JP2005247229A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device capable of achieving stable assist control, even when hydraulic pressure in an oil passage is changed. <P>SOLUTION: The power steering device is equipped with a hydraulic power cylinder for assisting steering force of a steering mechanism coupled to a steering wheel, and assists a reversible pump by a normally/reversely rotating electric motor. The power steering device comprises a command current value outputting means for outputting a command current value on the basis of necessary steering assisting force detected by a necessary steering assisting force detecting means, a correction gain computing means for computing a correction gain correcting phase delay of the command current value, a command current value correcting means for correcting the command current value on the basis of the correction gain, a pump load estimating means for estimating a pump load of the reversible pump, and a correction gain correcting means for correcting the correction gain to decrease when the pump load is not less than a predetermined value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power steering apparatus that assists steering by driving a pump by an electric motor.

Conventionally, a power steering device described in Patent Document 1 is known. In this apparatus, a power cylinder is connected to a pair of oil passages connected to a reversible pump, and the power cylinder is operated by sending hydraulic oil from the reversible pump to each hydraulic chamber of the power cylinder, and steering is performed. Assist force is generated.
JP 2002-145087 A.

  However, in the power steering device described above, the oil passage is a closed circuit, and therefore, when the oil pressure in the oil passage becomes high as in the case of abutting the steering wheel, the pump load increases and the pump The rotation of the motor that drives the motor becomes unstable. As described above, when the rotation of the electric motor becomes unstable, there is a problem that pulsation is generated in the pump discharge pressure and abnormal noise is generated from the apparatus.

  The present invention has been made paying attention to the above problem, and an object of the present invention is to provide a power steering device capable of achieving stable assist control even if there is a fluctuation in hydraulic pressure in the oil passage.

  In order to achieve the above object, a hydraulic power cylinder for assisting a steering force of a steering mechanism coupled to a steering wheel, and a pair for supplying hydraulic pressure to both pressure chambers of the hydraulic power cylinder through first and second passages. A reversible pump having a discharge port, an electric motor for rotating the reversible pump forward and backward, a necessary steering assist force detecting means for detecting a necessary steering assist force to be applied to the steering wheel, and the necessary steering assist force Based on the necessary steering assist force detected by the detection means, a command current value output means for outputting a command current value to the electric motor, and a correction gain calculation means for calculating a correction gain for correcting a phase delay of the command current value Command current value correcting means for correcting the command current value based on the correction gain, pump load estimating means for estimating the pump load of the reversible pump, and the pump load. When the above value, and a power steering device that includes a correction gain correction means for decreasing correcting the correction gain.

  When the pump load is greater than or equal to a predetermined value, that is, when the hydraulic pressure in the hydraulic circuit is high, the current noise component caused by the excessive response to the counter electromotive force can be reduced by reducing the correction gain. Therefore, abnormal noise from the apparatus can be suppressed.

  Hereinafter, the best mode for realizing the power steering apparatus of the present invention will be described based on Example 1 shown in the drawings.

  FIG. 1 is a diagram illustrating an overall schematic configuration in the first embodiment. When the driver steers the steering wheel 1, the rack shaft 4 is moved in the axial direction by the so-called rack and pinion mechanism 3 via the steering shaft 2, and the steering wheel 7 is steered. The steering shaft 2 is provided with a torque sensor 12 that detects the steering torque of the driver, and outputs a torque signal to the control unit 10.

  The rack shaft 4 is provided with a power steering mechanism 5 that assists the movement of the rack shaft 4 according to the steering torque of the driver. The power steering mechanism 5 includes a reversible pump 6 driven by a motor 6 a and a power cylinder 5 a having a piston 5 b that defines a first hydraulic chamber 51 and a second hydraulic chamber 52. The first hydraulic chamber 51 and the pump 6 are connected via a first oil passage 61. The second hydraulic chamber 52 and the pump 6 are connected via a second oil passage 62. In addition, although the gear pump is applied as the pump 6 in the present Example 1, it is not specifically limited.

  In addition to the torque signal from the torque sensor 12, the control unit 10 receives the current value from the current sensor 13 that detects the current value of the motor 6a, the vehicle speed signal from the vehicle speed sensor 11, and the like. A steering assist force is determined based on these various signals, and a command signal is output to the motor 6a. Details of the control unit 10 will be described later.

