JPH054273B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle that steers the rear wheels in response to the steering of the front wheels. More specifically, the present invention relates to a four-wheel steering device in which a rear wheel steering mechanism is configured to steer the rear wheels with assistance from an assist force of a fluid actuator such as a power steering device.

(Prior art) Conventionally, four-wheeled vehicles were typically steered by turning only the front wheels using a steering wheel.
Problems have been pointed out in terms of maneuverability and steering, such as steering only the front wheels, which may cause sideslip in the rear wheels depending on the driving situation, or limit the turning radius, making it impossible to make small turns. In view of this, four-wheel steering devices that steer both the front wheels and the rear wheels have recently been proposed and researched.

As one such four-wheel steering device,
-There is one disclosed in Publication No. 128052. The four-wheel steering device disclosed in the publication is a four-wheel steering system for a vehicle that includes a steering device that steers front wheels, a rear wheel steering mechanism that steers rear wheels, and a controller that controls the rear wheel steering mechanism. The rear wheel steering mechanism includes a steering gear mechanism connected to a rear wheel tie rod, a power cylinder that provides a steering assist force to the rear wheel tie rod, and a steering gear mechanism that provides a steering assist force to the rear wheel tie rod. a control valve that controls the supply of pressure oil;
and a motor that drives an input shaft of the steering gear mechanism, and the controller receives at least a signal from a front wheel steering angle sensor and controls the motor to steer the rear wheels according to the front wheel steering angle. It is configured to do so.

However, in this way, the rear wheel steering mechanism is provided with a motor that changes the steering state of the rear wheels (in the above conventional example, a motor that drives the input shaft of the rear wheel steering mechanism), and the motor is used to change the steering state of the rear wheels. Assist force of the fluid actuator when changing the steering state (steering assist force of the power cylinder in the conventional example above)
4 configured to steer the rear wheels with assistance from
In a wheel steering system, if an attempt is made to operate the motor to change the steering condition of the rear wheels, such as the steering angle, when the fluid actuator is not operating, the fluid actuator cannot provide a steering assist force. Therefore, the steering angle is changed only by the motor, and as a result, the motor is overloaded, and in the case of a DC motor or stepping motor, which is normally used as a control means, the rear wheel cannot be controlled due to motor lock (DC motor (in the case of a stepping motor) or malfunction due to step-out (in the case of a stepping motor).

(Object of the Invention) In view of the above-mentioned circumstances, the object of the present invention is to solve the above-mentioned inconveniences caused by the motor operating when the fluid actuator is inoperative and attempting to change the steering state of the rear wheels, that is, motor lock and disengagement. An object of the present invention is to provide a four-wheel steering device that can prevent inconveniences caused by overloading a motor such as a steering wheel.

(Structure of the Invention) In order to achieve the above object, a four-wheel steering device for a vehicle according to the present invention is a four-wheel steering device for a vehicle configured to steer rear wheels in accordance with front wheel steering, and includes: The rear wheel steering mechanism that steers the rear wheels includes a motor whose output side is mechanically connected to the rear wheel steering member to vary the steering state of the rear wheels, and a rear wheel steering mechanism that receives fluid emitted from a fluid pump. A fluid actuator that applies a steering assist force to the wheel steering member, and a connecting member that connects the output side of the motor and the rear wheel steering member, and is provided on a connecting member that supplies and discharges fluid from the fluid pump to the fluid actuator. a control valve for controlling the fluid pump; and an operation detection means for detecting the operation of the fluid pump, and receiving an output from the operation detection means to enable the motor to operate only when the fluid pump is in the operation state. It is characterized in that it is provided with a setting means for holding.

(Examples) Hereinafter, the present invention will be described in detail with reference to examples shown in the drawings.

FIG. 1 is a schematic plan view showing an embodiment of the present invention. This embodiment applies the present invention to a four-wheel steering system in which there is no mechanical connection between the front wheel steering device and the rear wheel steering mechanism, and the rear wheel steering mechanism is directly driven by a motor. The steering device 2 that steers the left and right front wheels 1, 1 includes a steering wheel 3, a rack and pinion mechanism 4 that converts the rotational motion of the wheel 3 into linear reciprocating motion, and the operation of this mechanism 4. front wheel 1,
The steering wheel is comprised of left and right tie rods 5, 5 and knuckle arms 6, 6, which transmit signals to the steering wheel and steer the wheels.

