Abstrict
An electric heater for a motor vehicle uses heat generated by power
semiconductors as the heat source. The heat output by the power
semiconductors is used directly for heating. The power semiconductors
are regulated by circuit regulators to be able to adjust the heating
power continuously. In addition, switching devices are provided
which interrupt or shut down the respective branch circuits individually
in the event of short circuits in the power semiconductors.
Claims
What is claimed is:
1. An electric heater for a motor vehicle, comprising:
a plurality of branch circuits, each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater, wherein each of the power semiconductors
generates a respective power output, and wherein each of the respective
power outputs is regulated using a common predetermined setpoint
value and an actual value of a current flowing in a respective one
of the branch circuits.
2. An electric heater, for a motor vehicle, comprising:
a plurality of branch circuits, each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater; and
switching devices, each of the switching devices responding to
an overload and connected in series to the respective power semiconductor
in a corresponding branch circuit of the branch circuits;
wherein each of a first set of the power semiconductors generates
a respective first power output, each of the first respective power
outputs being controllable using a common predetermined setpoint
value and respective actual value of a current flowing in a respective
one of the branch circuits, and
wherein each of a second set of the power semiconductors generates
a respective second power output, each of the respective powers
output being controllable using a fixed predetermined control voltage
and respective actual values of a further current flowing in a respective
one of the branch circuits.
3. An electric heater for a motor vehicle, comprising:
a plurality of branch circuits, each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater, wherein each of the branch circuits includes
a low-resistance series resistor and an output for supplying power
to the low-resistance series resistor as a load impedance.
4. An electric heater for a motor vehicle, comprising:
a plurality of branch circuits, each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater, wherein each of the switching devices is
designed as a printed conductor part, the printed conductor part
burning out if an elevated current flows in the respective one of
the branch circuits, the elevated current being indicative of a
fault.
5. An electric heater for a motor vehicle, comprising:
a plurality of branch circuits, each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater, wherein the switching devices are looped
as shunts into the branch circuits, the branch circuits burning
out if an elevated current flows in a respective one of the branch
circuits, the elevated current being indicative of a fault.
6. An electric heater for a motor vehicle, comprising
a plurality of branch circuits, each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater, wherein the power semiconductors include
connecting wires, the connecting wires being utilized as switching
devices which burn out if an elevated current flows in a respective
one of the branch circuits, the elevated current being indicative
of a fault.
7. An electric heater for a motor vehicle, comprising:
a plurality of branch circuits. each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater; and
switching devices, each of the switching devices responding to
an overload and connected in series to the respective power semiconductor
in a corresponding branch circuit of the branch circuits;
wherein, if a short circuit occurs in a first respective semiconductor
of the power semiconductors which are connected in series in a respective
defective branch circuit of the branch circuits, the respective
defective branch circuit generating a control signal, the control
signal one of reducing a power output which is generated by a second
respective semiconductor of the power semiconductors and switching
a status of the second respective semiconductor to a disconnect
status.
8. An electric heater for a motor vehicle, comprising:
a plurality of branch circuits, each of the branch circuits including
a respective power semiconductor which operates in a high power
loss operation, the branch circuits being connected in parallel
for generating heat, the heat being generated by the respective
power semiconductor of each of the branch circuits as a heat source
for the electric heater, wherein the electric heater is a heater
module which includes a cooling body, and wherein the power semiconductors
are mounted, via a thermal contact, on the cooling body.
9. The electric heater according to claim 8, further comprising:
temperature sensors monitoring at least one of the power semiconductors
and the cooling body to detect whether a predetermined maximum temperature
threshold is exceeded, the temperature sensors generating output
signals, wherein the output signal of a particular sensor of the
temperature sensors at least one of:
reduces a power output of one of a respective semiconductor of
the power semiconductors and all of the power semiconductors, and
switches a status of the power semiconductors to a disconnect status.
10. The electric heater according to claim 9, wherein the temperature
sensors are integrated into the power semiconductors.
11. An electric heater for a motor vehicle, comprising:
a plurality of branch circuits, each of the branch circuits including
a respective pair of serially-connected power semiconductors which
operate in a high power loss operation, the branch circuits being
connected in parallel for generating heat, the heat being generated
by the respective pair of power semiconductors of each of the branch
circuits as a heat source for the electric heater.
12. The electric heater according to claim 11, further comprising:
switching devices, each of the switching devices responding to
an overload and connected in series to the respective pair of power
semiconductors in a corresponding branch circuit of the branch circuits.