(Power assist control action)
Here, normal power assist control will be described. For example, in the configuration shown in FIG. 1, it is assumed that the driver steers the steering wheel 1 to the right and moves the rack shaft 4 to the left. At this time, a motor drive signal corresponding to the torque signal detected by the torque sensor 12 is output to the motor 6a. Then, the pump 6 supplies oil from the second hydraulic chamber 52 side to the first hydraulic chamber 51 side by the rotation of the motor 6a. Therefore, the oil in the second hydraulic chamber 52 moves to the first hydraulic chamber 51 side. The piston 5b is pushed leftward in FIG. 1 by the hydraulic pressure of the first hydraulic chamber 51 generated at this time, and this force becomes a force for assisting the steering force of the driver.

  FIG. 2 is a block diagram showing the configuration of the control unit 10. The control unit 10 includes an assist control processing unit 200 that calculates a command current value to the motor 6a based on the detected torque signal, and a motor current control unit 300 that controls the current to the motor 6a.

  (Configuration of assist control processing unit)

FIG. 3 is a block diagram showing the configuration of the assist control processing unit 200. The assist control processing unit 200 is provided with a low-pass filter 201 that filters the torque signal T and two high-pass filters 202 and 203. Further, a gain multiplying unit 204, 205, 206 that multiplies each filter value by a low-pass filter gain K _L and a high-pass filter gain K _H , and an adder 207 that adds the values multiplied by the gains K _L , K _H Is provided. Further, the motor command value calculation unit 208 adjusts the phase and gain of the torque signal based on the added filtering torque signal TF, and calculates a motor command current (target value) I ^* corresponding to the optimum assist amount. .

(Motor current controller)
The motor current control unit 300 adjusts a current control gain (proportional gain k _p , integral gain k _i ) based on the torque signal T to a current response gain calculation processing unit 400 (a correction gain correction unit described in claims). Correspondence) is provided. Further, a deviation calculating unit 303 that calculates a deviation ΔI between the motor command current I ^* and the actual motor current I ′ detected by the current sensor 13, and a proportional gain multiplying unit 304 that multiplies the deviation ΔI by a proportional gain k _p. , an integrator 305 for integrating the deviation [Delta] i, the integral gain multiplication unit 306 that multiplies the integral gain k _i, the addition unit 307 is provided with the gain k _p, k _i is adds the multiplication values.

That is, the control unit 10 calculates a motor command current value I ^* , which is a target value, based on the detected torque signal T, and a deviation ΔI between the motor command current value I ^* and the detected actual current value I ′. Based on the above, so-called PI control for outputting the final motor command current value I is executed.

(About the current response gain calculation processor)
[Current response lowering flag set processing]
Hereinafter, the current response lowering flag setting process in the current response gain calculation processing unit 400 will be described with reference to the flowchart of FIG.

In step 401, it is determined whether or not the absolute value of the detected torque signal T is equal to or _greater than a predetermined value T _jdg . If T ≧ T _jdg , the process proceeds to step 402. _Otherwise , the process proceeds to step 407.

In step 402, it is determined whether or not the count value of the high load determination timer t1 is equal to or _greater than a predetermined value t1 _jdg . If t1 ≧ t1 _jdg , the process proceeds to step 404. _Otherwise , the process proceeds to step 403.

  In step 403, the high load determination timer t1 is counted up as time-up processing.

In step 404, it is determined whether or not the count value of the butting time timer t2 is equal to or _greater than a predetermined value t2 _jdg . If t2 ≧ t2 _jdg , the process proceeds to step 406. _Otherwise , the process proceeds to step 405.

  In step 405, the abutting time timer t2 is counted up as time-up processing.

  In step 406, the current response lowering flag f1 is set to 1.

  In step 407, the high load determination timer t1 and the butting time timer t2 are cleared as timer clear processing.

  In step 408, the current response lowering flag f1 is cleared.

  In step 409, a current response gain calculation process is executed.

(Current response gain calculation processing)
FIG. 5 is a flowchart showing the current response gain calculation process in step 409.

  In step 410, it is determined whether or not the current response reduction flag f1 is set to 1. If it is set, the process proceeds to step 412. Otherwise, the process proceeds to step 411.

In step 411, k _p = k _p (normal) and k _i = k _i (normal) are output as outputs of the current response gain calculation processing.

In step 412, the vehicle speed and torque signal T are read, and the current response decrease amount is determined with reference to the current response decrease amount map (k _dp = k _dp (map), k _di = k _di (map)).

In step 413, the abutting time timer value t2 counted up in step 405 is read, the elapsed time coefficient map (P _p = P _p (map), P _i = P _i (map)) is referred to, and the elapsed time coefficient To decide.

In step 414, as the current response gain calculation processing,
k _p = k _p (normal) − (k _dp・ P _p )
k _i = k _i (normal) − (k _di・ P _i )
Output proportional gain k _p and integral gain k _i .

