JPH06219312A - Electrically driven power steering device - Google Patents

Abstract

PURPOSE:To improve a returning characteristic by carrying out judgement as to whether it is a steering holding state or not from a detection result of a steering system torque detection means and viscosity compensating value enumeration and renewing enumeration viscosity compensating value in accordance with a judgement result in the device for a vehicle. CONSTITUTION:A detection signal of a torque sensor 11 is input to a viscosity compensating value enumeration part 52 of a motor speed feed back gain enumeration part 50 and a steering holding state judgement part 51 with an assist torque value indication function part 31 of an assist command part 30. Thereafter, the steering holding state judgement part 51 judges whether a steering handlewheel is in a steering holding state or not and outputs its judgement result to a viscosity compensating part renewal output part 53 (renewal output part hereinafter). In the meantime, the viscosity compensating value enumeration part 52 enumerates viscosity compensation (kv) in accordance with detection torque value and detection value of a car speed sensor 12, and it outputs it to the renewal output part 53. The renewal output part 53 renews the viscosity (kv) in accordance with judgement of the steering holding state judgement part 51, outputs the compensating value (kv) and adds it to output of the assist command part 30 and corrects it. By this corrected value, an electric current control part 35 controls an assist motor 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device suitable for use in a vehicle, and more particularly to an electric power steering device for assisting steering force by the rotational output of a motor.

[0002]

2. Description of the Related Art In recent years, electric power steering systems using a motor instead of a hydraulic type have been used as a vehicle power steering device, and the motor has an increasing tendency in the future due to advantages such as small size and light weight as an actuator.

In the conventional power steering apparatus, the tokle sensor detects the steering torque of the steering system, the vehicle speed sensor detects the vehicle speed, and the driving force of the motor connected to the steering system is controlled based on these detection results. , Power assist is done. In general, it is a vehicle speed sensitive type, and the assist force is controlled according to the torque sensor input so that it is light at low vehicle speed and heavy at high vehicle speed.

FIG. 5 is a block diagram showing an example of a mechanical system of a conventional electric power steering apparatus. In this figure, the rotational force of a steering handle 1 is transmitted to a steering gear 2 including a pinion gear via a handle shaft. At the same time, it is transmitted to the rack shaft 3 by the pinion gear, and the wheels 4 are turned through the knuckle arms and the like. Further, the rotational force of the steering assist (auxiliary) motor (DC motor) 6 controlled and controlled by the control device 5 is transmitted to the rack shaft 3 by the meshing of the steering shaft 7 including the pinion gear and the rack shaft 3, and the steering wheel 1 is used. It will assist steering.

The rotating shaft of the handle 1 and the motor 6 is a gear 2,
7 and the rack shaft 3 are mechanically connected. The steering torque (return torque) by the steering torque sensor 11.
Is detected, and the vehicle speed sensor 12 detects the vehicle speed.
Then, the motor 6 is controlled by the control device 5 based on the detected torque, the vehicle speed, and the like. The control device 5 and the motor 6 are supplied with operating power from a battery 8 mounted on the vehicle.

As shown in FIG. 6, the control device 5 includes a motor current detection circuit 21, a motor drive circuit 22 for driving the motor 6, and a CPU 2 for controlling the overall control of the motor 6.
3 (for example, a microprocessor), a memory 24, an interface circuit (not shown) between the computer and the input / output devices, and the like.

In FIG. 6, the steering torque detected by the steering torque sensor 11 is converted into a digital signal by the A / D conversion circuit 25 and then taken into the CPU 23. The vehicle speed detected by the vehicle speed sensor 12 is counted by the counter 26, and the count value indicating the vehicle speed is fetched by the CPU 23. The CPU 23 creates an assist command based on the input steering torque and vehicle speed, outputs a control signal based on the assist command to the motor drive circuit 22, and the motor drive circuit 22 drives the motor 6. As a result, the assist torque value (or motor current command value) output from the motor drive circuit 22 becomes a value determined by the detected torque V _T and the detected vehicle speed V _S , as shown in FIG. 7.

FIG. 7 shows that when the steering torque V _T is in a certain range, a motor current almost proportional to the steering torque V _T flows (assist torque is generated) and exceeds the above range. as constant motor current flows (the assist torque is generated), also according to the vehicle speed V _S, the motor current (assist when when the vehicle speed V _S is high to reduce the motor current (assist torque), the vehicle speed V _S is low It indicates that an assist command for controlling the motor 6 is generated so as to increase the torque.

Returning to FIG. 6, the motor current is detected by the motor current detection circuit 21, converted into a digital signal by the A / D conversion circuit 27, and then taken into the CPU 23. The memory 24 stores programs and data necessary for the processing of the CPU 23.

