JP2015229359A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of protecting a battery and carrying on a steering assist by estimating usable capacity of the battery when an IG switch is turned off.SOLUTION: When an IG signal is on, normal rotation control over an electric motor 1 is carried on, and when the IG signal turns off, a motor current value I detected by a current sensor 12 provided for an inverter 8 is read in and then a motor current value I in feeding after the IG signal turns off is integrated to compute battery usable capacity of a battery 100. A PIG voltage value and a battery temperature are read in, and based upon a discharge curve of previously set PIG voltage-battery remaining capacity characteristics, battery remaining capacity is found from the PIG voltage and battery temperature so as to determine battery usable capacity. When the battery usable capacity becomes equal to or larger than the battery usable capacity, a steering assist is stopped before the battery usable capacity exceeds the battery remaining capacity so as to protect the battery 100.

Description

  The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus that continues steering assistance when an IG switch is off.

  2. Description of the Related Art Conventionally, an electric power steering apparatus that includes an electric motor that applies a steering assist force (steering assist force) to a steering operation performed by a driver and adjusts an assist torque by performing energization control of the electric motor is often used in a vehicle. ing. In such an electric power steering apparatus, ECU (electronic control unit) adjusts the electric power supplied from the battery mounted in the vehicle, and performs rotation control of the electric motor (for example, refer patent document 1).

  Normally, the electric motor of the electric power steering device is switched on and off based on the IG signal from the IG switch (ignition switch). When the IG switch is turned off, the steering assist function is stopped. The In the electric power steering apparatus described in Patent Document 1, the ECU determines that the engine is stopped by the IG switch being turned off and the engine speed sensor, and detects the vehicle stop state when the vehicle speed becomes zero. Yes.

JP 2005-271640 A

  In response to the above operation, steering assist may be continued even if the IG switch is forcibly turned off from the outside during vehicle travel. That is, even after the IG switch is turned off, the ECU continues steering assistance in a situation where it is impossible to detect and judge during traveling even if a vehicle speed signal cannot be obtained. However, if steering assist is performed with electric power from the battery when the engine is stopped, the electric power steering apparatus consumes a large amount of power, and the battery may be overdischarged. Thus, for example, there is a case where the stop time is estimated from the vehicle speed immediately before the IG switch is turned off, and the steering assist is stopped after the estimated time has elapsed. There is a possibility that the steering assistance may be stopped while traveling.

  For this reason, there is a risk of giving the driver a sense of incongruity that the steering assistance has suddenly decreased even when the vehicle is traveling. In addition, many of the steering operations while the engine is stopped are stationary operations, and the required energization amount of the electric motor is large and a large amount of current is drawn from the battery. .

  The present invention has been made to solve the above-described problems, and its purpose is to estimate the usable capacity of the battery when the IG switch is turned off, thereby protecting the battery and continuing steering assistance. An object is to provide an electric power steering apparatus.

  In order to solve the above-mentioned problems, an invention according to claim 1 is an electric power steering apparatus, wherein an electric motor that generates a steering assist force applied to a steering mechanism of a vehicle, and a battery that supplies electric power to drive the electric motor. And an inverter that supplies a drive current to the electric motor, and a control circuit that controls the inverter, wherein the control circuit has an IG switch that stops the vehicle engine turned off. A battery consumption capacity calculation unit that determines a battery usage capacity of the battery that is running after a motor current value detected by a current sensor provided in the inverter and an energization time; and the battery in which the IG switch is off The battery usable capacity of the DC voltage value supplied to the inverter set in advance and It has a limit value calculation unit for determining from the battery temperature of the serial battery, and if the battery used capacity exceeds the battery available capacity, and summarized in that determining the prohibition of use of the battery.

  According to the above configuration, when the vehicle is running after the IG switch is turned off by an external operation, the battery consumption capacity (battery) is determined from the motor current value detected by the current sensor provided in the inverter and the energization time. Used capacity). Steering assistance is continued so that the battery use capacity does not exceed the battery usable capacity obtained from the DC voltage value (PIG voltage) supplied to the inverter and the battery temperature. As a result, even when the IG switch is off and the vehicle running state and the engine operating state cannot be determined, the electric power steering device alone can prevent overdischarge of the battery and continue steering assistance. it can.

