JP2001157485A - Motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor drive circuit in which conduction strength of each circuit element, e.g. a motor drive element, can be reduced. SOLUTION: Switches SW1-SW4 can switch connection of each motor drive element Tr1-Tr4 between the terminals M1 and M2 of a motor M. When the vehicle speed is higher than a predetermined speed, the motor drive elements Tr1, Tr2 are connected with the terminal M1 and the motor drive elements Tr3, Tr4 are connected with the terminal M2. When the vehicle speed is lower than the predetermined speed, the motor drive elements Tr1, Tr3 are connected with one of the terminals M1, M2 and the motor drive elements Tr2, Tr4 are connected with the other of the terminals M1, M2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive circuit for driving an electric motor used as, for example, a drive source of an electric power steering device.

[0002]

2. Description of the Related Art Conventionally, an electric power steering device has been used which transmits torque (steering assist force) generated by an electric motor to a steering mechanism of a vehicle to thereby assist steering. In such an electric power steering device, a target current is set according to the steering torque applied to the steering wheel, and the motor drive circuit is controlled based on the set target current, so that the target current is set according to the steering torque. A steering assist force is applied to the steering mechanism.

FIG. 4 is an electric circuit diagram showing a configuration of a conventional motor drive circuit. The motor drive circuit includes a motor drive element 91 and a battery (voltage + Vcc) mounted on the vehicle.
It comprises a bridge circuit in which a series circuit of 92 and a series circuit of motor drive elements 93 and 94 are connected in parallel. The electric motor M that generates the torque to be given to the steering mechanism is
Connection point between motor drive elements 91 and 92 and motor drive element 9
It is connected between 3,94 connection points.

[0004] For example, when the electric motor M is to generate torque in a direction to assist the rightward steering, the pair of motor driving elements 92 and 93 are cut off and the pair of motor driving elements 91 and 94 are turned off. A drive pulse signal having a duty corresponding to the magnitude of the torque to be generated from the electric motor M is input. On the other hand, when the electric motor M is to generate torque in a direction to assist leftward steering, the pair of the motor driving elements 91 and 94 is turned off, and the pair of the motor driving elements 92 and 93 is connected to the electric motor M. A drive pulse signal having a duty corresponding to the magnitude of the torque to be generated from M is input.

[0005]

For example, when the steering wheel is stationary for garage entry, it is input to the pair of motor drive elements 91 and 94 or the pair of motor drive elements 92 and 93. It is necessary to generate the maximum torque from the electric motor M by setting the duty of the drive pulse to 100%. However, such a state occurs only for a small period within the entire vehicle traveling period. In other words, the period during which the maximum current is applied to the electric motor M in order to generate the maximum torque from the electric motor M is short during the entire period during which the electric motor M is energized.

Nevertheless, each circuit element (component) of the motor drive circuit must be configured to withstand the maximum current supply to the electric motor M. For this reason, in the conventional motor drive circuit, for example, an FET having a capacity to withstand the maximum current is used.
1, 92, 93, 94, or one motor drive element 91, 9 by connecting a plurality of FETs in parallel.
2, 93, 94, which is one of the factors that increase the cost of the motor drive circuit.

An object of the present invention is to solve the above-mentioned technical problems and to provide a motor drive circuit that can reduce the withstand current of each circuit element such as a motor drive element.

[0008]

In order to achieve the above object, the present invention provides a method for controlling the drive current of an electric motor (M) by switching between conduction and interruption by a drive pulse signal. The first to fourth motor driving elements (Tr1, Tr2, Tr3, Tr4) and the connection destination of the first motor driving element (Tr1) are connected to one terminal (M1) and the other terminal (M2) of the electric motor. First connection switching means (SW1) for switching, and second connection switching means (SW2) for switching the connection destination of the second motor drive element (Tr2) to one terminal and the other terminal of the electric motor. ) And the third motor drive element (Tr
Third connection switching means (SW3) for switching the connection destination of 3) to one terminal and the other terminal of the electric motor;
A motor drive circuit (8) including a fourth connection switching means (SW4) for switching a connection destination of the fourth motor drive element (Tr4) to one terminal and the other terminal of the electric motor. ).

