[0021] Gazette of Japanese Unexamined Patent Publication No. 94620/1999
[0022] [Patent Document 6]
[0023] Gazette of Japanese Unexamined Patent Publication No. 821/1987
[0024] [Patent Document 7]
[0025] Gazette of Japanese Unexamined Patent Publication No. 316145/1999
[0026] [Patent Document 8]
[0027] Gazette of Japanese Unexamined Patent Publication No. 337382/1999
[0028] In general, a relationship between an output of a thermal
flow meter using a heat generating resistor and a flow rate of air
is expressed by an equation as follows that is called as a King's
equation.
Ih.sup.2.multidot.Rh=C1+C2{square root}{square root over (Q)})(Th-Ta)
(1)
[0029] where, Ih denotes a heating current flowing in the heat
generating resistor, Rh denotes a resistance value of the heat generating
resistor, Th denotes a surface temperature of the heat generating
resistor, Ta denotes an air temperature, Q denotes a low rate of
air, C1 C2 denote a constant defined by the heat generating resistor.
[0030] It is generally applied to set an output of the air flow
meter that the heating current Ih is detected as a voltage value
using the detecting resistor. In the engine control unit used for
controlling an internal combustion engine, an output current value
of the sensor is converted into a flow rate value in reference to
the relation of the equation (1) to control a ratio between air
and fuel for the internal combustion engine and the like.
[0031] A certain linear forming means becomes necessary for detecting
a flow rate because a relationship between an output signal of the
thermal flow meter and an actual flow rate is a non-linear relation
(the four root of the flow rate is a voltage value) as indicated
in the equation (1).
[0032] In addition, when a dynamic flow variation element such
as a pulsation or the like is contained in a flow of fluid, there
has been already proposed to provide means as a method for reducing
its detection error to be performed such that after a flow rate
detecting signal is converted into a digital form, the signal is
converted into an air flow rate, changed into a linear form (linear
formation), the pulsation amplitude is reduced or pulsation is unified
using a low-pass filter and the like in a linear region; and after
these operations, the signal is returned back again to a non-linear
signal of its own original signal form as required and finally the
signal is changed into a signal hardly influenced by the pulsation.
[0033] In this case, the signal having pulsation amplitude reduced
using a low-pass filter and the like shows a response delay, so
that the control unit (the engine control unit, for example) requires
a processing for recovering its responding characteristic.
[0034] At that time, when the low-pass filter is constituted by
a digital means, the delay in response of the signal after reduction
in pulsation also produces dispersion (variation).
[0035] Accordingly, if a sufficient arrangement is not applied
to dispersion in delay of response, an effect attained through a
recovery processing is also widely dispersed even if the recovery
processing for the response characteristic is carried out at the
engine control unit side. Although the dispersion in response characteristic
after recovering operation is reduced if a high precision clock
signal as found in a crystal or the like at the digital means, a
cost of the sensor device is increased.
SUMMARY OF THE INVENTION
[0036] It is an object of the present invention to realize a flow
meter capable of reducing a pulsation error of the flow meter and
further capable of reducing dispersion in correction during a correction
in delay in response (a recovering of delay in response) under an
environment of pulsation of an internal combustion engine or a substantial
inverse flow.
[0037] In order to attain the aforesaid object, the present invention
basically provides means as follows.
[0038] A thermal flow meter having a flow rate detecting element
for outputting a non-linear signal in response to a flow rate has
a response delay element for adding a response delay during a process
(a pre-processing step) for processing an output signal of the flow
rate detecting element, and means for transmitting information on
this delay in response to the control unit having a response delay
recovering function. As the information on the delay in response,
there are provided some parameters indicating a degree in delay
in response or dispersion.
[0039] The control unit described above has a function for correcting
the delay in response described above and a function for reducing
dispersion in correction of delay in response on the basis of the
aforesaid parameters.
[0040] In order to reduce an error in measurement when the flow
rate shows a pulsation, for example, the pre-processing digital
device of the control unit comprises means for converting an output
voltage of the sensor detecting a flow rate, a converting means
(a linear processing means) for converting the digital value to
a flow rate, means for smoothening the flow rate value (for example,
this is a low-pass filter which becomes an element for adding the
delay in response), and means for converting the smoothened flow
rate value into a voltage value and the like. In addition, the digital
pre-processing device is provided with a selecting means for changing
over between the output signal after the pre-processing and a clock
signal of the device using a selecting signal and outputting it.
[0041] Then, the control unit (a device at a side for receiving
the output signal of the flow meter) detects a degree of the delay
in response in reference to dispersion of the clock signal, recovers
the delay in response and performs a correction for reducing the
dispersion.
