JP2013177136A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of using a cell of an auxiliary power source up to temperature near to heat resistant temperature.SOLUTION: An electric power steering device includes a motor 4 for generating steering assisting force, a main power source 7 for supplying electric power to the motor 4, an auxiliary power source 8 for connecting a plurality of cells in series and/or parallel, a charge-discharge circuit 9 for charging the auxiliary power source 8 based on the main power source 7 and selectively constituting a first output state of supplying the electric power to the motor 4 only by the main power source 7 and a second output state of supplying the electric power to the motor 4 from the main power source 7 and the auxiliary power source 8, a circuit 5 for driving the motor 4, temperature sensors 12 installed in the plurality of respective cells of the auxiliary power source and detecting the temperature of the respective cells, and a control circuit 6 for selecting the output state of the charge-discharge circuit 9 in response to the required steering assisting force and restricting charge-discharge on the auxiliary power source 8 when at least one of the temperatures detected by the respective temperature sensors 12 reaches a predetermined upper limit threshold value.

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force by a motor, and more particularly to a configuration of an electric circuit thereof.

  The electric power steering device is a device that generates a steering assist force by a motor in accordance with a driver's steering torque. In recent years, the demand for electric power steering devices for large vehicles has increased rapidly, and the steering assist force required for such large vehicles has also increased. Therefore, more power must be supplied to the motor. However, there are cases where such a large amount of power cannot be adequately provided by using only the battery as the main power source. Therefore, a configuration in which an auxiliary power source is provided separately from the battery, and normally only the battery is supported. When a larger amount of power is required, the battery and the auxiliary power source are connected in series to supply power from both power sources. Has been proposed (see, for example, Patent Document 1).

  Such an auxiliary power supply generally has a configuration in which a plurality of cells are combined with a cell including a capacitor as a constituent element. Each cell has a low withstand voltage, but a required voltage can be ensured as a whole by connecting a plurality of cells in series. Further, in order to satisfy a certain current capacity, it is also necessary to connect cell groups (modules) connected in series in parallel.

Japanese Patent Laying-Open No. 2005-287222 (FIG. 1)

  In the conventional electric power steering apparatus as described above, the auxiliary power source cell has a property that it is weaker than the battery at a high temperature. However, providing a cooling device (for example, a fan or a Peltier element) so that the cell does not reach a high temperature causes a complicated structure and an increase in cost. Therefore, it is reasonable to detect the temperature of the entire auxiliary power supply with a temperature sensor and limit the charging / discharging of the auxiliary power supply (stop or reduce the current) to cool the cell naturally when a predetermined upper limit value is reached. it is conceivable that.

  However, the amount of heat generated in each cell varies. In consideration of such variation, under the condition that any cell must absolutely avoid overheating exceeding the heat-resistant temperature, one temperature is measured as a whole auxiliary power supply, and control based on this temperature is performed. It is necessary to allow a sufficient margin for the upper limit of the temperature. That is, it is necessary to perform a safe control by setting a temperature considerably lower than the heat resistant temperature of the actual cell as the upper limit value, and as a result, it becomes difficult to use the cell to near the heat resistant temperature. In other words, since an excessive margin is taken, the heat resistance performance of the cell is not fully utilized, and as a result, a cell having a large capacity is used.

  An object of the present invention is to provide an electric power steering device that can use a cell of an auxiliary power source up to a temperature close to a heat-resistant temperature in view of such a conventional problem.

  (1) In the electric power steering apparatus of the present invention, a motor that generates a steering assist force, a main power source that supplies electric power to the motor, and a plurality of cells are connected in series and / or in parallel. An auxiliary power source capable of supplying power; charging the auxiliary power source based on the main power source; and a first output state for supplying power to the motor only by the main power source; the main power source; A charge / discharge circuit that selectively configures a second output state for supplying power from an auxiliary power source to the motor, a circuit that drives the motor, and a plurality of cells, and is attached to each of the cells. A temperature sensor for detecting the temperature, and an output state of the charge / discharge circuit according to a required steering assist force, and at least one of the temperatures detected by the temperature sensors. An electric power steering apparatus comprising a control circuit that limits charging / discharging of the auxiliary power supply when a predetermined upper limit threshold is reached, wherein the main power supply and the auxiliary power supply are connected in series with each other, and the charging / discharging circuit Has a first transistor and a second transistor, the first transistor is connected so that the source is on the main power supply side and the drain is on the drive circuit side, and the second transistor is connected on the drive circuit side, The drain is connected so as to be on the auxiliary power source side.

