JPH11198842A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the max. steering angle in accordance with attaching and detaching of a tire chain. SOLUTION: A power steering device is composed of a tire chain fitting judging apparatus 15 to judge that a tire chain is fitted on a front wheel, a steering angle limit torque setting means 16, and a changeover means 19 to make chaning-over when judgement is passed that tire chain is fitted, and the steering angle limit torque Tr outputted from the setting means 16 when the specified steering angle value is attained, is subtracted from the aux. steering torque Ta as a control value to make control of a motor 9 which conducts assisting of the steering force, and on the basis of the result from subtracting, a steering reaction force is generated by a motor. This enables limitation of the max. steering angle when tire chain is fitted, and in normal running with no tire chain fitted, the max. steering angle is made possible to the maximum position in terms of layout so as to increase the max. steering angle of the vehicle wheel(s) to make steering as much as practicable, and it is possible to enhance the small-radius cornering performance of the vehicle during normal running.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus in which an electric motor generates an assisting force for driving a steered wheel according to a steering torque of a steering wheel.

[0002]

2. Description of the Related Art Conventionally, in a steering device such as an automobile,
Stopper means for defining the maximum turning angle during turning are provided to limit the maximum turning angle of the turning wheels. For example, in a rack-and-pinion structure, stoppers are provided at both ends of a rack, and the stoppers abut against a gear box to limit the stroke of the rack. In the case of the recirculated ball structure, the pitman arm strikes the frame or the like.

[0003] The turning angle of the steered wheels can be adjusted to achieve the target maneuvering performance of the vehicle under constraints such as the size and arrangement of the engine / transmission and interference with the vehicle frame or suspension arms. It is set as large as possible. One of the constraints is:
It is necessary to consider the tire chain to be attached at the time of snowfall or when the road surface is frozen.

[0004]

The above requirement is to prevent interference with other parts at the time of maximum steering even when the tire chain is mounted. Will be set. Therefore, during normal running (when the tire chain is not mounted), there is a margin before the maximum steering angle, and there is a problem that the maximum steering angle during normal running is sacrificed.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems and to realize that the maximum turning angle of the steered wheels can be suitably set, in the present invention, according to the present invention, according to the steering torque of the steering wheel. In an electric power steering apparatus configured to generate an assist force when driving a steered wheel by an electric motor, a chain attachment determining unit that determines that a non-slip unit such as a tire chain is attached to the steered wheel.
When the mounted state of the non-slip means is determined by the chain mounted determination means, when the limited steering angle smaller than the maximum steering angle in the non-mounted state of the non-slip means is reached, further turning is restricted. And a steering reaction force generation control means for generating a large steering reaction force by the electric motor.

[0006] With this arrangement, when anti-slip means such as a tire chain is mounted, a large steering reaction force is generated when the steering angle reaches a limit steering angle smaller than the maximum steering angle when the anti-slip means is not mounted. However, further steering cannot be performed, and the maximum steered angle of the steered wheels is more restricted than usual, so that interference between the tire chain and the inner surface of the wheel house can be prevented. As described above, since the steering angle is limited only when the chain is mounted, the maximum steering angle can be maximized as much as possible without taking into account the interference of the chain with the wheel house inner surface when the chain is not mounted. .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to specific examples shown in the accompanying drawings.

FIG. 1 shows a schematic configuration of a steering device for a steered wheel of a vehicle to which the present invention is applied. The device includes a pinion 4 connected to a steering shaft 2 integrally connected to a steering wheel 1 via a connecting shaft 3 having a universal joint, and a reciprocating motion in the vehicle width direction by meshing with the pinion 4. A rack-and-pinion mechanism composed of a rack shaft 8 having both ends connected to knuckle arms 7 of left and right front wheels 6 as steered wheels via wheels 5. Further, an electric motor 9 is coaxially arranged at an intermediate portion of the rack shaft 8 so as to generate an auxiliary steering force for reducing the manual steering force via the rack and pinion.

Further, a steering torque sensor 11 for detecting a steering torque acting on the pinion 4 and a steering angle sensor 12 for detecting a rotation angle (steering angle) of the steering wheel 1 by a rack and pinion mechanism. And a vehicle speed sensor 13 for outputting a vehicle speed signal corresponding to the traveling speed of the vehicle, and a control unit 14 for controlling the output of the electric motor 9 based on these detected values. Further, a tire chain attachment discriminator 15 is provided as non-slip attachment discriminating means according to the present invention, and a discrimination signal from the tire chain attachment discriminator 15 is input to the control unit 14. Thus, the steering reaction force generation control means is provided.

