JP2005262936A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain rapid fluctuation of damping torque by performing gradual reduction processing when steering is shifted from a restoring region to a turning region continuously, and to prevent deterioration of steering feeling. <P>SOLUTION: This electric power steering device is provided with an electric motor for generating assist torque for assisting the steering toque, and damping torque in accordance with a steering speed is applied to the assist torque. A motor command torque calculating means of a control unit is provided with a steering state determination part 39 for determining turning and restoring states of steering based on matching or mismatching of a steering torque code and a steering speed code, and the damping torque is applied for a predetermined time period while gradual reduction processing to torque zero side is performed by a gradual reduction timer 40 when it is determined that steering is shifted from the restoring region to the turning region continuously by the steering state determination part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus including an electric motor that generates a steering assist force (assist force) for a steering system of a vehicle.

  In the conventional electric power steering device, in order to assist the steering torque at the time of steering by the driver, the steering torque is detected by the torque sensor, the vehicle speed is detected by the vehicle speed sensor, and the vehicle speed and the steering torque are detected. Thus, the assist electric motor is driven and the assist torque is added to the steering torque to improve the operability of the steering wheel.

  Further, in the conventional electric power steering apparatus, as described in the following Patent Document 1 filed earlier by the present applicant, a reaction force (damping torque) for damping the movement of the steering wheel is applied. There is also provided a system that performs the given damping control and prevents the irregular behavior of the vehicle.

This electric power steering device discriminates between a steering cut state and a cut back state, and applies a larger damping torque in the cut back state than in the cut state.
JP 2003-137120 A

  In the electric power steering device disclosed in Patent Document 1, since the steering damping torque is continuously applied not only in the switchback region but also in the cut region, this damping torque becomes the steering assist resistance. ing.

  Therefore, in order to solve this problem, it is conceivable to perform control so that the damping torque is applied only in the cut-back region and not applied in the cut-in region.

  However, in such damping control, when the damping torque applied in the switchback region shifts to the cutting region, the damping torque immediately becomes zero. The steering feeling may be deteriorated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a damping torque in accordance with the steering state, and gradually reduce the damping torque at the stage of transition from the return region to the infeed region. An object of the present invention is to provide an electric power steering device that can suppress the occurrence of vibrations in the system.

  In order to solve the above-described problem, the electric power steering apparatus according to claim 1 includes, in particular, a steering state determination unit that determines whether the steering is cut or turned back, and the steering state determination unit determines whether the steering is switched back. Gradual reduction processing means for applying the damping torque applied in the cutback region for a predetermined time while gradually reducing the torque to the zero side in the cut region when it is determined that the transition is continuously made to the cutting region from It is characterized by having.

  According to the present invention, when the steering state discriminating means detects that the steering shifts from the return state to the infeed region, the damping torque applied so far is gradually reduced to zero over a predetermined time by the gradual reduction processing means. To control. For this reason, since the damping torque does not suddenly become zero at the time of transition to the incision region, the occurrence of vibrations in the steering system is suppressed and a stable state is obtained, and the steering feeling is improved. .

  The invention according to claim 2 is characterized in that the gradual reduction processing means reduces the damping torque to zero in the dead zone region.

  According to the present invention, the damping torque is applied in the dead zone region. However, if the damping torque is applied in the region where the assist torque is applied, the steering assist resistance is generated and the steering operation is uncomfortable. In this assist region, the damping torque is controlled to zero to prevent the generation of steering assist resistance in the assist region.

  Embodiments of an electric power steering apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows the overall configuration of an electric power steering apparatus to which the present invention is applied. In FIG. 1, a steering wheel 1 is connected to a pinion shaft 6 via an input shaft side steering shaft 2 a, an output shaft side steering shaft 2 b, a universal joint 3, an intermediate shaft 4 and a universal joint 5.

