JP2002220064A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent steering assisting force from being reduced suddenly. SOLUTION: A target flow rate Q is set to a flow rate Qv in response to a vehicular speed in a period between times t1, t2 when a steering speed dθ/dt is a threshold value S or more. When the steering speed dθ/dt reaches the threshold value S at the time t2 and when the steering speed dθ/dt becomes thereafter less than the threshold value S, a reduced flow rate K is set in response to a steering angle θ at that time (just after the time t2). A value Q-K provided by subtracting the reduced flow rate K from the present target flow rate Q (target flow rate just before the steering speed dθ/dt reaches to the threshold value S) is made a new target flow rate Q. The reduced flow rate K is set in every control cycle for the processing shown in Fig. 2 hereinbefore in a period between times t2, t3 when a steering speed dθ/dt is less than the threshold value S, and the target flow rate Q is reduced by the flow rate K in the every control cycle until reaching to a predetermined stand-by flow rate Qu.

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 that generates a steering assist force for assisting steering by a hydraulic pressure generated by a pump driven by an electric motor.

[0002]

2. Description of the Related Art Conventionally, there has been used a power steering device which supplies hydraulic oil from an oil pump to a power cylinder connected to a steering mechanism, thereby generating a steering assist force from the power cylinder. Among such power steering devices, there is one in which an oil pump is driven by an electric motor such as a brushless motor.

In this motor-driven pump type power steering apparatus, stop and go control of an electric motor is performed. That is, when the operation speed (steering speed) of the steering wheel is lower than the predetermined speed, the electric motor is driven at a constant low rotation speed (including zero), and the flow rate of the working oil sent from the oil pump is suppressed to a small value. Can be On the other hand, when the steering speed is equal to or higher than the predetermined speed, the electric motor is driven at a rotation speed corresponding to the vehicle speed so that an appropriate steering assist force corresponding to the vehicle speed is generated. By this stop-and-go control, energy saving can be improved.

[0004]

However, in the stop-and-go control described above, when the steering speed decreases from a speed higher than the predetermined speed and falls below the predetermined speed, a response is made in response to this. Since the rotation speed of the electric motor is rapidly reduced from the rotation speed corresponding to the vehicle speed to the constant low rotation speed, the flow rate of the working oil supplied from the oil pump to the power cylinder sharply decreases. There is a problem that the steering assist force applied to the steering mechanism from the power cylinder is rapidly reduced. If the steering assist force decreases sharply, not only does the driver feel uncomfortable in steering, but also the steering wheel cannot be maintained in a steered state, and the vehicle may wobble left and right.

An object of the present invention is to solve the above-mentioned technical problems and to provide a power steering device capable of preventing a sharp decrease in steering assist force.

[0006]

According to the first aspect of the present invention, there is provided a pump (23) mounted on a vehicle and used by an electric motor (27). A power steering device that supplies hydraulic oil delivered from a hydraulic cylinder to a power cylinder (26) and generates a steering assist force from the power cylinder in accordance with an operation of an operating member (11) for steering a vehicle. A vehicle speed detecting means (5) for detecting a vehicle speed (V), a steering angle data output means (4) for outputting steering angle data according to a change in the steering angle by operating an operation member, and a steering angle data output means. Steering speed calculating means (3, S1) for calculating a steering speed (dθ / dt), which is a time change rate of the steering angle of the operating member, based on the output steering angle data; Sa It is determined whether the steering speed is equal to or higher than a predetermined threshold value (S). If the steering speed is equal to or higher than the threshold value, the steering speed is set based on the vehicle speed detected by the vehicle speed detection means. Flow rate (Qv; Qv + Δ
Q) is set as a new target flow rate, and if the steering speed is lower than the threshold value, a standby flow rate (Q-K) obtained by subtracting a predetermined reduced flow rate (K) from the current target flow rate is set in advance. The target flow rate setting means (3, S2, S3, S4, S5, S6, S
7) and motor control means (3, 6) for controlling the drive of the electric motor so that the hydraulic oil of the target flow rate set by the target flow rate setting means is sent from the pump. It is a power steering device.

