JP3631456B2 - Coaxial type electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a coaxial electric power steering apparatus capable of easily performing a steering operation even when steering is in a heavy load state.
[0002]
[Prior art]
FIG. 4 is a cross-sectional view showing a configuration of a conventional coaxial electric power steering device disclosed in, for example, Japanese Patent Laid-Open No. 2000-302051. In the figure, the steering shaft 1 moves a wheel (not shown) via tie rods (not shown) provided at both ends of the shaft by moving in the left-right direction in the figure. Although not shown, based on the steering of the motor, a well-known rack-and-pinion mechanism comprising a rack provided on the steering shaft 1 and a pinion provided on the steering shaft of the steering wheel, and assistance by an electric motor described later is used. is there. The steering shaft of the steering wheel is provided with steering torque detecting means for assisting operation described later.
[0003]
The steering shaft 1 is supported by a housing 2 so as to be movable in the axial direction by a bearing (not shown), and an electric motor 3 is provided on the inner diameter of the housing 2 coaxially with the steering shaft 1. The electric motor 3 includes a stator 4 fixed to the inner diameter of the housing 2 and a rotating shaft 6 which is formed in a cylindrical shape and the steering shaft 1 passes through the inner diameter and is rotatably supported by the housing 2 by a bearing 5 or the like. And a rotor 7 having the same. A ball screw 1 a is provided on the steering shaft 1, and a ball screw nut 11 is screwed to the ball screw 1 a via a ball 10. The ball screw nut 11 is rotatably mounted on the housing 2 by bearings 12 and 13. It is supported.
[0004]
The speed reduction mechanism 8 includes a sun gear 9 provided at one end of the rotary shaft 6, an internal gear 14 fixed to the housing 2, and a planetary gear 15 that meshes with the sun gear 9 and the internal gear 14. The planetary gear speed reduction mechanism is configured such that the planetary gear 15 is rotatably fitted to a pin 16 provided on the ball screw nut 11 and is fixed to the pin 16 in the axial direction by a holding member 17.
[0005]
In the conventional coaxial electric power steering apparatus configured as described above, when a driver operates a steering wheel (not shown), a thrust is applied to the steering shaft 1 via a rack and pinion mechanism (not shown), and the driver moves in the operated direction. At the same time, the steering torque detection means provided on the steering shaft of the steering wheel detects the steering torque at this time, and is input to the control means (not shown) to drive the electric motor 3. The rotation of the electric motor 3 is transmitted to the speed reduction mechanism 8, and a torque increase corresponding to the speed reduction ratio is made and transmitted to the ball screw nut 11. The torque in the rotational direction applied to the ball screw nut 11 is converted into an axial thrust by the ball screw 1a, and assists the steering by the driver.
[0006]
[Problems to be solved by the invention]
Thus, since the thrust with respect to the steering shaft 1 by the steering force of the driver is assisted by the thrust of the steering shaft 1 by the electric motor 3, the driver is steered lightly and smoothly. However, for example, when a vehicle wheel is in contact with an obstacle such as a curb at the end of a road or is on a road, a large force is required for steering the wheel, and the conventional coaxial electric power steering as described above. In the apparatus, since the torque of the electric motor 3 is increased only by an amount corresponding to the reduction ratio of the speed reduction mechanism 8, the electric motor 3 may be locked. In order to enable steering in such a state, the reduction ratio of the speed reduction mechanism 8 may be increased. However, an increase in the reduction ratio leads to deterioration of steering feeling during normal driving, and safety of driving. It was an obstacle.
[0007]
The present invention has been made to solve such a problem. By detecting the steering force of the driver and switching the reduction ratio of the speed reduction mechanism, the steering feeling is good during normal driving. An object of the present invention is to obtain a coaxial electric power steering device that can be easily steered under a heavy load of steering.
