JP2005067296A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for reducing impact at a stroke end while consistently keeping steering performance good independently of the condition of a steering angle. <P>SOLUTION: The rack and pinion type electric power steering device comprises a motor rotating speed detecting means 43, a rack position detecting means 42, a storage means 45 for storing a preset relationship between a motor rotating speed near the stroke end of a rack and a motor damping control starting rack position farther from the stroke end depending on the motor rotating speed, a collating means 44 for collating and determining whether a combination of the motor rotating speed and the rack position corresponds to the relationship between the motor rotating speed stored by the storage mean 45 and the motor damping control starting rack position, and motor damping control means 41, 44 for controlling the damping of the motor 20 in accordance with a preset motor assist reducing rate when the collating means 44 determines the correspondence. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rack and pinion type electric power steering apparatus.

  The rack and pinion type electric power steering device that assists the steering by transmitting the driving force of the motor to the steering wheel through the rack that moves to the left and right from the pinion shaft penetrates the gear box that houses the rack and pinion mechanism. The rack to be stopped stops at the stroke end when the rack stopper comes into contact with the gear box.

  If the steering notch is strong, the stopper part of the rack will strike the gear box at the stroke end, and the large impact load will cause an unpleasant noise and damage the gear box, and an excessive current will flow in the motor drive current. A malfunction occurs.

Thus, an example in which the motor drive current is gradually reduced when the rack reaches the vicinity of the stroke end has been proposed (see Patent Document 1).
Japanese Utility Model Publication No. 8-8943

  In this embodiment, the rack end proximity sensor 10 is provided in the embodiment, and when detecting when the rack moves near the stroke end, the time constant circuit 28 is activated, and the current reduction control circuit 29 gradually increases the motor drive current. And then controlled so as to be kept at a relatively low level current value.

  When the rack moves near the stroke end, the motor drive current is always attenuated at a constant damping rate set by the time constant circuit 28 regardless of the rack moving speed, so the steering is strong and the rack moving speed is fast. If the damping rate is set so that there is no hindrance, the motor drive current is attenuated at the same damping rate near the stroke end even when the steering notch is weak and the rack moving speed is slow. Therefore, the time that must be steered while the steering is heavy becomes long, and the steering performance is not good.

  The present invention has been made in view of such points, and an object thereof is an electric power steering capable of alleviating an impact at a stroke end while always maintaining good steering performance regardless of the state of turning of the steering. The point is to provide the device.

  In order to achieve the above object, the present invention provides a rack and pinion type electric power steering device that assists steering by transmitting a driving force of a motor to a steering wheel via a rack that moves left and right from a pinion shaft. Motor rotation speed detection means for detecting the rotation speed of the motor, rack position detection means for detecting the position of the rack, and the motor rotation speed near the stroke end of the rack and the distance from the stroke end according to the motor rotation speed The combination of the storage means for storing the preset relationship with the motor attenuation control start rack position at which the distance is increased, the motor rotational speed detected by the motor rotational speed detection means and the rack position detected by the rack position detection means is It matches with the relationship between the motor rotation speed stored in the storage means and the motor damping control start rack position. And collating means for judging whether or not, and said checking means electric power steering system including a motor damping control means for damping controlling the motor based on a predetermined motor assist reduction rate when it is determined that match.

  Motor attenuation in which the combination of the motor rotation speed detected in the vicinity of the rack stroke end and the rack position by the collation means collates with the motor rotation speed set and stored in advance, and the distance from the stroke end increases according to the motor rotation speed. When it is determined that the relation with the control start rack position is coincident, the motor is attenuated based on a predetermined motor assist reduction rate. Regardless of, it is possible to alleviate the impact at the stroke end while always maintaining good steering performance.

An embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 shows a schematic rear view of the electric power steering apparatus 1 according to the present embodiment.

  In the electric power steering apparatus 1, a rack shaft 3 is accommodated in a substantially cylindrical rack housing 2 oriented in the left-right direction of the vehicle (corresponding to the left-right direction in FIG. 1) so as to be slidable in the left-right axis direction.

  The tie rods 4 and 4 are connected to both ends of the rack shaft 3 projecting from the openings at both ends of the rack housing 2 via joints, respectively, and the tie rods 4 and 4 are moved by the movement of the rack shaft 3, and further via the steering mechanism. The steered wheels of the vehicle are steered.

