JP4003702B2 - Motor drive device for motor mounted on vehicle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric motor drive device for driving an electric motor, and more particularly to an electric motor drive device for an electric motor mounted on a vehicle such as an electric motor of an electric power steering device for a vehicle.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering apparatus that uses an electric motor that can improve fuel efficiency and the like has been put into practical use as compared with a hydraulic power steering apparatus that uses hydraulic pressure as power.
[0003]
In such an electric power steering apparatus, for example, as shown in FIG. 7, a microcomputer (hereinafter referred to as a microcomputer) 1 has a torque sensor 2 for detecting a steering torque, a vehicle speed sensor 3 for detecting a vehicle speed, and an electric motor M. Based on signals from various sensors such as the current sensor 4 that detects the current of the motor, in order to give an auxiliary steering force to the steering system, the drive direction and output torque of the motor M are determined, and the drive circuits 5a and 5b are driven. The electric motor M is driven. Reference numeral 7 denotes a relay circuit that cuts off the power supply to the apparatus, which opens and closes according to the operation of an ignition switch (not shown), and cuts off the power when the apparatus breaks down.
[0004]
As shown in FIG. 7, such a device includes a bridge circuit 6 composed of four n-channel field effect transistors (hereinafter referred to as FETs) Q1 to Q4, and a battery B between its input terminals. An electric motor M is connected between the output terminals, and the FETs forming the opposite sides are driven to the right or left by driving them on or PWM. Rq is a discharge resistance that becomes a discharge path when the FET is turned off.
[0005]
By the way, in order to turn on an n-channel type field effect transistor, it is generally necessary to raise the gate potential by at least about 3 V with respect to the source potential, and in general, it is necessary to raise it further to stably turn on. Are known.
[0006]
In this bridge circuit 6, in order to turn on each FET, the high potential side FETs, that is, Q1 and Q2, have a source potential equal to the battery voltage when turned on. 5a is driven at a voltage higher than the battery voltage boosted by the booster circuit 10. On the other hand, the low potential side FETs, that is, Q3 and Q4 are driven by the battery voltage because the source potential is the ground potential by the drive circuit 5b.
[0007]
[Patent Document 1]
Japanese Patent No. 2864474 [0008]
[Problems to be solved by the invention]
In the device as described above, when the battery voltage decreases, the high-potential side FETs Q1 and Q2 driven by the voltage boosted by the booster circuit 10 are given a sufficient voltage to turn on, but the battery voltage The low-potential side FETs Q3 and Q4 that are driven by the above are not supplied with a sufficient voltage to be stably turned on, and in the worst case, they cannot be turned on and the motor M cannot be driven.
[0009]
The present invention solves the above-described problem, and even when the power supply voltage (battery voltage) is lowered, all the FETs constituting the bridge circuit can be driven, and the motor driving device capable of driving the motor stably and effectively The purpose is to provide.
[0010]
[Means for Solving the Problems]
An electric motor driving apparatus according to the present invention includes a bridge circuit using an n-channel field effect transistor, an electric motor driving power source is connected between input terminals of the bridge circuit, an electric motor is connected between output terminals, and the bridge Among the n-channel field effect transistors constituting the circuit, the n-channel field effect transistor connected to the high potential side of the motor driving power source is driven through the first booster circuit, and the motor driving power source the n-channel type field effect transistor connected to the low potential side, and driven through the second boost circuit, the output voltage of the first boost circuit, rather high than the output voltage of the second booster circuit, The output of the second booster circuit is branched, one drives an n-channel field effect transistor connected to the low potential side, and the other is input to the first booster circuit. It is those that.
[0011]
[0012]
[0013]
[0014]
Further, when a failure of the motor drive device is detected by the failure detection means for detecting a failure of the motor drive device, the operation of the booster circuit is stopped.
[0015]
Reference Example 1
Reference Example 1 will be described below. FIG. 1 is a diagram illustrating Reference Example 1. The same parts as those in the conventional apparatus shown in FIG.
[0016]
The difference between the above-described conventional device and Reference Example 1 is that the voltage boosted by the booster circuit 10 is also applied to the drive circuit 5b that drives the low-potential side FETs Q3 and Q4. In this way, by driving the low potential side FETs Q3 and Q4 via the booster circuit 10 as well, even when the battery voltage as a power source is lowered, all the FETs constituting the bridge circuit 6 are driven. The motor M can be driven stably and effectively. Therefore, the motor driving device can set a wide operating range with respect to the power supply voltage, or can set a large margin for a drop in the power supply voltage.
[0017]
Reference Example 2
In the reference example 1, the high-potential side FETs Q1 and Q2 and the low-potential side FETs Q3 and Q4 are configured to directly apply the voltage boosted by the common booster circuit 10, but as shown in FIG. 10 may be configured to apply a voltage to the low voltage side FETs Q3 and Q4 via the voltage dividing resistor Rs. In this case, the voltage dividing resistor Rs divides the voltage boosted by the booster circuit 10 with the discharge resistor Rq, and the power supplied to the low potential side FETs Q3 and Q4 is lower than the output voltage of the booster circuit 10, The resistance value is set to be higher than the power supply voltage. With this configuration, in addition to the effect that the electric motor can be driven stably and effectively, it is not necessary to use the booster circuit 10 to increase the voltage unnecessarily, and the power consumption can be suppressed. Further, the voltage supplied to the low potential side FETs Q3 and Q4 is relatively low, and an element having a low withstand voltage can be used as the low potential side FETs Q3 and Q4. Can do.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