[0008]
[Means for Solving the Problems]
A coaxial electric power steering device according to the present invention includes a steering shaft that steers a vehicle wheel by steering a steering wheel, and an electric motor that applies auxiliary thrust to the steering shaft via a first or second ball screw mechanism. The first planetary speed reduction mechanism, the first rotation transmission element, and the first rotation transmission element can be coupled and separated from the rotation shaft of the motor, and the second planetary reduction mechanism. Through a first rotation transmission path for transmitting rotation to the first ball screw mechanism and a third rotation transmission element for holding the planet of the first planetary reduction mechanism from the rotating shaft of the motor. A second rotation transmission path for transmitting rotation to the second ball screw mechanism, a coupling and separation operation of the first rotation transmission element and the second rotation transmission element, and a fixation and release of the third rotation transmission element The first rotation transmission path and the second rotation And an electromagnetic clutch for switching and reaches the route, in which the reduction ratio of the first rotation transmission path and the second rotation transmission path is different.
[0009]
In addition, it has a control means for controlling the electromagnetic clutch, and the control means detects the steering torque of the steering wheel and controls the electromagnetic clutch to switch between the first rotation transmission path and the second rotation transmission path. It is a thing.
Furthermore, it has control means for controlling the electromagnetic clutch, and the control means detects the traveling speed of the vehicle and controls the electromagnetic clutch so as to switch between the first rotation transmission path and the second rotation transmission path. It is a thing.
[0010]
In addition, the first reduction mechanism and the second reduction mechanism are configured by a planetary gear reduction mechanism including a sun gear, an internal gear, and a planetary gear.
Further, the first speed reduction mechanism and the second speed reduction mechanism, or one of them is constituted by a planetary roller speed reduction mechanism including a sun roller, an inscribed roller, and a planetary roller.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
1 to 3 illustrate a coaxial electric power steering apparatus according to Embodiment 1 of the present invention. FIGS. 1 and 2 are cross-sectional views illustrating the configuration, and FIG. 1 illustrates a normal state. FIG. 2 shows a state where the electromagnetic clutch 23 is operated because a high torque is required for steering. FIG. 3 is an explanatory diagram for explaining the configuration and operation of the clutch 20. In FIGS. 1 and 2, the same reference numerals are given to the same functional portions as those in the conventional example.
[0012]
In the figure, the steering shaft 1 moves in the left-right direction in the figure, as in the above-described conventional example, to turn a wheel (not shown) via tie rods (not shown) provided at both ends of the shaft. This lateral movement is made by a rack (not shown) provided on the steering shaft 1 and a pinion provided on the steering shaft (not shown) of the steering wheel based on the steering of the driver. An and pinion mechanism is used, and a steering torque detecting means is provided on a steering shaft of a steering wheel (not shown) as will be described later. Further, the steering shaft 1 is supported by a housing 2 so as to be movable in an axial direction by a bearing (not shown), and an electric motor 3 having a coaxial configuration with the steering shaft 1 is provided on the inner diameter of the housing 2.
[0013]
The electric motor 3 includes a stator 4 fixed to the inner diameter of the housing 2 and a rotating shaft 6 which is formed in a cylindrical shape and the steering shaft 1 passes through the inner diameter and is rotatably supported by the housing 2 by a bearing 5 or the like. And a rotor 7 having the same. The steering shaft 1 is provided with a ball screw 1 a, and a second ball screw nut 18 and a first ball screw nut 19 are screwed to the ball screw 1 a via a ball 10. The ball screw 1a and the ball 10 constitute a second ball screw mechanism, and the first ball screw nut 19, the ball screw 1a and the ball 10 constitute a first ball screw mechanism. A third rotation transmission element 21 is provided on the outer periphery of the second ball screw nut 18 via a clutch 20 described later, and the first ball screw nut 19 is rotatably supported by the housing 2 by a bearing 22. ing.
[0014]
Reference numeral 23 denotes an electromagnetic clutch including an exciting coil 24, a first rotation transmission element 25, and a separation spring 26. The first rotation transmission element 25 also serves as a mover of the electromagnetic clutch 23, and the excitation coil 24 is not excited. In this case, the first rotation transmission element 25 is pushed out to the de-excitation coil 24 side by the pressing force of the separation spring 26, and the connecting portion 28 provided between the second rotation transmission element 27 as shown in FIG. And the second rotation transmitter 27 rotates together with the first rotation transmitter 25, and when the excitation coil 24 is excited, the first rotation transmitter 25 is attracted and fixed to the excitation coil 24 side. In addition, as shown in FIG. 2, the connecting portion 28 is separated and the second rotation transmitter 27 is not driven.
