JP2005145265A - Electric power steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering apparatus which carries out the steering assist even when the car speed detected by a car speed sensor is lower than a specified value. <P>SOLUTION: The electric power steering apparatus comprises an electric current limiting value setting means for setting the electric current limiting value output from an electric motor based on an ignition signal and an engine rotation signal, and an electric current limiting means for limiting the electric current based on the electric current limiting value and an indicated electric current. The electric current limiting means sets the electric current limiting value of the electric motor to a first specified value when the ignition current and the engine rotation signal are detected, and to a second specified value lower than the first specified value when the ignition current is detected but the engine rotation signal is not detected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus, in particular, an electric power steering apparatus that reduces the steering force of a driver by applying the power of an electric motor to a steering mechanism.

As a conventional electric power steering apparatus, a technique described in Patent Document 1 is disclosed. In this publication, even when the driving of the engine is not detected, the electric power steering device continuously drives the motor to perform steering assist when the vehicle speed detected by the vehicle speed sensor is equal to or higher than a predetermined value.
Japanese Patent Application Laid-Open No. 11-59458.

  For example, in the case of starting from a garage while largely turning the rudder, the vehicle speed is close to 0 and the vehicle speed detected by the vehicle speed sensor is equal to or less than a predetermined value, so steering assist is not performed and the driver's steering load increases. There is a problem.

  The present invention has been made paying attention to the above problems, and provides an electric power steering device capable of performing steering assist even in a case where the vehicle speed detected by the vehicle speed sensor is equal to or less than a predetermined value. For the purpose.

  In order to achieve the above object, according to the present invention, in the electric power steering apparatus, a current limit value setting means for setting a current limit value output from the motor from the ignition signal and the engine rotation signal, and a current from the current limit value and the indicated current. Current limiting means for limiting, and when the ignition signal is detected and the engine rotation signal is detected, the current limiting means sets the current limit value of the motor to a first predetermined value and detects the ignition signal When the engine rotation signal is not detected, the current limit value of the electric motor is set to a second predetermined value lower than the first predetermined value.

  Therefore, steering assist can be performed even when the vehicle speed detected by the vehicle speed sensor is equal to or less than a predetermined value, for example, when the vehicle is started from a garage with a large rudder.

  Hereinafter, the best mode for realizing the electric power steering apparatus of the present invention will be described based on Example 1 shown in the drawings.

  First, in describing the electric power steering apparatus of the present embodiment, the overall configuration of the electric power steering apparatus will be described.

FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to the present embodiment.
First, the configuration will be described. The steering wheel 1 is provided with a universal joint 3, an intermediate shaft 4, and a universal joint 5 via a column shaft 2. In the universal joint 5, the tie rod 11 is operated by a steering mechanism including a pinion shaft 9 and a rack shaft 10 connected to the input shaft 6, and the steering direction of the steered wheels 18 is determined.

  The input shaft 6 is provided with a torque sensor 7 that detects the steering torque of the driver and a speed reducer 8 that applies a steering assist force. The speed reducer 8 is driven by the electric motor 12 to assist the driver's steering force.

  The control unit 13 inputs a vehicle speed signal from the vehicle speed sensor 14, an engine rotation signal from the engine rotation sensor 17, and a torque signal from the torque sensor 7, and supplies current to the motor 12 using the battery 17 as a power source. When the driver operates the steering wheel 1, the rotation direction of the electric motor 12 is switched according to the operation direction, and assists the driver's steering force.

FIG. 2 is a block diagram showing the configuration inside the control unit 13 in the present embodiment.
The assist torque calculation means 201 calculates a basic assist torque (or assist current) that is a base of the motor drive current from a vehicle or the like from the vehicle speed signal obtained from the vehicle speed sensor 14 and the torque sensor signal obtained from the torque sensor 7. .

The command current calculation unit 202 calculates a command current I ^* for driving the motor from the basic assist torque obtained by the assist torque calculation unit 201.

  The current limit value setting means 203 sets a current limit value to be output to the current limit means 204 based on the engine speed obtained from the engine speed sensor 15 and the ignition ON / OFF information obtained from the ignition switch 16.

The current limiting unit 204 limits the command current I ^* calculated by the command current calculation unit 202 in order to protect the motor or the drive circuit.

