JP4816293B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an assist control from being stopped by resetting of a micro computer of an electronic control unit due to drop of a battery voltage in starting of an engine. <P>SOLUTION: The electric power steering device is provided with a booster circuit 40 from a power supply device 50 for a first power supply line 54 to a calculation circuit 31 of an electronic control unit 30. Boosted output voltage of the booster circuit 40 is set to be a constant value of not less than the minimum operating voltage of the calculation circuit 31 and sensors (a steering torque sensor 21, a rotation angle sensor 23, and a current sensor 33). The minimum operating voltage value of the booster circuit 40 is set to be lower than a start-time prediction battery voltage in consideration of the voltage drop in starting of the engine. An appropriate voltage power is supplied to the calculation circuit 31 and the sensors without the drop of the battery voltage, and the assist control can be normally performed. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering apparatus including an electric motor that applies a steering assist torque in accordance with an operation of a steering wheel.

  Conventionally, this type of electric power steering apparatus includes an electric motor that generates a steering assist torque in response to a steering operation of a steering wheel, and an electronic control unit that controls energization of the electric motor. The electronic control unit includes an arithmetic circuit that configures a main part by a microcomputer to calculate the control amount of the electric motor, and an inverter as a motor drive circuit that energizes the electric motor in response to a command signal from the arithmetic circuit. .

For example, the arithmetic circuit calculates a target assist torque value based on the steering torque acting on the steering wheel detected by the steering torque sensor and the vehicle speed detected by the vehicle speed sensor, and a target current value corresponding to the target assist torque value is calculated. The voltage command value to be applied to the electric motor is calculated according to the deviation from the actual current value actually flowing through the electric motor detected by the current sensor and output to the inverter. The inverter turns on / off the switching circuit at a duty ratio corresponding to the voltage command value from the arithmetic circuit, and applies a voltage corresponding to the voltage command value to the electric motor.
The direction of the steered wheels is changed by the sum of the steering assist torque generated by the electric motor and the steering torque applied to the steering wheel by the driver.
Hereinafter, the control performed by such an electronic control unit is referred to as assist control.

  Such an electric power steering apparatus is supplied with power from an in-vehicle battery. In-vehicle batteries (hereinafter simply referred to as “batteries”) are connected not only to an electric power steering device but also to a plurality of electric control systems such as an engine control device, and electric power required for each system is drawn from the batteries as needed.

  Generally, since a generator such as an alternator is connected to the in-vehicle battery, the fluctuation of the power supply voltage to each electric load is small. However, when the engine is started from a state where the engine is not operating, a large current is drawn from the vehicle-mounted battery, and the battery voltage temporarily drops significantly. For this reason, the power supply voltage supplied to the electronic control unit of the electric power steering apparatus is similarly lowered, and depending on the degree of voltage drop, the power supply voltage may be lower than the minimum operating voltage of the arithmetic circuit constituted by the microcomputer. is there. In this case, the arithmetic circuit performs a reset operation. The operation of the electric power steering apparatus is stopped by the reset operation of the arithmetic circuit. As a result, steering assist torque cannot be generated, and the steering wheel operation becomes heavy.

As a technology for achieving such fail-safe when the battery voltage decreases, Patent Literature 1 describes a configuration in which a booster circuit is provided in a power supply line to a steering control means including a microcomputer in a steer-by-wire type steering apparatus. ing.
JP 2005-29002 A

However, the booster circuit described in Patent Document 1 boosts the battery voltage by a predetermined voltage (2 V). For example, if the battery voltage is 6V, the voltage is boosted to 8V (6V + 2V). In other words, the final boosted voltage cannot always be held above a certain voltage.
Therefore, even if such a booster circuit is provided in the power supply line of the arithmetic circuit of the electric power steering apparatus, the battery voltage may be greatly reduced and the arithmetic circuit may be reset when the engine is started. Once the reset operation is performed, even if the battery voltage is recovered, the assist function cannot be obtained because the arithmetic circuit performs an initial diagnosis operation or the like for a predetermined time from the voltage recovery.

  In addition, the decrease in battery voltage affects the operation of the sensor. The electric power steering apparatus includes a steering torque sensor that detects a steering torque acting on the steering wheel, a rotation angle sensor that detects a rotation angle of the electric motor, a current sensor that detects a current flowing through the electric motor, and the like. The electric motor is controlled based on the signal. These sensors are also powered from the battery. When the battery voltage falls below the minimum operating voltage set for each sensor, the sensing operation becomes impossible and appropriate assist control cannot be performed.

