JPH03213463A - Motor-operated power steering device - Google Patents

Abstract

PURPOSE:To prevent the rapid change of power assist during failure in operation of a car speed detecting means by varying control based on a car speed to control based on the number of revolutions of an engine when a detecting car speed is zero during control of power assist of a steering according to a car speed. CONSTITUTION:An electric motor 30 is coupled to a steering mechanism 20, and steering torque of a steering wheel is assisted. In this case, steering torque of the steering wheel is detected by a means 41, and a car speed is detected by a means 44. Based on detecting steering torque and car speed, a current feed to the electric motor 30 is controlled by a means 71. Further, the number of revolutions of an engine is detected by a means 43. Based on a detecting car speed and the number of revolutions, when a car speed is zero, control of a car speed by the means 71 is varied to control based on the number of revolutions by means of a means 72. This constitution prevents the rapid change of an assist force during failure in operation of the means 41 and improves safety.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in electric power steering devices.

(Prior Art) Conventionally, as an electric power steering device, for example, as disclosed in Japanese Patent Laid-Open No. 62-29467, there is a steering mechanism that steers wheels by receiving steering torque from a steering wheel, and a steering mechanism that steers wheels by receiving steering torque from a steering wheel. There is known a vehicle that includes an electric motor mechanically connected to the steering wheel, and controls power supply to the electric motor according to the steering torque of the steering wheel so that the electric motor assists the steering torque of the steering wheel. In this case, if a sensor such as a torque sensor that detects steering torque, a vehicle speed sensor that detects vehicle speed, or a steering angle sensor that detects the steering angle of the steering wheel fails and the output of the sensor becomes excessive, or the control circuit If excessive current flows to the electric motor due to a failure, etc., the power supply circuit of the electric power steering device is set to 0FFL, or the clutch mechanism installed between the steering mechanism and the electric motor is turned off to stop power assist. However, this is done to prevent problems such as over-turning the steering wheel due to excessive power assist.

(Problem to be solved by the invention) However, when the power assist is stopped in this way, the steering wheel suddenly becomes heavier, making it extremely difficult for the driver to steer, and also when cornering at low speeds. etc., problems such as a delay in turning the steering wheel occur. Furthermore, this system also requires a separate means for detecting failure of the sensor.

The present invention has been made with attention to these points,
The purpose of this is to improve safety by preventing sudden changes in the assist force when the vehicle speed detection means (vehicle speed sensor) fails in an electric power steering system that controls the assist force according to the vehicle speed. It is about increasing.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, in an electric power steering device that controls assist force according to vehicle speed, when the vehicle speed is other than zero, the vehicle speed is adjusted to zero based on the vehicle speed. When this happens, the assist force is controlled based on the engine speed.

Specifically, the solution taken by the present invention, as shown in FIG. 1, includes a steering mechanism 20 that receives steering torque from a steering wheel and steers the wheels; An electric motor 30 that assists the steering torque of the wheel, a steering wheel torque detection means 41 that detects the steering torque of the steering wheel, and a vehicle speed detection means 4 that detects the speed of the vehicle.
4, a control means 71 which receives the outputs of the steering wheel torque detection means 41 and the vehicle speed detection means 44 and controls power supply to the electric motor 30 according to the steering torque of the steering wheel and the vehicle speed, and detects the engine rotation speed. The outputs of the rotation speed detection means 43, the vehicle speed detection means 44, and the rotation speed detection means 43 are received, and when the output of the vehicle speed detection means 44 is zero, the control based on the vehicle speed in the control means 71 is controlled based on the engine rotation speed. The configuration is such that a changing means 72 for changing to .

In that case, the control based on the engine rotation speed in the control means 71 includes control based on a signal obtained by processing the output of the rotation speed detection means 43 with a delay.

(Function) With the above configuration, in the present invention, when the output of the vehicle speed detection means 44 is other than zero, based on the steering torque detected by the steering wheel torque detection means 41 and the vehicle speed detected by the vehicle speed detection means 44, The control means 71 controls power supply to the electric motor 30 , and the electric motor 30 assists the steering torque of the steering wheel and transmits it to the steering mechanism 20 .