On the other hand, the rear wheel steering mechanism 8 that steers the left and right rear wheels 7, 7 includes a rear wheel operating rod 9 held slidably in the left and right directions on the vehicle body, and tie rods 10 at both left and right ends of the rod 9, respectively. The rear wheels 7 have left and right knuckle arms 11, 11 connected through a shaft 10, and the rear wheels 7, 7 are steered by the movement of the operating rod 9 in the axial direction.

A rack 12 is formed on the operating rod 9, and a pinion 13 meshing with the rack 12 is moved by a stepping motor 14 to a pair of bevel gears 15, 1.
6 and pinion shaft 17, the rotational direction of the stepping motor 14,
The rear wheels 7, 7 are steered in accordance with the amount of rotation.

Further, the rear wheel operating rod 9 passes through the power cylinder 18, and a piston 19 that partitions the inside of the cylinder 18 into left and right hydraulic chambers 18a, 18b is fixed to the operating rod 9.
Hydraulic pressure passages 21a and 21b led from a control valve 20 provided around the pinion shaft 17 are connected to a and 18b, respectively, and a hydraulic pressure supply passage 24 is connected between the control valve 20 and the pump 23. and a turn passage 25 are provided. Here, the control valve 20
is operated in response to the rotational force applied to the pinion shaft 17 when the stepping motor 14 rotates, and the pump 2
3 through the hydraulic pressure supply passage 24 is introduced into either one of the hydraulic chambers 18a or 18b of the power cylinder 18 depending on the direction of the rotational force, and the hydraulic oil in the other hydraulic chamber 18b or 18a is It acts to return to the pump 23 via the return passage 25. Therefore, the stepping motor 14 operates the bevel gears 15, 16 and the pinion shaft 1.
7. When the operating rod 9 is moved in the axial direction via the pinion 13 and the rack 12, the hydraulic pressure introduced into the power cylinder 18 is applied to the piston 19.
The movement of the operating rod 9 is assisted through.

That is, in the above embodiment, the rear wheel steering mechanism 8
On the output side, bevel gears 15, 16 and pinion shaft 17
A stepping motor 14 is provided which is mechanically connected to the rear wheel steering rod (rear wheel steering member) 9 by a connecting member consisting of a pinion 13 and a pinion 13, and which changes the steering state of the rear wheels 7. In this case, the pinion shaft 1 is assisted by the assisting force of a power cylinder (fluid actuator) 18 that operates in response to supply of oil (fluid) emitted from a hydraulic pump (fluid pump) 23, and is a part of the above-mentioned connecting member.
The control valve 20 for controlling supply and discharge of oil from the hydraulic pump 23 to the power cylinder 18 is disposed on the hydraulic pump 7 .

The stepping motor 14 is driven by a controller 31 via a stepping motor drive circuit 30.

In order to always realize the last rear wheel steering state by changing the rear wheel steering state according to the vehicle speed, the front wheel steering angle, etc., the controller 31 is provided with a characteristic switching means 32 that changes the rear wheel steering state according to the vehicle speed, the front wheel steering angle, etc., or the lateral direction. It is configured such that acceleration G, rear wheel steering angle, output from a characteristic changeover switch, etc. are input.

The present invention further includes an operation detecting means 33 for detecting the operation of the fluid pump 23, and an operation detecting means 33 for receiving the output of the means 33 to maintain the motor 14 in an operable state only when the fluid pump 23 is in an operating state. Setting means 34 are provided to prevent motor 14 from operating when motor 23 is inactive.

In the illustrated embodiment, since a hydraulic pump that generates oil pressure using engine rotation is used as the fluid pump 23, the fluid pump operation detection means 33 detects the engine rotation speed based on the ignition pulse 33a. It is constituted by an engine rotation speed calculating section 33b that calculates, and the setting means 34
is constituted by a bidirectional buffer provided on the line connecting the controller 31 and the stepping motor drive circuit 30, and when the engine rotation speed is below a predetermined rotation speed, the fluid pump generates no or sufficient assist force. When the motor 14 is not operating at a certain level, it is determined that the fluid pump is not operating, and the motor 14 is prevented from operating using a bidirectional buffer. The buffer is configured to maintain the motor 14 in an operable state.

