Abstrict
A control device for a catalyst having an electric heater: provided
at an exhaust pipe of an engine, having a catalyst for purifying
exhaust gas and an electric heater for heating the catalyst before
and after starting the engine comprises a battery charged by a generator
driven by the engine for supplying power to the electric heater
and for driving a starter; a current sensor for detecting charged
and discharged current of the battery; summing means for summing
a value of the charged and discharged current since a current to
the electric heater has started flowing until the engine starts
operating and until the engine stops operating; and means for comparing
the summed value with a predetermined value and for prohibiting
the current flowing to the electric heater during a period at least
before the engine starts operating when the summed value is equal
to or less than the predetermined value.
Claims
What is claimed is:
1. A control device for a catalyst having an electric heater:
provided at an exhaust pipe of an engine, having said catalyst
for purifying exhaust gas and said electric heater for heating the
catalyst before and after starting the engine comprising:
a battery charged by a generator driven by the engine for supplying
power to the electric heater and for driving a starter;
a current sensor for detecting charged and discharged current of
the battery;
summing means for summing a value of the charged and discharged
current since a current to the electric heater has started flowing
until the engine starts operating and until the engine stops operating;
and
means for comparing the summed value with a predetermined value
and for prohibiting the current flowing to the electric heater during
a period at least before the engine starts operating when the summed
value is equal to or less than the predetermined value.
2. A control device for a catalyst having an electric heater:
provided at an exhaust pipe of an engine, having said catalyst
for purifying exhaust gas and said electric heater for heating the
catalyst before and after starting the engine comprising:
a battery charged by a generator driven by the engine for supplying
power to the electric heater and for driving a starter;
means for calculating a discharged quantity of the battery by multiplying
a first value of a predetermined current flowing to the electric
heater by a time of flowing current to the electric heater;
engine revolution number detecting means for detecting a revolution
number of the engine;
means for calculating a generated current of a generator based
on the revolution number of the engine;
means for calculating a charged quantity of the battery by summing
a second value of the generated current; and
means for prohibiting the current flowing to the electric heater
during a period at least before the engine starts operating when
a third value of the charged quantity subtracted by the discharged
quantity is below a predetermined value.
3. A control device for a catalyst having an electric heater provided
at an exhaust pipe of an engine, having said catalyst for purifying
exhaust gas and said electric heater for heating the catalyst before
and after starting the engine comprising:
a battery charged by a generator driven by the engine for supplying
power to the electric heater and for driving a starter;
a temperature sensor for detecting a temperature of the engine;
and
means for comparing the temperature of the engine with a predetermined
value and prohibiting a current flowing to the electric heater before
the engine starts operating when the temperature of the engine is
equal to or less than the predetermined value.
Description BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a control device for a catalyst
having an electric heater for purifying exhaust gas of an engine
for a vehicle.
DISCUSSION OF BACKGROUND
The exhaust gas control of an automobile has become severer year
after year in view of the global environment protection. In recent
times, it is strongly requested to reduce a level of hydrocarbons
(HC) emitted during several minutes of a warming-up period after
an engine is started. To meet the social request, a method is proposed
wherein a catalyst is heated by an electric heater incorporated
in the catalyst during a predetermined period before and after the
starting of the engine, thereby reducing a time for the catalyst
to be activated.
FIG. 2 shows construction of a control device for a catalyst having
an electric heater incorporating a conventional engine control unit.
A reference numeral 1 designates an engine, 2, a pressure sensor
for detecting a load of the engine 1, 3, a revolution number sensor
for detecting a revolution number of the engine 1, 4, an intake
pipe, 5, an injector for supplying fuel to the engine 1, 6, an engine
control unit, 7, an exhaust pipe, 8, a catalyst unit for purifying
exhaust gas which is provided at the exhaust pipe 7, 9, an electric
heater incorporated in the catalyst unit 8, 10, a generator which
is driven by the engine 1, 11, a battery, 12, a control switch for
turning ON and OFF the electric heater 9, 13, a key switch, 14,
a catalyst control unit for controlling opening and closing of the
control switch 12, and 15, a starter for starting the engine 1.