  The invention according to claim 2 is the electric power steering apparatus according to claim 1, wherein the control circuit stops steering assist when the battery usage capacity exceeds the battery usable capacity. To do.

  According to the above configuration, since the steering assist is stopped before the battery usage capacity exceeds the battery usable capacity, it is possible to protect the battery from overdischarge while the IG switch is off. Thus, the steering assist can be continued as long as the remaining battery capacity can be used.

  According to a third aspect of the present invention, in the electric power steering apparatus according to the first or second aspect, the control circuit is configured such that the battery temperature is based on a detection value of a substrate temperature sensor provided on a control board of the control circuit. The gist is to estimate.

  According to the above configuration, when the ECU is disposed in the vicinity of the battery, the battery temperature can be estimated from the substrate temperature sensor mounted on the control board of the control circuit, so that the DC voltage value supplied to the inverter is estimated. The battery usable capacity can be obtained from the discharge curve of the battery temperature. As a result, battery consumption can be detected, and the battery can be protected.

  According to a fourth aspect of the present invention, in the electric power steering apparatus according to any one of the first to third aspects, the battery usage capacity exceeds the battery usable capacity, and the engine is stopped. The gist is to output an engine restart command.

  According to the above configuration, when the IG switch is turned off and steering assist is performed while the engine is stopped, the engine restart command can be output to the external device before the battery usage capacity exceeds the battery usage capacity. . Thereby, it becomes possible to protect the battery and continue the steering assist.

  According to a fifth aspect of the present invention, in the electric power steering device according to any one of the first to fourth aspects, when the battery usage capacity exceeds the battery usable capacity and the engine is not stopped. The gist is to output an engine automatic stop prohibition command.

  According to the above configuration, when the engine is operating even when the IG switch is turned off, the engine automatic stop prohibition command is output to the external device before the battery use capacity exceeds the battery use capacity, and the engine is not stopped. Can be. Thereby, it becomes possible to protect the battery and continue the steering assist.

  According to the present invention, it is possible to provide an electric power steering apparatus that can protect a battery and continue steering assistance by estimating the usable capacity of the battery when the IG switch is turned off.

The schematic diagram which shows schematic structure of the electric power steering apparatus which concerns on one Embodiment of this invention. The figure which shows the circuit structure of the electronic control unit of FIG. FIG. 3 is a control block diagram of the control circuit of FIG. 2. The graph which shows the PIG voltage-battery remaining capacity characteristic example corresponding to battery temperature. The flowchart explaining the example of a control procedure of the steering assistance of a control circuit.

  Hereinafter, an electric power steering device mounted on a vehicle according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 10 according to an embodiment of the present invention.
An electric power steering apparatus 10 shown in FIG. 1 includes an electric motor 1, a speed reducer 2, a torque sensor 3, a vehicle speed sensor 4, a motor rotation angle sensor (hereinafter referred to as a rotation angle sensor) 5, and an electronic control unit (hereinafter referred to as an ECU). ) 6 is a column assist type electric power steering device.

  As shown in FIG. 1, a steering wheel 101 is fixed to one end of the steering shaft 102, and the other end of the steering shaft 102 is connected to a rack shaft 104 via a rack and pinion mechanism 103. Both ends of the rack shaft 104 are connected to a wheel 106 via a connecting member 105 composed of a tie rod and a knuckle arm. When the driver rotates the steering wheel 101, the steering shaft 102 rotates, and the rack shaft 104 reciprocates accordingly. As the rack shaft 104 reciprocates, the direction of the wheels 106 changes.

  The electric power steering device 10 performs the following steering assist (hereinafter referred to as steering assist) in order to reduce the driver's load. The torque sensor 3 detects a steering torque τ applied to the steering shaft 102 by operating the steering wheel 101. The vehicle speed sensor 4 detects the vehicle speed V. The rotation angle sensor 5 detects the rotation position (motor rotation angle) θ of the rotor of the electric motor 1. The rotation angle sensor 5 is composed of, for example, a resolver.