The fluid pump operation detection means 33 may be any device as long as it can detect whether or not the fluid pump is in a state where it can generate the necessary assist force.
For example, in a case where the fluid pump is driven by a dedicated pump drive motor instead of using engine rotation, the pump operation can be detected based on the pump discharge pressure. Furthermore, the setting means 34 also includes the pump operation detection means 33.
It is sufficient that the motor 14 can be maintained in an operable state only when the pump is in an operating state in response to the output of the pump, and it may be constructed of a motor other than the one in the embodiment.

Next, the operation of the controller 31 in the above embodiment will be explained with reference to the main routine shown in FIG. First, start at step S1, initialize the system at step S2, read the vehicle speed (V) and front wheel steering angle (θ _F ) at step S3, and determine whether the vehicle speed V is zero at step S4. If it is zero, the rear wheel actuator (stepping motor 14) is initialized in step S5, and the target position P _T is set to P _T ←0 and the rear wheel actuator position P _M is set to P _M ← in step S6. Set to 0. Here, P _M means the actual position of the stepping motor, and in this embodiment, the position at which the initial setting is made when the vehicle speed V = 0 is 0 (P _M ← 0), and the other positions are from this 0 position. It is expressed as the number of steps driven. Furthermore, P _T is the control target position of the stepping motor that is controlled by the controller 31, and similarly, when the vehicle speed V=0 and the initial setting is performed, the target position is set to 0.
(P _T ←0), and other target positions are expressed by the number of steps from this 0 position. From step S6, the process returns to step S3. If vehicle speed V≠0 in step S4, step S7
Then, the data table address is calculated from the vehicle speed V and the front wheel turning angle θ _F , and the data table address is calculated from the next step S8.
Then, the aforementioned target position P _T is set to the ROM data M (ADR) at this address, the system register is reset at step S9, and the process returns to step S3.

In this main routine, in order to match the actual position P _M of the stepping motor 14 with the target position P _T set in step S8, an interrupt process is performed by the motor drive section interrupt subroutine shown in FIG. 5. This interrupt processing is performed every t=1/f (PPS) (f=stepping motor drive frequency) seconds. That is, when interrupt processing is started in the motor drive section in step S10, the above-mentioned target position P _T and actual position P _M of the stepping motor are determined in step S11.
A determination is made as to whether or not P _T
If = _PM , there is no need to drive the stepping motor, so the process proceeds to step S16, where the next interrupt generation timer is set, and the process returns to the aforementioned main routine in step S17. If P _T ≠ P _M , then step
In S12, the engine speed (N) is read, and it is determined whether N is larger than the set value (the predetermined speed that is the criterion for determining whether the fluid pump is in operation or not), and N > set value. At this time, the fluid pump 23 is in the operating state, so in step S14 a drive signal is output in the direction such that P _T = P _M to drive and control the stepping motor, and in step S15 the stepping motor is activated by the above drive signal. After being rotated forward or backward by the number of steps, the process returns to the main routine at step S17 through step S16. If N≦set value in step S13, the fluid pump 23 is inactive, so the stepping motor is not controlled and the step immediately returns to step S13.
After proceeding to S16, the process returns to the main routine in step S17.

4 and 5 above are flowcharts when the motor 14 to be controlled by the controller 31 as described above is a stepping motor, but the flowchart when the motor 14 is a DC motor is shown below. It is shown in Figure 6. To explain this diagram, first, start at step S18, initialize the system at step S19, read the vehicle speed (V) and front wheel steering angle (θ _F ) at step S20,
In step S21, the target position (DC motor control target position) is determined from the vehicle speed V and the front wheel steering angle θ _F.
P _T is calculated, the motor position (actual position of the DC motor) P _M is read from the rear wheel steering angle sensor (included in the characteristic switching means 32) in step S22, and P _T and P _M are calculated in step S23. It is determined whether or not they match, and if they match, there is no need to drive and control the DC motor, and the process returns to step S20. If they do not match, the engine speed (N) is read in step S24, and in step S25, it is determined whether N is greater than the set value in the same manner as in step S13 described above. In the next step S26
Drive control the DC motor so that P _T = P _M , and N
If ≦set value, the process returns to step S20 without performing motor drive control.