  In the electric power steering apparatus configured as described above, a temperature sensor for detecting the temperature of the cell is attached to each of the plurality of cells, and at least one of the temperatures detected by each temperature sensor is a predetermined upper limit. When the threshold is reached, the charging / discharging of the auxiliary power supply is limited. Therefore, compared to the case where the temperature of the entire auxiliary power supply is detected and charging / discharging is limited based on the detected temperature, the auxiliary power supply can be used up to a temperature closer to the heat resistant temperature of the cell.

(2) In the electric power steering apparatus of the present invention, it is desirable that the first transistor and the second transistor are driven so as to be alternately turned on.
By alternately turning on the first transistor and the second transistor, a current is supplied to the drive circuit from only the main power supply, and a current is supplied to the drive circuit from the main power supply and the auxiliary power supply connected in series to the main power supply. The state is selected.

(3) In the electric power steering apparatus of the present invention, it is preferable that the charge / discharge circuit further includes a third transistor, and the auxiliary power supply is charged by repeatedly turning on and off the third transistor.
If the temperature sensor detects that the temperature is above a certain level, the third transistor is turned off to stop charging, and if the temperature sensor detects that the temperature is below a certain level, Charging is started by turning on the third transistor.

(4) In the electric power steering apparatus according to the present invention, it is desirable that the control circuit performs control so that the steering assist state can be made only by the main power supply after the discharge current is gradually reduced.
After gradually reducing the discharge current, the steering assist force does not drop sharply when the steering assist state is set only by the main power source.

(5) An electric power steering apparatus according to another aspect of the present invention includes a motor that generates a steering assist force, a main power source that supplies power to the motor, and a plurality of cells connected in series and / or in parallel. An auxiliary power source capable of supplying power to the motor; and a first output state for charging the auxiliary power source based on the main power source and supplying power to the motor only by the main power source; A charge / discharge circuit that selectively configures a second output state that supplies power to the motor from the main power supply and auxiliary power supply, a circuit that drives the motor, and a plurality of cells attached to each of the plurality of cells. A temperature sensor for detecting the temperature of each cell, and an output state of the charge / discharge circuit according to a required steering assist force, and among the temperatures detected by the temperature sensors. An electric power steering device including a control circuit that limits charge / discharge of the auxiliary power when at least one reaches a predetermined upper threshold, wherein the main power and the auxiliary power are connected in series; The charge / discharge circuit includes a first transistor and a second transistor, and the first transistor and the second transistor are driven to be alternately turned on.
The main power source and the auxiliary power source are connected in series with each other, and the charging / discharging circuit includes a first transistor and a second transistor, and the first transistor and the second transistor are driven to be turned on alternately. A state in which current is supplied to the drive circuit from only the main power supply and a state in which current is supplied to the drive circuit from the main power supply and the auxiliary power supply connected in series to the main power supply are selected.

  According to the electric power steering apparatus of the present invention, the auxiliary power source cell can be used up to a heat resistant temperature or a temperature close thereto, so that the auxiliary power source can fully demonstrate its inherent capability, and as a result, the cell power The capacity can be reduced and the cost of the apparatus can be reduced.

1 is a block circuit diagram of an embodiment of an electric power steering device of the present invention. FIG. FIG. 2 is a circuit diagram illustrating an example of a more detailed circuit configuration of some of the circuits in the block circuit of FIG. 1. (A) is a figure which shows the internal structure of an auxiliary power supply, (b) is a circuit block diagram in one cell.

Embodiments of an electric power steering apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block circuit diagram showing a configuration mainly including an electric circuit of an electric power steering apparatus 1 according to an embodiment of the present invention.
In FIG. 1, a steering device 2 is driven by a driver's steering torque applied to a steering wheel (handle) 3 and a steering assist force generated by a motor 4. The motor 4 is a three-phase brushless motor and is driven by a drive circuit 5. The drive circuit 5 is controlled by a control circuit 6 including a microcomputer.

  The power source is composed of a main power source 7 including a battery and an auxiliary power source 8 made of an electric double layer capacitor, which are connected in series with each other. The charging / discharging circuit 9 controlled by the control circuit 6 charges the auxiliary power supply 8 based on the main power supply 7 and has a first output state in which power is supplied to the drive circuit 5 and the motor 4 only by the main power supply 7. The second output state in which power is supplied from the main power supply 7 and the auxiliary power supply 8 to the drive circuit 5 and the motor 4 can be selectively configured.