  Further, the ECU 6 is connected to an engine rotation signal detected by a rotation speed sensor (not shown) and an IG signal from an IG switch (ignition switch) 7 for performing a normal starting operation of the engine. Then, the ECU 6 starts and stops the electric motor 1 based on each output signal.

  In addition, the ECU 6 receives power supply from an in-vehicle battery (hereinafter referred to as a battery) 100 and drives the electric motor 1 based on the steering torque τ, the vehicle speed V, and the motor rotation angle θ. When the rotation of the electric motor 1 is controlled by the ECU 6, the electric motor 1 generates a steering assist force (hereinafter referred to as a steering assist force). The speed reducer 2 is provided between the electric motor 1 and the steering shaft 102. The steering assist force generated by the electric motor 1 acts to rotate the steering shaft 102 via the speed reducer 2.

  As a result, the steering shaft 102 rotates by both the steering torque τ applied to the steering wheel 101 and the steering assist force generated by the electric motor 1. As described above, the electric power steering apparatus 10 performs the steering assist by applying the steering assist force generated by the electric motor 1 to the steering mechanism of the vehicle.

  2 is a diagram showing a circuit configuration of the ECU 6 in FIG. 1, FIG. 3 is a control block diagram of the control circuit 9 in FIG. 2, and FIG. 4 is an example of PIG voltage-battery remaining capacity characteristics corresponding to the battery temperature. FIG.

  In FIG. 2, the electric motor 1 is a brushless motor having three-phase windings (U-phase, V-phase, and W-phase windings, not shown). The battery 100 is a DC power source (for example, 12 V) that is connected to the inverter 8 and drives the electric motor 1.

  As shown in FIG. 2, a battery 100 is connected in series to a smoothing capacitor 15, and charges the capacitor 15 to supply power to the inverter 8. An inverter 8 is connected in parallel to the capacitor 15, and the electric motor 1 is connected via the inverter 8.

  Capacitor 15 is provided between power supply line 13 between battery 100 and inverter 8 and ground line (hereinafter referred to as an earth line) 14. The capacitor 15 supplies power to the inverter 8 from both the battery 100 and the battery 100. In particular, a large amount of power is instantaneously supplied from the capacitor 15 to the inverter 8. Specifically, the capacitor 15 accumulates electric charge, and discharges the accumulated electric charge when the current flowing from the battery 100 to the inverter 8 is insufficient. Thus, the capacitor 15 functions as a capacitor that absorbs current ripple and smoothes the power supply voltage for driving the electric motor 1.

  The inverter 8 includes a plurality (six in this embodiment) of switching elements (power transistors such as IGBTs, MOSFETs, etc.) 11. Three circuits in which two of these six switching elements 11 are connected in series to form upper and lower arms are provided in parallel between the power supply line 13 and the earth line 14. Each connection point of the switching elements 11 of the upper and lower arms is directly connected to one end of a three-phase winding. The other end of the three-phase winding of the electric motor 1 is connected to a common connection point (neutral point) (not shown).

  Further, a current sensor (for example, a resistor) 12 for detecting a motor current value I flowing through each phase (U phase, V phase, W phase) is connected between the switching element 11 of the lower arm and the earth line 14. Has been. Each motor current value I is input to the control circuit 9, and the power consumption of the battery 100 described later is calculated from the motor current value I and the energization time.

  The control circuit 9 controls the switching element 11 included in the inverter 8. More specifically, the control circuit 9 sets the target of three-phase drive currents (U-phase, V-phase, and W-phase currents) to be supplied to the electric motor 1 based on the input data (motor rotation angle and the like). Determine the value (target current). Then, the control circuit 9 outputs a PWM signal for making the motor current value I of each phase detected by the current sensor 12 coincide with the target current. The PWM signal of each phase output from the control circuit 9 is supplied to the gate terminal of the switching element 11 included in the inverter 8. In addition, the control voltage (for example, 12V) used as the power supply of the control circuit 9 is supplied from the battery 100 or an auxiliary battery. Alternatively, power may be supplied from a high voltage battery via a DC / DC converter or the like.

