JP2005212515A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control lighting of car-mounted lighting equipment with less space and less burden of cost. <P>SOLUTION: The car-mounted lighting equipment is lighted by switching motion of a light driving circuit 23 by taking a PWM signal Sb into the light driving circuit 23 from a PWM signal generating means 20 to generate the PWM signal Sb (Sc) for motor driving on a power steering device to assist steering by driving an electric motor 5 by the PWM signal in accordance with operation of a steering member 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power steering device that assists a driver's steering by driving an electric motor with a PWM (pulse width modulation) signal in accordance with an operation of a steering member such as a steering wheel (handle) performed by the driver, More specifically, the present invention relates to a power steering device that can perform lighting control of an in-vehicle lighting device such as a headlight.

  As a vehicle steering device, a so-called electric power steering device that reduces a steering force of a driver by adding a steering assist torque by an electric motor to a steering mechanism when a steering wheel is operated has been widely used in recent years.

  Among such electric power steering devices, there is one that drives an electric motor by a PWM signal. The device is usually composed of an electric motor, various sensors such as a torque sensor for detecting steering torque and a vehicle speed sensor for detecting the speed (vehicle speed) of the vehicle, and an electronic control unit (ECU). Includes at least a microcomputer, an interface that performs necessary processing on sensor signals from various sensors and gives the microcomputer, a PWM signal generation circuit, and a motor drive circuit including a plurality of switching elements such as power MOSFETs. ing.

  In the electric power steering apparatus described above, the sensor signal of each sensor is processed by the interface in the ECU and then taken into the microcomputer. The microcomputer uses the built-in steering assistance program and steering assistance data from the taken sensor signal. Accordingly, the motor drive amount required to generate the torque suitable for the steering assist is calculated, a duty ratio control signal corresponding to the drive amount is generated, and this is output to the PWM signal generation circuit. The PWM signal generation circuit generates a PWM signal having a duty ratio corresponding to the duty ratio control signal, applies the PWM signal to the motor drive circuit, and switches the switching elements constituting the motor drive circuit to operate the electric motor. Drive (refer to Patent Document 1).

By the way, about the vehicle-mounted apparatus, the apparatus which carries out lighting drive of vehicle-mounted illumination apparatuses, such as a headlight, with a PWM signal is proposed separately from the above-mentioned electric power steering apparatus (refer patent document 2). According to this device, the voltage applied to the headlight can be adjusted by changing the setting of the duty ratio of the PWM signal, compared with the case where the lighting of the headlight or the like is controlled by an opening / closing means such as a relay. Power consumption can be reduced.
Japanese Patent Laid-Open No. 10-327597 JP-A-5-168164

  As described above, a device for lighting and driving an in-vehicle lighting device such as a headlight by a PWM signal requires a dedicated mounting space for that purpose, and also requires a harness to be routed, both in terms of space and cost. In addition, there is a problem, and the burden of signal transmission / reception in a CAN (controller area network) which is an in-vehicle network increases.

  A power steering apparatus according to the present invention is a power steering apparatus that assists steering by driving a motor with a PWM signal in accordance with an operation of a steering member, and includes a PWM signal generating means for generating the PWM signal and an on-vehicle vehicle using the PWM signal. A lighting drive circuit for lighting the lighting device is provided.

  In the power steering device having the above-described configuration, on-vehicle lighting equipment such as a headlight can be driven to be lit by a PWM signal, and thus the lighting equipment can be PWM-driven to reduce power consumption by the lighting equipment. In addition, since the PWM signal generating means built in the power steering device is shared for lighting control of the in-vehicle lighting device, a dedicated device for lighting control of the in-vehicle lighting device conventionally proposed, and for the device Necessary spaces and wirings can be omitted, and the burden can be reduced in terms of both space and cost.

