JP3205651B2 - Electric power steering device with power supply voltage control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for a vehicle provided with a power supply voltage control device for controlling power supply from a power supply which is a vehicle-mounted battery to a motor for assisting steering.

[0002]

2. Description of the Related Art In general, in an electric power steering system using a steering assist motor, a power supply voltage of a vehicle-mounted battery is supplied to the motor via an electronic control circuit in accordance with a driving state of the vehicle. Specifically, the electronic control circuit outputs a control signal to which a vehicle speed response characteristic according to the detected vehicle speed and a steering response characteristic according to the detected steering (steering speed, steering torque) are added. The electric power steering device is configured to decrease the steering assist force as the vehicle speed increases, or to increase the steering assist force as the steering speed and the steering torque increase.

[0003] In such a conventional electric steering device, when a maximum load for steering assist (during dry parking and ultra-low speed driving), for example, a current of several tens of amperes flows through a 12-volt on-board battery, the internal electric steering device is internally driven. A significant voltage drop due to the resistance occurs, thus reducing the voltage input to the electronic control circuit. Further, this input voltage receives a voltage drop of a semiconductor element (for example, MOSFET) in the electronic control circuit and a voltage drop of a wire cable connecting the electronic control circuit and the motor, so that the voltage actually supplied to the motor is about 7 volts. And there is a disadvantage that the power supply efficiency is significantly reduced.

[0004]

The problem to be solved by the present invention is that the efficiency of energizing the motor from the vehicle-mounted battery to the motor when the steering assist is at the maximum load is significantly reduced.

Further, in the conventional electric power steering apparatus, since a relatively large current is supplied to the motor winding, electromagnetic wave noise due to the exciting current is generated.

Further, in the conventional electric power steering apparatus, a semiconductor element having an appropriate large current capacity must be used so as to endure a large current at the time of the maximum steering load. There were also problems of large size and high cost.

In general, it is well known that the above-mentioned voltage drop and electromagnetic wave noise are both proportional to the square of the current value. Therefore, if such a reduction in current value is possible, very good results can be expected.

[0008]

SUMMARY OF THE INVENTION The present invention provides a power supply voltage control device for increasing the power supply voltage of an on-vehicle battery in response to a decrease in vehicle speed during steering assist, thereby making the electronic control circuit and the motor a high-voltage device. As a result, the resistance loss of the entire electric system has been reduced.

Further, the present invention provides a power supply voltage control device for boosting the power supply voltage of a vehicle-mounted battery according to a decrease in vehicle speed and an increase in steering speed during steering assist.

[0010]

FIG. 1 is a schematic diagram of an electric power steering apparatus according to the present invention to which a power supply voltage control apparatus can be applied.

Referring to FIG. 1, the operation of the electric power steering apparatus will be described. Steering of the steering wheel 1 moves the rack bars at both ends of the rack gear in the axial direction via the rack and pinion gear 2 and the rack gear in the housing 3. The axial movement of the rack bar is further transmitted to the wheel 5 via the tie rod 4. A steering gear motor 6 is connected to the rack gear in the housing 3, and is configured to assist the axial movement of the rack bar by the rotation of the motor 6. The power supply voltage of the vehicle-mounted battery 7 is supplied to the motor 6 via the electronic control circuit 8. Electronic control circuit 8
Is the vehicle speed signal detected by the vehicle speed sensor 9, the steering speed sensor 1
A steering speed signal detected at 0 and a steering torque signal detected by the steering torque sensor 11 are input, and a control signal indicating a vehicle speed response characteristic and a steering response characteristic is output. Therefore, the rotation of the motor 6 is controlled in accordance with the control signal output from the electronic control circuit 8 to achieve a desired steering assist force.

FIG. 2 is a block circuit diagram of an electric power steering device provided with the power supply voltage control device of the present invention.
It comprises a vehicle-mounted battery 7, a power supply voltage control device 20, a vehicle speed sensor 9, a steering torque sensor 11, a power drive circuit 21, a power output circuit 22, and a three-phase motor 6.

The power supply voltage control device 20 includes a voltage doubler circuit and receives a speed signal from a speed sensor 9 as described later with reference to FIG. Is configured to boost the voltage.