  As shown in FIG. 3, the control circuit 9 includes a microcomputer (hereinafter referred to as a CPU) 16 that executes normal assist control and outputs a motor control signal, and a switching element included in the inverter 8 based on the motor control signal. 11 includes a pre-driver 17 that outputs a PWM signal. Each control block shown below is realized by a computer program executed by the CPU 16. Then, the CPU 16 detects each state quantity at a predetermined sampling period, and generates a motor control signal by executing each arithmetic processing shown in the following control block at every predetermined period.

  The CPU 16 receives an IG signal, a PIG voltage (PIG, see FIG. 2), a battery temperature, a vehicle speed V, a steering torque τ, a motor current value I, and a motor rotation angle θ as state quantities, and outputs a motor control signal. The In addition, an engine rotation signal, an engine restart command, and an engine automatic stop prohibit command can be input / output as the engine control signal.

  The CPU 16 includes an assist control unit 18 that performs normal steering assist control. The assist control unit 18 includes a current command value calculation unit (not shown) that calculates a current command value corresponding to the target assist force to be generated in the electric motor 1, and a motor control signal based on the calculated current command value. And a motor control signal output unit (not shown). The assist control unit 18 is a basic assist control amount that becomes a target assist force based on the steering torque τ detected by the torque sensor 3 (see FIG. 1) and the vehicle speed V detected by the vehicle speed sensor 4 (see FIG. 1). (Assist torque) is calculated.

  More specifically, the steering torque τ and the vehicle speed V are input to the assist control unit 18 and a current command value is calculated. Further, the motor rotation angle θ detected by the rotation angle sensor 5 (see FIG. 1) and the motor current value I detected by the current sensor 12 (see FIG. 2) are input to the assist control unit 18. Then, the assist control unit 18 calculates a basic assist control amount for generating an assist force corresponding to the input steering torque τ.

  Specifically, the assist control unit 18 calculates a basic assist control amount having a larger absolute value so that a larger assist force is applied to the steering system as the absolute value of the steering torque τ increases. . In this embodiment, the calculation of the basic assist control amount for generating the assist force is performed using a vehicle speed sensitive three-dimensional map. Thereby, the assist control part 18 calculates the basic assist control amount which has a larger absolute value, so that the vehicle speed V is small.

  As described above, the current command value calculation unit calculates the current command value to be supplied to the electric motor 1 using the basic assist control amount calculated by the assist control unit 18 as the target assist force of the assist control. The motor control signal output unit receives a motor current value I that is an actual current value of the electric motor 1 detected by the current sensor 12 together with the current command value calculated by the current command value calculation unit. The motor control signal output unit of the present embodiment generates a motor control signal by executing current feedback control so that the motor current value I follows the current command value.

  In the ECU 6 of this embodiment, the CPU 16 outputs the motor control signal generated in this way to the pre-driver 17. The inverter 8 supplies driving electric power based on the PWM signal from the pre-driver 17 to the electric motor 1, thereby controlling the rotation of the electric motor 1 and executing assist control.

  Further, the CPU 16 includes a battery consumption capacity calculation unit 20 and a limit value calculation unit 19. Referring to FIG. 2, battery consumption capacity calculation unit 20 calculates an integrated value during energization from each phase motor current value I (Iu, Iv, Iw) detected by current sensor 12 provided in inverter 8. The battery usage capacity of the battery 100 is determined. The limit value calculation unit 19 shows the PIG voltage (V) -battery remaining capacity (Ah) characteristic provided in advance shown in FIG. 4 from the PIG voltage that is the DC voltage value supplied to the inverter 8 and the battery temperature. The remaining battery capacity is obtained based on the graph of the discharge curve, and the usable battery capacity corresponding to the remaining battery capacity is determined. When the battery 100 is disposed in the vicinity of the ECU 6, the battery temperature can be estimated and obtained from a detection value of a substrate temperature sensor (not shown) mounted on the control substrate of the control circuit 9, for example. The battery use capacity and the battery usable capacity are input to the assist control unit 18, and steering assist is executed in a range where the battery use capacity does not exceed the battery usable capacity.