  The present invention has been made to address the above-described problem, and an object of the present invention is to satisfactorily perform assist control even when the battery voltage decreases.

In order to achieve the above object, the present invention is characterized in that a steering mechanism that steers a steered wheel by steering a steering wheel, and a steering assist torque that is provided in the steering mechanism and that is provided for steering operation of the steering handle. An electric motor that generates a motor, a calculation circuit that calculates a control amount of the electric motor in accordance with a steering operation of the steering handle, and a motor drive that drives and controls the electric motor in accordance with the control amount calculated in the calculation circuit An electric power steering apparatus for a vehicle that is supplied with power from a vehicle-mounted battery that supplies power for starting a vehicle engine, and that supplies power from the vehicle-mounted battery to a power supply line from the vehicle-mounted battery to the arithmetic circuit a booster circuit for boosting the voltage up to the minimum operating voltage higher than the constant predetermined voltage of the operational circuit is provided, the minimum operating voltage of the booster circuit, the In that it is set lower than the expected voltage of the vehicle battery during both engine starting.

In the present invention configured as described above, the control amount of the electric motor corresponding to the steering operation of the steering handle is calculated by the arithmetic circuit, and the motor drive circuit controls the drive of the electric motor according to the calculated control amount. . An appropriate steering assist torque is applied to the steering operation of the steering wheel by the drive control of the electric motor. The control amount means a target current value or a target voltage value for driving and controlling the electric motor.
The in-vehicle battery is used as a power supply source for starting the vehicle engine and also supplies power to the electric power steering apparatus. The on-vehicle battery supplies a large amount of power when the engine is started, and thus the voltage drops greatly. In this case, the operation of the booster circuit provided in the power supply line from the in-vehicle battery to the arithmetic circuit supplies a constant voltage to the arithmetic circuit regardless of the battery voltage drop. Since the output voltage value of the booster circuit is set to a predetermined voltage that is equal to or higher than the minimum operating voltage of the arithmetic circuit, the arithmetic circuit is not reset even when the engine is started. Therefore, it is possible to perform the assist control satisfactorily even when the battery voltage is lowered.
Note that the minimum operating voltage (input voltage of the booster circuit) at which the booster circuit can properly boost is set to be lower than a predetermined start-up predicted battery voltage in consideration of a voltage drop during engine start-up.

Another feature of the present invention is a steering mechanism that steers the steered wheels by steering the steering handle, and an electric motor that is provided in the steering mechanism and generates a steering assist torque in response to a steering operation of the steering handle. A motor; a calculation circuit that calculates a control amount of the electric motor in accordance with a steering operation of the steering handle; and a motor drive circuit that drives and controls the electric motor in accordance with the control amount calculated in the calculation circuit. In the electric power steering apparatus for a vehicle that is supplied with power from a vehicle-mounted battery that supplies electric power for starting the vehicle engine, the arithmetic circuit detects a steering operation state of the steering wheel and a control state of the electric motor. The detection information from the vehicle battery is input to calculate the control amount of the electric motor, and the power supply line from the vehicle battery to the at least one sensor is calculated. In a booster circuit for boosting a power supply voltage from the vehicle battery to a minimum operating voltage higher than the constant predetermined voltage of the sensor is provided, the minimum operating voltage of the booster circuit, the vehicle at the start of the vehicle engine This is because it is set lower than the predicted voltage of the battery .

  In this case, the sensor supplied with power through the booster circuit is a steering torque sensor that detects a steering torque applied to the steering handle, or a current sensor that detects a current flowing through the electric motor, or It can be set as the rotation angle sensor which detects the rotation angle of the said electric motor.

In the present invention configured as described above, the arithmetic circuit calculates the control amount of the electric motor by inputting detection information from a plurality of sensors that detect the steering operation state of the steering wheel and the control state of the electric motor, The motor drive circuit controls the drive of the electric motor according to the calculated control amount. An appropriate steering assist torque is applied to the steering operation of the steering wheel by the drive control of the electric motor.
The arithmetic circuit inputs detection information from a plurality of sensors for calculating the control amount. As this sensor, for example, a steering torque sensor that detects a steering torque applied to the steering wheel, a current value that actually flows through the electric motor A current sensor for detecting is used. When a brushless motor is used as the electric motor, a rotation angle sensor that detects the rotation angle of the rotor of the electric motor is used.

