JP3472624B2 - Drive circuit for electric power steering device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an electric power steering apparatus provided with a device for preventing a motor drive element from overheating. 2. Description of the Related Art FIGS. 4 and 5 show a drive circuit of a conventional electric power steering apparatus. In such an electric power steering device, the steering force is assisted by the electric motor 1 according to the running state of the vehicle. FIG. 4 is a drive circuit diagram of a conventional electric power steering apparatus. The electric motor 1 is connected to motor driving elements 2 to 5.
The motor drive elements 2 to 5 control the value of the current flowing through the electric motor 1. In addition, the motor drive elements 2 and 5 are opened and the motor drive elements 3 and 4 are closed, or conversely, the motor drive elements 3 and 4 are opened and the motor drive elements 2 and 5 are closed to flow to the electric motor 1. The direction of the current is changed to make the motor rotate forward or reverse to control the energization of the electric motor 1. Further, the motor driving elements 2 to 5
Is connected via a relay 7 to a battery 6 which is a power source of the present drive circuit. The relay 7 is driven by the transistor 8 and opens and closes a circuit between the battery 6 and the motor driving elements 2 to 5. The motor drive elements 2 to 5 are connected to a power MOSFET drive circuit 10, and the power MOSFET drive circuit 10 is connected to output terminals 12 to 15 of a control device 9. Power M
The OSFET drive circuit 10 is connected to the output terminal 12 of the control device 9.
15 is operated, the gate voltage to the motor drive elements 2 to 5 is changed, and the energization to the electric motor 1 is controlled. The control device 9 outputs a signal to assist the steering force according to the running state of the vehicle.
The temperature sensor 18 detects the temperature of the motor drive elements 2 to 5 and feeds back the same to the control device 9 to prevent the functions of the motor drive elements 2 to 5 from being deteriorated due to overheating, or to prevent destruction or burning. The output terminal 11 of the control device 9 is
It is connected to the transistor 8. The resistor 16 is for adjusting the base current of the transistor 8. FIG. 5 shows a general component arrangement in the above-described drive circuit. When the motor driving elements 2 to 5 generate heat,
There is a possibility that its function is deteriorated and sometimes it is destroyed or burned out. Therefore, the motor drive elements 2 to 5 are attached to the radiator 17 in order to release the heat. This radiator 17
Is made of a material having a high thermal conductivity such as aluminum, a heat radiation effect can be obtained, and the temperature of the radiator 17 becomes almost the same as the temperature of the motor drive elements 2 to 5. The radiator 17 includes a temperature sensor 18 and a motor driving element 2 to 2.
Attach to the center of 5. By attaching the temperature sensor 18 to a portion close to the motor drive elements 2 to 5, the temperature sensor 18 can detect the temperature of the radiator 17, that is, the temperature almost equal to that of the motor drive elements 2 to 5. Become. Further, the transistor 8 is formed on the substrate 19 similarly to other components.
Installed in Next, the operation of the present driving circuit will be described.
When the transistor 8 is energized by a signal from the output terminal 11 of the control device 9, the relay 7 is closed.
At this time, according to the signal from the control device 9, the power MO
The SFET drive circuit 10 operates and the motor drive elements 2 to 5
Controls the energization of the electric motor 1. When the system is abnormal, the power supply to the transistor 8 is stopped, the relay 7 is opened,
Protect circuits and motors. Further, by opening the relay 7, it is possible to stop the automatic movement of the electric motor 1 at the time of abnormality, and to continue safe driving by manual steering. In the drive circuit of the electric power steering apparatus as described above, consider a case where the motor drive elements 2 to 5 generate heat due to, for example, long-time energization. At this time, the temperature is detected by the temperature sensor 18 and fed back to the control device 9.
When the temperature exceeds the set value, the relay 7 is opened to stop energization, or the energization of the motor drive elements 2 to 5 is controlled to suppress the heat generation of the motor drive elements 2 to 5,
Prevent destruction and burning. As described above, since the temperature detecting means for the motor driving elements 2 to 5 requires the dedicated temperature sensor 18, the number of parts is increased, The number of manufacturing processes increases, and costs increase. In addition, the larger the number of parts, the higher the probability of failure and the lower the reliability. According to the present invention, there is provided an electric motor, a power supply source, a control device, an electric motor provided between the electric motor and the power supply source, and an electric motor driven by a signal from the control device. A motor drive element for controlling the supply of current to the motor, a relay provided between the motor drive element and a power supply source for opening and closing a current supply path to the motor drive element, and a transistor for driving the relay In the drive circuit of the electric power steering device having the above, the motor drive element and the transistor are mounted on the same radiator on the same radiator, and the control device controls the relay drive.
By detecting the base-emitter voltage of the above transistor, the heat generation of the motor drive element is detected, and when the base-emitter voltage becomes lower than the set voltage, the power supply to the motor drive element is controlled. Alternatively, the power supply to the transistor is stopped and the relay is opened. According to the present invention, the temperature of the motor drive elements 2 to 5 can be detected by detecting the base-emitter voltage of the transistor 8. In other words, trucks that use relay drive
