JP2006008055A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize an electric motor and to reduce outputs by suppressing steering auxiliary torque required in the vicinity of a lock end, etc. to a low value. <P>SOLUTION: This device drives an electric motor 5 according to an operation of a steering member 1 to assist the steering. The device is provided with a means 16 for detecting a steering angle of a wheel 12 for steering and a vehicle height adjusting means (an active suspension 13) for adjusting the height of a vehicle body in relation to each wheel. When a steering angle of the wheel 12 for steering is included in a prescribed range, a control to adjust the vehicle height is performed by driving a part or all of the vehicle height adjusting means 13 by a vehicle height adjustment control means (a microcomputer 14). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that assists a driver's steering force by driving an electric motor in accordance with an operation of a steering member such as a steering wheel.

  In general, an electric power steering apparatus generally includes various sensors (such as a torque sensor for detecting a steering torque applied to a steering member, a vehicle speed sensor for detecting a vehicle speed), an electric motor for assisting steering, and the rotation of the electric motor. A speed reduction mechanism that transmits to the steering shaft and the like, and an electronic control unit (ECU) that controls the drive of the electric motor by calculating a motor current command value to the motor drive circuit based on sensor signals from various sensors, The electric motor is driven and controlled by the control command of the ECU, and steering assist torque is added to the steering mechanism to reduce the driver's steering force (see Patent Document 1).

  By the way, in the electric power steering apparatus as described above, when the steering wheel is turned and the direction of the steering wheel is changed to one, the closer to the lock end (the steering angle limit of the steering wheel), the larger the steering. An auxiliary torque is applied to the steering mechanism. This is because the resistance to steering increases as the steering angle of the steering wheel increases.

  This will be described with reference to FIG. 6. FIG. 6 is an explanatory diagram schematically showing the movement of the steering wheel.

  The steering wheel W of an automobile is normally set with a camber angle α that is open upward. On the other hand, the kingpin shaft P that should be the turning center of the steering wheel W is viewed from the front. The downward-opening kingpin inclination (angle β) is set. The steering wheel W moves from the neutral position shown in the figure to the circumscribed surface of the cone having the kingpin axis P as the central axis in accordance with the steering. As can be seen from the figure, since the center Wo of the steering wheel W turns around the kingpin axis P, the steering wheel W moves to a lower position as it moves away from the neutral position. Actually, since the height of the road surface S with which the steering wheel W contacts does not change, the height of the steering wheel W does not change, and the vehicle body is pushed up via the steering wheel W. For this reason, the resistance to steering increases, for example, because the ground pressure of the steering wheel W increases.

  Further, as the steering wheel W from the neutral position increases, the inclination angle toward the road surface S increases and the amount of falling increases, so the contact area with the road surface S increases. Also increases the resistance to steering.

  Moreover, in the left and right steering wheels W, W, the turning angle of the turning inner wheel is larger than the turning angle of the turning outer wheel, so the turning inner wheel is inclined more than the turning outer wheel, The wheel on the inside of the turn pushes the car higher on the same side. Therefore, of the left and right steering wheels W, W, the resistance to steering caused by the inner wheel is greater than the resistance to steering of the other wheels.

As described above, if the resistance to steering generated near the lock end is large, the required steering assist torque must be set to a large value accordingly. A large reduction gear is required. This increases cost and increases the size of the device. Further, if a high-output electric motor is used, the amount of heat generation increases, and a heat design corresponding to the amount of heat generation becomes necessary, increasing the design burden.
JP-A-6-56045

  It is an object of the present invention to suppress the steering assist torque required near the lock end or the like to a low value and to reduce the size and output of the electric motor.

  An electric power steering apparatus according to the present invention is an electric power steering apparatus that assists steering by driving an electric motor in accordance with an operation of a steering member, and detects a steering angle of a steering wheel, Vehicle height adjusting means for adjusting the height of the vehicle body, and control for adjusting the vehicle height by driving part or all of the vehicle height adjusting means when the steering angle of the steering wheel is within a predetermined range. The vehicle height adjustment control means to perform is provided.

  In the electric power steering apparatus having the above configuration, when the steering angle of the steering wheel is included in a predetermined range, for example, an angle range close to the lock end (the limit of the steering angle), the vehicle height provided on each wheel A part or all of the adjusting means is driven to adjust the height of each part of the vehicle body.