Such sensors are powered by a vehicle battery. A booster circuit is provided in a power supply line from the in-vehicle battery to at least one sensor. When the engine is started, the battery voltage is greatly reduced, but the operation of the booster circuit supplies a constant voltage power to the sensor regardless of the battery voltage drop. Since the output voltage value of the booster circuit is set to a predetermined voltage that is equal to or higher than the minimum operating voltage of the sensor, the sensor does not malfunction even when the engine is started. Therefore, it is possible to perform the assist control satisfactorily even when the battery voltage is lowered.
Note that the minimum operating voltage (input voltage of the booster circuit) at which the booster circuit can properly boost is set to be lower than a predetermined start-up predicted battery voltage in consideration of a voltage drop during engine start-up.

The booster circuit is provided in a common power supply line from the in-vehicle battery to the arithmetic circuit and the at least one sensor, and the power supply voltage from the in-vehicle battery exceeds the minimum operating voltage of the arithmetic circuit and You may comprise so that it may pressure-up to the fixed predetermined voltage more than the minimum operating voltage of a sensor.
In this case, a stable power supply voltage can be supplied to the arithmetic circuit and the sensor regardless of the decrease in the battery voltage, and the malfunction of the sensor and the reset of the arithmetic circuit can be prevented to perform good assist control. be able to. Further, since the booster circuit is provided in the common power supply line to the arithmetic circuit and the sensor, a large number of booster circuits are not required, and the cost can be reduced.

  Hereinafter, an electric power steering device for a vehicle according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows an electric power steering device for a vehicle according to the embodiment, and FIG. 2 schematically shows a power supply system to the electric power steering device.

The electric power steering device for a vehicle can be broadly divided into a steering mechanism 10 that steers a steered wheel by steering a steering handle 11, an electric motor 15 that is assembled to the steering mechanism 10 and generates a steering assist torque, and a steering. The electronic control unit 30 controls the operation of the electric motor 15 in accordance with the steering state of the handle 11, and the booster circuit 40 boosts the power supply voltage supplied from the power supply device 50.
The steering mechanism 10 includes a steering shaft 12 connected to a steering handle 11 so as to integrally rotate at an upper end thereof, and a pinion gear 13 is connected to a lower end of the shaft 12 so as to integrally rotate. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1, FW2 are steerably connected to both ends of the rack bar 14 via tie rods and knuckle arms (not shown). The left and right front wheels FW1 and FW2 are steered left and right in accordance with the axial displacement of the rack bar 14 accompanying the rotation of the steering shaft 12 around the axis.

An electric motor 15 for steering assist is assembled to the rack bar 14. The electric motor 15 is configured by, for example, a three-phase synchronous permanent magnet motor (brushless motor). The rotating shaft of the electric motor 15 is connected to the rack bar 14 via the ball screw mechanism 16 so that power can be transmitted, and assists the steering of the left and right front wheels FW1, FW2 by the rotation.
The ball screw mechanism 16 functions as a speed reducer and a rotation-linear converter. The ball screw mechanism 16 reduces the rotation of the electric motor 15 and converts it into a linear motion and transmits it to the rack bar 14. Further, instead of assembling the electric motor 15 to the rack bar 14, the electric motor 15 is assembled to the steering shaft 12, and the rotation of the electric motor 15 is transmitted to the steering shaft 12 via the speed reducer so that the shaft 12 is axially connected. You may comprise so that it may drive around.

A steering torque sensor 21 is provided on the steering shaft 12. The steering torque sensor 21 detects a steering torque T acting on the steering shaft 12 by a turning operation of the steering handle 11. The steering torque T represents the magnitude of the steering torque when the steering handle 11 is steered in the right direction and the left direction by positive and negative values, respectively.
Further, instead of assembling the steering torque sensor 21 to the steering shaft 12, the steering torque T may be detected from the amount of distortion in the axial direction of the rack bar 14 by being assembled to the rack bar 14.

  The electric motor 15 is provided with a rotation angle sensor 23. The rotation angle sensor 23 is incorporated in the electric motor 15 and outputs a detection signal corresponding to the rotation of the rotor of the electric motor 15, and is constituted by a resolver sensor, for example. The detection signal from the rotation angle sensor 23 is used for calculating the rotation angle θ of the electric motor 15. On the other hand, since the rotation angle θ of the electric motor 15 is proportional to the steering angle of the steering handle 11, the rotation angle θ is also commonly used as the steering angle of the steering handle 11.