Next, the front wheel steering device and the rear wheel steering mechanism are mechanically connected, and the steering ratio (ratio of the rear wheel steering angle to the front wheel steering angle), which is one aspect of the rear wheel steering state, is adjusted at least according to the vehicle speed. An embodiment in which the present invention is applied to a four-wheel steering system equipped with a control means for changing the steering angle will be described.

FIG. 2 is a conceptual plan view showing the embodiment, and FIG. 3 is an enlarged plan view of the variable steering ratio mechanism portion in FIG. 2.

In FIG. 2, the same parts as those in FIG. 1 are given the same reference numbers, and the explanation thereof will be omitted, and only the parts that are different from the embodiment of FIG. 1 will be explained below.

A pinion 4b that transmits the amount of movement of the rack 4a to the rear wheel steering mechanism 8 is engaged with the rack 4a of the rack and pinion mechanism 4 of the front wheel steering device 2. This pinion 4b is connected to a bevel gear 41 via a connecting rod 40, and the bevel gear 41 is integrated with a rotating shaft 42a (see FIG. 3) that rotates an oscillator 43 that swings a rear wheel drive rod 44. It meshes with a bevel gear 42 which is fixed to the ground. Rotation axis 42
is a rocking shaft 43 that is integrally fixed with a rocker 43.
It has a cylindrical portion 42b that protrudes in the radial direction and is slidably fitted in the axial direction with the cylindrical portion 42b, and is rotatably supported by a bearing 42c.

The rear wheel drive rod 44 is inserted into the through hole 43 of the rocker 43.
b, one end 44a is pivotally supported by a ball joint to the drive rod 20a of the control valve 20, and the other end 44b is connected to the tip 45a of a swinging arm 45 for controlling the steering ratio by a ball joint or the like. Pivotally supported by a joint. The drive rod 20a of the control valve 20 is movable in the axial direction, and the swing arm 45 is integrally supported by a support arm with a swing shaft 46 so as to be swingable.

This support arm 47 is integrally fixed to a shaft 47a and is rotatable together with this shaft 47a. This shaft 47a is integrated with the shaft of a worm wheel 49 rotated by a worm 48 rotated by the stepping motor 14, and is rotated by the stepping motor 14 to change the steering ratio. A steering ratio sensor 50 is disposed on the worm wheel 49 to detect the rotation angle of the shaft 47a, that is, the support arm 47, and input a steering ratio signal to the controller 31.

In the configurations shown in FIGS. 2 and 3 above, when the stepping motor 14 is driven by the controller 31 via the drive circuit 30 and the worm 48 is rotated, the worm wheel 49 is rotated and the shaft 4 is rotated.
7a is rotated, the support arm 47 is rotated, the rotation axis of the swing shaft 46 is tilted, and the swing locus (swing plane) of the swing arm 45 is changed. On the other hand, front wheel 1,
1 is steered, the pinion 4b that moves the front wheel rack 4a in the left-right direction rotates, and the bevel gear 41 rotates via the connecting rod 40.

As a result, the other bevel gear 42 rotates, and the rotation shaft 42a causes the rocker 43 to rock. Then,
The rear wheel drive rod 44 passing through this
It swings around 4a as an axis. At this time, the other end 44b
moves while being restrained by the swing surface of the swing arm 45, so that the one end 44a moves the drive rod 20a of the control valve 20 in the axial direction.

As a result, either one of the hydraulic chambers 1 of the power cylinder 18 that operates the rear wheel operating rod 9 left or right
Oil pressure is introduced into 8a or 18b, and the rear wheels are steered by the oil pressure. At this time, the amount of steering is determined by the inclination of the swing shaft 46, that is, the rotation angle of the worm wheel 49, and the amount of steering of the front wheels. The rudder ratio will be determined.

