JPH0696386B2 - Steering torque detector for electric power steering system - Google Patents

Description

The present invention relates to a steering torque detector for a power steering device, and more particularly to a steering torque detector for a power steering device, which detects the magnitude of steering torque. The present invention relates to a steering torque detector of an electric power steering device that controls a driving force of an electric motor of a power steering device according to a detection output.

(Prior Art) As a steering torque detector of a conventional electric power steering apparatus of this type, there is one disclosed in Japanese Patent Laid-Open No. 59-11966.

In this device, relative rotation between both shafts, which is generated by twisting a torsion bar connecting an input shaft and an output shaft, is made to rotate a ring carrier via a planetary gear, and the rotation of the ring gear is
Axial movement of the spool by a pin with a spherical head, one end of which fits into a notch on the outer peripheral surface of the ring gear and the other end of which is fitted and fixed to the center of the spool that can slide in the housing The position of the spool is converted into an electric signal by a potentiometer or the like to detect the steering torque. However, in this torque detector,
There are problems that the structure is complicated due to the mechanism for holding the neutral position of the spool and the detection speed is slow.

Therefore, in order to solve this problem, a steering torque detector using a strain gauge is disclosed in Japanese Patent Laid-Open No. 59-209964, which discloses an input shaft connected to a steering shaft of a vehicle and a vehicle. Sensor means for generating a first signal representing the magnitude of the torque applied to the twisting members connecting the output shafts connected to the steering gear box with each other, and a second signal representing the direction in which the torque is applied. A power amplifier having a magnitude responsive to a second signal that varies as a function of the first signal to produce an amplified signal having a polarity representative of the second signal; and a magnitude representative of the amplified signal. It is composed of a gear train that transmits the rotational torque output of a low-speed high-torque reversible motor that generates a rotational output having a direction to an output shaft.

(Problems to be Solved by the Invention) The steering torque detector has a bridge strain gauge attached to the center of a steel plate. Even if the strain gauge can be attached stably, the strain gauge is connected to the lead wire. When pulling out, the lead wire is wound around the steel plate in advance,
Or, it was necessary to use slip ring and the like, and the reliability was poor for repeated use.

Also, a method of directly attaching the strain gauge to the steering shaft can be considered, but if the steel plate to which the strain gauge is attached is a round bar such as a torsion bar, the attached strain gauge itself will be distorted in the initial state. , There was a problem with that output. In particular, in the case where the strain gauge is attached to the torch bar with a small diameter in order to increase the strain output, the strain gauge attachment state is not uniform, so strain occurs in the initial state, and the strain gauge bridge balance However, the reliability of the detection output is a problem.

Therefore, a technical problem of the present invention is to obtain a highly reliable electric signal from a torque sensor in a steering torque detector of an electric power steering device.

[Structure of Invention]

(Means for Solving Problems) The technical means taken for solving the above technical problems are:
A torque-axial displacement conversion mechanism that converts steering torque generated between the input shaft and the output shaft into an axial displacement, a plate that rotates integrally with the output shaft, and the output shaft by the torque-axial displacement conversion mechanism. A sliding member that is displaced in the axial direction above, a compression spring interposed between the plate and the sliding member, and strain gauges at both ends are attached, one end is fixed to the housing and the other end holds the steel ball by a holding means. And a cantilever supported by a sliding member through the steel ball is provided.
That is.

(Operation) A sliding member that displaces in the axial direction that constitutes a torque-axial displacement conversion mechanism that converts the direction and magnitude of the steering torque applied to the steering shaft into the axial displacement of the input shaft or the output shaft. Therefore, one end of the cantilever is axially displaced according to the direction and magnitude of the force of the steering torque through a steel ball with low contact resistance, and the cantilever is distorted between the other end fixed to the housing. Is detected by a strain gauge, and the detected output of the strain gauge is used to rotate the electric motor in a predetermined direction to apply a necessary rotational force to the output shaft. Further, since the compression spring is interposed between the plate and the sliding member, the compression spring constantly urges the plate to urge the sliding member. Displacement (backlash) can be prevented.

(Embodiment) In FIG. 1, a housing 11 is fixed to a vehicle, and divided parts 11a, 11b, 11c and 11d are integrally formed by bolts or welding.

The input shaft 12 in the housing 11 has a hollow shaft body 13 having a flange 13a on the outer periphery of its lower end, and a connection integrally fitted with a coupling pin 14 which is fitted into a hole portion of the hollow shaft body and extends in the radial direction. It consists of a shaft 15. An upper end of the hollow shaft body 13 is rotatably supported by the housing 11 via a needle bearing 16. A spline 13b for connecting to a steering shaft (not shown) is formed on the upper portion of the inner wall of the hollow shaft body 13.

