JP4869771B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

2. Description of the Related Art Conventionally, in an electric power steering device that applies a steering assist force to a steering mechanism by driving an electric motor according to a steering input by a driver, for example, a boosting circuit that boosts a supply voltage to a motor driving device such as an inverter There is known an electric power steering device that limits an output current or an output voltage of a booster circuit according to an increase in current supplied to the electric motor via the booster circuit (for example, Patent Document 1, Patent Document) 2).
JP 2003-54430 A JP 2005-199899 A

By the way, in the electric power steering apparatus according to the above prior art, since the output current or output voltage of the booster circuit is simply limited to a predetermined upper limit value or less, for example, the maximum steering wheel corresponding to the maximum turning of the steered wheels. In the vicinity of the steering angle or the like, the assist torque by the electric motor may be reduced or insufficient, and the steering input required by the driver may be excessively increased.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an electric power steering apparatus capable of outputting an appropriate assist torque.

In order to solve the above-described problems and achieve the object, an electric power steering apparatus according to a first aspect of the present invention is a motor that generates a turning force of a vehicle in accordance with a steering input (for example, in the embodiment). 11), steering input detecting means for detecting the steering input (for example, the steering torque sensor 10a in the embodiment), and at least the motor in accordance with the steering input detected by the steering input detecting means. Calculation means (for example, target current calculation unit 33 in the embodiment) for setting a target current, which is a target value of current to be supplied to the motor, and drive control means for driving and controlling the motor by pulse width modulation based on the target current (For example, the PWM inverter 31 in the embodiment), boosting means for boosting the power supply voltage and supplying it to the motor (for example, the boosting circuit 42 in the embodiment), An electric power steering apparatus including motor current detection means (for example, phase current sensor 10c in the embodiment) for detecting a motor current, the duty of the pulse width modulation and a detection value by the motor current detection means Based on the above, the output current from the power storage device (for example, the battery 41 in the embodiment) that constitutes the power source is calculated, and the input voltage applied to the booster when the output current exceeds a predetermined value It is characterized by comprising limiting means (for example, the control circuit 43 in the embodiment) for limiting the current or voltage output from the boosting means according to the value .

According to the above electric power steering apparatus, the or the output current from the power storage device is equal to or more than a predetermined value, without limiting the current or voltage outputted from the step-up means, suitably output a desired assist torque from the motor Can be made.

  As described above, according to the electric power steering apparatus of the present invention described in claim 1, the current or voltage output from the booster is limited in a state where the power storage device has a predetermined remaining capacity. Therefore, a desired assist torque can be appropriately output from the motor.

Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.
An electric power steering apparatus 10 according to this embodiment is provided in a manual steering force generation mechanism 1 as shown in FIG. 1, for example. In this manual steering force generation mechanism 1, a steering shaft provided integrally with a steering wheel 2. 3 is connected to a pinion 5a of a rack and pinion mechanism 5 provided in a steering gear box (not shown) via a connecting shaft 4 having universal joints 4a and 4b. The pinion 5a meshes with the rack teeth 6a of the rack shaft 6, and the rotational motion input from the steering wheel 2 is converted into the reciprocating motion of the rack shaft 6 via the pinion 5a. Two steered wheels W, W connected via tie rods 7, 7 are steered. A ball screw mechanism 8 is provided coaxially with the rack shaft 6, and a rotation of a motor 11 that forms a brushless DC motor of a plurality of phases (for example, three phases of U phase, V phase, and W phase) connected to the rack shaft 6. The force is converted into thrust through the ball screw mechanism 8 and acts on the rack shaft 6 (that is, the ball screw shaft 8a).

  The electric power steering device 10 includes a motor 11, a motor control device 12, and a power supply device 13. The motor control device 12 is provided in, for example, a steering gear box and acts on the pinion 5a. A detection signal output from the steering torque sensor 10a for detecting the steering torque Td, that is, the manual steering force input to the steering wheel 2 by the driver, and the vehicle speed Vs output from the vehicle speed sensor 10b for detecting the vehicle speed (vehicle speed). , A detection signal of at least two phase currents (for example, a U-phase current iu and a V-phase current iv) output from a phase current sensor 10 c that detects an energization current of the motor 11, and a rotor of the motor 11 Resolver or encoder that detects the angle θ, that is, the state quantity related to the rotation angle of the magnetic pole of the rotor from the predetermined reference rotation position Detection signal and it is input to be output from the rotation sensor 10d forming the over da like.

The motor control device 12 includes, for example, a PWM inverter 31 that drives the motor 11 by pulse width modulation (PWM), a current control unit 32, and a target current calculation unit 33. The target current calculation unit 33 is, for example, According to the detected values of the steering torque Td and the vehicle speed Vs and the command torque τ ^* input from an external control device, an assist torque for power steering that assists the driver's manual steering force is calculated. A target current required to output torque from the motor 11 is set. Then, according to the target current set by the target current calculation unit 33, the current control unit 32 sets the current so that the deviation between the actual current based on the detection result of the phase current sensor 10c and the target current becomes zero. Feedback control is performed to control energization of the motor 11.

  The PWM inverter 31 of the motor control device 12 includes, for example, a bridge circuit such as an H bridge formed by bridge connection using a plurality of switching elements of transistors, converts DC power supplied from the power supply device 13 into AC power, By sequentially commutating energization to the stator windings (not shown) of each phase of the motor 11, the magnitude (ie amplitude) and phase of the applied voltage of each phase is controlled in accordance with each phase voltage command value of a plurality of phases. Then, each phase current is supplied to each phase of the motor 11.

  For example, as illustrated in FIG. 2, the power supply device 13 includes a battery 41, a booster circuit 42 connected to the battery 41, and a control circuit 43 that controls the operation of the booster circuit 42.

