JP3606398B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in an electric power steering device of a type in which auxiliary torque is applied via a clutch.
[0002]
[Prior art]
For example, as proposed in Japanese Patent Application Laid-Open No. 61-81868 “Electric Power Steering Device”, there is a technique for appropriately adding auxiliary torque from the electric motor to the steering system in order to reduce the operating force of the steering wheel. .
FIG. 14 is a principle diagram of a conventional electric power steering apparatus, in which a steering torque from the steering wheel 101 is detected by a steering torque sensor 102, and an electric motor 104 is controlled by a control apparatus 103 based on the magnitude of the torque and the turning direction. And the electromagnetic clutch 105 are controlled and driven. At this time, the auxiliary torque from the electric motor 104 is applied to the steering system 107 via a booster mechanism 106 such as a worm gear or a hypoid gear, and the steering is performed with the total torque of the auxiliary torque and the steering torque from the steering wheel. Therefore, the steering can be performed easily and the steering torque itself can be reduced.
[0003]
FIG. 15 is a torque diagram of a conventional electric power steering apparatus. Since the steering torque sensor 102 is based on a torsion bar in a vehicle, it is represented by a spring mark.
The steering torque applied from the driver by the steering wheel 101 is TS, the torque detected by the steering torque sensor 102 is TC, the auxiliary torque added via the boost mechanism 106 is TA, and the load side torque (load torque) is TL. The following equation holds.
TS + TA = TL (a)
TC = TS (b)
If the generated torque of the motor 104 is TM, and the influence of inertia, viscosity resistance, and friction resistance of the motor or speed reducer is α,
TA = TM−α (c)
Substituting (c) into (a) and organizing TS,
TS = TL-TM + α (d)
[0004]
[Problems to be solved by the invention]
If the control gain of the motor 104 is k,
TM = k · TC (e)
According to (b) above
TM = k · TS (f)
Substituting (f) into (d) above and organizing TS,
TS = (TL + α) / (1 + k) (g)
[0005]
As described above, the total torque of the steering torque TS and the auxiliary torque TA matches the load torque TL. For example, assuming that the steering torque TS is 1/3 of the load torque TL, TS = (1/3) TL, substituting this into the above (g), and ignoring α,
(1/3) = 1 / (1 + k)
k = 2.
[0006]
FIG. 16 is a graph showing the relationship between the conventional steering torque signal and the motor torque, and is a graph based on TM = 2 · TC obtained by substituting k = 2 into the equation (e).
As is apparent from the graph, the control gain is high and the motor control tends to become unstable.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a first aspect of the present invention includes an input shaft, an intermediate shaft, and an output shaft in a steering system, wherein the input shaft and the intermediate shaft are connected by an auxiliary elastic member, The intermediate shaft and the output shaft are connected by an elastic member having a spring coefficient larger than that of the auxiliary elastic member, and the torque from the electric motor is positioned closer to the steering wheel than the steering torque detecting means via the transmission means and from the auxiliary elastic member. also with added to the steering system at a position remote from the steering wheel, the transmission means, the torque applied to the steering wheel you characterized in that interposed the clutch means in a non-connected state when the predetermined value or less.
[0008]
The input shaft and the intermediate shaft are connected by auxiliary elastic member, by the intermediate shaft output shaft and connected by an elastic member of a larger spring coefficient than the auxiliary elastic member, the auxiliary elastic member is somewhat to the steering wheel spring Since power is applied, a feeling of lingering remains and a steering feeling is improved.
In addition, since the torque from the electric motor is added to the steering system at a position closer to the steering wheel than the steering torque detecting means and at a position farther from the steering wheel than the auxiliary elastic member, the gain can be lowered. As a result, the motor control can be further stabilized. Further, since the electric motor system is separated from the steering system when the torque is less than a predetermined value by the clutch means, components accompanying the inertia and friction of the electric motor and the speed reducer can be cut, and the steering filling can be prevented from being lowered.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to the present invention. The electric power steering apparatus 1 includes a steering torque detecting means 3 for detecting a steering torque of a steering system generated by a steering wheel 2, and the steering torque. An electric motor 4 that generates an auxiliary torque in response to a signal from the detection means 3, and a clutch means that transmits the auxiliary torque generated by the electric motor 4 to the steering system at a position closer to the steering wheel 2 than the steering torque detection means 3 5 and a transmission means 6 such as a booster mechanism and an electric motor control means 10 for controlling the electric motor 4, and the wheels 9 and 9 are steered via a pinion 7 and a rack 8.