[0042] With the aforesaid means being applied, it is possible to
increase a measurement precision for the pulsation or the flow rate
at the time of response without losing a characteristic of original
signal of the sensor during pulsation of the flow rate or during
a response in its transmission.
[0043] Further, as an element to add the aforesaid delay in response,
although the low-pass filter for smoothing the output signal corresponds
to the element, the element for adding the delay in this response
is also used under the following situation, for example. That is,
the situation is set such that as the flow rate detecting element,
an element having a high speed responding characteristic (for example,
a semi-conductor element type) is used and as the control unit receiving
it, a relative less-expensive unit of a type in which a responding
characteristic is not so fast is used. In such a case as above,
although it can be considered that the response delay element can
be added for a pre-processing operation so as to cause both of them
to be adapted for it, it is also effective for correcting dispersion
in delay of response (caused by a dispersion of the clock signal,
for example) generated at that time.
[0044] It is possible to reduce an error caused by a non-linear
characteristic without damaging a basic characteristic of the sensor
output of the thermal flow meter and further it is possible to release
some limiting conditions using the flow meter of the present invention.
In addition, it becomes possible to realize the flow meter having
the correction dispersion reduced at the time of response delay
correction (a recovering of the response delay, and drivability
of an automobile can be improved and its productivity can be improved.
In addition, the measurement error at the time of pulsation and
transmission is reduced to enable a more superior precise control
to be attained when the present invention is applied for the engine
control and then it has an effect of reducing an amount of discharging
gas or improving a fuel consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a configuration view for showing a flow meter
and a system using the same according to a first preferred embodiment
of the present invention;
[0046] FIG. 2 is a block diagram for showing a digital processing
for a flow rate output signal of the first preferred embodiment;
[0047] FIG. 3 is a block diagram for showing a digital processing
of an engine control unit for inputting a flow rate output signal;
[0048] FIG. 4 is an illustrative view for showing a response delay
according to the preferred embodiment of the present invention;
[0049] FIG. 5 is a block diagram for showing a thermal air flow
meter used in the aforesaid preferred embodiment;
[0050] FIG. 6 is a pattern diagram for showing a resistor formed
on a silicon substrate;
[0051] FIG. 7 is a sectional view for showing a resistor formed
on a silicon substrate;
[0052] FIG. 8 is a configuration view for showing a flow meter
and a control system according to a second preferred embodiment
of the present invention;
[0053] FIG. 9 is a block diagram for showing a digital processing
of the thermal flow meter according to a second preferred embodiment
of the present invention;
[0054] FIG. 10 is a block diagram for showing a digital processing
of an engine control unit according to a second preferred embodiment
of the present invention;
[0055] FIG. 11A is an illustrative view for showing a frequency
signal transmittance according to a second preferred embodiment
of the present invention;
[0056] FIG. 11B is an illustrative view for showing a frequency
signal transmittance according to a second preferred embodiment
of the present invention;
[0057] FIG. 12 is an operative illustration for setting an output
when a power supply is turned on;
[0058] FIG. 13 shows an algorism for selecting an output at a sensor
side used in the aforesaid preferred embodiment;
[0059] FIG. 14A shows an algorism (clock mode) for selecting an
output at a control unit used in the aforesaid preferred embodiment;
[0060] FIG. 14B shows an algorism (delay determination mode) for
selecting an output at a control unit used in the aforesaid preferred
embodiment; and
[0061] FIG. 15 shows a relationship among a flow rate, a frequency
and the number of counted clocks.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0062] Referring now to the drawings, some preferred embodiments
of the present invention will be described as follows.
[0063] FIG. 1 shows a block circuit of a flow rate control device
according to a first preferred embodiment of the present invention.
In FIG. 2 is shown a digital circuit (a pre-processing circuit)
2 for pre-processing an output of a flow meter according to a first
preferred embodiment and sending it to a control unit (a signal
processing unit) 5.
[0064] A driving circuit (a sensor circuit) 1 for the thermal flow
meter is connected to a power supply 10 so as to control a heating
for current flowing in a heat generating resistor 11 in such a way
that a temperature difference between the heat generating resistor
11 and a temperature compensating resistor 12 may keep a predetermined
temperature difference. The heat generating resistor 11 is arranged
at a passage for a flow rate measured object so as to perform a
heat exchanging operation between it and fluid in correspondence
with flow rate. Then, as the flow rate is increased, a calorie of
the heat generating resistor to be removed is increased, so that
a heating current for use in keeping the temperature difference
between it and the temperature compensating resistor is increased.
