JPH11334632A - Power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power steering system which can prevent delay in response to steering assistance even though a vehicle has been used for a long period. SOLUTION: Steering assistance force is generated by oil pressure by a pump driven by an electric motor 27. When an output pulse number of a steering angle sensor 11 which generates the number of pulse according to the steering angle change reaches a start up pulse number, an electronic control unit 30 starts up the electric motor 27. For a certain time immediately after the electric motor 27 started up, a current integration portion 31 integrates motor current. When the number of times when thus obtained motor current integral value exceeds the predetermined reference value reaches a reference time, the start up pulse number is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for applying a steering assist force to a steering mechanism by a hydraulic pressure generated by a pump driven by an electric motor.

[0002]

2. Description of the Related Art Conventionally, a power steering apparatus has been used which assists operation of a steering wheel by supplying hydraulic oil from an oil pump to a power cylinder connected to a steering mechanism. The oil pump is driven by an electric motor, and a steering assist force corresponding to the rotation speed is generated from a power cylinder. Since no steering assist force is required when the steering is not turned, the electric motor is stopped in a straight-ahead steering state where the steering is in the vicinity of the midpoint of the steering angle, and a change in the steering angle exceeding a certain value is detected. The so-called stop-and-go control is performed in such a manner that the electric motor is started in response to the control.

[0003] Further, since the necessity of steering assist decreases as the vehicle speed increases, the motor is started in response to the detection of a large change in the steering angle during high-speed running, and a small amount of steering is performed during low-speed running and when stopped. In some cases, so-called vehicle speed sensitive control is performed so as to start the motor in response to the angle change. Thereby, the catch-up (feeling of catching) is reduced particularly at the time of low-speed running, and at the same time, the energy saving can be improved.

The change in the steering angle is detected by a steering angle sensor that generates a pulse signal every time a constant change in the steering angle occurs.
The electronic control unit of the power steering device activates the motor when the number of pulses output by the steering angle sensor reaches a predetermined threshold determined according to the vehicle speed. In this case, the threshold value is set as large as possible within a range where a response delay of the steering assist does not occur. Thereby, the energy saving property is improved.

[0005]

The gears of the steering mechanism and the gears that constitute the gear mechanism for transmitting the torque of the motor to the oil pump, and the like, become longer as the vehicle is used for a longer period of time. It changes. Therefore,
The familiarity of gears and the size of play are not constant throughout the life of the vehicle.

However, the above-mentioned threshold value for starting the electric motor is determined without taking into account the degree of gear familiarity and the change in the backlash. For this reason, as the use period of the vehicle becomes longer, there is a possibility that the motor may not be able to be started at an optimum timing, and a response delay of the steering assist may be caused.

An object of the present invention is to solve the above-mentioned technical problems and to provide a power steering apparatus capable of preventing a delay in response to steering assist.

[0008]

According to the first aspect of the present invention, there is provided a power steering apparatus for generating a steering assist force by a hydraulic pressure generated by a pump driven by an electric motor. A motor start control means (30, S3) for starting the electric motor in response to a predetermined start condition (X) being satisfied;
A motor current detecting means (14) for detecting a motor current flowing through the electric motor; and a motor current detected by the motor current detecting means for a predetermined time after the electric motor is started, Current integrator (31, S5) for obtaining a motor current integrated value, and changing the start condition in the motor start controller when the motor current integrated value obtained by the current integrator satisfies a predetermined condition. A power steering device characterized by including a starting condition changing means (30, S10).

[0009] The contents in parentheses indicate corresponding components in the embodiment described later. Hereinafter, the same applies in this section.

If the steering assist is delayed, the load on the electric motor increases and the motor current increases. Therefore, according to the present invention, the motor current is integrated over a predetermined time after starting the electric motor, and the thus obtained motor current integrated value is illuminated under predetermined conditions. To change the start condition.