The operation in the control process will be described.
(Temporary high load during normal turning)
In steps 401 and 402, the torque signal detected by the torque sensor 12 is greater than or equal to a predetermined value T _jdg representing a state where the steering torque is large, and the state where the steering torque is large by the high load determination timer t1 continues for a predetermined time t1 _jdg or longer. Determine if you did. The purpose of this determination is to determine whether or not there is a temporary high load state that occurs when the vehicle is steered suddenly in a normal steering state. When the torque signal T falls below the predetermined value T _jdg while the high load determination timer t1 has not reached the predetermined time t1jdg, the high load determination timer t1 and the butting time timer t2 are immediately reset to reduce the current response. Set the flag f1 to 0.

Next, when the process proceeds to the current response gain calculation process, since the current response decrease flag f1 is set to 0, k _p = k _p (normal), k _i = k _i ( normal) is output. As a result, it is possible to ensure normal steering response without lowering the gain to a temporary high load state.

(High load when hitting the steering wheel)
In steps 401 and 402, the torque signal detected by the torque sensor 12 is greater than or equal to a predetermined value T _jdg representing a state where the steering torque is large, and the state where the steering torque is large by the high load determination timer t1 continues for a predetermined time t1 _jdg or longer. If it is determined that it has been, it is determined that it is not a high load state due to temporary sudden steering. At this time, it is determined that the steering wheel is in a high load state, and the current response lowering flag f1 is set to 1 and the abutting time timer t2 starts to be counted up.

Next, when proceeding to the current response gain calculation process, since the current response decrease flag f1 is set to 1, the current response decrease amounts k _dp and k _di are determined from the current response decrease amount map shown in FIG. At this time, the vehicle speed and the torque signal are read, and the reduction amount corresponding to the vehicle speed and the torque signal is determined. Specifically, the lowering amount is increased when the torque signal is large, and the lowering amount is decreased when the vehicle speed is high.

Next, in order to avoid a sudden change in characteristics due to a sudden decrease in gain, a coefficient for gradually decreasing the current response gain is determined according to the count value of the abutting time timer t2. Set the current response gain as the value obtained by subtracting the determined current response reduction amount k _dp , k _di and the elapsed time coefficients P _p , P _i from the normal current response gain k _p (normal), k _i (normal) To do.

  That is, in the power steering apparatus of the first embodiment, the pump 6 is driven by the motor 6a, and this pump discharge pressure is used as the assist force. At this time, compared to a power steering device that directly applies assist torque to the rack shaft or steering shaft by a so-called electric motor, the assist is via oil, so smooth assist control is performed without giving the driver a sense of incongruity. Can be achieved. However, since delay due to the movement of oil is likely to occur, the normal control gain is set high to ensure responsiveness (corresponding to the correction gain calculation means described in the claims).

  When the pump 6 is driven and the piston 5b is in a stroke, the volume of the first hydraulic chamber 51 or the second hydraulic chamber 52 is changed, so that the pressure does not become so high, and the pump load (motor load) Is not too big. At this time, when the steering wheel 1 is in the abutting state, the movement of the piston 5b stops and the volume of the first hydraulic chamber 51 or the second hydraulic chamber 52 becomes constant, so that a hard hydraulic circuit configuration is obtained. Therefore, the hydraulic chamber and the hydraulic circuit on the assist side become high pressure at once, and the pump load increases rapidly. Further, the torque signal of the torque sensor 12 also increases at a stretch by the driver's steering.

  In the control unit 10, since the motor current command value is calculated based on the torque signal, a command signal for further increasing the assist force is output even if the torque signal is increased when the steering wheel hits. As a result, the pump load (motor load) increases. In normal motor current control, a value obtained by adding a back electromotive voltage generated by the rotation of the motor is output. However, when the number of rotations of the motor 6 decreases due to the motor load, the back electromotive voltage decreases and the current value increases at a stretch.

  In addition, when the pump load exceeds a certain level, a phenomenon occurs in which the hydraulic pressure instantaneously leaks between the high pressure side and the low pressure side of the pump 6 (sometimes accompanied by abnormal noise). Then, since the pump load is suddenly reduced, the motor load is reduced and the motor starts rotating at once. The value of the current flowing through the motor 6a is reduced by the increase of the counter electromotive voltage generated at this time. That is, there are a plurality of elements that make the rotation of the motor 6a unstable when the steering wheel is abutted.

  Since the motor current control unit 300 determines the motor current output command value by PI control, a sudden change in the current value flowing through the motor 6a also leads to a sudden change in the command value, resulting in control hunting. At this time, if the motor current output command value tends to hunting, there is a possibility that abnormal noise may be generated even if the steering wheel 1 is not affected as a torque fluctuation.