By the way, in the above-described conventional electric power steering apparatus, the torque of the motor 6 is reduced by the gears and transmitted to the rack shaft and the like. There are problems that it acts as if it were large, the friction of the gears influences, the astringency at high vehicle speed deteriorates, and the steering wheel return at low vehicle speed deteriorates. In order to solve this problem, a device for adding a viscosity compensation value according to the steering angular velocity has been developed as disclosed in, for example, Japanese Patent Laid-Open No. 3-178868.

[0011]

However, in such an improved conventional electric power steering device, the viscosity compensation value is changed only in accordance with the vehicle speed. There is a problem that the return characteristic is not good, such as not returning to the neutral point or overshooting from the neutral point, depending on the steering state, since it is not taken into consideration whether or not the state is returned to the neutral point. That is, the returning force is different when the angle at which the steering wheel 1 starts to return is large and when it is small. Therefore, when the angle is large, the force is too strong and goes past the neutral point, and conversely when the angle is small. There is not enough power to reach the neutral point.

Therefore, an object of the present invention is to provide an electric power steering apparatus in which the return characteristic is improved by considering the steering state of the steering wheel.

[0013]

In order to achieve the above object, an electric power steering apparatus according to the invention of claim 1 is an electric power steering apparatus, which is connected to a steering system to generate a steering assist torque and a steering torque of the steering system. Steering system torque detecting means for detecting the vehicle speed, vehicle speed detecting means for detecting the vehicle speed, an assist command is created based on the outputs of the steering system torque detecting means and the vehicle speed detecting means, and the motor is driven by the assist command. In an electric power steering equipped with a control means for controlling, a determination means for determining whether or not the steering system is in a steering holding state based on a detection result of the steering system torque detection means, and a detection by the steering system torque detection means. Calculating means for calculating the viscosity compensation value based on the result, and updating the viscosity compensation value obtained by the calculating means based on the determination result of the determining means, Characterized by providing a force updating means.

According to a second aspect of the present invention, there is provided an electric power steering apparatus, wherein the calculating means in the electric power steering apparatus according to the first aspect includes the detection result of the steering system torque detecting means and the vehicle speed detecting means. It is characterized in that the viscosity compensation value is calculated based on the detection result.

[0015]

According to the first aspect of the present invention, an appropriate viscosity compensation value for returning the steering wheel to the neutral point is given according to the steering state at the time of starting the returning of the steering wheel. Therefore, the return angle is improved because the residual angle of the steering wheel is reduced.

According to the second aspect of the present invention, an appropriate viscosity compensation value for returning the steering wheel to the neutral point is given according to the steering state at the start of the return when the steering wheel is returned and the vehicle speed at that time. Therefore, since the vehicle speed is also taken into consideration, the return characteristic is further improved as compared with the invention according to claim 1.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing various functions of a computer incorporated in a control device 5A of an embodiment of an electric power steering device according to the present invention, along with blocks showing other input / output devices and various circuits. is there.

In the figure, the assist command section 30 includes a detection torque VT of the steering torque sensor 11 and a vehicle speed sensor 1.
The detected vehicle speed Vs of 2 is given. Assist command unit 30
The assist torque value instruction function unit 31 in the
A command value representing the assist torque to be generated by the motor 6 is output in accordance with the above.

Further, the multiplication constant function unit 32 detects the detected vehicle speed Vs.
A constant is generated in accordance with the above, and the constant is multiplied by the assist torque command value in the multiplication calculation unit 33. As a result, the assist torque value (or motor current command value) output from the multiplication calculator 33 becomes a value determined by the detected torque VT and the detected vehicle speed Vs, as shown in FIG.

The detected torque VT is also given to the phase compensator 34, and the differential value of the detected torque VT is added to the output of the multiplication calculator 33 by the phase compensator 34.
The output (reference current command value) of the assist command unit 30 is supplied to the current control unit 35.

On the other hand, the output of the motor speed feedback gain calculation unit 50 is added to the current control unit 35 in addition to the assist command value 30. The motor speed feedback gain calculation unit 50 includes a steering state determination unit 51 that determines the steering state of the steering wheel 1, that is, the steering wheel position based on the output of the steering torque sensor 11, the output of the steering torque sensor 11, and the vehicle speed sensor 12. And a viscosity compensation value update output unit 53 that updates the output of the viscosity compensation value calculation unit 52 based on the judgment of the steering holding state determination unit 51. Is configured.

