JPH01247273A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To ensure fail safe characteristic in the event of failure in a motor and the assist to the motor by furnishing a clutch to raise the engaging force of an outer sleeve with an output shaft in accordance with the magnitude of relative displacement of the input shaft to output shaft. CONSTITUTION:A window 11d is provided in the major dia. portion 11b of an input shaft 11 in its position mating with the flat portion 12b of an output shaft 12. In this window 11d a pair of rollers 22a, 22b are fitted so that their axes are oriented in the axial direction of an input and an output shaft 11, 12, and a compression coil spring 33 is interposed between these roller 22a, 22b. Outside the major dia. part 11b of the input shaft 11 an outer sleeve 23 is supported rotatably by bearings 35, 32 while forming a certain gap between the rollers 22a, 22b. A clutch is composed of this window 11d, flat part 12b, rollers 22a, 22b, and outer sleeve 23.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an electric power steering for a vehicle that uses an electric motor as a power source in order to reduce the steering force of the steering wheel of the vehicle. More specifically, the present invention relates to an electric power steering device equipped with a clutch device for ensuring a fail-safe in the event of an abnormality such as a failure of the electric motor, and for ensuring assistance of the electric motor under any steering conditions.

(Prior Art) As a conventional device, for example, there is one shown in Japanese Patent Laid-Open No. 61-37581.

This device drives an electric motor using a control circuit in response to a signal from a torque detector that detects steering torque generated between an input shaft and an output shaft or a signal from a vehicle speed detector, and transfers the driving force of the electric motor to a clutch. The power is transmitted to the output shaft via the speed reducer and reduces the steering force of the steering wheel connected to the input shaft.

This device uses an electromagnetic clutch that is controlled by a control circuit as a clutch interposed between the electric motor and the reduction gear. -OFF control not only improves the steering feeling, but also enables manual steering by turning OFF when an abnormality occurs, ensuring fail-safety. In addition, as an example of another clutch adopted by this device, a ball is interposed between the electric motor and the speed reducer in the fitting gap between the cylindrical shaft and the hexagonal cross-section shaft, and the driving force from the electric motor is transmitted to the output shaft. On the other hand, a mechanical clutch that prevents the driving force from the output shaft from being transmitted to the electric motor side is mentioned. By employing this mechanical clutch, even if the electric motor becomes abnormal, for example in a locked state, manual steering will not be hindered, ensuring fail-safety.

(Problem to be Solved by the Invention) However, among the clutches interposed between the electric motor and the speed reducer in the conventional device described above, in the case of an electromagnetic clutch that is O'N-OFF controlled by a control circuit, The electromagnetic clutch may become inoperable due to factors other than the clutch itself, such as malfunction of the control circuit, and the steering feeling may deteriorate significantly. In other words, for example, when the electric motor malfunctions and becomes unable to rotate, the electromagnetic clutch may not be turned off due to factors other than the electromagnetic clutch itself as described above, and steering becomes impossible. It may happen that the electric motor is rotated in a direction opposite to the direction of rotation input to the input shaft, and that steering becomes impossible without the clutch being turned off. In addition, in this device, when the electric motor becomes unable to rotate due to a foreign object being caught in the electric motor, the electromagnetic clutch is not turned off and steering becomes impossible. It may not be possible to immediately determine whether this means that there is an abnormality in the electric motor, which may make the vehicle run unstable.

On the other hand, in the case of mechanical clutches mentioned on the other side, for example, when an abnormality occurs in the control circuit and the electric motor rotates in the opposite direction to the steering direction, a load is applied to the electric motor and steering becomes impossible. In this case, similar to the electromagnetic clutch described above, since the abnormality cannot be detected immediately, running stability may be lost and an accident may occur. Furthermore, since this mechanical clutch has a structure in which a freely rotating ball is simply interposed, the connection between the electric motor and the reducer is unstable, and especially when sudden steering is performed under high load, the electric motor also becomes unstable. As the ball starts rotating at high speed, it moves at high speed into a narrow tapered space between the hexagonal shaft and the cylindrical shaft, and the impact may cause it to bounce back into the wider space, causing the clutch to instantly disengage and assist. As a result of the loss of power, a problem arises in that the steering force suddenly becomes heavy.

