Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-05-30
2001-12-25
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S798000, C318S599000
Reexamination Certificate
active
06333617
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Application No. 11-163996 filed on Jun. 10, 1999.
BACKGROUND OF THE INVENTION
The present invention relates to an electrical inductive load drive control which is applicable to, for instance, an electronic throttle control apparatus for vehicles for driving a throttle valve disposed in an engine intake pipe by a direct current motor in accordance with an accelerator pedal position and the like.
An H-bridge drive circuit is conventionally used as a load drive apparatus for driving an electrical load such as a direct current motor having inductive coils. In this load drive device, four switching devices are diagonally connected to cross each other. The energization or deenergization of the load are switched by turning on or off the switching devices at certain duty ratios.
It is necessary to extinguish energy which is generated in the coil of the direct current motor, when the switching device is turned off to change the direct current motor from the energized condition to the deenergized condition.
In JP-A-9-18313, it is proposed to turn on two switching devices at high side or low side to form a closed loop including the load, thereby extinguishing the energy generated in the coil of the direct current motor through the closed loop. It is also proposed to connect diodes in parallel with the drive terminals of the switching device to extinguish the energy generated in the coil. For instance, the body diode integrally built in a MOSFET is forward-biased when the direct current motor is deenergized, thereby extinguishing the generated energy between a power source and the ground through the body diode.
MOSFETs are generally used as switching devices. In the MOSFET, as shown in
FIG. 12A
, power loss Pm between its drain and its source increases remarkably as electric current between its drain and its source. The power loss Pm of the MOSFET at the time of energy extinction increases in proportion to the square of the current I and the on-resistance R of the MOSFET, that is, Pm=R×I
2
.
In diodes, a forward voltage Vf increases gradually as a forward current I increases, so that power loss Pd in the forward direction increases as shown in
FIG. 12B
, that is, Pd=Vf×I.
Accordingly, the power loss Pm increases remarkably as the current I increases at the time of deenergization of the direct current motor in the case of extinguishing the energy through the closed loop, while the power loss Pm is rather small as long as the current I is relatively low. The change rate of power loss Pd is relatively low at the time of deenergization of the direct current motor in the case of the diode when the current I is low, while the power loss Pd is relatively low in comparison with the case of the closed loop when the current I is high.
If the low power loss should be reduced over a wide range of current I, the MOSFET must be sized large in chip size for a low on-resistance over the wide current range in the case of the closed loop. The MOSFET must be sized large to have a large allowable power loss in the case of the diode. In either case, the switching devices become expensive.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an inductive load drive control capable of reducing power loss at the time of energy extinction and reducing cost of switching devices.
According to the present invention, an electrical inductive load such as a direct current motor is energized and deenergized by switching devices such as MOSFETs. Diodes are connected in parallel with the switching devices, respectively. A current supplied to the inductive load immediately before deenergizing the inductive load is detected. The inductive load is energized and deenergized by turning on and off the switching devices. The switching devices are forcedly turned on or off to extinguish energy generated in the inductive load at the time of changing from an energization to a deenergization of the inductive load. The switching devices are forced to turn on to extinguish the energy by circulating the energy therethrough when the current is small, while the switching devices are forced to turn off to extinguish the energy through the diodes when the current is large. Thus, power loss is minimized over an entire range of the current.
REFERENCES:
patent: 5343382 (1994-08-01), Hale et al.
patent: 5379209 (1995-01-01), Goff
patent: 5712550 (1998-01-01), Boll et al.
patent: 6075334 (2000-06-01), Sagues et al.
patent: 6130831 (2000-10-01), Matsunaga
patent: 5-038188 (1993-02-01), None
patent: 9-18313 (1997-01-01), None
patent: 9-183113 (1997-01-01), None
Itabashi Toru
Tamai Hideaki
Denso Corporation
Masih Karen
Nixon & Vanderhye P.C.
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