13. The electric heater according to claim 12, wherein each of
the pairs of power semiconductors generates a respective power output,
and wherein each of the respective power outputs is regulated using
a common predetermined setpoint value and an actual value of a current
flowing in a respective one of the branch circuits.
14. The electric heater according to claim 11,
wherein a first one of the respective pair of power semiconductors
generates a respective first power output, each of the first respective
power outputs being controllable using a common predetermined setpoint
value and respective actual value of a current flowing in a respective
one of the branch circuits, and
wherein a second one of the respective pair of power semiconductors
generates a respective second power output, each of the respective
powers output being controllable using a fixed predetermined control
voltage and respective actual values of a further current flowing
in a respective one of the branch circuits.
15. The electric heater according to claim 11, wherein the power
semiconductors are interruptible in response a short circuit.
16. The electric heater according to claim 11, wherein each of
the branch circuits includes a low-resistance series resistor and
an output for supplying power to the low-resistance series resistor
as a load impedance.
17. The electric heater according to claim 11, wherein each of
the switching devices is designed as a printed conductor part, the
printed conductor part burning out if an elevated current flows
in the respective one of the branch circuits, the elevated current
being indicative of a fault.
18. The electric heater according to claim 11, wherein the switching
devices are looped as shunts into the branch circuits, the branch
circuits burning out if an elevated current flows in a respective
one of the branch circuits, the elevated current being indicative
of a fault.
19. The electric heater according to claim 11, wherein the power
semiconductors include connecting wires, the connecting wires being
utilized as switching devices which burn out if an elevated current
flows in a respective one of the branch circuits, the elevated current
being indicative of a fault.
20. The electric heater according to claim 11, wherein, if a short
circuit occurs in a first semiconductor of the respective pair of
power semiconductors connected in series in a respective defective
branch circuit of the branch circuits, the respective defective
branch circuit generating a control signal, the control signal one
of reducing a power output which is generated by a second semiconductor
of the respective pair of power semiconductors and switching a status
of the second semiconductor to a disconnect status.
21. The electric heater according to claim 11, wherein the electric
heater is a heater module which includes a cooling body, and wherein
the power semiconductors are mounted, via a thermal contact, on
the cooling body.
22. The electric heater according to claim 21, further comprising:
temperature sensors monitoring at least one of the power semiconductors
and the cooling body to detect whether a predetermined maximum temperature
threshold is exceeded, the temperature sensors generating output
signals, wherein the output signal of a particular sensor of the
temperature sensors at least one of:
reduces a power output of one of a respective semiconductor of
the power semiconductors and all of the power semiconductors, and
switches a status of the power semiconductors to a disconnect status.
23. The electric heater according to claim 22, wherein the temperature
sensors are integrated into the power semiconductors.
Description FIELD OF THE INVENTION
The present invention relates to an electric heater for a motor
vehicle, using the heat generated by power semiconductors as the
heat source.
BACKGROUND INFORMATION
Such a heater is described in German Patent No. 34 42 350. With
this known heater, the power semiconductor controls the electric
drive motor. The power semiconductor is connected to a cooling body
through which a liquid coolant flows, so the heat generated is transferred
to the liquid coolant by heat exchange. The liquid coolant circulates
in a closed line system having a pump and the actual heater installation.
The efficiency of this known electric heater is not especially
great, because the heat generated by the power semiconductor must
be converted repeatedly. In addition, the heater installation has
a complicated design, depends on the engine current present and
thus cannot be regulated independently of the latter.
SUMMARY OF THE INVENTION
The object of the present invention is to create an electric heater,
where the efficiency is greatly increased with a simple design and
independent regulation of heating power is possible.
This object is achieved according to a first embodiment of the
present invention by connecting several branch circuits, each with
one power semiconductor operated in high power loss operation, in
parallel for generation of heat, or according to a second embodiment
by connecting several branch circuits, each with two series-connected
power semiconductors operated in high power loss operation, in parallel
for generation of heat.
In these embodiments, the current is converted directly into heat
by the power semiconductors, which greatly increases efficiency.
Another advantage of the new heater is that no additional control
module is needed for the heater. Installation of the heater in the
motor vehicle is also greatly simplified. In addition, the cabling
complexity and manufacturing costs of the new electric heater are
also reduced.
No separate fuse protection for the heater in the vehicle electrical
system is necessary. When starting operation of the heater, the
high starting current surge can be prevented by a regulated smooth
current rise. The new heating module can be cascaded in any desired
fashion to increase the heating power and can also be integrated
easily into a fan regulator.