[0015]
A first speed reduction mechanism 30 is provided between the rotating shaft 6 of the electric motor 3 and the first rotation transmitter 25. The first speed reduction mechanism 30 includes a sun gear 31 provided on the rotation shaft 6, an internal gear 32 fixed to the first rotation transmission element 25, and a pin 33 provided on the third rotation transmission element 21. The planetary gear 34 is composed of a planetary gear 34 that is rotatably supported. The planetary gear 34 has its axial position fixed to the internal gear 32 by stoppers 35 and 36, and the planetary gear 34 is fixed by a holding member 37. The pin 33 is also fixed in the axial direction. Accordingly, when the electromagnetic clutch 23 is operated and the first rotation transmitter 25 is moved, the planetary gear 34 is moved together with the internal gear 32, and the third rotation transmitter 21 is moved together with the planetary gear 34. ing.
[0016]
A second reduction mechanism 38 is provided between the first ball screw nut 19 and the second rotation transmitter 27. The second speed reduction mechanism 38 is provided on the sun gear 39 provided on the first ball screw nut 19, the internal gear 40 fixed on the second rotation transmission element 27, and the protrusion 2 a of the housing 2. It is a planetary reduction mechanism comprising a planetary gear 42 rotatably supported on a pin 41, and a connecting portion 43 is formed at one end of the pin 41 and is configured to be coupled to the third rotation transmitter 21. The coupling portion 43 is coupled such that when the electromagnetic clutch 23 is operated and the first rotation transmitter 25 is moved to the exciting coil 24 side, the third rotation transmitter 21 is also moved through the planetary gear 34. It is configured to leave.
[0017]
FIG. 3 shows a configuration of the clutch 20 interposed between the second ball screw nut 18 and the third rotation transmitter 21. The clutch 20 includes a groove 44 provided on the inner diameter side of the third rotation transmission element 21 with a predetermined length in the circumferential direction, two rollers 45a and 45b housed in the groove 44, a roller It consists of springs 46 and 47 that determine the positions of 45a and 45b. The groove 44 is formed symmetrically in the circumferential direction from the center, and the depth of the groove 44 with respect to the outer diameter of the second ball screw nut 18 located on the inner diameter side is smaller than the outer diameter of the rollers 45a and 45b at the center. The left and right ends are formed larger than the outer diameter of the rollers 45a and 45b, and the bottom surface is formed as a continuous surface from the left and right ends to the center.
[0018]
Also, the springs 47 disposed on both sides of the rollers 45a and 45b and the springs 46 disposed between the rollers 45a and 45b are both compression coil springs, and the force of the spring 46 is formed stronger than the force of the spring 47. Has been. Therefore, in a normal state, the rollers 45 a and 45 b are pushed to both ends of the groove 44, and a gap is formed between the bottom surface of the groove 44. In this state, considering the case where the second ball screw nut 18 on the inner diameter side rotates counterclockwise, for example, the rollers 45a and 45b try to move in the rotational direction. The roller 45b moves in a direction in which the clearance between the groove and the bottom surface of the groove 44 increases, and the roller 45b has a large amount of force of the spring 46. .
[0019]
Considering the case where the third rotation transmission element 21 on the outer diameter side also rotates counterclockwise, the groove 44 moves with the rollers 45a and 45b stopped with respect to the second ball screw nut 18. Since the force of the spring 47 is weak, the roller 45a moves relative to the groove 44, the gap between the bottom surface becomes zero and the second ball screw nut 18 and the third rotation transmitter 21 are locked, The second ball screw nut 18 is driven by the rotation of the third rotation transmitter 21. That is, the clutch 20 transmits the drive from the third rotation transmitter 21 side (outer diameter side) to the second ball screw nut 18 (inner diameter side), but from the second ball screw nut 18 side (inner diameter side). Has a function of not transmitting to the third rotation transmitter 21 (outer diameter side).
