JPH0256270B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an electric power steering device that applies power from a motor to a steering wheel shaft of an automobile.

(Prior art) Hydraulic power steering devices have conventionally been used as power steering devices for automobiles, but the actuator is built into the steering gear, and a hydraulic circuit is required because pressure-resistant seals and oil leakage seals are required. This has the drawback of requiring high-precision machining, increasing the overall size, and increasing costs because parts cannot be shared with manual steering.

Therefore, an electric power steering device was considered, but since it supports all running power, it required high-precision machining as described above, and the overall size became large.
The disadvantage was that the cost was high because manual steering parts could not be standardized.

(Purpose) The present invention does not provide full-travel power assistance, but uses general DC
It uses a series motor, etc. to provide power assistance when the vehicle speed is below a certain speed, and can be attached to a conventional manual steering system.
The aim is to provide power assistance by driving a series motor at a speed synchronized with the rotational speed of the steering wheel, thereby optimizing the steering feel and eliminating the drawbacks of the conventional system.

(Example) Next, an example of the present invention will be described. FIG. 1 shows a first embodiment. 1 is a motor, and a torque limiter 3 that slips at a constant torque is attached to the drive shaft 2, and a gear 4 rotatably supported on the drive shaft 2 transmits the rotation of the drive shaft 2 only when the torque limiter 3 is in operation. It's becoming like that. A gear 5 is connected to the gear 4, and a gear 6, which is coaxial with the gear 5, meshes with a gear 8 pivotally supported on a handle shaft 7 to form a speed reduction device. 9 is an electromagnetic clutch attached to the handle shaft 7, and 10 is a steering sensor that detects the twist angle and rotation direction of the handle shaft 7. 11 is the vehicle speed sensor 12
A control circuit that controls signals from the steering sensor 10 and signals from the steering sensor 10 when the detected speed of the vehicle speed sensor 12 is below a certain speed.
The DC series motor 1 is turned on and off by the signal from
At the same time, the rotation direction of the gear 8 is determined by turning the electromagnetic clutch 9 on and off, and the rotation of the gear 8 is controlled by the handle shaft 7.
come into contact with and separate from it. 13 is a pinion of the handle shaft 7, 1
4 is a rack bar, and 15 is a handle wheel.

Next, the effect will be explained. When the handle wheel 15 is steered, the handle shaft 7 is twisted by the load acting on the rack bar 14, and when the handle shaft 7 is twisted by more than a certain angle, the contact point of the steering sensor 10 is activated.

At this time, if the vehicle speed is below a certain speed, the control circuit 11 is activated to turn on the DC series motor 1 and the electromagnetic clutch 9. As shown in Figure 3, the motor 1 has a characteristic in which the load torque and the motor rotation speed are inversely proportional to each other. Therefore, when the load torque is large and the motor rotation speed is at point a in Figure 3, the steering wheel steering Even if the motor starts rotating, the steering wheel will not be steered beyond the rotation speed at point a. Now, if you turn the steering wheel at a rotation speed higher than point a, the input from the steering wheel will naturally provide power assistance to the motor, so the load on the motor will be correspondingly lighter, and the motor will be reduced from point a to point b. The rotational speed also increases from point a to point b, and when the rotational speeds match each other, a balance is maintained. The drive shaft 2 rotates as described above,
If this rotational torque is within a range where the torque limiter 3 does not slip, it is transmitted to the electromagnetic clutch 9 which is turned on by gears 4, 5, 6, 7, 8, power is assisted to the steering wheel shaft 7, and the torque is lighter than the general steering torque. The steering wheel is steered by the steering torque. Furthermore, when steering is completed and the steering wheel returns to its original state due to resistance on the road surface, the contact point of the steering sensor 10 on the steering wheel is separated, stopping the rotation of the motor 1 and turning off the electromagnetic clutch 9. The same level of resiliency can be obtained. Furthermore, when the vehicle speed exceeds a certain value, control circuit 1
1 turns off the motor 1 and the electromagnetic clutch 9, resulting in normal manual steering.
If the steering speed is very slow, the motor rotation speed will exceed the steering wheel rotation speed, causing the steering wheel to be steered by itself. To prevent this phenomenon, the motor characteristics have been adjusted until the vehicle speed range in which the motor is not activated. , so that it changes depending on the vehicle speed.

FIG. 4 shows this situation, and as the vehicle speed v increases (v ₃ > v ₂ < v ₁ ), the motor rotation start torque T is set smaller (T ₃ <
T ₂ < T ₁ ). This makes motor control extremely easy as all you have to do is adjust the voltage applied to the motor (lower the voltage).