  In the power steering apparatus having the above-described configuration, for example, as a motor drive circuit, two pairs of transistors connected in series are connected in parallel between a power source and the ground, and a connection is made between the connection points of each pair of transistors. Thus, in the case of an H bridge configuration in which an electric motor is connected, when two PWM signals for this bridge circuit are in a complementary relationship (both signals have a duty ratio of 50%), a motor current flows to the electric motor. Can be eliminated. When the PWM signals are set in a complementary relationship in this way, the steering member is hardly operated and the electric motor is not driven, for example, when the steering wheel is in a neutral position or when the steering torque is zero. However, it is preferable that a lighting device such as a headlight can be driven to turn on by the PWM signal from the PWM signal generating means.

  According to the present invention, it is possible to control lighting of an in-vehicle lighting device such as a headlight with little burden in terms of space and cost.

  Hereinafter, an electric power steering apparatus according to the best mode of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing the electric power steering apparatus together with a vehicle configuration related thereto.

  The electric power steering apparatus will be described with reference to FIG. 1. The electric power steering apparatus includes a steering shaft 2 whose one end is fixed to a handle (steering wheel) 1 as a steering member, and the other end of the steering shaft 2. In order to reduce a driver's load caused by a steering operation (steering operation), a steering mechanism 3 including a connected rack and pinion mechanism, a torque sensor 4 for detecting a steering torque applied to the steering shaft 2 by the operation of the steering wheel 1, and the like. The electric motor 5 that generates a steering assist force, the reduction gear 6 that transmits the steering assist force generated by the electric motor 5 to the steering shaft 2, and the power supplied from the in-vehicle battery 7 via the ignition switch 8, Sensor 4, vehicle speed sensor 9, and engine rotation sensor 10 And an electronic control unit (ECU) 11 for controlling the driving of the electric motor 5 based on al of the sensor signal.

  When the driver operates the steering wheel 1 in a vehicle equipped with the electric power steering device, the steering torque by the operation is detected by the torque sensor 4, and the detected steering torque and the vehicle speed detected by the vehicle speed sensor 9 are detected. Based on the above, the electric motor 5 is driven by the ECU 11. As a result, the electric motor 5 generates a steering assist force, and this steering assist force is applied to the steering shaft 2 via the reduction gear 6, thereby reducing the burden on the driver due to the steering operation.

  That is, the sum of the steering torque applied by the steering operation and the torque (steering assist torque) by the steering assist force generated by the electric motor 5 is given to the steering mechanism 3 via the steering shaft 2 as an output torque. As a result, when the input shaft of the steering mechanism 3 rotates, the rotation is converted by the steering mechanism 3 into a reciprocating motion of the rack shaft that is the output shaft. Both ends of the rack shaft are connected to a steering wheel 13 via a connecting member 12 including a tie rod and a knuckle arm, and the direction of the wheel 13 changes according to the reciprocating motion of the rack shaft.

  In the electric power steering apparatus having the above configuration, the electric motor 5 is driven (PWM drive) controlled by a PWM signal. In the present embodiment, the lighting control of the in-vehicle lighting device such as the headlight 14 can be performed together using the PWM signal for driving the electric motor 5. That is, in the present embodiment, a signal indicating the on / off state of a lighting operation switch (lighting operation means) 15 for lighting an in-vehicle lighting device, for example, the headlight 14, is taken into the ECU 11, and the microcomputer 16 (see FIG. 2), the power supply voltage of the in-vehicle battery 7 is supplied to the headlight 14 in accordance with the on / off state of the lighting operation switch 15, and the headlight 14 is turned on.

  The configuration of the ECU 11 will be described with reference to FIG.