The current feedback control means 205 calculates a deviation ε of the motor current I with respect to the command current I ^*, and calculates a PWM duty for driving the power element by PI control or PID control.

  The power element driving means 206 is a drive for turning on and off the power elements (FETs) 207a, 207b, 207c, and 207d constituting the H bridge of the motor driving means 207 according to the PWM duty calculated by the current feedback control means 205. Output a signal.

In the motor driving means (H bridge circuit) 207, when the battery voltage 17 is turned to the right, for example, by turning ON / OFF the power elements (FETs) 207a, 207b, 207c, 207d, the power element 207c, the electric motor 12, and the power element 207b. , GND and apply current corresponding to the indicated current I ^* .

  The current sensor circuit includes a shunt resistor 208 and motor current detection means 209, detects the current value supplied from the battery 17 to the drive circuit 207, and outputs it to the current feedback control means 205.

(Current limit value setting when there is no self-holding circuit)
FIG. 3 is a flowchart showing the contents of the current limit value setting process when the control unit 13 does not have a self-holding circuit. Note that the operation start of the control unit is simultaneously with the ignition switch ON, so it is assumed that the ignition switch ON / OFF determination has already been performed.

  In step 301, an engine ON / OFF determination process is performed, and the process proceeds to step 302. Details of the engine ON / OFF determination process will be described later with reference to FIG.

  In step 302, a current limit value setting process is performed. The details of the current limit value setting process will be described later with reference to FIG.

(Engine ON / OFF judgment processing)
FIG. 4 is a flowchart showing the contents of the engine ON / OFF determination process.

  In step 401, it is determined whether or not the engine state flag FENG = 0. When FENG = 0, the process proceeds to step 402, and when FENG = 1, the process proceeds to step 407.

[Judgment of engine OFF → ON]
In step 402, the engine speed _Reng is compared with a predetermined speed. When R _{eng ≥predetermined} number of revolutions, the process proceeds to step 403, and when R _eng <predetermined number of revolutions, the process proceeds to step 404 and R _count = 0 and the process is terminated.

In step 403, R _count is incremented (added by 1), and the process proceeds to step 405.

In step 405, R _count is compared with a predetermined value. When R _count ≧ predetermined value, the process proceeds to step 406, and when R _count <predetermined value, the process is terminated.

  In step 406, the engine state flag FENG = 1 is set and it is determined that the engine is ON.

[Judgment of engine ON → OFF]
In step 407, the engine speed _Reng is compared with a predetermined speed. When R _eng <predetermined number of revolutions, the process proceeds to step 408, and when R _eng ≧ predetermined number of revolutions, the process proceeds to step 409 and R _count = 0 and the process is terminated.

In step 408, R _count is incremented (added by 1), and the process proceeds to step 410.

In step 410, R _count is compared with a predetermined value. When R _count ≧ predetermined value, the process proceeds to step 411, and when R _count <predetermined value, the process is terminated.

  In step 411, the engine state flag FENG = 0 is set and it is determined that the engine is OFF.

(Current limit value setting process)
FIG. 5 is a flowchart showing the contents of the current limit value setting process in the first embodiment.

  In step 501, it is determined whether or not the engine state flag FENG = 1. When FENG = 1, the process proceeds to step 502. When FENG = 0, the process proceeds to step 506.

[Increase current limit value when the engine is on]
In step 502, the current limit value A _limit is compared with a predetermined value 1 (corresponding to a first predetermined value in the claims). When A _limit <predetermined value 1, the process proceeds to step 503, and when A _limit ≧ predetermined value 1, the process is terminated.

  In step 503, the current limit increment Δb is added to the current current limit value, and the process proceeds to step 504.

In step 504, the current limit value A _limit is compared with the predetermined value 1. When A _limit ≧ predetermined value 1, the process proceeds to step 505. When A _limit <predetermined value 1, the process is terminated.

In step 505, the limiter process of the predetermined value 1, that is, the current limit value A _limit is set to the predetermined value 1, and the process ends.

[Increase processing of current limit value when engine is OFF]
In step 506, the current limit value A _limit is compared with a predetermined value 2 (corresponding to a second predetermined value in the claims). When A _limit <predetermined value 2, the process proceeds to step 507. When A _limit ≥predetermined value 2, the process ends.