The output shaft 17 in the housing 11 has a connecting shaft 15 at its upper end.
Has a fitting hole 17a into which the lower part thereof is loosely fitted, and its center and lower ends are rotatably supported by the housings 11b and 11c via ball bearings 18 and 19, respectively.

Inside the housing 11c at the bottom of the housing 11 in the drawing, a necessary number of gears for transmitting the output of the electric motor 20 fixed to the housing 11b from the electric motor output shaft 20a to the output shaft 17 is used.
A reduction gear mechanism 21 for reducing the rotation of the is arranged. The reduction gear mechanism 21 includes a gear 21a coaxial with the motor output shaft 20a.
And gears 25 and 26 mounted on a shaft 24 rotatably supported in the housing 11b and the housing 11c via ball bearings 22 and 23, and a gear 27 coaxial with the output shaft 17.

Inside the housing 11a above the housing 11, there is arranged a torque-axial displacement conversion mechanism 28 that causes a torsion angle displacement corresponding to the torque of the input shaft 12 between the two shafts. The torque-axial displacement conversion mechanism 28 is composed of a torque parallel detector 28A (see FIG. 2) and an axial conversion means 28B (see FIG. 3).

In FIG. 1 and FIG. 2, the torque balance detector 28A is
A spring formed by molding a wire for spring into a substantially C shape
29, a pin 30 fixed to the flange 13a of the hollow shaft body 13 and sandwiched between both ends 29a and 29b of the tip of the spring 29 which are parallel to each other, and a pin 31 fixed to the output shaft 17 in the vertical direction. A pin 32 which has a groove 32a slidably fitted in, is fixed to a plate 32 which is designed to rotate integrally with the output shaft 17, and is sandwiched between both ends 29a, 29b of a spring 29. It consists of The plate 32 has a boss portion 32b guided by an arcuate portion 29c between both ends of the spring 29. A washer 34 is interposed between the spring 29 and the lower end surface of the hollow shaft 13.

In the torque balance detection unit 28A having such a configuration, when the torque is not applied to the input shaft 12, the spring 29
However, both ends thereof are restored to the state where they are closest to each other with the pins 30 and 33 interposed therebetween, and the input shaft 12 and the output shaft 17 have a neutral positional relationship of zero torsional angular displacement. Further, when torque is applied to the input shaft 12, this acts so as to separate the both ends 29a, 29b of the spring 29, and the elastic deformation of the spring 29 causes the input shaft 12 and the output shaft 17 to be separated from each other. Torsional angular displacement occurs according to the torque of.

Axial direction conversion means 28B is arranged below the torque balance detector 28A. As shown in FIGS. 1 and 3, the axial direction converting means 28B is fixed in the lower end portion of the connecting shaft body 15 of the input shaft 12 and passes through a relief hole 17b provided in the output shaft 17 to radiate the axial direction. And a long hole 37 into which the pin 36 is slidably fitted by being slidably fitted to the upper end of the output shaft 17.
An upper flange 3 provided at the lower end of the sliding member 37 having a
7b and the lower flange 37c, a pin 43 fixed to the output shaft 17 and extending in the radial direction are slidably fitted, and are composed of a sliding member 37 having a slot 37d in the direction of the output shaft 17.

The sliding member 37 can be displaced in the vertical direction with respect to the output shaft 17 by the pin 43 and the slot 37d, but cannot rotate. Then, the sliding member 37 is fitted with a tubular body 44 for preventing the pin 36 and the pin 43 from coming off.

The long hole 37a of the sliding member 37 is provided in the spiral direction, and when the torsional angular displacement between the input shaft 12 and the output shaft 17 is zero, the pin 36
Is located in the center between both ends of the long hole 37a, and the input shaft 12 and the output shaft 17 are
When twist angle displacement occurs between the pin 36 and the long hole 37
Due to the contact with the side surface of a, the sliding member 37 is displaced by the cam action on the output shaft 17 in the axial direction according to the amount of torsional angular displacement,
The upper flange 37B and the lower flange 37c are adapted to be displaced.

Slider groove between upper flange 37b and lower flange 37c
As shown in FIG. 5, the steel ball 39 held by the caulking connection of the first base 100a and the second base 100b is clamped at the free end of one end of the cantilever 40, and slides by the steel ball 39 at 37e. The contact resistance with respect to the displacement of the upper flange 37b and the lower flange 37c of the member 37 is reduced.