[0010]
FIG. 2 is a block diagram of the control device in the electric power steering apparatus of the present invention. The electric motor control means 10 determines a target auxiliary torque Ta to be generated by the electric motor 4 based on a signal Ts from the steering torque detection means 3. The target auxiliary torque determining means 11, the control signal generating means 14 for generating a control signal for driving the motor 4 based on the signal Ta from the target torque determining means 11, and the motor 4 based on the signal of the control signal generating means 14 The motor drive unit 15 is driven.
[0011]
FIG. 3 is a sectional view of the electric power steering apparatus (first embodiment) of the present invention.
The electric power steering device 1 is disposed on an input shaft 21 that is rotated by a steering wheel (not shown), a fork member 22 formed at a tip (lower end in the figure) of the input shaft 21, and an outer periphery of the fork member 22. A wheel 23, an intermediate shaft 24 disposed inside the fork member 22, and an elastic member 26 such as a torsion bar housed in the intermediate shaft 24 and mechanically connected via an upper pin 25. The output shaft 28 coupled to the front end (lower end in the figure) of the elastic member 26 via the spline shaft 27, the steering torque detecting means 3 disposed so as to surround the spline shaft 27, and the steering The clutch means 5 and the electric motor 4 are arranged at a position closer to the input shaft 21 than the torque detection means 3. The steering torque detecting means 3 and the clutch means 5 will be described in detail.
In the figure, 31 is a housing, 32 is an oil seal, and 33a, 33b and 33c are bearings.
[0012]
The steering torque detecting means 3 includes a cylindrical slider 34 spanned between the intermediate shaft 24 and the output shaft 28, a magnetic body 35 fitted to the outer peripheral surface of the slider 34, and a coil 36 surrounding the magnetic body 35. A slanted long hole 37 opened obliquely in the axial direction in the slider 34; a pin 38 protruding from the output shaft 28 and loosely fitted in the slanted long hole 37; and a groove 39 opened in the axial direction in the slider 34; The pin 12 protrudes from the intermediate shaft 24 and is loosely fitted in the groove 39, and the spring 13 urges the slider 34 downward in the figure to remove the play.
[0013]
The operation of the steering torque detecting means 3 will be described first. The steering torque given by the driver is transmitted in the order of the input shaft 21 → the clutch means 5 → the intermediate shaft 24 → the pin 25 → the elastic member 26 → the output shaft 28.
At this time, since the elastic member 26 is twisted, an angle shift corresponding to the steering torque occurs between the intermediate shaft 24 and the output shaft 28 which are front and rear members thereof. The slider 34 is connected to the pin 12 of the intermediate shaft 24 via the axial groove 39 and the pin 38 of the output shaft 28 via the inclined long hole 37. Accordingly, the slider 34 slides in the axial direction in accordance with the relative angular displacement between the intermediate shaft 24 and the output shaft 28. The amount of the slide is electrically measured by a differential transformer composed of a magnetic body 35 and a coil 36.
The elastic member 26 has a known relationship between torque and torsion angle, and the steering torque can be obtained by converting the amount of the slide into torque.
[0014]
4 is a cross-sectional view taken along line 4-4 of FIG. 3, showing the engagement state of the input shaft 21 and the intermediate shaft 24. The convex surfaces 24a, 24a are formed in the holes of the input shaft 21 having the parallel surfaces 21a, 21a. The intermediate shaft 24 is fitted, and there is a play of δ and δ in the rotation direction. Accordingly, the intermediate shaft 24 starts to rotate when the input shaft 21 is rotated by δ or more.
[0015]
FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 3, showing the engagement state of the intermediate shaft 24 and the output shaft 28. The convex surfaces 28a and 28a are formed in the holes of the intermediate shaft 24 having the parallel surfaces 24b and 24b. The output shaft 28 is fitted, and there is Δ and Δ play in the rotation direction.
As described with reference to FIG. 3, since the intermediate shaft 24 is connected to the output shaft 28 via the elastic member 26, the play Δ does not normally become zero. However, the elastic member 26 may be excessively twisted. At that time, the intermediate shaft 24 is directly connected to the output shaft 28. Since the torsion of the elastic member 26 does not increase beyond that, this structure provides a means for regulating the maximum torsion angle of the elastic member 26.
[0016]
FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 3, and the auxiliary torque generation and transmission mechanism will be described with reference to FIG.