[0065] As a flow rate signal of the thermal flow meter, an output
signal for converting a current flowing at the heat generating resistor
11 into a voltage is used or temperature detecting resistors are
arranged at an upstream side and a downstream side of the heat generating
resistor 11 and then an output difference of these temperature
detecting resistors is utilized. The latter system calculates an
air flow rate in reference to a difference in output signals of
both temperature detecting resistors while noticing the fact that
the temperature of the temperature detecting resistor positioned
at the upstream side of the heat generating member is decreased
as the flow rate is increased than that of the temperature detecting
resistor positioned at the downstream side in reference to a flow
of the fluid, and it has an advantage that a direction characteristic
of the fluid can also be detected.
[0066] An output of the thermal flow rate detecting element (a
thermal flow meter) is a non-linear output and contains a pulsation
component and they become a cause for flow rate error of the output
signal. The digital processing device 2 constitutes a digital error
adjustment device for correcting such an error as above and becomes
a pre-processing circuit for a subsequent stage control unit (a
signal processing unit). The digital processing device 2 is constituted
by digital means such as a microcomputer or an exclusive logic and
the like.
[0067] The content of the error adjustment of the output signal
executed by the digital means 2 is described in detail in the gazette
of Japanese Unexamined Patent Publication No. 316145/1999 for example.
[0068] In the preferred embodiment of the present invention, this
digital processing circuit 2 is further added with an intentional
response delay means, means for transmitting the response delay
information to a subsequent stage control unit 5 (I/O 26 a selection
switch 27 in FIG. 1; an output selection processing unit 46 and
a selection switch 49 in FIG. 2); and means for selecting whether
or not the response delay processing is executed in response to
an instruction of the control unit 5 (I/O 26 in FIG. 1; an output
selection processing unit 46 and a selection switch 48 in FIG. 2).
[0069] The error adjustment converts an output signal Vin of the
sensor circuit 1 into a digital value through an analog/digital
converter (A/D converter) 21. An arithmetic circuit 22 applies an
error correction (linear forming and smoothening processing) to
this digital signal by using the correction data prepared in a re-writing
memory 23 and outputs a voltage value (a signal applied with an
error adjustment) similar to the output of the sensor circuit 1
to the engine control unit 5 through an output signal selection
means (SW) 27 by the digital/analog converter (D/A converter) 24.
[0070] In this case, referring now to FIG. 2 a flow of an error
adjustment arithmetic processing 40 executed by the arithmetic circuit
22 of the digital processing circuit 2 will be described as follows.
[0071] An output Vin of the sensor circuit 1 is inputted at the
arithmetic processing part 40 the analog/digital conversion processing
41 is executed to cause the output Vin to become a digital value
Vad.
[0072] Then, a V-Q conversion processing (a conversion of a voltage-flow
rate) 42 is applied to the digital value Vad. The V-Q conversion
processing 42 is carried out such that the digital value Vad indicating
a non-linear characteristic in respect to the flow rate is converted
into a flow rate Qa under application of a VQ map mapped in the
re-writing memory 23 (FIG. 1). This processing causes the output
signal to be processed in a linear form. Further, prior to the V-Q
conversion, a response of the sensor output may be recovered with
a voltage value. In this case, it is possible to attain a more accurate
flow rate value Qa.
[0073] Then, the flow rate value Qa is applied with a smoothening
processing 43 (a response delay adding processing) through a low-pass
filter, for example.
[0074] Whether or not this response delay processing 43 is executed
can be selected by the soft switch 48 at the time of outputting.
Operation of the soft switch 48 is carried out through the output
selection processing 46 in response to an instruction from the control
unit 5.
[0075] If the response delay processing 43 is selected, the flow
rate value Qa is processed with the digital Q-V conversion (a conversion
of flow rate--voltage) after selection elapses, and if the response
delay processing 43 is not selected, the flow rate value Qa is processed
directly with the digital Q-V conversion (a conversion of flow rate--voltage),
thereby a non-linear signal similar to the inputted voltage signal
Vin is formed and an analog signal is outputted by the digital/analog
converter 45. Further, these series of processing are carried out
using adjustment parameters.
[0076] Digital processing 40 enables the output selection processing
46 to be carried out with a control signal Qset from the engine
control unit and the like. With this operation, it is possible to
change over the flow rate output signal and a reference clock signal
fck through the switch 49 (the switch 27 in FIG. 1) and output them
or to select either a presence or a non-presence of the response
delay through the switch 48.
