JP3579489B2 - Power steering device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a power steering device that generates a steering assist force using pressure oil from a pump driven by an electric actuator.
[0002]
[Prior art]
In a power steering apparatus including a steering member that steers wheels by moving in an axial direction by steering, a pump driven by an electric actuator, and a hydraulic actuator that generates a steering assist force by pressure oil from the pump, Attempting to keep the pump at a speed necessary for assisting steering always wastes energy of a battery serving as a power source of the electric actuator.
[0003]
Accordingly, energy saving is improved by increasing the speed of the pump to the steering assist speed by the electric actuator only at the time of steering, and performing control to reduce the speed to the standby speed at the time of going straight, that is, at the middle point of the steering angle ( JP-A-56-99859 and JP-A-3-132474).
[0004]
That is, the steering angle is detected from a pulse signal corresponding to the rotation angle of the steering wheel using an absolute type rotary encoder or the like, and it is determined whether or not steering is being performed based on the steering angle from the steering middle point.
[0005]
Since the steering angle detected by the pulse signal sent from such an absolute type rotary encoder is relative and not absolute with reference to the steering angle midpoint, the determination of the steering angle midpoint must be performed. I needed to do it. For example, utilizing the fact that the steering torque decreases at the steering angle midpoint, a torque sensor for detecting the steering torque is provided, and the time when the steering torque becomes smaller than the set value is determined as the steering angle midpoint (see Japanese Patent Laid-Open No. U.S. Pat. No. 5,972,086), utilizing the fact that the statistical distribution of the frequency of the detected pulse signal becomes a normal distribution that is maximized at the steering angle midpoint, and based on the statistical distribution of the frequency of the pulse signal. It has been proposed to determine the steering angle midpoint (see Japanese Patent Publication No. 6-43188).
[0006]
[Problems to be solved by the invention]
However, it is not possible to determine whether steering is being performed until the midpoint of the steering angle is determined, and therefore, it is necessary to maintain the pump at the steering assist speed by the electric actuator. Therefore, when the vehicle is stopped and the idling state is continued before the determination, there is a problem that wasteful energy is consumed. Further, if a torque sensor is used to determine the steering angle midpoint, there is a problem that the structure becomes complicated and the size becomes large.
[0007]
Also, in the case where the steering wheel is rotated to the lock position for stationary installation or the like, the steering wheel is held in the lock position, so that there is no need to assist the steering. To maintain the steering assist speed. Therefore, there is a problem that wasteful energy is consumed, seizure of the electric actuator occurs, and the flow noise of the pressure oil increases.
[0008]
An object of the present invention is to provide a power steering device that can solve the above problems.
[0009]
[Means for Solving the Problems]
The present invention provides a steering member that steers wheels by moving axially by steering, a hydraulic actuator that generates a steering assist force by pressure oil from a pump driven by an electric actuator, and that the pump is steered by an electric actuator. Means for increasing the speed to the steering assist speed when the assist condition is satisfied and decelerating to the standby speed when the steering assist release condition is satisfied, and detects the amount of axial movement of the steering member from the steering angle midpoint. Means for determining whether or not the steering assist condition is satisfied according to the axial movement amount of the steering member from the midpoint of the steering angle.
[0010]
It has at least two steering assist release conditions, one steering assist release condition is set so that the pump can be decelerated to the standby speed by the electric actuator during straight traveling, and the other steering assist release condition is that the steering member is It is preferable that the pump is set so that the pump can be decelerated to the standby speed by the electric actuator when located at the moving end.
[0011]
Function and Effect of the Invention
According to the configuration of the present invention, since the wheels are steered by the axial movement of the steering member due to the steering, the steering is performed by detecting the axial movement amount from the steering angle midpoint of the steering member. Can be determined. Thus, the electric actuator increases the speed of the pump to the steering assist speed only during steering, and reduces the speed to the standby speed during straight traveling, thereby improving energy saving.