  In step 507, the current limit increment Δa is added to the current current limit value, and the process proceeds to step 508.

In step 508, the current limit value A _limit is compared with the predetermined value 2. When A _limit ≧ predetermined value 2, the process proceeds to step 509, and when A _limit <predetermined value 2, the process is terminated.

In step 509, the limiter process of the predetermined value 2, that is, the current limit value A _limit is set to the predetermined value 2, and the process ends.

FIG. 6 is a time chart showing the contents of the current limit value setting process in the first embodiment.
At time t1, the control unit 13 starts operating simultaneously with turning on the ignition switch, and the ignition state flag FIGN = 1 is set. At this time, the engine is OFF. The current limit value A _limit is because not reached the predetermined value 2, the value obtained by adding the current limiting increment Δa to the current limit value A _limit as the current limit value A _limit.

Since the current limit value A _limit reaches the predetermined value 2 at time t2, the limiter process of the predetermined value 2, that is, the current limit value A _limit is set to the predetermined value 2. At this time, since the engine is not turned on, no further increase is made.

Since the engine is turned on at time t3, the engine state flag FENG = 1 is set. The current limit value A _limit and the predetermined value 1 are compared. Since A _limit has not reached the predetermined value 1, the current limit increment Δb is added to the current limit value A _limit .

Since the current limit value A _limit reaches the predetermined value 1 at time t4, the limiter process of the predetermined value 1, that is, the current limit value A _limit is set to the predetermined value 1.

At time t5, the ignition switch is turned off, so the ignition state flag FIGN = 0 is set. Since the engine is also turned off, the engine state flag FENG = 0 is set. At this time, the current limit value A _limit also instantaneously becomes zero.

As described above, in the first embodiment, after the ignition signal is detected, the current limit value A _limit is set to the predetermined value 1 when the engine signal is detected regardless of whether the vehicle speed is detected. . In addition, when the engine signal is not detected, the current limit value A _limit is set to a predetermined value 2 lower than the predetermined value 1.

That is, even when the vehicle speed signal is not detected, the steering assist can be given, so that the steering assist can be performed in a situation where the steering force is low but a large steering force is required, for example, when starting from the garage. . Further, steering assist can be achieved even when the engine signal is not detected due to disconnection of the engine rotation sensor, for example. Therefore, the driver's steering load can be reduced. In the situation where the engine rotation is not detected, 1) the engine rotation is not detected due to disconnection of the engine rotation sensor or the like, but 2) the engine is not actually rotating. If no rotation is detected, it is assumed. When the engine is not actually rotating as in 2), the battery 17 cannot be charged. Therefore, if the current limit value A _limit is not provided when engine rotation is not detected, the amount of power stored in the battery 17 may be insufficient when the power consumption by the electric motor 12 is too large.

Therefore, by setting the current limit value A _limit , it is possible to protect the amount of power stored in the battery 17 and to achieve stable steering assist (corresponding to claim 1).

  Further, when the current limit value is set to the predetermined value 1 or the predetermined value 2, the current limit value is gradually increased to the predetermined value.

  That is, since the current limit value does not change abruptly, the steering assist force does not change abruptly even when the current limit value increases in a state where the steering torque is input. Therefore, stable steering assist can be performed (corresponding to claim 2).

  If the engine ON is detected when the engine signal is not detected and the current limit value is set to the predetermined value 2, the current limit value is changed from the predetermined value 2 to the predetermined value 1.

  That is, by raising the current limit value from the predetermined value 2 to the predetermined value 1, the steering assist force increases, so that the driver's steering load can be further reduced (corresponding to claim 3).

  Next, Example 2 will be described. Since the basic configuration is the same as that of the first embodiment, description thereof is omitted.

(Current limit value setting with self-holding circuit)
FIG. 7 is a flowchart showing the contents of the current limit value setting process when the self-holding circuit of the control unit 13 is provided in the second embodiment. The control unit 13 starts to operate at the same time as the ignition switch is turned on, as in the case where the self-holding circuit of the first embodiment is not provided. However, the ON / OFF determination of the ignition switch is necessary to determine the self-holding end. .

  In step 601, the ignition switch is turned ON / OFF, and the process proceeds to step 602. Details of the ON / OFF determination of the ignition switch will be described later with reference to FIG.