In the above construction, the engine control unit 6, receiving
information of a load of an engine obtained based on the pressure
sensor 2 and information of a revolution number of an engine obtained
based on the revolution number sensor 3, calculates a fuel quantity
to be supplied to the engine 1, that is, a driving pulse width of
the injector 5, and controls the engine 1 so that the air-fuel ratio
of the engine 1 becomes a predetermined one. After combustion in
the engine 1, poisonous gases (HC, CO, NOx) are purified by passing
them through the catalyst unit 8. To promote a purification efficiency
of the catalyst unit 8 up to about 80%, it is necessary that a temperature
of the catalyst reaches 400 to 500.degree. C. or more. The battery
11 is charged by the generator 10 driven by the engine 1. The starter
15 is driven by the battery 11 through the key switch 13.
However, since the temperature of the catalyst is not sufficiently
elevated several minutes after starting the engine 1, the purification
efficiency is low and the poisonous exhaust gas components (especially
HC) are much emitted. As a means of solving the problem, a method
is proposed wherein preheating and heating after starting are performed
by an electric heater incorporated in the catalyst unit 8.
FIG. 3 is a flow chart showing operation of the catalyst control
unit 14. In step 101, the operation determines whether the key switch
13 is normally turned on to IG position (refer to FIG. 2). When
the key switch 13 is turned on, in step 102, the operation turns
on the control switch 12 and flows current from the battery 11 to
the electric heater 9 during a predetermined period (about 20 seconds
for preheating, about 20 seconds for heating after starting). By
flowing current to the electric heater 9, the catalyst temperature
is elevated as shown in curve "b" in FIG. 4. Curve "a"
in FIG. 4 shows elevation of the catalyst temperature when the electric
heater 9 is not used. When the preheating and the heating after
starting are performed by the electric heater 9, the elevation of
the catalyst temperature is accelerated as shown in curve "b",
and the catalyst temperature reaches an activation temperature in
a short time.
However, a power required for heating the electric heater 9 is
3 to 5 kW. Therefore, a discharge current of the battery 11 of 12V
is 250 to 400 A. Although the discharging is performed in a short
time, the discharged quantity of the battery 11 is not negligible.
As stated above, in the conventional control device for a catalyst
having an electric heater, since the power applied to the electric
heater is very large, a residual capacity of the battery 11 is considerably
lowered as shown in FIG. 5. Accordingly, when the engine 1 is stopped
after the engine 1 has been started and before the charging of the
battery 11 by the generator 10 is sufficiently performed, and thereafter
the operation for starting is performed again, the residual capacity
of the battery 11 is further lowered by the power consumption for
the preheating. Accordingly, the starter 15 can not be driven by
the battery 11 by a sufficient revolution number and the engine
1 falls into incapacitance in starting.
Furthermore, since the power supply to the electric heater 9 in
the conventional device is very large, when current flows from the
battery 11 to the electric heater before starting (cranking), the
residual capacity of the battery 11 is lowered, and as shown in
curve "d" in FIG. 13, the voltage applied to the starter
15 in cranking is considerably lowered. (Curve "c" shows
a normal battery voltage.) As a result, the revolution number of
the engine in starting is lowered from curve "e" to curve
"f" in FIG. 14, thereby deteriorating the starting performance.
Especially, when a temperature of the engine is as low as -10.degree.
C. or less, since the viscosity of an engine oil is large, a load
torque of the starter 15 is increased. With this increase, a starting
current "g" in FIG. 14 is also increased, the voltage
of the battery 11 is considerably lowered, and the revolution number
for cranking the engine 1 is also considerably lowered thereby falling
into incapacitance in starting.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control device
for a catalyst having an electric heater capable of preventing lowering
of a capacity of a battery by flowing current from a battery to
an electric heater of a catalyst and smoothly performing starting
of an engine.
According to a first aspect of the present invention, there is
provided a control device for a catalyst having an electric heater:
provided at an exhaust pipe of an engine, having a catalyst for
purifying exhaust gas and an electric heater for heating the catalyst
before and after starting the engine comprising:
a battery charged by a generator driven by the engine for supplying
power to the electric heater and for driving a starter;
a current sensor for detecting charged and discharged current of
the battery;
summing means for summing a value of the charged and discharged
current since a current to the electric heater has started flowing
until the engine starts operating and until the engine stops operating;
and
means for comparing the summed value with a predetermined value
and for prohibiting the current flowing to the electric heater during
a period at least before the engine starts operating when the summed
value is equal to or less than the predetermined value.