  The control circuit 6 receives an output signal from a torque sensor 10 that detects a steering torque applied to the steering wheel 3. Further, an output signal of the vehicle speed sensor 11 that detects the vehicle speed is input to the control circuit 6. Further, a temperature sensor 12 is provided in each of the plurality of cells constituting the auxiliary power supply 8, and each output signal (temperature detection signal) is input to the control circuit 6. In FIG. 1 and FIG. 2 described later, only one temperature sensor is illustrated for simplicity.

  FIG. 2 is a circuit diagram showing an example of a more detailed circuit configuration of some of the circuits in the block circuit of FIG. In FIG. 2, the main power source 7 is composed of a battery 7B and an alternator (having rectification and regulator functions) 7A connected in parallel thereto. The voltage of the battery 7B is guided to the drive circuit 5 and the motor 4 through the electric circuit L1 and the electric circuit L3 in which the MOS-FET 91 is inserted. The MOS-FET 91 is an N channel, and is connected such that the source is on the main power supply 7 side and the drain is on the drive circuit 5 side. The parasitic diode 91d is configured such that the current flows in the forward direction when power is supplied from the main power supply 7 to the motor 4.

  The high potential side electric circuit L <b> 2 of the auxiliary power supply 8 connected in series with the main power supply 7 is connected to the connection point between the drain of the MOS-FET 91 and the drive circuit 5 through the MOS-FET 92. The voltage in the state where the main power supply 7 and the auxiliary power supply 8 are connected in series with each other (voltage of the electric circuit L2) is guided to the drive circuit 5 and the motor 4 via the electric circuit L2 and the electric circuit L3 in which the MOS-FET 92 is inserted. It is burned. The MOS-FET 92 is an N channel, and is connected so that the source is on the drive circuit 5 side and the drain is on the auxiliary power supply 8 side. Further, the parasitic diode 92d is in a direction opposite to the direction in which a current flows when power is supplied from the main power supply 7 and the auxiliary power supply 8 to the motor 4.

  A booster circuit (bootstrap circuit) 93 is connected to the electric circuit L1 to which the voltage of the main power supply 7 is applied, and the output voltage is applied to the gate drive circuit (FET driver) 94. By the gate drive circuit 94, the MOS-FETs 91 and 92 are driven so as to be alternately turned on.

  On the other hand, the anode of a diode 96 is connected to the electric circuit L1 through a reactor 95. The cathode of the diode 96 is connected to the high potential side electric circuit L <b> 2 of the auxiliary power source 8. A P-channel MOS-FET 97 is provided between the anode of the diode 96 and the ground side electric circuit LG. The MOS-FET 97 is driven by a gate drive circuit 98. When the MOS-FET 97 is in an on state, a current flows from the main power supply 7 through the reactor 95 and the MOS-FET 97. When the MOS-FET 97 is turned off from this state, a reverse high voltage is generated in the reactor 95 so as to prevent the magnetic flux change due to the current interruption, and as a result, the output voltage of the main power supply 7 is boosted, and the diode The auxiliary power supply 8 is charged via 96. Therefore, the auxiliary power supply 8 can be charged by repeatedly turning on and off the MOS-FET 97. Charging is performed, for example, when the torque sensor 10 does not detect the steering torque, or when there is still enough power even if all the required power is paid only by the main power supply 7.

  The drive circuit 5 includes a motor drive circuit 51 including a three-phase bridge circuit constituted by six MOS-FETs (not shown), and a gate drive circuit for applying a gate voltage for PWM control of these MOS-FETs. 52 and a smoothing electrolytic capacitor 53 connected in parallel to the motor drive circuit 51.

FIG. 3A is a diagram illustrating an internal configuration of the auxiliary power supply 8. As shown in the figure, the auxiliary power supply 8 is composed of a plurality of cells. For example, a module in which m (≧ 2) cells are connected in series is regarded as one module, and this module is divided into n (≧≧). 1) Connected in parallel. On the outer skin of each of the plurality of cells, for example, temperature sensors 12-11... 12-1m, 12-21... 12-2m. 12 nm is closely attached, and an output signal (temperature detection signal) of each temperature sensor is input to the control circuit 6. In FIG. 3A, for the sake of simplicity, temperature sensors are illustrated only for some of the cells.
FIG. 3B is a circuit configuration diagram in one cell. As shown, one cell includes a capacitor C and an internal resistance R existing in series with the capacitor C. The resistance value of the internal resistance R varies slightly from cell to cell. Therefore, the same current flows through m cells in series, but the amount of heat generated varies from cell to cell.

