JPS61215166A - Motor power steering device - Google Patents

Abstract

PURPOSE:To follow the steering speed of a handle by providing a motor acceleration/deceleration function in response to the motor rotating speed and using this function against the increase/decrease of a handle steering force to control the motor speed. CONSTITUTION:A torque sensor 6 detects the torque applied to a pinion 3 from a handle 1 via a handle shaft 2 and generates a signal tau. A motor 7 acts as an electric actuator applying an auxiliary steering force to a rack 4 via a reduction mechanism 8 and a pinion 9. A steering angle sensor 10 detects the steering angle of tires 5 and generates a steering angle theta, where the steering angle is sensed as zero when the turning angle of tires 5 is at the neutral position. The steering angle sensor 10 is constituted with a rotary encoder consisting of a variable resistor detecting the turning angle of a member rotated as tires 5 are turned and a linear encoder detecting the movement of a member doing a linear motion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a power steering device for an automobile or the like, and particularly to a power steering device with excellent steering feel.

[Background of the invention]

In automobiles, which have a wide variety of users, power gear rings are widely installed in both large and small vehicles, and are useful for reducing fatigue and thereby ensuring safe driving. By the way, as this power steering device, a hydraulic type has conventionally been mainly used. However, in recent years, electric power steering devices have been put into practical use, focusing on the richness of control contents and their effectiveness in terms of energy conservation.

In order to obtain the large operating force required for the electric actuator used in this electric power steering device, an electric motor is used as the actuator, and its output is decelerated to perform the final auxiliary steering operation. The method of obtaining power is mainly used.

As a result, the conventional electric power steering...
- In the steering system, the auxiliary steering force is applied by a high-speed rotating electric motor via a speed reduction mechanism.
Due to the inertia of the electric motor and the large frictional resistance that is applied when the electric motor is rotated from the output side of the speed reduction mechanism, extremely unfavorable characteristics in terms of steering feeling appear in the operation of the steering wheel.

Among these, it appears when the steering wheel is operated due to the inertia of the electric motor. Regarding characteristics that are unfavorable in terms of steering feeling, a method of imparting differential characteristics to the control of the electric motor can be considered, as proposed in, for example, Japanese Patent Application Laid-open No. 55-76760, which is expected to have a significant effect on improving steering feeling. be done.

However, this method requires an extra differential circuit, etc., and providing differential characteristics requires additional consideration for noise, which tends to increase costs. Therefore, no improvement effect can be expected, and it is not possible to obtain a sufficient improvement in the steering feeling as a whole. Note that the deterioration of the steering feeling due to this frictional resistance appears in the form of a significant reduction or disappearance of the restoring force that should originally appear when the steering angle is other than zero (neutral position).

Also, when a steering force is applied to the steering wheel, the assist force is applied by the motor, but since the motor has inertia, the motor's inertial energy, which is proportional to the square of the motor's rotation speed, must be added. To accelerate the motor, the driver must use the steering force of the steering wheel, and to stop the motor, the driver must use the steering wheel to stop the motor. In particular, if you try to turn the handle quickly, you will feel the shock of the load and force that it takes to reach the required number of revolutions of the motor. In order to compensate for this load, there is a control circuit that uses differentiation as described above. However, this method has the disadvantage that the energy compensated by the steering speed is insufficient because it does not take into account the acceleration/deceleration engineering required for the motor.

[Purpose of the invention]

An object of the present invention is to provide an electric power steering device that can sufficiently follow the steering speed of a steering wheel.

[Summary of the invention]

The present invention provides a motor acceleration/deceleration function according to the rotational speed of the motor, and uses this function to adjust the motor speed in response to increases and decreases in the steering wheel steering force, thereby making it possible to sufficiently follow the steering speed of the steering wheel. The idea is to do so.

[Embodiments of the invention]

Hereinafter, a power steering control device according to the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 shows an example in which the present invention is applied to an automobile electric power steering system, where 1 indicates a steering wheel (
(hereinafter simply referred to as a handle), 2 is a handle shaft, 3 is a pinion, 4 is a rack, 5 is a turning tire (wheel), 6
7 is a torque sensor, 7 is a power assist electric motor, 8 is a reduction mechanism, 9 is a binion, 10 is a steering angle sensor, and 11 is a control device. B is a battery for power supply.

This embodiment is of a so-called rack and pinion type, in which the steering force applied to the steering wheel 1 by the driver is transmitted from the steering wheel shaft 2 to the rack 4 via the pinion 3.
Move the tires 5 to a predetermined steering angle.

