JPH0522465Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an electric power steering device that reduces steering force by applying torque generated by an electric motor to a steering system.

(Prior art) Conventionally, as an electric power steering device that uses the power of an electric motor, for example,
There is one shown in Publication No. 59-50864. This type of electric power steering device uses a shaft-like member (rack shaft) that is supported by the case so that it can be displaced in the axial direction.
A rack part is formed on one end side, and a pinion part connected to the steering shaft via a joint etc. meshes with this rack part, and one end side of the shaft member is supported by the pinion part and the rack part. Rotation of the steering wheel is transmitted to the steered wheels as axial displacement via the shaft-like member.

Further, a helical groove is formed on the outer periphery of the other end of the shaft-like member, and a screw shaft made of this shaft-like member, and a nut member that is ringed around the outer periphery of the helical groove of the screw shaft and has a helical groove on its inner peripheral surface. The other end side of the shaft member is supported by a ball nut mechanism composed of a ball inserted between both spiral grooves, and a rotor of an electric motor is fixed to the outer periphery of the nut member, so that the electric motor is connected to the ball nut mechanism. It has a directly connected structure.

The rotational torque of the electric motor is converted into axial displacement of a shaft member in a ball screw mechanism and transmitted, and smooth operation is expected with low friction loss and high transmission efficiency.

(Problem to be solved by the invention) In general, the larger the lead angle of the ball screw mechanism used in electric power steering devices, the more
Transmission efficiency increases.

On the other hand, when the lead angle is β, the lead is L, and the shaft diameter is ds, the relational expression tanβ=L/(πds) holds true. The motor torque, reduction ratio, and lead L are determined based on the design specifications, and since L remains constant thereafter, it can be seen from the above relational expression that the smaller the shaft diameter ds, the larger the lead angle β becomes.

Therefore, in the ball screw mechanism, the smaller the diameter of the screw shaft, the higher the transmission efficiency can be obtained.

However, in the conventional electric power steering device described above, a spiral groove is formed on the rack shaft that receives loads in the axial and shear directions, and this is used as a threaded shaft, so it is difficult to reduce the diameter of the rack shaft due to its strength. However, it has been difficult to improve the transmission efficiency of the ball screw mechanism and the output loss of the electric motor has increased, and it has also been difficult to improve the characteristics during the steering return operation.

Furthermore, in the past, since the rack shaft, which has a spiral groove over the required range, moves in the axial direction, it is difficult to seal the rack housing and the rack shaft, leading to the intrusion of dust and the generation of rust.
If the rack has a rubber boot at the end of the shaft, there is a possibility that the loss of the rubber boot will have an adverse effect. As a result, there was a risk that the ball screw mechanism would not operate smoothly and the steering feeling would be deteriorated.

Therefore, the present invention provides the screw shaft of the ball screw mechanism separately from the rack shaft and makes it possible to reduce the diameter of this screw shaft, thereby increasing the transmission efficiency of the ball screw mechanism and improving the steering return characteristics. It is an object of the present invention to provide an electric power steering device that can reduce the output loss of an electric motor, and further improve reliability by making sealing easy and reliable.

(Means for Solving the Problems and Their Effects) In order to achieve the above object, the present invention connects the steering wheel to the steering wheels via a rack and pinion mechanism, and transfers the torque generated by the electric motor to the rack and pinion mechanism. In an electric power steering device that aims to reduce steering force by applying it to a rack shaft, a screw shaft, which is arranged parallel to and apart from the rack shaft and has a spiral groove carved on its outer circumferential surface, is connected to the electric motor. At the same time, a nut member having a spiral groove carved on its inner peripheral surface is coupled to the spiral groove of the screw shaft via a ball, and this nut member is coupled to the rack shaft via an elastic member. Features.

When the steering wheel is operated, the electric motor drives a screw shaft which moves a nut member which in turn drives a rack shaft via an elastic member.

The steering wheel is connected to the steered wheels via a rack and pinion mechanism, and the torque of the electric motor is applied to the rack shaft to reduce the steering force.

(Example) An example of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a longitudinal sectional view showing the electric power steering device of this embodiment, and in FIG.
2 is a pinion shaft connected to the steering wheel via a steering shaft (not shown); 2 is a pinion holder that rotatably supports the pinion shaft 1; and this pinion holder 2 includes a steering torque sensor 3, a steering rotation sensor 4, A control device 5 is provided that drives and controls an electric motor 10, which will be described later, based on detection signals from each of these sensors. Also,
Reference numeral 7 denotes a rack shaft having a rack portion 7a that meshes with a pinion (not shown) of the pinion shaft 1. As the pinion shaft 1 rotates, the rack shaft 7 is supported by a bearing 9 against a rack housing 8 and moves in the left-right direction in the figure. can do.

Further, an electric motor 10 is provided around the rack shaft 7. This electric motor 10 includes a cylindrical stator 11 that is integrally fixed to a rack housing 8.
, at least one pair of magnets 12 fixed to the inner surface of the stator 11 , and a rotor 13 rotatably disposed around the rack shaft 7 . The rotor 13 is connected to the rack shaft 7 via bearings 14 and 15.
A cylindrical shaft 16 is rotatably mounted on the cylindrical shaft 16, and an iron core 1 having a skew groove on the outer periphery of the cylindrical shaft 16 is provided.
7. Multiple windings 18 are sequentially and integrally wrapped around each other. Further, the cylindrical shaft 16 is provided with a commutator 19 connected to the multiplex winding 18, and a brush 20 in pressure contact with the commutator 19 is housed in a brush holder 21 fixed to the housing 8.
and are connected by lead wires.