  In the electric power steering apparatus 1 (FIG. 2) configured as described above, the control circuit 6 is based on a steering torque signal sent from the torque sensor 10 or a vehicle speed signal sent from the vehicle speed sensor 11. In order to generate an appropriate steering assist force, the motor drive circuit 51 is operated via the gate drive circuit 52 to drive the motor 4.

  Further, the control circuit 6 estimates a required power for obtaining a required steering assist force based on the steering torque and the vehicle speed, and compares this with a reference value. When the required power is less than or equal to the reference value, the control circuit 6 turns on the MOS-FET 91 and turns off the MOS-FET 92 (first output state of the charge / discharge circuit 9). Accordingly, the voltage of the main power supply 7 is smoothed by the smoothing capacitor 53 and supplied to the motor drive circuit 51. The gate drive circuit 52 drives the motor drive circuit 51 based on a control signal from the control circuit 6. In this case, the power of the auxiliary power supply 8 is not supplied to the drive circuit 5. Since the on-resistance of the MOS-FET 91 is much smaller than the forward resistance of the parasitic diode 91d (for example, about 1 mΩ), most of the current flowing from the main power supply 7 to the drive circuit 5 passes from the source to the drain. The current flowing through the parasitic diode 91d is very small.

  On the contrary, when the required power exceeds the reference value, that is, when the required power cannot be covered by the main power supply 7 alone, the control circuit 6 turns off the MOS-FET 91 and turns on the MOS-FET 92 (charge). Second output state of the discharge circuit 9). As a result, the voltage is supplied to the drive circuit 5 with the main power supply 7 and the auxiliary power supply 8 connected in series with each other. As a result, large power exceeding the power that can be output from only the main power supply 7 can be supplied to the drive circuit 5. At this time, since the cathode of the parasitic diode 91d of the MOS-FET 91 is at a higher potential than the anode, that is, a reverse voltage, current from the auxiliary power supply 8 to the main power supply 7 is prevented.

  On the other hand, the control circuit 6 receives a temperature detection signal that is an output signal of each temperature sensor 12 and monitors whether or not at least one value thereof reaches a predetermined upper limit threshold value. As the upper limit threshold, a heat resistant temperature (upper limit) of the cell is set. When the value of the temperature detection signal reaches a predetermined upper limit threshold during charging of the auxiliary power supply 8, the control circuit 6 continuously turns off the MOS-FET 97 to stop charging. Since the heat generation stops when the charging is stopped, the temperature of all the cells decreases. Thereby, it can prevent that the function of a cell is inhibited by high temperature.

  Further, when the value of the temperature detection signal reaches a predetermined upper limit threshold value during the discharge of the auxiliary power supply 8, the control circuit 6 controls the gate drive circuit 52 (PWM control) to suppress the current flowing through the motor drive circuit 51. To do. Thereby, the electric current which flows into all the cells in the auxiliary power supply 8 falls, and a temperature rise is also suppressed. In addition, since steering assist force also falls in connection with this, it is preferable to suppress gradually current suppression so that steering assist force may not fall rapidly. In addition, after the gradual decrease, the MOS-FET 92 can be turned off and the MOS-FET 91 can be turned on so that only the main power supply 7 is in a steering assist state. Thereby, the discharge of the auxiliary power supply 8 is stopped, and the temperature of all the cells is lowered.

  As described above, in the electric power steering apparatus 1 according to the present embodiment, of the temperatures detected by the temperature sensors 12 attached to each of a plurality (n × m) cells constituting the auxiliary power supply 8. When at least one reaches a predetermined upper limit threshold, the control circuit 6 limits charging (discharging or current reduction) of the auxiliary power supply 2. Therefore, if the heat-resistant temperature of the cell is set as the upper limit threshold, charging / discharging is limited only when the cell with the largest heat generation reaches the heat-resistant temperature. At that time, all other cells are close to the heat-resistant temperature. The temperature has been reached.