[0020]
In the coaxial electric power steering apparatus according to Embodiment 1 of the present invention configured as described above, when the driver operates the steering wheel, the steering shaft 1 moves in the direction in which the steering shaft 1 is operated via a rack and pinion mechanism (not shown). At the same time, the steering torque detecting means provided on the steering shaft of the steering wheel (not shown) detects the steering torque and outputs a torque signal. When this torque signal is input to a control means (not shown), the control means performs an operation based on the signal and drives the motor 3 with a predetermined rotation direction and drive torque. When the steering torque with respect to the steering wheel is equal to or less than a predetermined value, the control means operates only the electric motor 3 and does not operate the electromagnetic clutch 23. Therefore, the operation starts in the configuration shown in FIG.
[0021]
When the electric motor 3 is driven, the driving torque is transmitted from the sun gear 31 of the first reduction mechanism 30 to the planetary gear 34 and the internal gear 32. The third rotation transmitter 21 holding the planetary gear 34 is coupled to the pin 41 by the connecting portion 43 and is prevented from rotating. Therefore, the planetary gear 34 only rotates and does not revolve, and the internal gear 32 rotates. introduce. Since the first rotation transmission element 25 having the internal gear 32 is coupled to the second rotation transmission element 27 at the connecting portion 28, the rotation of the internal gear 32 passes through the second rotation transmission element 27. To the internal gear 40 of the second reduction mechanism 38. Since the planetary gear 42 of the second speed reduction mechanism 38 is held in the housing 2 by the pin 41, it does not revolve, but only rotates to drive the first ball screw nut 19 having the sun gear 39.
[0022]
The rotation of the first ball screw nut 19 is converted into an axial thrust of the steering shaft 1 by the ball 10 and the ball screw 1a, and the steering shaft 1 moves to steer a wheel (not shown). Thus, when the steering torque for the steering wheel is equal to or less than the predetermined value, the first ball screw nut 19 is driven at a predetermined reduction ratio by the first reduction mechanism 30 and the second reduction mechanism 38, and the steering wheel When the steering shaft 1 is moved by this operation, the second ball screw nut 18 is driven via the ball 10 to rotate, but the clutch 20 is driven from the inner diameter side. Is not transmitted, the second ball screw nut 18 is idled. The above rotation transmission path is the first rotation transmission path.
[0023]
For example, when the vehicle wheel is in contact with an obstacle such as a curb on the road and the steering cannot be performed with a normal steering force, the driver increases the steering force with respect to the steering wheel. When the steering torque exceeds a predetermined value, the control means first operates the electromagnetic clutch 23 to attract and move the first rotation transmitter 25 to the exciting coil 24 side against the pressing force of the separation spring 26. When the first rotation transmitter 25 moves to the exciting coil 24 side, the coupling of the connecting portion 28 is separated and the second rotation transmitter 27 becomes free, and at the same time, the inscribed portion fixed to the first rotation transmitter 25 is fixed. The gear 32, the planetary gear 34 whose axial position is fixed to the internal gear 32 by the stoppers 35 and 36, and the third rotation transmitter 21 that holds the planetary gear 34 are the first rotation transmitter. The third rotation transmitter 21 is removed from the rotation prevention state and the first rotation transmitter 25 is attracted to the excitation coil 24 to be in the rotation prevention state.
[0024]
FIG. 2 shows this state. When the motor 3 is driven in FIG. 2, the driving torque is transmitted from the sun gear 31 of the first reduction mechanism 30 to the planetary gear 34 and the internal gear 32, and the internal torque is reduced. The first rotation transmission element 25 having the contact gear 32 is adsorbed and fixed to the electromagnetic clutch 23, and the third rotation transmission element 21 is separated from the rotation blocking state, and thus is held by the third rotation transmission element 21. The planetary gear 34 revolves to drive the third rotation transmitter 21 in a predetermined direction. If the third rotation transmission element 21 rotates, the clutch 20 is driven from the outer diameter side, so that the clutch 20 is locked, and the second ball screw nut 18 is driven from the third rotation transmission element 21. The rotation of the second ball screw nut 18 is converted into thrust in the axial direction of the steering shaft 1 by the ball 10 and the ball screw 1a, and the steering shaft 1 moves to steer a wheel (not shown). This is the second rotation transmission path.