  Here, as shown in FIG. 4, the higher the battery temperature, the smaller the PIG voltage, and the lower the remaining battery capacity with respect to the PIG voltage, the smaller the battery temperature. The battery usable capacity determined by the limit value calculation unit 19 is set to a value smaller than the remaining battery capacity in consideration of the consumption of the battery 100.

  Furthermore, an engine restart command or an engine automatic stop prohibition command can be output to an external device (not shown) (for example, an engine ECU or an idling stop ECU). Thereby, even when the IG switch 7 is turned off, the steering assist can be continued without restarting the engine or stopping the engine.

Next, FIG. 5 is a flowchart for explaining a control procedure example of steering assist of the control circuit 9 in the electric power steering apparatus 10.
In the present embodiment, the CPU 16 (see FIG. 3) in the control circuit 9 reads the program stored in the ROM, and executes the processes of steps S501 to S509 shown in the flowchart of FIG. The processing in the flowchart shown below is executed at predetermined time intervals.

  First, the CPU 16 always reads the ON / OFF state by the operation of the IG switch (ignition switch) 7 (step S501). Thereafter, it is determined whether or not the IG signal from the IG switch 7 is turned off (step S502).

  When it is determined that the IG signal is on (step S502: NO), normal rotation control for the electric motor 1 is continued (step S509, steering assist control).

  On the other hand, when it is determined that the IG signal has been turned off (step S502: YES), for example, it is determined that the IG switch 7 has been turned off by the driver's operation due to occurrence of an abnormality or the like, and a current sensor provided in the inverter 8 The motor current value I detected by 12 is read (step S503).

  Subsequently, the CPU 16 integrates the motor current value I being energized by the inverter 8 after the IG signal is turned off, and calculates the battery usage capacity (consumption capacity) of the battery 100 (step S504).

  Next, the PIG voltage value supplied to the inverter 8 and the battery temperature of the battery 100 are read (step S505). As the battery temperature in this case, for example, the battery temperature estimated from the detected temperature of the substrate temperature sensor mounted on the control board of the control circuit 9 is used.

  Subsequently, the CPU 16 obtains the remaining battery capacity from the PIG voltage value and the battery temperature based on the preset graph of the discharge curve of the PIG voltage-remaining battery capacity characteristic, and determines the battery usable capacity (step S506). Here, the battery usable capacity is set to a value smaller than the actual usable value (remaining battery capacity) in consideration of battery consumption.

  Then, it is determined whether or not the battery use capacity exceeds the battery usable capacity (step S507). When the battery usage capacity does not exceed the battery usable capacity (step S507: YES), normal rotation control for the electric motor 1 is continued (step S509, steering assist control).

When the battery usage capacity is equal to or greater than the battery usable capacity (step S507: NO), the rotation control for the electric motor 1 is stopped and the flow is exited (step S508).
As described above, the steering assist is stopped before the battery usage capacity exceeds the remaining battery capacity.

  Next, the operation and effect of the electric power steering apparatus 10 according to the embodiment of the present invention configured as described above will be described.

  According to the above-described embodiment, for example, when the vehicle is running after the IG switch 7 is turned off by a driver's operation when an abnormality of the vehicle occurs, the steering assist control by the electric power steering device 10 is continued. The CPU 16 of the control circuit 9 in the ECU 6 calculates the consumed capacity (battery usage capacity) of the battery 100 by integrating the motor current value I detected by the current sensor 12 provided in the inverter 8 and the energization time. Further, based on a preset discharge curve, the remaining battery capacity is obtained from the PIG voltage that is the supply voltage to the inverter 8 and the battery temperature, and the battery usable capacity is determined.

  Since the CPU 16 stops the steering assist before the battery usage capacity exceeds the battery usable capacity, the CPU 16 can continue the steering assistance as long as the remaining battery capacity can be used. Further, when the ECU 6 is disposed in the vicinity of the battery 100, the battery temperature can be estimated from the substrate temperature sensor mounted on the control board of the control circuit 9, so that the battery can be determined from the discharge curve of the PIG voltage and the battery temperature. The remaining capacity can be estimated.