FIG. 2 is a block diagram showing the detailed structure of the motor speed feedback gain calculating section 50. The steering holding state determination unit 51 includes delay circuits 55 and 57 and subtractors 56 and 5
8, absolute value circuits 59 and 61, comparators 60 and 62, and an AND gate 63. The delay circuit 55 and the subtractor 56 determine the amount of change ΔV _T corresponding to the speed from the output of the steering torque sensor 11. Also, the delay circuit 5
7 and the subtractor 58, the amount of change Δ ² V _T corresponding to the acceleration
Is required.

The absolute value circuit 59 takes the absolute value of the variation ΔV _T corresponding to the speed. Then, the comparator 60 compares it with a preset design constant α ₁ . In this case, if | ΔV _T | <α ₁ , the output of the comparator 60 is “1”.
Otherwise, it becomes "0". On the other hand, the absolute value of the variation Δ ² V _T corresponding to the acceleration is taken by the absolute value circuit 61. Then, the comparator 62 compares the preset constant α ₂ with the preset value. In this case, | Δ ² V _T | <
If α ₂ , the output of the comparator 62 becomes “1”, and otherwise it becomes “0”. The outputs of the comparators 60 and 62 are supplied to the AND gate 63 and are logically ANDed. The output of the AND gate 63 is "1" when the steering wheel 1 is in the steering holding state, and is "0" when the steering wheel 1 is being returned.

The viscosity compensation value calculation unit 52 includes an absolute value circuit 64.
And a viscosity compensation value calculation circuit 65. The absolute value of the output of the steering torque sensor 11 in the absolute value circuit 64 | V _T
| Is taken. Then, the absolute value | V _T | and the viscosity compensation value K _v whose variable is the output V _s of the vehicle speed sensor 12 are obtained by the viscosity compensation value calculation circuit 65. This viscosity compensation value K
_v is a value that changes momentarily due to changes in the output of the steering torque sensor 11 and changes in the output of the vehicle speed sensor 12.

The viscosity compensation value updating section 53 comprises a switching circuit 66 and a storage circuit 67. The switching circuit 66 switches depending on the output state of the steering holding state determination unit 51. That is,
When the output of the steering holding state determination unit 51 is "1" (in the steering holding state), the neutral contact c is connected to the contact a, and when the output is "0" (while the steering wheel is returning). , Neutral contact c
Is connected to the contact b. When it is connected to the contact point a, the viscosity compensation value K _v, which is the output of the viscosity compensation calculation unit 52, is directly output from the viscosity compensation value updating unit 53.

The storage circuit 67 stores the viscosity compensation value K _v , and is stored and updated at predetermined intervals while the neutral contact c of the switching circuit 66 is connected to the contact a. Then, when the neutral contact c of the switching circuit 66 is switched to the contact b, that is, when the output of the steering holding state determination unit 51 becomes "1" (in other words, when the steering handle 1 is released). Then, the viscosity compensation value K _v stored at that time is output. In this way, when in the steering holding state, the viscosity compensation value K _v according to the steering holding state is obtained. This viscosity compensation value K _v is added to the output of the assist command unit 30 and supplied to the current control unit 35.

Here, FIG. 3 is a time chart comparing the state of the steering wheel 1 with the passage of time between the case according to the present invention and the case according to the related art. In this figure, time t ₁
Previously, the steering was held, and the recovery is started at time t ₁ . In the present invention, the viscosity compensation value K _v is determined according to the steering state at that time t ₁ at which the recovery is started. As a result, as shown by the curve Ca, the steering wheel residual angle is not generated and the steering wheel is returned to the neutral point.

On the other hand, conventionally, since the viscosity compensation value K _v is updated during the recovery (excessive state), an overshoot may occur as shown by the curve Cb or the neutral point may not be recovered as shown by the curve Cc. To do.

Returning to FIG. 1, the current controller 35 controls the drive of the motor 6 by a chopper operation using a PWM (Pulse Width Modulation) pulse according to the H-bridge drive method including four switching elements. ,
Performs current feedback control. That is, the armature current detector 36 detects the armature current of the motor 6,
The deviation between the target current command value given and the detected current is calculated in the current deviation calculator 37. The absolute value of this deviation is obtained by the absolute value converter 38, and the duty ratio of the PWM pulse is determined by the duty generator 39 based on this absolute value.

On the other hand, the polarity (positive or negative) of the deviation is discriminated by the positive / negative discriminating section 40, and the generated duty ratio and the discriminated polarity are given to the motor driving section 41, and the motor driving section 41 determines these values. Based on the above, the four switching elements wired in the H-bridge type are turned on / off to drive the motor 6.