[0025]
Thus, the steering shaft 1 is normally operated via the first rotation transmission path, and the steering shaft 1 is operated by the second rotation transmission path when a large steering force is required. In the case of the first rotation transmission path, since the second speed reduction mechanism 38 is driven from the internal gear 40 side, the reduction ratio with the first speed reduction mechanism 30 is canceled and becomes smaller, so that the second rotation transmission path In this case, the reduction ratio becomes large. Accordingly, when the steering force of the steering wheel exceeds a predetermined value, the assist force by the electric motor 3 is increased. By selecting this reduction ratio, the normal rotation speed is reduced by the first rotation transmission path during normal driving. The ring can be steered satisfactorily, and if the steering becomes heavy due to an obstacle such as a curb stone, the ring can be switched to the second rotation transmission path and steered easily.
[0026]
Embodiment 2. FIG.
In the coaxial electric power steering apparatus according to Embodiment 2 of the present invention, the first reduction mechanism 30 and the second reduction mechanism 38 are planetary roller reduction mechanisms. In the first embodiment, the speed reduction mechanism is a planetary gear speed reduction mechanism. However, even if this is replaced with a sun roller, a planetary roller, and an inscribed roller, the same functions and effects as in the first embodiment can be obtained. For example, by forming at least the contact surface of each roller with an elastic member or the like, it is possible to obtain a quiet electric power steering device without gear noise. It is also possible to select one of the first reduction mechanism 30 and the second reduction mechanism 38 as a planetary roller reduction mechanism.
[0027]
Embodiment 3 FIG.
The coaxial electric power steering device according to the third embodiment of the present invention is configured to control the operation of the electromagnetic clutch 23 according to the traveling speed of the vehicle with respect to the coaxial electric power steering device according to the first embodiment. The steering of the vehicle becomes heavier as the traveling speed decreases, and becomes quite heavy in the extremely low speed region. On the other hand, since the steering delay does not impair safety in the extremely low speed region, if the vehicle speed is detected and the extremely low speed region (for example, 10 km / h or less) is reached, the electromagnetic clutch 23 is operated to increase the steering reduction ratio. To do. By configuring in this way, it is possible to easily steer even in a low speed range or in a stationary stop.
[0028]
【The invention's effect】
As described above, in the coaxial electric power steering apparatus according to the present invention, according to the first aspect of the present invention, the steering shaft for steering the wheels of the vehicle and the first or second steering shaft. An electric motor that provides auxiliary thrust via the ball screw mechanism, and a second planetary speed reduction mechanism, a first rotation transmission element, and the first rotation transmission element that can be coupled and separated from the rotation shaft of the electric motor. The first rotation transmission path for transmitting rotation to the first ball screw mechanism via the rotation transmission element and the second planetary reduction mechanism, and the planetary element of the first planetary reduction mechanism from the rotating shaft of the motor are held. A second rotation transmission path for transmitting rotation to the second ball screw mechanism via the third rotation transmission element, coupling and separation of the first rotation transmission element and the second rotation transmission element, and The first rotation transmission path is operated by fixing and releasing the third rotation transmission element. And an electromagnetic clutch for switching between the second rotation transmission path and the reduction ratio between the first rotation transmission path and the second rotation transmission path are different, so that the operation differs between the operation and non-operation of the electromagnetic clutch. A plurality of steering patterns having a reduction ratio can be obtained, and a steering pattern can be selected according to the weight of steering.
[0029]
According to the second aspect of the present invention, the control means for controlling the electromagnetic clutch is provided, the control means detects the steering force of the steering wheel to control the electromagnetic clutch, and the first rotation transmission path. And the second rotation transmission path are switched, so that during normal driving, the first rotation transmission path with a small reduction ratio can be steered with a good feeling at the normal reduction ratio. If the steering becomes heavy, it is possible to switch to the second rotation transmission path having a large reduction ratio and to easily steer.