This is because the clutch in the above device connects and disconnects the electric motor and the output shaft using electrical signals, or unilaterally transmits the drive from the electric motor to the output shaft, and is linked to the rotation of the input shaft. This is because the connection is not mechanically interrupted.

As described above, the problem remains that the conventional devices do not sufficiently ensure safety and reliability as an electric power steering device.

Therefore, the present invention was made with the aim of solving these problems, and even when an abnormality occurs in the electric motor, the clutch is mechanically engaged and engaged in relation to the relative displacement between the input shaft and the output shaft. , aims to further improve the safety and reliability of the electric power steering device, and to improve the steering feeling of the electric power steering device.

[Structure of the invention]

(Means for Solving the Problems) The measures taken to solve the above technical problems are the steering torque applied between the input shaft connected to the steering wheel of the vehicle and the output shaft connected to the steering gear. a steering torque detector that detects a steering torque detector, an electric motor whose rotation is controlled by a control signal from a control means in response to a detection signal from the steering torque detector, and whose rotation is transmitted to an output shaft; In an electric power steering device comprising a clutch interposed between shafts and controlling transmission of the rotation of the electric motor to the output shaft intermittently, the cylindrical outer ring that decelerates the rotation of the electric motor is arranged concentrically with the output shaft and A retainer is arranged to leave a gap between the two, and is interlocked with the input shaft within the gap to increase the engagement force between the cylindrical outer ring and the output shaft according to the magnitude of relative displacement between the input shaft and the output shaft. It consists in arranging the members.

(Function) According to the above configuration, even if the electric motor is rotated in the opposite direction to the rotation according to the steering torque detected by the steering torque detector due to a malfunction of the control means, etc., the inner surface of the outer ring The clutch is disengaged to push back the engagement member in the direction opposite to the rotation of the input shaft, while manual steering is possible because the input shaft and output shaft are connected via an elastic body.

In this way, only when the direction of rotation of the electric motor, the direction of rotation of the input shaft, and the direction of elastic deformation of the elastic body match, the rotation of the electric motor is engaged to be transmitted to the output shaft, and the force from the electric motor to the output shaft is transmitted. Whenever the three parties do not match, including when the electric motor is locked, the clutch disengages and no force is transmitted between the electric motor and the output shaft, allowing manual steering and disabling steering operation. It will never be.

Furthermore, in the present invention, the retaining member acts to increase the engagement force between the outer ring and the output shaft depending on the magnitude of the relative displacement between the input shaft and the output shaft, so for example, when sudden steering is performed under high load, Also, the retaining member reliably engages the outer ring and the output shaft to ensure assistance from the electric motor.

(Example) Hereinafter, an example of an electric power steering device according to the present invention will be described based on the drawings.

In FIGS. 1 and 2, the input shaft 11, which has one end connected to the steering wheel 10, has a hollow stepped tube shape, and the other end is one end of the torsion bar 13, which is connected to the output shaft 12 by a pin 15b. are connected to each other by a pin 15a. As a result, the input shaft 11 is connected to an output shaft 12 connected to a steering gear (not shown) of the vehicle via the torsion bar 13, and one end of the output shaft 12 is allowed to play freely within the large diameter portion 11b of the input shaft 11. The steering force applied to the input shaft 11 is transmitted to the output shaft 12 via the torsion bar 13.

The input shaft 11 is rotatably supported on the steering wheel 10 side by a bearing 16 press-fitted into the upper housing 14a, and the output shaft 12 is rotatably supported by a bearing 17 press-fitted into the lower housing 14b. has been done.

A dust cover 36 is fitted on the outer periphery of the small diameter portion 11a of the input shaft 11 on the outside of the upper housing 14a, and a cylindrical slider 18 is loosely fitted inside the upper housing 14a. A portion is also loosely fitted to the output shaft 12, and the output shaft 12 is attached to the output shaft 12 side.
A radial hole 18a is provided into which a ball 19 that is engaged with a spiral groove 12a formed on the outer circumferential surface is inserted.

