JP2539629B2 - Electric power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric power steering device, and more specifically to a power steering device in which an electric motor assists an operating force required for steering a vehicle.

[Conventional technology]

FIG. 2 is a cross-sectional view of an electric power steering device according to the prior application of the present inventors (Actual Application No. 61-127562). An upper column shaft 2A having a steering wheel 1 attached to an upper end is rotatably supported by a column housing 3, and a lower end portion thereof is connected to a rack 5 of a steering mechanism via a torsion bar 4 and a pinion 5a. It is connected to the upper side of the side column shaft 2B. A torque sensor 6 for detecting the torque acting on the upper column shaft 2A is provided in the middle of the torsion bar 4. A known direct drive motor DM is provided on the upper side of the lower column shaft 2B. The direct drive motor DM surrounds the rotor 7 fixed to the lower column shaft 2B and the rotor 7, The stator 8 has a coil 8a, and the stator 8 is fixed inside a motor case 9 attached to the column housing 3.

At the lower part of the motor case 9, a rotational position sensor 10 composed of a Hall element for detecting the rotational position of the rotor 7 is arranged to excite the coil in accordance with the magnetic pole position of the rotor 7. The output of the torque sensor 6 is the motor case 9
It is led out via a slip ring 11 provided in the column housing 3 on the upper side of the. Also the rotational position sensor
The output of 10 and both ends of the coil 8a of the stator 8 are led out from the motor case by lead wires (not shown).

In addition, this electric power steering device is equipped with a steering wheel 1
When you rotate the upper column shaft 2A
Torque is applied to the torque sensor 6, and the torque sensor 6 detects the torque. The output of the torque sensor 6 and the rotational position sensor
The energization control unit (not shown) is switching-controlled based on the output of 10 and the current flows through the coil 8a of the stator 8, the rotor 7 rotates together with the lower column shaft 2B, and the rotational force is added to assist the steering force. Will be given.

[Problems to be solved by the invention]

As described above, in the conventional electric power steering device, the torque sensor 6 is provided at a position different from the mounting position of the direct drive motor DM, so that the entire power steering device becomes large and the cost of the device increases. There is.

In view of the above problems, it is an object of the present invention to provide a small and inexpensive electric power steering device by providing a rotational position sensor that detects the rotational position of the rotor of a direct drive motor.

[Means for solving problems]

In the electric power steering apparatus according to the present invention, a rotational position sensor that detects the rotational position of the rotor of the direct drive motor is attached to the upper column shaft, and the rotational position sensor detects the amount of twist between the upper column shaft and the lower column shaft. It is configured to detect.

[Action]

When the steered wheels are rotated, the upper column shaft is twisted with respect to the lower column shaft via the torsion bar. Since the rotor of the motor is fixed to the lower column shaft, the rotational position sensor attached to the upper column shaft detects the rotational position relative to the rotor. The output signal of the rotational position sensor corresponds to the twist between the upper and lower column shafts,
Detect the torque acting on the upper column shaft.

Therefore, the rotor can be rotated based on the output signal of the rotational position sensor to assist the steering force.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing its embodiments. FIG. 1 is a partially cutaway sectional view of an electric power steering device according to the present invention. An upper column shaft 2A having steering wheels 1 attached to the upper ends is rotatably supported by a column housing 3. The lower end of the upper column shaft 2A faces the upper end of the lower column shaft 2B, whose lower end is connected to the rack 5 of the steering mechanism via the pinion 5a, at an appropriate distance. And the upper column shaft 2A
One end of a torsion bar 4 disposed in a hollow portion P formed at the axis of the lower column shaft 2B is fixed to the lower end of the torsion bar 4, and the other end of the torsion bar 4 is attached to the lower column shaft 2B. It is fixed. The twist amount of the upper column shaft 2A is limited to a rotation angle range of 3 to 5 °.
A known direct drive motor DM is provided on the upper side of the lower column shaft 2B. The direct drive motor DM is composed of a rotor 7 fitted on the lower column shaft 2B and a stator 8 surrounding the rotor 7 and facing each other and having a coil 8a. The stator 8 is a lower end of the column housing 3. It is fixed to the inside of the motor case 9 attached to the section. The motor case 9 is composed of, for example, a Hall element fixed to the lower end of the upper column shaft 2A, and detects the rotational position of the rotor 7 by the output voltage that detects the leakage magnetic flux of the magnetic pole of the rotor 7 to detect the upper column shaft 2A.
A rotational position sensor 12 for detecting the twist of the is provided. Further, in the lower part of the motor case 9, a rotational position sensor 10 composed of a Hall element for detecting the rotational position of the rotor 7 is provided in order to excite the coil 8a of the stator 8 according to the magnetic pole position of the rotor 7. There is. This rotational position sensor
Three Hall elements 10 (only one is shown) are provided at an appropriate distance in the circumferential direction of the rotor 7. Further, the rotational position sensor 10 detects a signal which is an output voltage obtained by detecting the leakage magnetic flux of the magnetic pole of the rotor 7 by each Hall element. The output signal of the rotational position sensor 12 is derived via a slip ring 11 provided on the upper side of the motor case 9, and both ends of the coil 8a of the stator 8 and the respective outlet ends of the rotational position sensor 10 are connected to the motor. It extends through the case 9.