When the vehicle speed detection means 44 fails and its output shows zero, the change means 72 changes the control based on the vehicle speed in the control means 71 to the control based on the engine speed detected by the rotation speed detection means 43. be done. This prevents the steering wheel from suddenly becoming too light when driving at high speeds, and also prevents the steering wheel from suddenly becoming heavy when driving at low speeds, suppressing sudden changes in assist force.

Further, there is no need to separately provide a means for detecting a failure of the vehicle speed detecting means 44, which is advantageous in terms of the structure and cost of the device.

Particularly, when control based on the engine speed in the control means 71 is performed based on a signal obtained by processing the output of the speed detecting means 43 with a delay, the influence of sudden fluctuations in the engine speed is alleviated.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows an embodiment of the invention. In the figure, reference numeral 1 denotes left and right front wheels of a vehicle, which are connected to the vehicle body via steering knuckles (not shown) so as to be rotatable around a vertical axis. A knuckle arm (not shown) is attached to this steering knuckle. These two wheels 1 are steered by a steering mechanism 20.

The above steering mechanism 20 will be explained.

The knuckle arms of the left and right wheels 1 are connected by a rack joint 21, and a rack 22 is provided at the center of the rack joint 21. On the other hand, a steering shaft 24 is provided in the vehicle body. One end of the steering shaft 24 is introduced into the vehicle interior, and the steering wheel 2 is attached to the end.

A pinion 23 is attached to the other end of the steering shaft 24, and the pinion 23 meshes with the shaft 22. Therefore, when the steering wheel 2 is rotated, the left and right wheels 1 are steered left and right by the steering mechanism 20 in response to the steering torque.

Steering shaft 24 of the steering mechanism 20
An electric motor 30 is mechanically connected to. That is, the drive shaft of the electric motor 30 is connected to the steering shaft 24 via a gear mechanism, and the drive shaft of the electric motor 30 is connected to the steering shaft 24 via a gear mechanism.
The steering torque of the steering wheel 2 is assisted by the driving torque of the steering wheel 2. The driving torque of the electric motor 30 is determined according to the current value supplied to the electric motor 30. A clutch 32 is provided on the drive shaft of the electric motor 30, and in the event of an abnormality, the transmission of the drive torque of the electric motor 30 to the steering shaft 24 is interrupted to perform fail-safe operation. The above electric motor 30
and clutch 32 are controlled by controller 40.

The steering shaft 24 is provided with a torque sensor 41 as a handle torque detection means, and the torque sensor 41 detects the steering torque of the steering wheel 2. Further, the steering shaft 24 is provided with a steering angle sensor 42, and the steering angle of the steering wheel 2 is detected by this steering angle sensor 42. Furthermore, this vehicle includes a rotation speed sensor 43 as a rotation speed detection means for detecting the engine rotation speed, a vehicle speed sensor 44 as a vehicle speed detection means for detecting the speed of the vehicle, and a voltage sensor 45 for detecting the voltage of the alternator. It is provided. Further, the transmission connected to the engine is provided with a reverse switch 46 for detecting a shift state to a reverse position. Output signals from these sensors 41 to 46 are input to the controller 40.

A schematic configuration of the controller 40 is shown in FIG. In the figure, 50 is a CPU, and this CPU 50 is driven by a constant voltage circuit 51.

Reverse switch 46, voltage sensor 45, vehicle speed sensor 4
4. The output signal of the rotation speed sensor 43 is sent to the digital buffer 5
2 is processed and input to the CPU 50. In that case, the output signals of reverse switch 46 and voltage sensor 45 are passed through a waveform processing circuit and counter 53,54. Further, the output signals of the torque sensor 41 and the steering angle sensor 42 are processed by an analog buffer 55, further A/D converted by an A/D converter 56, and then input to the CPU 50.

On the other hand, the electric motor control signal output from the CPU 50 is D/A converted by a D/A converter 57 and then input to the electric motor 30 via a current control circuit 58, a driver 60, and a power circuit 61. In that case, a signal is inputted to the current control circuit 58 from the fail-safe logic circuit 59, and in the event of a failure, the current supply to the electric motor 30 is cut off and the clutch 32 is disengaged. Also, 62
is a current detection circuit that detects the current value of the power circuit 61, and the output of this current detection circuit 62 is input to the current control circuit 58 and the A/D converter 5.
The signal is A/D converted in step 6 and then input to the CPU 50.

