JPH0627433U - Electric power steering device - Google Patents

Abstract

(57) [Summary] [Construction] When the ignition key switch 27 is turned on, the current from the battery 21 flows into the capacitor 40 from the preliminary charging circuit 41, and the capacitor 40 is charged. After that, the fail-safe relay circuit 22 is closed. [Effect] Since the fail-safe relay circuit 22 is closed after the voltage across the fail-safe relay circuit 22 becomes substantially zero, a large inrush current does not flow into the fail-safe relay circuit 22.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an electric power steering device that rotates a motor in response to steering and transmits the rotational force of the motor to a steering mechanism to assist the steering force.

[0002]

[Prior art]

 Conventionally, an electric power steering device has been used that assists the steering force by applying a rotational force from the motor to the steering mechanism according to the torque applied to the steering shaft when the steering wheel is rotated for steering. ing. More specifically, a DC motor is attached to the steering column holding the steering shaft, and the rotational force of the DC motor is transmitted to the steering shaft via the worm gear. A torsion bar is installed in the middle of the steering shaft. When the steering wheel is operated, the torsion bar is slightly twisted, causing relative displacement between the input shaft and output shaft connected by the torsion bar. This relative displacement is detected by the torque sensor, and the input current to the DC motor is controlled based on the detection result. This makes it possible to assist the steering force in accordance with the torque applied to the steering shaft.

FIG. 4 is a block diagram showing an electrical configuration of the above electric power steering apparatus. Electric power from the battery 1 mounted on the vehicle is given to the motor drive circuit 3 via the fail-safe relay 2. A DC motor 4 is connected to the motor drive circuit 3, and the rotational force of the DC motor 4 is transmitted to the steering shaft to assist the steering force. A large-capacity smoothing capacitor 5 is connected in parallel to the motor drive circuit 3 to smooth the power supply and remove noise.

Electric power from the battery 1 is also supplied to the system power supply circuit 7. The system power supply circuit 7 is responsive to the ignition key switch 6 being conductive to generate an operating voltage to be given to an electric component mounted on the vehicle. This operating voltage is applied to the control circuit 8 including a microcomputer and the like. The control circuit 8 gives a control signal to the motor drive circuit 3 to control the rotation of the DC motor 4. That is, the control circuit 8 creates a control signal to be given to the motor drive circuit 3 based on the output of the torque sensor 9 described above. As a result, the steering force is assisted according to the torque applied to the steering shaft.

When the ignition key switch 6 is turned on, the control circuit 8 performs an abnormality detection process for checking whether the torque sensor 9 or the like has any abnormality. After this abnormality detection process, the control circuit 8 derives the switching control signal on the line 10, and the fail safe relay 2 is closed. After that, when the control of the motor drive circuit 3 is started, the power supply to the motor drive circuit 3 is started.

[0006]

[Problems to be solved by the device]

 However, in the above configuration, a large inrush current flows when the failsafe relay 2 is closed. Therefore, problems such as welding of the contacts of the fail-safe relay 2 have occurred. Therefore, an object of the present invention is to solve the above technical problems and to provide an electric power steering apparatus capable of preventing a large current from flowing in an opening / closing connection means for connecting a motor drive circuit and a power supply. Is.

[0007]

[Means for Solving the Problems]

 The electric power steering device of the present invention for achieving the above object transmits the rotational force of a motor driven by a drive circuit supplied from a power source through an opening / closing connection means to a steering mechanism to assist the steering force. In the electric power steering device, the drive circuit side of the open / close connecting means is connected in parallel to the open / close connecting means between the capacitor connected in parallel to the drive circuit and the power source and the capacitor. And a pre-charging circuit for charging the capacitor with a current from the power source.

The pre-charging circuit can be configured to include, for example, a resistor that determines a charging current. Further, the preliminary charging circuit may be configured to include a thermistor that determines a charging current and has a negative characteristic with respect to temperature change.

[0009]

[Action]

 According to the above configuration, the pre-charging circuit charges the capacitor connected to the drive circuit side of the opening / closing connection means with the current from the power source. As a result, the voltage between both terminals of the switching connection means connected to the power supply becomes small. Therefore, when the open / close connecting means is closed, no large current flows through this open / close connecting means.

If a thermistor having a negative characteristic is used to determine the charging current in the preliminary charging circuit, the current at the beginning of charging can be increased due to self-heating of the thermistor. Therefore, the capacitor can be charged quickly.

[0011]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. Electric power from a battery 21 as a power source mounted on the vehicle is given to a motor drive circuit 23 via a fail-safe relay circuit 22 which is an open / close connection means. The motor drive circuit 23 supplies a drive current to a DC motor 25 attached to a steering column (not shown) holding a steering shaft. The rotation of the DC motor 25 is transmitted to the steering shaft via a worm gear (not shown) to assist the steering force.

