JP2940564B2 - Electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering system, and more particularly, to an output of an assist motor (electric motor) in an automobile in accordance with an output of a torque sensor for detecting a steering torque. The present invention relates to an electric power steering device that performs power assist according to steering torque by the motor.

[0002]

2. Description of the Related Art Conventionally, in an automobile, in order to reduce the operation at the time of steering of a steering wheel, the motor current of an assist motor is increased or decreased or turned on / off according to a steering wheel torque and a vehicle speed to control the assist motor. 2. Description of the Related Art A relatively large number of so-called vehicle speed-sensitive electric power steering devices that perform power assist in a steering direction according to a steering torque by using a rotational force have been developed and put into practical use. In this vehicle speed-sensitive electric power steering device, the auxiliary steering force is increased during low-speed running so that light steering can be performed, and the auxiliary steering force is gradually reduced as the vehicle speed increases. In the middle / high speed range, the electromagnetic clutch for connecting / disconnecting the assist motor to / from the speed reducer provided on the torque transmission shaft side is turned off (OF).
By performing F), the torque of the motor is not transmitted to the torque transmission shaft, and a manual steering state is established, so that stable steering performance can be obtained.

[0003]

However, in the conventional power steering apparatus, from the viewpoint of ensuring stable steering performance in the middle / high speed range, the manual steering is performed in the middle / high speed range. -The clutch is turned on and off with the high-speed range. For this reason, there has been a disadvantage that the clutch sound is harsh, or the steering feeling is not good at the moment when the clutch is engaged or at the time of manual steering with the clutch off. On the other hand, in order to achieve full-time electric power steering, it is necessary to prevent motor failure such as motor lock during middle / high speed running, or to detect the occurrence of motor failure and immediately disconnect the motor. A special mechanism or the like that can ensure smooth steering is required.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to eliminate the need for providing a special mechanism for detecting motor lock or the like, and to provide a method for when motor lock or the like occurs. It is an object of the present invention to provide a full-time type electric power steering device capable of performing a smooth steering operation in all regions of low, middle and high speed.

[0005]

The present invention SUMMARY OF THE INVENTION includes a handle input shaft having a steering wheel, a torque transmission shaft connected to the handle input shaft, connecting or disconnecting capable via an electromagnetic clutch to the torque transmission shaft An assist motor that is provided and applies the rotational torque to the torque transmission shaft; and a control unit that controls the assist motor and the electromagnetic clutch. The control unit controls the motor of the assist motor according to the vehicle speed and the steering wheel steering torque. In an electric power steering apparatus configured to perform power assist in a steering direction according to a steering torque by increasing or decreasing a current, a control unit includes the electromagnetic clutch.
Slip limit torque of blood, so that the motor output torque becomes barely adequate determined from the motor control current value, adopts a by being, that the structure has a clutch exciting current control function of controlling the excitation current of the electromagnetic clutch. This aims to achieve the above-mentioned object.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a vehicle equipped with a power steering apparatus (vehicle speed sensitive type) of this embodiment. FIG.
In the power steering device 10, the vehicle body 100
Equipped on the front of the. The power steering device 10 includes a steering shaft 2 as a handle input shaft having a steering handle (steering wheel) 1 at one end, and a torque transmission shaft 3 connected to the other end of the steering shaft 2 via a universal joint (not shown). And a steering gear section 20 for steering the left and right front wheels 5A, 5B via the tie rods 4 by the transmission torque from the torque transmission shaft 3.

The steering shaft 2 is rotatably supported by a steering column 6, and a portion of the steering shaft 2 in the steering column 6 is provided with a torsion bar (not shown). A torque sensor (steering sensor) 7 is provided at an end of the steering column 6 opposite to the steering handle 1 for detecting a torsion angle of the torsion bar, that is, a steering torque value of the steering wheel and outputting a voltage corresponding thereto. Have been. The steering shaft 2 and the torque transmission shaft 3
And an assist motor 8 for assisting (assisting) the steering force by rotating the torque transmission shaft 3 by its rotational force via a speed reducing mechanism (not shown) provided in the gear box 9 in the vicinity of the connecting portion with the gear box 9. Is equipped. Here, an electromagnetic clutch 11 is provided between the assist motor 8 and the speed reduction mechanism for connecting and separating the two. The steering gear unit 20 is a kind of reduction mechanism that converts the rotational movement of the torque transmission shaft 3 into a reciprocating movement of the tie rod 4. In this embodiment, a rack and pinion mechanism is used. gear·
Ratio.

Further, in this embodiment, the assist motor 8
A controller 30 is provided as a control unit for controlling the motor current and the exciting current of the electromagnetic clutch as described later. The controller 30 performs predetermined calculations (calculation of a steering wheel torque based on the output of the torque sensor, calculation of an assist force according to the speed, and the like) based on the output signals of the vehicle speed sensor (speedometer) 15 and the torque sensor 7. The magnitude and direction of the assist force of the assist motor 8 are determined, and the motor current value is controlled. In FIG. 1, reference numeral 40 denotes a battery as a power supply.

FIG. 2 shows a circuit configuration of this embodiment. In this figure, the outputs of the torque sensor 7 and the vehicle speed sensor 15 that detect the steering torque input to the steering shaft 2 are input to an input circuit (not shown) of the controller 30. Each of these signals is subjected to required processing by an input circuit including an A / D converter (not shown) and the like.
To be entered. On the other hand, controller 3
0 is connected to the assist motor 8 and the electromagnetic clutch 11 described above.