Next, the electronic control unit 30 will be described in detail.
The electronic control unit 30 (hereinafter referred to as the ECU 30) includes an arithmetic circuit 31 mainly composed of a microcomputer composed of a CPU, ROM, RAM, and the like, and an electric motor 15 based on a motor control signal output from the arithmetic circuit 31. And an inverter 32 as a motor drive circuit for driving the motor.
The arithmetic circuit 31 inputs detection signals from the steering torque sensor 21, the rotation angle sensor 23, the vehicle speed sensor 22, and the current sensor 33. The vehicle speed sensor 22 outputs a vehicle speed signal v corresponding to the traveling speed of the vehicle. The current sensor 33 detects the magnitude of the current flowing from the inverter 32 to the electric motor 15. In the present embodiment, as shown in FIG. 2, the two-phase power out of the three-phase power supply to the electric motor 15 ( For example, it is provided in a power line of U phase and W phase. This is because the sum of the U, V, and W phase currents is always kept at a value of 0 for the three-phase AC flowing through the electric motor 15, so that the remaining one-phase current is detected by detecting the current for two phases. It is because it is calculated | required by calculation.

  The arithmetic circuit 31 calculates the optimum magnitude of the steering assist torque for the steering operation performed by the driver, and calculates the target current value of the electric motor 15 so as to obtain this steering assist torque. Then, by feeding back the target current value with the actual current value detected by the current sensor 33, the target drive voltage of the electric motor 15 is set according to the deviation between the target current value and the actual current value. A motor control signal (PWM control signal) according to (corresponding to the control amount of the present invention) is output to the inverter 32. The assist control process performed by the arithmetic circuit 31 will be described later.

  The inverter 32 converts the direct current power supplied from the power supply device 50 into a three-phase alternating current power supply and applies the adjusted power supply voltage to the electric motor 15. The inverter 32 is provided with two switching elements in series between the power supply side (+ side) and the ground side of the power supply device 50 for each of the U, V, and W phases, and includes a total of six switching elements as a main circuit. A three-phase power line to the electric motor 15 is connected between the two switching elements of the V, W, and W phases. The arithmetic circuit 31 outputs a PWM control signal for turning on / off each switching element of the inverter 32. The inverter 32 controls the voltage applied to each coil of the electric motor 15 by adjusting the ON / OFF ratio of the switching element, that is, the duty ratio, by this PWM control signal.

Here, the assist control process performed by the ECU 30 will be described.
FIG. 3 shows an assist control routine executed by the arithmetic circuit 31, which is stored as a control program in the ROM of the arithmetic circuit 31, and is repeatedly executed in a short cycle.

  When the present control routine is activated by turning on the ignition switch 56, the arithmetic circuit 31 first, in step S11, the vehicle speed v information detected by the vehicle speed sensor 22 (hereinafter simply referred to as the vehicle speed v) and the steering torque sensor 21. The steering torque T information (hereinafter simply referred to as steering torque T) detected by the above is read.

Subsequently, with reference to the assist torque table shown in FIG. 4, a basic assist torque Tas set in accordance with the input vehicle speed v and steering torque T is calculated (S12). The assist torque table is stored in the ROM of the arithmetic circuit 31 and is set so that the basic assist torque Tas increases as the steering torque T increases, and increases as the vehicle speed v decreases.
The characteristic graph of FIG. 4 shows only the relationship between the positive region, that is, the steering torque T and the basic assist torque Tas in the right direction, but the negative region, that is, the left direction steering torque T and the basic assist torque Tas, 4 is moved to a point-symmetrical position around the origin. In this embodiment, the basic assist torque Tas is calculated using the assist torque table. However, a function that defines the basic assist torque Tas that changes according to the steering torque T and the vehicle speed v instead of the assist torque table. May be prepared, and the basic assist torque Tas may be calculated using the function.
Further, the calculation of the basic assist torque Tas is not necessarily calculated from the combination of the vehicle speed v and the steering torque T, and may be performed based on at least a detection signal corresponding to the steering state.

Subsequently, in step S13, the arithmetic circuit 31 calculates the target command torque T * by adding the compensation torque Trt to the basic assist torque Tas. The compensation torque Trt is a return force corresponding to a return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θ and a resistance force that opposes the rotation of the steering shaft 12 that increases in proportion to the steering angular velocity ω. Calculate as the sum of torque. In this calculation, the rotation angle of the electric motor 15 detected by the rotation angle sensor 23 (corresponding to the steering angle θ of the steering wheel) and the angular velocity ω of the electric motor 15 (the steering obtained by differentiating the steering angle θ of the steering wheel 11 with time). (Corresponding to the angular velocity ω).
Next, in step S14, the arithmetic circuit 31 calculates a target current I * that is proportional to the target command torque T *. The target current I * is obtained by dividing the target command torque T * by the torque constant.