[0077] In this case, the response delay processing 43 can be carried
out by applying a processing enabling an average value to be variable
at the time of pulsation through some adjustment parameters when
the voltage signal of the sensor is converted into a flow rate to
apply a smoothening state.
[0078] In the present preferred embodiment, it is possible to output
different signals such as a normal voltage output Vout and the reference
clock fck or the like through one signal line via the switch 49
in reference to a selection signal or the like from an external
part (or a repeating processing of the digital error adjustment
device 2 itself when an internal specified condition is fulfilled)
from the sensor (a flow meter).
[0079] The output signal selecting means (SW) 27 switches between
the reference clock signal fck of an oscillator (OSC) 25 and an
output Vout of the analog/digital converter (D/A converter) 24 in
reference to an external selection signal Qset set through the I/O
(interface) device 26.
[0080] Next, referring to FIG. 3 a flow of arithmetic processing
of the engine control unit 5 will be described as follows. The output
signal Vout of the sensor is received, changed into a digital value
by the analog/digital conversion processing 62 through the analog
filter 61 and further converted into a flow rate value through a
V-Q conversion (voltage to flow-rate conversion) 63. After this
processing, the flow rate Qsp (a value in which the output signal
Vout of the sensor having a response delay is converted into a flow
rate) is applied with a response recovery processing 64 to attain
a signal Qai having its responding characteristic recovered. In
this case, a responding characteristic of the response recovery
processing 64 is adjusted with an adjustment parameter T1 for use
in recovering the response. Although it will be described here only
with T1 applied as one time constant of a representing example,
there occurs no problem even if a plurality of parameters are present.
[0081] There occurs sometimes that the reference clock signal fck
is inputted to the control unit 5 in place of the flow rate output
signal Vout through a sensor selection switch 27 at the time of
starting operation or using the control signal Qset got from the
engine control unit and the like. In that case, it is possible to
acknowledge a dispersion of the reference clock fck by detecting
either a frequency of the reference clock or the counted number
of pulses within a specified time. If the dispersion of the reference
clock is acknowledged, it becomes also possible to attain an automatic
production of some parameters for adjustment applied at the response
recovery processing 64.
[0082] Effects of the present invention will be described in reference
to a step response shown in FIG. 4 as follows.
[0083] At first, as shown in FIG. 4(a), the output signal of the
sensor processed at the engine control unit shows a gradual rising
through a response delay processing performed at the sensor side.
In this case, if it is assumed that the reference clock at the sensor
side shows a variation due to its dispersion, the signal shows a
changing responding characteristic and becomes a signal indicated
by a dotted line having a dispersed response. A responding characteristic
is recovered by applying the response recovery processing 64 to
this signal.
[0084] As shown in FIG. 4(b), if the correction is performed in
compliance with the original characteristic of the central value,
the flow rate after response accommodation is widely dispersed due
to variation in clock or dispersion. This dispersed situation becomes
remarkable as a dispersion of the clock is high.
[0085] To the contrary, as shown in FIG. 4(c), it becomes possible
to restrict substantially the dispersion after accommodation of
response by changing the adjustment parameters in response to a
dispersion of the clock in the present invention.
[0086] In particular, the response delay recovery processing 64
in the present invention provides an effective operation even when
it is used under a combination of a flow sensor having a high-speed
responding characteristic, a semiconductor sensor constituted on
a silicon diaphragm, for example. That is, although the flow sensor
having a high-speed response characteristic itself has no response
delay and has a less amount of dispersion, if the sensor is passed
through the response delay element such as a smoothening processing
and the like, it may produce a response delay and further a dispersion
is generated in the response delay under an influence of the dispersion
of the clock signal. Even under such a case as above, it is possible
to perform a recovering against the response delay while reducing
the dispersion. Accordingly, it becomes possible to provide a sensor
that can be conveniently used by a user.
[0087] Referring to FIG. 5 a practical hardware configuration
will be described as follows.
[0088] A control system shown in FIG. 5 is made such that temperature
detecting resistors 211d to 211g are arranged at positions thermally
influenced by the heat generating resistor 11 (upstream and downstream
positions of the heat generating resistor 11). Such a structure
as above can attain a flow rate accompanied with a directional characteristic
with a voltage signal corresponding to a temperature difference
of the resistor and this is called as a so-called differential temperature
type flow meter. This system is suitable for detecting a flow rate
including a large pulsation such as enabling a detection of an inverse
flow rate through detection of an orientation of the flow to be
carried out.