[0007] Alphanumeric characters in parentheses indicate corresponding components in the embodiment described later. Hereinafter, the same applies in this section. According to the present invention, after the steering speed decreases and reaches the predetermined threshold, while the state in which the steering speed is lower than the threshold continues, the reduced flow rate is set every predetermined control cycle. Then, the target flow rate is reduced by the reduced flow rate until the target flow rate reaches a predetermined standby flow rate. As a result, the target flow rate is gradually reduced at the rate of the reduced flow rate / control cycle, and accordingly, the steering assist force generated from the power cylinder is gradually reduced. Therefore, it is possible to prevent the driver from feeling uncomfortable due to the sudden decrease in the steering assist force, and to prevent the vehicle from wobbling due to the sudden decrease in the steering assist force.

According to a second aspect of the present invention, the power steering apparatus detects a steering angle (θ) of the operating member based on steering angle data output from the steering angle data output means. The system further includes an angle detection means (3, S1), wherein the target flow rate setting means is detected by the steering angle detection means when the steering speed calculated by the steering speed calculation means is less than the threshold value. The flow reduction may be set based on the steering angle, and the flow obtained by subtracting the set flow reduction from the current target flow may be set as a new target flow.

Further, the target flow rate setting means is detected by the vehicle speed detecting means when the steering speed calculated by the steering speed calculating means is equal to or higher than the threshold value. (31, 32, 33) that sets a flow rate obtained by adding an additional flow rate corresponding to the steering speed calculated by the steering speed calculation means to a basic flow rate corresponding to the vehicle speed to a new target flow rate. Good. Further, the additional flow rate is preferably generated by multiplying the magnitude of the steering speed by a predetermined proportional term, and the proportional term is based on the pressure receiving area (Ap) of the piston (263) of the power cylinder and the steering angle. More preferably, it is the product of the ratio of the amount of movement of the piston to the change (r).

[0010] In this case, the additional flow rate is set to a value substantially equal to the volume change rate (volume change amount per unit time) of the oil chamber of the power cylinder according to the steering speed.
Therefore, when the addition value of the basic flow rate and the additional flow rate is set as the target flow rate, and the electric motor is driven and controlled based on the target flow rate, the volume of the oil chamber of the power cylinder changes with the change in the volume.
The flow rate of hydraulic oil delivered from the pump at a speed approximately equal to the rate of change in volume increases or decreases. As a result, the hydraulic fluid having an appropriate flow rate in accordance with the steering speed can be sent from the pump, and a feeling of steering discomfort due to an insufficient flow rate or an excessive flow rate of the hydraulic oil supplied to the power cylinder (feeling of steering during sudden steering, (A feeling of missing torque at the time of a decrease in the steering speed) can be eliminated.

[0011]

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 device according to an embodiment of the present invention. This power steering device is provided in association with a steering mechanism 1 of a vehicle, and is for applying a steering assist force to the steering mechanism 1.

The steering mechanism 1 includes a steering wheel 11 operated by a driver, a steering shaft 12 connected to the steering wheel 11, and a pinion gear 1 provided at a distal end of the steering shaft 12.
3 and a rack shaft 14 extending in the left-right direction of the vehicle. A rack gear portion 14a is formed on the rack shaft 14, and a pinion gear 13a is formed on the rack gear portion 14a.
Are engaged. Tie rods 15 are respectively connected to both ends of the rack shaft 14.
Numerals 5 are respectively connected to a knuckle arm 16 that supports a front left wheel FL and a front right wheel FR as steering wheels. The knuckle arm 16 is provided rotatably around the king pin 17. With this configuration, when the steering wheel 11 is operated and the steering shaft 12 is rotated, the rotation is converted by the pinion gear 13 and the rack shaft 14 into linear motion along the left-right direction of the vehicle, and this linear motion is converted to the knuckle arm 16. Kingpin 1
The rotation of the front left wheel FL and the front right wheel FR is achieved by being converted into a rotation around 7.