[0030]
Further, according to the invention described in claim 3, the control means for controlling the electromagnetic clutch is provided, the control means detects the traveling speed of the vehicle and controls the electromagnetic clutch, and the first rotation transmission path and Since the second rotation transmission path is switched, the vehicle can be easily steered without being heavy even when the vehicle is traveling at a very low speed or stopped.
[0031]
Furthermore, according to the invention described in claim 4, since the first reduction mechanism and the second reduction mechanism are constituted by a planetary gear reduction mechanism including a sun gear, an internal gear, and a planetary gear, A coaxial electric power steering apparatus having two rotation transmission paths can be obtained with a simple configuration, and according to the invention described in claim 5, the first speed reduction mechanism and the second speed reduction mechanism, or Any one of them is constituted by a planetary roller speed reduction mechanism comprising a sun roller, an inscribed roller, and a planetary roller, so that the construction is facilitated, and at least the contact surface of the roller is constituted by an elastic member or the like, It is possible to obtain a silent electric power steering device without sound.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a coaxial electric power steering apparatus according to Embodiment 1 of the present invention in a non-operating state of an electromagnetic clutch.
FIG. 2 is a cross-sectional view of the coaxial type electric power steering apparatus according to Embodiment 1 of the present invention in an operating state of an electromagnetic clutch.
FIG. 3 is an explanatory diagram of a clutch used in the coaxial electric power steering device according to Embodiment 1 of the present invention;
FIG. 4 is a cross-sectional view of a conventional coaxial electric power steering device.
[Explanation of symbols]
1 Steering shaft, 2 Housing, 3 Electric motor, 5 Stator, 6 Rotating shaft,
7 rotor, 18 second ball screw nut,
19 first ball screw nut, 20 clutch,
21 third rotation transmitter, 23 electromagnetic clutch, 24 exciting coil,
25 first rotation transmitter, 26 separation spring, 27 second rotation transmitter,
28, 43 connecting portion, 30 first planetary speed reduction mechanism,
31, 39 Sun gear, 32, 40 Internal gear, 33, 41 pin,
34, 42 planetary gear, 35, 36 stopper, 44 groove,
45a, 45b Roller, 46, 47 Spring.

Claims (5)

A steering shaft that steers a vehicle wheel by steering a steering wheel, an electric motor that provides auxiliary thrust to the steering shaft via a first or second ball screw mechanism, and a first planetary speed reduction mechanism from the rotating shaft of the electric motor And the first rotation transmission element and the first rotation transmission element rotate to the first ball screw mechanism via a second rotation transmission element and a second planetary reduction mechanism that can be coupled and separated. Rotation is transmitted to the second ball screw mechanism from the rotation axis of the motor via the third rotation transmission element that holds the planet of the first planetary speed reduction mechanism. The first rotation transmission path, the operation of coupling and separating the first rotation transmission element and the second rotation transmission element, and the operation of fixing and releasing the third rotation transmission element Between the rotation transmission path of the second rotation transmission path and the second rotation transmission path. Coaxial type electric power steering apparatus comprising an electromagnetic clutch, speed reduction ratio of the second rotation transmitting path between the first rotation transmission path are different from each other to obtain. And a control means for controlling the electromagnetic clutch, wherein the control means detects a steering torque of the steering wheel to control the electromagnetic clutch, and the first rotation transmission path and the second rotation transmission path. The coaxial electric power steering apparatus according to claim 1, wherein: Control means for controlling the electromagnetic clutch, the control means detects the traveling speed of the vehicle to control the electromagnetic clutch, and the first rotation transmission path and the second rotation transmission path, The coaxial electric power steering apparatus according to claim 1, wherein: 4. The planetary gear reduction mechanism according to claim 1, wherein the first reduction mechanism and the second reduction mechanism are planetary gear reduction mechanisms including a sun gear, an internal gear, and a planetary gear. The coaxial electric power steering device according to the item. The first reduction mechanism and the second reduction mechanism, or one of them is a planetary roller reduction mechanism comprising a sun roller, an inscribed roller, and a planetary roller. The coaxial electric power steering device according to claim 3.

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