The drive circuit 30 and controller 3 for the motor (in this embodiment, a stepping motor that changes the steering ratio) that changes the rear wheel steering state
1. The characteristic switching means 32, the fluid pump operation detection means 33, and the setting means 34 are the same as those in the embodiment shown in FIG. Further, in the figure, the steering ratio sensor 50 is shown separately from the characteristic switching means 32, and its output is inputted to the controller 31, but this is because the control means 14 of this embodiment changes the steering ratio. This steering ratio sensor 50 is included in the characteristic switching means 32.

In this embodiment as well, the stepping motor 14 is driven to change the steering ratio, except when the swing arm 45 is in the horizontal plane.
7 around its axis 47a, the position of one end 44a of the rear wheel drive rod changes, resulting in a state in which the rear wheels are steered, and therefore the fluid actuator 18
When the stepping motor 14 is not operating
If the motor 14 is driven, an overload may be applied to the motor 14.

The flow of the control 31 in this embodiment is almost the same as in FIGS. 4 and 5 described above, however, in this embodiment, the front wheel steering angle is controlled by the rear wheel steering mechanism via a mechanical connection rod 40. Since there is no need to refer to the front wheel steering angle θ _F when setting the target position P _T of the stepping motor 14 that changes the steering ratio, step S3 in FIG. Vehicle speed (V)READ”
Step S7 is "Data table address calculation".
It simply becomes "ADR=f(V)".

Furthermore, in this embodiment as well, a DC motor can be used instead of the stepping motor as described above, and the flow in the case of a DC motor is almost the same as the flow shown in FIG. 6 described above. The difference is that for the same reason as above, step S20 is "vehicle speed (V) READ" and step S21 is "P _T = f(V)".
It is just a calculation.

In addition, in a four-wheel steering device of the type in which the front wheel steering device 2 and the rear wheel steering mechanism 8 are connected by a mechanical connection rod 40 as in this embodiment,
If a fluid actuator is provided to assist front wheel steering, part of its steering assist force also assists rear wheel steering via the connecting rod 40. Therefore, in the case of this type of four-wheel steering device, the fluid actuator for assisting rear wheel steering according to the present invention may be a front wheel steering fluid actuator in addition to the rear wheel steering fluid actuator.

(Effects of the Invention) As described above, the four-wheel steering device according to the present invention includes an operation detection means for detecting the operation of a fluid pump that is a drive source of a fluid actuator that assists rear wheel steering. A motor that changes the steering state of the rear wheels based on the output only when the fluid pump is in an operating state is maintained in an operable state, and when the fluid pump is in an inactive state, operation of the control means is prohibited. It is configured as follows,
To prevent inconveniences caused by an attempt to change the steered state of the rear wheels by operating the motor when the fluid actuator is not operating, that is, inconveniences caused by overloading the motor such as motor lock or step-out. It has the effect of being able to

[Brief explanation of the drawing]

Fig. 1 is a conceptual plan view showing one embodiment of the device according to the present invention, Fig. 2 is a plan view showing another embodiment, and Fig. 3 is an enlarged plan view of the variable steering ratio mechanism portion in Fig. 2. 4 is a flowchart showing the main routine of the controller in FIG. 1, FIG. 5 is a flowchart showing the motor drive unit interrupt processing subroutine, and FIG. 6 is a flowchart showing the control means of the embodiment shown in FIG. 12 is a flowchart showing the main routine of the controller when the controller is a motor. DESCRIPTION OF SYMBOLS 1... Front wheel, 7... Rear wheel, 8... Rear wheel steering mechanism, 14... Motor, 18... Rear wheel actuator, 23... Fluid pump, 33... Fluid pump operation detection means, 34... Set means.

Claims (1)

[Scope of Claims] 1. A four-wheel steering device for a vehicle configured to steer rear wheels in response to front wheel steering, wherein a rear wheel steering mechanism for steering the rear wheels has an output side that steers rear wheels. a motor that is mechanically connected to the member to vary the steering state of the rear wheels; a fluid actuator that receives fluid emitted from a fluid pump and applies a steering assist force to the rear wheel steering member; a control valve provided on a connecting member connecting between the output side and the rear wheel steering member to control supply and discharge of fluid from the fluid pump to the fluid actuator; A vehicle characterized in that it is provided with an operation detecting means for detecting the motor, and a setting means for receiving the output of the operation detecting means and maintaining the motor in an operable state only when the fluid pump is in an operating state. 4-wheel steering device.