JPH0520624Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to an electric power steering device.

(Prior Art) Devices that assist steering force when driving at low speeds or while the vehicle is stopped, that is, power steering devices, include those that utilize hydraulic pressure and those that utilize the power of an electric motor. These electric types include those that use a rotary motor and those that use a linear motor. Japanese Unexamined Patent Publication No. 55-44058 or Japanese Utility Model Application No. 57-69764 discloses an electric power steering device using the linear motor. In both of these, an excitation coil is fixedly placed inside the rack shaft housing of the rack and pinion steering mechanism, and the resulting magnetic field is applied to a slider integrated with the rack shaft to generate electromagnetic force, thereby driving the rack shaft. assist in the ability to In the device described in Japanese Patent Application Laid-Open No. 55-44058, a large number of conductors are arranged in a slide rudder, and the steering assist force is controlled by controlling the current flowing therein. The device described in Japanese Utility Model Application Publication No. 57-69764 has a permanent magnet layer on the outer periphery of the rack shaft, and by controlling the current flowing through the coil of the stator, a thrust is generated in the permanent magnet layer and the desired amount is generated. Obtains steering assist power.

(Problems to be solved by the invention) What is described in the above-mentioned Japanese Patent Application Laid-open No. 55-44058 is as follows:
A slider constructed separately from the rack shaft is attached to the rack shaft, and since it is difficult to miniaturize the slider, there is a drawback that the rack and pinion steering mechanism cannot be used in common with a manual type steering mechanism. The slider described in the above-mentioned Japanese Utility Model Application Publication No. 57-69764 solves this drawback, but since the slider is simply a permanent magnet layer provided on the circumferential surface of a cylindrical rack shaft, it is not strong enough. It is not possible to perform proper magnetization.
It is difficult to generate sufficient thrust.

(Means for solving the problem) In order to solve the above problem, the present invention provides a circumferential groove on the circumferential surface of the rack shaft and magnetizes the protrusion formed by the groove. A linear motor is constructed by forming a salient pole magnet and providing a coil corresponding to the salient pole on the rack shaft housing side.

(Function) When a current controlled according to the steering torque detected from the shaft of the steering wheel is passed through the coil, attraction and repulsion occur between the resulting magnetic field and the salient pole magnet formed on the circumference of the rack shaft. A force is generated which provides thrust to the rack shaft and assists in steering effort. Since the magnet on the rack shaft side is composed of salient poles, it can be strongly magnetized and a sufficient thrust can be obtained.

(Example) FIG. 1 shows an example of the present invention. 1
is a steering shaft, and a steering handle (not shown) is attached to the upper end of the steering shaft. A pinion shaft 2, which is an input shaft of a rack and pinion type steering mechanism, is connected to the lower end of the steering shaft 1. The pinion shaft 2 is provided with a pinion that meshes with a rack provided on the rack shaft 3 within the pinion housing 4. The rack shaft 3 is supported so as to be slidable in the axial direction within a rack shaft housing 9 fixed to the vehicle body by end bushes 11, etc., and both ends thereof are connected to a well-known steering mechanism.

A part of the rack shaft 3 constitutes a slider of a linear pulse motor. That is, a large number of circumferential grooves 12 are provided at a constant pitch on the circumferential surface of the rack shaft 3, and the protrusions 13 formed between them are magnetized to form salient permanent magnets. A plurality of coils 10 are fixedly arranged on the inner surface of the rack shaft housing 9, and a linear pulse motor is constituted by these coils and the permanent magnet.

FIG. 2 shows one embodiment of the linear pulse motor. Projection 13a provided on rack shaft 3
are magnetized with different polarities for each strip to become salient permanent magnets, and a coil 10a that excites a ring-shaped magnetic pole 14a whose pitch coincides with these is wound around the axis of the rack shaft 3. .

When the torque sensor 5 installed on the pinion shaft 2 or the steering shaft 1 detects steering torque, its output signal is amplified by the amplification circuit 6 and sent to the characteristic calculation circuit 7 along with signals from the vehicle speed sensor, steering angle sensor, etc. is input. The characteristic calculation circuit 7 calculates the necessary steering assist force from these input signals and provides a control signal to the motor drive circuit 8. Motor drive circuit 8
supplies electric power to the coil 10a according to the control signal, and excites the magnetic pole 14a with a predetermined phase. As a result, the protrusion 13a of the rack shaft 3 operates as a slider of a linear pulse motor, giving thrust to the rack shaft 3.

FIG. 3 shows another embodiment of the linear pulse motor. In this example, the coil 10b is wound around axes X and Y that are perpendicular to the axis of the rack shaft 3, and is provided with magnetic poles 14b as required. Although four coils 10b are arranged radially, the number can be increased or decreased as appropriate.

In the example shown in FIG. 4, the coil 10b itself is
Although it is the same as the one in the figure, the protrusion 13b provided on the rack shaft 3 has a spiral shape, and the coil 1
The arrangement of 0b is also different in that it is spirally arranged accordingly. In addition, the polarity of the magnetized state changes in the circumferential direction as shown in the figure, and the coil 1
The excitation phase of 0b also differs in the circumferential direction. As a result, in this example, the protrusion 13b as a slider generates both rotational force and thrust, so in order to release the rotational force that is unnecessary as a steering assist force, the slider 15 is made separate from the rack shaft 3. It is formed into a cylindrical shape and fitted onto the rack shaft 3 so that it can only rotate.

As the torque sensor 5, a torsion bar used in a hydraulic power steering device can be used, and the torsion angle of the torsion bar can be detected with a potentiometer. However, other methods include a resistance wire strain meter, Differential transformer type displacement gauges and magnetic displacement gauges can also be used. Furthermore, if a screw gear or a helical gear is used as the pinion, a thrust corresponding to the steering force will be generated on the pinion shaft 2, and this may be detected by a piezoelectric element or the like. In addition to using an analog circuit as the characteristic calculation circuit, a digital circuit using a microcomputer may be used.

(Effects) As described above, in the present invention, a part of the rack shaft is configured as a slider of a linear motor, so that it does not become large unlike the case where separate sliders are connected. In addition, a protrusion is provided on the rack shaft to magnetize it,
Since it is a permanent magnet, it can be strongly magnetized and generate sufficient thrust, thereby providing sufficient steering assist force.

[Brief explanation of drawings]

FIG. 1 is a front view showing an embodiment of the present invention, and FIG. 2 is an example of a linear motor section.
B shows a front view and B shows a side view. FIGS. 3 and 4 show second and third examples of the linear motor section, with A being a front view and B being a side view, respectively. 3...Rack shaft, 5...Torque sensor, 9...
Rack shaft housing, 10... Coil, 13...
Projection.

Claims (1)

[Scope of utility model registration request] In a rack and pinion type electric power steering device that includes a linear motor that is controlled according to the output of a torque sensor that detects steering torque, and a rack shaft that receives thrust generated by the linear motor, the circumferential surface of the rack shaft An electric power steering device in which a protrusion in the circumferential direction is provided on the shaft, the protrusion is used as a permanent magnet as a slider of a linear motor, and a coil that acts on the slider is fixed in a rack shaft housing.