On the motor drive circuit 23 side of the fail-safe relay circuit 22, a large-capacity electrolytic capacitor 40 is connected in parallel with the motor drive circuit 23. The capacitor 40 plays a role of smoothing the power supply voltage and suppressing noise. Power from the battery 21 is also provided to the system power circuit 26 which creates the operating voltage of the device. The system power supply circuit 26 derives an operating voltage on the line 28 in response to the ignition key switch 27 becoming conductive. This operating voltage is applied to the control circuit 30 including a microcomputer (not shown) and the like.

A key switch monitoring circuit 29 for monitoring the state of the ignition key switch 27 is connected to the control circuit 30. The key switch monitoring circuit 29 outputs a predetermined detection signal when the ignition key switch 27 is turned on. The electric power from the battery 21 via the ignition key switch 27 is further connected to the capacitor 40 via the preliminary charging circuit 41. That is, the backup charging circuit 41 is connected in parallel with the fail-safe relay circuit 22 between the battery 21 and the capacitor 40. The precharging circuit 41 comprises a series circuit of a diode D1 which prevents the capacitor 40 from being destroyed when the battery 21 is reversely connected, and a resistor R1 which regulates a charging current to the capacitor 40.

On the other hand, the control circuit 30 outputs interface signals (I / F) 35 and 36 to the output signals of the torque sensor 33 that detects the torque applied to the steering shaft and the vehicle speed sensor 34 that detects the speed of the vehicle. Have been entered through. The control circuit 30 gives a control signal from the line 37 to the motor drive circuit 23 based on the output signals of the torque sensor 33 and the vehicle speed sensor 34.

The control of the motor drive circuit 23 is basically performed based on the detection signal of the torque sensor 33. That is, when the detected torque is large, the motor drive circuit 23 is controlled so that a large current flows through the DC motor 25, and when the detected torque is small, the motor current becomes small. However, when the vehicle is traveling at high speed, the steering shaft can be rotated with a small steering force, so that the assistance of the steering force by the DC motor 25 is not so necessary. Therefore, in the present embodiment, the motor drive circuit 23 is controlled by also referring to the output of the vehicle speed sensor 34.

Specifically, a table is prepared in which the vehicle speed is divided into predetermined speed ranges and the output signal of the torque sensor 33 and the motor current are associated with each other in each speed region. This table is stored in the memory 39 in the control circuit 30. The control circuit 30 refers to the table stored in the memory 39 based on the output signals of the vehicle speed sensor 34 and the torque sensor 33, and creates a control signal to be given to the motor drive circuit 23.

The motor drive circuit 23 is configured by bridge-connecting four transistors Q1, Q2, Q3 and Q4. That is, the series circuit of the transistors Q1 and Q2 and the series circuit of the transistors Q3 and Q4 are connected in parallel to the fail-safe relay circuit 22. A series circuit of the DC motor 25 and the current detection resistor 46 is connected between the connection point 44 of the transistors Q1 and Q2 and the connection point 45 of the transistors Q3 and Q4.

The voltage across the current detection resistor 46 is monitored by a current detection circuit 47 that detects the current flowing through the DC motor 25. The current detection circuit 47 gives a signal corresponding to the voltage across the current detection resistor 46 to the control circuit 30. For example, when the steering wheel is rotated to the right, the control circuit 30 turns on the transistors Q1 and Q4 and keeps the transistors Q3 and Q2 off. As a result, the current from the fail-safe relay circuit 22 flows from the transistor Q1 to the transistor Q4 via the DC motor 25 and the current detection resistor 46. At this time, the control circuit 30 gives a pulse-width-modulated control signal to the transistors Q1 and Q4 based on the output signal of the torque sensor 33. As a result, a current corresponding to the torque applied to the steering shaft flows into the DC motor 25, and a torque corresponding to the torque is applied to the steering shaft.

On the other hand, the current detection circuit 47 detects the current flowing through the DC motor 25, and the detection result is fed back to the control circuit 30. The control circuit 30 compares the motor current read from the memory 39 with the current detected by the current detection circuit 47 based on the output signals of the torque sensor 33 and the vehicle speed sensor 34, and based on the comparison result, the transistor The pulse width modulation signal given to Q1 and Q4 is changed.

When the steering wheel is rotated counterclockwise, the control circuit 30 brings the transistors Q3 and Q2 into conduction and keeps the transistors Q1 and Q4 in a cutoff state. At this time, a current flows in the DC motor 25 in a direction opposite to that when the steering wheel is rotated clockwise. Therefore, this DC motor 25 generates a rotational force in the opposite direction to that when the steering wheel is rotated to the right. Other operations are the same as those in the case of the clockwise rotation described above.

Next, the operation immediately after the ignition key switch 27 is turned on to start the apparatus will be described. When the ignition key switch 27 is turned on, this is detected by the key switch monitoring circuit 29. Then, in response to the output of the key switch monitoring circuit 29, the control circuit 30 performs an abnormality detection process for checking whether or not the output signals of the vehicle speed sensor 34, the torque sensor 33, the current detection circuit 47, etc. are abnormal values. I do. Then, if no abnormality has occurred, the control circuit 30 outputs a switching control signal for closing the fail-safe relay circuit 22 to the line 31.