The control procedure of the control unit 14 will be described below with reference to the circuit block diagram of FIG. In the control unit 14, the steering angle limiting torque setting means 16 to which the steering angle signal θH detected by the steering angle sensor 12 is input, and the steering angle signal θH similarly to the steering torque sensor 11, There is provided an auxiliary steering torque setting means 17 to which the detected steering torque signal Ts and the vehicle speed signal Vs detected by the vehicle speed sensor are respectively input.

The auxiliary steering torque setting means 17 calculates an auxiliary steering torque Ta which is the basis of a drive signal output to the electric motor 9 from the respective signal values, and the steering angle limiting torque setting means 16 determines whether the steering angle signal θH is a predetermined value. The steering angle limiting torque Tr for limiting the auxiliary steering torque when the value exceeds the value.
Is calculated. The torque signal values Ta and Tr are input to an adder 18 provided in the control unit 14, but the steering angle limiting torque Tr is switched by the switching means 1.
9 to the adder 18. The switching means 19 is provided with a tire chain attachment discriminator 15.
The switching operation is performed by the discrimination signal Cr from the controller 18 so that the steering angle limiting torque Tr is input to the adder 18 when the tire chain is mounted.

Further, in the control unit 14, target current setting means 20 for calculating a target drive current of the electric motor 9 based on the output signal of the adder 18, and the target current setting means 20 calculates the target drive current. Output current control means 2 for inputting target current It and for controlling driving of electric motor 9
1 is provided. The output current control means 21 receives a feedback current signal from a drive circuit 22 provided to output a drive current to the electric motor 9 outside the control unit 14. In this manner, the auxiliary steering torque is generated by the electric motor 19, and the steering can be performed with a small steering force.

The steering angle limiting torque setting means 16 according to the present invention obtains the steering angle limiting torque Tr in accordance with the steering angle θH as described above. The control thereof will be described below with reference to the flowchart of FIG. . In FIG. 3, in a first step ST1, a steering angle signal θH is read, and a next second step ST1 is executed.
In step ST2, a steering angle limiting torque corresponding to the steering angle θH read in the first step ST1 is obtained from the table shown in FIG.

FIG. 4 is a table showing a signal output state of the steering angle limiting torque Tr with respect to the steering angle θH. As shown in FIG. 4, the steering angle is 0 to a predetermined limited steering angle θc (for example, right rotation). The steering angle limit torque Tr is 0 during the period when the left side is negative and -θc is negative when the left side is negative. When the steering angle exceeds the limit steering angle θc, the steering angle limit torque Tr becomes a predetermined limit value. Tc. The limited steering angle θc is the maximum steering angle when a space for the tire chain mounted on the front wheels 6 is secured between the inner surface of the tire house and the front wheels 6. Therefore, the maximum steering angle θmax during normal running without the tire chain attached
Is larger than the limited steering angle θc.

Then, in a third step ST3, the steering angle limiting torque Tr obtained from FIG. 4 in the second step ST2 is output. The steering angle limiting torque Tr is not output to the adder 18 when the switching unit 19 is off. Therefore, when the switching means 19 is off (corresponding to normal traveling), the maximum turning angle is mechanically defined.

On the other hand, when the switching means 19 is on, the steering angle limiting torque Tr is output to the adder 18 via the switching means 19. In this case, when the steering angle becomes equal to or larger than the limit steering angle θc (−θc), the limit value Tc is output as described above, and a signal value obtained by subtracting the limit value Tc is input to the target current setting means 20. Therefore, by setting the limit value Tc to be large, a negative signal is input to the target current setting means 20, and a steering reaction force is generated by the electric motor 19.

As a result, the front wheel 6 is moved to the limited steering angle θc (−
When θc) is reached, a large steering reaction force occurs, and it becomes impossible to further steer as in the case where it is limited by the mechanical stopper. This limited steering angle θc (−θ
By setting the value of c) so as to provide a gap between the front wheel 6 and the inner surface of the wheel house so as to avoid a bulge of the chain in a state where the chain is mounted on the front wheel 6, the steering wheel can be turned to the limit in the state where the chain is mounted. In this case, interference between the chain and the inner surface of the wheel house can be prevented.

FIG. 5 shows the change of the steering angle θT of the tire (front wheel 6) with respect to the steering angle θH according to the present invention. It is a change. As shown in the figure, the tire steering angle becomes θ1 at the maximum steering angle θmax when the mechanical stopper is used, but the maximum steering angle when the tire chain attachment is determined as described above is the maximum steering angle θmax.
Is limited by a smaller limit steering angle θc, and in this case, the tire steering angle is θ2 (<θ1).