Multiple use of transistor 8 for temperature detection
That is. When the voltage between the base and the emitter of the transistor 8 becomes lower than the set value, that is, when an abnormality occurs in the motor driving elements 2 to 5, the relay 7 is opened to energize the entire circuit. Stopping or controlling the energization of the motor driving elements 2 to 5 prevents the motor driving elements 2 to 5 from being broken or burnt. The drive circuit of the electric power steering apparatus according to the embodiment shown in FIGS. 1 to 3 utilizes the characteristic that the base-emitter voltage of the transistor 8 changes with the temperature. It is used as
In the drive circuit shown in FIG. 1, the base-emitter voltage of the transistor 8 is fed back to the input terminal 20 of the control device 9. And this transistor 8
As shown in FIG. 3, the motor drive elements 2 to 5 are installed on the radiator 17 at both ends of the transistor 8 and connected to the substrate 19 at both ends of the transistor 8. When the radiator 17 is made of a material having a high thermal conductivity such as aluminum, the temperatures of the radiator 17 and the motor driving elements 2 to 5 become substantially the same. Therefore, since the transistor 8 is attached to a portion close to the motor driving elements 2 to 5, the temperatures of the two become almost the same via the radiator 17. In the circuit diagram of FIG. 1, the same components as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted. Transistor 8
2 has a relationship shown in FIG. 2 between the base-emitter voltage and the temperature. That is, as the temperature of the transistor 8 increases, the base-emitter voltage decreases almost in proportion thereto. Therefore, the temperature of the transistor 8 is substantially the same as the temperature of the motor driving elements 2 to 5, so that a base-emitter voltage corresponding to a temperature exceeding the allowable range of the motor driving elements 2 to 5 is set in advance as a set value. Next, the operation of this embodiment will be described. For example, when the motor driving elements 2 to 5 generate heat due to, for example, long-time energization, the temperature of the transistor 8 becomes almost the same through the radiator 17. At this time, as shown in FIG. 2, the base-emitter voltage of the transistor 8 changes. This base-emitter voltage is fed back to the input terminal 20 of the control device 9, and when this voltage becomes lower than the set value, the control device 9 determines that one of the motor driving elements 2 to 5 is abnormal. Then, the power supply to the transistor 8 is stopped, the relay 7 is opened to stop the power supply, or the power supply control signal is sent to the power MOSFET drive circuit 10 to control the power supply to the motor drive elements 2 to 5 by this signal. Therefore, it is possible to suppress heat generation of the motor drive elements 2 to 5 and prevent destruction or burning, and because of the destruction or burning, it becomes impossible to control the power supply to the motor and perform unnecessary steering assist. Can be avoided and driving can be continued safely. In this embodiment, the radiator 17 and the substrate 19 are shown as separate members.
The transistor 8 may be provided on the substrate 19 in the case where the transistor 9 itself is formed of a material having a high heat dissipation property such as aluminum and also serves as a radiator. In this case, the number of parts can be further reduced as compared with the above embodiment. According to the present invention, a relay driving transistor which is indispensable for a driving circuit of an electric power steering device is used as a temperature detecting means for a motor driving element at the same time.
Since the temperature sensor is also used, there is no need to provide a dedicated temperature sensor. In this way, one transistor is multiplexed.
As a result , the number of parts can be reduced, the number of manufacturing steps can be reduced, and the cost can be reduced. In addition, the reduced number of components reduces the probability of failure and increases reliability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a drive circuit diagram of an electric power steering device according to an embodiment of the present invention. FIG. 2 is a diagram showing characteristics of transistor temperature and base-emitter voltage. FIG. 3 is a diagram showing a component arrangement according to the embodiment of the present invention. FIG. 4 is a diagram showing a drive circuit of a conventional electric power steering device. FIG. 5 is a diagram showing a component arrangement of a conventional example. [Description of Signs] 1 Electric motors 2 to 5 Motor drive element 6 Battery 7 Relay 8 Transistor 9 Control device 10 Power MOSFET drive circuit 16 Resistance 17 Radiator 18 Temperature sensor 19 Substrate

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B62D 5/04 B62D 6/00-6/06 H02P ^7/ 00-7/34

Claims (1)

(57) [Claims 1] An electric motor, a power supply source, a control device, and a control device are provided between the electric motor and the power supply source. A motor drive element that controls the energization of the motor, a relay that is provided between the motor drive element and a power supply source, and opens and closes a current supply path to the motor drive element, and a transistor that drives the relay. In a drive circuit of an electric power steering apparatus provided with the above, a motor drive element and a transistor are mounted on the same radiator and in close proximity to each other, while a control device controls a base-emitter voltage of the transistor for driving a relay. To detect the heat generated by the motor driving element, and when the base-emitter voltage becomes lower than the set voltage, the motor driving element is detected. Or controlling the energization, or stopping the energization of the transistor, the driving circuit of the electric power steering apparatus being characterized in that a configuration in which the relay is opened.