JP2938494B2 - Electric power steering device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device, and more particularly to a vehicle speed-sensitive electric power steering device.

[Conventional technology]

A general electric power steering device has a structure as shown in FIG. That is, a steering shaft 2 is fixed to the steering wheel 1, and a pinion 3 is connected to a tip of the shaft 2. The pinion 3 is meshed with a rack 4 which can reciprocate in the axial direction. A torque sensor 5 is mounted in the middle of the steering shaft 2, and detects a steering torque acting on the steering shaft 2. A pinion 6 for assisting steering torque is also meshed with the rack 4, and the pinion 6 is driven by an electric motor 7. Both ends of the rack 4 are connected to left and right steered wheels 10, 10 via tie rods 8, 9.
It is connected to steering knuckles 12 and 13 that support 11.

The steering torque signal of the torque sensor 5 and the vehicle speed signal of the vehicle speed sensor 14 are input to the controller 20. Based on these input signals, the assist current is controlled as shown in FIG. Input to assist steering force. This facilitates steering operation when cornering at low speed or entering the garage,
When driving at high speeds, the driver can feel a sense of response to the steering wheel and can maintain driving stability.

However, simply controlling the assist current as shown in FIG. 5 by the steering torque signal and the vehicle speed signal as described above tends to cause a response delay due to the inertia of the motor and its drive system. However, there is a problem that the steering wheel 1 is heavy because only a small current flows through the steering wheel.

In order to eliminate such a delay in responsiveness, a drive current of the motor 7 is obtained by adding a differential correction current corresponding to a time change rate (time derivative) of the steering torque to the assist current as shown in FIG. Are known. That is, the controller 20 includes an assist current determination circuit 21, a differential correction circuit 22, and a motor drive circuit 23. The assist current determination circuit 21 detects the vehicle speed V detected by the vehicle speed sensor 14 and the vehicle speed V detected by the torque sensor 5. The steering torque T is input, and only the steering torque T is input to the differential correction circuit 22. Assist current decision circuit
Numeral 21 outputs an assist signal for obtaining an assist current which increases as the steering torque T increases and decreases as the vehicle speed V increases as shown in FIG. Further, the differential correction circuit 22 outputs a differential correction signal for obtaining a differential correction current corresponding to the time change rate of the steering torque T as shown in FIG.
The assist signal and the differential correction signal are added at an addition point 24 and input to the motor drive circuit 23. Here, the addition signal is amplified and input to the motor 7 as a drive current.

As described above, by adding the differential correction current to the assist current, a large driving current instantaneously flows to the motor 7 when the steering wheel starts to be turned, so that the response delay can be eliminated.

[Problems to be solved by the invention]

However, in the case of the power steering device as described above, the differential correction current changes only in accordance with the time rate of change of the steering torque regardless of the vehicle speed. However, there is a problem that the steering wheel becomes too light due to the assist force. That is, the driving stability at the time of high-speed driving, which is an advantage of the vehicle speed-sensitive power steering device, is impaired.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering apparatus that has improved steering response during low-speed running while maintaining a feeling of handle response during high-speed running.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a torque sensor that detects a steering torque of a steering system, a vehicle speed sensor that detects a vehicle speed of a vehicle, an electric motor that assists the steering torque and transmits the steering torque to a steered wheel, In an electric power steering apparatus including a controller that controls a drive current of an electric motor according to a detection signal from the sensor, the controller increases as a steering torque increases and decreases as a vehicle speed increases. An assist current determination circuit for determining an assist current, a differential correction circuit for determining a differential correction current that increases in accordance with an increase in the time rate of change of the steering torque, and a motor drive obtained by adding the assist current and the differential correction current A motor drive circuit that outputs a current to a motor, wherein the differential correction circuit is configured to output the differential correction current as the vehicle speed increases. It is characterized in that it has smaller.

[Action]

When the steering wheel is steered, an addition current of an assist current corresponding to the steering torque and the vehicle speed and a differential correction current corresponding to a time change rate of the steering torque sensor flows to the motor, and the steering wheel steering force is assisted. At this time, the differential correction current is set in relation to the vehicle speed and the steering torque. In particular, the rate of increase of the differential correction current with the increase in the time rate of change of the steering torque becomes smaller during high-speed running than during low-speed running. Therefore, a large differential correction current flows at a low speed and a large assist force can be exerted. On the contrary, only a small differential correction current flows at a high speed and only a small assist force is generated. Therefore, the assist response delay at low speed can be eliminated, and the feeling of steering response at high speed can be ensured.