Accordingly, even if the state of gears such as the steering mechanism changes with the prolonged use of the vehicle,
By changing the starting condition, the response delay of the steering assist force can be eliminated. Thus, a good steering feeling can be maintained. Preferably, the starting condition changing means includes means (S6) for determining whether or not the motor current integrated value has exceeded a predetermined reference value. The starting condition changing means includes means for counting the number of times the motor current integrated value exceeds a predetermined reference value (S6, S7). When the counted number exceeds the predetermined reference number, It is more preferable to include means for changing the start condition (S8, S10). In this case, it is preferable that a means (S9) for clearing the counted number after the counted number exceeds a predetermined reference number is further included.

It is preferable that the starting condition includes one of the conditions that a steering angle change amount reaches a predetermined starting threshold value. In this case, it is preferable that the change of the activation condition includes reducing the activation threshold.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram showing a basic configuration of a power steering apparatus according to one embodiment of the present invention. The power steering device is provided in association with a steering mechanism 1 of a vehicle.
To provide a steering assist force to the vehicle.

The steering mechanism 1 includes a steering wheel 2 operated by a driver, a steering shaft 3 connected to the steering wheel 2, a pinion gear 4 provided at a tip end of the steering shaft 3, and a pinion gear. 4 and a rack shaft 5 extending in the left-right direction of the vehicle. Tie rods 6 are respectively connected to both ends of the rack shaft 5, and the tie rods 6 are respectively connected to knuckle arms 7 that support front left and right wheels FL and FR as steering wheels. The knuckle arm 7 is provided rotatably around the king pin 8.

With this configuration, the steering wheel 2
Is operated to rotate the steering shaft 3, the rotation is converted by the pinion gear 4 and the rack shaft 5 into a linear motion along the left-right direction of the vehicle. This linear motion
The rotation is converted into the rotation of the knuckle arm 7 around the king pin 8, whereby the steering of the front left and right wheels FL and FR is achieved.

In the middle of the steering shaft 3, a torsion bar 9 that twists according to the direction and magnitude of the steering torque applied to the steering wheel 2, and according to the direction and magnitude of the twist of the torsion bar 9. And a hydraulic control valve 23 whose opening degree changes. The hydraulic control valve 23 is connected to a power cylinder 20 that applies a steering assist force to the steering mechanism 1. The power cylinder 20 has a piston 21 provided integrally with the rack shaft 5 and a pair of cylinder chambers 20a and 20b partitioned by the piston 21. The cylinder chambers 20a and 20b are respectively provided with oil. Supply / Return path 2
It is connected to the hydraulic control valve 23 via 2a and 22b.

The hydraulic control valve 23 further includes an oil circulation passage 24 that passes through a reservoir tank 25 and an oil pump 26.
It is interposed in the middle of. The oil pump 26 is driven by a motor 27, extracts hydraulic oil stored in the reservoir tank 25, and supplies the hydraulic oil to the hydraulic control valve 23. Excess hydraulic oil is returned from the hydraulic control valve 23 to the reservoir tank 25 via the oil circulation path 24.

When the torsion bar 9 is twisted in one direction, the hydraulic control valve 23 is connected to one of the cylinder chambers 20a, 20b of the power cylinder 20 via one of the oil supply / return paths 22a, 22b. Supply hydraulic oil to one of the two. When the torsion bar 9 is twisted in the other direction, the oil supply / return path 22a,
22b via the other one of the cylinder chambers 20a, 20b.
Supply hydraulic oil to the other of the two. When the torsion bar 9 is hardly twisted, the hydraulic control valve 23 is in a so-called equilibrium state, and the hydraulic oil circulates in the oil circulation path 24 without being supplied to the power cylinder 20.

When hydraulic oil is supplied to any one of the cylinder chambers of the power cylinder 20, the piston 21 moves in the vehicle width direction. As a result, the steering assist force acts on the rack shaft 5.

