JPS62218272A - Control method for motor driven power steering - Google Patents

Abstract

PURPOSE:To improve a follow-up characteristic to the high speed steering action, by controlling a power steering in such a manner that a motor is isolated from a rack shaft by decreasing an electromagnetic slip clutch current in accordance with a steering speed when the handle steering speed increases to a predetermined value or more. CONSTITUTION:The second rack toothed part 6b is separately provided from a rack toothed part, meshed with the first pinion shaft controlled by a handle, of a rack shaft 6, and the second pinion shaft 18, turned by a DC motor 13 through an electromagnetic slip clutch 14, worm shaft 15, worm wheel shaft 16 and an electromagnetic clutch 17, is meshed with the second rack toothed part 6b. Each control element 13, 14, 17 is controlled by a control unit 9. And here the control unit 9 is constituted providing a measuring means 9c, which measures a steering speed of the handle 1, and a determining means 9d which decreases a slip clutch current in accordance with the measured value of said steering speed, when it is in a predetermined value or more, while determines the slip clutch current in accordance with steering torque when the measured value is in the predetermined value or less.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motor-driven power steering control method for assisting and energizing a steering device of an automobile with the rotational force of a motor.

[Conventional technology]

Conventionally, there is a device of this type in which the driving force of a motor is auxilially biased to a steering shaft by a transmission mechanism such as a gear or a belt via a reduction gear.

[Problem that the invention seeks to solve]

Since conventional steering devices are configured as described above, there was a problem that during high-speed steering, if the steering speed was higher than the no-load rotation speed of the motor, the motor would not be loaded and the steering torque would increase. .

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a motor-driven nose wheel steering control method that improves followability to high-speed steering.

[Means for solving problems]

The power steering control method according to the present invention reduces the electromagnetic slip clutch current in accordance with the steering speed to disconnect the motor from the rack shaft when the steering wheel steering speed is equal to or higher than a predetermined value.

[Effect]

The steering control method according to the present invention prevents the motor from becoming a load during high-speed steering, and improves followability to high-speed steering simply by adding a steering speed sensor and changing the control program. I can do it.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a schematic diagram of a motor-driven power steering device, where 1 is a steering wheel that receives steering torque, 3 is a torque sensor that outputs an electric signal according to the rotational force applied to the steering wheel 1, and 19 is a steering wheel that receives a steering torque. a steering speed sensor that outputs an electric signal according to the steering speed; 4a is a first universal joint; 4b is a second universal joint;
2a is a first steering shaft that connects the handle 1 and the torque sensor 3, 2b is a second steering shaft that connects the torque sensor 3 and the first universal joint 4a f'a'j, and 2c is the first steering shaft. Universal joint 4a and i2 universal joint in) 4b
This is the third steering shaft that connects the two. 5 is a first pinion shaft connected to the second universal joint 4b; 6 is a rack shaft having a first rack tooth 6a and a second rack tooth 6b that mesh with the first pinion shaft 5; 7a; 7b is a ball joint connecting one tie rod 8a and one end of the rack shaft 6, and 7b is the other tie rod 8.
This is a monkey joint that connects b and the other end of the rack shaft. 9 is a control unit, 1° is a vehicle speed sensor that detects the vehicle speed, 11 is an in-vehicle battery, 12 is a key switch, 13 is a DC motor having a shunt winding or a magnet field, and the control unit 9 is connected from the battery □-11 to the control unit 9.
Driven through. Reference numeral 14 denotes an electromagnetic clutch that is directly connected to and driven by the output shaft of the motor 13, and is, for example, a clutch clutch or a hysteresis clutch. 15 is a worm shaft connected to the output shaft of the subvesi clutch 14 to form a speed reducer; 16 is a worm wheel shaft that engages with the worm shaft 15 and is driven; 17 is a worm wheel shaft 16
This is an electromagnetic clutch that mechanically connects and disconnects the second pinion shaft 18 that engages with the second tooth portion 6b of the rack shaft 6 according to instructions from the control unit 9.

FIG. 2 is a block diagram showing the specific configuration of the control unit 9, in which 9a is a steering torque measuring means for measuring steering torque based on the input from the torque sensor 3, and 9b is a voltage applied to the motor based on the measured value of the torque measuring means 9a. 9c is a steering speed sensor 1
Steering speed measuring means 9d measures the steering speed of the steering wheel l based on the input from 9. When the measured value of the steering speed measuring means 9C is above a predetermined value, it is decreased according to this measured value, 9e is a motor applied voltage control means that controls the voltage applied to the motor 13 based on the output of the motor applied voltage determining means 9b; 9f is a clutch current determining means 9d; 9g is an electromagnetic clutch control means that controls the engagement and disengagement of the electromagnetic clutch 17 under conditions determined by the vehicle speed.

Next, the operation will be explained with reference to FIGS. 3 to 6.

FIG. 3 is a clutch current versus transmission torque characteristic diagram of the electromagnetic slip clutch 14, and FIG. 4 is a control characteristic diagram of steering torque versus voltage applied to the motor 13 and slip clutch 14 current.

FIG. 6 is a flowchart of the control program of the control unit 9.

First, when the gear switch 12 is turned on when starting the engine, the electromagnetic clutch 17 is turned on and the worm wheel shaft 16 and the second pinion shaft 18 are connected. When a rotational force is applied to the handle 1 in this state, the control unit 9 controls the motor 13 and the electromagnetic slip clutch 14 as shown in FIG. Thus, in controlling the motor 13, when the steering torque is increased to the right, the motor 13 is turned on at point a and 100% voltage is applied to the motor (b
point). When the steering torque is further increased and the steering torque reaches point C, the current in the slip clutch 14 begins to flow, and increases approximately logarithmically with respect to the increase in steering torque, reaching 100% current (
point d). Conversely, when the torque is decreased, the current of the slip clutch 14 decreases from point d and reaches 0% at point C. When the torque further decreases to point e, the motor 13 is turned off and the applied voltage becomes 0% (point F). Almost the same control is performed in the left direction as well. As shown in FIG. 3, the characteristics of the slip clutch 14 are such that the transmission torque, that is, the slip torque, increases substantially proportionally to the clutch current. Therefore, in Figure 4, the torque increases and when it reaches point a, 100% voltage is applied to the motor, so
The motor begins to rotate and further increases the torque until the torque reaches C.
Since the current of the slip clutch 14 is gradually increased from this point, the output torque to the worm shaft 15 is gradually increased, and an auxiliary torque corresponding to the force applied to the handle 1 is applied to the worm wheel shaft 16. Electromagnetic clutch 17° 2nd h=
This is transmitted to the second rack tooth portion 6b via the on-shaft 18, and the handle 1 becomes lighter.

The above is a static operation of the steering device, but when the steering wheel 1 is suddenly turned, if the steering speed becomes higher than the no-load rotation speed of the motor 13, the motor 13 becomes a load, and the steering torque increases. The steering wheel feels heavier than without the steering wheel. Therefore, as shown in the flowchart of FIG. 6, this device reduces the current of the slip clutch 14 in accordance with the steering speed when the steering wheel speed is equal to or higher than a predetermined value W, thereby reducing the current between the motor 13 and the rack shaft 6. By cutting off the connection, the motor was prevented from being loaded during high-speed steering. This prevents the steering wheel from becoming heavier than when no power steering is used during high-speed steering.

Next, when the car is in a running state, the current of the electromagnetic slip clutch 14 decreases in inverse proportion to the increase in vehicle speed, as shown in the vehicle speed vs. p clutch current and electromagnetic clutch voltage characteristics diagram in Figure 5. At point f, no current flows through the slip clutch 14 even if rotational force is generated in the handle l.