  The lower end portion of the pinion shaft 6 meshes with a horizontally extending rack shaft 7, and the rack shaft 7 and the pinion shaft 6 constitute a rack and pinion mechanism. Both end portions of the rack shaft 7 are connected to steering wheels (not shown) via tie rods 8a and 8b, respectively, and the left and right wheels are steered by moving the rack shaft 7 in the horizontal direction.

  The steering shaft 2 a is provided with a torque sensor 9 that detects the steering torque of the steering wheel 1 by twisting the torsion bar, and an electric motor 10 that assists (assists) the steering force of the steering wheel 1 via the reduction gear mechanism 11. Are connected to the steering shaft 2b.

  In the figure, reference numeral 12 denotes a control unit for controlling the power steering apparatus. Electric power is supplied from the battery 13 via the ignition switch 14, the steering torque detected by the torque sensor 9, the vehicle speed and engine rotation detected by the vehicle speed sensor 15. A motor drive current (target current command value) is obtained based on the number sensor 16, and a current supplied to the electric motor 10 is controlled based on the target current command value.

  The control unit 12 is continuously operated from a steering state determination function for determining a steering state such as steering turning and returning, a damping torque applying function for applying a damping torque according to the determined steering state, and a switching back state. For example, a microcomputer is provided which executes a gradual reduction processing function for gradual reduction of the damping torque when the transition to the incision region is performed. Specifically, the microcomputer is configured as shown in FIG.

  That is, reference numeral 21 in the figure denotes vehicle speed calculation means for calculating the vehicle speed based on the output of the vehicle speed sensor 15, and 22 denotes engine speed calculation means for calculating the engine speed based on the output of the engine speed sensor 16.

  In the figure, reference numeral 20 denotes motor command torque calculation means for calculating motor command torque based on the output of the torque sensor 9 and detection signals from the vehicle speed calculation means 21 and the engine speed calculation means 22.

  In the figure, reference numeral 23 denotes instruction current calculation means. The instruction current calculation means 23 is based on the total assist torque from the basic assist torque, differential correction torque and damping correction torque described later of the motor command torque calculation means 20. The command current is calculated. Specifically, the command current is calculated by multiplying a constant by, for example, 1 / torque of the obtained total assist torque or the total assist torque: motor current correspondence map. Is done by referring to

  In the figure, reference numeral 24 denotes a PWM for determining an on / off duty ratio for pulse width modulation (PWM) control of each FET of the bridge circuit 29 to be described later based on the outputs of the motor current detection means 25 and the instruction current calculation means 23. Duty determining means.

  The electric motor 10 has its terminal voltage detected by a motor terminal voltage detection means (not shown), and the flowing current is based on the current flowing through the current detection resistor 28, for example, the motor current detection means having an operational amplifier. 25 is detected.

  In the figure, reference numeral 26 denotes power element driving means for performing pulse width modulation (PWM) control of each FET (field effect transistor) of the bridge circuit 29 based on the duty ratio determined by the PWM duty determining means 24.

  The bridge circuit 29 is formed by bridge-connecting the plurality of FETs 29 a to 29 d, and the electric motor 10 is connected to the bridging point to function as a drive circuit for the electric motor 10. The common connection point of the FET 29 a and the FET 29 b is connected to the positive electrode of the battery 13 through the current detection resistor 28. A common connection point of the FET 29c and the FET 29d is grounded.

  The bridge circuit 29 is controlled as follows, for example. That is, the FET 29a or 29b is subjected to pulse width modulation control, and the FET 29c or 29d is continuously turned on. For this reason, the current supplied from the battery 13 to the bridge circuit 29 through the current detection resistor 28 flows through a path of FET 29a (or 29b) → electric motor 10 → FET 29d (or 29c) → ground, and the electric motor 10 Rotate (or rotate left). Accordingly, the steering force is assisted by rotating in the direction in which the steering operation is performed by the steering wheel 1.

  Reference numeral 27 in the figure denotes an abnormality determination means for determining that the system is abnormal as a reverse assist state when it is determined that the assist direction and the steering direction do not match.

  Further, the steering angular speed of the steering is estimated based on the output signals of the motor terminal voltage detection means and the motor current detection means 25.