[0012]
The detection of the axial movement amount from the steering angle midpoint of the steering member is performed, for example, using an incremental linear encoder having a grid scale and a sensor, attaching the grid scale to the steering member side, and attaching the sensor to the fixed side, This can be performed by reading the scale of the scale with a sensor using the midpoint of the steering angle as a reference point in advance. That is, when the steering angle is detected from the rotation angle of the steering wheel as in the related art, since the rotation angle range of the steering wheel exceeds 360 degrees, a detection means such as an incremental encoder that can set a reference point in advance should be used. Can not. On the other hand, in the present invention, by detecting the axial movement amount of the steering member, an incremental encoder or the like capable of setting a reference point in advance can be used, so that it is not necessary to determine the steering angle midpoint. Thus, the pump does not need to be maintained at the steering assist speed by the electric actuator until the midpoint of the steering angle is determined, and the energy saving can be improved. Moreover, a torque sensor for determining the steering angle midpoint is not required, and the structure does not become complicated or large.
[0013]
Also, when the steering member is located at the moving end, that is, when the steering wheel is rotated to the lock position, the pump is decelerated to the standby speed by the electric actuator, so that the steering wheel is rotated to the lock position. In such a case, energy saving can be improved, seizure of the electric actuator can be prevented, and the flow noise of the pressure oil can be reduced.
[0014]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
The rack and pinion type power steering device 1 shown in FIGS. 1 and 2 includes an input shaft 2 connected to a steering wheel H, and an output shaft 4 connected to the input shaft 2 via a torsion bar 3. The torsion bar 3 is connected to the input shaft 2 via a pin 5 and to the output shaft 4 via a serration 6. A pinion 7 is formed on the output shaft 4, and each end of a rack (steering member) 8 that meshes with the pinion 7 projects from openings formed at both ends of the rack housing 10 b. Steering wheels (not shown) are connected to each end of the rack 8 via ball joints 19a and 19b, tie rods, and the like. The input shaft 2 is supported by a valve housing 10 a via a bearing 9, and is supported by an output shaft 4 via a bush 11. The output shaft 4 is supported by the rack housing 10b via bearings 12 and 13. Thus, the rotation of the input shaft 2 due to the steering of the handle H is transmitted to the pinion 7 via the torsion bar 3, and the rotation of the pinion 7 causes the rack 8 to move in the axial direction. The wheels are steered by the movement of the rack 8. Note that oil seals 14, 15 are provided between the input / output shafts 2, 4 and the valve housing 10a. Further, a support yoke 16 for supporting the rack 8 is provided, and the support yoke 16 is pressed against the rack 8 by the elastic force of a spring 17.
[0016]
As shown in FIG. 2, a piston 20 is attached to the rack 8 between the inner periphery of the rack housing 10 b and the outer periphery of the rack 8, thereby having a pair of oil chambers 21 and 22 partitioned by the piston 20. An auxiliary hydraulic cylinder (hydraulic actuator) 18 is configured. An annular stopper 45 is attached to the rack housing 10b outside the seal member 44 that seals the one oil chamber 21. The stopper 45 prevents one of the ball joints 19a from moving inward of the rack housing 10b. Further, a step 10c is formed on the inner periphery of the other opening of the rack housing 10b, and the other ball joint 19b abuts on the step 10c, thereby preventing the rack 8 from moving inward of the rack housing 10b. . Thus, the axial movement amount of the rack 8 is restricted to a certain range.
[0017]
The oil chambers 21 and 22 of the hydraulic cylinder 18 are connected to a rotary hydraulic control valve 23 via pipes 46a and 46b. As shown in FIGS. 1 and 3, the control valve 23 includes a cylindrical first valve member 24 and a second valve member 25 inserted into the first valve member 24 so as to be relatively rotatable. . The first valve member 24 is rotatably attached to the output shaft 4 via a pin 26. The second valve member 25 is formed integrally on the outer periphery of the input shaft 2.
[0018]
A plurality of recesses along the axial direction are formed at equal intervals in the circumferential direction on the inner periphery of the first valve member 24 and the outer periphery of the second valve member 25.
The first valve member-side recess is composed of four right steering recesses 27 located at equal intervals in the circumferential direction and four left steering recesses 28 located at equal intervals in the circumferential direction.
The second valve member-side recess is composed of four pressure oil supply recesses 29 located at equal intervals in the circumferential direction and four pressure oil discharge recesses 30 located at equal intervals in the circumferential direction.
The right steering recesses 27 and the left steering recesses 28 are alternately arranged in the circumferential direction, and the pressure oil supply recesses 29 and the pressure oil discharge recesses 30 are alternately arranged in the circumferential direction.