  In step 602, engine ON / OFF determination processing is performed, and the process proceeds to step 603. The details of the engine ON / OFF determination process are as described in FIG.

  In step 603, a current limit value setting process is performed, and the process ends. The details of the current limit value setting process will be described later with reference to FIG.

(Ignition switch ON / OFF judgment processing)
FIG. 8 is a flowchart showing the contents of the ignition switch ON / OFF determination process in the second embodiment.

  In step 701, it is determined whether or not the ignition state flag FIGN = 0. When FIGN = 0, the process proceeds to step 702, and when FIGN = 1, the process proceeds to step 707.

[Ignition switch ON → OFF judgment]
In step 702, the ignition voltage _Vign is compared with a predetermined voltage. When V _ign ≧ predetermined voltage, the process proceeds to step 703, and when V _ign <predetermined voltage, the process proceeds to step 704, where V _count = 0 and the process is terminated.

In step 703, the ignition voltage V _ign is incremented (added by 1), and the process proceeds to step 705.

In step 705, V _count is compared with a predetermined value. When V _count ≥predetermined value, the process proceeds to step 706, and when V _count <predetermined value, the process is terminated.

  In step 706, the ignition state flag FIGN = 1 is set, and it is determined that the ignition switch is ON.

[Ignition switch OFF → ON judgment]
In step 707, the ignition voltage _Vign is compared with a predetermined voltage. If V _ign <predetermined voltage, the process proceeds to step 708. If V _{ign ≥predetermined} voltage, the process proceeds to step 709, where V _ign = 0 is set, and the process is terminated.

In step 708, the ignition voltage V _ign is incremented (added by 1), and the process proceeds to step 710.

In step 710, V _count is compared with a predetermined value. When V _count ≥predetermined value, the process proceeds to step 711, and when V _count <predetermined value, the process is terminated.

  In step 711, the ignition state flag FIGN = 0 is set, and the process ends.

(Current limit value setting process)
FIG. 9 is a flowchart showing the contents of the current limit value setting process in the second embodiment.

  In step 801, it is determined whether or not the ignition state flag FIGN = 1. When FING = 1, the process proceeds to step 802. When FING = 0, the process proceeds to step 811.

  In step 802, it is determined whether or not the engine state flag FENG = 1. When FENG = 1, the process proceeds to step 803, and when FENG = 0, the process proceeds to step 807.

[Increase processing of current limit value after engine ON judgment]
In step 803, the current limit value A _limit is compared with the predetermined value 1. When A _limit <predetermined value 1, the process proceeds to step 804. When A _limit ≥predetermined value 1, the process ends.

  In step 804, the current limit increment Δb is added to the current current limit value, and the process proceeds to step 805.

In step 805, the current limit value A _limit is compared with the predetermined value 1. When A _limit ≧ predetermined value 1, the process proceeds to step 806, and when A _limit <predetermined value 1, the process is terminated.

In step 806, the limiter process of the predetermined value 1, that is, the current limit value A _limit is set to the predetermined value 1, and the process ends.

[Increase current limit value when ignition switch is ON before engine ON is determined]
In step 807, the current limit value A _limit is compared with the predetermined value 2. When A _limit <predetermined value 2, the process proceeds to step 808, and when A _limit ≧ predetermined value 2, the process is terminated.

  In step 808, the current limit increment Δa is added to the current current limit value, and the process proceeds to step 809.

In step 809, the current limit value A _limit is compared with the predetermined value 2. When A _limit ≧ predetermined value 2, the process proceeds to step 810, and when A _limit <predetermined value 2, the process is terminated.

In step 810, the limiter process of the predetermined value 2, that is, the current limit value A _limit is set to the predetermined value 2, and the process ends.

[Reduce current limit when ignition is off]
In step 811, it is determined whether A _limit > 0. When A _limit > 0, the process proceeds to step 812, and when A _limit ≦ 0, the process ends.

  In Step 812, the current limit increment Δc is subtracted from the current limit value, and the process proceeds to Step 813.

In step 813, it is determined whether A _limit <0. When A _limit <0, the process proceeds to step 814, and when A _limit ≧ 0, the process ends.

In step 814, the current limit value A _limit = 0 is set, and the process is terminated.

  FIG. 10 is a time chart showing the contents of the current limit value setting process in the second embodiment. Note that the times t11 to t14 are the same as the times t1 to t4 in FIG.