  Here, the reason why the steering angular speed can be estimated based on the outputs of the motor terminal voltage detection means and the motor current detection means 25 will be described below.

  The motor voltage equation is shown as follows.

V = (L · dI / dt) + IR + E
= (LS + R) · I + Ke · ω (1)
Where V is the terminal voltage [V], L is the inductance [H], S is d / dt, I is the current [A], R is the resistance [Ω], E is the back electromotive voltage [V], and Ke is the reverse The electromotive voltage constant [V / rad / s], ω is the angular velocity [rad / s] of the motor.

Since the influence of inductance can be ignored in the steady state, the above equation (1) is simplified,
V = IR + Ke · ω (2)
From the equation (2), the motor angular velocity is expressed by the following equation.

ω = (V−IR) / Ke (3)
Since the resistance value R [Ω] and the back electromotive force constant Ke [V / rad / s] are constant values inherent to the motor, the motor terminal voltage V [V] and the motor current I [A] are measured to measure the motor. Angular velocity is required.

  The steering angular velocity [rad / s] can be obtained as 1 / speed reduction gear ratio of the motor angular velocity in a steady state.

  However, the calculation of the formula (3) and the final stage steering angular velocity is a simple method in a steady state ignoring the transient state, the current control is feedback control by PI control, and the motor drive is by PWM. Since high-speed switching of voltage causes high-frequency noise to be superimposed on the measured current value and terminal voltage value, a simple estimation of the motor angular speed, that is, the estimation of the steering angular speed, is simply applied to equation (3). Is impossible. Therefore, practically, at least LPF (low-pass filter) processing is performed on the output of equation (3), the average value of the current value and the terminal voltage value is used, the moving average is performed, that is, the LPF processing of the input value is performed. It is something to give.

  As shown in FIG. 3, the motor command torque calculating means 20 calculates a basic assist torque based on the steering torque signal from the torque sensor 9 and the vehicle speed signal from the vehicle speed calculating means 21, as shown in FIG. 30 and a torque differential correction torque calculation unit 31 that calculates a differential correction torque based on the steering torque signal and the vehicle speed signal from the vehicle speed calculation means 21. In addition, a damping correction torque calculation unit 32 that calculates a damping torque based on the steering torque signal, the vehicle speed signal from the vehicle speed calculation means 21 and the output signals of the steering angular speed signal from the steering angular speed estimation means is provided. The motor current limit processing unit 33 that calculates the motor current limit by adding signals from the calculation units 30 to 32 outputs the motor command torque signal to the command current calculation unit 23.

  As shown in FIG. 4, the damping correction torque calculation unit 32 basically outputs a numerical value obtained by converting the steering angular velocity into an absolute value by the absolute value conversion unit 34 to the damping calculation unit 35, and this damping calculation unit In 35, a damping torque is calculated and output.

  The vehicle speed signal output from the vehicle speed detection means 21 is output as a signal amplification signal by a map in the vehicle speed gain unit 36.

  The damping correction torque calculation unit 32 includes a torque signal encoding unit 37 that encodes the steering torque signal, a steering angular velocity encoding unit 38 that encodes the steering angular velocity, and both the encoding units 37 and 38. A steering state discriminating unit 39, which is a steering state discriminating means for judging the current steering state based on the coincidence (true) or mismatch (false) of the output codes, is provided.

  The steering state discriminating unit 39 discriminates that it is in the current reverting state when the codes output from the two encoding units 37 and 38 do not match, while it switches back when the codes match. It is determined that the state has been switched to the cut area. If it is determined that the cut-back area has been shifted to the cut-in area, the signal is input to the gradual decrease timer 40 (gradual decrease processing means), and the gradual decrease timer 40 performs the gradual decrease process.

  That is, the basic damping torque obtained by the damping calculation unit 35 based on the rudder angular velocity is applied as it is in the switchback region, but when gradually shifting from the switchback to the cut region, the taper timer 40 gradually decreases. The damping torque is processed so as to gradually become 0, and is output to the motor current limit processing unit 33 as a damping correction torque.