As shown in FIG. 1, each right steering recess 27 is provided with one oil of the hydraulic cylinder 18 via a first flow path 31 formed in the first valve member 24 and a first port 32 formed in the valve housing 10a. Each left steering recess 28 communicates with the other oil chamber 22 of the hydraulic cylinder 18 through a second flow path 33 formed in the first valve member 24 and a second port 34 formed in the valve housing 10a. Lead to.
Each pressure oil supply recess 29 communicates with a pump 37 as shown in FIG. 1 via a third flow path 35 formed in the first valve member 24 and an inlet port 36 formed in the valve housing 10a. The pump 37 is driven by a motor (electric actuator) 50, and can be configured by, for example, a vane pump that discharges pressure oil at a flow rate according to the rotation speed. An in-vehicle battery is used as a power supply for driving the motor 50.
Each pressure oil discharge recess 30 is formed in the first discharge passage 38 formed in the second valve member 25, the passage 47 between the input shaft 2 and the inner and outer circumferences of the torsion bar 3, and the input shaft 2 shown in FIG. It communicates with the tank 41 via a second discharge path 39 and a discharge port 40 formed in the valve housing 10a.
Thus, the pump 37, the tank 41, and the oil chambers 21 and 22 of the hydraulic cylinder 18 communicate with each other through the inter-valve flow path 42 between the inner and outer circumferences of the first valve member 24 and the second valve member 25.
Between the first valve member side concave portion and the second valve member side concave portion in the inter-valve flow path 42, there are formed throttle portions A, B, C, D whose opening degree changes due to relative rotation of the two valve members 24, 25. The hydraulic pressure acting on the hydraulic cylinder 18 is controlled by the change in the degree of opening of the throttle portions A, B, C, and D.
[0019]
FIG. 3 shows the relative positions of the two valve members 24 and 25 at the steering angle midpoint where steering is not performed. In this state, each pressure oil supply recess 29 and each pressure oil discharge recess 30 Are communicated through all the throttle portions A, B, C, and D, the pressure oil supplied from the pump 37 is directly returned to the tank 41, and no steering assist force is generated. Therefore, the pump 37 is necessary for assisting steering. It is not necessary to drive at the steering assist speed.
[0020]
When the steering is performed rightward from the steering angle midpoint, the torsion bar 3 is twisted in accordance with the steering torque, and the two valve members 24 and 25 rotate relatively. As a result, the opening degree of the throttle portion A between each right steering recess 27 and each pressure oil supply recess 29 and the throttle portion B between each left steering recess 28 and each pressure oil discharge recess 30 are determined. The opening degree increases, and the opening degree of the throttle portion C between each left steering recess 28 and each pressure oil supply recess 29 and the throttle between each right steering recess 27 and each pressure oil discharge recess 30. The opening degree of the portion D becomes small. As a result, pressure oil is supplied from the pump 37 to one oil chamber 21 of the hydraulic cylinder 18, and the pressure oil is returned from the other oil chamber 22 of the hydraulic cylinder 18 to the tank 41, and the steering assist force to the right of the vehicle is provided. Acts on the rack 8.
[0021]
When the steering is steered to the left from the steering angle midpoint, the opening of each of the throttle portions A, B, C, and D changes in reverse to the case where the steering is steered to the right. Act on.
[0022]
As shown in FIG. 2, a moving distance detecting device 51 for detecting an axial moving amount of the rack 8 from the midpoint of the steering angle is provided. The moving distance detecting device 51 is, for example, a known incremental type linear encoder having a lattice scale 51a and a sensor 51b for transmitting a reading pulse of a scale of the scale 51a. The scale 51a is attached to the rack 8 so as to move together, and the sensor 51b is attached to a fixed side such as the rack housing 10b or the vehicle body. The sensor 51b is arranged on the scale 51a so as to read a reference scale formed on the scale 51a at the middle point of the steering angle and transmit a reference pulse. As shown in FIG. 1, the sensor 51a is connected to a control device 52 constituted by a computer.
