JP2009119900A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device, in which cells of an auxiliary power source can be used up to close temperature to their heat-resistant temperature. <P>SOLUTION: Among the cells, a temperature sensor 12 is installed on the one with the largest inner resistance value. In a case where temperature detected by the temperature sensor 12 has reached a specified upper limit value, a control circuit 6 limits charge and discharge concerning the auxiliary power source 8. By setting the heat-resistant temperature of the cell for the upper limit value, the cell on which the temperature sensor 12 is installed can be used up to its heat-resistant temperature. Other cells can also be used up to close temperature to their heat-resistant temperature. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 order to perform control based on this temperature by measuring one temperature as a whole auxiliary power supply under the condition that only overheating exceeding the heat-resistant temperature must be avoided in any cell, assuming such variation. It is necessary to allow sufficient margin for the upper limit of temperature. That is, it is necessary to perform a safe control by setting a temperature considerably lower than the actual heat resistant temperature of the cell as an upper limit value, and as a result, it becomes difficult to use the cell to near the heat resistant temperature.

  In view of such a conventional problem, 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.

  The present invention is an electric power steering apparatus that generates a steering assist force by a motor, and includes a main power source that supplies electric power to the motor and a module formed by connecting a plurality of cells in series, and the electric power is supplied to the motor. An auxiliary power supply that can be supplied, a first output state that charges the auxiliary power supply based on the main power supply, and that supplies power to the motor only by the main power supply, and the main power supply and the auxiliary power supply A charge / discharge circuit that selectively configures a second output state that supplies power to the motor from the motor, and a temperature that detects the temperature of the cell that is attached to the cell having the largest internal resistance value When the output state of the charge / discharge circuit is selected according to the sensor and the necessary steering assist force, and when the temperature detected by the temperature sensor reaches a predetermined upper limit value Wherein in which a control circuit for limiting the charge and discharge of the auxiliary power supply.

  In the electric power steering apparatus configured as described above, the temperature sensor detects the temperature of the cell having the largest resistance value of the internal resistance, that is, the cell having the largest calorific value, and the detected temperature is a predetermined upper limit value. When this is reached, the control circuit limits charging and discharging. Therefore, if the heat-resistant temperature of the cell is set as the upper limit, charging / discharging is restricted when the cell with the largest heat generation reaches the heat-resistant temperature, and all other cells at that time are temperatures close to the heat-resistant temperature. Will be reached.

In the electric power steering apparatus, the auxiliary power source is formed by connecting a plurality of modules in parallel to each other, and the temperature sensor is a module having the lowest resistance value as one module, and is included in the cell constituting the module. It may be configured to be attached to a resistor having the largest resistance value.
In this case, even when the current flowing through each module is not uniform, the temperature of the cell that generates the largest amount of heat in the entire auxiliary power supply can be detected by the temperature sensor.

  According to the electric power steering apparatus of the present invention, since the auxiliary power source cell can be used up to or near the heat-resistant temperature, the auxiliary power source can be fully utilized and as a result, the auxiliary power source can be used. It is possible to reduce the probability that the use of is limited.

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 the figure, 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, the auxiliary power supply 8 is provided with a temperature sensor 12, and its output signal (temperature detection signal) is input to the control circuit 6.

  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 (voltage of the electric circuit L2) in a state where the main power supply 7 and the auxiliary power supply 8 are connected in series is guided to the drive circuit 5 and the motor 4 via the electric circuit L2 in which the MOS-FET 92 is inserted and the electric circuit L3. It is burned. The MOS-FET 92 is an N channel, and is connected such 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 for applying a gate voltage for PWM control of these MOS-FETs. A circuit 52 and a smoothing electrolytic capacitor 53 connected in parallel to the motor drive circuit 51 are provided.