The power drive circuit 21 is a three-phase step pulse signal generation circuit, and controls the ignition of the power output circuit 22 according to the steering signal detected by the steering torque sensor 11. That is, the three-phase step signal output from the power drive circuit 21 is subjected to pulse width modulation (PWM) control in which the ON-OFF duty ratio is changed according to the magnitude of the steering torque when the steering wheel 1 is rotated,
Also steering. This is a three-phase step pulse signal whose polarity is discriminated according to the steering rotation direction when the wheel 1 is rotated. Therefore, the power drive circuit 21 has a steering torque response characteristic, and is configured to sequentially output a three-phase step pulse signal according to the magnitude and polarity of the steering torque.

The power output circuit 22 supplies a control power supply voltage from the power supply voltage control device 20 having the above-described speed-sensitive boosting characteristic to each winding of the three-phase motor. At this time, the power supply to each winding is sequentially performed by the ignition control of the three-phase step pulse signal from the power drive circuit 21 having the steering torque response characteristic as described above.

FIG. 3 is a detailed diagram of the block circuit diagram of FIG. 2, and particularly shows details of the power supply voltage control device 20.

The power supply voltage control device 20 includes MOS field effect transistors T1 and T2, backflow blocking diodes D1 and D2, boost capacitors C1 and C2, an oscillation circuit OSC, a flip-flop FF, and a pulse width modulation circuit P.
It is composed of WM1 and PWM2, and power supply drive circuits DV1 and DV2. In the power supply voltage control circuit 20, the transistors T1 and T2, the diodes D1 and D
2. The boost capacitors C1 and C2 constitute a voltage doubler functioning as a DD converter, and the remaining circuit elements constitute a drive circuit of the voltage doubler.

The operation of the circuit of FIG. 3 will be described below.

The flip-flop FF has an oscillation circuit OS
Upon receiving the output signal of C, an alternating pulse signal is sequentially applied to pulse width modulation circuits PWM1 and PWM2. Each of the pulse width modulation circuits PWM1 and PWM2 receives the vehicle speed signal detected by the vehicle speed sensor 9 as an output signal of the frequency-voltage converter F / V, and turns ON / OFF the alternating pulse signal from the flip-flop FF. Change the duty ratio. Therefore, the alternating pulse signal output from the pulse width modulation circuits PWM1 and PWM2 is provided with a vehicle speed response characteristic, and the ON period of each pulse increases as the vehicle speed decreases.
Such an alternating pulse signal is supplied to the transistor T of the voltage doubler circuit via the power supply driving circuits DV1 and DV2, respectively.
1 and T2 are given to the terminals G1 and G2 as gate signals.

The voltage doubler circuit boosts the power supply voltage of the vehicle battery 7 in response to the alternating pulse signal as a gate signal. That is, when the first alternating pulse output from the pulse width modulation circuit PWM1 turns on the transistor T1,
First, battery 7, transistor T1, capacitor C
1, a closed circuit of the diode D1 and the battery 7 is formed, and the capacitor C1 is charged up to the power supply voltage at the maximum,
Next, when the second alternating pulse output from the pulse width modulation circuit PWM2 turns on the transistor T2, a closed circuit of the battery 7, the diode D2, the capacitor C2, the transistor T2, and the battery 7 is formed, and the capacitor C2 is replaced by the capacitor C1. It is charged up to the power supply voltage with the same polarity as the maximum. Therefore, as a result, a voltage twice the power supply voltage is obtained across the capacitors C1 and C2 connected in series.

As shown in FIG. 4, the output characteristic of the voltage doubler circuit is determined by the vehicle speed response characteristic. Specifically, at a low speed, for example, at a speed of 10 km / H or less, twice the power supply voltage. Is determined so as to obtain the maximum voltage, and is determined to gradually decrease as the vehicle speed further increases.

The output of the voltage doubler circuit to which the vehicle speed response characteristic is added, that is, the power supply voltage control device 20 is a power output circuit 2
Under the control of FIG. 2 (FIG. 2), each winding Lu,
Lv and Lw are sequentially supplied. As described with reference to FIG. 2, the phase rotation control of the three-phase motor 6 is performed by the three-phase step pulse signal output from the power drive circuit 21 to which the steering torque characteristic is added, Gates G of the field-effect transistors Tu, Tv and Tw
This is done by sequentially triggering u, Gv and Gw. The steering rotation direction is performed by phase conversion of a three-phase step pulse signal by polarity discrimination of the steering torque signal.