[0009] Alphanumeric characters in parentheses indicate corresponding components in the embodiment described later. According to the present invention, the first to fourth connection switching means are provided, and the connection destination of each motor drive element can be switched between one terminal and the other terminal of the electric motor. For example, the first and third
Are provided on the upstream side of the electric motor with respect to the driving current direction of the electric motor.
Is provided downstream of the electric motor with respect to the driving current direction of the electric motor, and when it is necessary to supply a relatively large driving current to the electric motor, the first and third motor driving elements are provided. Preferably, the element is connected to one of the two terminals of the electric motor, and the second and fourth motor drive elements are connected to the other. Then, it is preferable that all of the first to fourth motor driving elements are made conductive. In this case, the drive current of the electric motor flows through the first and third motor drive elements, is supplied to the electric motor, passes through the electric motor, and flows through the second and fourth motor drive elements. Therefore,
The current flowing through each motor drive element can be reduced to about half the current flowing through the electric motor.

Therefore, compared with the conventional motor drive circuit, the current-carrying capability of the circuit elements such as the motor drive element can be reduced. Therefore, when a plurality of FETs and the like are connected in parallel to form one motor drive element, the F
The number of ET and the like can be reduced, and the configuration can be made cheaper than in the past. On the other hand, the first and third motor drive elements are provided upstream of the electric motor with respect to the drive current direction of the electric motor, and the second and fourth motor drive elements are provided with respect to the drive current direction of the electric motor. If the drive current to be supplied to the electric motor can be relatively small, the first and second motor drive elements are connected to one of both terminals of the electric motor, and the third And a fourth motor drive element is preferably connected to the other. In this case, the motor drive circuit has a circuit pattern similar to that of the conventional motor drive circuit. However, since the drive current to be supplied to the electric motor is small, the current flowing through each motor drive element is also small. Even if an FET or the like is used for the motor drive element, the motor drive element is not destroyed.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electric configuration of an electric power steering device provided with a motor drive circuit according to one embodiment of the present invention. This electric power steering device transmits a torque generated by an electric motor M to a steering mechanism 1 of a vehicle to assist steering.

The steering mechanism 1 is connected to a base end of a steering shaft 3 having a steering wheel 2 attached to a distal end. Steering shaft 3
Is divided into an output shaft 31 coupled to the steering mechanism 1 side and an input shaft 32 coupled to the steering wheel 2 side, and the output shaft 31 and the input shaft 32
Are connected to each other by a torsion bar 4.
The torsion bar 4 twists according to the steering torque input from the steering wheel 2,
The direction and amount of the twist are detected by a torque sensor 5 provided in association with the torsion bar 4. That is, the torque sensor 5 detects the direction and amount of torsion of the torsion bar,
The steering torque input from the steering wheel 2 is detected.

An output signal of the torque sensor 5 is input to a controller (ECU) 6. Further, an output signal from a vehicle speed sensor 7 for detecting a traveling speed (vehicle speed) of the vehicle is input to the controller 6. The controller 6 determines a target current value of the electric motor M according to the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 7, and controls the motor drive circuit 8 based on the target current value. I do. This allows
A current corresponding to the steering torque, the vehicle speed, and the like is supplied from the motor drive circuit 8 to the electric motor M, and the electric motor M outputs a torque required for steering assistance.

FIG. 2 is an electric circuit diagram showing the configuration of the motor drive circuit 8. The motor drive circuit 8 includes a motor drive element Tr1 and a battery (voltage + Vcc) mounted on the vehicle.
It comprises a bridge circuit in which a series circuit of Tr2 and a series circuit of motor drive elements Tr3 and Tr4 are connected in parallel. Terminals M1 and M2 of the electric motor M are connected to a connection point 81 between the motor driving elements Tr1 and Tr2 and a connection point 82 between the motor driving elements Tr3 and Tr4, respectively.