A steering gear box 10 is provided at the right end of the rack housing 2.
In the steering gear box 10, an input shaft 11 connected via a joint to a steering shaft to which a steering wheel (not shown) is integrally attached is rotatably supported via a bearing. 11 is connected to the steering pinion shaft 13 via the torsion bar 12 in the steering gear box 10 so as to be capable of relative twisting.

The helical teeth 13 a of the steering pinion shaft 13 are engaged with the rack teeth 3 a of the rack shaft 3.
Therefore, the steering force transmitted to the input shaft 11 by the turning operation of the steering wheel rotates the steering pinion shaft 13 via the torsion bar 12, and meshes with the helical teeth 13a of the steering pinion shaft 13 and the rack teeth 3a. The rack shaft 3 is slid in the left-right axis direction.

The rack shaft 3 is pressed from behind by a rack guide 15 biased by a rack guide spring 14.
A rotary encoder 35 for detecting the moving position of the rack shaft 3 that slides in the left-right axis direction is provided at a substantially central position of the rack housing 2.

  A motor 20 is attached to the upper portion of the steering gear box 10, and a worm reduction mechanism 25 that decelerates the driving force of the motor 20 and transmits it to the steering pinion shaft 13 is configured in the steering gear box 10.

  The worm speed reduction mechanism 25 is configured by a worm wheel 26 fitted on the upper portion of the steering pinion shaft 13 and a worm 27 connected coaxially to the drive shaft of the motor 20.

  The driving force of the motor 20 is applied to the steering pinion shaft 13 via the worm reduction mechanism 25 to assist the steering.

A torque sensor 30 is provided further above the worm reduction mechanism 25.
Reflective disks 31 and 32 are fixed to the input shaft 11 side and the steering pinion shaft 13 side with the torsion bar 12 interposed therebetween, and the barcode patterns 31a and 32a provided on the reflective disks 31 and 32 can be read. A torque sensor 30 is configured by mounting a possible optical module 33.

  In the torque sensor 30, the optical module 33 reads the barcode patterns 31a and 32a of the reflecting disks 31 and 32, and detects the steering torque t from the angle difference.

  The torque sensor 30 can detect the rotational position of the steering pinion shaft 13 with respect to the fixed member by reading the barcode pattern 32a of the reflection disk 32 on the one steering pinion shaft 13 side, and the steering pinion shaft rotational position. It also serves as a detection means.

The motor 20 for assisting steering is driven and controlled by a computer, and a schematic block diagram of the control system is shown in FIG.
The CPU 40 of the computer has functions of a motor drive control means 41, a rack position detection means 42, a motor rotation speed detection means 43, a collation means 44, etc., and the torque sensor 30, rotary encoder 35, motor ammeter 22, motor voltage Detection signals from the total 23 are input, a control signal is output from the motor drive control means 41 to the motor driver 21, and the motor 20 is driven by the motor driver 21.

  The motor drive control means 41 performs PWM control for controlling the drive of the motor by changing the ratio (time ratio) r = Ton / T of the time Ton in which current flows at a constant period T, and the motor is increased as the time ratio r increases. Assist amount increases.

The motor ammeter 22 measures the current supplied to the motor 20, the motor voltmeter 23 measures the voltage between the terminals of the motor 20, and the measured current value i and the measured voltage value v are the motor rotation of the CPU 40. Input to the speed detection means 43.
Other information stored in the memory 45 is input to the verification means 44.

The motor rotation speed detecting means 43 calculates a voltage applied to the motor 20 from the measured current value i and the motor resistance value, and subtracts this voltage from the measured voltage between the motor terminals v to obtain an induced voltage. The motor rotation speed n is estimated from the voltage value and the induced voltage constant.
In order to obtain the motor rotation speed n, the rotation of the rotation drive shaft of the motor may be detected directly using a rotary encoder.

  The rack position detection means 42 counts the detection signal of the rotary encoder 35 and detects the rack movement amount p from the neutral position of the rack shaft 3 that moves left and right as the rack position. The rack position) p is output to the collating means 44.

  The memory 45 stores a normal time ratio (motor assist amount) ro based on the steering torque t and the vehicle speed, and starts control to reduce the motor assist amount when the rack shaft 3 approaches the stroke end. The optimum rack movement amount (rack position) p is stored in relation to the motor rotation speed n.

The relationship between the optimum motor rotation speed n for starting the control to decrease the motor assist amount and the rack movement amount (rack position) p is shown as a decrease control start curve in the rectangular coordinates of FIG.
The decrease control start curve is near the stroke end, and the rack movement amount p is farther from the stroke end as the motor rotational speed n is larger.

