JP2009280039A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device in which the setting of a threshold value regarding the starting of discharge of an auxiliary power source is made more favorable. <P>SOLUTION: The electric power steering device 1 includes a battery 7; the auxiliary power source 10 connected to the battery 7 in series; electric power detection means (8, 9, 11) for detecting electric power fed to a motor 5; a charge circuit 21 for performing charge of the auxiliary power source 10; and a discharge circuit 15 for selectively constituting the first state that electric power is fed only from the battery 7 to the motor 5 and the second state that the electric power is fed from the battery 7 and the auxiliary power source 10 to the motor 5, wherein an acceleration sensor 27 for detecting acceleration of the vehicle; and a control circuit 20 for selecting the first state or the second state by the discharge circuit 15 based on comparison of the electric power fed to the motor 5 with a threshold value and increasing-reducing the threshold value according to increase-reduction of the acceleration are provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering device that is mounted on a vehicle and generates a steering assist force by a motor.

  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, an auxiliary power source for secondary batteries is provided separately from the battery. Usually, only the battery can be used. When a larger amount of power is required, the battery and auxiliary power source are connected in series to supply power from both power sources. Has been proposed (see, for example, Patent Document 1).

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

  In the conventional electric power steering apparatus as described above, the threshold value of power that is used as a reference for whether or not to use the auxiliary power source is a constant value, and if the power consumption of the battery exceeds this threshold value, the auxiliary power steering apparatus The power supply is used and discharged. The lower the threshold is set, the earlier the timing of starting use of the auxiliary power supply. As a result, the frequency of use of the auxiliary power supply is increased, and carrying out of large power from the battery is suppressed. However, if the auxiliary power supply is not quickly charged, charging may not be in time. Conversely, the higher the threshold is set, the later the timing for starting use of the auxiliary power supply. As a result, although the frequency of use of the auxiliary power supply is reduced, large power is often taken out from the battery, and there is a possibility that the battery is consumed quickly or the power supply to other electrical components is insufficient. That is, the problem remains wherever the threshold is set.

  In view of such a problem, an object of the present invention is to provide an electric power steering device in which a threshold setting related to the start of discharge of an auxiliary power supply is more suitable.

The present invention is an electric power steering device that is mounted on a vehicle and generates a steering assist force by a motor,
A battery for supplying power to the motor; an auxiliary power source connected in series to the battery and capable of supplying power to the motor; and a power detection means for detecting the power supplied to the motor; A charging circuit for charging the auxiliary power source based on the voltage of the battery; a first state in which power is supplied to the motor only from the battery; and a second state in which power is supplied to the motor from the battery and auxiliary power source. Based on a comparison between a discharge circuit selectively configured, an acceleration detection means for detecting acceleration of the vehicle, and a power supplied to the motor and a threshold value. And a control circuit for selecting the state or the second state and increasing / decreasing the threshold in accordance with increase / decrease in acceleration in the traveling direction of the vehicle.

  Normally, steering that requires high power is not performed when the acceleration of the vehicle is large, and steering that requires high power is performed when the acceleration is small or negative (decrease). Therefore, in the electric power steering apparatus as described above, the control circuit increases the threshold value as the vehicle acceleration increases, and the battery bears a relatively large amount of power. On the other hand, as the acceleration decreases, the control circuit decreases the threshold value so that the auxiliary power supply can be used from the stage where the required power is relatively small.

Further, in the electric power steering apparatus, the control circuit, when the first state is selected, causes the auxiliary power source to be charged by the charging circuit when the electric power detected by the electric power detection means becomes equal to or lower than the charging threshold, and The charging threshold may be increased / decreased according to the increase / decrease in acceleration.
In this case, when the acceleration of the vehicle increases, the control circuit increases the charging threshold, and the auxiliary power supply is charged even if the required power is relatively large. That is, when the acceleration is relatively large and the possibility of high power steering is low, the charging threshold can be increased to promote charging. Conversely, when the acceleration decreases, the control circuit decreases the charging threshold so that the auxiliary power supply is not charged unless the required power is relatively small.

