JP3427876B2 - 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 apparatus, and more particularly to an electric motor drive means for driving an electric motor, in which the reliability of the operation is improved.

[0002]

2. Description of the Related Art Generally, an electric power steering apparatus is provided with an electric motor control section composed of a microcomputer and the like, and an electric motor drive means for driving the electric motor, and an operation amount acting on a steering system, such as a steering torque and a steering rotation speed. , The steering angle, etc. are detected, the electric motor control unit determines the electric motor control signal based on these detection signals, and the electric motor drive means controls the driving of the electric motor by this control signal, thereby improving the response performance of the electric motor and steering. We are trying to improve the feeling.

FIG. 6 is a circuit system diagram showing a conventional electric power steering apparatus according to Japanese Patent Publication No. 7-96387. This electric power steering apparatus includes a detection unit 1 that detects a steering torque and a steering rotation speed, and a detection unit 1.
An electric motor control unit 2 that determines an electric motor control signal based on the output signal of the electric motor, an electric motor drive unit 3 that drives the electric motor, and an electric motor 4 that generates an auxiliary torque for the steering system.
It is composed of a power supply circuit 5.

The detection unit 1 includes sensors 11 and 1 for detecting steering torque and steering rotation speed applied to the steering system.
2 and sends out the respective detection signals S ₁ , S ₂ and S ₃ , S ₄ to the electric motor control section 2 via the respective interface circuits 13, 14. The electric motor control unit 2 includes an A / D converter 21 and a microcomputer unit (MCU) 22, and determines and outputs a control signal for the electric motor 4. That is, MCU2
2, the steering torque detection signal T (T = | S1-S2
Based on |), the electric motor control duty D _T stored in the memory (not shown) is read out, and the steering rotation speed N (N = | S3−
Similarly, the motor rotation speed control duty D _M is read based on S4 |), and the motor control signals T3 and T4 are read by these.
Is determined and output.

The electric motor drive circuit 3 is a drive unit 3
0 and four field effect transistors (FET) 31, 3
2, 33, and 34, each of which is a bridge circuit in which each arm is combined. The contents of these FETs are first elements that are adjacent to each other as elements due to their diode junctions.
And a connection point of the second FETs 31 and 32 and third and fourth FETs 33 and 3 which are symmetrically located adjacent to each other and are adjacent to each other.
The connection point of 4 serves as a power supply terminal, and the relay circuit 54 of the power supply circuit 5 is connected to one connection point. Further, the connection points of the fourth and first FETs 34 and 31 and the connection points of the second and third FETs 32 and 33 serve as output terminals and are connected to the electric motor 4 via a relay circuit (switch means) 39. The current flowing through the relay circuit 39, that is, the armature current of the motor 4 is detected by the current detection circuit 40, and the A / D
It is input to the MCU 22 via the converter 21 and used as fault diagnosis data for the electric motor system.

By driving the gates of the FETs 31 to 34 with the output signal of the drive unit 30,
Operate FET31-34 as a switching element,
The electric motor 4 is drive-controlled. Here, when the electric motor system is normal, the relay control signal O _R is input as O _R = 1 to the relay circuits 39 and 54 to maintain the connection state, and when O _R = 0 is input. The circuit of the electric motor 4 is opened by shutting off. The power supply circuit 5 supplies the electric power of the vehicle battery 50 to the relay circuit 5 via a fuse circuit 51, a key switch 52 such as an ignition switch, and a fuse circuit 53.
4 and the constant voltage circuit 55. The relay circuit 54 connects and disconnects electric power to the FETs 31 to 34 of the drive circuit 3, and the constant voltage circuit 55 operates the MCU 22 and the like.

As described above, in the electric power steering apparatus of FIG. 6, even if one of the FETs 31 to 34 forming the bridge arm of the electric motor system, that is, the electric motor drive circuit is broken and becomes conductive, this The FET detection is detected by the current detection circuit 40, and the relay circuit 3 is detected by the MCU 22.
By shutting off 9, the formation of a closed circuit can be avoided, and no braking current will flow to the electric motor 4.