[0089] The hot-wire driving circuit 1 is connected to a power supply
101. The hot-wire driving circuit 1 is constituted by a Wheatstone
bridge circuit having a heat generating resistor 211a, a temperature
accommodation resistor 211c, resistors 13 14 and 17. In addition,
it is constituted such that a current flowing at the heat generating
resistor 211a is adjusted by a differential amplifier 15 and a transistor
16 in such a way that a potential at the middle point of the bridge
may become a zero.
[0090] When a heating temperature of the heat generating resistor
211a is low, an output of the differential amplifier 15 is increased
and further it is operated to heat the resistor. With this constitution
as above, the current flowing at the heat generating resistor 211a
is controlled without being dependent on a flow speed (a flow rate),
but controlled in such a way that a resistance value of the heat
generating resistor 211a is kept constant, i.e. a temperature difference
becomes a specified value.
[0091] The temperature detecting resistors 211d, 211e, 211f and
211g arranged at the upstream side and the downstream side of the
heat generating resistor 211a constitute a bridge, and a temperature
difference of the resistors is detected in reference to a difference
between the middle point potentials Vb1 Vb2. In this system, an
output corresponding to a direction of flow can be attained.
[0092] In this case, the temperature detecting resistors 211d,
211e , 211f and 211g are driven by a power supply voltage Vref1
at its specified voltage. A system for detecting the temperature
difference of the resistor has a superior sensitivity at a low flow
rate side due to its differential detection and this is suitable
for detection of flows in both directions such as an inverse flow.
[0093] In this preferred embodiment, the heat generating resistor
211a is formed at a silicon semiconductor substrate 211 in its thin
film and one example of the pattern is shown in FIG. 6.
[0094] The heat generating resistor 211a is longitudinally extended
in its shape, its resistor has a folded back pattern and the resistor
is constructed such that the resistors 211d, 211e, 211f and 211g
for detecting a temperature are arranged at both sides of the pattern.
The heat generating resistor 211a, and the resistors 211d, 211e,
211f and 211g for use in detecting temperature are arranged at the
diaphragm structure etched from the rear surface of the silicon
substrate 211 for example, and having a low heat capacity.
[0095] The temperature compensating resistor 211c for use in compensating
for an air temperature is arranged at such a location as one where
it is hardly influenced by a temperature caused by heating at the
heat generating resistor 211a. Its sectional structure is shown
in FIG. 7. Its structure is set such that the location where the
resistor pattern is present has the thickest thickness.
[0096] Potentials Vb1 Vb2 at the bridge middle points of the temperature
detecting resistors 211d, 211e, 211f and 211g are inputted to the
digital error adjustment device 220. The digital error adjustment
device 220 has two analog/digital converters 221a, 221b in correspondence
with the input potentials Vb1 Vb2 so as to convert the voltage
value corresponding to a flow rate into a digital value and read
it.
[0097] CPU 222a of the microcomputer 222 performs a digital arithmetic
operation for executing a pre-processing in FIG. 2 that has already
been described, and a digital/analog converter 224 converts the
pre-processed output voltage Vout into an analog form and sends
it to the engine control unit and the like.
[0098] In this case, the digital error adjustment device 220 has
a configuration that is similar to that of the aforesaid preferred
embodiment. A voltage Vcc supplied from an external unit is inputted
to a power supply and protection circuit 228 inside the device as
a power supply. The power supply and protection circuit 228 supplies
the power supply voltage Vref1 depending on the external voltage
Vcc to the analog/digital converters 221a, 221b and the digital/analog
converter 224 as a reference voltage through a switch 225a.
[0099] The switch 225a switches between a voltage Vref2 generated
at the reference voltage circuit 229 inside the digital error adjustment
device 2 and the power supply voltage Vref1 depending on the prior
external voltage Vcc. In this case, the analog/digital converters
221a, 221b require a precision because the outputs Vb1 Vb2 and
the like of the bridge circuit are directly inputted. In order to
assure the precision and keep a size of the circuit small, it is
satisfactory to apply .DELTA..SIGMA. type analog/digital converter,
for example.
[0100] The digital/analog converter 224 can also similarly change
the reference voltage through the switch 225. This is used for making
a free selection of a reference value when the interface is attained
with an analog value. When the reference voltage of the analog/digital
converter at the control unit side connected to the error adjustment
device (the pre-processing device) 2 and the voltage Vcc supplied
from the external unit are changed similarly or in a synchronized
state, the power supply voltage Vref1 is applied as a reference
value and in turn when it has no relation with the control unit,
the independent reference voltage Vref2 is selected. With this operation,
a correspondence between the pre-processing device and its corresponding
control unit can become easy and then an error caused by an un-matching
with the analog interface can be reduced.