  Thus, even when the IG switch 7 is off and the vehicle running state or the engine operating state cannot be determined, the electric power steering device 10 alone prevents overdischarge of the battery 100 and continues steering assist. can do. As a result, the exhaustion of the battery 100 can be detected while the IG switch 7 is off, and the battery 100 can be protected from overdischarge.

  Further, when steering assist is performed while the engine is stopped with the IG switch 7 turned off, an engine restart command is output to an external device (for example, an engine ECU) before the battery usage capacity exceeds the battery usage capacity. can do. Further, when the engine is still operating even when the IG switch 7 is turned off, an engine automatic stop prohibition command can be output to the external device before the battery usage capacity exceeds the battery usage capacity. As a result, the battery 100 can be protected from overdischarge and the steering assist can be continued.

  As described above, according to the embodiment of the present invention, it is possible to provide an electric power steering apparatus capable of protecting the battery and continuing the steering assist by estimating the usable capacity of the battery when the IG switch is turned off. .

  As mentioned above, although embodiment which concerns on this invention was described, this invention can also be implemented with another form.

  In the above embodiment, the battery usable capacity is calculated from the PIG voltage and the battery temperature. However, the present invention is not limited to this. For example, the upper limit of the integrated value is determined for the capacity consumed from the battery 100. Alternatively, the power supply current may be detected to suppress overdischarge and protect the battery 100.

  In the above embodiment, the battery temperature is estimated from the substrate temperature sensor on the control board. However, the present invention is not limited to this. For example, when the mounting positions of the ECU 6 and the battery 100 are separated, the battery Another temperature sensor may be installed near 100 to detect the battery temperature.

1: motor, 2: speed reducer, 3: torque sensor, 4: vehicle speed sensor, 5: rotation angle sensor,
6: ECU, 7: IG switch, 8: Motor drive circuit (inverter), 9: Control circuit,
10: Electric power steering device (EPS), 11: Switching element,
12: current sensor, 13: power line, 14: earth line, 15: capacitor
16: microcomputer, 17: pre-driver, 18: normal assist control unit, 19: limit value calculation unit, 20: battery consumption capacity calculation unit, 100: battery, 101: steering wheel,
102: Steering shaft, 103: Rack and pinion mechanism, 104: Rack shaft, 105: Connecting member, 106: Wheel,
τ: steering torque, V: vehicle speed, θ: motor rotation angle, PIG: DC voltage, I: motor current value

Claims (5)

An electric motor for generating a steering assist force applied to the steering mechanism of the vehicle;
A battery for supplying electric power to drive the electric motor;
An inverter including a plurality of switching elements and supplying a driving current to the electric motor;
A control circuit for controlling the inverter,
The control circuit determines the battery usage capacity of the battery that is running after the IG switch for stopping the engine of the vehicle is turned off from a motor current value detected by a current sensor provided in the inverter and an energization time. A battery consumption capacity calculation unit, and a limit value calculation unit that determines a battery usable capacity of the battery when the IG switch is off from a preset DC voltage value supplied to the inverter and a battery temperature of the battery And having
An electric power steering apparatus characterized by determining prohibition of use of the battery when the battery use capacity exceeds the battery usable capacity. The electric power steering apparatus according to claim 1, wherein
The control circuit stops steering assistance when the battery usage capacity exceeds the battery usable capacity. In the electric power steering apparatus according to claim 1 or 2,
The electric power steering apparatus, wherein the control circuit estimates the battery temperature based on a detection value of a substrate temperature sensor provided on a control board of the control circuit. In the electric power steering device according to any one of claims 1 to 3,
An electric power steering apparatus that outputs an engine restart command when the battery use capacity exceeds the battery useable capacity and the engine is stopped. In the electric power steering apparatus according to any one of claims 1 to 4,
An electric power steering apparatus that outputs an engine automatic stop prohibition command when the battery use capacity exceeds the battery usable capacity and the engine is not stopped.

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