[0008]

In the conventional electric motor power steering apparatus shown in FIG. 6, when a brushless motor is used as the electric motor 4, the brushless motor is provided between the motor drive circuit 103 and the brushless motor 104 as shown in FIG. Usually connected by three leads. Therefore, if a relay circuit 139 (switch means) that shuts off the motor current is provided between the motor drive circuit 103 and the brushless motor 104 in order to avoid the formation of the above-mentioned closed circuit, as shown in FIG. It is necessary to install the relay circuits 139 at two locations and to control the relay circuits 139 at the two locations. Further, since the relay circuit 139 is provided at two places, the number of parts of the electric power steering device is increased, resulting in high cost and limitation of layout of parts.

The present invention has been made to solve the above-mentioned problems, and when a brushless motor is used, the closed loop of the motor drive current can be cut off, and the number of parts of the entire apparatus can be reduced. Accordingly, it is an object of the present invention to provide an electric power steering device that can reduce costs and improve layout.

[0010]

According to a first aspect of the present invention, there is provided an electric power steering apparatus in which a brushless motor is energized by a motor drive circuit section to apply motor power to a steering system, wherein the motor drive circuit section has a plurality of switching elements. The power supply is connected to the input terminal of the bridge circuit, the brushless motor is connected to the output terminal of the bridge circuit, and the closed loop opening switch means is connected to the neutral point of the brushless motor. It is characterized by

According to a second aspect of the invention, in an electric power steering apparatus for energizing a brushless motor by a motor drive circuit section to apply motor power to a steering system, steering torque, steering speed, vehicle speed, engine speed, etc. are detected. Connected to the input terminal of the bridge circuit, and a motor control circuit unit having a bridge circuit composed of a plurality of switching elements, a motor control unit that determines a motor control signal based on the output signal of the detection unit. A power supply circuit, a brushless motor connected to the output terminal of the bridge circuit, a switch means for closing the closed loop connected to the neutral point of the brushless motor, and a current detection circuit for detecting the armature current of the motor. The switch means is turned off when a closed loop is formed in the motor drive circuit.

The invention of claim 3 is characterized in that a switch means for opening a closed loop is provided in the motor portion of the brushless motor.

The invention of claim 4 is characterized in that the motor drive circuit portion of the brushless motor is provided with a switch means for opening the closed loop.

[0014]

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1. FIG. 1 is a circuit system diagram showing an electric power steering device according to a first embodiment, and FIG. 2 is a schematic diagram showing a system configuration of the electric power steering device. In the figure, the electric power steering system includes a conventional steering mechanism (rack and pinion steering mechanism), a detection unit 101 for detecting steering torque, a steering rotation speed, a vehicle speed, an engine rotation speed, and the like. Motor control unit 102 that determines a motor control signal based on the output signal
A motor drive circuit unit 103 for driving the motor, a brushless motor 104 for generating an auxiliary torque for the steering system, and a power supply circuit 105.

The detection unit 101 is composed of a torque sensor 111 for generating a voltage signal according to a steering input torque, a vehicle speed sensor 112 for detecting a vehicle speed, and an engine speed detection sensor 113 for detecting an engine speed. The signal is input to the motor control unit 102. The motor control unit 102 is composed of an interface circuit, a microcomputer, etc., calculates the steering assist force based on the signals from the above-mentioned sensors, determines the current control signal of the brushless motor 104, and outputs it.

The motor drive circuit section 103 comprises a drive unit 130 and a bridge circuit BR in which switching elements 131 to 136 constituted by six diode elements and relay contacts (FET; field effect transistor) are combined as each arm. The bridge circuit BR is
First, second and third switching elements 1 adjacent to each other
A connection point of 31, 132, 133 and a connection point of the fourth, fifth and sixth switching elements 134, 135, 136 which are symmetrically located and adjacent to each other serve as a power supply / ground terminal, and one connection point is The power supply circuit 105 is connected. Also, the first and fourth switching elements 131, 1
34 connection point, second and fifth switching element 13
The connection points of 2,135 and the connection points of the third and sixth switching elements 133,136 serve as output terminals and are connected to the three input terminals of the brushless motor 104.