[0101] As the heat generating resistor 211 a hot-wire type can
be applied in addition to a polysilicon resistor (a semiconductor
type). The hot-wire type is made such that either a platinum hot-wire
or a tungsten hot-wire acting as a heat generating member is wound
around the surface of either a cylindrical or column-like bobbin
made of insulation material having a superior thermal conduction
such as a ceramic material, for example, and either glass or ceramics
is applied as coating for a covered material. In addition, it may
also be applicable that either a thin film or a thick film made
of platinum or tungsten acting as the heat generating member or
the like is formed on the substrate such as a plate-like glass or
ceramics, silicon and the like.
[0102] The heat generating resistor 211 temperature detecting
resistors 211d to 211g and temperature compensating resistor 211c
are installed in an intake passage of an internal combustion engine
such as one applied in an automobile or the like and then a voltage
output of the temperature detecting resistor (it may be a voltage
output of the heat generating resistor) corresponding to an air
flow rate flowing in the intake passage can be attained as an output.
[0103] This output voltage is inputted to the analog/digital converters
221a, 221b stored in the digital error adjustment device 220 constituted
by a digital means such as a microcomputer or an exclusive logic
and converted into a digital form.
[0104] CPU 222a in the digital error adjustment device 2 applies
a response recovery processing against the converted digital value
as required and subsequently performs an output adjustment for compensating
for a respective dispersion of the sensor characteristic. Subsequently,
the voltage signal of the sensor is converted into a flow rate by
an optional first conversion equation f.times.1 to attain its smoothening,
and then a non-uniform linear processing such as adjustment of sensitivity
with a second conversion equation f.times.2. As an output after
performing the non-linear formation, the linear formation processing
is applied again as required and then a non-linear voltage value
is outputted at the engine control unit and the like under application
of the digital/analog converter 224.
[0105] The digital error adjustment device 220 comprises a non-volatile
memory (ROM) 222c having either a flow rate conversion map or a
program stored therein acting as a reference for various kinds of
flow rate conversion equation; a rewritable memory (PROM) 223 recording
individual difference information such as a dispersion of resistance
value of the heat generating element 11 a smoothening degree in
the smoothening processing (a frequency characteristic and the like),
some adjustment parameters for changing various functions for applying
the non-uniform linear formation and a degree of response recovery
processing; a random access memory (RAM) 222b used in an arithmetic
work area of the CPU 222a; and an oscillator (OSC) 226 for generating
an internal clock and the like. Although the rewritable PROM 223
is not stored in the digital error adjustment device 220 if there
is provided one capable of performing more than one time writing
operation, it may also be applicable to provide a fuse-type ROM
or an electrically erasable EEPROM, a total erasing flash ROM and
a high-speed non-volatile memory utilizing a polarization phenomenon
of a ferroelectric film and the like.
[0106] In accordance with such a first preferred embodiment described
above, there are provided some effects that an error caused by the
non-linear characteristic can be reduced without damaging a basic
characteristic of sensor output from the thermal flow meter and
a restriction in use against a user utilizing this sensor is reduced.
In addition, it becomes possible to realize a flow meter having
a correction dispersion at the time of response delay correction
(recovering of the response delay), and it is possible to improve
a drivability of an automobile and its productivity.
[0107] Then, referring to FIG. 8 a second preferred embodiment
of the present invention will be described as follows. This is one
example in which a frequency signal is applied in I/F (interface)
signal.
[0108] A feature differing from that of the previous preferred
embodiment consists in outputting a signal using the digital/frequency
converter (D/f converter) 28 and there is provided an advantage
that handling of a pulse signal facilitates an overlapping of signals.
[0109] The engine control unit 5 has a constitution in which there
is provided a timer 5 for use in counting a frequency, and a reference
signal Tref such as a crank angle of the engine or the like can
be inputted. A selection of responding characteristic of the output
signal fout from the sensor or a changing-over between the output
signal and the reference clock signal fck and the like can be carried
out in the same manner as that of the prior preferred embodiment.
[0110] Referring to FIG. 9 a flow of detailed arithmetic processing
will be described as follows. At the arithmetic part 40 an output
Vin of the sensor circuit 1 is applied as an input, it is changed
into a digital form through the analog/digital conversion processing
41 it is further processed with the response recovery processing
as required, thereafter it is processed with V-Q conversion 42 (a
changing-over of voltage--flow rate) and a response delay processing
43 is carried out. Presence or non-presence of application of the
response delay processing 43 can be selected through a software
switch 48 at the time of output.