In the above description of the embodiment, the vehicle speed is monitored and the vehicle speed response characteristic is added to the power supply voltage control device 20 in order to increase the power supply voltage in response to the increase in the load of the steering assist. Is caused not only when the vehicle is stopped or traveling at an extremely low speed, but also when the operating speed of the steering wheel is increased. Therefore, it is effective to monitor the vehicle speed as well as the steering speed.

In this case, as shown by a broken line in FIG.
The steering speed sensor 1 is added to the pulse width modulation circuits PWM1 and PWM2.
The steering speed signal detected at 0 is input, and a steering speed response characteristic is added to the alternating pulse signal together with the vehicle speed response characteristic. When the steering speed response characteristic is reflected in the power supply voltage-vehicle speed characteristic curve of FIG.
It can be understood as a difference between a broken line and a solid line.

Further, in the above description of the embodiment, a three-phase motor is exemplified as an electric motor for assisting steering, but a multi-phase stepping motor such as a three-phase or four-phase motor,
It is also possible to use a general DC motor, AC servo motor or the like.

In the description of the embodiment, an electric power steering apparatus of a type in which a rack shaft is directly driven by an electric motor to apply a steering assist force is exemplified.
It is a matter of course that the electric power steering device includes a hydraulic type in which a hydraulic pump is driven by an electric motor and a steering assist force is applied by hydraulic pressure.

[0027]

As described above, according to the present invention,
By utilizing the DC-DC conversion function, during the steering assist, by increasing the power supply voltage of the vehicle-mounted battery as the vehicle speed decreases and as the vehicle speed decreases and the steering speed increases,
Since the load current is substantially reduced, the resistance loss can be reduced throughout the electric system of the electric power steering device. Therefore, the power supply efficiency from the vehicle-mounted battery to the steering assist motor can be improved.

Further, according to the present invention, the semiconductor element constituting the electronic control circuit and the motor itself can be constituted by a high voltage device having a relatively small current capacity by reducing the load current. In particular, the power unit can be reduced in size, and electromagnetic noise leaking from a wire cable connecting the electronic control circuit and the motor can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electric power steering device of the present invention to which a power supply voltage control circuit can be applied.

FIG. 2 is a block circuit diagram of an electric power steering device provided with the power supply voltage control device of the present invention.

FIG. 3 is a detailed diagram of the block circuit of FIG. 2;

FIG. 4 is a diagram showing an operation characteristic curve of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 steering wheel 2 rack and pinion gear 3 housing 4 tie rod 5 wheel 6 (three-phase) motor 7 on-board battery 8 electronic control circuit 9 vehicle speed sensor 10 steering speed sensor 11 steering torque sensor 20 power supply voltage control device 21 power drive circuit 22 Power Output Circuit T1, T2, Tu, Tv, Tw MOS Field Effect Transistor D1, D2 Backflow Blocking Diode C1, C2 Boost Capacitor OSC Oscillator FF Flip-Flop PWM1, PWM2 Pulse Width Modulator DV1, DV2 Power Supply Driver F / V frequency-voltage converter

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B62D 5/04 B62D 6/00

Claims (2)

(57) [Claims] An electronic control circuit for outputting a control signal to which a vehicle speed response characteristic is added in response to a vehicle speed signal detected by a vehicle speed sensor, and a power supply voltage of a vehicle-mounted battery supplied to a steering assist motor. Is controlled in accordance with the control signal, wherein the electronic control circuit is further detected by a steering speed sensor.
A power supply voltage control device that increases a power supply voltage of the vehicle-mounted battery in response to a decrease in vehicle speed and an increase in steering speed in response to the steering speed signal. Electric power steering device. 2. The system according to claim 1, wherein said power supply voltage control device is at or below a predetermined vehicle speed.
At the time, the maximum of the power supply voltage of the vehicle-mounted battery
The feature is that it is configured to boost up to twice the voltage
The electric power steering apparatus according to claim 2 , wherein