Subsequently, the arithmetic circuit 31 reads the current value (actual current value Ix) flowing through the electric motor 15 from the current sensor 33 in step S15. Subsequently, in step S16, a deviation ΔI between the actual current value Ix and the previously calculated target current value I * is calculated, and a target command voltage V * is calculated by PI control (proportional integral control) based on the deviation ΔI. To do.
For example, it calculates by the following formula.
V * = Kp · ΔI + Ki · ∫ΔI dt
Here, Kp is a control gain of a proportional term in PI control, and Ki is a control gain of an integral term in PI control.

Then, the arithmetic circuit 31 outputs a PWM control voltage signal corresponding to the target command voltage V * to the inverter 32, and once ends this control routine. This control routine is repeatedly executed at a predetermined fast cycle. Therefore, by executing this control routine, the duty ratio of the switching element of the inverter 32 is controlled by PWM control, and a desired assist torque (target command torque T *) corresponding to the driver's steering operation is obtained.
In the present embodiment, when the electric motor 15 (three-phase permanent magnet synchronous motor) is driven and controlled by a three-phase power source from the inverter 32, it is described in a two-phase rotating magnetic flux coordinate system (dq coordinate system). Vector control is used. When performing this vector control, the rotation angle sensor 23 detects the rotation angle of the electric motor 15 (electrical rotation angle position of the rotor), and two-phase / three-phase coordinate conversion (from two-phase to three-phase conversion) is performed based on this rotation angle. Coordinate conversion to phase and coordinate conversion from 3 phase to 2 phase) are performed.

By the way, such assist control can be performed when power of an appropriate voltage is supplied to the ECU 30 and sensors (the steering torque sensor 21, the vehicle speed sensor 22, the rotation angle sensor 23, and the current sensor 33). When the power supply voltage drops, it cannot be performed properly. That is, when the voltage of the power source supplied to the arithmetic circuit 31 whose main part is constituted by a microcomputer is lower than the minimum operating voltage (minimum value of the power source voltage necessary for the arithmetic circuit 31 to operate normally) The microcomputer is reset and assist control is stopped. In addition, if the power supply voltage supplied to the sensors falls below the minimum operating voltage (minimum value of the power supply voltage necessary for the sensor to operate normally) determined for each sensor, the sensor can operate normally. As a result, proper assist control cannot be performed.
Therefore, the electric power steering apparatus of the present embodiment constitutes the following power supply circuit.

FIG. 2 is a configuration diagram illustrating a power supply circuit to the electric power steering apparatus. In the figure, a thick solid line represents a power supply system, and a thin solid line represents a signal system.
The electric power steering apparatus is supplied with power from a power supply apparatus 50 including a battery 51 and an alternator 52 that generates electric power by rotating the engine. As the battery 51, a general in-vehicle battery having a rated output voltage of 12V is used.
The power supply device 50 commonly supplies power to not only the electric power steering device but also other on-vehicle electric loads such as the engine control system 100. A first power supply line 54 and a second power supply line 55 are connected to the main power supply line 53 connected to the power supply terminal (+ terminal) of the battery 51 as a power supply line to the electric power steering.
The first power supply line 54 is a control power supply line for the ECU 30. On the other hand, the second power supply line 55 is a power supply line to the electric motor 15.

  The first power supply line 54 is provided with an ignition switch 56 in the middle thereof. Therefore, only when the ignition switch 56 is turned on, the control power is supplied to the arithmetic circuit 31 and the inverter 32 of the ECU 30 on the secondary side. The first power supply line 54 includes a booster circuit 40 that boosts the voltage of the power supplied from the power supply device 50 between the ignition switch 56 and the arithmetic circuit 31, and a diode provided on the secondary side of the booster circuit 40. 56. The diode 56 is a backflow prevention element that is provided with the cathode on the power supply output side (the arithmetic circuit 31 side) and the anode on the power supply device side (the booster circuit 40 side), and allows energization only in the power supply direction.

  As shown in FIG. 5, the booster circuit 40 includes a booster coil 41 provided in series with the first power supply line 54, and a ground line 42 branched from the first power supply line 54 on the output side of the booster coil 41. And a switching element 43 provided. Further, the first power supply line 54 is provided with a diode 44 on the power output side (the arithmetic circuit 31 side) from the connection point of the ground line 42. The diode 44 is a backflow prevention element that is provided with the cathode on the power output side and the anode on the power supply device 50 side, and allows energization only in the power supply direction. Further, the first power supply line 54 is provided with a branching ground line 46 provided with a power smoothing capacitor 45 on the power output side of the diode 44.

