JPH02212269A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To suppress ripples on current by controlling a motor drive circuit with a pair of drive elements of a drive element for motor driver circuit, controlling the motor direction with another pair of drive elements, and thereby mitigating change in the gate voltage of the drive elements. CONSTITUTION:In an arrangement according to the present invention, wherein drive control is made for a motor, which is to assist the front wheel steering from a control unit 10 on the basis of output of a car speed sensor 7 and a steering torque sensor 3, the control unit 10 determines the differential integral value 32a of the motor indicative current value 30a with the motor current value 31a, and according to the value obtained duty pulses 33a are emitted. Drive elements (FET) 24-27 constituting a chopping circuit of H bridge are controlled by AND gates 18-21 from a current direction signal 34a, output 35a of a comparator 23 to judge the upper limit of the motor current value 31a, and duty pulses 33a, and chopping is performed by a pair of drive elements, while another pair of drive elements make control of the rotating direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive control circuit for a motor in an electric power steering device.

[Conventional technology]

In order to reduce the steering wheel operation force when steering,
A torque sensor is provided to detect one steering torque during a steering operation, and the steering torque is converted into an electrical quantity according to the output signal of the torque sensor, and the output of the electric device is varied according to changes in the electrical quantity. An electrically controlled electric power steering device is known, for example, from Japanese Patent Publication No. 46-5168.

In addition, when actually driving the above-mentioned electric device, the simplest and simplest method is to chop the current of the drive circuit using an H bridge using an FET. US Patent No. 4
, 454,454.

(Problems to be Solved by the Invention) The above-mentioned conventional technology does not take into consideration the fact that the chopping noise that occurs when the motor drive circuit is subjected to chopping control has an adverse effect on in-vehicle communication equipment, such as radios and televisions. The current pulsation generated by chopping control is high, and in particular, harmonics higher than the chopping frequency are generated, so noise from radio etc. is noticeably cursed, causing discomfort to passengers.

An object of the present invention is to provide an electric power steering device that suppresses current pulsations caused by chopping control to a low level and does not generate noise.

Another object of the present invention is to provide an electric power steering device in which a motor drive circuit has good heat dissipation.

[Means to solve the problem]

In order to achieve the above object, one pair of drive elements for a motor drive circuit controls the motor drive circuit, and the other pair of drive elements controls the rotational direction of the motor.

Furthermore, the switching speed of the motor drive circuit element is slower than that of other rotational direction control drive elements.

Furthermore, in order to suppress changes in motor current, the rise of the gate voltage of a field effect transistor (hereinafter referred to as FET) is made gradual.

Furthermore, in order to balance the heat generation due to chopping loss and the heat generation due to the regenerative current, 4 FETs in the bridge are used.
Of these, it is a combination of upstream comrades and downstream comrades.

[Effect]

The drive element (FET) used in the motor drive circuit is configured such that one pair of drive elements controls the motor drive circuit, and another pair of drive elements controls the rotation direction of the motor.
It operates by switching between chopping control and direction control.

As a result, the gate voltage of the drive element changes slowly, and current pulsations in the battery line and motor line that supply current to the motor can be kept low, so communication equipment such as in-vehicle radios and televisions can be used to reduce noise. Can be kept low.

In addition, there are FETs that perform chopping control and FEs that do not operate.
Combining T comrades, F for chopping control and direction control
By balancing the amount of heat generated by the ET, the heat generated by the FET caused by increased chopping loss is effectively diffused, and the control element does not malfunction due to thermal effects.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

In FIG. 2, a steering shaft 1 has one end connected to a steering wheel 2, and the other end engaged with a rack 4 on the drive shaft side via a pinion 3. 5 is a torque sensor that detects the steering force from the steering wheel 2;
is a motor driven according to the output signal of the torque sensor 5 and the output signal of the vehicle speed sensor 7, which engages with the steering shaft 1 through the omitted gear mechanism and connects to the battery 9 through the key switch 8. It is controlled by a control unit 10 connected thereto.

When the driver steers the steering wheel 2, a steering torque is applied to the steering shaft 1, and the steering torque transmits a steering force to the rack 4 via the pinion 3.
Steering the wheels. In the power steering device of the present invention, in addition to the steering force obtained by the driver's steering, the steering torque sensor 3 detects the driver's steering force and direction, and the control unit 10 detects the driver's steering force and direction based on the signal from the vehicle speed sensor 7. A steering assist force corresponding to the steering force is calculated, and a current corresponding to the assist force is supplied to the motor 6 attached to the steering shaft 1 to assist the driver's steering force.

The control unit 10 further includes a vehicle speed sensor 7.
Based on the vehicle speed information, the motor current is determined so that the steering force is heavy at high speeds and light at extremely low speeds, achieving both drivability at low speeds and high-speed running stability.

FIG. 3 shows the relationship between the steering force of the steering wheel 2, the vehicle speed, and the motor current. When the vehicle speed is zero, as the steering torque of the steering wheel increases,
Increase motor current gradually. Furthermore, as the vehicle speed increases, the motor current is decreased to obtain the running stability shown above, as shown in the figure showing the relationship between the steering torque and the motor current.