  Thus, in this embodiment, all the cells of the auxiliary power supply 8 can be used up to the heat resistant temperature or a temperature close thereto. Therefore, the auxiliary power supply 8 can fully exhibit its inherent capability, and as a result, the cell capacity can be reduced and the cost of the apparatus can be reduced.

In the above embodiment, the electric power steering apparatus 1 having a circuit configuration in which the auxiliary power supply 8 is connected in series to the main power supply 7 has been described. However, the circuit in which the auxiliary power supply is connected in parallel to the main power supply. Similarly, in the electric power steering apparatus having the configuration, it is possible to perform control for limiting charging and discharging by providing a temperature sensor.
In addition, the auxiliary power source in the above embodiment is composed of a plurality of modules composed of a plurality of cells connected in series, but the auxiliary power source is composed of a plurality of cells connected in series. Alternatively, it may be composed of a plurality of cells connected in parallel.

  Furthermore, in the above embodiment, when determining whether or not to use the auxiliary power supply 8 to supply power to the motor 4, the control circuit 6 estimates the required power to obtain the required steering assist force, Although this was compared with the reference value, other ways of determination are possible. For example, the current supplied to the motor drive circuit 51 changes according to the steering assist force required by the assist control by the control circuit 6, the gate drive circuit 52, and the motor drive circuit 51. Accordingly, the voltage of the main power supply 7 and the current supplied to the motor drive circuit 51 are actually detected and multiplied to obtain the current value of power, and this current value supplies power only from the main power supply 7. The power may be supplied only from the main power supply 7 if it is less than the maximum power of the case, and the power may be supplied from the series power supply of the main power supply 7 and the auxiliary power supply 8 if the maximum power is exceeded.

  DESCRIPTION OF SYMBOLS 1: Electric power steering apparatus, 4: Motor, 6: Control circuit, 7: Main power supply, 8: Auxiliary power supply, 9: Charge / discharge circuit, 12: Temperature sensor

Claims (5)

A motor that generates steering assist force;
A main power supply for supplying power to the motor;
A plurality of cells connected in series and / or in parallel, an auxiliary power supply capable of supplying power to the motor;
A first output state for charging the auxiliary power source based on the main power source and supplying power to the motor only by the main power source; and a second output state for supplying power to the motor from the main power source and auxiliary power source A charge / discharge circuit that selectively configures the output state of
A circuit for driving the motor;
A temperature sensor attached to each of the plurality of cells and detecting the temperature of each cell;
When the output state of the charge / discharge circuit is selected in accordance with the necessary steering assist force, and when at least one of the temperatures detected by the temperature sensors reaches a predetermined upper limit threshold, the charging / discharging of the auxiliary power supply is performed. An electric power steering device comprising a control circuit for limiting discharge,
The main power source and the auxiliary power source are connected in series with each other,
The charge / discharge circuit includes a first transistor and a second transistor,
The first transistor is connected such that the source is on the main power supply side and the drain is on the drive circuit side,
The second transistor is connected so that a source is on the driving circuit side and a drain is on the auxiliary power source side;
An electric power steering device.   The electric power steering apparatus according to claim 1, wherein the first transistor and the second transistor are driven so as to be alternately turned on. The charge / discharge circuit further includes a third transistor,
The electric power steering apparatus according to claim 1 or 2, wherein the auxiliary power supply is charged by repeatedly turning on and off the third transistor.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the control circuit performs control so that a steering assist state can be obtained only by a main power supply after the discharge current is gradually reduced. A motor that generates steering assist force;
A main power supply for supplying power to the motor;
A plurality of cells connected in series and / or in parallel, an auxiliary power supply capable of supplying power to the motor;
A first output state for charging the auxiliary power source based on the main power source and supplying power to the motor only by the main power source; and a second output state for supplying power to the motor from the main power source and auxiliary power source A charge / discharge circuit that selectively configures the output state of
A circuit for driving the motor;
A temperature sensor attached to each of the plurality of cells and detecting the temperature of each cell;
When the output state of the charge / discharge circuit is selected in accordance with the necessary steering assist force, and when at least one of the temperatures detected by the temperature sensors reaches a predetermined upper limit threshold, the charging / discharging of the auxiliary power supply is performed. An electric power steering device comprising a control circuit for limiting discharge,
The main power source and the auxiliary power source are connected in series with each other,
The charge / discharge circuit includes a first transistor and a second transistor,
The electric power steering apparatus, wherein the first transistor and the second transistor are driven so as to be alternately turned on.

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