The booster circuit 40 includes a boost controller 47. The step-up controller 47 outputs a pulse signal to the switching element 43, turns the switching element 43 on and off at a fast cycle, intermittently passes a current through the step-up coil 41, and is charged in the step-up coil 41 accordingly. The power supply voltage is boosted so that power is output through the diode 44.
The step-up controller 47 operates with the power supplied from the first power supply line 54. The step-up controller 47 monitors the step-up voltage Vout after step-up, and performs step-up control by adjusting the duty ratio of the switching element 43 so that the step-up voltage Vout becomes the preset step-up rated voltage Voo.

  In this case, as shown in FIG. 6, when the input voltage Vin (output voltage of the power supply device 50) is equal to or higher than Vio, the booster circuit 40 operates so that the output voltage Vout becomes a constant boosted rated voltage Voo. . In the present embodiment, Vio = 3V and Voo = 9V are set. Therefore, even if the output voltage of the power supply device 50 decreases, the booster circuit 40 always outputs a constant voltage of 9 V if the output voltage is 3 V or higher. That is, the minimum operating voltage of the booster circuit 40 is 3V. When the input voltage Vin of the booster circuit 40 is higher than 9V, the supply voltage of the power supply device 50 is output as it is without performing the voltage adjustment operation.

The boosted rated voltage Voo of the booster circuit 40 is higher than the minimum operating voltage of the arithmetic circuit 31 (7 V in this embodiment).
The arithmetic circuit 31 includes a microcomputer as a main part, and includes a regulator (not shown) in a power input part of the microcomputer in order to supply a power of an appropriate voltage to the microcomputer. The regulator also has an appropriate input voltage at which it can operate. When the power supply voltage deviates from the appropriate input voltage, it is impossible to supply an appropriate voltage power supply to the microcomputer. The proper input voltage of the regulator in the present embodiment is 7V to 12V. Therefore, the minimum operating voltage of the arithmetic circuit 31 is 7 V, which is the minimum operating voltage of the regulator.
When the power supply voltage to the arithmetic circuit 31 falls below the minimum operating voltage, the microcomputer of the arithmetic circuit 31 performs a reset operation. For this reason, assist control becomes impossible. The arithmetic circuit 31 is restarted when the power supply voltage returns to the predetermined voltage after being reset once. In this case, the assist control is performed after performing a preset initial routine such as an initial diagnosis operation. Start.

The second power supply line 55 electrically connects the main power supply line 53 and the power input part of the inverter 32, and a power relay 57 is provided in the middle thereof. The power supply relay 57 is turned on by a control signal from the arithmetic circuit 31 to form a power supply circuit to the electric motor 15.
The second power supply line 55 is connected to the first power supply line 54 by a connecting line 58 on the load side of the power relay 57. The connection line 58 is connected between the diode 56 and the arithmetic circuit 31 in the first power supply line 54. A diode 59 is provided in the connection line 58. The diode 59 is provided with the cathode facing the first power supply line 54 and the anode facing the second power supply line 55, and can be energized only from the second power supply line 55 toward the first power supply line 54. Is a backflow prevention element.

The sensor power supply line 60 is connected to the second power supply line 55 closer to the arithmetic circuit 31 than the connection point with the connection line 58. The sensor power supply line 60 is a power supply line to the steering torque sensor 21, the rotation angle sensor 23, and the current sensor 33. On the way, the steering torque sensor power supply line 61, the rotation angle sensor power supply line 62, and the current sensor power supply line are provided. Branch to 63.
Accordingly, the steering torque sensor 21, the rotation angle sensor 23, and the current sensor 33 are supplied with the power supply voltage that is the output of the booster circuit 40.
The vehicle speed sensor 22 outputs vehicle speed information to a plurality of control systems in the vehicle, and is supplied with power from another control system (not shown).

In the state where the engine is not operating, the power supply device 50 cannot supply power generated by the alternator 52, and therefore power is supplied only from the battery 51. Therefore, when starting the engine, a large current is drawn from the battery 51, and the battery voltage is greatly reduced.
In addition, even when the engine is in operation, power is supplied only from the battery 51 in the case of power generation failure such as when the alternator 52 is disconnected from the main power supply line 53. The voltage drops greatly.