[0023]
The vehicle speed sensor 53 and the pump driving motor 50 are connected to the control device 52. The control device 52 stores a control program for the motor 50. As one part of the control program, one steering assist condition and two steering assist cancel conditions are stored. The control device 52 sends a steering assist signal to the motor 50 via a power amplifier (not shown) when the steering assist condition is satisfied, thereby driving the motor 50 with a control voltage corresponding to the steering assist signal, and From the standby speed to the steering assist speed. Further, the control device 52 decelerates the pump 37 to the standby speed by canceling the steering assist signal sent to the motor 50 when each of the steering assist canceling conditions is satisfied.
[0024]
The steering assist condition is satisfied when the amount of axial movement of the rack 8 from the midpoint of the steering angle exceeds zero.
[0025]
The first steering assist release condition is satisfied when the axial movement amount of the rack 8 is zero for a set time. The set time may be empirically determined and set so as to minimize useless increase in the speed of the pump 37, and is set to, for example, 1 second.
[0026]
The second steering assist release condition is set such that the pump 37 can be decelerated to the standby speed by the motor 50 when the rack 8 is located at the moving end. In the present embodiment, the second steering assist release condition is satisfied when the rack 8 reaches a preset position near the moving end.
[0027]
The control device 52 changes the control voltage of the motor 50 during the steering assist according to the vehicle speed detected by the vehicle speed sensor 53. That is, the steering assist speed of the pump 37 corresponding to the control voltage of the motor 50 at the time of steering assist decreases in proportion to the vehicle speed as shown by a solid line K in FIG. 4, and is set to a maximum value Nmax when the vehicle speed is zero. Above the set vehicle speed Va, the minimum value Nmin is set. As a result, the steering assist speed of the pump 37 is changed according to the vehicle speed. At low vehicle speeds, the steering assist force is increased to improve the turning performance of the vehicle, and at high speeds, the steering assist force is decreased to improve the running stability of the vehicle. are doing. Further, the control device 52 drives the motor 50 so that the standby speed becomes the minimum value Nmin at the time of assisting the steering as indicated by the one-dot chain line L. Accordingly, the flow rate of the pressure oil sent from the pump 37 is the maximum value Qmax until the rack 8 reaches a preset position ± E near the moving end as shown by a solid line M in FIG. When the rack 8 reaches a preset position ± E in the vicinity of the moving end, the rack 8 starts decreasing, and at the moving end, the minimum value Qmin is set. Further, the pressure oil flow rate during traveling at a constant vehicle speed is a value Qn corresponding to the vehicle speed until the rack 8 reaches a preset position ± E near the moving end as shown by a solid line N in FIG. When the rack 8 reaches a preset position. ± .E near the moving end, the rack 8 starts decreasing and reaches the minimum value Qmin at the moving end. At the start of the steering assist, the pressure oil flow rate gradually increases according to the amount of movement of the rack 8 from the midpoint of the steering angle, as indicated by the broken line in the figure.
[0028]
The control procedure of the pump 37 via the motor 50 will be described with reference to the flowchart of FIG.
[0029]
First, the engine is started (step 1), and the pump 37 is set to the standby speed by the motor 50 (step 2). Next, the amount of movement of the rack 8 is detected (step 3), and it is determined whether or not the rack 8 is located at the steering angle midpoint (step 4). If the rack 8 is located at the steering angle midpoint, the process returns to step 2, and if it is not located at the steering angle midpoint, it is determined whether the rack 8 has reached the vicinity of the moving end (step 5). If the rack 8 has reached near the moving end, the process returns to step 2, and if not, the motor 50 increases the pump 37 to the steering assist speed by the motor 50 (step 6). Next, the amount of movement of the rack 8 is detected (step 7), and it is determined whether the rack 8 is located at the steering angle midpoint (step 8). If the rack 8 is located at the steering angle midpoint, it is determined whether the set time has elapsed (step 9). If it is determined in step 8 that the rack 8 is not located at the middle point of the steering angle during the progress of the timing for determining whether or not the set time has elapsed, the progress of the timing is canceled, and step 8 is performed again. , The timing is newly advanced after it is determined that the timepiece is located at the steering angle midpoint. If the set time has not elapsed, the process returns to step 6. If the set time has elapsed, the process returns to step 2 and the pump 37 is reduced by the motor 50 to the standby speed. If it is determined in step 8 that the rack 8 is not located at the midpoint of the steering angle, it is determined whether the rack 8 has reached the vicinity of the moving end (step 10). If the rack 8 has not reached the vicinity of the moving end, the process returns to step 6, and if the rack 8 has reached the vicinity of the moving end, the process returns to step 2 and the motor 50 reduces the pump 37 to the standby speed.