In this embodiment, the brushless motor 104 is used.
A switch means (relay circuit) 109 for opening the closed loop is provided at the neutral point n. In addition, the brushless motor 10
The armature current of 4 is detected by the current detection circuit 140,
It is input to the microcomputer of the motor control unit 102 via the A / D converter. The motor stop command signal ST from the motor control unit 102 is input to the switch drive circuit 150.

Next, the operation of the electric power steering system according to the first embodiment will be described. Motor control unit 10
2 calculates a steering assist force based on signals from the torque sensor 111, the vehicle speed sensor 112, and the engine speed detection sensor 113, and determines a drive current control signal for the brushless motor 104. Then, the brushless motor 104
Rotation, the drive unit 130 is operated by a command from the motor control unit 102, and the switching elements 131 to
This is performed by controlling ON / OFF of 136. For example, first, when the switching elements 133 and 135 are turned on, a motor current flows as indicated by the broken line arrow in FIG. 3A, and further, the switching elements 132 and 134.
ON and the switching elements 131 and 136 are ON,
By sequentially switching the switching elements, a drive current flows through the three-phase brushless motor 104, and the motor rotates.

Here, when the switching element 133 has an ON failure, a closed loop current circuit is formed in the brushless motor 104 as shown by the solid line arrow in FIG.
At this time, if an external force for rotating the brushless motor 104 is applied, a braking force acts on the motor due to the induced electromotive force of the motor, and the steering feeling becomes heavy.

In this embodiment, for example, when an ON failure occurs in the switching element 133 as described above, the switch means 1 installed at the neutral point of the brushless motor 104.
By turning off 09, the abnormal closed loop current circuit is opened. That is, the current detection circuit 150 constantly detects the motor current and transmits it to the motor control unit 102, and the motor control unit 102 determines whether or not a closed loop current circuit is formed due to a short circuit or the like, and an abnormal closed loop is formed. If it is determined that the motor stop command signal ST has been sent, the switch drive circuit 150 turns off the switch means 109.

As described above, according to the first embodiment, any one of the switching elements (FETs and the like) 131 to 136 forming the bridge circuit BR of the motor drive circuit section 103 is broken to be in a conductive state. Also, the current detection circuit 140 detects this FET breakdown and the like, and the motor control unit 102,
Brushless motor 1 via switch drive means 150
By opening and closing only the switch means 109 provided at the neutral point of 04, the whole circuit of the motor drive can be cut off,
The formation of an abnormal closed circuit can be avoided.

Embodiment 2. FIG. 4 is a circuit diagram showing a motor drive unit of the electric power steering device according to the second embodiment. In this embodiment, the brushless motor 104
The neutral point switch means 109a is provided in the brushless motor section. The switch drive circuit 150
Is provided on the side of the motor drive circuit unit 103 as in the first embodiment.

According to the second embodiment, by providing the switch means 109a for opening the closed loop in the brushless motor section, not only the ON failure of the switching elements 131 to 136 but also the motor drive circuit section 103 and the brushless motor 104 are prevented. It is also more effective against lead wire short circuit. Further, as a lead wire between the motor drive circuit unit 103 and the brushless motor 104, the O of the switch means 109a is used.
It is possible to use a small amount of electric power for only N / OFF control and to use two wirings, so that the wirings can be thinned and simplified.

Embodiment 3. FIG. 5 is a circuit diagram showing a motor drive unit of the electric power steering apparatus according to the third embodiment. In this embodiment, the brushless motor 104
The neutral point switch means 109b is used as the motor drive circuit unit 1
No. 03 is provided. The rest of the configuration is similar to that of the first embodiment.

According to the third embodiment, by providing the switch means 109b for opening the closed loop in the motor drive circuit section 103, the wiring between the motor drive circuit section 103 and the brushless motor 104 is made different from that in the second embodiment. Thick lines and three lines are required, but the configuration of the brushless motor unit 104 is simplified, and the motor drive circuit unit 103 is generally advantageous in environmental conditions such as vibration resistance, heat resistance, and water resistance as compared with the motor unit. The environment resistance condition of the means does not need to be as severe as that of the motor part, inexpensive switch means can be used, and it can be further integrated with the motor drive circuit.