The other end of the cantilever 40 is fixed to the housing 11d with a bolt 42.
It is firmly screwed to the mounting base 45 fixed to. The mounting base 45 seals the housing 11d with an O-ring or the like as will be described later in detail, and the cantilever 40 is firmly fixed by screwing it with a bolt 42 with a washer interposed. Moreover, it is accurately positioned and attached. The cantilever 40 has strain gauges 41a, 41b, 41c, 41c having resistance bridges on both sides from the center to the mounting hole side of the bolt 42, as shown in the perspective view of the relationship between the cantilever and the steel ball in FIG.
A strain gauge that forms a resistance bridge when d is formed and no displacement is applied to the free end of the cantilever 40.
The output of 41a, 41b, 41c, 41d is minimized, and when the maximum displacement of the free end of the cantilever 40 is given, the output of the strain gauges 41a, 41b, 41c, 41d forming a resistance bridge is maximized. Is.

In this embodiment, the material of the cantilever 40 is phosphor bronze, an insulating layer is coated on the surface of the cantilever 40, and the surface of the strain gauges 41a, 41b, 41c, 41d is a thin film circuit on the insulating layer. Moisture-proof coating is applied to eliminate the effect of humidity, and silicone rubber is used for coating.

FIG. 6 is a perspective view of another embodiment of the holding means for the steel balls of the cantilever, in which the first flange 200a and the second flange 200b are screwed to the free end of the cantilever 40 to fix the steel balls. 39, and strain gauges 41a, 41b,
41c and 41d are pasted with an adhesive such as a thermosetting adhesive. The surface treatment of the strain gauges 41a, 41b, 41c, 41d is as follows.
The procedure is the same as shown.

The strain gauges 41a, 41b, 41c, 41d are bridge circuits,
In FIG. 7 showing a well-known distortion detecting circuit for extracting the output, E is a constant voltage power source and AMP is an amplifying circuit. FIG. 8 shows the relationship between the torque detection output voltage of the input shaft 12 and the vertical displacement of the sliding member 37. The vertical displacement of the sliding member 37 and the torque detection output voltage are the amplification circuit. It can be arbitrarily set by the amplification factor or bias voltage of the AMP, the resistance value of the strain gauge, and the like.

In the above embodiment, the outer periphery of the pin 36 fixed to the connecting shaft body 15 integrally coupled to the input shaft 12 by the coupling pin 14 and the sliding member.
The gap of the long hole 37a of 37 has an influence on the correspondence between the torsional angular displacement between the input shaft 12 and the output shaft 17 and the axial displacement of the sliding member 37. , Sliding member
A compression spring (60) is interposed between the upper flange (37b) of the plate (37) and the plate (32), and the compression spring (60) causes a sliding member.
It is preferable to urge the pin 37 downward so that the outer periphery of the pin 36 contacts only the upper side surface of the elongated hole 37a.

Further, the relative vertical displacement (play) between the input shaft 12 and the output shaft 17 is eliminated, and the gap between the fitting portions of the shafts 12 and 17 causes twisting between the shafts to cause the pin 36 and the long hole 37a. Of the sliding member 37 and the balance between the upper flange 37b and the lower flange 37c of the sliding member 37 and the cantilever 40 supporting the free end through the steel ball 39 between the flanges are prevented. Therefore, as shown in FIG. 3, a tapered recess 15a is formed at the center of the lower end surface of the connecting shaft body 15 integrally connected to the input shaft 12 by the connecting pin 14, and a fitting hole 17a of the output shaft 17 is formed. Tapered recesses 17c are provided at the center of the bottom surface, and both tapered recesses 15c
Hollow shaft body 1 of input shaft 12 with steel ball 46 interposed between a and 17c
The upper side of the flange 13a of 3 is provided with a compression spring 48 whose upper end is received by the inner surface of the housing 11a via a needle bearing (thrust bearing) 47 and whose lower end is received by the flange 13a. 12 steel balls
It is pressed against the output shaft 17 via 46.

In FIG. 1, 50 is a retaining ring screwed into the housing, and 51, 52 and 53 are snap rings.

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

When the driver applies a steering torque to the input shaft 12, the relative angular displacement corresponding to the torque of the input shaft 12 is changed by the elastic force of the spring 29 that constitutes the torque balance detection unit 28A.
This angular displacement occurs between 17 and the sliding member 37 constituting the axial direction converting means 28B is set as the axial displacement, and the displacement of the sliding member 37 is held by the holding means 100 at the free end of the cantilever 40. Since the contact resistance is reduced by the steel ball 39 and the free end of the cantilever 40 is displaced, the strain gauge 41 of the cantilever 40 outputs the torque magnitude applied to the input shaft 12 and the torque detection signal output in that direction. Can be obtained.

Therefore, by using this torque detection signal output, as an input of the controller of the electric power steering device, the electric power is supplied to the electric motor 20 by the output, and the rotational force of the electric motor 20 is transmitted through the reduction gear mechanism 21. As a result, a rotational force can be applied to the output shaft 17.