The booster circuit 42 is controlled by the control circuit 43, boosts the input voltage from the battery 41 to a predetermined output voltage, and outputs the boosted voltage to the motor control device 12.
The control circuit 43 controls the boosting operation of the boosting circuit 42, and from the battery 41 based on the duty of the pulse width modulation in the PWM inverter 31 of the motor control device 12 and the detected value by the phase current sensor 10c, for example. The output current to be output is calculated, and when the output current becomes a predetermined value or more, the current or voltage output from the booster circuit 42 is limited to a predetermined value or less.

For example, as shown in FIG. 3, the control circuit 43 includes a map or the like for setting a predetermined upper limit value for the input current corresponding to the input voltage input to the booster circuit 42, and the motor detected by the phase current sensor 10c. It is determined whether or not the input current obtained by multiplying the current by the pulse width modulation duty in the PWM inverter 31 is equal to or less than a predetermined upper limit value corresponding to the input voltage.
When the calculated input current is larger than a predetermined upper limit value, for example, the target current calculation unit 33 of the motor control device 12 sets the difference between the input current and the predetermined upper limit value. Reduce the target current.

For example, in the map showing the correspondence relationship between the input voltage and the input current shown in FIG. 3, in the normal region where the input voltage is equal to or higher than the predetermined first input voltage Va, the input current is equal to or lower than the predetermined first upper limit value Ia. Is set to The first upper limit value Ia is a threshold value for preventing, for example, destruction or overheating of various elements included in the booster circuit 42, the PWM inverter 31, and the like.
Further, in the transition region where the input voltage increases from the predetermined second input voltage Vb (<Va) to the first input voltage Va, the input current ranges from the predetermined second upper limit value Ib (<Ia) to the first upper limit value Ia. The input current is set to be less than the predetermined second upper limit value Ib in a limited region where the input voltage is set to change in an increasing tendency and the input voltage is less than the predetermined second input voltage Vb.
The second upper limit value Ib and an appropriate upper limit value between the second upper limit value Ib and the first upper limit value Ia in the transition region are threshold values for preventing an excessive voltage drop in the battery 41. ing.

The electric power steering apparatus 10 according to the present embodiment has the above-described configuration. Next, the operation of the electric power steering apparatus 10 will be described.
First, for example, in step S01 shown in FIG. 4, the detected value of the steering torque Td is acquired.
Next, in step S02, the detected value of the vehicle speed Vs is acquired.
Next, in step S03, for example, for power steering that assists the driver's manual steering force according to the detected values of the steering torque Td and the vehicle speed Vs and the command torque τ ^* input from an external control device. Is calculated, and a target current required to output the assist torque from the motor 11 is set.

Next, in step S04, an input current limiting process described later is executed.
Next, in step S05, the duty of pulse width modulation in the PWM inverter 31 is calculated according to the target current.
In step S06, the energization of each phase of the motor 11 is controlled according to the calculated pulse width modulation duty, and the series of processing ends.

Hereinafter, the input current limiting process in step S04 described above will be described.
First, for example, in step S11 shown in FIG. 5, a motor current is acquired.
Next, in step S12, the motor current detected by the phase current sensor 10c is multiplied by the duty of the pulse width modulation in the PWM inverter 31 to calculate the input current of the booster circuit.

Next, in step S13, for example, with reference to a map or the like for setting a predetermined upper limit value for the input current corresponding to the input voltage input to the booster circuit 42, a predetermined upper limit value (input limit) corresponding to the input voltage is set. Current).
Then, it is determined whether or not the input current calculated from the motor current and the pulse width modulation duty is equal to or less than the input limit current.
When the determination result is “NO”, the series of processes is terminated.
On the other hand, if the determination is “YES”, the flow proceeds to step S15.
In step S15, the target current is reduced according to the deviation between the input current and the input limit current, and the series of processing ends.

  As described above, according to the electric power steering apparatus 10 according to the present embodiment, until the output current from the battery 41 becomes a predetermined value or more, that is, in a state where the battery 41 has at least a predetermined remaining capacity. The desired assist torque can be appropriately output from the motor 11 without limiting the current or voltage output from the booster circuit 42.

It is a lineblock diagram of an electric power steering device concerning an embodiment of the invention. It is a block diagram of the power supply device and motor control apparatus which are shown in FIG. It is a graph which shows an example of the map which sets the predetermined | prescribed upper limit with respect to the input current according to the input voltage input into a booster circuit. It is a figure which shows the flowchart which shows operation | movement of the electric power steering apparatus shown in FIG. It is a figure which shows the flowchart which shows the input current limiting process shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 10a Steering torque sensor 10c Phase current sensor 11 Motor 31 PWM inverter (drive control means)
33 Target current calculation part (calculation means)
41 battery (power storage device)
42 Booster circuit (Boosting means)
43 Control circuit (limitation means)

Claims (1)

A motor that generates a turning force of the vehicle in response to a steering input;
Steering input detection means for detecting the steering input;
Calculating means for setting a target current that is a target value of a current to be supplied to the motor in accordance with at least the steering input detected by the steering input detecting means;
Drive control means for driving and controlling the motor by pulse width modulation based on the target current;
Boosting means for boosting a power supply voltage and supplying it to the motor;
An electric power steering device comprising motor current detection means for detecting the current of the motor,
Based on the duty of the pulse width modulation and the value detected by the motor current detecting means, an output current from the power storage device that constitutes the power source is calculated, and when the output current becomes a predetermined value or more, the boosting means An electric power steering apparatus comprising: a limiting unit that limits a current or voltage output from the boosting unit in accordance with an applied input voltage value .

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