In the electric power steering apparatus, the control circuit may increase / decrease the charging target current when charging the auxiliary power supply in accordance with the increase / decrease in acceleration.
In this case, when the acceleration is relatively large and the possibility of high power steering is low, the charging target current can be increased to perform high-speed charging.

In the above electric power steering apparatus, the control circuit causes the discharge circuit to select the second state and increase / decrease the acceleration when the power detected by the power detection means becomes equal to or greater than the discharge threshold greater than the charge threshold. Accordingly, the discharge threshold value may be increased or decreased.
In this case, since there is a difference between the discharge threshold and the charge threshold, it is possible to prevent frequent switching between discharge and charge.

In the electric power steering apparatus, the control circuit may prohibit charging by the charging circuit when the voltage between the terminals of the auxiliary power source reaches a predetermined value indicating full charging.
In this case, useless charging can be prevented.

Further, in the electric power steering apparatus, the control circuit may discharge when the voltage between the terminals of the auxiliary power source is lower than a predetermined lower limit value, even if the power detected by the power detection unit is greater than or equal to the discharge threshold value greater than the charge threshold value. The circuit may be maintained in the first state.
In this case, excessive discharge can be prevented.

In the electric power steering apparatus, the acceleration detection means may estimate the acceleration in the traveling direction based on the acceleration in the lateral direction of the vehicle.
Usually, the greater the acceleration in the lateral direction, the less the intention of acceleration in the traveling direction, and conversely, the smaller the acceleration in the lateral direction, the more it can be determined that the vehicle is trying to accelerate in the traveling direction. Based on the acceleration, the acceleration in the traveling direction can be estimated.

  According to the electric power steering apparatus of the present invention, when the acceleration is relatively small or negative, the threshold value can be lowered in preparation for high power steering and the timing at which discharge of the auxiliary power source is started can be accelerated. Setting becomes more suitable.

  FIG. 1 is a circuit diagram illustrating 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, the steering device 3 is driven by the driver's steering torque applied to the steering wheel (handle) 4 and the steering assist force generated by the motor 5. The motor 5 is a three-phase brushless motor and is driven by a motor drive circuit 6. The motor drive circuit 6 includes six switching elements (MOS-FETs) 61 to 66 constituting a three-phase bridge circuit, and a drive circuit (FET driver) 67 for switching them. The drive circuit 67 is controlled by the control circuit 20.

The motor drive circuit 6 is connected to the negative electrode of the battery 7 through the ground side electric circuit LG. The battery 7 supplies power to the motor drive circuit 6 as a main power source. The battery 7 is connected in series with a current detector 8 and in parallel with a voltage detector 9. The current detector 8 detects a current (I _B ) output from the battery 7 and sends a detection signal to the control circuit 20. The voltage detector 9 detects the voltage (V _B ) generated between the terminals of the battery 7 and sends the detection signal to the control circuit 20. The control circuit 20 performs multiplication processing based on the two detection signals to obtain power (V _B · I _B ).

The auxiliary power supply 10 is composed of an electric double layer capacitor and is connected in series to the battery 7. A voltage detector 11 is connected in parallel to the auxiliary power supply 10. The voltage detector 11 detects a voltage (V _C ) generated between the terminals of the auxiliary power supply 10 and sends a detection signal to the control circuit 20. If the voltage drop in the current detector 8 is small and neglected, the voltage V _{B of the} battery 7 is applied to the electric circuit L1, while the voltage V _{B of the} battery 7 and the voltage V _{C of the} auxiliary power supply 10 are applied to the electric circuit L2. Voltage (V _B + V _C ) is applied. Therefore, when the auxiliary power supply 10 is used, the electric power supplied to the motor 5 via the motor drive circuit 6 is (V _B + V _C ) · I _B. Further, when the auxiliary power supply 10 is not used, the electric power supplied to the motor 5 via the motor drive circuit 6 is V _B · I _B. Thus, the current detector 8 and the voltage detectors 9 and 11 together with the control circuit 20 constitute a means for detecting the power supplied to the motor 5.