When carrying out the present invention, in the present embodiment, as the torque-axial direction displacement converting mechanism, the torque balance detecting unit and the axial direction converting means are used to convert the steering torque into axial displacement, that is, vertical displacement. However, the present invention is not limited to the above-described embodiment when implementing the present invention, and may be any means that converts steering torque into displacement of reciprocal movement, preferably axial displacement proportional to steering torque. .

Further, since the sliding member constituting the torque-axial displacement conversion mechanism moves in the axial direction in accordance with the torque of the means for converting the displacement in the axial direction, the torque is changed by using the input shaft or the output shaft as a ball screw. When a torque-axial displacement conversion mechanism including a mechanism in which the ball screw rotates in accordance with the above, the sliding member can be a nut-shaped member that is screwed with the ball screw. Alternatively, it may be a member that engages with the ball screw portion.

Furthermore, although the housing of this embodiment is divided into four, it is not necessarily limited to this when implementing the present invention. In particular, the housing 11d is designed with its opening so that the cantilever can be taken out freely, but it may be integrated with another housing as long as the cantilever can be freely attached and detached.

〔The invention's effect〕

In the present invention, it suffices to form a strain gauge on a flat plate-shaped cantilever, and even if the strain gauges used as a resistance bridge circuit are stuck, they can be easily and uniformly formed.
Since the bridge of the strain gauge can be easily balanced, a large output with high noise resistance and drift resistance can be obtained, and the reliability of the output can be improved. Moreover, since the steering torque detector (cantilever) is independent, it can be easily replaced.

It is also conceivable to fix the steel ball directly to the free end of the cantilever by welding, gluing, etc., but it is difficult to ensure the accuracy of the fitting gap with the groove of the sliding member and the durability against repeated use. There is a possibility that a malfunction of the power steering device, that is, a problem that the steering wheel operating force is heavy may occur. In the present invention, however, since the steel ball is reliably fixed to the cantilever by the holding means, the above-mentioned problems do not occur. Moreover, since the compression spring is interposed between the plate and the sliding member,
Since the plate constantly biases the sliding member by this compression spring, relative vertical displacement (backlash) of the torque-axial displacement conversion mechanism can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a steering torque detector of an electric power steering apparatus according to the present invention, FIG. 2 is a sectional view of a main part of a torque balance detecting portion in FIG. 1, and FIG. FIG. 1 is a sectional view of an essential part of the axial displacement conversion means in FIG. 1, and FIG.
FIG. 5 is a perspective view of the cantilever in the drawing, FIG. 5 is a sectional view taken along the line AA in FIG. 4, and FIG. 6 is a sectional view of a main portion of the cantilever showing another embodiment of the holding means for the steel ball of the cantilever. FIG. 7 is a known strain detection circuit diagram in which a strain gauge is used as a bridge circuit to take out an output, and FIG. 8 is a characteristic diagram showing a sliding member displacement amount-torque detection output voltage characteristic. 11,11a, 11b, 11c, 11d …… Housing, 12 …… Input shaft, 17…
Output shaft, 28 ... Torque-axial displacement conversion mechanism, 28A ...
Torque balance detector, 28B …… Axial direction converter, 37 …… Sliding member, 39 …… Steel ball, 40 …… Cantilever, 41a, 41b, 41c, 41d
…… Strain gauge, 100 …… Holding means In the drawings, the same reference numerals and symbols indicate the same or corresponding parts.

Continuation of the front page (56) Reference JP-A-47-15824 (JP, A) JP-A-58-53562 (JP, A) JP-A-58-133957 (JP, A) JP-A-57-190240 (JP , A) JP 58-177773 (JP, A) Actual opening Sho 60-137339 (JP, U) Actual opening Sho 60-189472 (JP, U) Actual opening Sho 59-72529 (JP, U) Actual opening Sho 59-68235 (JP, U) Actual development Sho-59-68234 (JP, U)

Claims (1)

[Claims] 1. A steering torque detector of an electric power steering device for detecting a steering torque applied between an input shaft connected to a steering wheel of a vehicle and an output shaft connected to a steering gear and a torque transmission device of an electric motor. In the above, the torque-axial displacement conversion mechanism and the cantilever are configured, and the torque-axial displacement conversion mechanism converts steering torque generated between the input shaft and the output shaft into axial displacement, and the output shaft and the output shaft. A plate that rotates together
The cantilever includes a sliding member that slides on the output shaft, and a compression spring that is interposed between the plate and the sliding member. Steering torque for an electric power steering device, comprising: a holding means that is supported by a sliding member and has strain gauges attached to both end surfaces thereof, and holds a spherical member at the other end supported by the sliding member. Detector.