A ring 20 having flanges at both ends and forming an annular groove 20a between the flanges is fixed to the outer periphery of the slider 18. Further, a long hole 18c in the axial direction is formed in a part of the outer circumference of the slider 18, into which a pin 21 fixed to the large diameter part of the input shaft 11 is inserted, so that the slider 18 is integrated with the input shaft 11. Thus, it is rotatable and freely movable in the axial direction.

On the outer peripheral surface of the output shaft 12, the above-mentioned spiral groove 12a is carved, and as shown in FIG. It extends to the flat part 12b of the shaft 12.

A window 11d is provided in the large diameter portion 11b of the input shaft 11 at a position corresponding to the flat portion 12b of the output shaft 12. Inside the window lid is a pair of cylindrical rollers 22a.

22b are fitted so that their axes coincide with the axial direction of the input/output shafts 11.12, and each pair of rollers 22a.

A compression coil spring 33 is interposed between 22b. As a result, each roller 22a, 22b has a window lid.
is pressed against the circumferential end surface of the flat portion 12b, and is also brought into contact with one end surface of the flat portion 12b.

Further, on the outside of the large diameter portion 11b of the input shaft 11, an outer sleeve 23 forms a predetermined gap between the rollers 22a and 22b, and a bearing 35 and an output shaft are press-fitted and fixed to the outer sleeve housing 14a. It is rotatably supported by a bearing 32 fixedly mounted on 12. A worm wheel 23a that meshes with a worm 25 fixed to an output shaft 24a of an electric motor 24 is formed on the outer peripheral surface of the outer sleeve 23, and the worm 25 and the worm wheel 23a constitute the reducer of the present invention. and window lid, flat part 12b,
Koro 22a.

22b and the outer sleeve 23 constitute a clutch in the present invention.

In addition, in FIG. 2, 30 and 31 are bearings that support the large diameter portion 11b of the input shaft 11 and the outer sleeve 23, respectively.

Further, a case 26 is attached to the upper housing 14a, and a ball 27 is provided at one end of the case 26.
A lever 2 consisting of a leaf spring-like metal plate holding a
The other end of 8 is fixed.

The ball 27 held at one end of the lever 28 is attached to the ring 20
The lever 28 is fitted into an annular groove 20a, and a strain gauge (not shown) forming a resistance bridge is attached to the side surface of the lever 28, which is coated with an insulating layer. The strain gauge constitutes a well-known strain detection circuit consisting of a bridge circuit, and the electrical signal from the strain gauge is input to the control circuit 29, which controls the electric motor 24 in accordance with the electrical signal. Control the supply current.

The operation of this embodiment having the above configuration will be explained.

When the steering wheel 10 is rotated, the input shaft 11
The torsion bar 13 is twisted with respect to the output shaft 12 connected to the steering gear, which rotates and is subjected to a load such as a road reaction force, and a relative rotation occurs between the output shaft 12 and the input shaft 11.

As a result, the relative rotation of this input shaft 11, that is, the output shaft 1
2, the slider 18 rotates relative to the spiral groove 12a, and this rotation applies a thrust in the axial direction of the input shaft 11 to the slider 18 via the ball 19, causing the slider 18 to move toward the input shaft 11. and the relative rotation of the input shaft 11. The axial displacement of the slider 18 is determined via the ball 27 that engages with the annular groove 20a of the ring 20, by bending the lever 28 that holds the slider, and adjusting the amount of relative rotation between the human power shaft 11 and the output shaft 12 into the strain gauge. Generates a corresponding electrical signal. This electrical signal is transmitted to the control circuit 2
9, the control circuit 29 sends a supply current corresponding to this electric signal to the electric motor 24, rotates the electric motor 24 in a direction corresponding to the rotation direction of the input shaft 11, and the rotation of the electric motor 24 is performed in a worm mode. 25 and worm wheel 23
The speed is reduced by a and transmitted to the outer sleeve 23.