[0111] After the response delay processing 43 the signal is applied
as a non-linear signal similar to the voltage signal Vin inputted
through Q-A conversion (flow-rate to voltage conversion) and a compressed
frequency signal is outputted in a non-linear form by the digital/frequency
converter 451. In addition, it is possible to output the sensor
output signal and the reference clock signal fck while being changed
over or to select presence or non-presence of the response delay
by the output selecting processing 46 operated by the control signal
Qset from the engine control unit and the like. In this case, since
there occurs a case in which a dynamic range can be set relatively
large, it is not necessary that the signal is set to the non-linear
signal similar to the voltage signal Vin inputted through the Q-V
conversion (a conversion of flow rate--voltage) 44.
[0112] It is possible to output, from the sensor through one signal
line, both a usual frequency output fout and a different signal
such as the reference clock fck or the like by a selection signal
or the like obtained from the external unit (or the repeating processing
of the digital error adjustment device 2 itself and the like when
an internal specified condition is fulfilled).
[0113] Then, referring to FIG. 10 a flow of arithmetic processing
of the engine control unit 5 will be described as follows. The control
unit 5 inputs the frequency output fout of the flow rate sensor,
the frequency signal is changed into a digital value through the
synchronized sampling processing 66 it is changed into a flow rate
value through a F-Q conversion (a conversion of frequency--flow
rate) 67 thereafter the response recovery processing is applied
against the flow rate value Qsp having a response delay (one in
which the frequency output fqaf of the sensor is changed into a
flow rate) through the response recovery processing 64 to attain
a signal Qai having its responding characteristic recovered. At
this time, a responding characteristic of the response recovery
processing 64 is adjusted with an adjustment parameter T1 for use
in recovering the responding characteristic.
[0114] As shown in FIG. 11A, as to the reference clock signal fck
in regard to the frequency signal fout, dispersion information of
a clock is attained by counting the clock using the reference signal
between it and Tref. In this case, as shown in FIG. 11B, it is also
applicable that the reference clock signal fck is outputted while
overlapping the reference clock signal fck on the frequency output
signal fout. It is possible to acknowledge a dispersion of the reference
clock signal fck by detecting either the frequency of the reference
clock or the number of counting of the pulses within a specified
time through the response parameter detection processing 65. If
the dispersion of the reference clock is found, it becomes also
possible to perform an automatic production of the adjustment parameters
used in the response recovery processing 64. In FIG. 15 are shown
a relationship between a flow rate and an output frequency and a
relationship between the flow rate and the number of clock count.
[0115] The counted number for a clock is an inverse number in respect
to an output frequency that becomes a non-linear output against
the flow rate. If the counted number of a clock pulse at a point
of zero flow rate and a certain flow rate point are measured at
two points in regard to a specified reference characteristic fcnt0
a dispersion caused by the entire clock can be estimated. Accordingly,
it is possible to correct a dispersion in response delay in regard
to a flow rate (caused by a dispersion of a clock) in a highly accurate
manner by a method wherein a representing characteristic of the
counted number of clock is stored in a memory or the like in advance
and corrected on the basis of the estimated dispersion.
[0116] In the preferred embodiment of the present invention, applying
a frequency in a signal enables a precision in responding characteristic
to be improved while preventing a deterioration in precision caused
by floated signal at the ground side which is specific to an analog
signal.
[0117] Next, a third preferred embodiment of the present invention
will be described as follows. Optional adjustment in regard to a
response delay (fast, delay) of an I/F signal, type of signal transmittance
(a voltage output, a frequency output) can be carried out with a
signal SCI (Serial Communication Interface) of an external controller
such as the engine control unit or the like, or the selection signal
Qset and the like that has already been described. If a real time
adjustment for the responding characteristic becomes possible as
described above, a matching operation can be easily carried out
even if either an engine or an intake system is changed.
[0118] Referring to FIG. 12 an operation caused by a practical
external controller will be described as follows. Although this
operation corresponds to a case where an output is a voltage, a
similar case can be applied for a frequency.
[0119] At first, noticing a raising of a battery voltage VB at
the time of turning-on of the power supply, this is determined in
reference to an operation of the digital error adjustment device
2 itself while a specified time Tvb1 just after the battery voltage
VB, for example, is applied as a just-after energization of VB.
When the output selection signal Qset shows elapsing of a specified
time H1 under this state (Tset1), it is determined as an outputting
operation after turning-on operation through the output selection
processing 46 (FIG. 9), and the clock signal fck is selected as
the output signal. In this case, a digital signal of high frequency
corresponding to the clock signal is outputted as the output signal
of the sensor. When the output selection signal Qset becomes Lo,
the clock operation ends and the operation becomes a usual outputting
operation (an operation with a response delay in this case).