According to a second aspect of the present invention, there is
provided a control device for a catalyst having an electric heater:
provided at an exhaust pipe of an engine, having a catalyst for
purifying exhaust gas and an electric heater for heating the catalyst
before and after starting the engine comprising:
a battery charged by a generator driven by the engine for supplying
power to the electric heater and for driving a starter;
means for calculating a discharged quantity of the battery by multiplying
a first value of a predetermined current flowing to the electric
heater by a time of flowing current to the electric heater;
engine revolution number detecting means for detecting a revolution
number of the engine;
means for calculating a generated current of a generator based
on the revolution number of the engine;
means for calculating a charged quantity of the battery by summing
a second value of the generated current; and
means for prohibiting the current flowing to the electric heater
during a period at least before the engine starts operating when
a third value of the charged quantity subtracted by the discharged
quantity is below a predetermined value.
According to a third aspect of the present invention, there is
provided a control device for a catalyst having an electric heater
provided at an exhaust pipe of an engine, having a catalyst for
purifying exhaust gas and an electric heater for heating the catalyst
before and after starting the engine comprising:
a battery charged by a generator driven by the engine for supplying
power to the electric heater and for driving a starter;
a temperature sensor for detecting a temperature of the engine;
and
means for comparing the temperature of the engine with a predetermined
value and prohibiting a current flowing to the electric heater before
the engine starts operating when the temperature of the engine is
equal to or less than the predetermined value.
In the first aspect of the present invention, the charged and discharged
current is detected by the current sensor. The value of the charged
and discharged current is summed up thereby calculating the charged
quantity of the battery. When the charged quantity is equal to or
less than the predetermined value, the current flowing to the electric
heater is prohibited at least before the engine starts operating.
In the second aspect of the present invention, the discharged quantity
of the battery is calculated by multiplying the predetermined value
of the current flowing to the electric heater by the time of flowing
current to the electric heater. The charged quantity is calculated
by summing up the generated current of the generator which is calculated
by the revolution number of the engine. When the value of the charged
quantity subtracted by the discharged quantity is the predetermined
value or less, the current flowing to the electric heater is prohibited
at least before the engine starts operating.
In the third aspect of the present invention, the temperature of
the engine is detected by the temperature sensor. When the temperature
of the engine is the predetermined value or less, the current flowing
to the electric heater before the engine starts operating, is prohibited.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a construction diagram of an embodiment 1 of the invented
device;
FIG. 2 is a construction diagram of the conventional device;
FIG. 3 is a flow chart showing operation of the conventional device;
FIG. 4 is a diagram showing a relationship between time and temperature
of a catalyst;
FIG. 5 is a characteristic diagram showing a residual capacity
of a battery due to flowing currents to an electric heater;
FIGS. 6(a) through 6(d) are time charts showing operation of the
embodiment 1 of the invented device;
FIG. 7 is a characteristic diagram of an output of current of a
generator according to the embodiment 1 of the present invention;
FIG. 8 is a flow chart showing operation of the embodiment 1 of
the invented device;
FIG. 9 is a flow chart showing operation of the embodiment of the
invented device;
FIG. 10 is a construction diagram of an embodiment 2 of the invented
device;
FIG. 11 is a flow chart showing operation of the embodiment 2 of
the invented device;
FIG. 12 is a construction diagram of an embodiment 3 of the invented
device;
FIG. 13 is a diagram showing a current-voltage characteristic of
a battery;
FIG. 14 is a diagram showing a relationship among a temperature
of an engine, a revolution number of the engine and a starting current
when the engine is started; and
FIG. 15 is a flow chart showing operation of the embodiment 3 of
the invented device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Explanation will be given to a first embodiment of this invention
referring to the drawings as follows. FIG. 1 shows construction
of a control device for a catalyst having an electric heater incorporating
an embodiment of an engine control unit. A notation 14a designates
a catalyst control unit, and 16, a current sensor for detecting
a charged and discharged current of the battery 11. The other construction
is the same as in FIG. 2.