As is well known, the electric motor 4 includes a stator (magnet) 4b housed in a case 4a, a rotor (electron winding) 4c surrounded by the stator 4b, and a motor shaft 4d. The structure is connected to the planetary speed reducer 60 via a friction engagement means 50 described later, and the rear end of the motor shaft 4d is supported by the bearing 41 and pressed by the transmission torque adjusting mechanism 40 via the bearing 41. It is .
[0017]
The transmission torque adjusting mechanism 40 includes a spring member 42, a push bolt 43, a lock nut 44, and a cover 45, and pushes out the push bolt 43 to push out the motor shaft 4d. Can be increased. When the push bolt 43 is returned, the transmission torque is reduced. When the adjustment is completed, the push bolt 43 may be locked with the lock nut 44 and the cover 45 may be covered.
[0018]
FIG. 7 is a perspective view for explaining the frictional engagement means and the planetary speed reducer of FIG. 6. The frictional engagement means 50 includes a male tapered surface 51 formed at the tip of the motor shaft 4d and the planetary speed reducer 60. This is a simple means that includes a tapered surface 52 formed on the inner ring 61 and is capable of generating a friction torque by thrusting the motor shaft 4d with the transmission torque adjusting mechanism 40.
[0019]
The planetary speed reducer 60 includes an inner ring 61, rolling elements 62 (... indicates a plurality, the same applies hereinafter), an outer ring 63, and a retainer 64 that accommodates the rolling elements 62. Thus, when the outer ring 63 is fixed and the inner ring 61 is rotated, the retainer 64 can be gently rotated via the rolling elements 62.
[0020]
Returning to FIG. 6, in this embodiment, the transmission means 6 as a boosting means is a worm reduction mechanism comprising a worm shaft 66 and the wheel 23, and the planetary reduction gear 60 is formed at one end of the worm shaft 66. The planetary speed reducer 60 supports the front end side of the motor shaft 4d.
Next, the clutch means 5 built in the wheel 23 will be described.
The clutch means 5 includes an inner peripheral surface 23a formed on the wheel 23, a cam surface 24c ... recessed in the intermediate shaft 24, and the cam surface 24c ... between the inner peripheral surface 23a. Steel balls 67... And springs 68... Arranged in a space surrounded by the inserted fork members 22, cam surfaces 24 c, inner peripheral surface 23 a, and fork members 22.・ ・ Consists of
[0021]
The operation of the electric power steering apparatus 1 described above will be described focusing on the clutch means 5.
FIGS. 8A to 8C are explanatory views of the operation of the clutch means according to the present invention.
In (a), when the worm shaft 66 and the wheel 23 are stopped, that is, when the electric motor is stopped, when the steering wheel (not shown) is rotated counterclockwise, the fork member 22 rotates as indicated by the arrow (1). Since the play δ described with reference to FIG. 4 exists, the fork member 22 rotates prior to the intermediate shaft 24, and the play δ becomes zero at the position (2) indicated by an imaginary line. From the position (2), the fork member 22 rotates the intermediate shaft 24 as shown by the arrow (3).
Therefore, when the electric motor is stopped, the output shaft can be driven manually by the steering wheel.
[0022]
In (b), the wheel 23 is rotated counterclockwise through the worm shaft 66 while the fork member 22 is in the neutral position (same as the initial state of (a) above). In this state, the intermediate shaft 24 remains stopped only by turning the wheel 23. This is because the steel ball 67 is in the unconnected position.
[0023]
In (c), the fork member 22 is rotated to the arrow (4) side while the worm shaft 66 is rotated. Due to the presence of the play δ, only the fork member 22 moves prior to the intermediate shaft 24. As a result, the steel ball 67 pushed by the spring 68 is sandwiched between the inner peripheral surface 23a and the cam surface 24c, and When this steel ball 67 is pushed by the wheel 23, it becomes a so-called “wedge” and mechanically connects the wheel 23 and the intermediate shaft 24, and the clutch is turned on. Thereafter, auxiliary torque from the electric motor is transmitted to the steering system.
[0024]
When the steering force acting on the steering wheel is weakened below a certain level, the transition is made from (c) to (b). That is, the fork member 22 forcibly removes the engaged steel ball 67, so that the clutch is turned off.
In (a) to (c), when the wheel 23 is rotated in the reverse direction (right rotation in the figure), the wedge action of the steel ball 67 is eliminated. Therefore, the action (c) occurs when the rotation direction of the wheel 23 and the rotation direction of the intermediate shaft 24 are the same, and the torque applied to the steer wheel is greater than a certain level.
(A)-(c) demonstrated the left rotation of a figure, However, Since the steel ball 67 is arrange | positioned symmetrically on the left and right of the fork member 22, the same effect | action is acquired also about a right rotation.