Further, 63 is a current control circuit that controls the current supplied to the control system of the clutch 32, and 64 is a drive circuit that controls the drive system of the clutch 302. This drive circuit 6
The output of 4 is detected by the monitor circuit 65 and sent to the CPU 5.
It is entered as 0. Note that 3 is a battery and 4 is an ignition switch.

Next, the control of the controller 40 will be explained based on the flow shown in FIG. 4. After starting, first in step S1, the vehicle speed ■, the steering torque T1, the steering angle θH2, the differential value θH of the steering angle θH
and engine speed E. Here, the signal of the engine rotation speed E is a signal obtained by performing first-order delay processing on the output signal of the rotation speed sensor 43. And step S2
Calculates various control variables. That is, the assist force A corresponding to the steering torque T is calculated based on FIG. 5, and the assist force A corresponding to the differential value θH of the steering angle θH is calculated based on FIG.
θH is calculated, correction values α and β are calculated according to the vehicle speed V based on FIGS. 7 and 8, and correction value γ is calculated according to the engine rotation speed E based on FIG. Next, in step S3, it is determined whether the vehicle speed V is zero. Vehicle speed V
is not zero, the process proceeds to step S4, and the assist force A by the electric motor 310 is set to "A-α・AT-β・AθH".
The electric motor 3 is calculated according to this assist force A.
Controls the supply current value to 0 and returns. Here, as shown in FIG. 5, the assist force AT is set larger as the steering torque T increases, and the larger the steering torque T is, the larger the assist force A is set, and the driver's steering force is reduced. Ru. In this case, as shown in FIG. 7, the correction value α is set to decrease as the vehicle speed V increases, so that the higher the vehicle speed becomes, the smaller the assist force A becomes, thereby ensuring steering stability. Further, as shown in Fig. 6, the assist force AθH is set to be large according to the increase in the differential value θH of the steering angle θH, and the larger the steering angle speed is, the larger the reduction in the assist force A is set, and the resistance during steering is increased. This increases steering feel and improves steering feel. In that case, as shown in FIG. 8, the correction value β is set to increase as the vehicle speed V increases, so the higher the vehicle speed, the more the assist force A.
The weight loss increases and the feeling improves.

2 Further, when the vehicle speed V is zero (YES in step S3), the process proceeds to step S5. In step S5, the electric motor 30
The assist force A is calculated from "A=γ・A, -ε・AθH", and the current value supplied to the electric motor 30 is controlled according to this assist force A and returned. The difference from step S4 in the calculation is as follows:
By setting the correction value of the assist force AT to γ and the correction value of the assist force AθH to ε, it is determined that the correction value is based on the engine rotation speed. As a result, as shown in FIG. 9, the correction value γ is set to decrease as the engine rotation speed E increases, so the assist force A decreases as the engine rotation becomes higher. In addition, the correction value ε is a function of the engine rotation speed, has the same characteristics as the correction value β in FIG. 8, and is set to increase as the engine rotation speed increases. The higher the rotation becomes, the greater the reduction in assist force A becomes. In this case, the vehicle is normally steered when the vehicle speed V is zero, such as when parking the vehicle or parking the vehicle. As a result, the driver's steering effort is reduced.

Furthermore, if the vehicle speed sensor 44 fails, normally the vehicle speed sensor 44 will only indicate zero, so the control in step S5 will be performed in this case as well. That is, if the vehicle speed sensor 44 fails, control based on the engine speed is immediately performed, and since the engine speed is in a relatively high speed range while driving at high speed, the steering wheel is prevented from suddenly becoming too light. Ru. Additionally, while driving at low speeds, the engine speed is also in the low speed range, which prevents the steering wheel from suddenly becoming heavy. Therefore, sudden fluctuations in assist force can be suppressed and safety can be improved.

In the above flow, in step 5l-84, the outputs of the steering wheel torque detection means (torque sensor) 41 and the vehicle speed detection means (vehicle speed sensor) 44 are received, and power is supplied to the electric motor 30 according to the steering torque of the steering wheel and the vehicle speed. Control 4 constitutes control means 71. Further, in step S5, the outputs of the vehicle speed detection means (vehicle speed sensor) 44 and the rotation speed detection means (rotation speed sensor) 43 are received, and when the vehicle speed is zero, the control based on the vehicle speed in the control means 71 is based on the engine rotation speed. It constitutes a changing means 72 for changing the control.