The electric power steering device configured in this way is
Normally, the rotational position sensor 12 detects the intermediate position of the adjacent magnetic poles arranged side by side in the circumferential direction of the rotor 7. On the other hand, the rotational position sensor 10 detects the rotational position of the rotor 7 so that when the rotor 7 is driven, a current flows through the coil 8a of the stator 8 according to the magnetic pole position of the rotor 7.

When the steering wheel 1 is rotated, the upper column shaft 2A is twisted with respect to the lower column shaft 2B via the torsion bar 4 by the operation. Therefore, the rotational position sensor 12 rotates together with the upper column shaft 2A to detect a rotational position of the rotor 7 different from that before, that is, a twist between the upper and lower column shafts. The output signal of the rotational position sensor 12 changes according to the amount of twist (torque) of the upper column shaft 2A. When this output signal is given to an energization control unit (not shown), the energization control unit performs a switching operation based on the output signal, and the switching-controlled current is based on the rotational position of the rotor 7 detected by the rotational position sensor 10. And flows through the coil 8a of the stator 8. Therefore, the rotor 7 rotates together with the lower column shaft 2B, and the direct live motor DM assists the steering force according to the detected twist amount. When the steering operation is stopped in one direction, the rotation of the upper column shaft 2A stops at that position, and the lower column shaft 2B is twisted with the upper column shaft 2A by the steering force assisted by the rotation of the rotor 7. Resolve. Therefore, the rotational position sensor 12
Is to detect the same rotational position of the rotor 7 as before steering operation, the output signal of the rotational position sensor 10 disappears, the current to the coil 8a of the stator 8 is stopped, and an operation to assist the steering force is performed. Stop.

The torque acting on the upper column shaft 2A in this way is measured by the rotational position sensor attached to the upper column shaft 2A.
It can be obtained from 12 output signals. Therefore, it is not necessary to provide a large-shaped torque sensor at a position different from the mounting position of the direct drive motor DM, and the electric power steering device can be significantly downsized. Further, since a single rotational position sensor may be provided in addition to the rotational position sensor that determines the rotational direction of the rotor of the direct drive motor, it is possible to provide an inexpensive electric power steering device with a simple structure.

In this embodiment, the rotary position sensor is composed of the Hall element, but the same effect can be obtained by using another magnetic sensor such as SMD.

〔The invention's effect〕

As described in detail above, according to the present invention, a rotational position sensor for detecting the rotational position of the rotor is attached to the upper column shaft, and the amount of twist (torque) between the upper and lower column shafts is detected by the output signal thereof. obtain. Therefore, it is possible to obtain an excellent effect that the electric power steering device can be significantly downsized and can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view of an electric power steering apparatus according to the present invention, and FIG. 2 is a sectional view of a conventional electric power steering apparatus. 2A ... upper column shaft, 2B ... lower column shaft, 7 ... rotor, 8 ... stator, 8a ... coil, 9
...... Motor case, 10,12 …… Rotary position sensor, DM ……
Direct drive motor

Claims (2)

(57) [Claims] Claim: What is claimed is: 1. An upper column shaft having steering wheels attached thereto and a lower column shaft connected to the wheels are connected by a torsion bar which causes a twist between the shafts, and the rotor is concentrically fixed to the lower column shaft. In the electric power steering device configured to rotate the lower column shaft to assist the steering force by driving the direct drive motor according to the amount of twist between the shafts, An electric power steering apparatus, comprising: a rotation position sensor for detecting a relative rotation position with respect to the rotor, mounted on the upper column shaft, and the rotation position sensor detecting the twist amount. 2. The electric power steering apparatus according to claim 1, wherein the rotational position sensor is a magnetic sensing element.