Next, the operation of the above construction will be explained
based on time charts of FIGS. 6(a) through 6(d). First, when preheating
and heating after starting are performed by flowing current to the
electric heater 9 incorporated in the catalyst unit 8 as shown in
FIG. 6(a), the battery 11 discharges by a large current as shown
in FIG. 6(c), and as a result, the residual capacity of the battery
11 is considerably reduced as shown in FIG. 6(d). Even after the
engine 1 is started, current flows from the battery 11 to the electric
heater 9 for the heating after starting. Although the generator
10 driven by the engine 1 starts generating power, compared with
the generated current, the current consumed by the electric heater
9 is predominantly large (the generated current is 60 to 90 A, the
consumed current is 200 to 400 A). Accordingly, the battery 11 keeps
discharging. When the heating after starting of the electric heater
9 is finished, the charging to the battery 11 is made possible.
The revolution number of the engine varies in correspondence with
a running state of a vehicle as shown in FIG. 6(b). The revolution
number of the generator 10 which is mechanically coupled with the
engine 1 by a belt, similarly varies. Since an output current of
the generator 10 with respect to the revolution number thereof has
a saturation characteristic as shown in FIG. 7, the charged current
of the battery 11 is as shown in FIG. 6(c). The residual capacity
of the battery 11 gradually recovers by the charged current as shown
in FIG. 6(d). Naturally, when the output current of the generator
10 is consumed by an electric load such as a headlamp, the charged
quantity to the battery 11 is reduced, and the recovery of the battery
11 is delayed.
As the current sensor 16 for detecting the charged and discharged
current of the battery 11, one using a shunt resistance or one using
a Hall element is reduced to practice. Since they belong to a well-known
technology, a detailed explanation will be omitted.
Next, explanation will be given to the operation of the catalyst
control unit 14a. Normally, the control switch 12 is turned on for
a predetermined time since the key switch 13 has been turned on
to the IG position, thereby flowing current to the electric heater
9. Receiving the output of the current sensor 16, the catalyst control
unit 14aoperates as shown in a flow chart of FIG. 8. First, in step
200, the operation samples an output signal I of the current sensor
16 at every predetermined time interval T.sub.O (for instance, 0.1
seconds). In step 201, the operation sums up the value at every
sampling.
The current value I has a minus value when the battery 11 is discharged,
and a plus value when the battery 11 is charged. In this way, the
current value I is sampled since the current flowing to the electric
heater 9 has been started until the operation of the engine 1 is
stopped. A charged quantity Ah(c) is obtained by summing up the
current value I multiplied by the sampling time T.sub.O. This value
is retained in a nonvolatile memory even after the engine stops.
In the conventional device, current always flows to the electric
heater after the engine stops and when the next starting is performed.
In this embodiment, the device operates as shown in a flow chart
of FIG. 9.
In step 300, the operation determines whether the key switch 13
is turned on. When the key switch 13 is turned on, in step 301,
the operation determines whether the charged quantity Ah of the
battery in the previous running is larger than a criteria Ah(x).
When the charged quantity Ah of the battery is larger than the criteria
Ah(x), the operation proceeds to step 302, and flows current to
the electric heater for a predetermined time. When Ah <Ah(x),
the operation prohibits at least the flowing current to the electric
heater 9 before starting. As for the heating after starting, it
is desirable to prohibit the flowing current thereafter in view
of protection of the battery 11. However, this matter should be
decided in relation to the purification of the exhaust gas.
As a rule, the criteria Ah(x) is preferable to have a value a little
larger than 0. The reason is because the charging efficiency of
the battery 11 is not 100%, and the battery has a charging loss.
By using the criteria, repetition of the flowing current to the
electric heater in a short interval, is prohibited thereby preventing
to reduce the residual capacity of the batter 11.