  Hereinafter, specific control by the damping correction torque calculation unit 32 will be described based on the flowchart of FIG.

  First, in step 1, it is determined whether or not the steering torque code and the steering angular velocity code are the same. If YES is determined, that is, if it is determined that they are the same, the cut-in from the reversion is performed. Since the state is shifted to the area, the process shifts to Step 2.

  In step 2, the gradual decrease timer 40 is incremented, and the process proceeds to step 3.

  In step 3, it is determined whether or not the counted-up gradually decreasing timer value is larger (equal) than the gradually decreasing time constant. If NO is determined here, that is, it is not yet large (not equal). If it is determined, the process proceeds to step 4.

  In this step 4, the damping torque coefficient is calculated from the formula of (gradually decreasing time constant−gradually decreasing timer value) / gradually decreasing time constant (0 ≦ damping torque coefficient <1). For example, the damping torque value is gradually decreased from 1 to 0. And return as it is.

  If it is determined in step 1 that the answer is NO, that is, if it is determined that the two codes do not match, it is determined that the switch-back state exists and the process proceeds to step 5.

  In step 5, the damping torque coefficient is calculated by setting the gradual decrease timer value to 0, and the damping torque coefficient is set to 1. Then, the process proceeds to step 4. Here, since the damping torque coefficient is 1, normal damping torque is applied.

If it is determined in step 3 that the gradual decrease timer value is greater than or equal to the gradual decrease time constant, the process proceeds to step 6. In step 6, the gradual decrease timer value is processed to a value equal to the gradual decrease time constant, and the process proceeds to step 4.
Here, since the gradual decrease timer value is processed to a value equal to the gradual decrease time constant, the damping torque coefficient becomes 0 and no damping torque is applied.

  Further, in the gradual reduction processing of the damping torque, control is performed to reduce the damping torque to 0 even in the assist torque application region other than the dead zone region.

  That is, when the steering torque code and the steering angular velocity code match in step 1 and the gradual decrease timer value is 0 in step 3, the state changes from the switchback state to the wearing state. Thereafter, if the cutting state continues continuously, the gradual decrease time is determined in Step 3, and if the gradual decrease time constant is exceeded, the damping torque is processed to be 0 in Step 6. Therefore, only by comparing the steering torque code and the rudder angular velocity code in Step 1, it is determined whether the current state is a continuous cut-back state or a state where the cut-back state is shifted to the cut-in state.

  Further, although a little damping torque is applied in the dead zone region, if a damping torque is applied in a region where the assist torque other than this is to be applied, a steering assist resistance is generated, which may cause a feeling of strangeness in the steering operation. For this reason, in the assist torque application region other than the dead zone region, the damping torque can be controlled to 0 to prevent the generation of steering assist resistance in the assist region. However, the damping torque may be applied in the assist torque application region to such an extent that the driver does not feel uncomfortable steering.

  The abnormality detection means 27 receives the output signals from the vehicle speed calculation means 21, the engine speed calculation means 22, and the command current calculation means 23 and the output signals from the motor current detection means 25.

  Although not specifically illustrated, an assist direction determining unit that determines the assist direction of the electric motor 10 based on the respective input signals, a steering direction determining unit that determines the steering direction of the steering, and the assist directions A comparison unit for comparing the steering direction, and when the comparison unit determines that the inconsistency state between the assist direction and the steering direction continues for a predetermined time, the system is set as a reverse assist state. An abnormality discriminating unit for discriminating from the above abnormalities.

  When the abnormality determining unit determines that the system is abnormal, the abnormality determining unit performs the abnormality determining process after a predetermined time elapses when the damping torque gradually decreasing process is completed.

  As described above, according to this embodiment, when the steering state discriminating unit 39 detects that the steering shifts from the return state to the infeed region, the damping torque that has been applied so far is reduced by the gradual reduction timer 40 for a predetermined time. And gradually control to zero.