[0120] To the contrary, when the output selection signal Qset becomes
a specified time Hi (Tset2) upon elapsing the specified time Tvb1
just after the battery voltage VB, it is outputted while the response
delay processing is eliminated, and an output signal Vout having
a less amount of response delay (or the response delay is scarcely
none) can be attained. In this way, it becomes possible to perform
a controlling operation with reduced response delay at the controller
by outputting a clock signal becoming a reference in response and
a presence or non-presence of response delay from an external unit.
[0121] In FIGS. 13 and 14 is shown a practical algorism. FIG. 13
shows an algorism operated with the digital error adjustment device
2 and FIGS. 14A and 14B show an algorism operated at the external
controller 5. They become operations closely related to each other.
[0122] At first, in FIG. 13 a selected value Qset is read out
through an output selection setting 301 determining an inputted
state in respect to a signal set by the external controller 5.
[0123] Next, either 1 or 0 (Hi or Lo) is determined through a determination
processing 302. If it is 0 (Lo), the output selection processing
is finished as a mode having a delay in initial operation.
[0124] To the contrary, when the selected value Qset is 1 (Hi),
it is determined through a discrimination processing 303 whether
or not it is just after energization of the battery voltage VB.
If it is determined that this is a just-after energization, the
operation is carried out as a clock mode, the output switch 49 is
changed over to the fck inputting side and then the signal fck corresponding
to the clock is outputted from the sensor output terminal. Upon
completion of this mode, the operation jumps to the determination
processing 302 for the selected Qset and when the output selection
value Qset becomes 0 (Lo), the operation is completed.
[0125] When the determination processing 303 determines that the
operation is not carried out just after energization of the battery
voltage VB, the output switch 48 is changed over to a side of non-presence
of response delay processing (305). As a result, the output signal
Vout becomes an operation mode in which a signal having no response
delay (a signal having a less amount of delay) is outputted, and
the output setting processing is finished. In this preferred embodiment,
as long as the output setting is not performed again, it is assumed
that the output operation mode is continued.
[0126] Next, referring to FIGS. 14A and 14B, the algorism at the
external controller 5 will be described as follows. In FIG. 14A
is shown the algorism of the external controller 5 corresponding
to the clock mode. In this case, the output selection value Qset
is set to 1 (Hi) just after energization of the power supply VB
to make a clock mode (401). After this operation, the clock signal
is read (402). A correction coefficient with dispersion is calculated
in reference to the read-out clock (403). As a result, a correction
coefficient for correcting a response caused by displacement of
the clock is set and finished (404).
[0127] To the contrary, in FIG. 14B is shown a delay discrimination
mode other than the time of just-after energization of VB. In this
case, the output selection value Qset is set to either 1 (Hi) or
0 (Lo) (501), the response delay mode is determined by itself (502)
and when the output selection value Qset is 1 (Hi), various kinds
of processing are carried out under an assumption that response
delay is not present. In this case, an amount of correction for
the discharging gas of an internal combustion engine when no response
delay occurs, for example, is learned (505). To the contrary, when
the output selection value Qset is 0 (Lo), the response delay recovery
processing (503) is carried out and an amount of correction of the
discharging gas at the time of response delay is learned (504).
The response delay recovery processing (503) may be present or not
present. As a result, a difference between the presence or non-presence
of the response delay is applied as a correction value for study
to enable some effects of study for the discharging gas in response
to a precision such as error in correction caused by the presence
or non-presence of response delay and the presence or non-presence
of correction of the response delay (503) to be attained, and further
some effects that adaptation for the discharging gas becomes easy
under various conditions. It is also applicable that these operations
are carried out only when an adjustment such as a test of discharging
is performed.
[0128] In accordance with the aforesaid preferred embodiments,
even if the error in pulsation is changed due to a modification
of an engine or an intake system, the reduction in error of pulsation
can be easily carried out without making any substantial modification
of the characteristic in the intake system or sensor itself. As
a result, it shows an effect that a development period for a measuring
system for an engine intake system can be remarkably shortened.
[0129] In all the preferred embodiments described up to now, the
measurement error at the time of pulsation or a transmittance response
is reduced to enable some effects to be attained that a more superior
precise control is performed when it is applied in an engine control
and the discharging gas is reduced or fuel consumption is improved.
[0130] In addition, even if the flow meter used in the prior art
flow meter is used for a gas detection of hydrogen gas as found
in a fuel cell and the like, a similar effect can be attained. |