FIG. 3 shows the configuration of the control unit 10, and the motor current steering torque sensor 5 shown in FIG.
, the signal from the vehicle speed sensor 7 is input to the signal input circuit 11 shown in FIG.
．． 12, the microcomputer 13 calculates the result and instructs the motor current control circuit.The result of the calculation by the microcomputer 13 is converted into an analog value 30a by the D/A converter 15, and the current value flowing through the motor 4 is converted by the D/A converter 15. 31a and the differential integration 16 into the duty level 32a, and further compares the triangular wave generated by the triangular wave generator 23 with the comparator 17.
Determine the on-duty ratio of chopping control (PWM).

FIG. 4 shows a time chart from 30a to 33a.

Motor instruction current value 30a and motor current value 31 shown earlier
A duty pulse 33a is obtained from the differential integral value 32a and the triangular wave 33a.

Further, the current direction signal 34a outputted from the microcomputer 13, the output 35a of the comparator 23 for determining the upper limit value of the motor current value 31a, and the signal of the previous duty pulse 33a are used to select the FET of the H bridge by AND gates 18 to 21. Driving logic is obtained as 18a-21a in FIG.

That is, the output 18a of the AND gate 18 drives the FET 25 via the processing circuit 22. At this time, 1
When the logic of 8a is "High" level, the operation of FET 25 is turned on. Similarly, for AND gate 19, FE
T24, and FET27 for AND gate 20,
Regarding the AND gate 21, F
Determine the drive logic of ET26.

Current flows when the FET is ON, so in the state shown in Figure 4, the gate 2o is ON, the gate 19 is 0N-OFF, and the gates 18 and 21 are ON, so the FET
25 is turned OFF, and FET 24 performs ON-OFF chopping.

Also, since FET21 is OFF, FET2
The current flowing from 4 passes through motor 6 and is applied to FET 27.
On the other hand, when the gate 19 is turned from ON to OFF, the regenerative current passes through the reverse diode of the FET 26, flows through the motor 6, and then flows through the FET 19. In this way, when FET 24 is chopping, no current flows through FET 25, but in this case, current flows through FET 26 and 27, which is the FE with the largest amount of heat generation.
T is 24 with chopping loss, but FET26
, 27, there is no chopping loss, but there is heat generated due to the resistance loss when the current passes.

Therefore, when FETs 24 and 25 and FETs 26 and 27 are combined, the amount of heat generated by them is almost the same, and neither one of them generates heat rapidly.

FIG. 6 shows the arrangement of this FET on a printed circuit board. Connectors 51, 5 on the printed circuit board 50
2. A microcomputer chip 53 and the like are arranged, and FETs 24 to 27 are also arranged at the same time. FET
On the back of 24 and 25, there is an aluminum block 54 and FET26.
, 27, an aluminum block 55 is arranged on the back.

As explained above, the heat generation of the FETs is approximately the same for the combination of the FETs 24 and 25 and the FETs 26 and 27, so the temperature rises of the aluminum blocks 54 and 55 are approximately the same.

FIG. 6 shows, from above FIG. 5, a plate for mounting the aluminum material.

The heat generated by the aluminum blocks 54 and 55 is transferred to the frame 56 and the mounting plate 57.

There are two factors that can be considered for the thermal destruction of FETs: the first is steady temperature, and the second is transient temperature.The first is steady temperature rise, which depends on the heat dissipation area. Since the mounting plate has a large area, it provides good heat dissipation.

Secondly, the heat capacity of the aluminum blocks 54 and 55 influences the transient state, but in this case as well, it can be said that good heat dissipation is achieved because there is a degree of freedom in designing the size of the aluminum blocks.

In the present invention, the current flowing to the motor is detected by amplifying the voltage drop caused by the current passing through the resistors 28 and 29 using the amplifier 38. As shown in FIG. 4, FET 26 or 27 only switches the current direction and does not perform chopping control. Therefore, as shown in FIG. 7, the voltage corresponding to the motor current is directly obtained. On the other hand, when the FETs 26 and 27 are used for chopping control, the passing current becomes zero during the OFF period of the FETs, so the measured current waveform becomes as shown in (3), which does not match the current waveform flowing to the motor at this time. In this case, it becomes necessary to sample and hold the voltage during the ON period of the FET, which requires an additional circuit.

Furthermore, due to variations in the resistance values of resistors 28 and 29,
The detection voltage varies accordingly, and therefore a detection voltage adjustment step is required. Therefore, FET26, 27
By using a sensing FET, the resistor 28.2
9 will be abolished. Sensing FET is a power MOSF
One of the hundreds of gates built into the ET is taken out and the weak current flowing through it is measured. Therefore, there is no variation and exhibits stable characteristics. Therefore.

This has the effect of eliminating the adjustment process.