In the reference examples 1 and 2 described above, all FETs are driven through the common booster circuit 10. However, as shown in FIG. 3, the booster circuit 11 for driving the high potential side FET and the low potential side FET drive are provided. Each booster circuit 12 may be provided. In this case, for example, the high potential side FET drive booster circuit 11 boosts the power supply voltage to three times, while the low potential side FET drive booster circuit 12 boosts the power supply voltage to twice. Thus, by providing separate booster circuits 11 and 12 on the high potential side and the low potential side and boosting the voltage to a voltage necessary for driving each FET, the motor can be driven stably and effectively. In addition to the effect, it is not necessary to boost the voltage in the booster circuit 11, and power consumption can be suppressed.
[0019]
In the first embodiment, the booster circuit 11 for driving the high potential side FET and the booster circuit 12 for driving the low potential side FET are configured as separate circuits. 11 is constituted by a booster circuit of triple voltage, a booster circuit to double voltage is constructed as a preceding stage. The booster circuit to double voltage included in this booster circuit 11 is a low potential side FET. It may be configured to be used as the driving booster circuit 12. With this configuration, it is possible to reduce the circuit scale and the number of parts.
[0020]
Embodiment 2. FIG.
This type of electric motor drive device is generally provided with a device failure diagnosis function. Since this failure diagnosis function itself is irrelevant to the present invention, detailed description thereof is omitted. In the first embodiment, the operation of the booster circuit 11 or 12 may be stopped when any failure is detected in the apparatus by the failure diagnosis function. With this configuration, the operation of the booster circuit 11 or 12 is stopped at the time of a device failure, the boosting operation is not continued unnecessarily, and the power consumption can be further suppressed. In this case, the power supply is shut off by turning off the relay circuit 7, or the operation of the booster circuit 11 or 12 is stopped by a command signal (not shown) from the microcomputer 1 while the relay circuit 7 remains on. Any method may be used to stop the operation of the booster circuit. In short, it is only necessary that the operation of the booster circuit can be prevented from being unnecessarily continued by stopping the operation of the booster circuit when any failure occurs in the apparatus.
[0021]
Other Embodiments In the first and second embodiments, the case where a DC motor is used as the motor has been described. However, the same applies to a drive circuit of a multiphase motor such as a three-phase AC motor. That is, a three-phase bridge circuit for driving a three-phase AC motor is composed of six FETs, and the same effect can be obtained by applying the first and second embodiments to the high potential side FET and the low potential side FET, respectively. Play.
[0022]
Furthermore, in the first and second embodiments, the electric motor used in the electric power steering apparatus has been described. However, the present invention is not limited to this, and other electric motors mounted on the vehicle such as a motor for driving a hydraulic pump of the power steering are used. Needless to say, the present invention can be applied.
[0023]
【The invention's effect】
As described above, the electric motor drive device according to the present invention can drive all the FETs constituting the bridge circuit even when the battery voltage as the power source is lowered, and makes the electric motor stable and effective. Can be driven. Therefore, the electric motor driving device has an effect that the operation range with respect to the power supply voltage can be set wide, or the margin for the reduction of the power supply voltage can be set large.
[0024]
In addition, the voltage supplied to the low-potential side FET can be reduced, and an element with a low withstand voltage can be used as the low-potential side FET, and the electric motor drive device can be made inexpensive. .
[0025]
Further, there is no need to use the booster to boost the voltage unnecessarily, and in addition to the effect that the electric motor can be driven stably and effectively, the power consumption can be suppressed. In addition, the circuit can be reduced in size and the number of parts can be reduced.
[0026]
Furthermore, the operation of the booster circuit is stopped when the device fails, and the power consumption can be further suppressed without wastefully continuing the boosting operation.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an electric motor drive device according to Reference Example 1. FIG.
FIG. 2 is a diagram showing a configuration of an electric motor drive device according to Reference Example 2;
FIG. 3 is a diagram showing the configuration of Embodiment 1 of the electric motor drive device according to the present invention.
FIG. 4 is a diagram showing a configuration of a bridge circuit in a conventional electric motor drive device.
[Explanation of symbols]
1: microcomputer, 2: torque sensor, 3: vehicle speed sensor, 4: current sensor, 5a, 5b: drive circuit, 6: bridge circuit, M: electric motor, B: battery, Q1 to Q4: n-channel field effect transistor 10-12: Booster circuit, Rq: Discharge resistor, Rs: Divider resistor

Claims (2)

An n-channel type field effect comprising a bridge circuit using an n-channel type field effect transistor, connecting a motor driving power source between input terminals of the bridge circuit, and connecting an electric motor between output terminals, and constituting the bridge circuit. Among the transistors, an n-channel field effect transistor connected to the high potential side of the motor driving power source is driven through the first booster circuit, and the n channel is connected to the low potential side of the motor driving power source. the type field effect transistor, driven through the second boost circuit, the output voltage of the first boost circuit, the second rather high than the output voltage of the booster circuit, the output of the second booster circuit branch is, one drives the n-channel type field effect transistor connected to the low potential side and the other, electrostatic is onboard, characterized in that it is input to the first boosting circuit The electric motor drive system of the machine. 2. The motor drive device for an on-vehicle motor according to claim 1 , wherein when a failure of the motor drive device is detected by a failure detection means for detecting a failure of the motor drive device, the operation of the booster circuit is stopped. .

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