[0026]

As described above, according to the first and second aspects of the present invention, since the switch means for opening the closed loop is provided at the neutral point of the brushless motor, the bridge circuit of the motor drive circuit section is constructed. When one of the switching elements is broken and becomes conductive, only one switch means is turned off to shut off the entire motor drive circuit, thereby forming an abnormal closed circuit. It can be avoided. That is, the switch means for opening the closed loop with respect to the brushless motor need only be installed in one place,
Only the opening / closing control of the switch means is sufficient.

Further, the cost can be reduced by reducing the number of parts of the entire apparatus, and the layout property can be further improved.

According to the third aspect of the present invention, by providing the switch means for opening the closed loop in the brushless motor section, not only the ON failure of the switching element but also the lead wire short circuit between the motor drive circuit section and the brushless motor is prevented. But it will be more effective. Further, the switch means is turned on as a lead wire between the motor drive circuit section and the brushless motor.
It is possible to use a small amount of power for which only ON / OFF control is performed and to use two wirings, so that the wirings can be thinned and simplified.

According to the fourth aspect of the present invention, by providing the closed loop opening switch means in the motor drive circuit section, the structure of the brushless motor section is simplified, and the motor drive circuit section is generally resistant to vibration and heat. Since the environmental conditions such as water resistance are more advantageous than the motor part, the environmental resistance condition of the switch means does not have to be as severe as that of the motor part, and inexpensive switch means can be used. Can be integrated with.

[Brief description of drawings]

FIG. 1 is a circuit system diagram showing an electric power steering device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a system configuration of the electric power steering apparatus according to the first embodiment.

FIG. 3 is a circuit diagram for explaining a motor drive current according to the first embodiment.

FIG. 4 is a circuit diagram showing a motor drive unit of the electric power steering device according to the second embodiment.

FIG. 5 is a circuit diagram showing a motor drive unit of an electric power steering device according to a third embodiment.

FIG. 6 is a circuit system diagram showing a conventional electric power steering device.

FIG. 7 is a circuit diagram showing a motor drive unit when a brushless motor is used in the electric power steering device.

FIG. 8 is a circuit diagram showing a motor drive unit when a brushless motor is used in the electric power steering device.

[Explanation of symbols]

101 detection unit, 102 motor control unit, 103 motor drive circuit unit, 104 brushless motor, n brushless motor neutral point, 105 power supply circuit, 109, 109
a, 109b switch means, 111 torque sensor,
112 vehicle speed sensor, 113 engine speed detection sensor, 130 drive unit, 131 to 136 switching element, 140 current detection circuit, 150 switch drive circuit.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI B62D 119: 00 H02P 6/02 371C (56) References JP-A-8-163889 (JP, A) JP-A-5-292725 ( JP, A) JP 63-206186 (JP, A) JP 8-322264 (JP, A) JP 7-96387 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 6/24 B62D 5/04 B62D 6/00

Claims (4)

(57) [Claims] 1. An electric power steering apparatus for energizing a brushless motor by a motor drive circuit unit to apply motor power to a steering system, wherein the motor drive circuit unit includes a bridge circuit including a plurality of switching elements, A power supply is connected to an input terminal of the bridge circuit, a brushless motor is connected to an output terminal of the bridge circuit, and a closed loop opening switch means is connected to a neutral point of the brushless motor. apparatus. 2. An electric power steering apparatus for energizing a brushless motor by a motor drive circuit section to apply motor power to a steering system, and a detection section for detecting steering torque, steering rotation speed, vehicle speed, engine rotation speed, and the like. A motor control unit that determines a motor control signal based on the output signal of the detection unit, a motor drive circuit unit having a bridge circuit composed of a plurality of switching elements, and a power supply circuit connected to an input terminal of the bridge circuit. A brushless motor connected to an output terminal of the bridge circuit, a switch means for closing a closed loop connected to a neutral point of the brushless motor, and a current detection circuit for detecting an armature current of the motor, The switch means is turned off when a closed loop is formed in the motor drive circuit. Electric power steering device that. 3. The electric power steering apparatus according to claim 1, wherein the motor portion of the brushless motor is provided with switch means for opening the closed loop. 4. The electric power steering apparatus according to claim 1, wherein the motor drive circuit portion of the brushless motor is provided with switch means for opening a closed loop.