[0025]
Next, in the present invention, the actions of “providing the auxiliary torque closer to the steering wheel than the steering torque detecting means” and “providing the clutch means that is disconnected when the torque is not more than a predetermined value” are performed. A description will be made sequentially.
FIG. 9 is a torque diagram of the electric power steering apparatus according to the present invention. Since the steering torque detecting means 3 is based on a torsion bar in a vehicle, it is represented by a spring mark.
The steering torque applied from the driver by the steering wheel 2 is TS, the torque detected by the steering torque detection means 3 is TC, the auxiliary torque added via the transmission means 6 also serving as a boost mechanism is TA, and the load side torque When (load torque) is defined as TL, the following equation is established.
TS + TA = TL (a)
TC = TL (b)
When the generated torque of the motor 4 is TM and the influence of the inertia, viscosity resistance, and friction resistance of the motor is α,
TA = TM−α (c)
Substituting (c) into (a) and organizing TS,
TS = TL-TM + α (d)
[0026]
If the control gain of the motor 4 is k,
TM = k · TC (e)
According to (b) above
TM = k · TL (f)
Substituting (f) into (d) above,
TS = (1-k) TL + α (g)
[0027]
As described above, the total torque of the steering torque TS and the auxiliary torque TA matches the load torque TL. For example, assuming that the steering torque TS is 1/3 of the load torque TL, substituting TS = (1/3) TL into the above (g) and ignoring α,
(1/3) = 1-k
k = 2/3.
[0028]
FIG. 10 is a graph showing the relationship between the steering torque signal and the motor torque according to the present invention, and is a graph based on TM = 2/3 · TC obtained by substituting k = 2/3 into the equation (e). .
As is apparent from the graph, the control gain is low and the control of the motor is stable.
The above is the action of “providing auxiliary torque closer to the steering wheel than the steering torque detecting means”.
[0029]
Next, the operation of “providing clutch means that is disengaged when the torque is equal to or less than a predetermined value” will be described.
FIG. 11 is a graph showing the relationship between the motor torque and the auxiliary torque of the electric power steering apparatus of the present invention, where (a) shows a conventional comparative example and (b) shows a first embodiment of the present invention, both of which are horizontal. The axis is the motor torque TM, and the vertical axis is the auxiliary torque TA.
As described above, TA = TM−α, where α is the influence of the inertia, viscous resistance, and frictional resistance of the electric motor or reduction gear.
[0030]
In (a), if the first and third quadrants of the graph are set to the right (steering direction right) and the other is set to the left, a straight line a → b → c (TA = TM−α) is obtained in the region TM ≧ 0. In the region of TM <0, the straight line is symmetric with respect to the origin 0 of the straight line (d → e → f).
When the steering wheel is turned back from the right steering torque state to the left steering torque state, TA changes in the order of a → b → c → d → e → f, but TA is negative during b → c and the steering wheel is heavy. Become. The same applies during d → e.
Since the hatched area of the graph has the highest steering frequency, it is not preferable that the steering wheel becomes heavy.
[0031]
On the other hand, as described in detail in FIG. 8B, the first embodiment employs a structure in which the clutch means 5 is turned off and the electric motor system is separated from the steering system when the steering torque is below a certain level.
As a result, as shown in FIG. 11B, the relationship between TM and TA is a → b → e → f. That is, the α component associated with the inertia and friction of the electric motor and the speed reducer is cut, and the problem that the handle becomes heavy in the range of b → e has been solved.
This is the effect of “providing clutch means that is disconnected when torque is equal to or less than a predetermined value”.
[0032]
FIG. 12 is a cross-sectional view of the electric power steering apparatus (second embodiment) of the present invention. The same components as those in FIG.
That is, in the electric power steering apparatus 1A, the input shaft 21 has a hollow structure, and the intermediate shaft 24 has a thin elastic portion 71 (referred to as an “auxiliary elastic member 71” to distinguish it from the elastic member 26. The auxiliary elastic member. 71 is a member having a lower spring coefficient than that of the elastic member 26), and the auxiliary elastic member 71 is inserted into the hollow portion of the input shaft 21 and connected to each other by a pin 72. Others are the same as the first embodiment. Next, the operation of the auxiliary elastic member 71 will be described.
[0033]
FIGS. 13A and 13B are comparative operation diagrams of the first embodiment and the second embodiment.
(A) shows a first embodiment that does not include the auxiliary elastic member 71. For example, when the steering wheel is turned back from the left steering torque state to the right steering torque state, the clutch 5 is released by a → b, and b → 0. → e turns only the input shaft by a small amount by 2 × δ (see FIG. 4), and the clutch 5 is engaged by e → f.