Next, a method for delaying the rise of the gate voltage will be explained with reference to FIG. The FET that performs chopping has a resistor R at its gate, a capacitor between its drain and gate, and an internal capacitance of the FET between its source and gate. As the resistance value of the resistor R becomes larger, the rise speed of the gate voltage becomes slower, so the current of the drain resource that depends on the gate voltage also rises more slowly.

Looking more closely at the rise of the current, we can see that the moment the value of the voltage Vas between the source and gate of the FET exceeds a certain level, the current C suddenly flows, so the source voltage rises and Vas increases accordingly. descend. This reduces the current C.

In other words, when the 0FF-ION of the FET rises, the current waveform pulsates as shown in the figure d, and this frequency is about IM
Since it is approximately Hz, it matches the frequency of the AM band of the radio, and this current fluctuation becomes radio wave noise, which adversely affects radio reception.

In order to avoid this, it is necessary to delay the rise speed of Vas as much as possible, and in the present invention,
A resistor R and a capacitor C were inserted to delay the rise of Vos.

The increase in chopping loss due to the delay in the rise of Vas is
This can be dealt with by dissipating heat effectively as shown above.

〔Effect of the invention〕

According to the present invention, the drive circuit of the motor is controlled by a pair of drive elements of the drive element for a motor drive circuit, and the rotation direction of the motor is controlled by the other pair of drive elements. Since voltage changes can be made gentler and current pulsations can be suppressed to a low level, an electric power steering device that does not generate noise can be provided, which has the effect of suppressing noise generation in in-vehicle communication equipment.

[Brief explanation of the drawing]

FIG. 1 is a control circuit diagram of an electric power steering device according to an embodiment of the present invention, FIG. 2 is a schematic diagram of the same electric power steering device, FIG. 3 is a motor current characteristic diagram with respect to steering torque, and FIG. 4 is a diagram of motor current characteristics with respect to steering torque. Figure 5 is a plan view of the board on which the control circuit shown in Figure 1 is wired, Figure 6 is a side view and plan view of the same board, and Figure 7 is a diagram of the FET shown in Figure 1. FIG. 8 is a motor current waveform and chopping voltage waveform diagram for control waveforms, and FIG. 8 is a gate control circuit diagram and control waveform diagram of the FET of FIG. 1. 1... Steering shaft, 5... Torque sensor, 10... Control unit, 24-27...
Drive diagram 2 Figure 3 Steering torque diagram Figure (a) (bl Figure R547 ET27 Figure

Claims (1)

[Scope of Claims] 1. An electric power steering device in which a steering force of a steering shaft is detected by a torque detection means, and an auxiliary steering force is applied to the steering shaft by a motor in accordance with an output signal of the torque detection means, control means for calculating an output signal of the torque detection means;
An electric power steering device comprising: a pair of drive elements that control a drive circuit of a motor according to a signal from the control means; and a pair of drive elements that control a rotational direction of the motor. 2. The electric power according to claim 1, wherein the driving element is constituted by an H-bridge chopping circuit, and chopping is performed on either the upstream side or the downstream side, and the rotation direction is controlled on the other side. Steering device. 3. The electric power steering device according to claim 2, wherein the upstream and downstream drive elements are arranged close to each other and fixed to a heat sink. 4. In an electric power steering device in which a torque detection means detects a steering force on a steering shaft, and a motor applies an auxiliary steering force to the steering shaft in accordance with an output signal of the torque detection means, the output of the torque detection means a control means for calculating the signal;
A pair of drive elements for controlling a motor drive circuit according to a signal from the control means, and a pair of drive elements for controlling the rotational direction of the motor, the switching speed of the motor drive circuit drive element being controlled by the other drive element. An electric power steering device characterized in that the drive element for controlling the rotational direction is delayed. 5. The electric power steering device according to claim 4, wherein the drive element is constituted by an H-bridge chopping circuit, and chops on either the upstream side or the downstream side, and controls the rotation direction on the other side. . 6. In claim 4, the driving element is a power MOSFET.
An electric power steering device characterized in that the rise speed of gate voltage is limited by using 7. The electric power steering device according to claim 4, wherein the drive element constituting the H-bridge is subjected to chopping control on the upstream side, and a sensing FET is arranged on the downstream side. 8. The electric power steering device according to claim 5, wherein the chopping drive element has a capacitor disposed between the gate and the drain. 9. An electric power steering device in which a torque detection means detects a steering force on a steering shaft, and a motor applies an auxiliary steering force to the steering shaft according to an output signal of the torque detection means, the output of the torque detection means; a control means for calculating the signal;
An electric power steering device comprising a power MOSFET that controls a motor drive circuit in accordance with a signal from the control means, and in which a gate voltage rise speed is limited. 10. An electric power steering device in which a steering force of a steering shaft is detected by a torque detecting means, and an auxiliary steering force is applied to the steering shaft by a motor according to an output signal of the torque detecting means. An electric power steering device characterized in that an FET is operated separately on an upstream side and a downstream side, and heat generation due to chopping loss and heat generation due to regenerative current are balanced.