〔Example〕

FIG. 1 shows a control system of an electric power steering apparatus according to the present invention. The structure of the drive system of the power steering device is the same as that of FIG. 4, and the description is omitted.

The controller 30 includes an assist current determination circuit 31, a differentiation correction circuit 32, and a motor drive circuit 33. A vehicle speed signal V and a steering torque signal T are input to the assist current determination circuit 31 from the vehicle speed sensor 14 and the torque sensor 5, respectively. The vehicle speed signal V and the steering torque signal T are also input from the vehicle speed sensor 14 and the torque sensor 5 to the differential correction circuit 32, respectively. The assist current determination circuit 31 outputs an assist signal S _A for obtaining an assist current that increases as the steering torque T increases and decreases as the vehicle speed V increases, as in FIG. Further, the differential correction circuit 32 outputs a differential correction signal _SD for obtaining a differential correction current corresponding to the time change rate of the steering torque T and the vehicle speed V as shown in FIG. The differential correction current is set so that the degree of increase with respect to an increase in the steering torque is large at low speeds and small at high speeds. That is, the differential coefficient is set so as to gradually decrease as the vehicle speed increases as shown in FIG.

The assist signal S _A and the differential correction signal _SD are added at an addition point 34 and input to the motor drive circuit 33. Here, the addition signal is amplified and input to the motor 7 as a drive current.

The operation of the electric power steering device having the above configuration will be described.

First, when the steering wheel 1 is steered during low-speed running, the assist current is large as shown in FIG. 5 and the differential correction current is also large as shown in FIG. 2, so that the driving current of the motor, which is the added current of both, becomes very large. . Therefore, a large current instantaneously flows through the motor 7, so that the response delay due to the inertia of the motor 7 and its drive system can be eliminated, and steering can be performed extremely smoothly.

On the other hand, when the steering wheel 1 is steered during high-speed running, the assist current is small as shown in FIG. 5, and the differential correction current is also small as shown in FIG. 2, so that the motor drive current is also small. Therefore, the assist force by the motor 7 is very small, and the feeling of response of the steering wheel 1 can be secured. Therefore, the problem that the steering wheel 1 is turned too much during high-speed running can be solved.

In the above embodiment, the assist control is performed using only the vehicle speed and the steering torque. However, the control may be performed in consideration of other signals, for example, the steering angle.

In addition, the degree of increase of the differential correction current, that is,
As shown in the figure, the present invention is not limited to the one that is continuously reduced as the vehicle speed increases, and may be a stepwise reduction.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the factor of the vehicle speed is adopted not only in the assist current but also in the differential correction current, and the differential correction current is reduced as the vehicle speed increases, so that the weight at the start of turning the steering wheel at low speed is reduced. And the feeling of response at high speed can be ensured. Therefore, the advantages of the vehicle speed-sensitive electric power steering device can be maximized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a control system of an electric power steering apparatus according to the present invention, FIG. 2 is a diagram showing a relationship between a differential correction current, a time change rate of steering torque and a vehicle speed, and FIG. FIG. 4 is a diagram showing the relationship between the assist current, steering torque and vehicle speed, and FIG. 6 is a diagram showing a conventional control system. FIG. 7 is a diagram showing the relationship between the conventional differential correction current and the time change rate of the steering torque. 1 ... steering wheel, 5 ... torque sensor, 7 ... electric motor, 10, 11 ... steering wheel, 14 ... vehicle speed sensor, 30 ... controller, 31 ... assist current determination circuit, 32 ... differential correction circuit , 33 ... Motor drive circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 5/04 B62D 6/00

Claims (1)

(57) [Claims] A torque sensor for detecting a steering torque of a steering system, a vehicle speed sensor for detecting a vehicle speed of the vehicle, an electric motor for assisting the steering torque and transmitting the steering torque to a steered wheel, and at least a detection signal from the sensor. An electric power steering apparatus comprising: a controller that controls a drive current of an electric motor in accordance with an assist current that determines an assist current that increases with an increase in steering torque and decreases with an increase in vehicle speed. A determination circuit, a differential correction circuit that determines a differential correction current that increases in accordance with an increase in the time rate of change of the steering torque, and a motor that outputs a motor drive current obtained by adding the assist current and the differential correction current to the motor A driving circuit, wherein the differential correction circuit sets the differential correction current to be smaller as the vehicle speed increases. Electric power steering system