The magnitude of the steering assist force is determined by the oil pump 26
Is adjusted by controlling the voltage applied to the electric motor 27 that operates the motor. The motor 27 is controlled by the electronic control unit 30. The electronic control unit 30 includes an output signal of a steering angle sensor 11 for detecting a steering angle of the steering wheel 2, an output signal of a vehicle speed sensor 12 for detecting a speed of the vehicle, and a torsion bar 9.
The voltage applied to the motor 27 is determined based on the output signal of the torque sensor 13 for detecting the direction and magnitude of the torque applied to the motor and the output signal of the motor current detection circuit 14. Accordingly, the steering assist force according to the steering angle, the steering torque, the vehicle speed, and the load of the motor 27 is applied to the steering mechanism 1.
Will be given to

Specifically, the drive circuit 2 is connected to the motor 27.
The current from the battery 29 is supplied via the power supply 8. The driving circuit 28 includes the motor 2
7 is connected to a motor current detection circuit 14 for detecting a current flowing through the motor 7 (motor current). Since the current flowing through the motor 27 increases as the load increases, the magnitude of the load on the motor 27 can be detected based on the output signal of the motor current detection circuit 14.

The steering angle sensor 11 outputs a pulse signal every time the steering angle changes by a fixed amount. The electronic control unit 30 counts the number of output pulses of the steering angle sensor 11 to determine the steering angle. Measure the change. Then, when the number of output pulses of the steering angle sensor 11 reaches a predetermined activation threshold, the electronic control unit 30 activates the electric motor 27.

The electronic control unit 30 includes a CPU and a CPU.
And a ROM for storing an operation program of the CPU and the like. The electronic control unit 30 includes a steering angle, a steering torque,
PWM (Pulse Width Mod) according to vehicle speed and motor current
drive pulse signal having a duty
To control the driving of the motor 27.

The electronic control unit 30 further includes a current integration unit 31 for integrating the motor current detected by the motor current detection circuit 14. The current integrator 31 integrates the motor current value immediately after the motor 27 is started over a certain period of time (for example, several milliseconds) to obtain a motor current integrated value. When the motor current integral satisfies a certain condition, the electronic control unit 30
To change the starting condition when starting up.

FIG. 2 is a graph showing a time change of the motor current immediately after the start of the motor 27. Curve L1 is
The change in the motor current when the use period of the vehicle is short is shown, and the curve L2 shows the change in the motor current when the use period of the vehicle is long. From the comparison between the curves L1 and L2, it can be understood that the motor current temporarily increases immediately after the motor is started when the use period of the vehicle becomes longer. This is because the start timing of the motor 27 is changed due to changes in the degree of familiarity, the size of the backlash, etc. of the gears of the steering mechanism 1 and the gears that transmit the torque of the motor 27 to the oil pump 26. It is no longer appropriate. That is, a delay in the activation of the motor 27 causes a response delay in the generation of the steering assist force. As a result, the driver applies a large torque to the steering wheel 2, so that the load on the motor 27 increases and the motor current increases. Becomes larger.

The current integrator 31 of the electronic control unit 30
Calculates the motor current integrated value by integrating the motor current over a fixed time T (for example, several milliseconds) immediately after the start of the motor 27. Since the motor current integrated value increases as the response delay increases, the presence or absence of a response delay can be determined based on the magnitude of the motor current integrated value.

FIG. 3 is a flowchart for explaining the operation of the electronic control unit 30 related to the activation of the motor 27.

First, the electronic control unit 30 clears a counter C for counting the number of times the response delay of the steering assist has occurred (step S1). Further, the electronic control unit 30 sets a starting pulse number X which is the number of output pulses of the steering angle sensor 11 corresponding to a steering angle change threshold value for starting the motor 27 to an initial value (step S2).

The value of the counter C and the value of the starting pulse number X are stored in a data rewritable non-volatile memory (not shown) provided in the electronic control unit 30, and are stored even after the vehicle engine is stopped. The value is kept. The non-volatile memory may be, for example, a memory whose contents are stored by electric power from the battery 29 of the vehicle, or may be configured by an EPROM, an EEPROM, or the like.

The start pulse number X may be set to a plurality of values according to the vehicle speed, but here, for simplicity of description, it is assumed that only one start pulse number X is set.