In the first embodiment, explanation has been given to the case
wherein the charged quantity of the battery 11 is detected by the
current sensor 16. A second embodiment will be explained according
to FIGS. 10 and 11. FIG. 10 shows construction of the embodiment
2 of the invented device. A notation 14b designates a catalyst control
unit. An output of the revolution number sensor 3 is inputted to
the catalyst control unit 14b other than to the engine control unit
6. The other construction is the same as in FIG. 2.
Next, explanation will be given to the operation of the catalyst
control unit 14 referring to a flow chart of FIG. 11. In step 400,
the operation reads the operation of the electric heater 9. In step
401, the operation reads a value I.sub.H of a current to the electric
heater which has previously been memorized in a memory of the catalyst
control unit 14b. The operation multiplies the value I.sub.H by
an operating time T.sub.1 of the electric heater 9 thereby calculating
a discharged quantity Ah(d) of the battery 11. In step 402, the
operation samples a revolution number of the engine N.sub.e by an
output of the revolution number sensor 3 at every predetermined
interval T.sub.O. In step 403, the operation reads a generated current
I.sub.G from the N.sub.e -I.sub.g characteristic of the generator
10 shown in FIG. 7. In step 404, the operation multiplies I'.sub.g,
the generated current I.sub.G subtracted by an average of various
electric loads which are normally utilized such as in an ignition
coil (for instance, I.sub.G .times.0.6 ) by the sampling interval
T.sub.O, and obtains a presumed value of a charged quantity Ah(c)
by summing up the products until the engine 1 stops. In step 405,
the operation obtains a charged and discharged quantity Ah from
a difference between the discharged quantity Ah(d) of the battery
obtained in step 401 and the charged quantity Ah(c) obtained in
step 404. This charged and discharged quantity Ah is memorized in
a nonvolatile memory even after the key switch 13 is turned off.
In starting up the engine 1 at the next time, current flows to the
electric heater 9 only when the charged and discharged quantity
Ah is equal to or more than a predetermined value Ah(x) as in the
first example using the current sensor 16.
As stated above, according to the first and the second aspects
of the present invention, in flowing current to the electric heater
of the catalyst, a charged state of the battery is determined. When
the charged electricity is insufficient, the flowing current to
the electric heater is prohibited at least before the engine starts
operating. Accordingly, the device can prevent the lowering of the
capacity of the battery, the voltage applied from the battery to
the starter is sufficiently procured, and the starting of the engine
by the starter can smoothly be performed.
Next, explanation will be given to a third embodiment of the present
invention referring to the drawings as follows. FIG. 12 shows construction
of the third embodiment. The same portion as in FIG. 2 is attached
with the same notation and the explanation is omitted. A notation
14c designates a catalyst control unit, and 20, a temperature sensor
for detecting a temperature of the engine 1. The temperature sensor
20 is provided at a position capable of detecting a temperature
of cooling water or engine oil.
Explanation will be given to the operation of the above construction
referring to a flow chart of FIG. 15. In step 501, the operation
determines whether the key switch 13 is turned on. When the key
switch 13 is turned on, the operation proceeds to step 502, and
reads an output of the temperature sensor 20. In step 503, the operation
compares a temperature "t" obtained from the output of
the temperature sensor 20 with a predetermined value "t.sub.1
". When t >t.sub.1, the operation proceeds to step 504 and
flows current to the electric heater 9 from the battery 11 for a
predetermined time before starting the engine. When t .ltoreq.t.sub.1,
the operation returns to step 501 and does not flow current to the
electric heater 9.
When the flowing current before starting is finished, driving (cranking)
of the starter 15 by the battery 11 is performed. Naturally, the
flowing current to the electric heater 9 after starting the engine
is performed for a predetermined time. The predetermined value t.sub.1
is determined in consideration of the temperature dependency of
the viscosity of the engine oil, the capacity of the battery 11
and the temperature characteristic of the internal resistance of
the battery. To obtain a good starting performance, t.sub.1 is pertinently
in a range of 0 to-10.degree. C. Accordingly, when the temperature
of the engine is below the lowest value of the range, the flowing
current to the electric heater before the engine is started (preheating)
is prohibited. When t.sub.1 is determined as t.sub.1 =-10.degree.
C., the flowing current to the electric heater 9 before the starting
is prohibited when the temperature of the engine is equal to or
less than -10.degree. C. Accordingly, as shown in curve "e"
of FIG. 14, the revolution number of the engine in cranking is provided
with a high value, and the engine 1 is excellently started.
As stated above, according to the third aspect of the present invention,
the engine temperature is detected. When the engine temperature
is equal to or less than the predetermined value, the flowing current
to the electric heater before the engine starts operating, is prohibited.
Accordingly, the lowering of the capacity of the battery before
the starting of the engine can be prevented, and a comparatively
high revolution number of the engine can be procured even when the
engine is cold wherein the load torque of the starter is large,
thereby preventing the in capacitance of starting. |