  In the present invention, the vehicle height is adjusted in relation to the steering of the steering wheel as described above. In the conventional case where the vehicle height is not adjusted, the vehicle is adjusted by the steered steering wheel. The part corresponding to the wheel is pushed up, and the resistance to steering of the steering wheel increases. On the other hand, according to the present invention, the height of the vehicle body is adjusted to be low at a position corresponding to the steering wheel, for example, and an increase in the ground pressure of the steering wheel is suppressed, and the steering wheel is steered. The resistance to is suppressed to a low value. Therefore, less steering assist torque is required.

  The vehicle height adjustment may be performed at the front part and the rear part of the vehicle body, but at the front part of the vehicle body where the steering wheel is provided, the vehicle turns according to the steering direction of the steering wheel. The vehicle height adjusting means provided on the inner wheel side is preferably set so as to adjust the vehicle height relatively lower than the vehicle height adjusting means provided on the outer wheel side. . The relative vehicle height adjustment may be performed by adjusting at least one of the left and right vehicle height adjustment means.

  In the left and right steering wheels, the turning angle of the turning inner wheel is larger than the turning angle of the turning outer wheel, so the turning inner wheel pushes up the vehicle body higher than the turning outer wheel. In this way, the portion inside the turning of the vehicle body is low and the portion outside the turning of the vehicle body is high, and the vehicle height is adjusted respectively. This prevents excessive ground pressure from acting only on the steering wheel on the inner side of the turn, and equalizes the resistance to steering applied to the left and right steering wheels, thereby reducing the required steering assist torque. it can.

  According to the present invention, the steering assist torque required near the lock end or the like is suppressed to a low value, and the electric motor can be reduced in size and output, and the amount of generated heat is reduced with the reduction in the size of the electric motor. And the burden of thermal design is reduced.

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

  Referring to FIG. 1, the electric power steering apparatus according to the present embodiment includes a steering shaft 2 having one end fixed to a steering member 1 such as a steering wheel (handle), and a driver's steering torque applied to the steering shaft 2. Steering assistance for reducing the driver's load due to the operation (steering operation) of the steering member 1 and the torque mechanism 3 to be detected, the steering mechanism 4 composed of a rack and pinion mechanism or the like connected to the other end of the steering shaft 2 An electric motor 5 that generates torque, a speed reduction mechanism 6 that transmits the steering assist torque generated by the electric motor 5 to the steering shaft 2 after being decelerated by a gear that meshes with each other, and power supply from an in-vehicle battery 7 via an ignition switch 8 And an electric power steering electronic control unit (EPS ECU) 10 for controlling the drive of the electric motor 5.

  The steering shaft 2 is divided into at least a portion on the steering member 1 side and a portion on the steering mechanism 4 side, and both portions are connected by a torsion bar 9. Is arranged. A steering wheel 12 is connected to the output side of the steering mechanism 4 via a connecting member 11 including a tie rod and a knuckle arm.

  In the present embodiment, each wheel is provided with an active suspension as a vehicle height adjusting means. Of these, FIG. 1 shows active suspensions 13fa and 13fb provided on the steering wheels 12 and 12 side. ing.

  The EPS ECU 10 includes a microcomputer 14 that controls the center of electric power steering control and a CAN (controller area network) controller 101 inside. The EPS ECU 10 is connected to the CAN bus 15 via the CAN controller 101, and constitutes an in-vehicle CAN communication system together with the other ECUs 20, 30, 40, 50 connected to the CAN bus 15.

  The CAN controller 101 has functions of data reception processing, response data creation processing, and data transmission processing, and CAN communication with CAN controllers 201, 301, 401, and 501 included in other ECUs 20, 30, 40, and 50. And the sensor signal of the sensor contained in the said other ECU20-50 can be received, or the sensor signal of the sensor contained in the own ECU10 can be transmitted to other ECU20-50. The CAN bus 15 includes two communication lines and can perform differential serial communication.

  In general, the CAN communication system is known as a network system for connecting a plurality of devices such as in-vehicle devices and home appliances, and has a maximum transmission rate of 1 Мbps, compared with a communication method used conventionally. It has the feature of being very fast. Moreover, since it is serial communication which replaces a digital signal with the differential voltage between two wires, it also has the feature of being excellent in noise resistance.