The torque sensor 6 detects the torque applied from the handle 1 to the pinion 3 via the handle shaft 2 when the driver turns the handle 1, and generates a signal τ representing the magnitude of the torque. For example, it consists of a strain gauge attached to the handle shaft 2 or a torsion spring mechanism installed on the handle shaft 2, and a variable resistor that detects the amount of torsion, as shown in Fig. 2. It has unique characteristics.

The electric motor 7 operates as an electric actuator that applies an auxiliary steering force to the rack 4 via a speed reduction mechanism 8 and a pinion 9, which are comprised of gears and the like.

The steering angle sensor 10 detects the steering angle (turning angle) of the tire 5,
It functions to generate a signal θ representing the steering angle in accordance with the characteristics shown in FIG. 3, for example, assuming that the steering angle is zero when the vehicle is traveling straight and the turning angle of the front wheels 5 is at a neutral position. It consists of a rotary encoder consisting of a variable resistor that detects the rotation angle of a member that rotates as the tire turns, and a near encoder that detects the movement of a member that moves linearly. be.

The electric motor 7 used in this power steering device is
It has a torque-rotational speed characteristic as shown in FIG. When the armature current (2) of the electric motor 7 is large, the torque characteristic with respect to the rotational speed becomes C, D→F→G in FIG. Also, when the armature current I is small, the torque characteristics for one rotation speed are as follows:
E → F, G.

The characteristics of the armature current (2), rotational speed, and torque of the electric motor 7 are as shown in FIG.

FIG. 6 shows an embodiment of the control device 11, in which the torque function circuit 2
1, restoring force function circuit 22, acceleration/braking judgment circuit 23,
Acceleration function circuit 24, braking function circuit 25, switching judgment circuit 2
6. Torque duty conversion circuit 27, chopper control circuit 28
, a motor control circuit 29, and a lock detection circuit 30.

Next, the operation will be explained.

When the driver operates the steering wheel 1 and applies torque to the steering wheel shaft 2, the torque is detected by the torque sensor 6 according to the characteristics shown in FIG. 2, and a torque signal τ is output.

This torque signal τ is input to the chopper control circuit 28 via the torque function circuit 21 and the torque duty conversion circuit 27, and is converted into a pulse signal CP with a duty ratio corresponding to the absolute value at that time. is input.

At this time, the switching determination circuit 26 outputs either a clockwise rotation signal R or a counterclockwise rotation signal depending on the sign of the input signal, and inputs these signals R and L to the motor control circuit 29. do.

Note that the polarity of the torque signal τ generated from the torque sensor 6 is, for example, positive with respect to the torque that appears when the knob 1 is rotated clockwise (clockwise), and when it is rotated counterclockwise (counterclockwise). It is designed so that the torque that appears when it is rotated has a negative polarity. Therefore, when the torque signal τ is positive, the vehicle will turn to the right, and when it is negative, the vehicle will turn to the left.

Next, the torque function circuit 21 will be explained.

This torque function circuit 21 outputs a corrected torque value in accordance with the rotational speed of the electric motor 7 so as to have corrected torque output characteristics a and b as shown in FIG. 7(5). The output characteristic a is when the handle operation speed of the electric motor 7 is high, and the output characteristic b in FIG. 7 (5) is when the handle operation speed is low. Note that C in FIG. 7(A) indicates a correction value based on conventional differentiation. By adding such correction torque values, it is possible to sufficiently compensate for the inertia of the electric motor 7 when a steering force is applied as shown in Fig. 7 (BJ a). The steering force characteristics are determined by the differential method of , and it is not possible to remove the influence of inertia that varies depending on the steering speed.

FIG. 8 shows an embodiment of the motor control circuit 29, which includes two power transistors TRI.

TR2 (hereinafter simply referred to as 'I'R1, TR2),
It consists of freewheel diodes DI and D2. TRI is supplied with a signal based on the AND of the left rotation signal R and pulse signal CP, and TR2 is supplied with a signal based on the AND of the right rotation signal R and pulse signal OP. When the rotation signal R appears, when the 1-lux signal τ has a positive polarity, TR2 turns on, and a current is supplied to the motor 7 in the direction of the arrow in the figure, and the magnitude of this current is It is controlled by the duty ratio of the pulse signal CP. Furthermore, when the torque signal τ has negative polarity and the left rotation signal I appears, T
RI is turned on, and a current is supplied to the motor 7 in the direction opposite to the arrow in the figure, and the current value at this time is also equal to the pulse signal C.
It will be controlled by the duty ratio of P.

In any of these cases, the magnitude of the current flowing through the motor 7 is detected by the current detector and supplied to the chopper control circuit 28 as a feedback current signal, thereby controlling the torque conduction rate. A feedback loop is formed to ensure that current corresponding to the signal given from the conversion circuit 27 is accurately supplied to the electric motor 7.