  The electric circuits L1 and L2 are connected to the electric circuit L3 from the switching elements 12 and 13 (MOS-FET) through the reactor 25, respectively. This electric circuit L3 is connected to the motor drive circuit 6. A smoothing capacitor 28 is connected to the motor drive circuit 6 in parallel. The switching elements 12 and 13 are switched when a drive signal controlled by PWM (pulse width modulation) is applied from a drive circuit (FET driver) 14. The drive circuit 14 is controlled by the control circuit 20.

The discharge circuit 15 including the switching elements 12 and 13 and the drive circuit 14 includes a first state in which power is supplied from only the battery 7 to the motor 5, and a power source in which the auxiliary power source 10 is connected to the battery 7 in series. The second state in which power is supplied is selectively configured by turning on and off the switching elements 12 and 13. Further, by switching the switching elements 12 and 13 at a high speed, a voltage having an arbitrary value between the two voltages (V _B and (V _B + V _C )) can be applied to the motor drive circuit 6.

  The auxiliary power supply 10 is charged by the charging circuit 21. The charging circuit 21 includes a reactor 16, switching elements 17 and 18 (MOS-FET) that are alternately turned on, and a drive circuit (FET driver) 19 that switches the switching elements 17 and 18. The drive circuit 19 is controlled by the control circuit 20. A current detector 26 is interposed between the charging circuit 21 and the auxiliary power supply 10, and this current detector 26 detects the charging current from the charging circuit 21 to the auxiliary power supply 10 and outputs the detection signal. Send to control circuit 20. Note that the current detector 8 may be substituted without providing the current detector 26.

  An output signal is input to the control circuit 20 from a torque sensor 22 that detects a steering torque applied to the steering wheel 4. Further, an output signal of the vehicle speed sensor 23 for detecting the vehicle speed and an output signal of the acceleration sensor 27 as means for detecting acceleration in the forward direction of the vehicle are respectively input to the control circuit 20. The motor 5 is provided with an angle sensor 24 that detects the rotational angle position of the rotor, and its output signal is input to the control circuit 20.

  In the electric power steering apparatus configured as described above, the control circuit 20 receives the steering torque signal sent from the torque sensor 22, the vehicle speed signal sent from the vehicle speed sensor 23, and the angle sensor 24. Based on the incoming rotor angle position signal, the motor drive circuit 6 is operated to drive the motor 5 in order to generate an appropriate steering assist force.

On the other hand, when the switching element 17 is on and the switching element 18 is off in the charging circuit 21, current flows from the battery 7 through the reactor 16 and the switching element 17. When the switching element 17 is turned off from that state (the switching element 18 is turned on), a high voltage is generated in the reactor 16 so as to prevent a magnetic flux change due to current interruption, thereby boosting the output voltage of the battery 7. The auxiliary power supply 10 is charged with the voltage. Therefore, the auxiliary power supply 10 can be charged by repeatedly turning on and off the switching elements 17 and 18. The control circuit 20 monitors the voltage V _C of the auxiliary power supply 10, and turns on and off the switching elements 17 and 18 via the drive circuit 19 to charge the auxiliary power supply 10 when the voltage does not reach a certain voltage. .

  Next, charge / discharge control performed mainly by the control circuit 20 will be described with reference to the flowchart of FIG. The charge / discharge control shown in the flowchart of FIG. 2 is repeatedly executed in the control circuit 20. First, the control circuit 20 detects the electric power supplied to the motor 5 based on the output signals from the current detector 8 and the voltage detectors 9 and 11 (step S1). Further, based on the characteristics of FIGS. 3 and 4 stored in advance, the charging target current (FIG. 3) corresponding to the current acceleration, and the discharge threshold and the charging threshold (FIG. 4) corresponding to the current acceleration are obtained. Ask.

  Here, as shown in FIG. 3, the charging target current increases / decreases in proportion to the increase / decrease in acceleration. Further, as shown in FIG. 4, the discharge threshold and the charge threshold increase / decrease in proportion to the increase / decrease in acceleration. Here, the discharge threshold is a value for discharging the auxiliary power supply 10 when the electric power becomes equal to or higher than this value. The charging threshold value is a value for charging the auxiliary power supply 10 when the power becomes equal to or lower than this value.