A torsion bar 21 which twists in the middle of the steering shaft 12 according to the direction and magnitude of the steering torque applied to the steering wheel 11,
A hydraulic control valve 22 whose opening changes in accordance with the direction and size of the twist of the torsion bar 21 is interposed. The hydraulic control valve 22 has four ports 221, 22
2, 223 and 224 are provided, and the operating oil pumped from the reservoir tank 24 by the oil pump 23 is supplied to the port 221 through the oil pipe 251. The port 222 communicates with the reservoir tank 24 via an oil pipe 252. Port 22
The oil chambers 2 and 3 of the power cylinder 26 that generate a steering assist force via oil pipes 253 and 254, respectively.
61 and 262. A piston 263 is provided between the oil chambers 261 and 262 of the power cylinder 26 to move in the vehicle width direction due to a difference in oil pressure in the oil chambers 261 and 262. This piston 263 is configured integrally with the rack shaft 14.

When the steering wheel 11 is rotated left or right, the torsion bar 21 is twisted, and an amount corresponding to the twist of the torsion bar 21 is transmitted from the hydraulic control valve 22 to the oil chamber of the power cylinder 26. 26
Hydraulic oil is supplied to one of the first and second 262. As a result, a hydraulic pressure difference is generated between the oil chambers 261 and 262, and the piston 263 of the power cylinder 26 moves according to the hydraulic pressure difference, whereby the steering assist force is applied to the rack shaft 14. At this time, the excess hydraulic oil is returned from the hydraulic control valve 22 to the reservoir tank 24 via the oil pipe 252. When the torsion bar 21 is hardly twisted, the hydraulic control valve 22 is in an equilibrium state, and the hydraulic oil supplied from the oil pump 23 to the hydraulic control valve 22 is not supplied to the power cylinder 26 , Oil pipe 2
It is returned to the reservoir tank 24 via 52.

The oil pump 23 is driven by an electric motor 27. The electric motor 2
7 is an electronic control unit 3 including a microcomputer
Is driven and controlled. The electronic control unit 3 is provided with steering angle data output from the steering angle sensor 4. The steering angle sensor 4 is provided in association with the steering wheel 11, and sets the steering angle of the steering wheel 11 when the ignition key switch is turned on and the engine is started to an initial value “0”, and sets the steering angle from this initial value. Steering angle data having a code corresponding to the relative steering angle and corresponding to the steering direction is output. The electronic control unit 3 obtains a steering angle midpoint, which is a steering angle when the vehicle is in a straight running state, based on the steering angle data, and further calculates the wheels FR, FR based on the steering angle midpoint and the steering angle data. An absolute steering angle (steering angle) θ corresponding to the direction of FL is obtained. The steering angle midpoint is detected, for example, by sampling the steering angle data output from the steering angle sensor 4, creating a histogram of the steering angle data values, and detecting the most frequently occurring data after a predetermined sampling number of data has been collected. This is achieved by obtaining the steering angle data as steering angle data at the steering angle midpoint. Further, the electronic control unit 3 controls the steering angle θ
Is differentiated with respect to time to obtain a steering speed dθ / dt.

The electronic control unit 3 is further provided with vehicle speed data output from the vehicle speed sensor 5. The vehicle speed sensor 5 calculates the running speed (vehicle speed) V of the vehicle.
May be directly detected, or the vehicle speed V may be calculated based on an output pulse of a wheel speed sensor provided in connection with the wheel. Further, current data output from the motor current detection circuit 6 is provided to the electronic control unit 3. The motor current detection circuit 6 outputs current data proportional to the current flowing through the electric motor 27 (motor current).