Next, the operation of the present invention will be explained below based on FIG. 5, which shows the relationship between the torque of the handle, the torque of the motor, and their rotational speeds.

In the region where the motor torque T is positive, as described above, the rotational speed of the motor and the rotational speed of the handle are synchronized at a certain point on the NT curve. For example, if synchronization occurs at point A in the diagram, the synchronized rotational speed will be
N _A , the motor torque is T _A , the load is T _X , and the steering wheel torque at this time is (T _X − T _A ).
In other words, the sum of the torque of the steering wheel and the torque of the motor balances the load, and steering assistance is performed.

Next, the characteristics when the motor torque T is negative, that is, the handle rotation speed N _H exceeds the maximum motor rotation speed N _MAX (≡ the motor rotation speed when the motor torque T is zero) is shown by the dashed-dotted line in the figure. In this region, a torque corresponding to the difference between the rotation speed of the handle and the N _MAX (for example, torque T _B when the rotation speed of the handle is N _B at point B in the figure) is applied to the motor from the handle side. The torque of the handle at this time is the sum T _H of this torque T _B and the load torque T _Y.

As the difference (N _B - N _MAX ) increases, the torque applied to the motor by the handle increases, and when this torque exceeds the set torque T _L of the torque limiter, the torque limiter starts to slip. Handle rotation speed
_NL ).

In other words, the difference between the rotation speed N _H of the handle and the maximum rotation speed N _MAX of the motor (N _H − N _MAX ) is greater than or equal to (N _L − N _MAX ), which means that the torque that the handle side gives to the motor is a constant torque. The torque limiter is designed to slip when the torque is T _L or higher. Therefore, the steering feel is natural and natural, and unpleasant phenomena are eliminated.

FIG. 2 shows a second embodiment of the present invention, in which a motor 20 has characteristics similar to those of the first embodiment, the rotation of its drive shaft is reduced by a reducer 21 and transmitted to a torque limiter 22, and a gear 23, 24 to the intermediate shaft 25, and the timing belt 2 connects the timing pulley 26 fixed to the intermediate shaft 25 and the timing pulley 28 fixed to the handle shaft 27.
It is linked with 9. The second embodiment is a motor 2
0, the torque limiter 22, and the reducer 21 are integrated into one unit, but the overall operation is exactly the same as in the first embodiment.

(Effects) According to the present invention, the motor, which is activated when the vehicle speed is below a certain speed and when the steering wheel is twisted above a certain level, is connected to the steering gear input shaft via a torque limiter and an electromagnetic clutch. By incorporating a motor, reducer, clutch, and torque limiter, when the vehicle speed is below a certain speed, the motor's torque and rotational speed are inversely proportional to each other to synchronize the motor speed and the steering wheel rotational speed to provide power assistance. Since it is an electric power steering device, parts can be shared with manual steering, and it can be manufactured at low cost. High-precision machining is not required, and the entire system can be made more compact. In addition, by utilizing the motor's inverse proportionality to torque and rotational speed characteristics and by installing a torque limiter, the steering wheel has a good steering feel, and since complex motor control is not required, the control circuit is extremely simple. In addition, since a portion of the power is assisted, the restoring performance of a conventional power steering device can be used as manual steering, so the restoring performance can be improved.

[Brief explanation of the drawing]

Figure 1 is an overall configuration diagram of the first embodiment of the present invention;
The figure is a partially cutaway front view of the second embodiment of the present invention, Figure 3 is a characteristic diagram of the torque and rotational speed of the motor used in the present invention, and Figure 4 is the start of rotation of the motor when the vehicle speed is different according to the present invention. A graph showing the torque and the rotational speed of the motor. FIG. 5 is a characteristic diagram showing the relationship between the torque of the handle, the torque of the motor, and their rotational speed according to the present invention. 1...Motor, 2...Drive shaft, 3...Torque limiter, 7...Handle shaft, 9...Electromagnetic clutch, 10
... Steering sensor, 11... Control circuit, 12... Vehicle speed sensor, 20... Motor, 22... Torque limiter, 25... Intermediate shaft, 26, 28... Timing pulley, 27... Handle shaft.

Claims (1)

[Scope of Claims] 1 A motor operated by a vehicle speed below a certain speed and a twist of the steering wheel above a certain level is connected to a steering gear input shaft via a torque limiter and a clutch, and the motor has an inversely proportional characteristic of torque to rotation speed. An electric power steering device characterized by synchronizing the speed of the motor and the rotational speed of the steering wheel to provide power assistance. 2. The electric power steering device according to claim 1, wherein the motor and the clutch stop operating when the vehicle speed exceeds a certain speed.