  For this reason, at the time of shifting to the incision region, the damping torque does not become 0 and does not change suddenly, so that the occurrence of vibration of the steering system is suppressed and a stable state is obtained. As a result, the steering feeling is improved.

  Further, as described above, the abnormality detection in the steering assist direction is determined by whether the abnormality determination unit determines whether or not the state in which the assist direction by the electric motor 10 matches the steering direction of the steering has continued for a predetermined time or more. Yes.

  Therefore, when the damping control in the steering incision region is controlled by a parameter other than time, the damping control itself may be erroneously recognized as being abnormal in the steering assist direction (reverse assist state). Therefore, the abnormality detection means 27 in the present embodiment detects the abnormality in the steering assist direction after a predetermined time has elapsed when the gradual reduction process is completed. This can prevent the confusion between the damping control and the steering assist direction abnormality.

  The technical ideas other than the invention described in the claims, as grasped from the embodiment, will be described below.

Assist direction determining means for determining an assist direction of the motor;
Steering direction determining means for determining the steering direction of the steering;
Comparing means for comparing the assist direction determined by the assist direction determining means with the steering direction determined by the steering direction determining means;
When the comparing means determines that the assist direction and the steering direction do not match, an abnormality determining means for determining a system abnormality as a reverse assist state,
3. The electric power steering apparatus according to claim 1, wherein the abnormality determination unit performs an abnormality determination process after a lapse of a predetermined time when the damping torque gradual decrease process is completed by the gradual decrease process unit.

  In order to detect an abnormality in the steering assist direction, determination is made based on whether or not the state in which the assist direction by the electric motor matches the steering direction of the steering continues for a predetermined time or more.

  Therefore, when the damping control in the steering incision region is controlled by a parameter other than time, the damping control itself may be erroneously recognized as being abnormal in the steering assist direction (reverse assist state). Therefore, in the present invention, the abnormality in the steering assist direction is detected after the elapse of the predetermined time after the gradual reduction process is completed, so that the confusion between the damping control and the abnormality in the steering assist direction can be prevented.

It is a lineblock diagram showing an example of an electric power steering device to which the present invention is applied. It is a control block diagram of a control unit provided for the present invention. It is a control block diagram of the motor command torque calculation means used for the control of the present invention. It is a control block diagram of a damping torque correction torque calculation unit of the motor command torque calculation means. It is a control flowchart figure of the control unit provided to this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Steering wheel 9 ... Torque sensor 10 ... Electric motor 12 ... Control unit 15 ... Vehicle speed sensor 16 ... Engine speed sensor 20 ... Motor command torque calculation means 21 ... Vehicle speed calculation means 22 ... Engine speed calculation means 23 ... Instruction current calculation Means 24 ... PWM duty determining means 25 ... Motor current detecting means 26 ... Power element driving means 27 ... Abnormality detecting means 28 ... Current detecting resistor 29 ... Bridge circuits 29a to 29d ... FET
DESCRIPTION OF SYMBOLS 30 ... Basic assist torque calculation part 31 ... Differential correction torque calculation part 32 ... Damping correction torque calculation part 33 ... Motor current limit process part 35 ... Damping calculation part 39 ... Steering state discrimination | determination part 40 ... Gradually decreasing timer

Claims (2)

An electric power steering apparatus including an electric motor that generates an assist torque for assisting a steering torque by a driver, assisting a steering force of the steering system by the electric motor, and applying a damping torque corresponding to a steering angular velocity to the assist torque In
Steering state determination means for determining steering infeed and return state;
When it is determined by the steering state determination means that the steering is continuously shifting from the switchback region to the cut region, the damping torque applied in the switch region is set to the torque zero side in the switch region. An electric power steering apparatus comprising: a gradual decrease processing unit that applies a predetermined time while gradually decreasing the amount of the electric power. 2. The electric power steering apparatus according to claim 1, wherein the gradual reduction processing means reduces the damping torque to zero within a dead zone region.

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