The first motor drive element Tr1 and the connection point 81
And a switch SW as first connection switching means.
1 is interposed. By switching the switch SW1, the connection destination of the motor drive element Tr1 can be switched between the terminal M1 and the terminal M2 of the electric motor M. Further, a switch SW2 as a second connection switching means is interposed between the second motor drive element Tr2 and the connection point 81, and by switching this switch SW2, the motor drive element Tr2 is switched.
2 can be switched between the terminal M1 and the terminal M2 of the electric motor M.

Further, a switch SW3 as a third connection switching means is interposed between the third motor driving element Tr3 and the connection point 82. By switching this switch SW3, the motor driving element Tr3 is switched. Can be switched between the terminal M1 and the terminal M2 of the electric motor M. Further, a switch SW4 as fourth connection switching means is interposed between the fourth motor drive element Tr4 and the connection point 82. And
By switching the switch SW4, the connection destination of the motor drive element Tr4 can be switched between the terminal M1 and the terminal M2 of the electric motor M.

The switching of these switches SW1 to SW4 is controlled by the controller 6 (see FIG. 1) according to the vehicle speed. Specifically, the vehicle speed sensor 7
When the vehicle speed detected by (see FIG. 1) is higher than a predetermined speed, the motor drive elements Tr1, Tr2
Are connected to the terminal M1 of the electric motor M and the switches SW1 to SW by the controller 6 so that the motor driving elements Tr3 and Tr4 are connected to the terminal M2 of the electric motor M.
4 is switched. Thereby, the motor drive circuit 8
Is an H-bridge circuit similar to a conventional motor drive circuit, as shown in FIG.

When a torque (rightward torque) in a direction assisting rightward steering is to be generated from the electric motor M, a duty ratio corresponding to the steering torque and the vehicle speed is applied to the pair of motor drive elements Tr1 and Tr4. Is input. At this time, the motor drive elements Tr2,
No driving pulse signal is input to the pair of Tr3, and the motor driving elements Tr2 and Tr3 are kept in the cutoff state. As a result, a drive current flowing from the terminal M1 to the terminal M2 flows through the electric motor M, and a rightward torque corresponding to the drive current is output from the electric motor M.

On the other hand, when a torque (leftward torque) for assisting leftward steering is to be generated from the electric motor M, a duty ratio corresponding to the steering torque and the vehicle speed is applied to the pair of motor drive elements Tr2 and Tr3. Is input. At this time, the motor driving elements Tr1, T
No drive pulse signal is input to the pair of r4, and the motor drive elements Tr1 and Tr4 are kept in the cutoff state. As a result, a drive current flowing from the terminal M2 to the terminal M1 flows through the electric motor M, and a leftward torque having a magnitude corresponding to the drive current is output from the electric motor M.

When the vehicle speed is equal to or lower than the predetermined speed and the electric motor M is to generate a rightward torque, the motor driving elements Tr1 and Tr3 are driven by the electric motor M
Of the motor drive elements Tr2, Tr4
Are connected to the terminal M2 of the electric motor M, the switches SW1 to SW4 are switched by the controller 6. Thus, the motor drive circuit 8 has a circuit pattern as shown in FIG. Then, a drive pulse signal having a duty according to the steering torque and the vehicle speed is input to all the motor drive elements Tr1 to Tr4, and these motor drive elements Tr1 to Tr4 are simultaneously turned on / off. As a result, a drive current flowing from the terminal M1 to the terminal M2 flows through the electric motor M, and a rightward torque corresponding to the drive current is output from the electric motor M.

When the vehicle speed is equal to or lower than the predetermined speed and a leftward torque is to be generated from the electric motor M, the motor driving elements Tr2 and Tr4 are driven by the electric motor M
Of the motor drive elements Tr1, Tr3
Are connected to the terminal M2 of the electric motor M, the switches SW1 to SW4 are switched by the controller 6. Thus, the motor drive circuit 8 has a circuit pattern as shown in FIG. Then, a drive pulse signal having a duty according to the steering torque and the vehicle speed is input to all the motor drive elements Tr1 to Tr4, and these motor drive elements Tr1 to Tr4 are simultaneously turned on / off. As a result, a drive current flowing from the terminal M2 to the terminal M1 flows through the electric motor M, and a leftward torque having a magnitude corresponding to the drive current is output from the electric motor M.