When the power supply voltage to the arithmetic circuit 31 falls below the minimum operating voltage, the microcomputer is reset and the assist control becomes impossible. Further, the minimum operating voltage is also set for the sensors such as the steering torque sensor 21, the rotation angle sensor 23, and the current sensor 33. When the power supply voltage to each sensor falls below the minimum operating voltage, proper sensing becomes impossible. As a result, good assist control cannot be performed.
Therefore, the booster circuit 40 is provided in the first power supply line 54 serving as a common power supply line to the arithmetic circuit 31 and the sensors so that the decrease in the battery voltage does not cause the assist control disabled state. In the present embodiment, the minimum operating voltage of the arithmetic circuit 31 is 7V, and the minimum operating voltage of the sensors is 9V. Therefore, in the present embodiment, the output voltage of the booster circuit 40 is set to 9 V that is equal to or higher than the minimum operating voltage of the arithmetic circuit 31 and equal to or higher than the minimum operating voltage of the sensors.
For this reason, even if the battery voltage falls below the power supply voltage 9V required for the electric power steering apparatus, a constant 9V power supply can always be obtained for the arithmetic circuit 31 and sensors, so that appropriate assist control can be performed. .

In the present embodiment, the minimum operating voltage of the booster circuit 40 is set to 3V. This is based on the experimental result that the battery voltage when starting the engine is reduced to about 5 V under bad conditions, and is set to 3 V in consideration of the safety factor.
FIG. 7 shows the magnitude relationship of these operating voltages.
Therefore, the battery voltage at which the ECU 30 can operate in the electric power steering apparatus is set lower than the predicted battery voltage (5 V) at the time of starting the engine.

As a result, it is possible to prevent a problem that the assist control is suddenly stopped due to a decrease in the battery voltage. Therefore, the steering assist torque does not disappear and the steering operation does not suddenly become heavy. Further, there is no problem that the steering handle 11 is moved by the restoring force from the tire due to the sudden disappearance of the steering assist torque, and the behavior of the vehicle suddenly changes during traveling.
Therefore, the electric power steering apparatus of this embodiment has high safety, reliability, and operability.
In addition, since the booster circuit 40 is provided on a common power supply line for the arithmetic circuit 31 and the sensors, a large number of booster circuits are not required and can be implemented at low cost.

Next, the electric power steering apparatus of 2nd Embodiment is demonstrated using FIG. 8, FIG.
The electric power steering apparatus according to the second embodiment includes an arithmetic circuit 31 ′ having a minimum operating voltage lower than that of the arithmetic circuit 31 in place of the arithmetic circuit 31 of the first embodiment, and supplies boosted power only to sensors. It is. Since other configurations are the same as those of the first embodiment, only differences will be described here.

As shown in FIG. 8, the electric power steering apparatus of the second embodiment includes a booster circuit 40 in the sensor power supply line 60. The booster circuit 40 is the same as that of the first embodiment.
The arithmetic circuit 31 ′ is set such that the minimum operating voltage of the regulator provided therein is set lower than the predicted battery voltage at the time of starting the engine (for example, 4 V), and the other functions are the arithmetic circuit 31 of the first embodiment. Is the same. Therefore, it can be said that the minimum operating voltage of the arithmetic circuit 31 ′ is set lower than the predicted start-up battery voltage in consideration of the voltage drop at the start of the engine.
On the other hand, the sensors (steering torque sensor 21, rotation angle sensor 23, current sensor 33) are the same as those in the first embodiment, and the minimum operating voltage is 9V. FIG. 9 shows the magnitude relationship between these operating voltages.
Therefore, in the second embodiment, the booster circuit 40 is provided in the sensor power supply line 60 that is a power supply line to the sensors.

  In the electric power steering apparatus according to the second embodiment, as in the first embodiment, even if the battery voltage decreases at the time of starting the engine or the like, the arithmetic circuit 31 ′ is reset or the sensors cannot be sensed. Thus, good assist control can be performed, and as a result, safety, reliability, and operability can be improved.

As mentioned above, although the electric power steering apparatus of two embodiment was demonstrated, this invention is not limited to the said embodiment, A various change is possible unless it deviates from the objective of this invention.
For example, in the present embodiment, the configuration in which the booster circuit 40 is provided outside the electronic control unit 30 is shown, but it may be incorporated in the electronic control unit 30.
In the first embodiment, the booster circuit is provided in the common power supply line for the arithmetic circuit and the sensors. However, the booster circuit is provided only in the power supply line to the arithmetic circuit. Alternatively, the booster circuit may be provided only on the power supply line to a specific sensor. Moreover, the structure which provided separately the booster circuit only for an arithmetic circuit and the booster circuit only for a sensor may be sufficient.
Further, the boosted voltage value and the minimum operating voltage value of the booster circuit can be arbitrarily set according to the system specifications of the battery and the electric power steering apparatus.