  The ECU 11 is provided corresponding to each of the microcomputer 16, the torque sensor 4, the vehicle speed sensor 9, the engine rotation sensor 10, etc., and an interface 17 that processes sensor signals into a form suitable for the processing of the microcomputer 16. 18 and 19, a PWM signal generating circuit (PWM signal generating means) 20 for generating PWM signals Sb and Sc having a predetermined duty ratio based on a duty ratio control signal Sa given from the microcomputer 16, and a plurality of power MOSFETs Of the PWM signals Sb and Sc generated by the motor drive circuit 22 having the transistors 21A, 21B, 21C and 21D (generally referred to as 21) such as H-bridge and the PWM signal generating circuit 20, the PWM signal Sb is captured. The headlight 14 is turned on by the PWM signal Sb. A lighting drive circuit (lighting drive means) 23 for switching, an opening / closing means 24 for switching between input and cutoff of the PWM signal Sb on the signal input side of the lighting drive circuit 23, and a power source for supplying power to each circuit in the ECU 11 And a circuit (power supply means) 25.

  The microcomputer 16 includes a CPU that controls the center of the electric power steering apparatus, a program memory, and a data memory, although not particularly shown in hardware. The program memory is based on a control program for controlling the entire electric power steering device and a PWM signal Sb based on sensor signals of the torque sensor 4 and the vehicle speed sensor 9 and the like given by the processing of each of the interfaces 17, 18 and 19. , Sc for calculating a duty ratio and the like. The data memory stores data necessary for electric power steering control, such as an assist table memory described later, and provides a work area for the operation of the CPU.

  The CPU of the microcomputer 16 functions as drive arithmetic means 16a that executes the arithmetic program stored in the program memory. The data memory of the microcomputer 16 includes an assist table memory 16b that stores an assist table necessary for execution of the calculation of the drive calculation means 16a. The drive calculation means 16a calculates a target current value to be supplied to the electric motor 5 based on the steering torque information obtained from the sensor signal of the torque sensor 4, the vehicle speed information obtained from the sensor signal of the vehicle speed sensor 9, and the like. The assist table memory 16b stores an assist table that indicates the relationship between the target current value to be supplied to the electric motor 5 and the steering torque in order to generate an appropriate steering assist force, using the vehicle speed as a parameter. The means 16a refers to this assist table for setting the target current value.

  The drive calculation means 16a calculates the deviation between the motor current detection value obtained from the motor current detection circuit and the target current value, and the PWM signal Sb generated by the PWM signal generation circuit 20 so that the deviation becomes zero. A duty ratio control signal Sa that determines the duty ratio of Sc is generated.

  For example, when the steering wheel 1 is steered to the right, the drive calculation unit 16a rotates the electric motor 5 to the right to perform right steering assistance, so that the duty ratio of the PWM signal Sb is larger than the duty ratio of the PWM signal Sc. When the steering wheel 1 is steered to the left, the duty ratio control signal is set so that the duty ratio of the PWM signal Sc is larger than the duty ratio of the PWM signal Sb in order to rotate the electric motor 5 counterclockwise and perform left steering assist. Sa is generated. The drive calculation means 16a stops the steering assistance by stopping the rotation of the electric motor 5 when the steering wheel 1 is in the neutral position and the vehicle is traveling straight or when the steering torque is zero. The duty ratio control signal Sa is generated so that the duty ratio of both the PWM signals Sb and Sc is 50%.

  The CPU of the microcomputer 16 also functions as switching command means 16c for executing the arithmetic program stored in the program memory. The switching command means 16c turns on / off the opening / closing means 24 in response to turning on / off of the lighting operation switch 15, and switches between input and cutoff of the PWM signal Sb to the lighting drive circuit 23.

  In response to the duty ratio control signal Sa from the microcomputer 16, the PWM signal generation circuit 20 generates PWM signals Sb and Sc having complementary pulse widths as shown in FIGS. To do. The PWM signal generation circuit 20 can also be configured by the microcomputer 16 and has a complementary pulse width relationship as shown in FIGS. 3A and 3B in accordance with the duty ratio control signal Sa. Since the circuit configuration and functional configuration for generating the PWM signals Sb and Sc are well known, the details thereof are omitted.