The electronic control unit 3 provides a target flow rate Q of hydraulic oil to be supplied from the oil pump 23 to the hydraulic control valve 22 based on steering angle data given from the steering angle sensor 4 and vehicle speed data given from the vehicle speed sensor 5. Set.
Then, a rotation speed of the electric motor 27 according to the target flow rate Q is set, and the electric motor 27 is set at the set rotation speed.
Is driven based on the output signal of the motor current detection circuit 6 so that the motor current is driven.

FIG. 2 is a flowchart showing a flow of processing for setting a target flow rate Q of hydraulic oil to be supplied from the oil pump 23 to the hydraulic control valve 22. The target flow rate setting processing shown in FIG. 2 is repeatedly executed by the microcomputer of the electronic control unit 3 at a constant control cycle. First, the steering angle θ and the steering speed dθ / dt of the steering wheel 11 are obtained by calculation based on the steering angle data output from the steering angle sensor 4, and the vehicle speed data is taken in from the vehicle speed sensor 5 to obtain the vehicle speed. V is obtained (step S1).

Next, it is determined whether or not the absolute value of the steering speed dθ / dt is equal to or greater than a predetermined threshold value S (step S2). If the absolute value of the steering speed dθ / dt is equal to or larger than the threshold value S, a flow rate Qv corresponding to the vehicle speed V is set, and the set flow rate corresponding flow rate Qv is set to the target flow rate Qv.
(Step S3), and the target flow rate setting process is returned. The vehicle speed corresponding flow Qv is set to a smaller value as the vehicle speed V increases within a predetermined flow range, for example, according to a vehicle speed-target flow characteristic curve shown in FIG.

On the other hand, if the absolute value of the steering speed dθ / dt is less than the threshold value S (NO in step S2), the reduced flow rate K corresponding to the steering angle θ is set (step S2).
4). According to the steering angle-flow reduction characteristic line shown in FIG. 4, the reduced flow rate K is set so as to monotonously decrease (in this embodiment, linearly decrease) as the absolute value of the steering angle θ increases. It is determined between zero. When the reduced flow rate K is set, subsequently, the reduced flow rate K is subtracted from the current target flow rate Q, and the resulting value Q−K is set to the new target flow rate Q.
(Step S5).

Thereafter, it is determined whether or not the newly set target flow rate Q is less than a predetermined standby flow rate Qu (step S6). Target flow rate Q is standby flow rate Q
If u or more, the target flow rate setting process is immediately returned. On the other hand, if the target flow rate Q is less than the standby flow rate Qu, the target flow rate Q is reset to the standby flow rate Qu (step S7), and the target flow rate setting process is returned. As a result, while the state where the absolute value of the steering speed dθ / dt is less than the threshold value S continues, the target flow rate Q
Is gradually reduced until the standby flow rate Qu is reached.

FIG. 5 is a time chart for explaining the characteristic operation of the power steering apparatus according to this embodiment. FIG. 5A shows a change over time in the steering speed dθ / dt of the steering wheel 11, and FIG. 5B shows a change over time in the target flow rate Q. FIG. 5 shows an example in which the vehicle speed V is kept constant. In the period from time t1 to time t2 when the steering speed dθ / dt is equal to or higher than the threshold value S, the target flow rate Q is set to the vehicle speed corresponding flow rate Qv. At time t2, the steering speed dθ / dt reaches the threshold value S, and thereafter, when the steering speed dθ / dt falls below the threshold value S, the steering angle θ at that time (immediately after time t2).
Is set in accordance with. Then, a value Q−K obtained by subtracting the reduced flow rate K from the current target flow rate Q (the target flow rate immediately before the steering speed dθ / dt reaches the threshold value S) is set as a new target flow rate Q. In the period from time t2 to time t3 when the steering speed dθ / dt is less than the threshold value S, the reduced flow rate K is set for each control cycle of the processing shown in FIG. The flow rate is reduced by the decrement flow rate K until it reaches Qu.