The steering torque sensor 11 corresponds to steering system torque detecting means, and the vehicle speed sensor 12 functions as vehicle speed detecting means. The steering holding state determination unit 51 corresponds to determination means, and the viscosity compensation value calculation unit 52 corresponds to calculation means.
The viscosity compensation value update output means 53 corresponds to the update means. Further, the assist command section 30 and the current control section 35 constitute the control means 100.

Next, the operation will be described with reference to the time chart shown in FIG. First, in the running state, when the steering wheel 1 is turned at a certain angle to hold the steering wheel,
The output of the steering holding state determination unit 51 is "1", and the neutral contact c of the switching circuit 66 of the viscosity compensation value update output unit 53 is connected to the contact a. In this state, the viscosity compensation value calculation unit 52 outputs the viscosity compensation value K _v corresponding to the current steering angle via the viscosity compensation value update output unit 53, is supplied to the memory circuit 67, is stored, and is assisted. It is added to the output of the command unit 30 and supplied to the current control unit 35.

When the hand is released from the steering wheel ₁ at time t ₁ , the output of the steering holding state determination section 51 becomes “0”, and the neutral contact of the switching circuit 66 of the viscosity compensation value update output section 53. c is connected to contact b. As a result, the output of the viscosity compensation value calculation unit 52 is not output from the viscosity compensation value update output unit 53, and the viscosity compensation value K _v at time t ₁ stored in the storage circuit 67 is output from the viscosity compensation value update output unit 53. Is output.
This output is not changed until the steering wheel 1 returns to the neutral point at time t ₂ .

[0034] When the steering wheel 1 is returned to the neutral point, at that time t ₂ the output of the steering holding state determining section 51 is "1", switching circuits of the viscosity compensation value updating output 53 path 6
The neutral contact c of 6 is connected to the contact a. by this,
The output of the viscosity compensation value calculation unit 52 is the viscosity compensation value update output unit 5
It is output from 3.

In the above embodiment, the viscosity compensation value K _v is
The steering state at the time of starting the return to start returning the steering wheel 1,
Although the calculation is performed according to the vehicle speed at that time, the calculation may be performed only according to the steering state at the time of starting the return to start returning the steering wheel 1. In this case, the return characteristic is slightly reduced as compared with the above case, but there is an advantage that the cost can be reduced.

[0036]

According to the first aspect of the present invention, an appropriate viscosity compensation value for returning the steering wheel to the neutral point is obtained according to the steering state at the start of returning the steering wheel. The residual angle of the steering wheel is reduced, and the return characteristics are improved.

According to the second aspect of the present invention, an appropriate viscosity compensation value for returning the steering wheel to the neutral point is obtained in accordance with the steering state at the start of returning when the steering wheel is returned and the vehicle speed at that time. Therefore, the effect that the return characteristic is further improved as compared with the invention according to claim 1 is obtained because the vehicle speed is taken into consideration.

[Brief description of drawings]

FIG. 1 is a block diagram of a control device of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a detailed block diagram of a motor speed feedback gain calculation unit in the embodiment.

FIG. 3 is a time chart of steering wheel angles for explaining the features of the embodiment.

FIG. 4 is a time chart of an output state of the steering torque sensor according to the embodiment.

FIG. 5 is a configuration diagram showing an example of a mechanical system of a conventional power steering device.

FIG. 6 is a detailed block diagram of a control device of a conventional power steering device.

FIG. 7 is a diagram showing characteristics of assist torque of a conventional power steering device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering wheel 6 Motor 11 Steering torque sensor (steering system torque detection means) 12 Vehicle speed sensor (vehicle speed detection means) 30 Assist command section 35 Current control section 51 Steering state determination section (determination section) 52 Viscosity compensation value calculation section (calculation) Means) 53 Viscosity compensation value update output means (update means) 100 Control means

Claims (2)

[Claims] 1. A motor connected to a steering system for generating a steering assist torque, a steering system torque detecting means for detecting a steering torque of the steering system, a vehicle speed detecting means for detecting a vehicle speed, and the steering system torque detecting means. And an electric power steering including a control unit that creates an assist command based on the output of the vehicle speed detection unit and controls the drive of the motor by the assist command, and a detection result of the steering system torque detection unit. Based on the determination result of the determination means, the determination means for determining whether or not it is in the steering holding state, the calculation means for calculating the viscosity compensation value based on the detection result of the steering system torque detection means, An electric power steering apparatus comprising: an updating unit that updates and outputs the viscosity compensation value obtained by the calculating unit. 2. The electric power steering system according to claim 1, wherein the calculating means calculates a viscosity compensation value based on a detection result of the steering system torque detecting means and a detection result of the vehicle speed detecting means. apparatus.