Therefore, in the embodiment 1, the vehicle speed sensor 44
If the vehicle speed sensor fails, control based on the engine speed is immediately executed, so if the vehicle speed sensor fails, the steering wheel suddenly becomes too light while driving at high speeds, resulting in a lack of steering stability, or when driving at low speeds, the steering wheel suddenly becomes too light. The system does not become heavy, and it suppresses sudden changes in assist force, increasing safety.

Further, there is no need to separately provide means for detecting whether or not there is a failure in the vehicle speed sensor 44, which is advantageous in terms of device configuration and cost.

In addition, since the output signal of the rotation speed sensor 43 is not used for control as it is, but this output signal is subjected to first-order delay processing before being used for control, the influence of sudden changes in the engine rotation speed such as when changing a shift is eliminated. eased.

In this case, the delay processing is not limited to first-order delay.

In short, any process that slows down the rise of the output signal of the rotation speed sensor 43 is sufficient.

(Effects of the Invention) As explained above, according to the electric power steering device of the present invention, there is a steering mechanism that steers the wheels by receiving the steering torque of the steering wheel; When the vehicle speed is other than zero, the power supply to the electric motor is controlled according to the steering torque of the steering wheel and the vehicle speed, and when the vehicle speed is zero, the electric motor is equipped with an electric motor that assists the steering torque of the steering wheel. Since the power supply to the electric motor was controlled according to the steering torque and engine speed,
Not only does it easily detect a failure in the vehicle speed detection means, but when the failure occurs, it prevents the steering wheel from suddenly becoming light while driving at high speeds and from suddenly becoming heavy when driving at low speeds, thereby suppressing sudden changes in assist force. Safety can be increased.

6 In that case, if the control based on the engine speed is based on a signal obtained by processing the output of the speed detecting means with a delay, the influence of sudden fluctuations in the engine speed can be alleviated.

[Brief explanation of drawings]

The drawings illustrate embodiments of the present invention, and FIG. 1 is a block diagram showing the configuration of the present invention. Figure 2 and below show examples,
Figure 2 is an overall schematic configuration diagram, Figure 3 is a configuration diagram of the controller, Figure 4 is a flowchart diagram showing controller control, Figure 5 is a map diagram showing the relationship between steering torque and assist force, and Figure 6 is a diagram showing the relationship between steering torque and assist force. is a map diagram showing the relationship between the differential value of the steering angle and the assist force, Figures 7 and 8 are map diagrams showing the relationship between vehicle speed and correction value, and Figure 9 is a map diagram showing the relationship between engine speed and correction value. FIG. 2... Steering wheel 20... Steering mechanism 30... Electric motor 41... Torque sensor (handle torque detection means) 7 43... Rotation speed sensor (rotation speed detection means) 44... Vehicle speed sensor (Vehicle speed detection means) 71... Control means 72... Changing means 8 \-10 0 r- (To N (1) Dimension (1) Dimension - (G) Dimension Toto 4th figure ■ Figure β Diagram

Claims (2)

[Claims] (1) A steering mechanism that steers the wheels in response to the steering torque of the steering wheel; an electric motor that is mechanically connected to this steering mechanism and assists the steering torque of the steering wheel; and detecting the steering torque of the steering wheel. a steering wheel torque detecting means; a vehicle speed detecting means for detecting the speed of the vehicle; and receiving outputs from the steering wheel torque detecting means and the vehicle speed detecting means, and controlling power supply to the electric motor according to the steering torque of the steering wheel and the vehicle speed. a control means, a rotation speed detection means for detecting the engine rotation speed, and receives the outputs of the vehicle speed detection means and the rotation speed detection means, and when the output of the vehicle speed detection means is zero, controls the engine based on the vehicle speed in the control means. 1. An electric power steering device comprising a changing means for changing control to control based on rotational speed. (2) The electric power steering device according to claim 1, wherein the control based on the engine rotation speed in the changing means is control based on a signal obtained by processing the output of the rotation speed detection means with a delay.