On the other hand, when the present invention is not applied, the maximum steering angle is set so that the chain does not interfere with the inner surface of the wheel house in consideration of mounting even when the tire chain is not mounted. The maximum steering angle is θc in FIG. 5, and the tire maximum steering angle is also θ2 in FIG.

That is, in a vehicle to which the present invention is not applied, the maximum steering angle is θ2 regardless of the presence or absence of the chain.
However, according to the present invention, the same applies to the chain mounted state, but in the chain non-mounted state, it is not necessary to consider the interference between the tire chain and the inner surface of the wheel house. Therefore, the steering angle θH can be set as large as possible. Therefore, the small turning performance of the vehicle can be significantly improved.

In the present embodiment, the steering angle θH when the chain is not mounted is limited by using a mechanical stopper, but the limit value Tc is set to the maximum steering angle θmax.
At the same time, control may be performed such that the limit value Tc is output at the time of the predetermined steering angle θc and at the time of the maximum steering angle θmax in accordance with the signal of the tire chain attachment discriminator 15. In this case, the setting of the left and right maximum turning angles can be electrically adjusted, and the turning angle in the completion inspection can be easily adjusted.

The determination as to whether or not the chain is mounted is determined by a signal from the tire chain mounting determiner 15. The tire chain mounted determiner 15 may be, for example, a manual changeover switch. The driver may switch the switch on / off in accordance with the wearing / non-wearing of the vehicle. Further, for example, a vehicle body vertical movement detection G sensor may be used to detect a specific vehicle body vibration frequency when traveling with the tire chain mounted, and automatically determine whether or not the tire chain is mounted.

[0023]

As described above, according to the present invention, a non-slip attachment discriminating signal for discriminating whether or not a tire chain is attached is input to the motor control means of the conventional electric power steering apparatus, and the discrimination signal is provided. The maximum steering angle is limited by increasing the reaction force of the electric motor when the steering angle reaches an arbitrary (set according to vehicle type) when the tire chain is mounted by setting the steering angle limiting torque based on the It is possible to increase the maximum steering angle of the steered wheels as much as possible during normal driving without a tire chain and to increase the maximum turning angle of the steered wheels as much as possible in layout to improve the small turning performance of the vehicle during normal driving. be able to. In addition, the maximum steering angle when the tire chain is not mounted may be limited by using a mechanical means such as a stopper.In this case, the reaction force of the electric power steering device by the electric motor of the electric power steering device is only used when the tire chain is mounted. Since it is sufficient to limit the maximum steering angle by increasing it, the apparatus can be simplified and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a steering device for a steered wheel of a vehicle to which the present invention is applied.

FIG. 2 is a circuit block diagram showing a steering reaction force generation control unit based on the present invention.

FIG. 3 is a control flow diagram based on the present invention.

FIG. 4 is a diagram showing a control table of a steering angle limiting torque with respect to a steering angle.

FIG. 5 is a diagram showing a change in a tire steering angle with respect to a steering angle.

[Explanation of symbols]

 Reference Signs List 1 steering wheel 2 steering shaft 3 connecting shaft 4 pinion 5 tie rod 6 front wheel 7 knuckle arm 8 rack shaft 9 electric motor 11 steering torque sensor 12 steering angle sensor 13 vehicle speed sensor 14 control unit 15 tire chain mounted discriminator 16 steering angle limiting torque setting means 17 Auxiliary steering torque setting means 18 Adder 19 Switching means 20 Target current setting means 21 Output current control means 22 Drive circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B62D 13:00

Claims (2)

[Claims] 1. An electric power steering apparatus in which an assisting force for driving a steered wheel according to a steering wheel steering torque is generated by an electric motor, wherein a non-slip means such as a tire chain is mounted on the steered wheel. Chain mounting determining means for determining, and when the mounting state of the anti-slip means is determined by the chain mounting determining means, when the steering angle reaches a limit steering angle smaller than the maximum steering angle in the non-mounting state of the anti-slip means, more. An electric power steering device comprising: a steering reaction force generation control unit for generating a large steering reaction force by the electric motor for limiting the turning of the vehicle. 2. The motor according to claim 2, wherein said steering reaction force generation control means generates a large steering reaction force for limiting further turning when the maximum steering angle is reached in a state in which said non-slip means is not mounted. The electric power steering device according to claim 1, wherein: