JP2015145210A - Electrically-driven type power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically-driven type steering device that reduces the impact force that a collision part of a knuckle gives to a stopper when a steering wheel of a forklift rear shaft is turned to the right and left up to a maximum turning angle.SOLUTION: An electrically-driven type power steering device equipped with a rack and pinion type steering mechanism indirectly detects the turning angle of a steering wheel 10 from a parallel position by measuring the movement distance of a rack shaft 8 from a reference point where the steering wheel is at a parallel position, and gradually decreases a maximum supply voltage to a motor 15 to zero during a period in which the movement distance of the rack shaft increases from a predetermined movement distance at which the steering wheel is turned from the parallel position up to right before the maximum turning angle to a maximum movement distance at which the steering wheel is turned to the maximum turning angle.

Description

  The present invention relates to an electric power steering apparatus, and more particularly, to an electric power steering apparatus having a rack-and-pinion type steering mechanism and power assisting a pinion by a motor.

Patent Document 1 describes a conventional example in which an electric power steering device is incorporated in a forklift.
This electric power steering apparatus includes a rack and pinion type steering mechanism. The rack-and-pinion type steering mechanism has an axle frame that is attached to a horizontal central turning shaft that protrudes from the rear part of the main frame of the vehicle body and that can turn in the vertical direction.

  Knuckles that support the steered wheels are attached to the left and right sides of the axle frame, and a cylindrical housing is attached to the axle frame and extends in the longitudinal direction of the axle frame. A rack shaft is inserted into the housing and guided so as to be slidable in the axial direction.

  Both ends of the rack shaft are connected to corresponding knuckles by tie rods. In addition, a pinion that engages with a tooth portion of the rack shaft is attached to a central portion of the axle frame. The rotation shaft of the pinion is transmission-coupled to one end of the handle shaft by a coupling mechanism. A handle is fixed to the other end of the handle shaft.

When the center of the tooth portion of the rack shaft engages with the pinion, the steering wheel is in a parallel position.From this position, the rack shaft slides according to the forward / reverse rotation of the steering wheel, thereby turning the steering wheel left and right. It is supposed to be.
In addition, a collision part is provided on one of the knuckle and the axle frame, and a stopper that is paired with the collision part is provided on the other. When the steering wheel is cut to the maximum turning angle, the corresponding collision part is a stopper. It comes to contact with.

  The electric power steering device further includes means for power assisting the rack and pinion type steering mechanism. This is composed of an actuator including a motor as a drive source, which is attached to an axle frame and rotationally drives the pinion, a control unit for controlling the motor of the actuator, and a torque sensor for detecting the rotational torque of the handle. However, the supply voltage to the motor is controlled based on the detection signal of the torque sensor.

  In this way, the pinion is rotationally driven by the combined driving force of the driving force from the steering wheel and the driving force from the motor, whereby the rack shaft slides and the steered wheels are steered left and right accordingly.

  By the way, in this configuration, the position information (cutting angle) of the steered wheels remains unknown, and the assist by the motor is performed exclusively based on the detection signal of the torque sensor, so the signal intensity of the detection signal of the torque sensor is the same. If there is, the motor rotates at the same rotational speed regardless of the current position of the steered wheels.

For this reason, the steering wheel may be assisted from the position where the steered wheel is cut to the vicinity of the maximum turning angle in the direction of turning to the maximum turning angle without decreasing the rotational speed of the motor. In such a case, the collision part provided on one of the knuckle and the axle frame vigorously collides with a stopper paired with that provided on the other of the knuckle and the axle frame, thereby promoting the wear of the stopper. Also, there is a problem that the impact due to this collision is transmitted to the handle side.
In addition, when the stopper becomes extremely worn, the steering wheel turns beyond the maximum turning angle due to an external force applied to the steering wheel during traveling, and as a result, the pinion teeth end up at the end of the rack shaft teeth. Could cause damage to the pinion teeth.

  Further, in the conventional electric power steering device for a forklift, when the steered wheel is cut to the left and right to the vicinity of the maximum turning angle, the end portion of the tooth portion of the rack shaft is exposed from the housing. Therefore, after mud or water splashed by the steering wheel adheres to the end of the tooth part, it enters the housing with the sliding movement of the rack shaft, and further reaches the pinion, causing rust and damage of related members. It was the cause.

JP-A-8-216898

Therefore, the subject of this invention is reducing the impact force which the collision part of a knuckle exerts on a stopper when a steered wheel is turned to the maximum turning angle from side to side.
Another object of the present invention is to warn the driver that the steered wheel is turning beyond the maximum turning angle, for example, when the stopper is significantly worn.
Still another object of the present invention is to prevent mud, water and the like from adhering to the tooth portion of the rack shaft while the steered wheel is being steered.

  In order to solve the above-mentioned problems, the present invention provides a handle and a handle shaft provided on a vehicle body, and a horizontal central swing that extends in the width direction of the vehicle body and protrudes from a front portion or a rear portion of a main frame of the vehicle body. An axle frame attached to a shaft and capable of turning in the vertical direction; a knuckle attached to the left and right sides of the axle frame for rotatably supporting a steering wheel; and an axle frame attached to the axle frame. A cylindrical housing extending in the longitudinal direction, a rack shaft inserted through the housing and guided so as to be slidable in the axial direction, tie rods that connect both ends of the rack shaft to corresponding knuckles, and a center of the housing Attached to the housing and through the opening formed in the side wall of the housing. A pinion that engages with a tooth portion of the rack shaft, and a transmission coupling mechanism that is provided on the main frame of the vehicle body and that transmits and connects the rotation shaft of the pinion to the handle shaft. When the center of the steering wheel engages with the pinion, the steering wheel is in a parallel position, and the steering wheel is cut to the left and right by sliding movement of the rack shaft according to the forward and reverse rotation of the handle from this position, The knuckle is provided with a collision part, and the axle frame is provided with a stopper that makes a pair with the collision part, and when the steering wheel is cut to the maximum turning angle, the corresponding collision part comes into contact with the stopper. Therefore, turning beyond the maximum turning angle of the steered wheel is regulated, and further, it is attached to the axle frame. An actuator including a motor as a drive source for rotating the pinion, a control unit for controlling the motor of the actuator, and a torque sensor provided on the handle shaft, the control unit comprising: In the electric power steering apparatus that controls a supply voltage to the motor based on a detection signal of a torque sensor, the electric power steering apparatus includes a detector that detects a rotation direction and a rotation angle of the rotation shaft of the motor or the rotation shaft of the pinion, The control unit measures the movement distance of the rack shaft from the reference point to the left and right sides based on the position at which the center of the tooth portion of the rack shaft engages with the pinion based on the detection signal of the detector. The moving distance is such that the steered wheel is before the maximum turning angle from the parallel position. The maximum supply voltage to the motor is gradually reduced to zero while the steering wheel increases from the predetermined travel distance when turned to the maximum travel distance when the steered wheel is turned from the parallel position to the maximum turning angle. The electric power steering apparatus is characterized in that the electric power steering apparatus is characterized.

In the above configuration, preferably, the control unit is configured such that the maximum supply voltage to the motor is proportional to the movement distance of the rack shaft while the movement distance of the rack shaft increases from the predetermined movement distance to the maximum movement distance. Decrease.
Further preferably, the control unit issues a warning when it is determined that the movement distance of the rack shaft exceeds the maximum movement distance and reaches a second predetermined movement distance based on a detection signal of the detector. It has become.

  Further, the tooth portion of the rack shaft is set to a length such that an end of the tooth portion does not protrude outside the housing when the steering wheel is cut to the left and right maximum cutting angles. Is preferred.

  According to the present invention, the turning angle from the parallel position of the steered wheel is indirectly detected by measuring the movement distance from the reference point of the rack shaft, with the reference point when the steered wheel is in the parallel position, While the travel distance of the rack shaft increases from the predetermined travel distance when the steered wheel is cut from the parallel position to the front of the maximum turning angle, the motor travels from the predetermined travel distance when the steered wheel is turned to the maximum turning angle. The maximum supply voltage is gradually reduced to zero.

For this reason, if the motor assists when the steered wheel is cut to the maximum turning angle before the maximum turning angle, the position at which the steering wheel starts to be turned is the position of the maximum turning angle. The closer to, the lower the maximum rotation speed of the motor, and the lower the rotation speed of the motor during assist.
As a result, the impact when the collision part provided on the knuckle collides with the stopper provided on the axle frame is mitigated, thereby reducing the wear of the stopper to a minimum and reducing the impact force transmitted to the handle side. It is done.

  In addition, if the control unit is configured to issue a warning when it is determined that the rack shaft travel distance exceeds the maximum travel distance and has reached the second predetermined travel distance, the stopper may be significantly worn. By warning the driver that the steered wheel is turning beyond the maximum turning angle, the driver is encouraged to replace the stopper, etc., and the pinion due to the collision between the end of the rack shaft teeth and the pinion teeth It is possible to prevent damage to the teeth.

  Furthermore, when the tooth portion of the rack shaft is configured to have such a length that the end of the tooth portion does not protrude to the outside of the housing when the steering wheel is cut to the left and right maximum cutting angles, While the steered wheels are being steered, mud, water or the like adheres to the teeth of the rack shaft and is prevented from entering the housing.

1 is a schematic sectional side view of a forklift incorporating an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration near an axle frame when the steered wheels are in a parallel position in the electric power steering apparatus of FIG. 1, (A) is a perspective view seen from the rear of the vehicle body, and (B) is a top view. is there. FIG. 3 is a view similar to FIG. 2 showing a configuration in the vicinity of the axle frame when the steered wheel is turned to the maximum left turning angle in the electric power steering apparatus shown in FIG. 1. It is a top view which shows the positional relationship of a rack shaft and a pinion when the steering wheel of the electric power steering apparatus shown in FIG. 1 is steered, (A) is a positional relationship when a steering wheel is in a parallel position, (B) shows the positional relationship when the steering wheel is turned to the maximum turning angle to the right, and (C) shows the positional relationship when the steering wheel is turned to the maximum turning angle to the left. It is a graph which demonstrates concretely the control of the supply voltage with respect to the motor by a control unit, and the timing of warning.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic sectional side view of a forklift incorporating an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration in the vicinity of the axle frame when the steered wheels are in a parallel position in the electric power steering apparatus of FIG. 1, (A) is a perspective view seen from the rear of the vehicle body, and (B) Is a top view. FIG. 3 is a view similar to FIG. 2 showing the configuration in the vicinity of the axle frame when the steered wheel is turned to the left by the maximum turning angle in the electric power steering apparatus shown in FIG. FIG. 4 is a plan view showing the positional relationship between the rack shaft and the pinion when the steered wheels of the electric power steering apparatus shown in FIG. 1 are steered, and FIG. 4A shows the steered wheels in parallel positions. (B) shows the positional relationship when the steered wheel is turned to the maximum turning angle to the right, and (C) shows the positional relationship when the steered wheel is turned to the maximum turning angle on the left. Show.

As shown in FIGS. 1 to 3, according to the present invention, the handle 2 and the handle shaft 3 are arranged at the driver's seat of the body of the forklift, and the horizontal projecting from the rear portion of the main frame 1 of the vehicle body. An axle frame 5 extending in the width direction of the vehicle body is attached to the central turning shaft 4 so that it can turn in the vertical direction. A driving wheel 19 is attached to the front portion of the main frame 1.
In this embodiment, the axle frame 5 is attached to the rear portion of the main frame 1. However, when the electric power steering apparatus is applied to a work vehicle other than a forklift, the axle frame 5 is attached to the front portion of the main frame 1. In some cases, a drive wheel is attached to the rear portion of the main frame 1.

  A knuckle 6 that rotatably supports the steering wheel 10 is attached to each of the left and right sides of the axle frame 5, and a cylindrical housing 7 that extends in the longitudinal direction of the axle frame 5 is attached to the axle frame 5. ing. A rack shaft 8 is inserted into the housing 7 and guided so as to be slidable in the axial direction. Both ends of the rack shaft 8 are connected to the corresponding knuckles 6 via tie rods 9, respectively.

  A pinion 13 is attached to the center of the housing 7. The pinion 13 engages with the tooth portion 8 a of the rack shaft 8 through an opening formed in the side wall of the housing 7. In addition, a transmission coupling mechanism 16 for transmission coupling the rotation shaft of the pinion 13 to the handle shaft 3 is provided.

  When the center of the tooth portion 8a of the rack shaft 8 engages with the pinion 13, the steering wheel 10 is in a parallel position (see FIG. 4A), and the rack shaft 8 slides from this position in accordance with forward / reverse rotation of the handle 2. By moving, the steered wheel 10 is cut to the left and right.

In this case, the knuckle 6 is provided with a collision portion 11, and the axle frame 5 is provided with a stopper 12 that is paired with the collision portion 11. As shown in FIG. 3, the steering wheel 10 is cut to the maximum turning angle. Sometimes, the corresponding collision part 11 abuts against the stopper 12, so that the turning of the steered wheel 10 beyond the maximum turning angle is restricted.
Correspondingly, in the rack shaft 8, the steering wheel 10 is cut to the maximum turning angle on both the left and right sides of the reference point with the position where the center of the rack shaft 8 is engaged with the pinion 13 as a reference point (see FIG. 4A). It is possible to move up to the maximum movement distance (see FIGS. 4B and 4C).

4B and 4C, in this embodiment, the tooth portion 8a of the rack shaft 8 is such that the end of the tooth portion 8a is the housing when the steering wheel 10 is cut to the maximum left and right cutting angles. The length is set so as not to protrude outward from the end edges 7a and 7b.
This prevents mud, water, etc. from adhering to the tooth portion 8a of the rack shaft 8 and entering the housing 7 while the steered wheel 10 is being steered.

Further, an actuator 14 that rotates the pinion 13 is attached to the axle frame 5. The actuator 14 includes a motor 15 as a drive source. The motor 15 of the actuator 14 is controlled by the control unit 18.
Further, a torque sensor 17 for detecting the rotational torque of the handle 2 is provided on the main frame 1 of the vehicle body.

The control unit 18 controls the supply voltage to the motor 15 based on the detection signal of the torque sensor 17.
Thus, the steering wheel 10 is steered left and right by the combined driving force of the driving force from the handle 2 and the driving force from the motor 15.

Furthermore, according to the present invention, a potentiometer (not shown) for detecting the direction and angle of rotation of the rotating shaft is attached to the rotating shaft of the motor 15.
In this embodiment, the potentiometer is arranged on the rotating shaft of the motor 15. Alternatively, the potentiometer can be arranged on the rotating shaft of the pinion 13.
Instead of the potentiometer, another known detector (for example, a rotary encoder) that can detect the rotation direction and the rotation angle of the rotation shaft of the motor 15 or the pinion 13 can be used.

The control unit 18 measures the movement distance of the rack shaft 8 from the reference point to the left and right sides based on the detection signal of the potentiometer.
The control unit 18 then moves the rack shaft 8 relative to the motor 15 while the moving distance of the rack shaft 8 increases from a predetermined moving distance to a maximum moving distance when the steered wheel 10 is cut from the parallel position to a position near the maximum turning angle. The maximum supply voltage is gradually reduced to zero (in this embodiment proportional to the travel distance of the rack shaft 8).

Thus, when the motor 15 assists when the steering wheel 10 is further cut to the maximum turning angle from the position at which the steering wheel 10 is cut to the maximum turning angle, the starting position of the steering wheel 10 is the maximum turning angle. The closer the position is, the lower the maximum rotation speed of the motor 15 and the lower the rotation speed of the motor 15 during assist.
As a result, the impact when the collision part 11 provided on the knuckle 6 collides with the stopper 12 provided on the axle frame 5 is mitigated, and the wear of the stopper 12 is minimized and the handle 2 side is reduced. The impact force transmitted is also weakened.

Further, the control unit 18 issues a warning when it is determined that the movement distance of the rack shaft 8 exceeds the maximum movement distance and reaches the second predetermined movement distance.
In this case, the second predetermined movement distance is set to a movement distance until the end of the tooth portion 8 a of the rack shaft 8 reaches a position before the end of collision with the teeth of the pinion 13. Further, the warning is performed by sound, by displaying a warning on the driver's seat display, or both.

  As a result, the stopper 12 is worn significantly, and the driver is warned that the steered wheel 10 is turning beyond the maximum turning angle, so that the driver can be replaced, repaired or readjusted. It is possible to prevent the teeth of the pinion 13 from being damaged by the collision between the end of the tooth portion 8a of the rack shaft 8 and the teeth of the pinion 13.

  FIG. 5 is a graph for specifically explaining the control of the supply voltage to the motor 15 by the control unit 18 and the timing of warning. The vertical axis represents the maximum supply voltage for the motor (the maximum supply voltage value during normal operation). The horizontal axis represents the travel distance of the rack shaft 8 from the reference point to the left and right sides (the reference point is taken at the origin of the graph, and the travel distance to the right is plotted on the horizontal axis). In the positive direction, the distance to the left is the negative direction on the horizontal axis).