Therefore, after the time t2, the target flow rate Q is gradually reduced by the reduction flow rate K / the speed of the control cycle. Accordingly, the target flow rate Q is supplied from the power cylinder 26 to the steering mechanism 1 (rack shaft 14). The steering assist force is gradually reduced. As a result, it is possible to prevent the driver from feeling uncomfortable due to the sudden decrease in the steering assist force, and to prevent the vehicle from wobbling due to the sudden decrease in the steering assist force. Further, during the period from time t3 to t4, the target flow rate Q is set to the standby flow rate Qu, and the electric motor 27 is driven at a constant low rotation speed (including zero), so that energy is saved by stop-and-go control. Nature can be secured.

When the steering speed dθ / dt reaches the threshold value S at time t4, the target flow rate Q is set to the vehicle speed corresponding flow rate Qv, and the flow rate of the working oil supplied from the oil pump 23 to the hydraulic control valve 22 is reduced. From standby flow Qu to target flow Q =
It is quickly increased to Qv. Then, the steering speed dθ /
During a period from time t4 to time t5 when dt is equal to or larger than the threshold value S,
The target flow rate is set to the vehicle speed corresponding flow rate Qv. At time t5, when the steering speed dθ / dt reaches the threshold value S and further when the steering speed dθ / dt becomes less than the threshold value S, the target flow rate Q
Is gradually reduced from the vehicle speed corresponding flow rate Qv. If the steering speed dθ / dt exceeds the threshold value S at time t6 before the target flow rate Q reaches the standby flow rate Qu, the target flow rate Q becomes the target flow rate Q immediately before the time t6. From the vehicle speed corresponding flow rate Qv.

As described above, according to this embodiment, the target flow rate Q of the hydraulic oil to be supplied from the oil pump 23 to the hydraulic control valve 22 is determined by the fact that the steering speed dθ / dt becomes smaller than the threshold value S. Is not suddenly reduced to the standby flow rate Qu in response to the
The flow rate is gradually reduced to u at a rate of the reduced flow rate K / control cycle. As a result, it is possible to prevent the driver from feeling uncomfortable due to the sudden decrease in the steering assist force, and to prevent the vehicle from wobbling due to the sudden decrease in the steering assist force.

In this embodiment, the steering speed dθ /
When dt is equal to or greater than the threshold value S, the target flow rate Q
Is set to the flow rate Qv corresponding to the vehicle speed, but the target flow rate Q in this state is set to a flow rate Qv + ΔQ obtained by adding an additional flow rate ΔQ corresponding to the steering speed dθ / dt to the flow rate (basic flow rate) Qv corresponding to the vehicle speed. It may be. The configuration for that is shown in FIG. Each unit shown in FIG. 6 is realized, for example, by the microcomputer of electronic control unit 3 executing a program process. That is, the electronic control unit 3 determines the steering speed dθ /
When dt is greater than or equal to threshold value S, target flow rate Q = Qv + ΔQ
In order to set the basic flow rate Qv, a basic flow rate generating section 31 that generates a basic flow rate Qv according to the vehicle speed V, an additional flow rate generating section 32 that generates an additional flow rate ΔQ according to the absolute value of the steering speed dθ / dt, An addition unit 33 that adds the additional flow rate ΔQ to generate the target flow rate Q = Qv + ΔQ is included.

In the additional flow rate setting section 32, the additional flow rate Δ
Q is generated by multiplying the absolute value of the steering speed dθ / dt by a predetermined proportional term. The proportional term is, for example, the pressure receiving area of the piston 263 of the power cylinder 26 (the contact area with the hydraulic oil in one oil chamber) as Ap, and the ratio of the change in the movement amount x of the piston 263 to the change in the steering angle θ ( Ratio) is r = x / θ, and the pressure receiving area Ap
And a fixed value Ap · r obtained by multiplying by the ratio r. Therefore, the additional flow rate ΔQ is set to a value substantially equal to the volume change rate (volume change per unit time) of the oil chambers 261 and 262 of the power cylinder 26 according to the steering speed dθ / dt.