  Returning to FIG. 2, the control circuit 20 determines whether or not the power detected in step S1 is equal to or greater than the discharge threshold (step S2). Here, the control circuit 20 determines “NO”, that is, if the power is smaller than the discharge threshold, whether the power is equal to or less than the charge threshold (step S3). If it is below the charging threshold, it is determined whether or not the voltage of the auxiliary power supply 10 (the voltage detected by the voltage detector 11) is greater than or equal to the upper limit value (step S4). The upper limit value means a voltage between terminals when the auxiliary power supply 10 is in a fully charged state. If the power exceeds the charging threshold value in step S3, the process ends without charging. If the auxiliary power supply voltage is equal to or higher than the upper limit value in step S4, the process ends because charging is not necessary.

  On the other hand, if “NO” in step S4, that is, if the auxiliary power supply voltage is smaller than the upper limit value, the control circuit 20 controls the drive circuit 19 to charge the auxiliary power supply 10. This charging is performed by current feedback control. The current feedback control is executed so that the charging current becomes the charging target current (FIG. 3) while comparing the charging target current with the charging current fed back from the current detector 26.

  Returning to step S2 of FIG. 2 again, the control circuit 20 determines whether or not the auxiliary power supply voltage is equal to or higher than the lower limit value when the power is equal to or higher than the discharge threshold (step S6). This lower limit value is the minimum voltage value that can discharge the auxiliary power supply. Here, when the auxiliary power supply voltage is smaller than the lower limit value, the processing is ended. On the other hand, if the auxiliary power supply voltage is equal to or higher than the lower limit value, the control circuit 20 determines whether or not the power is equal to or lower than the power target value (step S7). If the power is less than or equal to the power target value in step S7, the process ends because there is no need for power feedback control.

  On the other hand, when the power is larger than the power target value in step S7, the control circuit 20 performs power feedback control (step S8). The power feedback control is executed so that the power becomes the power target value while comparing the power target value with the power based on the values fed back from the voltage detector 9 and the current detector 8.

  As described above, in the present embodiment, the charging threshold, the discharging threshold, and the charging target current are changed in proportion to the acceleration. Normally, steering that requires high power is not performed when the acceleration of the vehicle is high, and steering that requires high power is performed when the acceleration is low. Therefore, the control circuit 20 increases the threshold value as the vehicle acceleration increases, and the battery 7 bears a relatively large amount of power. On the other hand, as the acceleration decreases, the control circuit 20 decreases the threshold value so that the auxiliary power supply 10 can be used from the stage where the required power is relatively small. Thereby, when the acceleration is relatively small, the threshold value can be lowered in preparation for high-power steering and the timing at which the discharge of the auxiliary power supply 10 is started can be advanced, so that the threshold setting becomes more suitable.

When the acceleration of the vehicle increases, the control circuit 20 increases the charging threshold, and the auxiliary power supply 10 is charged even if the required power is relatively large. That is, when the acceleration is relatively large and the possibility of high power steering is low, the charging threshold can be increased to promote charging. Conversely, when the acceleration decreases, the control circuit 20 decreases the charging threshold so that the auxiliary power supply 10 is not charged unless the required power is relatively small.
Further, when the acceleration is relatively large and the possibility of high power steering is low, the charging target current can be increased to perform high-speed charging.

Further, in FIG. 4, there is a difference in power between the discharge threshold and the charge threshold. Due to the presence of such an inter-threshold region, frequent switching between discharging and charging can be prevented.
On the other hand, in step S4 of FIG. 2, when the voltage between the terminals of the auxiliary power supply 10 has reached the upper limit value indicating full charge, the control circuit 20 prohibits charging by the charging circuit 21, thereby performing unnecessary charging. Can be prevented.
Further, in step S6 of FIG. 2, the control circuit 20 does not discharge when the voltage between the terminals of the auxiliary power supply 10 is lower than the lower limit (maintaining the discharge circuit 15 in the first state), thereby forcibly discharging. Can be prevented.