  The motor drive circuit 22 includes a connection point between two transistors 21A and 21C among bridge-connected transistors (for example, N-channel power MOSFETs) 21A, 21B, 21C, and 21D and a connection between the other two transistors 21B and 21D. The electric motor 5 is connected so as to bridge the points. In the motor drive circuit 22, each pair of transistors 21A and 21D (or 21B and 21C) connected in series via the electric motor 5 supplies the PWM signals Sb and Sc from the PWM signal generation circuit 20 to the respective gates. To be driven. Since the PWM signals Sb and Sc have a complementary relationship as described above, for example, when both the PWM signals Sb and Sc have a duty ratio of 50%, a current (motor current) is supplied to the electric motor 5 as described later. Does not flow.

  The transistors constituting the motor drive circuit 22 are not limited to MOSFETs, and may be IGBTs or normal bipolar transistors. Further, in this embodiment, the motor drive circuit 22 has a configuration in which four transistors are connected to a full bridge, but may have a configuration in which two transistors are connected to a half bridge or other configurations. Good. Further, the electric motor 5 may be a normal DC motor, and is not limited to, for example, a brushless type or a brush type.

  The PWM signals Sb and Sc given to the motor drive circuit 22 are shown in FIGS. 3A and 3B for convenience of illustration so that the two pairs of transistors 21A and 21C (or 21B and 21D) are not turned on simultaneously. Although it is not clarified, it is necessary to provide a required dead time. The drive calculation means 16a functions to generate a dead time between the PWM signals Sb and Sc when generating the PWM signals Sb and Sc.

  The lighting drive circuit 23 includes a switching element 23 a composed of a transistor or the like that is turned on / off by a PWM signal. One of the PWM signals Sb and Sc from the PWM signal generation circuit 20 is passed through the opening / closing means 24. The switching element 23a of the lighting drive circuit 23 is switched by the PWM signal Sb. As described above, the PWM signal generation circuit 20 has a steering torque of zero when the steering wheel 1 is steered to the right or when the steering wheel 1 is steered to the left, and when the steering position of the steering wheel 1 is in a neutral position and the vehicle is in a straight traveling state. In this case, since the PWM signals Sb and Sc having the duty ratios corresponding to the respective signals are generated, the PWM signal Sb can be supplied from the PWM signal generation circuit 20 to the lighting drive circuit 23.

  When the duty ratio of the PWM signal Sb may be set to 0% or a value very close to it, the PWM signal Sc may be selected and taken into the lighting drive circuit 23.

  Here, the operation of the motor drive circuit 22 corresponding to the duty ratio of the PWM signals Sb and Sc will be described. When the steering wheel 1 is steered in one direction, for example, in the right direction, the duty ratio of the PWM signal Sb becomes larger than the duty ratio of the PWM signal Sc. In this case, when the PWM signal Sb is on (high level) and the PWM signal Sc is off (low level), the transistors 21A and 21D are on, the transistors 21B and 21C are off, and the motor current is the transistor 21A and the electric motor. 5. Flow through transistor 21D.

  Next, when the PWM signal Sb is off and the PWM signal Sc is on, the transistors 21A and 21D are off and the transistors 21B and 21C are on. However, due to the inductance of the electric motor 5, the motor within the electric motor 5 is turned on. An induced voltage is generated in a direction that prevents a sudden change in current. This induced voltage becomes dominant over the voltage of the in-vehicle battery 7, and the motor current flows through the transistor 21C, the electric motor 5, and the transistor 21B. As a result, a current in the same direction flows in the electric motor 5, and steering assist in the right steering direction is performed.