Here, the control of the assist motor 8 and the electromagnetic clutch 11 by the controller 30 will be described in detail with reference to the flowchart of FIG.

When an ignition switch (not shown) is turned "ON" at the start of the engine, power is supplied to the controller 30 and control by the controller 30 is started. After the control is started, the CPU (not shown) in the controller 30 first sets an I / O port,
Initial setting of the register and the RAM is performed (S101). Next, the CPU reads the detected value of the steering torque from the torque sensor 7 via an input circuit (not shown) (S10).
2) Then, the magnitude of the torque value and the direction of the torque are determined (S103). Next, the CPU reads the vehicle speed signal from the vehicle speed sensor 5 (S104) and calculates the vehicle speed (S105). At this stage, since the steering torque and the vehicle speed are obtained, the CPU calculates the steering torque and the motor control current corresponding to the vehicle speed from the input torque-motor control current map shown in FIG. It is determined (S106).

Next, in the CPU, based on the motor control current-motor output torque map shown in FIG. 5 and the clutch excitation current-slip limit torque map shown in FIG. The clutch excitation current is determined so that the motor output torque determined from the motor control current value determined in (1) becomes the slip limit torque (S107). The CPU controls the motor current so that the motor current of the assist motor 8 becomes the current value determined above (S108), and the exciting current of the electromagnetic clutch 11 becomes the current value determined above. The clutch current is controlled as described above (S109). Since then
Returning to step S102, the above control operation is repeated.

In the present embodiment, the clutch excitation current is determined as described above in the event that the assist motor 8 is locked ( mechanical restraint) during traveling by using the electromagnetic clutch by the steering force of the steering wheel. This is because the eleventh clutch plate is slid so that the steering can be performed. That is, the motor current of the assist motor 8 and its output torque have a relationship as shown in FIG. 5, and if the motor current is determined, the output torque of the assist motor 8 is also uniquely determined. In order to sufficiently transmit the torque to the speed reduction mechanism side as an assist force, the ability of the electromagnetic clutch 11 (hereinafter, referred to as "clutch capacity") is required so that the clutch plate does not slip even when the torque is received. Therefore, an exciting current for the electromagnetic clutch 11 corresponding to the torque is required. Paradoxically, the clutch capacity, that is, the limit torque that the electromagnetic clutch 11 can withstand (referred to as “slip limit torque”).
However, if the exciting current of the electromagnetic clutch 11 is controlled so that the output torque of the assist motor 8 becomes almost the same, when the torque greater than the output torque of the assist motor 8 is applied to the clutch plate, the capacity of the electromagnetic clutch 11 becomes insufficient. As a result, the clutch plate starts to slide. For this reason, by determining the clutch excitation current based on the clutch excitation current-slip limit torque map of FIG. 6 corresponding to the output torque of the assist motor 8, even when the motor lock occurs during the middle / high speed running, By steering the steering handle 1 with a torque that is equal to or greater than the slip limit torque of the electromagnetic clutch 11, a smooth steering operation can be performed.

As described above, according to this embodiment,
Without providing a special mechanism for detecting motor lock,
Even if a motor lock occurs,
Smooth steering operation can be performed.

[0016]

Since the present invention is constructed and functions as described above, according to this, the electromagnetic clutch slides in accordance with the motor output torque determined from the motor control current value by the clutch exciting current control function of the control unit. Since the exciting current of the electromagnetic clutch is controlled so as to be in the limit state, for example, even when a failure such as a motor lock occurs during middle / high speed running, the steering handle is operated with a torque equal to or more than the slip limit torque of the electromagnetic clutch. Steering makes it possible to perform a smooth steering operation. For this reason, an unprecedented full-time electric power steering system that can perform smooth steering operation in all low, middle and high speed ranges without providing a special mechanism for detecting motor lock. An apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a circuit unit of the embodiment of FIG.

FIG. 3 is a flowchart showing a main control program of the controller of FIG. 1;

FIG. 4 is a diagram showing an input torque-motor control current map stored in an internal memory of a CPU in the controller of FIG. 1;

5 is a diagram showing a motor control current-motor output torque map stored in an internal memory of a CPU in the controller of FIG. 1;

FIG. 6 is a diagram showing a clutch excitation current-slip limit torque map stored in an internal memory of a CPU in the controller of FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steering handle 2 steering shaft as handle input shaft 3 torque transmission shaft 7 torque sensor 8 assist motor 11 electromagnetic clutch 15 vehicle speed sensor 30 controller as control unit

Claims (1)

(57) [Claims] 1. A steering wheel input shaft having a steering wheel, a torque transmission shaft connected to the steering wheel input shaft, and a torque transmission shaft provided so as to be connected or disconnected via an electromagnetic clutch to the torque transmission shaft. An assist motor that applies the rotational torque; and a control unit that controls the assist motor and the electromagnetic clutch. The control unit increases or decreases the motor current of the assist motor according to the vehicle speed and the steering wheel steering torque. In the electric power steering apparatus configured to perform power assist in a steering direction according to a steering torque, the control unit may include a slip limit torque of the electromagnetic clutch.
But the motor output torque law determined from the motor control current value
As the law, it is, electric power steering apparatus characterized by comprising a clutch exciting current control function of controlling the excitation current of the electromagnetic clutch.