[0030]
According to the above configuration, since the wheels are steered by the axial movement of the rack 8 due to the steering, the steering is performed by detecting the amount of axial movement of the rack 8 from the midpoint of the steering angle. Can be determined. Thus, the speed of the pump 37 is increased to the steering assist speed only when the motor 50 is being steered by the motor 50, and the speed is reduced to the standby speed when the vehicle is traveling straight, thereby improving energy saving. Since the incremental distance encoder 51 that can set a reference point in advance can be used as the moving distance detecting device 51 that detects the axial movement amount of the rack 8 from the steering angle midpoint, it is necessary to determine the steering angle midpoint. And the pump 37 does not need to be maintained at the steering assist speed by the motor 50 until the steering angle midpoint is determined, so that energy saving can be improved. Moreover, a torque sensor for determining the steering angle midpoint is not required, and the structure does not become complicated or large. Further, when the rack 8 is located at the moving end, that is, when the steering wheel H is rotated to the lock position, the pump 37 can be decelerated to the standby speed by the motor 50, and the steering wheel H is rotated to the lock position. When cutting is performed, energy saving can be improved, seizure of the motor 50 can be prevented, and the flow noise of the pressure oil in the control valve 23 can be reduced.
[0031]
The present invention is not limited to the above embodiment. For example, the moving distance detection device 51 is not limited to the incremental type linear encoder, and converts an electric signal corresponding to the axial movement amount of the rack 8 obtained via a potentiometer into a digital signal by an A / D converter. In this case, the reference value of the electric signal corresponding to the steering angle midpoint is stored in the control device 52 at the time of assembling the power steering device. Without making a determination, the axial movement amount of the rack 8 from the steering angle midpoint can be detected according to the change from the reference value. In addition, even when the vehicle is traveling straight ahead, when the vehicle responds to unevenness of the road surface or when cornering on a gentle curve, the amount of axial movement of the rack 8 exceeds zero in order to improve energy saving without assisting steering. , The steering assist condition may be satisfied. When the steering assist condition is satisfied by the axial movement amount of the rack 8 exceeding the value exceeding zero, the first time when the axial movement amount of the rack 8 is equal to or less than the zero value for the set time, the first time. The first steering assist release condition may be satisfied. Further, the second steering assist release condition may be satisfied when the rack 8 reaches the moving end. Further, the standby speed of the pump 37 may be zero.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a hydraulic power steering device according to an embodiment of the present invention. FIG. 2 is a front view of the hydraulic power steering device according to the embodiment. FIG. 3 is a sectional view taken along line III-III of FIG. FIG. 5 is a diagram illustrating a relationship between a pump speed and a vehicle speed of the example power steering device. FIG. 5 is a diagram illustrating a relationship between a rack moving distance and a pressure oil flow rate of the power steering device according to the embodiment. Flow chart showing the control procedure of the pump of the present invention
1 Power steering device 18 Hydraulic cylinder 37 Pump 50 Pump driving motor 51 Moving distance detecting device 52 Control device 53 Vehicle speed sensor

Claims (1)

A steering member that steers wheels by moving in the axial direction by steering, a hydraulic actuator that generates a steering assist force by pressure oil from a pump driven by an electric actuator, and satisfies the steering assist condition with the electric actuator using the pump. Means for increasing the steering assist speed at the time and decelerating to the standby speed when the steering assist release condition is satisfied,
Means for detecting an axial movement amount of the steering member from a steering angle midpoint is provided,
It has at least two steering assist release conditions, one steering assist release condition is set so that the pump can be decelerated to the standby speed by the electric actuator during straight traveling, and the other steering assist release condition is that the steering member is It is set so that the pump can be decelerated to the standby speed by the electric actuator when located at the moving end,
A hydraulic power steering apparatus characterized in that it is determined whether or not a steering assist condition is satisfied according to an axial movement amount of the steering member from a steering angle midpoint.

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