Therefore, the sum of the basic flow rate Qv and the additional flow rate ΔQ is set as a target flow rate Q. When the electric motor 27 is driven and controlled based on the target flow rate Q, the volumes of the oil chambers 261 and 262 of the power cylinder 26 are changed. With the change, the flow rate of the hydraulic oil supplied to the hydraulic control valve 22 increases or decreases at a speed approximately equal to the volume change rate. This allows
Hydraulic oil having an appropriate flow rate in accordance with the steering speed dθ / dt can be sent from the oil pump 23, and a steering discomfort due to an insufficient flow rate or an excessive flow rate of the hydraulic oil supplied to the power cylinder 26 (eg, a sudden steering error). (E.g., a feeling of snagging, a feeling of missing torque when the steering speed decreases) can be eliminated.

Although the embodiments of the present invention have been described above, the present invention can be embodied in other forms, and various design changes are made within the scope of the matters described in the claims. It is possible.

[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 flowchart illustrating a flow of a process for setting a target flow rate.

FIG. 3 is a characteristic diagram showing a correspondence relationship between a vehicle speed and a target flow rate.

FIG. 4 is a characteristic diagram showing a correspondence relationship between a steering angle and a reduced flow rate.

FIG. 5 is a time chart for explaining a characteristic operation of the power steering device according to the embodiment;

FIG. 6 is a block diagram showing a configuration for setting a target flow rate to an addition flow rate of a flow rate corresponding to a vehicle speed and an additional flow rate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steering mechanism 3 electronic control unit 4 steering angle sensor 5 vehicle speed sensor 6 motor current detection circuit 11 steering wheel 23 oil pump 26 power cylinder 261, 262 oil chamber 263 piston 27 electric motor 31 basic flow generation unit 32 additional flow setting unit 33 addition Department

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B62D 117: 00 B62D 117: 00

Claims (3)

[Claims] 1. A hydraulic cylinder which is mounted on a vehicle and which is used by an electric motor and which is supplied from a pump driven by an electric motor, supplies hydraulic oil to a power cylinder for operating an operation member for steering the vehicle. A power steering device for generating a steering assist force according to the vehicle speed, comprising: vehicle speed detection means for detecting a vehicle speed; steering angle data output means for outputting steering angle data according to a change in steering angle by operating an operation member; A steering speed calculating means for calculating a steering speed, which is a time change rate of the steering angle of the operating member, based on the steering angle data output from the angle data output means; and a steering speed calculated by the steering speed calculating means. It is determined whether or not the steering speed is equal to or higher than a predetermined threshold value. If the steering speed is equal to or higher than the threshold value, the steering speed is set based on the vehicle speed detected by the vehicle speed detection means. Is set as a new target flow rate, and if the steering speed is less than the threshold value, a new target flow rate is set with a preset standby flow rate as a lower limit of a flow rate obtained by subtracting a predetermined reduced flow rate from the current target flow rate. And a motor control means for controlling the drive of the electric motor so that the hydraulic fluid of the target flow rate set by the target flow rate setting means is sent from the pump. Steering device. 2. The power steering apparatus according to claim 1, wherein said power steering device is configured to output steering angle data based on steering angle data output from said steering angle data output means.
Further comprising a steering angle detecting means for detecting a steering angle of the operating member, wherein the target flow rate setting means detects the steering angle when the steering speed calculated by the steering speed calculating means is less than the threshold value. The method according to claim 1, wherein a flow reduction is set based on the steering angle detected by the means, and a flow obtained by subtracting the set flow reduction from a current target flow is set as a new target flow. 2. The power steering device according to 1. 3. The target flow rate setting means, when the steering speed calculated by the steering speed calculation means is equal to or higher than the threshold value, sets the basic flow rate corresponding to the vehicle speed detected by the vehicle speed detection means to the basic flow rate. 3. The power steering apparatus according to claim 1, wherein a flow rate obtained by adding an additional flow rate corresponding to the steering speed calculated by the steering speed calculation means is set as a new target flow rate.