1 is an overall configuration diagram of an electric power steering apparatus according to a first embodiment of the present invention. It is a schematic circuit block diagram mainly showing the power supply system to the electronic control unit of 1st Embodiment. It is a flowchart showing the assist control routine of 1st Embodiment. It is explanatory drawing showing the assist torque table of 1st Embodiment. It is a schematic circuit block diagram of the booster circuit of 1st Embodiment. FIG. 3 is a boost characteristic diagram of the booster circuit according to the first embodiment. It is explanatory drawing showing the relationship, such as a boost voltage and a minimum operating voltage, of 1st Embodiment. It is a schematic circuit block diagram mainly showing the power supply system to the electronic control unit of 2nd Embodiment. It is explanatory drawing showing relation, such as a boost voltage and a minimum operating voltage of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 15 ... Electric motor, 21 ... Steering torque sensor, 22 ... Vehicle speed sensor, 23 ... Rotation angle sensor, 30 ... Electronic control unit (ECU), 31, 31 '... arithmetic circuit, 32 ... inverter, 33 ... current sensor, 40 ... booster circuit, 50 ... power supply, 51 ... vehicle battery, 52 ... alternator, FW1, FW2 ... left and right front wheels.

Claims (6)

A steering mechanism that steers the steered wheels by steering the steering wheel;
An electric motor that is provided in the steering mechanism and generates a steering assist torque in response to a steering operation of the steering handle;
An arithmetic circuit for calculating a control amount of the electric motor in accordance with a steering operation of the steering wheel;
A motor drive circuit that drives and controls the electric motor according to a control amount calculated by the arithmetic circuit;
In an electric power steering apparatus for a vehicle that is powered by an in-vehicle battery that supplies electric power for starting a vehicle engine,
In the power supply line from the in-vehicle battery to the arithmetic circuit, a booster circuit that boosts the power supply voltage from the in-vehicle battery to a predetermined voltage equal to or higher than the minimum operating voltage of the arithmetic circuit is provided .
The electric power steering apparatus according to claim 1, wherein a minimum operating voltage of the booster circuit is set lower than a predicted voltage of the vehicle battery when the vehicle engine is started . A steering mechanism that steers the steered wheels by steering the steering wheel;
An electric motor that is provided in the steering mechanism and generates a steering assist torque in response to a steering operation of the steering handle;
An arithmetic circuit for calculating a control amount of the electric motor in accordance with a steering operation of the steering wheel;
A motor drive circuit that drives and controls the electric motor according to a control amount calculated by the arithmetic circuit;
In an electric power steering apparatus for a vehicle that is powered by an in-vehicle battery that supplies electric power for starting a vehicle engine,
The arithmetic circuit calculates detection amounts from a plurality of sensors that detect a steering operation state of the steering wheel and a control state of the electric motor, and calculates a control amount of the electric motor,
A booster circuit that boosts the power supply voltage from the in-vehicle battery to a predetermined voltage that is equal to or higher than the minimum operating voltage of the sensor is provided in a power supply line from the in-vehicle battery to the at least one sensor ;
The electric power steering apparatus according to claim 1, wherein a minimum operating voltage of the booster circuit is set lower than a predicted voltage of the vehicle battery when the vehicle engine is started .   The booster circuit is provided in a common power supply line from the in-vehicle battery to the arithmetic circuit and the at least one sensor, and the power supply voltage from the in-vehicle battery exceeds the minimum operating voltage of the arithmetic circuit and the sensor 3. The electric power steering apparatus according to claim 2, wherein the voltage is boosted to a predetermined voltage that is equal to or higher than the lowest operating voltage.   4. The electric power steering apparatus according to claim 2, wherein the sensor supplied with power through the booster circuit is a steering torque sensor that detects a steering torque applied to the steering wheel.   4. The electric power steering according to claim 2, wherein the sensor supplied with power via the booster circuit is a current sensor that detects a current flowing through the electric motor.   4. The electric power steering apparatus according to claim 2, wherein the sensor supplied with power via the booster circuit is a rotation angle sensor that detects a rotation angle of the electric motor.

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