To protect the power semiconductors, one embodiment provides for
a switching device that responds to overload to be connected in
series with the power semiconductor in each branch circuit. In the
event of a fault, the branch circuit affected can be shut down with
this switching device without having to lose heater function as
a whole. Heating power is reduced only by the ratio of defective
branch circuits to total branch circuits.
According to another embodiment, regulation of the heating power
is easily made possible by the fact that the power output by the
power semiconductors can be regulated individually by a common predetermined
setpoint and by actual values derived from the power semiconductors,
or by the fact that the powers output by the respective first power
semiconductors of the branch circuits can be regulated individually
by a common predetermined setpoint and by actual values derived
at these power semiconductors, and the powers output by the respective
second power semiconductors can be regulated individually by a fixed
predetermined control voltage and by actual values derived at these
power semiconductors.
If the branch circuits are to supply power at the output to a low-resistance
series resistor as a load impedance, then the heat generated by
the series resistor can contribute to an increase in heating power.
Each power semiconductor can supply power to an individual series
resistor. All the power semiconductors may also supply power to
a common series resistor, or groups of power semiconductors may
each be connected to a group-individual series resistor.
The switching devices for interrupting the branch circuits can
be implemented in various ways. Thus, according to one embodiment,
the switching devices may be designed as a printed conductor part
of the branch circuits which burn out in the event of a fault at
the elevated current occurring in the respective branch circuit.
The same effect can also be achieved by looping the switching devices
as shunts into the branch circuits, which burn out in the event
of a fault at the elevated current occurring in the respective branch
circuit, in which case the shunt can also be used to derive another
control signal. The branch circuit can also be interrupted by using
the connecting wires of the power semiconductors which burn out
in the event of a fault at the elevated current occurring in the
respective branch circuit.
A controlled reduction or interruption in the current in a defective
branch circuit occurs when measures are taken to ensure that in
the event of a short circuit in one of the two power semiconductors
connected in series in a branch circuit, an additional control signal
can be derived from the defective branch circuit to reduce the power
output by the respective second power semiconductor or switching
it to a disconnect status. The control signal picked off at the
shunt can be used as the control signal.
The structural design of the new electric heater can be simplified
by designing it as a heater module, with the power semiconductors
mounted in thermal contact on a cooling body, with the heat transfer
via the cooling body being improved.
Simple temperature monitoring can be achieved with the electric
heater by the fact that the power semiconductors and/or the cooling
body are monitored by temperature sensors to detect whether a predetermined
maximum temperature is exceeded, and by the fact that the output
signals of the temperature sensor(s) reduce the power output by
the respective power semiconductors or all the power semiconductors
or switch them to a disconnect status. If the power semiconductors
are monitored by individual temperature sensors, the expense of
this is reduced by integrating the temperature sensors into the
power semiconductors.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a circuit diagram of a first embodiment of an electric
heater with n parallel branch circuits, each containing one power
semiconductor.
FIG. 2 show a circuit diagram of a second embodiment of the electric
heater with n parallel branch circuits, each having two series-connected
power semiconductors.
FIG. 3 is a cross-sectional view showing power semiconductors mounted
on a cooling body in accordance with the present invention.
DETAILED DESCRIPTION
As FIG. 1 shows, branch circuits Z1, Z2, . . . Zn are connected
in parallel to one another at power supply voltage Ubatt, with each
branch circuit Z1, Z2, . . . , Zn having a power semiconductor FET1,
FET2, . . . , FETn. The connection to power supply voltage Ubatt
is by way of switching devices FUSE1, FUSE2, . . . , FUSEn, which
perform an individual interruption of branch circuit Z1, Z2, . .
. , Zn in the event of a fault, e.g., a short circuit of the power
semiconductor at which the multiple current occurs. A shunt which
is not shown in detail may be added to the connection of power semiconductors
FET1, FET2, . . . , FETn at the ground potential, where an individual
actual value Istl, Ist2, . . . Istn can be derived for the branch
circuit Z1, Z2, . . . , Zn. In addition to the actual value detected
at the shunt, a setpoint Isoll is supplied to the gate terminal
of power semiconductors FET1, FET2,. . . , FETn via a comparator
or operational amplifier that serves as a circuit regulator to permit
continuous regulation of the power in the respective power semiconductor.
If the actual value exceeds setpoint Isoll, then the circuit regulator
switches the power semiconductor into the disconnect status or reduces
the power output. In addition, switching device FUSE1, FUSE2, .
. . , FUSEn can completely interrupt branch circuit Z1, Z2, . .
. , Zn in the event of a short circuit of respective power semiconductor
FET1, FET2, . . . , FETn.