  In this CAN communication system, each ECU 10 to 50 as a node can communicate data such as sensor signals on the CAN bus 15 as a packet as long as the CAN bus 15 is free. When the CAN bus 15 is occupied by packets from other ECUs 10 to 50, the packets to be sent stand by at the CAN controllers 101, 201, 301, 401, and 501 provided in the ECUs 10 to 50. Further, the plurality of ECUs 10 to 50 can simultaneously receive packets on the CAN bus 15.

  In the present embodiment, as other ECUs that constitute an in-vehicle CAN communication system together with the EPS ECU 10, a VSC (registered trademark) ECU 20 that stabilizes the turning behavior of the vehicle, and the acceleration and straightness of the vehicle. There are a TRC (registered trademark) ECU 30 for ensuring turning stability, an ABS (anti-lock brake system) ECU 40 for preventing wheel locking, a suspension control ECU 50, and the like. Among these, the VSC ECU 20 has a steering angle sensor 16 as a detecting means for detecting the steering angle of the steering wheel 12, and the ABS ECU 40 has a vehicle speed sensor 17 for detecting the rotational speed of each wheel. Each included. The active suspension (generally referred to as 13) of each wheel including the above-described active suspensions 13fa, 13fb for the steering wheel 12 is controlled by the suspension control ECU 50.

  In a vehicle equipped with the electric power steering device, normally, when the driver operates the steering member 1, the steering torque by the operation is detected by the torque sensor 3. The EPS ECU 10 drives and controls the electric motor 5 based on the information on the steering torque detected by the torque sensor 3 and the vehicle speed information of the vehicle speed sensor 17 captured by CAN communication. As a result, the electric motor 5 generates steering assist torque, and this steering assist torque is applied to the steering shaft 2 via the speed reduction mechanism 6, thereby reducing the burden on the driver who performs the steering operation.

  By the way, in a general electric power steering apparatus, when the steering member 1 is operated to change the direction of the steering wheel 12 to one of the steering wheels 12, the steering wheel 12 has its geometry (geometric arrangement). ), The closer to the lock end (the limit of the steering angle), the greater the resistance to steering, which requires a large steering assist torque. However, in the present invention, near the lock end of the steering wheel 12. The increase in resistance to steering is suppressed, and the required steering assist torque can be suppressed to a low value.

  The configuration and function for this purpose will be described with reference to FIGS. 2 is a block circuit diagram showing the internal configuration of the EPS ECU 10 together with the configuration of related parts, FIG. 3 is a functional block diagram showing the function of the microcomputer 14 of the EPS ECU 10, and FIG. 4 is a vehicle height adjusting means. FIG. 2 is a cross-sectional view of the active suspension shown in FIG.

  Referring to FIG. 2, in addition to the microcomputer 14 and the CAN controller 101, the EPS ECU 10 responds to an input interface 18 for processing the sensor signal of the torque sensor 3 and a control signal from the microcomputer 14. A motor drive circuit 19 for driving the electric motor 5 and a power supply circuit 21 for supplying power to a circuit other than the motor drive circuit 19, for example, the microcomputer 14 or the like.

  Around the motor drive circuit 19, a fail-safe relay 22 for turning on and off the current to the motor drive circuit 19 and a relay drive circuit 23 for the fail-safe relay 22 are provided.

  The microcomputer 14 includes a CPU 141, a program memory 142, a map memory 143, and a buffer memory 144, and outputs a control signal Sa indicating the driving amount of the electric motor 5 as well as an active for vehicle height adjustment. A vehicle height adjustment signal Sb indicating the extension / contraction drive amount of the suspension 13 is output. The vehicle height adjustment signal Sb is given to the suspension control ECU 50 via the CAN controller 101. The suspension control ECU 50 controls the expansion / contraction operation of the active suspension 13 (13fa, 13fb, 13ra, 13rb) of each wheel in response to the vehicle height adjustment signal Sb.

  The function of the CPU 141 of the microcomputer 14 and the contents stored in the map memory 143 will be described with reference to FIG. 3. In the present embodiment, the CPU 141 includes information on the steering torque from the torque sensor 3 and the vehicle speed sensor. In addition to functioning as control means 141a for determining the drive amount of the electric motor 5 based on the vehicle speed information from the vehicle 17, the vehicle height is adjusted by driving part or all of the active suspension 13 in connection with the steering operation. It also functions as the high adjustment control means 141b.