  In this example, the maximum movement distance of the rack shaft 8 when the steered wheels 10 are cut from the parallel position to the maximum turning angle is set to X2 mm (see points B and B ′ in the graph). The movement distance of the rack shaft 8 until the tooth portion 8a collides with the teeth of the pinion 13 is X4 mm (see points D and D ′ in the graph).

Then, after the travel distance of the rack shaft 8 reaches X1 mm (see points A and A ′ in the graph), the maximum supply to the motor 15 is performed while increasing to the maximum travel distance X2 mm (see points B and B ′ in the graph). The voltage is reduced linearly from 100% to 0%.
Further, when the movement distance of the rack shaft 8 exceeds the maximum movement distance and reaches X3 mm (see points C and C ′ in the graph), a warning is issued by the control unit 18.

  Needless to say, the maximum supply voltage during normal operation is always supplied to the motor 15 while the steered wheel 10 is returned from the position cut to the maximum turning angle to the parallel position.

DESCRIPTION OF SYMBOLS 1 Main frame 2 of a vehicle body Handle 3 Handle shaft 4 Center turning axis 5 Axle frame 6 Knuckle 7 Housing 7a, 7b Housing edge 8 Rack shaft 8a Tooth part 9 Tie rod 10 Steering wheel 11 Collision part 12 Stopper 13 Pinion 14 Actuator 15 Motor 16 Transmission coupling mechanism 17 Torque sensor 18 Control unit 19 Drive wheel

Claims (4)

A handle and a handle shaft provided on the vehicle body,
An axle frame that extends in the width direction of the vehicle body, is attached to a horizontal central pivot that protrudes from the front or rear of the main frame of the vehicle body, and is pivotable in the vertical direction;
A knuckle attached to the left and right sides of the axle frame and rotatably supporting the steering wheel;
A cylindrical housing attached to the axle frame and extending in the longitudinal direction of the axle frame;
A rack shaft inserted through the housing and guided so as to be slidable in the axial direction;
Tie rods that connect both ends of the rack shaft to the corresponding knuckles,
A pinion attached to a central portion of the housing and engaged with a tooth portion of the rack shaft through an opening formed in a side wall of the housing;
A transmission coupling mechanism that is provided on the main frame of the vehicle body and that transmissionally couples the rotation shaft of the pinion to the handle shaft;
When the center of the tooth portion of the rack shaft engages with the pinion, the steering wheel is in a parallel position. From this position, the rack shaft slides in accordance with forward / reverse rotation of the handle, whereby the steering wheel is moved. Cut to the left and right,
The knuckle is provided with a collision part, and the axle frame is provided with a stopper that is paired with the collision part. When the steering wheel is cut to the maximum turning angle, the corresponding collision part is brought into contact with the stopper. By contacting, turning beyond the maximum turning angle of the steered wheel is regulated,
An actuator that is attached to the axle frame and rotationally drives the pinion and includes a motor as a drive source;
A control unit for controlling the motor of the actuator;
A torque sensor for detecting the rotational torque of the handle,
In the electric power steering apparatus in which the control unit controls a supply voltage to the motor based on a detection signal of the torque sensor.
A detector for detecting a rotation direction and a rotation angle of the rotation shaft of the motor or the rotation shaft of the pinion;
The control unit is configured to determine a movement distance of the rack shaft from the reference point to the left and right sides based on a position where the center of the tooth portion of the rack shaft is engaged with the pinion based on a detection signal of the detector. When the steering wheel is cut from the parallel position to the maximum turning angle from a predetermined moving distance when the steering wheel is cut from the parallel position to the front of the maximum turning angle. An electric power steering apparatus characterized in that the maximum supply voltage to the motor is gradually reduced to zero while the maximum movement distance is increased.   The control unit reduces the maximum supply voltage to the motor in proportion to the movement distance of the rack shaft while the movement distance of the rack shaft increases from the predetermined movement distance to the maximum movement distance. The electric power steering apparatus according to claim 1.   3. The control unit according to claim 1, wherein the control unit issues a warning when it is determined that the travel distance of the rack shaft exceeds the maximum travel distance and reaches a second predetermined travel distance. 4. Electric power steering device.   The tooth portion of the rack shaft is set to a length such that an end of the tooth portion does not protrude outside the housing when the steering wheel is cut to the left and right maximum cutting angles. The electric power steering apparatus according to any one of claims 1 to 3.

Images