Printed conductor segments of branch circuit Z1, Z2 . . . . , Zn
themselves can be used as switching devices FUSE1, FUSE2 . . . .
, FUSEn. Depending on the design of branch circuits Z1, Z2, . .
. , Zn and the respective circuit regulator, the current may increase
to a level 25 to 50 times higher in the event of a short circuit,
so the printed conductor part burns out. The shunt can also be used
as a switching device if it burns out with this current rise and
interrupts branch circuit Z1, Z2 . . . . , Zn. Even the connecting
wires of power semiconductors FET1, FET2 . . . . , FETn can be dimensioned
to assume the function of switching devices FUSE1, FUSE2, . . .
. , FUSEn. The electric heater of this type may be designed as a
heater module, the power semiconductors (collectively shown as layer
1 in cross-sectional FIG. 3) mounted on a cooling body 10, and integrated
into a fan regulator; furthermore, the heater module itself need
no longer be fused with respect to the vehicle's electrical system.
However, it may be necessary to fuse the feeder lines to the heater
module.
In the embodiment shown in FIG. 2, each branch circuit Z1, Z2,
. . . , Zn has two series-connected power semiconductors FET11 and
FET12, FET21 and FET22, . . . FETnl and FETn2, each controlled by
its own circuit regulator. As in the embodiment according to FIG.
1, a switching device FUSE1, FUSE2, . . . , FUSEn and a shunt can
be looped into branch circuits Z1, Z2, . . . , Zn. Switching devices
FUSE1, FUSE2, . . . , FUSEn in turn can be designed in the variants
described. Control signals characterizing actual value Ist11, Ist2l,
. . . Istnl of branch circuit Z1, Z2, . . . , Zn can be picked off
at the shunts of the branch circuits and sent to the circuit regulators
of the respective first power semiconductors FET11, FET21, . . .
, FETnl to which can also be sent a setpoint Isoll to regulate the
power in branch circuit Z1, Z2, . . . , Zn. The second power semiconductors
FET12, FET22, . . . , FETn2 are controlled by separate circuit regulators
to which are sent a fixed predetermined control voltage ust and
an actual value Istl2, Ist22, . . . , Istn2, which is derived from
the voltage drop at the first upstream power semiconductor FET11,
FET21, . . . , FETnl. In the event of a short circuit or defect
in a power semiconductor such as FET11 with this design of the circuit
regulators, the respective second power semiconductor, such as FET12,
in branch circuit Z1 can be shut down or the power output by it
can be reduced. However, the functioning of the remaining system
is not affected, and the heating power is merely reduced by the
ratio of defective branch circuits to total branch circuits.
If both power semiconductors, e.g., FET21 and FET22, are short-circuited,
then the switching device, e.g., FUSE2 as in the embodiment shown
in FIG. 1, goes into operation and interrupts the branch circuit,
e.g., Z2, at the high current rise occurring.
If only one common heat-dissipating, low-resistance series resistor
is used as the load impedance for all branch circuits Z1, Z2, .
. . , Zn to increase the heating power, then this resistor is looped
into the common line leading to battery voltage Ubatt. This series
resistor does not change the operation of the electric heater, it
merely limits the current rise to a lower level in the event of
a short circuit in a single power semiconductor (FIG. 1) or both
power semiconductors (FIG. 2), but this lower level is still sufficient
for a reliable response of switching device FUSE1, FUSE2, . . .
, FUSEn. The heat generated by the series resistor is also used
for heating, but it entails a power distribution which can be utilized
at a predetermined maximum heating power to expand the temperature
use range for the heater.
Each power semiconductor or each pair of power semiconductors can
also be connected to battery voltage Ubatt across an individual
series resistor. Groups of branch circuits may also supply a series
resistor. In any case, all the series resistors are involved in
the production of heat.
Temperature monitoring can easily be incorporated into the new
heater. Thus, a temperature sensor may be provided for each power
semiconductor and may also be integrated into the power semiconductor.
If a predetermined maximum temperature is exceeded at the power
semiconductor, the output signal of the temperature sensor then
controls the respective power semiconductor so that its power output
is reduced or it is completely shut down.
It is also possible to provide just one temperature sensor for
measuring the temperature of the cooling body, with all the power
semiconductors of the electric heater being in thermal contact with
it. If the temperature of the cooling body 10 exceeds a predetermined
maximum temperature, then all the power semiconductors are controlled
with the output signal of the temperature sensor in such a way that
their power output is reduced or they are completely shut down.
Different values of the output signal of the temperature sensor
can be used for this purpose, with the output signal initially triggering
a power reduction at the first lower value and a complete shutdown
at the second higher value of the output signal.
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