At time t15, since the ignition state flag FIGN = 0, it is determined whether or not the current limit value A _limit = 0. Since a current limit value A _limit> 0, it is gradually reduced current limit value A _limit by subtracting the current limit decrement Δc from the current limit value A _limit.

Since the current limit value A _limit ≧ 0 at time t16, the process is terminated.

  As described above, in the second embodiment, the control unit 13 has a self-holding circuit. This self-holding circuit may be configured to determine whether the ignition switch 16 is ON / OFF, and when it is determined that the ignition switch is OFF, the power supply may be shut off after ensuring the supply of power for a predetermined time, for example. A configuration may be adopted in which the power is turned off after confirming that writing to the memory or the like is completed.

  While the power supply is secured by the self-holding circuit, the current limit value when the ignition switch is OFF can be gradually decreased instead of instantaneously decreasing. Therefore, it is possible to prevent a rapid decrease in the current limit value, and it is possible to achieve steering assist without giving the driver a sense of incongruity.

  Further, technical ideas other than the claims that can be grasped from the respective embodiments will be described below together with the effects thereof.

(A) In the electric power steering apparatus according to claims 1 to 3,
The electric power steering device according to claim 1, wherein the current limiting means gradually decreases the current limiting value when the ignition changes from ON to OFF.

  The current limit value gradually decreases when the ignition is OFF. Therefore, it is possible to prevent the current limit value from rapidly decreasing in a state where torque is input, and stable steering assist can be achieved.

1 is an overall configuration diagram of an electric power steering apparatus in the present embodiment. It is a block diagram showing the structure in the control unit in a present Example. 4 is a flowchart showing the contents of a current limit value setting process in a control unit in the first embodiment. 3 is a flowchart showing the contents of an engine ON / OFF determination process in the first embodiment. 3 is a flowchart illustrating the contents of a current limit value setting process in the first embodiment. 3 is a time chart illustrating the contents of a current limit value setting process in the first embodiment. 10 is a flowchart showing the contents of a current limit value setting process when the control unit has a self-holding circuit in the second embodiment. 6 is a flowchart showing the contents of an ignition switch ON / OFF determination process in the second embodiment. It is a flowchart showing the content of the current limiting value setting process in Example 2. 6 is a time chart showing the contents of a current limit value setting process in Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Column shaft 3 Universal joint 4 Intermediate shaft 5 Universal joint 6 Input shaft 7 Torque sensor 8 Reducer 9 Pinion shaft 10 Rack shaft 11 Tie rod 12 Electric motor 13 Control unit 14 Vehicle speed sensor 15 Engine rotation sensor 16 Ignition switch 17 Battery 18 Steering wheel

Claims (3)

An electric motor for applying a steering assist force to the steering mechanism;
Motor control means for outputting a motor control signal to the motor based on a steering torque generated in the steering mechanism;
Ignition signal detecting means for detecting an ignition signal;
Engine rotation signal detecting means for detecting the engine rotation signal;
Torque sensor signal detection means for detecting a torque sensor signal;
Vehicle speed signal detecting means for detecting a vehicle speed signal;
An assist torque calculating means for calculating an assist torque serving as a base of a motor driving current from the torque sensor signal and the vehicle speed signal;
An instruction current calculating means for calculating an instruction current for driving the motor from the assist torque;
In the electric power steering apparatus with
Current limit value setting means for setting a current limit value output from the electric motor from the ignition signal and the engine rotation signal;
A current limiting means for limiting current from the current limit value and the indicated current;
The current limiting means sets the current limit value of the electric motor to a first predetermined value when the ignition signal is detected and the engine rotation signal is detected, the ignition signal is detected, and the engine rotation When no signal is detected, the electric power steering apparatus is characterized in that the current limit value of the electric motor is set to a second predetermined value lower than the first predetermined value. The electric power steering apparatus according to claim 1,
The electric power steering apparatus characterized in that the current limiting means gradually increases the current limiting value to the first predetermined value or the second predetermined value. The electric power steering apparatus according to claim 1 or 2,
The current limiting means sets the current limit value of the motor to a first predetermined value when the engine rotation signal is detected when the motor driving means drives the motor at the second predetermined value. An electric power steering device.

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