  The program memory 142 stores a basic program for executing the operation of the CPU 141 and a program necessary for executing drive control of the electric motor 5 of this embodiment. The buffer memory 144 is used for temporary storage of data when the CPU 141 performs work.

  The map memory 143 stores a control map 143a necessary for execution of drive control of the electric motor 5 of this embodiment and a vehicle height adjustment map 143b necessary for vehicle height adjustment control by the active suspension 13 performed in association with the steering operation. is doing.

  The control map 143a shows the relationship between the steering torque applied to the steering shaft 2 and the driving amount of the electric motor 5, and uses the vehicle speed (km / h) as a parameter for each vehicle speed (for example, 0 km / h, 10 km / h). h, 60 km / h, 100 km / h, 180 km / h, etc.), the driving amount of the electric motor 5 with respect to the steering torque can be determined.

  The vehicle height adjustment map 143b shows the relationship between the steering angle of the steering wheel 12 and the expansion / contraction drive amount of the active suspension 13, and the steering angle of the steering wheel 12 for each vehicle speed using the vehicle speed as a parameter. The expansion / contraction drive amount of the active suspension 13 can be determined. The vehicle height adjustment signal Sb indicating the extension / contraction drive amount is sent from the vehicle height adjustment control means 141b of the CPU 141 to the suspension control ECU 50 via the CAN controller 101 of the EPS ECU 10, and is also given to the subtraction means 141c. In the subtracting means 141c, it is subtracted from the driving amount determined with reference to the control map 143a by the control means 141a. Therefore, when the vehicle height is adjusted by the active suspension 13 in relation to the steering operation, the drive amount of the electric motor 5 is reduced according to the vehicle height adjustment.

  With reference to FIG. 4, the structure of the active suspension 13 which is a vehicle height adjustment means is demonstrated. The active suspension 13 of the present embodiment is hydraulic and includes a power cylinder 131 and a coil spring 134 provided around a piston rod 132 of the power cylinder 131. Pressure oil is supplied to a hydraulic chamber 135 formed between the power cylinder 131 and the piston 133 through a pressure oil hole 131a of the power cylinder 131 and a switching valve 25fa driven by a solenoid 24fa. A hydraulic pressure supply circuit 28 including an oil pump 26 and a reservoir 27 is connected to the switching valve 25fa.

  FIG. 4 shows a cross-sectional structure of one active suspension 13fa among the four active suspensions 13 (13fa, 13fb, 13ra, 13rb) provided on each wheel. The same applies to the suspensions 13fb, 13ra, and 13rb. The other active suspensions 13fb, 13ra, and 13rb are also connected to pipelines having switching valves 25fb, 25ra, and 25rb for driving solenoids 24fb, 24ra, and 24rb, and are connected to the switching valves 25fb, 25ra, and 25rb of the respective pipelines. Is connected to the hydraulic pressure supply circuit 28 described above. Each of the active suspensions 13 (13fa, 13fb, 13ra, 13rb) is a solenoid 24fa, 24fb, 24ra, 24rb (generally referred to as 24) of a switching valve 25fa, 25fb, 25ra, 25rb (generally referred to as 25) attached thereto. By being driven by the control of the control ECU 50, it expands and contracts individually.

  The oil pump 26 for supplying pressure oil to the active suspension 13 may be driven by an engine, or may be driven by an electric motor different from the steering assisting electric motor 5, The power of the steering assisting electric motor 5 can be used, and the drive source is not particularly limited. Instead of the hydraulic active suspension 13 of the present embodiment, an active suspension that is extended and contracted by air or other gas can be used.

  Next, the operation when the microcomputer 32 of the EPS ECU 10 performs vehicle height adjustment in relation to the steering operation will be described with reference to the flowchart of FIG.

  The routines from step S1 to step S3 are routines for determining the drive amount of the electric motor 5 for assisting steering. In step S1, the CPU 141 fetches the steering torque information from the torque sensor 3, and in the next step S2, fetches the vehicle speed information obtained from the vehicle speed sensor 17, and in step S3, the steering torque information and the vehicle speed information are obtained. The drive amount of the electric motor 5 is determined with reference to the control map 143a of the map memory 143.