  Therefore, at the time of abutting the steering wheel, by reducing the current response gain, the motor current output command value does not increase suddenly even when the torque signal is large, and the pump load due to pump leakage Even if a change occurs, the motor current output command value does not suddenly increase. Therefore, stable assist control can be achieved without generating abnormal noise.

  Further, technical ideas other than the claims that can be grasped from the respective embodiments will be described below together with the effects thereof.

(A) In the power steering apparatus according to claim 1,
The power steering apparatus, wherein the pump load estimating means estimates a pump load from a driving torque of the electric motor.

  There is no need to provide a sensor or the like for detecting the pump load, and the cost can be reduced.

(B) In the power steering device according to claim 1 or (A),
The power steering apparatus according to claim 1, wherein the pump load estimating means estimates a pump load based on the necessary steering assist force detected by the necessary steering assist force detecting means.

  The pump load can be estimated on the basis of a sudden increase in the necessary steering assist force when the steering wheel is abutted or the like, so that it is not necessary to provide a sensor or the like, and the cost can be reduced.

(C) In the power steering device according to claim 1 and (a) and (b) above,
The correction gain correction means is provided with a time measuring means,
The time measuring means measures the time when the pump load is continuously at a predetermined position or more,
The power gain steering device according to claim 1, wherein the correction gain correction means corrects the correction gain to decrease when a time during which the pump load is a predetermined value or more is a predetermined time or more.

  When the inside of the hydraulic circuit is in a high pressure state, such as when the steering wheel is abutted, and this state occurs continuously for a predetermined time, an abnormal noise is generated from the device. On the other hand, even if the inside of the hydraulic circuit is in a high pressure state, if it occurs instantaneously, no abnormal noise is generated from the apparatus. Therefore, when the pressure instantaneously becomes high, it is possible to prevent the steering response from being lowered by not reducing the correction gain.

(D) In the power steering device according to claim 1 and (a), (b), (c) above,
The power gain steering device according to claim 1, wherein the correction gain correction means corrects the correction gain gradually.

  When the correction gain is suddenly decreased and corrected, there is a possibility that a feeling of strangeness may occur in the steering feeling. Therefore, the feeling of strangeness in the steering feeling can be suppressed by gradually decreasing the correction gain.

(E) In the power steering device according to claim 1 and (a), (b), (c), (d) above,
A steering angle detecting means for detecting the steering angle of the steered wheels is provided;
The necessary steering assist force detecting means is a torque sensor for detecting steering torque,
The correction gain correction means reduces and corrects the correction gain when the steering angle is a predetermined value or more and the steering torque is a predetermined value or more.

  If the steering angle is greater than or equal to a predetermined value and the steering torque is greater than or equal to a predetermined value, it is estimated that the steering wheel is in contact with the steering wheel. can do.

It is a figure showing the power steering device in Example 1. FIG. 3 is a block diagram illustrating a configuration of a control unit in Embodiment 1. FIG. 3 is a block diagram illustrating a configuration of an assist control processing unit in Embodiment 1. FIG. 3 is a flowchart illustrating a current response gain calculation process in the first embodiment. 3 is a flowchart illustrating a current response gain calculation process in the first embodiment. It is a figure showing the current response fall amount map in Example 1. FIG. It is a figure showing the elapsed time coefficient map in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Rack & pinion mechanism 4 Rack shaft 5 Power assist mechanism 5a Power cylinder 5b Piston 6 Pump 6a Motor 7 Steering wheel 10 Control unit 11 Vehicle speed sensor 12 Torque sensor 13 Current sensor 51 1st hydraulic chamber 52 2nd Hydraulic chamber 61 First oil passage 62 Second oil passage 200 Assist control processing unit 201 Low-pass filter 202, 203 High-pass filter 300 Motor current control unit 400 Current response gain calculation processing unit

Claims (1)

A hydraulic power cylinder for assisting the steering force of the steering mechanism connected to the steering wheel;
A reversible pump having a pair of discharge ports for supplying hydraulic pressure to both pressure chambers of the hydraulic power cylinder via the first and second passages;
An electric motor for rotating the reversible pump forward and reverse;
Necessary steering assist force detecting means for detecting necessary steering assist force to be applied to the steered wheels;
Command current value output means for outputting a command current value to the motor based on the required steering assist force detected by the required steering assist force detection means;
Correction gain calculating means for calculating a correction gain for correcting the phase delay of the command current value;
Command current value correcting means for correcting the command current value based on the correction gain;
A pump load estimating means for estimating a pump load of the reversible pump;
When the pump load is equal to or greater than a predetermined value, correction gain correction means for correcting the decrease of the correction gain;
A power steering apparatus comprising:

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