Furthermore, a gear 24 is formed on the outer periphery of the cylinder shaft 16 on the right end side in the figure, and a gear 25 having substantially the same diameter meshes with this gear 24. This gear 25 is integrally fixed to the right end in the figure of a screw shaft 26 having a spiral groove 26a over a required range. This screw shaft 2
6 is disposed in a rack housing 8 parallel to the rack shaft 7, and its both ends are supported by bearings 27 and 28. Therefore, the screw shaft 26 is connected to the gear 2
It is connected to the electric motor 10 via 4 and 25, and the electric motor power is transmitted thereto. On the outer periphery of this screw shaft 26,
As shown in FIG. 2, a non-rotating nut member 30 having a helical groove 30a formed on its inner circumferential surface is ring-mounted, and the helical groove 26a-30 between the screw shaft 26 and the nut member 30
A plurality of balls 31 are interposed therebetween, and a ball screw mechanism 32 is constituted by the screw shaft 26, the balls 31, and the nut member 30. The nut member 30 is provided with flanges 30a and 30b, which are connected to a rack holder 37 by bolts 35 and 36 via bushes 33 and 34, respectively. The rack holder 37 is integrally fixed to the rack shaft 7 by bolts 38, and the screw movement of the nut member 30 is transmitted as axial movement of the rack shaft 7 via the bolts 35, 36 and the rack holder 37. The bushes 33, 34 each consist of an inner cylinder 33a, 34a, an outer cylinder 33b, 34b, and elastic members 33c, 34c interposed between them. It is formed so rigid that it can be tolerated even if the parallel state is slightly lost. Therefore, even if a bending moment due to a steering reaction force is applied to the rack shaft 7, it is absorbed by the elastic members 33c, 34c, and unnecessary loads are prevented from being applied to the screw shaft 26 of the ball screw mechanism 32. In addition, 40, 41, 42, 4 in Figure 1
3, 44, and 45 are seal members, respectively.

Therefore, in this embodiment, the screw shaft 26 constituting the ball screw mechanism 32 is provided separately from the rack shaft 7, so that the screw shaft 26 is provided separately from the rack shaft 7.
6 can be made smaller, and if the leads are the same, the lead angle of the spiral groove 26a can be increased, and the transmission efficiency of the ball screw mechanism 32 can be increased. In particular, when the steering wheel is returned, the axial movement of the nut member 30 is converted into rotation of the screw shaft 26, and the reverse transmission efficiency is significantly increased, thereby improving the feeling of the return operation. As a result, as the transmission efficiency is improved, the output loss and power consumption when driving the motor can be reduced.

Further, since no spiral groove is formed on the rack shaft 7, the rack shaft 7 can be easily sealed, and the intrusion of dust and the occurrence of rust can be reliably prevented, thereby improving reliability.

Furthermore, since the electric motor 10 is arranged concentrically with the rack shaft 7 and no ball screw mechanism is interposed between them, the diameter of the rotor 13 of the electric motor 10 can be increased to increase the output torque. At the same time, it is possible to reduce the external size of the motor, and the device can be made more compact. Furthermore, by increasing the output of the electric motor 10, the lead of the ball screw mechanism 32 can be increased, further improving the transmission efficiency and reducing the maximum rotational speed of the electric motor 10. It also becomes possible to reduce noise generation.

(Effects of the invention) As explained above, according to the invention, the rack shaft and the screw shaft are arranged parallel to each other with a distance between them, so that only the rack shaft receives the load in the shear direction due to steering operation. Therefore, the shaft diameter of the screw shaft can be made smaller. By reducing the diameter of the screw shaft, its lead angle can be increased, and the transmission efficiency of the ball screw mechanism can be increased.

In addition, since the nut member is connected to the screw shaft and the nut member is connected to the rack shaft via the elastic member, even if the rack shaft is bent due to steering operation, this effect is absorbed by the elastic member and the nut member Not as good as that. Therefore, the fit between the nut member and the screw shaft is maintained well, and in cooperation with the high transmission efficiency of the ball screw mechanism, output loss of the electric motor can be prevented and the steering feeling can also be maintained well.

Furthermore, since the rack shaft and the screw shaft are arranged separately, and no spiral groove is provided on the rack shaft, the sealing between the rack housing and the rack shaft becomes easy and reliable, and the reliability of the seal is increased.

[Brief description of the drawings]

1 and 2 show an embodiment of the present invention, in which FIG. 1 is a longitudinal sectional view of an electric power steering device, and FIG. 2 is a sectional view taken along the - arrow in FIG. In the drawings, 1... Pinion shaft, 2... Pinion holder, 3... Steering torque sensor, 7... Rack shaft, 10... Electric motor, 26, 26a... Screw shaft and its spiral groove, 30, 30a... Nut member and its spiral groove, 31... Ball, 33c, 34
c...An elastic member.

Claims (1)

[Claims for Utility Model Registration] A steering wheel is connected to a steering wheel via a rack and pinion mechanism, and the torque generated by an electric motor is applied to the rack shaft of the rack and pinion mechanism to reduce the steering force. In the electric power steering device, a screw shaft arranged parallel to and apart from the rack shaft and having a helical groove carved on its outer peripheral surface is connected to the electric motor, and a screw shaft is connected to the electric motor and has a spiral groove carved on its inner peripheral surface. An electric power steering device characterized in that a nut member is connected to the helical groove of the screw shaft via a ball, and the nut member is connected to the rack shaft via an elastic member.