  Steps subsequent to step S4 are steps mainly related to vehicle height adjustment. In step S4, information on the steering angle of the steering wheel 12 is acquired from the steering angle sensor 16. In the next step S5, it is determined whether or not the steering angle of the steering wheel 12 falls within a predetermined range, specifically, a predetermined angle range close to the lock end.

  When the steering angle of the steering wheel 12 is not included in the predetermined range (NO in S5), the steering wheel 12 is not greatly cut to either one, and the corresponding part of the vehicle body is pushed up. Since the amount is small, there is no need to adjust the vehicle height. Therefore, in this case, the process proceeds from step S5 to step S6. In step S6, the control signal Sa corresponding to the drive amount of the electric motor 5 already determined in step S3 is output to the motor drive circuit 19, thereby The motor 5 is driven to perform necessary steering assistance.

  When the steering angle of the steering wheel 12 is included in the predetermined range (YES in S5), the steering wheel 12 is approaching the lock end and the amount of pushing up the corresponding part of the vehicle body is also increased. . Therefore, in this case, the process proceeds from step S5 to step S7, and in step S7, other necessary information such as vehicle speed information from the vehicle speed sensor 17 is captured.

  In the next step S8, by referring to the vehicle height adjustment map 143b of the map memory 143 based on the information on the steering angle of the steering wheel 12 and other information such as the vehicle speed, the expansion / contraction drive amount of each active suspension 13 is determined. The vehicle height adjustment signal Sb indicating the amount of expansion / contraction drive is output. The vehicle height adjustment signal Sb is given to the suspension control ECU 50 via the CAN controller 101. In response to the vehicle height adjustment signal Sb, the suspension control ECU 50 drives the solenoid 24 of the switching valve 25 attached to each active suspension 13 to drive each active suspension 13 to extend and contract by a required amount.

  Specifically, for example, when the steering wheel 12 is greatly cut to the left, the turning angle of the left wheel that is inside the turning is larger than the turning angle of the right wheel, and the left wheel is Therefore, the active suspension 13fa provided on the left steering wheel 12 is correspondingly shortened and the right active suspension 13fb is shortened to a small width. . As a result, the left side portion inside the turning of the vehicle body is adjusted to be lower than the portion outside the turning, so that an excessive ground pressure does not act only on the steering wheel 12 inside the turning.

  In step S9 following step S8, the drive amount of the electric motor 5 considering the vehicle height adjustment is calculated by subtracting the amount corresponding to the vehicle height adjustment signal Sb from the drive amount of the electric motor 5 already determined in step S3. Then, a control signal corresponding to the drive amount is output to the motor drive circuit 19, thereby driving the electric motor 5 and performing necessary steering assistance. This is a process corresponding to a decrease in the required steering assist torque due to the vehicle height adjustment.

The block diagram which shows the electric power steering device which concerns on the best form of this invention with the vehicle structure relevant to it 1 is a block circuit diagram showing the internal configuration of the EPS ECU 10 of the apparatus of FIG. 1 together with the configuration of related parts. 2 is a functional block diagram showing functions of the microcomputer of the EPS ECU 10 shown in FIG. FIG. 2 is a cross-sectional view of the active suspension of the apparatus of FIG. The flowchart which shows the operation | movement of the microcomputer of ECU10 for EPS of FIG. Explanatory drawing schematically showing the movement of the steering wheel

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering member 2 Steering shaft 3 Torque sensor 5 Electric motor 10 ECU for EPS
101 CAN controller 12 Steering wheel 13 (13fa, 13fb, 13ra, 13rb)
Active suspension (vehicle height adjustment means)
14 Microcomputer (Vehicle height adjustment control means)
16 Steering angle sensor (steering angle detection means)
17 Vehicle speed sensor

Claims (1)

An electric power steering device that assists steering by driving an electric motor according to an operation of a steering member,
Means for detecting the steering angle of the steering wheel;
Vehicle height adjusting means for adjusting the height of the vehicle body for each wheel;
Vehicle height adjustment control means for controlling the vehicle height by driving part or all of the vehicle height adjustment means when the steering angle of the steering wheel is included in a predetermined range;
An electric power steering apparatus comprising:

Images