  In the above embodiment, the acceleration sensor 27 is provided to detect the acceleration in the forward direction of the vehicle. However, instead of or in combination with this, the acceleration in the lateral direction of the vehicle (so-called lateral G) is provided. ) May be provided. Normally, the greater the acceleration in the lateral direction, the less the intention of acceleration in the traveling direction, and conversely, the smaller the acceleration in the lateral direction, the more the acceleration in the traveling direction can be determined. Based on the acceleration, the acceleration in the traveling direction can be estimated.

Further, without providing an acceleration sensor, the speed sensor 23 may cooperate with the control circuit 20 to constitute acceleration detection means by differentiating the output signal of the speed sensor 23 with respect to time to obtain acceleration. .
Furthermore, a sensor that detects the throttle opening (or the accelerator depression amount) may be used as the acceleration sensor.

In the above embodiment, the charging threshold value, the discharging threshold value, and the charging target current are shown to increase or decrease in proportion to the increase or decrease of acceleration. However, the present invention is not limited to “proportional”. For example, a higher-order function or a non-linear characteristic may be given. In short, it is only necessary to prepare a characteristic that the charging threshold and discharging threshold and the charging target current increase / decrease in accordance with the increase / decrease in acceleration.
Furthermore, if the characteristics are given hysteresis when the acceleration increases and decreases, it is possible to provide more advanced control.

1 is a circuit diagram illustrating a configuration mainly including an electric circuit of an electric power steering apparatus according to an embodiment of the present invention. It is a flowchart of charging / discharging control. It is a graph which shows the change characteristic of the target current at the time of charge with respect to acceleration. It is a graph which shows the change characteristic of the discharge threshold value with respect to an acceleration, and a charge threshold value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 7 Battery 8 Current detector 9 Voltage detector 10 Auxiliary power supply 11 Voltage detector 15 Discharge circuit 20 Control circuit 21 Charging circuit 26 Current detector

Claims (7)

An electric power steering device mounted on a vehicle and generating a steering assist force by a motor,
A battery for supplying power to the motor;
An auxiliary power source connected in series to the battery and capable of supplying power to the motor;
Power detection means for detecting power supplied to the motor;
A charging circuit for charging the auxiliary power source based on the voltage of the battery;
A discharge circuit that selectively configures a first state in which power is supplied from only the battery to the motor and a second state in which power is supplied from the battery and an auxiliary power source to the motor;
Acceleration detecting means for detecting acceleration of the vehicle;
Based on the comparison between the electric power supplied to the motor and a threshold value, the discharge circuit selects the first state or the second state, and according to the increase / decrease of acceleration in the traveling direction of the vehicle An electric power steering apparatus comprising: a control circuit for increasing / decreasing a threshold value.   In the case where the first state is selected, the control circuit causes the auxiliary power source to be charged by the charging circuit and sets the charging threshold when the power detected by the power detecting unit is equal to or lower than a charging threshold. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus increases / decreases in accordance with increase / decrease of the acceleration.   The electric power steering apparatus according to claim 2, wherein the control circuit increases / decreases a charging target current when charging the auxiliary power source in accordance with an increase / decrease in the acceleration.   The control circuit causes the discharge circuit to select the second state when the power detected by the power detection means is equal to or greater than a discharge threshold value that is greater than the charge threshold value, and the control circuit responds to the increase / decrease of the acceleration. The electric power steering apparatus according to claim 2, wherein the electric discharge threshold is increased / decreased.   The electric power steering apparatus according to claim 2, wherein the control circuit prohibits charging by the charging circuit when a voltage between the terminals of the auxiliary power source reaches a predetermined value indicating full charging.   When the voltage between the terminals of the auxiliary power source is lower than a predetermined lower limit value, the control circuit causes the first discharge circuit to be connected to the first discharge circuit even if the power detected by the power detection unit is greater than or equal to the discharge threshold value that is greater than the charge threshold value. The electric power steering apparatus according to claim 2, wherein the electric power steering apparatus is maintained in the state.   The electric power steering apparatus according to claim 1, wherein the acceleration detecting unit estimates an acceleration in a traveling direction based on an acceleration in a lateral direction of the vehicle.

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