Next, FIG. 3A is a diagram showing the 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 M is formed by connecting m (≧ 2) cells in series with each other, and n modules (≧≧). 1) It is configured to be connected in parallel.
FIG. 3B is a circuit configuration diagram in one cell. As shown in the figure, 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. Therefore, before assembling the auxiliary power supply 8, the resistance value of the internal resistance R is measured for each cell (m × n). As a result of the measurement, a cell having the highest resistance value, that is, a cell that generates heat most is selected, and the temperature sensor 12 is attached to the outer skin of the cell in close contact. For example, in the case of FIG. 3A, the temperature sensor 12 is attached to the cell 81 based on the measurement result that the resistance value of the internal resistance R of the cell 81 is the highest.

  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 which is an output signal of the temperature sensor 12 and monitors whether or not the value reaches a predetermined upper limit value. As the upper limit value, a heat resistant temperature (upper limit value) of the cell is set.
When the value of the temperature detection signal reaches a predetermined upper limit value 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 including the cell 81 is lowered.

  When the value of the temperature detection signal reaches a predetermined upper limit 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, the temperature sensor 12 detects the temperature of the cell having the largest resistance value of the internal resistance R, that is, the cell having the largest heat generation amount, and is detected. When the detected temperature reaches a predetermined upper limit value, 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, 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.

  In this way, all the cells of the auxiliary power supply 8 can be used up to the heat resistant temperature or a temperature close thereto. Accordingly, it is possible to sufficiently demonstrate the ability of the auxiliary power supply 8 and to reduce the probability that the use of the auxiliary power supply 8 is restricted as a result. Moreover, since the temperature of the cell with the largest calorific value is detected and charging / discharging is limited, there is no fear that other cells exceed the heat resistance temperature and overheat.

  In the above embodiment, the temperature sensor 12 is attached on the assumption that the cell having the largest resistance value of the internal resistance R is the cell that generates the largest amount of heat. This concept is illustrated in parallel in FIG. It is based on the premise that the resistance values of n modules M to be connected (series resistance values of m cells) are all the same, and the current flows through each module M evenly. In fact, as the value of m increases, the resistance value of each module M approaches the same, so it is reasonable to treat it as substantially the same, and there is no particular problem.

  However, strictly speaking, if there are variations in the resistance values of the n modules M, the currents flowing through the modules M are not the same value, so that the cell having the largest resistance value of the internal resistance R in the entire auxiliary power supply 8 is It is not necessarily the cell that generates the largest amount of heat. To be more careful in consideration of this, the resistance value of the internal resistance R of the cell constituting each module M is added to obtain the resistance value of the module M, and the module having the lowest resistance value (that is, the largest resistance value) What is necessary is just to select the module through which a current flows. The cell having the largest resistance value of the internal resistance R in the module can be regarded as the cell having the largest amount of heat generation in the entire auxiliary power supply 8.

  In the above embodiment, the electric power steering apparatus 1 having a circuit configuration in which the auxiliary power source 8 is connected in series to the main power source 7 has been described. However, a circuit configuration in which the auxiliary power source is connected in parallel to the main power source. Similarly, the electric power steering apparatus can be provided with a temperature sensor to control charging and discharging.

  In the above embodiment, when determining whether or not the auxiliary power supply 8 is used to supply power to the motor 4, the control circuit 6 estimates the required power for obtaining the required steering assist force, Is compared with the reference value, but 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.

1 is a block circuit diagram of an electric power steering apparatus according to an embodiment of the present invention. 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.

Explanation of symbols

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 (2)

An electric power steering device that generates a steering assist force by a motor,
A main power supply for supplying power to the motor;
An auxiliary power source including a module formed by connecting a plurality of cells in series, and 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 temperature sensor that is attached to the cell having the largest internal resistance value and detects the temperature of the cell;
Control for selecting the output state of the charge / discharge circuit according to the necessary steering assist force and limiting charge / discharge of the auxiliary power supply when the temperature detected by the temperature sensor reaches a predetermined upper limit value An electric power steering device comprising a circuit. The auxiliary power source is formed by connecting a plurality of the modules in parallel with each other,
2. The electric power steering apparatus according to claim 1, wherein the temperature sensor is attached to a module having the lowest resistance value as one module, among the cells constituting the module, having the highest resistance value of the internal resistance.

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