The electronic control unit 30 includes the steering angle sensor 11
When the number of output pulses of the motor exceeds the number of start pulses X, the motor 2
7, and otherwise the motor 27 is not started (steps S3, S4).

Immediately after the motor 27 is started, the electronic control unit 30 monitors the output signal of the motor current detection circuit 14, and the current integrator 31 outputs the motor current detection value over the above-mentioned fixed time T. Integrate (Step S
5). The electronic control unit 30 includes a current integrator 31
Is compared with a predetermined reference value REF (step S6).

If the current integral I exceeds the reference value REF, the electronic control unit 30 increments the value of the counter C by +1 assuming that a steering assist response delay has occurred (step S7). If the current integrated value I does not exceed the reference value REF, the counter C is kept at the previous value.

When the counter C is incremented, the electronic control unit 30 determines whether or not the value of the counter C has exceeded a predetermined reference number N (for example, N = 10) (step S8). When the value of the counter C exceeds the reference number N, it is determined that the frequency of the response delay of the steering assist is high. In this case, the electronic control unit 30 clears the value of the counter C to zero (Step S).
9), decrement the activation pulse number X by -1 (step S10). As a result, the change in the steering angle until the motor 27 starts is reduced, and the starting condition of the motor 27 is changed to a condition with higher starting sensitivity. As a result, the motor 27 can be started promptly, so that steering assist can be performed with appropriate responsiveness.

After the motor 27 is started, if a certain condition (for example, a condition that the steering angle is within the play angle of the steering wheel 2 for a certain period of time) is satisfied, the motor 27 will be stopped. Then, after the motor 27 stops, step S
The processing from Step 3 is repeated.

As described above, according to this embodiment, when a delay occurs in the steering assist due to mechanical deterioration of the gears, etc., the number of start pulses X is reduced to thereby reduce the small change in the steering angle. Then, the motor 27 is started. Thereby, the response of the steering assist is restored. Thus, excellent steering feeling can be maintained even when the use period of the vehicle is prolonged.

Although the embodiment of the present invention has been described above, the present invention can be implemented in other embodiments. For example, in the above-described embodiment, when a different starting pulse number X is set for each vehicle speed, and when the determination in step S6 is affirmative, the starting pulse numbers X for all vehicle speeds are each decremented by -1. Alternatively, a counter may be provided for each vehicle speed region corresponding to each of the number X of starting pulses, and the steps S6 to S1 may be performed.
The same processing as 0 may be performed.

Further, in the above-described embodiment, the case where the change in the steering angle reaches the start threshold value has been described as an example of the start condition. However, other physical quantities such as the steering speed and the magnitude of the torque satisfy the predetermined condition. May be set as the start condition. In any case, when the frequency at which the motor current integral value increases becomes large, if the starting condition is changed to a condition with higher starting sensitivity, a good steering feeling can be obtained even when the use period of the vehicle is prolonged. The ring can be maintained.

In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of a power steering device according to an embodiment of the present invention.

FIG. 2 is a graph showing a time change of a motor current immediately after starting an electric motor.

FIG. 3 is a flowchart illustrating an operation of an electronic control unit related to activation of an electric motor.

[Explanation of symbols]

 Reference Signs List 1 steering mechanism 11 steering angle sensor 12 vehicle speed sensor 13 torque sensor 14 motor current detection circuit 20 power cylinder 26 oil pump 27 electric motor 28 drive circuit 30 electronic control unit 31 current integration unit

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B62D 119: 00

Claims (1)

[Claims] 1. A power steering apparatus for generating a steering assisting force by a hydraulic pressure generated by a pump driven by an electric motor, the motor starting activating the electric motor in response to a predetermined start condition being satisfied. Control means; motor current detection means for detecting a motor current flowing in the electric motor; motor current integrated by the motor current detection means for a predetermined time after the electric motor is started; Current integration means for obtaining a current integration value; and starting condition changing means for changing the starting condition in the motor start control means when the motor current integration value obtained by the current integration means satisfies a predetermined condition. A power steering device comprising: