JPS62279171A - Safety circuit for electric type power steering device - Google Patents

Abstract

PURPOSE:To improve safety without the occurrence of malfunction during low speed steering in a non-running state, by providing a device which, based on an output from a car speed sensor, calculates an allowable current value, being decreased to a low value with the increase in the running speed of a vehicle. CONSTITUTION:A car speed sensor 11 and a torque sensor 12 are connected to a computer 10. A driving circuit 16, driving a motor 15 for assisting a steering force, a DA converter 17, and a comparator 18, to the one input terminal of which the output of the DA converter 17 is connected, are connected to the computer. In an ROM area in the computer 10, an allowable current value, being steppedly decreased to a low value with the increase in a car speed (v), is mapped and stored, and an allowable current value responding to a present car speed is read from the ROM area. When it is discriminated that a signal from the comparator 18 is outputted, the computer 10 provides a signal by means of which the motor 15 is stopped.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an electric power steering device! This relates to each horizontal circuit.

<Prior Art> In an electric power steering system, if an excessive current flows through the motor due to a failure or the like in a control circuit that controls the current supplied to the motor, an undesirable state may occur.

In order to solve this problem, an abnormality detection circuit is installed to detect when a current exceeding the allowable value flows into the motor, and when a signal is output from this abnormality detection circuit, the current to the motor is stopped. It is conceivable to configure the system so that the supply is cut off.

When such a circuit is used, it is necessary to set the allowable current value to a large value so that it is not determined to be abnormal even when a large current flows through the motor, such as when the motor is stopped at a low speed.

<Problems to be Solved by the Invention> However, if the allowable current value for determining an overcurrent is set to a large value that is not determined to be abnormal during low-speed stationary operation, a large steering torque will be generated during high-speed driving. Since an abnormality cannot be detected until after the abnormality has been activated, abnormal steering may not be reliably prevented even if the current supply to the motor is cut off in response to the detection of such an abnormality.

Means for Solving the Problems> The present invention has a vehicle speed sensor that detects the running speed of the vehicle, a current detection circuit that detects the current flowing to the motor, and a vehicle speed sensor that detects the running speed of the vehicle based on the output of the front vehicle speed sensor. permissible current value deriving means for deriving a permissible current value that takes a smaller value as the current value increases; a determining means for making a determination and outputting a signal; and a'a for cutting off the supply of current to the motor in response to the output of the determining means.
[r means] is provided.

When the running speed of the vehicle changes, the allowable value deriving means accordingly derives an allowable current value according to the changed vehicle speed, and determines that the current flowing to the motor exceeds the derived allowable current value. A signal is output from the means, and the current supply to the motor is cut off by actuation of the cutoff means. The permissible value deriving means derives a gradually smaller permissible current value as the vehicle speed increases, so that malfunctions do not occur when swinging off at low speeds, and at high speeds, an abnormality can be determined early and the motor can be controlled. The supply current can be cut off, greatly improving safety.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 1, 10 is a computer with a built-in memory, and this computer 10 includes a vehicle speed sensor 11 for detecting traveling speed and a torque sensor 12 for detecting steering torque.
is connected to the drive circuit 16 for driving the motor 15 for steering force assistance, a DA converter 17, and a comparator 18 to which the output of the DA converter 17 is connected to one input terminal.
is connected.

A motor 15 is connected between the drive circuit 16 and the motor 15.
A current detection circuit 20 is interposed to detect the current flowing in the
The output of this current detection circuit 20 is connected to the other input of the comparator 18. In addition, the current detection circuit 20 and the motor 1
A relay 21 is provided between the motors 5 and 5, which is driven by a relay driver 22 operated by a command from the computer 10 to cut off the supply of current to the motor 15.

As shown in FIG. 3, the ROM area in the computer 10 stores data from Is to (3/4) as the vehicle speed
Allowable current values that gradually decrease from Is, (3/4)Is to -(1/2)Is are stored as a map. That is, the maximum current value flowing through the motor 15 under normal steering conditions has a characteristic that it decreases as the road resistance decreases as the vehicle speed increases, and the RO
The allowable current value stored in the M area is set to be larger than the maximum current value flowing during normal steering in each speed range by a predetermined amount, and to decrease gradually as the speed increases. ing.

The computer 10 controls the motor 15 by executing the process shown in FIG. 2 at regular intervals.

That is, first, the vehicle speed sensor 11. The output signal from the torque sensor 12 is read (30), and based on this, a target current value ro to be supplied to the motor 15 is calculated or derived by referring to a map (31). Then, this target current value IO is output to the drive circuit 16 (32
), read the allowable current value Im corresponding to the current vehicle speed from the ROM area with reference to the map shown in FIG. 33),
This is output to the DA converter 17 (34).

As a result, a voltage corresponding to the allowable current value of 1 m read from the map is supplied to one input terminal of the comparator 18, and the current supplied to the motor 15 detected by the current detection circuit 20 is increased to the allowable current value of 1 m. When the value exceeds 0, a signal is output from the comparator 18.

In step (35), the computer 10 selects this comparator 1.
Comparator 1 determines whether or not a signal is output from Comparator 1.
If it is determined that a signal is being output from 8, it drives the relay 21 or gives an off command to the radar driver 22 (36). As a result, the supply of current to the motor 15 is stopped, resulting in a manual steering state. After this, the abnormality notification lamp is turned on (37).

Note that the comparison operation of the comparator 18 in the above embodiment may be performed by software of the computer 10.

<Effects of the Invention> As described above, in the present invention, when the current value flowing through the motor for steering force assistance exceeds the allowable current value, the current supply to the motor is stopped, and the current supply to the motor is stopped. The value is configured so that it decreases as the vehicle speed increases, so there will be no malfunction when the vehicle is stationary at low speed.
In addition, at high speeds, abnormality can be determined early and the current supplied to the motor can be cut off, which has the advantage of greatly improving safety.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 1 is a block diagram showing the overall configuration of a safety circuit in an electric power steering system, FIG. 2 is a flowchart showing the operation of the computer 10 in FIG. 1, and FIG. Figure 3 shows computer 1 in Figure 1.
FIG. 3 is a diagram showing changes in allowable current values mapped and stored within 0. 10... Computer, 11... Vehicle speed sensor, 12
...Torque sensor, 15...Motor, 16...Drive circuit, 17...DA converter, 18...Comparator, 2
0... Current detection circuit, 21... Relay.

Claims (1)

[Claims] (1) In an electric power steering device that detects a steering torque and supplies a current corresponding to the detected steering torque to a steering force auxiliary motor, a vehicle speed sensor that detects the running speed of the vehicle; a current detection circuit that detects the current flowing through the motor; an allowable value derivation means that derives an allowable current value that takes a smaller value as the vehicle speed increases based on the output of the front vehicle speed sensor; and a current detecting means that detects the current flowing through the motor. determining means for determining that the current applied exceeds the permissible current value derived by the permissible value deriving means and outputting a signal, and supplying current to the motor in response to the output of the determining means; 1. A safety circuit in an electric power steering device, characterized in that it is provided with a cutoff means for cutting off.