Note that the diodes DI and D2 function to provide a circulation path when 11R1 or TR2 is chopper-controlled and turned off by the pulse signal CP.

Therefore, when the driver operates the steering wheel 1, a predetermined value of current is supplied to the electric motor 7 from a predetermined direction depending on the direction and magnitude of the operating force (steering force) applied at that time.
As a result, the torque generated by the electric motor 7 is applied from the pinion 9 to the rack 4 and becomes an auxiliary steering force, so that the function as a power steering device is obtained.

Incidentally, even if the magnitude of the steering force required when the driver operates the steering wheel 1 is small, driving becomes difficult.
It is known that it is preferable for the steering feel to have the auxiliary steering force, that is, the current value of the electric motor 7, determined by a high-order function characteristic with an offset as shown in FIG.

Therefore, a torque function circuit 21 is provided for this purpose, and is designed to generate an output signal according to the characteristics shown in FIG. 9 in response to an input signal. In addition, in reality,
Since a function circuit that provides smooth characteristics as shown in FIG. 9 would increase the cost or be impossible to implement, it is recommended to use a torque function circuit 21 using broken line approximation as shown in FIG. 10, for example. Just do it. Furthermore, instead of this broken line approximation, it is also possible to use a staircase approximation as shown in FIG.

Next, the force required to turn the tires 5, the so-called steering force, is determined by the frictional resistance between the tires and the road surface in the turning direction, but this frictional resistance changes depending on the vehicle speed, and as the speed increases, Decrease. Therefore, this steering force increases as the vehicle speed decreases, and when the vehicle speed is zero, which is usually called stationary steering, it becomes extremely large to the point that it is almost impossible to operate the steering wheel.

However, from a practical standpoint, this stationary steering operation is necessary when parking the vehicle in a garage or parallel parking.

On the other hand, if the steering force is reduced at high speeds, it can become dangerous, so it is recommended to reduce the auxiliary steering force at high speeds.
Or it is preferable not to give it at all.

For this purpose, the torque function circuit 21 inputs the vehicle speed signal υ from the vehicle speed sensor 20, performs predetermined calculation processing on the torque signal τ, and obtains the characteristic given by the torque function circuit 21 as shown in FIG. The width of the offset is made wider according to the vehicle speed signal υ.

By the way, the brake torque that applies the electric motor 7 in the opposite direction,
That is, the relationship between the reverse braking torque and the motor 70 rotational speed has a characteristic as shown in FIG. That is, the larger the rotation speed of the electric motor 70, the stronger the reverse braking torque becomes. Therefore, the greater the rotation of the electric motor 7, the higher the force required to operate the handle and stop it at a certain position (the torque required to brake the electric motor and stop it). Further, the acceleration torque value with respect to the rotational speed of the electric motor 7 is shown in FIG. 14, and when the electric motor rotational speed is small, it is necessary to increase the acceleration torque.

Next, the restoring force function circuit 22 shown in FIG. 6 will be explained.

This restoring force function circuit 22 is a circuit that outputs a control signal for the electric motor 7 to give a restoring force (restoring force) to the tire 5, and is a circuit that outputs a control signal for the electric motor 7 to generate a return torque and a steering angle (steering angle sensor output).
This relationship is as shown in FIG. In other words, the larger the steering angle, the greater the torque required for restoration. This restoring characteristic is a major factor in determining the steering feel of a steering system equipped with power steering.

In other words, the steering system of an automobile generally uses the caster effect of turning wheels to provide a restoring characteristic, and therefore, after a predetermined steering angle is given by steering wheel operation, this restoring characteristic is applied. Driving operations that utilize the restoring force given to the steering wheel due to its characteristics are widely performed, and this is the key to providing a good steering feeling.
Therefore, even with power steering equipment, pressure must be applied so as not to impair this restoring force.

The lock detection circuit 30 shown in FIG. 6 detects when there is no output from the steering angle sensor 10 compared to the output from the torque sensor 6. When this is detected, the solenoid valve of the clutch 8 is turned off. 'F.

Next, the operation of assist torque calculation according to the embodiment of the present invention will be explained.

FIG. 16 shows a flowchart of assist torque calculation. This flowchart is 10 m5ec
Each timer interrupt is processed.