At this time, in the present invention, the clutch is engaged and engaged in the following manner. That is, in FIG. 4, (a) shows the state of the clutch mechanism when the torque sensor 26 is in the neutral position, and both the rollers 22a and 22b are connected to the outer sleeve 2.
3, and neither the input shaft 11 nor the output shaft 12 is connected to the outer sleeve 23, that is, the electric motor 24. (Relative rotational displacement Δθ between input shaft 11 and output shaft 12
=0) The same figure (bl is the input shaft 11 rotated to the left in the drawing, and the left roller 22b is connected to the inner surface of the outer sleeve 23 and the output shaft 1.
2, which is the starting point for clutch engagement. (Δθ=Δθ1) Figure (e) shows a state in which the input shaft 11 is further rotated to the left, and the left roller 22b is at the same position as fbl above, but it is in contact with the right end surface of the window lid of the input shaft 11. The roller 22a on the left bends the spring 33 and is displaced in the counterclockwise direction, and the roller 22b on the left
is separated from the left end surface of the window lid of the human power shaft 11. At this time, the supply of current to the motor 24 is started, and the outer sleeve 23 begins to rotate in the same left rotation direction as the input shaft 11.

(Δθ=Δθ2) Figure (d) shows a state where the road surface reaction force is large and the input shaft 11 is further rotated to the left in order to increase the current supplied to the motor 24, and the left roller 22b is The roller 22a on the right side further deflects the spring 33 and is displaced in the counterclockwise rotation direction.Therefore, a large road reaction force is applied.
As the relative rotational displacement of the output shafts 11 and 12 increases and the output of the motor increases, in order to increase the transmission force of the clutch, the pressing force of the left roller 22b by the spring 33 is increased to ensure that the clutch is engaged. match.

Figure 5 shows the relationship between the electric motor current, the relative rotational displacement (Δθ) of the input/output shafts 11 and 12, and the roller pressing force, and the figure fa) (b) shows this. As shown in FIG.
The input shaft 1 when the lever 28 is deflected due to the axial displacement of the input shaft 8 and the electric motor 24 starts rotating due to the supplied current controlled by the control circuit 29 according to the signal from the strain gauge.
Since the relative rotational displacement (Δθ−θ2) between the input shaft II and the output shaft 12 is smaller than the relative rotational displacement (Δθ−θ2), as shown in FIG. Only after the inner peripheral surface of the outer sleeve 23 and the end surface of the flat portion 12b are crimped in advance, the electric motor 24 starts rotating, and the rotation is transmitted to the outer sleeve 23. As a result, with the roller 22 on the rotation direction side pressed against the inner peripheral surface of the outer sleeve 23 and the end surface of the flat part 12b,
The rotation of the outer sleeve 23 is smoothly transmitted to the output shaft 12 via the rollers 22, thereby assisting the steering force applied to the steering wheel 10. Here, the rotation direction of the outer sleeve 23 is determined by the control circuit 29 by the electric motor 24 at a rotation speed and rotation direction corresponding to the relative rotation of the input shaft 11.
By controlling its rotation, the torsion bar 1
The direction of relative rotation of the input shaft 11 coincides with the elastic direction of No. 3. As a result, the rollers 22 are strongly pressed against the flat portion 12b by the frictional force thereof, and rotational force is reliably transmitted.

By the way, the window l formed in the large diameter portion 11b of the input shaft 11
Simply put the roller 22 in the id, or a pair of rollers 22a,
If appropriate pressing force is not applied to 22b, for example, if the relative rotation between the input shaft 11 and the output shaft 12 becomes large due to fast steering despite the large resistance on the ground side, the electrical When the motor starts rotating at high speed, the rollers 22 in the rotating direction suddenly engage with the output shaft 12, and as a result, the reaction force may cause the motor to rebound, causing the clutch to disengage and suddenly lose assist, causing the steering force to become momentarily heavy. It may happen.