In the period before the fail-safe relay circuit 22 is closed, the current from the battery 21 flows into the capacitor 40 via the preliminary charging circuit 41, and the capacitor 40 is charged thereby. That is, the fail-safe relay circuit 22 is closed after the capacitor 40 is charged. Therefore, when the fail-safe relay circuit 22 is closed, the voltage across the fail-safe relay circuit 22 is almost zero. Therefore, when the fail-safe relay circuit 22 is closed, a large inrush current does not flow in the fail-safe relay circuit 22.

As a result, welding of the contacts of the fail-safe relay circuit 22 is effectively prevented, so that its reliability is improved and the contact life can be extended. Moreover, since a large current does not flow when the fail-safe relay circuit 22 is closed, a small relay can be applied as the fail-safe relay circuit 22, which can contribute to cost reduction.

Further, since a large current does not flow when the fail-safe relay circuit 22 is closed, it is possible to reduce the generation of noise when the fail-safe relay circuit 22 is closed. As a result, it is possible to prevent the microcomputer contained in the control circuit 30 from running away. FIG. 2 is an electric circuit diagram showing the configuration of a pre-charging circuit 41A used in another embodiment of the present invention. In the description of this embodiment, reference is again made to FIG. 1 above. This pre-charging circuit 41A should be used in place of the pre-charging circuit 41 of FIG. The precharge circuit 41A is composed of a series circuit of a diode D11 and a thermistor TH having a negative characteristic with respect to temperature change.

FIG. 3 is a graph for explaining the operation. 3 (a) shows the time variation of the voltage Vc across the capacitor 40, FIG. 3 (b) shows the time variation of the current Ic flowing into the capacitor 40, and FIG. 3 (c) shows the resistance value R of the thermistor TH. Is shown. In each figure, the curve indicated by the chain double-dashed line corresponds to the configuration of this embodiment to which the pre-charging circuit 41A is applied. Further, in each drawing, for comparison, a curve corresponding to the case of the above-described first embodiment using the precharge circuit 41 shown in FIG. 1 is shown by a solid line.

When the ignition key switch 27 is turned on at time t1, the current Ic rises and charging of the capacitor 40 starts, as indicated by reference numeral A1 in FIG. 3 (b). As the charging progresses, the voltage Vc across the capacitor 40 gradually increases, as indicated by reference numeral A2 in FIG. 3 (a). On the other hand, when the current Ic flows, the thermistor TH self-heats. Due to this heat generation, the resistance value R of the thermistor TH decreases as shown by reference numeral A3 in FIG. 3 (c) during the period from time t1. Therefore, as shown in FIGS. 3 (a) and 3 (b), the capacitor 40 should be charged more quickly than the preliminary charging circuit 41 of FIG. 1 using the normal resistor R1 during the period from the resistance time t1. You can

The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. For example, in the above embodiment, the fail-safe relay circuit 22 is used as the switching connection means, but a power transistor or the like may be used as the switching connection means in addition to the relay. In this case, it is possible to prevent a large current from flowing through the power transistor, so that it is possible to prevent the power transistor from being destroyed.

In addition, various design changes can be made without changing the gist of the present invention.

[0029]

[Effect of device]

 As described above, according to the present invention, the capacitor connected to the drive circuit side of the opening / closing connection means is charged in advance, so that when the opening / closing connection means is closed, a large current is applied to this opening / closing connection means. It can be prevented from flowing. As a result, the reliability of the opening / closing connection means can be improved and the life of the opening / closing connection means can be extended.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a precharge circuit according to another embodiment of the present invention.

FIG. 3 is a graph for explaining the operation.

FIG. 4 is a block diagram showing an electrical configuration of a conventional electric power steering device.

[Explanation of symbols]

 21 Battery 22 Fail Safe Relay Circuit 23 Motor Drive Circuit 25 DC Motor 27 Ignition Key Switch 30 Control Circuit 33 Torque Sensor 40 Capacitor 41 Preliminary Charging Circuit D1 Diode R1 Resistor 41A Preliminary Charging Circuit D11 Diode TH Thermistor

Claims (3)

[Scope of utility model registration request] 1. An electric power steering apparatus for assisting a steering force by transmitting a rotational force of a motor driven by a drive circuit supplied from a power source through an opening / closing connection means to a steering mechanism, wherein the opening / closing connection means comprises: On the drive circuit side, a capacitor connected in parallel to this drive circuit is interposed between the power supply and the capacitor so as to be connected in parallel to the switching connection means, and the capacitor is charged by the current from the power supply. An electric power steering device, comprising: 2. The electric power steering apparatus according to claim 1, wherein the pre-charging circuit includes a resistor that determines a charging current. 3. The electric power steering apparatus according to claim 1, wherein the preliminary charging circuit includes a thermistor which determines a charging current and has a negative characteristic with respect to a temperature change.