  When the steering wheel 1 is steered to the left, the duty ratio of the PWM signal Sb becomes smaller than the duty ratio of the PWM signal Sc. In this case, when the PWM signal Sb is off and the PWM signal Sc is on, the transistors 21B and 21C are on, the transistors 21A and 21D are off, and the motor current flows through the transistor 21B, the electric motor 5, and the transistor 21C. Next, when the PWM signal Sb is on and the PWM signal Sc is off, the transistors 21B and 21C are off and the transistors 21A and 21D are on. However, due to the inductance of the electric motor 5, the motor within the electric motor 5 is turned on. An induced voltage is generated in a direction that prevents a sudden change in current. This induced voltage becomes dominant over the voltage of the in-vehicle battery 7, and the motor current flows through the transistor 21D, the electric motor 5, and the transistor 21A. As a result, a current in the same direction flows in the electric motor 5 and steering assist in the left steering direction is performed.

  Next, when the steering wheel 1 is in the neutral position and the vehicle is traveling straight, or when the steering torque is zero, the duty ratios of the PWM signals Sb and Sc are both 50%. However, as a result of the electric motor 5 being generated to the same extent in both directions, no motor current flows in the electric motor 5 and the electric motor 5 stops rotating, so that steering assist is not performed.

  As a result, the lighting drive circuit 23 generates a PWM signal via the opening / closing means 24 regardless of whether the steering wheel 1 is in the right steering, left steering, or neutral position, and the steering torque is zero. The PWM signal Sb is supplied from the circuit 20.

  The opening / closing means 24 is composed of, for example, a mechanical switch such as a relay, or an electronic open / close switch composed of a transistor or the like, and is turned on / off in response to the operation of the lighting operation switch 15. The signal Sb is switched between input and cutoff. The on / off operation of the opening / closing means 24 is controlled by a switching command signal Sd output from the switching command means 16c of the microcomputer 16. When the lighting operation switch 15 is turned on, the switching command means 16c of the microcomputer 16 outputs a switching command signal Sd, and the switching command signal Sd switches the opening / closing means 24 to the on state. Thus, the PWM signal Sb generated by the PWM signal generation circuit 20 is given to the lighting drive circuit 23, and the lighting drive circuit 23 performs a switching operation according to the PWM signal Sb, so that the power supply voltage is applied to the headlight 14. The headlight 14 is turned on.

  In the above embodiment, the required PWM signal Sb is supplied to the lighting drive circuit 23 in response to the operation of the lighting operation switch 15, but the opening / closing means is connected to the power supply circuit of the lighting device such as the headlight 14. The opening / closing means may be turned on / off in response to the operation of the lighting operation switch 15. Instead of the lighting operation switch 15, a sensor for detecting the illuminance outside the vehicle may be provided, and the switching command signal Sd may be output when the illuminance outside the vehicle is equal to or less than a predetermined value. Further, other in-vehicle lighting devices such as fog lamps may be controlled to be turned on in the same manner as the headlight 14 is turned on.

  The present invention is another type of power steering device that drives an electric motor with a PWM signal, for example, a pump is driven by an electric motor driven by a PWM signal, and pressure oil sent from the pump is supplied to a hydraulic actuator. The present invention can also be applied to a hydraulic power steering device that assists steering.

The figure which shows schematically the electric power steering measure which concerns on the best form for implementing this invention, and the vehicle structure relevant to it Control block diagram of electric power steering device Waveform diagram showing the waveform of the PWM signal of the electric power steering device

Explanation of symbols

1 Steering wheel (steering member)
2 Steering shaft 3 Steering mechanism 4 Torque sensor 5 Electric motor 7 Onboard battery 11 ECU (electronic control unit)
14 Headlight (vehicle lighting equipment)
15 lighting operation switch 16 microcomputer 20 PWM signal generating circuit (PWM signal generating means)
22 motor drive circuit 23 lighting drive circuit (lighting drive means)
Sa Duty ratio control signal Sb, Sc PWM signal

Claims (1)

A power steering device that assists steering by driving an electric motor with a PWM signal according to an operation of a steering member,
PWM signal generating means for generating the PWM signal;
Lighting driving means for lighting the in-vehicle lighting device by the PWM signal;
A power steering apparatus comprising:

Images