  The collating means 44 collates the combination of the rack movement amount p detected by the rack position detecting means 42 and the motor rotational speed n calculated by the motor rotational speed detecting means 43 with a decrease control start curve stored in the memory 45. Is a means for determining whether or not they coincide with each other, that is, the control start time.

  The motor drive control means 41 inputs the steering torque t detected by the torque sensor 30 and the discrimination result of the collating means 44 to determine the time ratio r, and sends a control signal for controlling the motor 20 with the time ratio r to the motor driver. Output to 21.

The motor control procedure by the control system of the CPU 40 as described above will be described with reference to the flowchart of FIG.
First, the steering torque t detected by the torque sensor 30, the rack movement amount p detected by the rack position detecting means 42, the motor current i detected by the motor ammeter 22, and the motor voltage v detected by the motor voltmeter 23 are read (step S1). 1).

Then, the normal time ratio ro is searched and extracted from the steering torque t and the vehicle speed (step 2).
Next, the motor rotation speed detecting means 43 calculates the motor rotation speed n from the motor current i and the motor voltage v (step 3).

  In the next step 4, the matching means 44 collates the combination of the detected rack movement amount p and the calculated motor rotation speed n (point coordinates (n, p)) with the decreasing control start curve stored in the memory 45, and this curve. Is determined (see FIG. 4).

  When the point coordinate (n, p) of the combination of the detected rack movement amount p and the calculated motor rotation speed n does not reach the decrease control start curve, the process proceeds to step 5 and the time ratio r is set to the normal time ratio ro and the process proceeds to step 7. The motor 20 is driven at this normal time ratio r.

  When the point coordinate (n, p) reaches the decrease control start curve in step 4, the routine proceeds to step 6 where ro is obtained by applying a predetermined motor assist decrease rate As (%) to the normal time ratio ro as the time ratio r. (1−As / 100) is used, the process proceeds to step 7 and the motor 20 is driven to attenuate at the reduced time ratio r (= ro · (1−As / 100)).

  Therefore, in the vicinity of the stroke end, as the motor rotational speed n increases, the rack movement amount p becomes farther from the stroke end, that is, when the rack shaft 3 approaches the stroke end, the motor 20 is controlled to be attenuated earlier. The impact at the stroke end can be alleviated while maintaining good steering performance regardless of the state of cutting.

  In the present embodiment, the PWM control is performed for driving the motor. However, the present invention can be applied by the attenuation control of the power supplied to the motor even when the drive control other than the PWM control is performed.

  The present invention can be applied to all vehicle power steering devices.

1 is a schematic overall rear view of an electric power steering apparatus according to an embodiment of the present invention. It is sectional drawing in a gear box. It is a schematic block diagram of a motor control system. It is a figure which shows the relationship between the optimal motor rotational speed n which starts the control which reduces the motor assist amount memorize | stored in memory, and the rack movement amount (rack position) p. It is a flowchart which shows the procedure of motor control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Rack housing, 3 ... Rack shaft, 4 ... Tie rod,
10 ... steering gear box, 11 ... input shaft, 12 ... torsion bar, 13 ... steering pinion shaft, 14 ... rack guide spring, 15 ... rack guide,
20 ... motor, 21 ... motor driver, 22 ... motor ammeter, 23 ... motor voltmeter,
25 ... Worm deceleration mechanism, 26 ... Worm wheel, 27 ... Worm,
30 ... Torque sensor, 31, 32 ... Reflective disk, 33 ... Optical module, 35 ... Rotary encoder,
40 ... CPU, 41 ... motor drive control means, 42 ... rack position detection means, 43 ... motor rotation speed detection means, 44 ... collation means, 45 ... memory.

Claims (1)

In a rack and pinion type electric power steering device that assists steering by transmitting a driving force of a motor to a steering wheel via a rack that moves left and right from a pinion shaft,
Motor rotation speed detection means for detecting the rotation speed of the motor;
Rack position detecting means for detecting the position of the rack;
Storage means for storing a preset relationship between a motor rotation speed in the vicinity of the stroke end of the rack and a motor attenuation control start rack position whose distance from the stroke end is increased according to the motor rotation speed;
The combination of the motor rotation speed detected by the motor rotation speed detection means and the rack position detected by the rack position detection means is collated with the relationship between the motor rotation speed stored in the storage means and the motor attenuation control start rack position. Collation means for determining whether or not they match,
An electric power steering apparatus comprising: motor attenuation control means for performing attenuation control of the motor based on a predetermined motor assist reduction rate when it is determined that the collating means coincides.

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