When the vehicle speed further increases and reaches point g, the electromagnetic clutch 17
Since the worm wheel shaft 16 and the second pinion shaft 18 are disengaged, the driver who turns the steering wheel 1 experiences steering without auxiliary bias.

〔Effect of the invention〕

As explained above, according to the present invention, when the steering wheel steering speed is above a predetermined value, the electromagnetic slip clutch current is reduced in accordance with the steering speed, and the motor is disconnected from the rack shaft. No load is applied to the motor during high-speed steering, and by simply adding a steering speed sensor and changing the control groudram, it is possible to perform power steering that can easily follow high-speed steering.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a motor-driven power steering device according to an embodiment of the present invention, Fig. 2 is a Glock circuit diagram of a control unit, Fig. 3 is a diagram of current versus transmission torque characteristics of an electromagnetic slip clutch, and Fig. 4 FIG. 5 is a characteristic diagram of steering torque versus motor applied voltage and electromagnetic clutch applied voltage, FIG. 5 is a characteristic diagram of vehicle speed versus vehicle speed, vector clutch current and electromagnetic clutch applied voltage, and FIG. 6 is a flowchart of the control system. ■... Handle, 3... Torque sensor, 5... First binion shaft, 6... Rack shaft, 6 a... First
Rack tooth portion -6b...Second rack tooth portion, 9...
Control unit, 9a... Steering torque measuring means, 9b... Motor applied voltage determining means, 9C... Steering speed measuring means, 9d... Clutch current determining means, 9e
...Motor applied voltage control means, 9f...Clutch current control means, 9g...Electromagnetic clutch control means, 10.
... Vehicle speed sensor, 13... Motor, 14... Electromagnetic slip clutch, 15... Worm M, 16... Worm wheel shaft, 17... Electromagnetic clutch, 18...
・Second pinion shaft. In addition, in Figure 1, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) In an automobile steering device, a vehicle speed sensor that detects the vehicle speed, a torque sensor installed in the middle of the steering shaft that detects the rotational force of the steering wheel, a steering speed sensor that detects the steering speed of the steering wheel, and a steering shaft that is connected to the steering wheel. and a first pinion shaft that is driven via a universal joint, a first rack tooth of a rack shaft that meshes with and is driven by this pinion shaft, and inputs signals from the vehicle speed sensor, torque sensor, and steering speed sensor. a DC motor that is pivoted from the vehicle battery via the control unit, and an electromagnetic slip clutch that is directly connected to the output shaft of the motor and increases the transmitted torque approximately proportionally to the output current of the control unit. A worm shaft and a worm wheel shaft that are directly connected to the output shaft of this clutch and constitute a reducer, and an electromagnetic system that connects and disconnects the rotational force between the worm wheel shaft and the first or second pinion shaft by means of a control unit. When the clutch is provided and the second pinion shaft is provided, the motor-driven power is driven by meshing the pinion shaft with the first rack teeth of the rack shaft and the second rack teeth that are cut continuously or separately. The steering control method includes: a steering torque measuring means for measuring steering torque based on an input from a torque sensor; a motor applied voltage determining means for determining a motor applied voltage based on a measured value of the torque measuring means; A steering speed measuring means for measuring the steering speed of the steering wheel, and when the measured value of the measuring means is above a predetermined value, the clutch current is decreased in accordance with the steering speed, and when it is below the steering speed, the clutch current is determined based on the measured value of the steering torque. motor applied voltage control means that controls the motor applied voltage based on the output of the motor applied voltage determining means; and clutch current control that controls the current of the electromagnetic slip clutch based on the output of the clutch current determining means. and electromagnetic clutch control means for controlling engagement and disengagement of an electromagnetic clutch under conditions determined by at least vehicle speed. (2) The motor-driven power steering control method according to claim 1, wherein the electromagnetic sliding clutch is a powder clutch or a hysteresis clutch.