JPH04232180A - Electric power steering device - Google Patents

Abstract

PURPOSE:To obtain an electric power steering device capable of steering smoothly at all speed ranges of low middle, and high, even if a motor lock, etc., is produced, without providing a special mechanism such as a motor lock detector, etc. CONSTITUTION:This device is provided with a control part 30 for controlling an assist motor 8 and an electromagnetic clutch 11. The control part 30 increases and decreases a motor current of the assist motor 8 according to the vehicle speed and steering wheel steering torque to assist power in the direction of steering according to the steering torque. Then the control part 30 controls an exciting current of the electromagnetic clutch 11 so that the electromagnetic clutch 11 is brought under the slip limit condition according to the motor output torque determined by the motor control current value.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an electric power steering device, and more specifically, in an automobile, the output of an assist motor (electric motor) is controlled according to the output of a torque sensor that detects steering torque. The present invention relates to an electric power steering device that uses the motor to perform power assist according to steering torque.

0002

[Background Art] Conventionally, in automobiles, in order to reduce the amount of steering operation required when steering the steering wheel, the motor current of an assist motor is increased/decreased or on/off controlled in accordance with the steering torque and the vehicle speed. A relatively large number of so-called vehicle speed-sensitive electric power steering devices that use rotational force to power assist in a steering direction according to steering torque have been developed and put into practical use. This vehicle speed-sensitive electric power steering device increases the auxiliary steering force when driving at low speeds to enable light steering, gradually decreases the auxiliary steering force as the vehicle speed increases, and further increases the auxiliary steering force when driving at a certain speed ( In medium and high speed ranges, the electromagnetic clutch that connects and disconnects the assist motor from the reducer installed on the torque transmission shaft side is turned off.
), the rotational force of the motor is not transmitted to the torque transmission shaft, a manual steering condition is established, and stable steering performance can be obtained.

0003

[Problems to be Solved by the Invention] However, in the conventional power steering device, from the viewpoint of ensuring stable steering performance in the medium and high speed ranges, manual steering is used in the medium and high speed ranges.・The clutch is turned on and off between the high speed range and the high speed range. As a result, there have been disadvantages in that the clutch noise is harsh and the steering feel is not good at the moment the clutch is engaged or during manual steering when the clutch is disengaged. On the other hand, in order to use full-time electric power steering, it is necessary to prevent motor failures such as motor locking during medium and high-speed driving, or to detect this occurrence and immediately disconnect the motor. A special mechanism is required to ensure smooth steering.

0004

[Object of the Invention] The present invention has been made in view of the problems of the conventional example, and its purpose is to detect when a motor lock occurs without providing a special mechanism such as detecting a motor lock. An object of the present invention is to provide a full-time type electric power steering device that can perform smooth steering operations over a wide range of low, medium, and high speeds.

[0005]

[Means for Solving the Problems] The present invention provides a steering wheel input shaft having a steering handle, a torque transmission shaft connected to the steering wheel input shaft, and a torque transmission shaft that is connected to or disconnected from the torque transmission shaft via an electromagnetic clutch. an assist motor that applies rotational torque to the torque transmission shaft; and a control unit that controls the assist motor and the electromagnetic clutch. In an electric power steering device configured to perform power assist in the steering direction according to the steering torque by increasing or decreasing The clutch excitation current control function is configured to control the excitation current of the electromagnetic clutch so that the electromagnetic clutch is in the state shown in FIG. This aims to achieve the above-mentioned objective.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 shows a vehicle equipped with a power steering system (vehicle speed sensitive type) according to this embodiment. Figure 1
In the power steering device 10, the vehicle body 100
equipped at the front of the This 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 that steers the left and right front wheels 5A, 5B via the tie rod 4 by the torque transmitted from the torque transmission shaft 3.

Among these, the steering shaft 2 is rotatably supported by a steering column 6, and a portion of the steering shaft 2 inside the steering column 6 is equipped with a torsion bar (not shown). Further, a torque sensor (steering sensor) 7 is provided at the end of the steering column 6 opposite to the steering handle 1, which detects the torsion angle of the torsion bar, that is, the steering wheel steering torque value, and outputs a voltage corresponding to the torsion angle. It is being In addition, the steering shaft 2 and the torque transmission shaft 3
An assist motor 8 is located near the connection part with the gear box 9 and assists the steering force by rotating the torque transmission shaft 3 with its rotational force via a reduction mechanism (not shown) installed in the gear box 9. is equipped with. Here, an electromagnetic clutch 11 is provided between the assist motor 8 and the speed reduction mechanism section to connect or separate the two. The steering gear section 20 is a type of reduction mechanism that converts the rotational motion of the torque transmission shaft 3 into a reciprocating motion of the tie rod 4. In this embodiment, a rack and pinion mechanism is used, and in this case, the number of teeth of the pinion is the same as the steering gear. It has a gear ratio.

Furthermore, in this embodiment, the assist motor 8
A controller 30 is provided as a control unit that controls the motor current and the excitation current of the electromagnetic clutch as described later. This controller 30 has a vehicle speed sensor (
Based on the output signals of the speedometer) 15 and the torque sensor 7, predetermined calculations (calculation of steering wheel torque using the torque sensor output, calculation of the assist force according to the speed, etc.) are performed to determine the magnitude of the assist force of the assist motor 8. The direction of the motor current is determined and the motor current value is controlled. In FIG. 1, reference numeral 40 indicates a battery as a power source.

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

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

When an ignition switch (not shown) is turned ON when starting the engine, power is supplied to the controller 30, and control by the controller 30 starts. After starting the control, the CPU (not shown) in the controller 30 first sets the I/O ports,
Initial settings of registers and RAM are performed (S101). Next, the CPU reads the detected value of the steering torque from the torque sensor 7 via an input circuit (not shown) (S102).
), 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 (S104).
105). At this stage, since the steering torque and vehicle speed have been obtained, the CPU calculates the steering torque and motor control current according to the vehicle speed from the input torque-motor control current map shown in FIG. 4, which is stored in the internal memory in advance. Decide (S
106).

Next, the CPU performs the step S106 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. 6, which are stored in advance in the internal memory. The clutch excitation current is determined so that the motor output torque determined from the motor control current value determined in (S107) becomes the slip limit torque. Then, the CPU performs motor current control so that the motor current of the assist motor 8 becomes the current value determined above (S108), and the excitation current of the electromagnetic clutch 11 becomes the current value determined above. The clutch current is controlled as follows (S109). Thereafter, the process returns to step S102 and the above control operation is repeated.

In this embodiment, the clutch excitation current is determined as described above in the event that the assist motor 8 is locked (opportunistic restraint) while driving, the electromagnetic clutch is activated by the steering force. This is to enable steering by sliding the clutch plate No. 11. 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 that torque to the reduction mechanism side as an assist force, the electromagnetic clutch 11 needs to have a capacity (hereinafter referred to as "clutch capacity") that does not cause the clutch plate to slip even when receiving that torque. Therefore, an excitation current for the electromagnetic clutch 11 commensurate with 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") is
So that the output torque of the assist motor 8 is at the limit,
If the excitation current of the electromagnetic clutch 11 is controlled, when a torque greater than the output torque of the assist motor 8 is applied to the clutch plate, the electromagnetic clutch 11 will lack capacity and the clutch plate will start to slip. Therefore, by determining the clutch excitation current based on the clutch excitation current-slip limit torque map shown in FIG. By steering the steering wheel 1 with a torque greater than the slip limit torque of the electromagnetic clutch 11, smooth steering operations can be performed.

As explained above, according to this embodiment,
without providing a special mechanism for motor lock detection.
Even if a motor lock occurs, the
Smooth steering operation can be performed.

[0016]

[Effects of the Invention] Since the present invention is configured and functions as described above, the clutch excitation current control function of the control section causes the electromagnetic clutch to slip in accordance with the motor output torque determined from the motor control current value. The excitation current of the electromagnetic clutch is controlled so that the electromagnetic clutch reaches its limit state, so even if a failure such as a motor lock occurs during medium or high-speed driving, the steering wheel cannot be turned with a torque exceeding the slip limit torque of the electromagnetic clutch. By steering, it becomes possible to perform a smooth steering operation. Therefore, there is no need to provide a special mechanism for detecting motor lock.
It is possible to provide an unprecedented full-time electric power steering device that can perform smooth steering operations throughout the high-speed range.

[Brief explanation of the drawing]

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

FIG. 2 is a block diagram showing the configuration of a circuit section in the embodiment of FIG. 1;

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

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

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

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

[Explanation of symbols]

1 Steering handle 2 Steering shaft 3 as a steering wheel input shaft
Torque transmission shaft 7 Torque sensor 8 Assist motor 11 Electromagnetic clutch 15 Vehicle speed sensor 30 Controller as a control unit

Claims (1)

[Claims] 1. A steering wheel input shaft having a steering handle, a torque transmission shaft connected to the steering wheel input shaft, and a torque transmission shaft connected to or disconnected from the torque transmission shaft via an electromagnetic clutch. An assist motor that applies the rotational torque, and a control unit that controls the assist motor and the electromagnetic clutch, and the control unit increases or decreases the motor current of the assist motor according to the vehicle speed and the steering torque. In the electric power steering device configured to perform power assist in a steering direction according to a steering torque, the control section causes the electromagnetic clutch to reach a slip limit state according to a motor output torque determined from a motor control current value. An electric power steering device characterized by having a clutch excitation current control function for controlling an excitation current of the electromagnetic clutch.