As described above, according to this embodiment, since the switches SW1 to SW4 are provided, the connection destination of each of the motor driving elements Tr1 to Tr4 is switched to the terminal M1 and the terminal M2 of the electric motor M. Is available. When the vehicle is traveling at a relatively low speed, the switches SW1 to SW4 are switched,
The motor drive circuit 8 is designed to have a circuit pattern as shown in FIG. 3 (b) or 3 (c). This allows
The driving current of the electric motor M supplied from the battery flows through the motor driving elements Tr1 and Tr3 and is supplied to the electric motor M, and after passing through the electric motor M, the motor driving element Tr
2 and Tr4. Therefore, the current flowing through each of the motor drive elements Tr1 to Tr4 is
About half of the current flowing through the

On the other hand, when the vehicle is running at a relatively high speed, the switches SW1 to SW4 are switched so that the motor drive circuit 8 has the same circuit pattern as the conventional one. Since a large steering assist force is not required, the duty of the driving pulse signal input to the pair of the motor driving elements Tr1 and Tr4 or the pair of the motor driving elements Tr2 and Tr3 is not made 100%. Therefore, compared to the conventional motor drive circuit,
The withstand current of the circuit elements such as the motor driving elements Tr1 to Tr4 can be reduced. When a plurality of FETs and the like are connected in parallel to form one motor drive element Tr1 to Tr4, the number of FETs and the like to be used can be reduced. Therefore, the motor drive circuit 8 can be configured at a lower cost than the conventional motor drive circuit.

The embodiment of the present invention has been described above, but the present invention can be embodied in other forms. For example, in the above-described embodiment, a case where the present invention is applied to a drive circuit of an electric motor for an electric power steering device is taken as an example. However, the present invention is applied to an electric motor provided in a device other than the electric power steering device. It can be widely applied to motor drive circuits. In addition, it is possible to make various design changes within the technical scope described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an electric configuration of an electric power steering device including a motor drive circuit according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a motor drive circuit.

FIG. 3 is a diagram for explaining switching of a switch according to a vehicle speed and a direction of a torque to be generated from an electric motor.

FIG. 4 is an electric circuit diagram showing a configuration of a conventional motor drive circuit.

[Explanation of symbols]

 8 Motor drive circuit M Electric motor M1 terminal (one terminal) M2 terminal (other terminal) SW1 switch (first connection switching means) SW2 switch (second connection switching means) SW3 switch (third connection switching means) SW4 Switch (fourth connection switching means) Tr1 Motor drive element (first motor drive element) Tr2 Motor drive element (second motor drive element) Tr3 Motor drive element (third motor drive element) Tr4 Motor drive element ( Fourth motor drive element)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Masaya Segawa 3-5-8, Minamisenba, Chuo-ku, Osaka-shi Inside Koyo Seiko Co., Ltd. (72) Tomoho Kada 3-5-2, Minamisenba, Chuo-ku, Osaka-shi F term (reference) in Seiko Co., Ltd. 5H570 AA21 BB04 CC01 DD06 EE01 FF07 FF08 HA04 HA08

Claims (1)

[Claims] In order to control a driving current of an electric motor,
First to fourth motor drive elements whose conduction and cutoff are switched by a drive pulse signal, and a first connection for switching a connection destination of the first motor drive element to one terminal and the other terminal of the electric motor. Switching means; second connection switching means for switching a connection destination of the second motor drive element to one terminal and the other terminal of the electric motor; and a connection destination of the third motor drive element to the electric motor. Third connection switching means for switching between one terminal and the other terminal of the motor; and fourth connection switching for switching the connection destination of the fourth motor drive element to one terminal and the other terminal of the electric motor. Means for driving the motor.