First, in step 100, the previous value TOLD of the torque sensor 6 is read out, and in step 101, the current output value TN EV from the torque sensor 6 is taken in. Next, in step 103, TOLD and TNEW
6 is compared to determine whether the increase ΔT in the output value of the Dorxe/S 6 is equal to or greater than a certain value ΔT=TNEW−TOLD. In this step 103, if it is determined that the increase in the torque sensor/su is larger than a certain value, in step 104 the increase in the value output from the steering angle sensor 10 is set to a certain constant value that corresponds temporally to the increase in the torque sensor 6. Determine whether it is greater than the value. In this step 104, if the increase in the steering angle sensor is not equal to or greater than a certain value, the process moves to step 108. Further, if it is determined in step 104 that the increase in the steering angle sensor is equal to or greater than a certain value, in step 105 acceleration torque is calculated by motor acceleration calculation (acceleration with characteristics as shown in FIG. 7), and the process moves to step 108. .

On the other hand, if it is determined in step 106 that the increase in the torque sensor is not equal to or greater than a certain value, then in step 106 it is determined whether or not the deceleration amount in the torque sensor is greater than or equal to a predetermined value. If it is determined in this step 106 that the deceleration of the torque sensor is not equal to or greater than a certain value, the process moves to step 108, and if it is determined that it is equal to or greater than a certain value, the process proceeds to step 107, where the deceleration torque is calculated by motor deceleration calculation (13th
(corresponding to the reverse braking torque characteristic shown in the figure) is performed, and the process moves to step 108. Next, in step 108,
The assist torque is calculated as shown in FIG.

FIG. 17 shows a block diagram of a series of operations using a microcomputer.

An interrupt flowchart of the task schedule for processing at this time is shown in FIG.

A specific circuit is shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to sufficiently follow the steering speed of the steering wheel.

[Brief explanation of drawings]

Fig. 1 is a system configuration diagram showing an embodiment of a power steering control device according to the present invention, Fig. 2 is a characteristic diagram of a torque sensor, Fig. 3 is a characteristic diagram of a steering angle sensor, and Fig. 4 is a rotation of an electric motor. Fig. 5 is a characteristic diagram of motor armature current and torque/rotational speed; Fig. 6 is a block diagram showing an embodiment of the present invention; Fig. 7 is a characteristic showing corrected torque output during acceleration. 8 is a detailed circuit diagram of the motor control circuit shown in FIG. 6, and FIG. 9 is a characteristic diagram showing an example of high-order function characteristics.
0 and 11 are explanatory diagrams of approximate characteristics for high-order function characteristics, Fig. 12 is an explanatory diagram showing an example of characteristics provided by an embodiment of the present invention, and Fig. 13 is an explanatory diagram of the rotation speed of the motor and reverse braking. Torque characteristic diagram, Figure 14 is a diagram showing acceleration torque characteristics with respect to motor rotation speed, Figure 15 is a characteristic diagram regarding restoring force, Figure 16 is an operation flowchart of assist torque calculation, and Figure 17 is a diagram using a microcomputer. FIG. 18 is a flowchart showing a processing time schedule, and FIG. 19 is a specific circuit diagram of the embodiment shown in FIG. 1... Steering handle, 2... Handle shaft, 3.9.
... Binion, 4... Rack, 5... Tire, (turning wheel) 6... Torque sensor, 7... Electric motor, 8...
...Deceleration mechanism, 10... Rudder angle sensor, 11... Control device, 20... Vehicle speed sensor, 21... Torque function circuit, 22.25... Adder, 24... Acceleration function Circuit, 25... Braking function circuit, 28... Chopper control circuit, 29... Motor control circuit, 30... Lock detection circuit. Agent Patent Attorney Tatsuyuki Unuma Figure 1 Figure 2 Figure 3 Bokao Irten 90) 7>at-Iketenko Figure 11 Figure 12 Figure 13 (σ-100) Figure 14 g

Claims (3)

[Claims] (1) In an electric power steering device in which a motor is controlled according to a predetermined function of a steering force applied to a steering wheel, and the motor provides an auxiliary steering force, the motor is controlled according to the rotational speed of the motor. An electric power steering device characterized in that an acceleration function is provided, and acceleration control of the motor is performed according to the function while the steering force of the steering wheel is increasing. (2) In an electric power steering device in which a motor is controlled according to a predetermined function of a steering force applied to a steering wheel, and the motor provides an auxiliary steering force, the motor is controlled according to the rotational speed of the motor. An electric power steering device characterized in that a subtractive function is provided, and motor deceleration control is performed in accordance with the function while the steering wheel steering force is decreasing. (3) In an electric power steering device in which a motor is controlled according to a predetermined function of a steering force applied to a steering wheel, and the motor provides an auxiliary steering force, the magnitude of the steering angle of the steering wheel is An electric power steering device characterized in that a restoring force function is provided according to the function, and the restoring force of the steering wheel is applied to the steering wheel according to the function.