In this regard, in this embodiment, a compression coil spring 33 is interposed between the pair of rollers 22a and 22b, so that the larger the relative rotational displacement, the thicker the pressing force of the rollers 22 in the rotation direction. Even in the above-mentioned cases, engagement of the clutch is ensured and stable assistance is obtained.

FIG. 5(d) shows the characteristics of the roller pressing force with respect to the relative rotation of the input shaft 11 and the output shaft 12 when the spring is preloaded and set in the window lid, which was made with these points in mind. ing.

Note that the slope A shown in FIGS. 1 and 5 (bl) is determined by the spring constant of the spring 33, and is selectively determined by the transmission force of the clutch and the magnitude of the output of the electric motor 24. The relative rotational displacement (Δθ=θ,) between the human power shaft 11 and the output shaft 12 when the gap between the roller 22 and the outer sleeve 23 disappears and the clutch becomes operable is:
Inner diameter dimension of outer sleeve 23, outer diameter of roller 22, dimension of flat part 12b of output shaft 12, window 11d of human power shaft 11
, the spring constant and dimensions of the spring 33 can be arbitrarily set by various combinations.

In this way, the clutch 7 according to this embodiment has an input shaft 11.
Rotation from the outer sleeve 23 is transmitted to the output shaft 12 only when the relative rotation (Δθ) of Operate. therefore,
Even if the electric motor 24 is rotated in the opposite direction to the rotation direction according to the relative rotation of the human-powered shaft 11 due to a malfunction of the control circuit 29, the left roller 22b in FIG. Plane portion 12 of surface and output shaft 12
When the outer sleeve 23 is in contact with the b end surface,
The outer sleeve 23 vibrates and rotates within the window lid due to the frictional force between the outer sleeve 23 and the outer sleeve 23, and the rotation of the outer sleeve 23 is not transmitted to the input shaft 11, while the rotation of the input shaft 11 is transmitted to the output shaft 12 via the torsion bar 13. , allowing manual steering. Furthermore, even if the electric motor 24 becomes unrotatable due to a foreign object being caught in the outer sleeve 23, the left roller 22b in FIG.
spring 3 due to the frictional force with the outer sleeve 23.
The rotation of the input shaft 11 is transmitted to the output shaft 12 via the rollers 22 by vibrating against the force 3 or rotating on its own axis.
Allows manual steering.

Furthermore, according to the device of this embodiment, the steering wheel I/O
When the outer sleeve 23 is in the locked state and the outer sleeve 23 is in the locked state, the clutch operates so that the rollers 22 maintain the state in which the steering wheel 10 is held by the spring force.
When the steering wheel 10 is in the free state B (when the steering wheel is turned and released) and the outer sleeve 23 rotates forward and backward, the clutch operates to prevent the steering wheel 10 from being obstructed from returning. Moreover, when the steering wheel 10 is further cut in and the outer sleeve 23 is rotating in the forward direction, when the electric motor 24 suddenly increases its rotational torque due to a malfunction of the control circuit 29, etc., the input shaft 11 The elastic deformation of the torsion bar 13 is reversed by the side acting as resistance, and the clutch operates to cut off the rotation transmission from the outer sleeve 23 to the input shaft 12. Also, when the vehicle is traveling straight, the control circuit 29 Even if the electric motor 24 rotates due to malfunction, etc., the clutch will not close to the outer sleeve unless the relative rotation (Δθ) between the input shaft 11 and the output shaft 12 exceeds the set value (Δθ=θ2) due to road reaction force. Since no force is transmitted between the output shaft 23 and the output shaft 12, the steering wheel 10 is not suddenly turned.

Furthermore, for example, when sudden steering is performed despite a large road load, the pressing force of the rollers 22 increases due to the large relative rotational displacement between the input shaft 11 and the output shaft 12, and the sudden force of the outer sleeve 23 increases. It follows the rotation start well and secures engagement with the output shaft.

As described above, according to the present embodiment, the clutch operates to connect and disconnect rotation transmission between the electric motor 24 and the reduction gear by utilizing the elastic deformation of the torsion bar 13 for detecting the relative rotation of the input shaft 11. By appropriately controlling the electric power steering, the safety and reliability of the electric power steering can be improved, and the device can be downsized. Moreover, at the same time, the steering feeling of the electric power steering device can be improved.