[0034]
(B) shows a second embodiment provided with an auxiliary elastic member 71, the clutch 5 is disengaged by a → b, and the input shaft rotates a small amount by one δ shown in FIG. When c → 0 → d, the input shaft is further rotated by a small amount, and the torsion of the auxiliary elastic member is switched from −β to + β. From d → e, the input shaft is further rotated by a small amount by δ. Are combined.
In the second embodiment, while the clutch means 5 is switched from on to off to on, the auxiliary elastic member 71 imparts a certain amount of resilience to the steering wheel while indicated by -β and + β. There is no backlash between the shaft 21 and the intermediate shaft 24, and the steering feeling is improved.
[0035]
In this embodiment, the steering torque detection means 3 is located between the transmission means 6 and the pinion 7. However, the position is not limited to this. For example, the steering torque detection means 3 may be arranged on the rack 8 axis. The position can be freely set as long as it is on the exit side of the transmission means 6.
[0036]
【The invention's effect】
The present invention exhibits the following effects by the above configuration.
According to the first aspect, the input shaft and the intermediate shaft are connected by the auxiliary elastic member, and the intermediate shaft and the output shaft are connected by the elastic member having a spring coefficient larger than that of the auxiliary elastic member. Since a resilient force is applied, a feeling of grip remains and steering feeling is improved.
[0037]
In addition, since the torque from the electric motor is added to the steering system at a position closer to the steering wheel than the steering torque detecting means and at a position farther from the steering wheel than the auxiliary elastic member, the gain can be lowered. As a result, the motor control can be further stabilized. Further, since the motor system can be disconnected from the steering system when the torque is below a predetermined value by the clutch means, components associated with the inertia and friction of the motor and the speed reducer can be cut, and a decrease in steering feeling can be prevented.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to the present invention. FIG. 2 is a configuration diagram of a control device in the electric power steering apparatus according to the present invention. FIG. 3 is an electric power steering apparatus according to the present invention (first embodiment). FIG. 4 is a sectional view taken along line 4-4 in FIG. 3. FIG. 5 is a sectional view taken along line 5-5 in FIG. 3. FIG. 6 is a sectional view taken along line 6-6 in FIG. FIG. 8 is a perspective view for explaining the engaging means and the planetary speed reducer. FIG. 8 is an operation explanatory view of the clutch means according to the present invention. FIG. 9 is a torque diagram of the electric power steering apparatus according to the present invention. Fig. 11 is a graph showing the relationship between the steering torque signal and the motor torque. Fig. 11 is a graph showing the relationship between the motor torque and the auxiliary torque of the electric power steering device of the invention. Fig. 12 is an electric power steering device of the invention (second embodiment). ) [Fig. 13] FIG. 14 is a principle diagram of a conventional electric power steering device. FIG. 15 is a torque diagram of a conventional electric power steering device. FIG. 16 is a conventional steering torque signal and motor torque. Graph showing the relationship between the [signs]
DESCRIPTION OF SYMBOLS 1,1A ... Electric power steering apparatus, 2 ... Steering wheel, 3 ... Steering torque detection means, 4 ... Electric motor, 5 ... Clutch means, 6 ... Transmission means, 10 ... Electric motor control means, 11 ... Target auxiliary torque determination means, 14 ... control signal generating means, 21 ... input shaft, 22 ... fork member, 24 ... intermediate shaft, 26 ... elastic member, 28 ... output shaft, 50 ... friction engagement means, 60 ... planetary speed reducer, 71 ... auxiliary elastic member.

Claims (1)

Steering torque detecting means for detecting steering torque of the steering system ;
An electric motor for adding torque to the scan tearing system,
The electric power steering system comprising a motor control unit for driving and controlling the motor based on the signal before Symbol steering torque detection means,
The steering system includes an input shaft, an intermediate shaft, and an output shaft,
The input shaft and the intermediate shaft are connected by an auxiliary elastic member,
Connecting the intermediate shaft and the output shaft with an elastic member having a spring coefficient larger than that of the auxiliary elastic member;
Torque from the electric motor is added to the steering system via the transmission means at a position closer to the steering wheel than the steering torque detection means and at a position farther from the steering wheel than the auxiliary elastic member ,
The electric power steering apparatus according to claim 1, wherein the transmission means is provided with a clutch means that is disconnected when a torque applied to the steering wheel is equal to or less than a predetermined value.

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