In the above embodiments, examples were explained in which a cantilever type using a strain gauge and a slip ring type were used as a detector for extracting the relative rotation of a human-powered axis as an electric signal, but potentiometers, photoelectric detectors, and magnetostrictive detectors It is also possible to employ the following in the present invention.

〔Effect of the invention〕

According to the present invention, the steering torque detector detects the steering torque according to the elastic deformation of the elastic body connecting the input shaft and the output shaft, and the engagement and disengagement of the clutch is detected by the steering torque detected by the steering torque detector. It is controlled by the rotation of the electric motor according to the rotation and the pressing force of the clutch engagement member based on the amount of relative displacement between the input and output shafts.

Therefore, even if the electric motor is rotated in the opposite direction to the rotation according to the steering torque detected by the steering torque detector due to a malfunction of the control means, etc., the pressing force of the clutch retaining member is reduced. , the clutch is disengaged and the driving force of the electric motor is not transmitted to the output shaft. Therefore, the clutch is engaged to transmit the rotation of the electric motor to the output shaft only when the direction of rotation of the reducer by the electric motor matches the steering direction. When the two do not match, the clutch is always disengaged and no force is transmitted between the electric motor and the output shaft, so manual steering is possible and the steering operation is not disabled.

In addition, especially in the present invention, since the clutch engagement force is changed according to the amount of relative displacement between the input and output shafts,
The clutch can be reliably engaged even when sudden steering is performed under high load, enabling stable steering. Therefore, the safety and reliability of the electric power steering device can be improved.

In addition, the present invention employs a reduction gear consisting of a worm and a worm wheel that is small and can obtain a large reduction ratio, and
Since the steering torque detector and the clutch share an elastic body that requires a large space, the electric power steering device can be made more compact.

Furthermore, according to the present invention, the elastic deformation of the elastic body when the clutch is activated is greater than the elastic deformation of the elastic body when the steering torque detector detects the steering torque and the electric motor starts rotating in response. It has been made smaller. Therefore, the rotation of the electric motor starts after the clutch is activated in advance, and the rotation is transmitted to the output shaft via the clutch, so there is no possibility that shocks or the like will be transmitted to the steering wheel during the transmission. Therefore, it is possible to obtain a smooth steering feeling, thereby improving the steering feeling of the electric power steering device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of an electric power steering device according to the present invention, FIG. 2 is a vertical sectional view showing the same embodiment in detail, and FIG. 3 is shown in FIG. FIG. 4 is an enlarged side cross-sectional view of the clutch in the example, FIG. 4 is an operation explanatory diagram of the same clutch, and FIG. 5 is a characteristic diagram showing the relationship between motor current, roller pressing force, and relative displacement of the input and output shafts in the same clutch. . Explanation of the main parts of the figure 11 - Human power shaft L2 - Output shaft 13 -) - Spring 22 - Roller 23 - Outer sleeve 23a - Worm wheel 25 - Worm 29 - Control circuit 33 - Spring 3 Figure 4 (α) l (C) Figure 5 (b) (CI)

Claims (1)

[Claims] A steering torque detector that detects steering torque based on relative displacement between an input shaft connected to a steering wheel of a vehicle and an output shaft connected to a steering gear, and control according to a detection signal from the steering torque detector. an electric motor whose rotation is controlled by a control signal from a means and whose rotation is transmitted to the output shaft; and an electric motor which is interposed between the electric motor and the output shaft and which transmits the rotation of the electric motor to the output shaft. In an electric power steering device equipped with a clutch that performs intermittent control, a cylindrical outer ring that decelerates the rotation of the electric motor is arranged concentrically with the output shaft with a gap left between them, and is connected to the input shaft within the same gap. An electric power steering device characterized in that an engaging member is provided that interlocks and increases the engagement force between the cylindrical outer ring and the output shaft according to the magnitude of relative displacement between the input shaft and the output shaft.