CN101734135A - Vehicle electric power steering control method and control device thereof - Google Patents

Abstract

The invention relates to a vehicle electric power steering control method and a control device thereof. The method comprises the steps of storing normal mode calculation data and abnormal mode calculation data in a power-assisted control device, and calculating target power-assisted torque by acquiring signals of steering torque and vehicle speed of a steering wheel; the fault detection device detects whether a fault factor causing the motor torque to deviate from a target power-assisted torque mapping value exists, and if the fault factor does not exist, the power-assisted control device calculates the target power-assisted torque based on a normal mode; and if the fault factor exists, selecting to calculate the target power-assisted torque or stop the steering power-assisted torque based on the abnormal mode according to the magnitude of the vehicle speed. The control device comprises a torque sensor and a vehicle speed sensor, the torque sensor and the vehicle speed sensor are respectively connected with an electric control unit, and the electric control unit is connected with a motor for power-assisted steering. The invention generates the steering power-assisted torque based on the safety and the necessary degree of the steering power-assisted, so that the control of the electric power-assisted steering is more scientific and reasonable.

Description

A vehicle electric power steering control method and control device thereof

technical field

The invention relates to a vehicle steering control technology, in particular to a vehicle electric power steering control method and a control device thereof.

Background technique

A vehicle electric power steering device that has been used so far detects steering torque applied by a driver turning a steering wheel (hereinafter referred to as "steering wheel"), and causes a motor to generate steering assist torque based on the detected steering torque. The controller controls the steering assist torque. The controller calculates a target assist torque based on, for example, the steering torque detected by the steering torque sensor and the vehicle speed detected by the vehicle speed sensor, and controls the amount of current flowing through the motor based on the target assist torque to generate a desired steering assist torque.

According to such an electric power steering apparatus, if a sensor fails, incorrect steering assist torque is generated. Therefore, in the electric power steering apparatus, when a malfunction signal of the steering torque sensor is detected, the amount of current flowing to the motor is gradually reduced to stop assisting the driver's turning operation of the steering wheel (hereinafter referred to as "steering assist"). ").

After stopping the power steering, the driver needs to use a lot of force to turn the steering wheel, which increases the driver's burden. If the fault caused in the sensor is not major, the driver will feel only a little uncomfortable feeling in the steering operation. For example, the driver feels only jerky torque fluctuations when turning the steering wheel, or there is an inconsistent steering feel between turning the steering wheel clockwise and counterclockwise, in which case it is not actually necessary to always stop the steering assist.

Contents of the invention

The object of the present invention is to provide a new type of vehicle electric power steering control method and its control device for the deficiencies of the current vehicle electric power steering control technology. The control of electric power steering is more scientific and reasonable, in order to minimize the burden on the driver.

In order to achieve the above object, the technical solution of the present invention is as follows: a vehicle electric power steering control method, the method stores normal mode calculation data and abnormal mode calculation data in the power control device, and obtains steering torque and vehicle speed signals of the steering wheel, Calculate the target assist torque; the fault detection device detects whether there is a fault factor that causes the motor torque to deviate from the target assist torque mapping value. If the fault factor does not exist, the assist control device calculates the target assist torque based on the normal mode to realize power steering control; When the torque deviates from the fault factor of the target assist torque mapping value and the vehicle speed is less than or equal to the set value, the assist control device calculates the target assist torque based on the abnormal mode to realize power steering control; if there is a fault factor that causes the motor torque to deviate from the target assist torque mapping value And when the vehicle speed is greater than the set value, the power assist control device stops the steering power assist.

Further, in the vehicle electric power steering control method as described above, the fault factors that cause the motor torque to deviate from the target power assist torque mapping value include: the value detected by the steering torque sensor deviates from the actual value; the signal of the current sensor fluctuates abnormally; Unusual fluctuations in the drive system; damage to the power line to the motor or to the wiring inside the motor.

Further, the vehicle electric power steering control method as described above, wherein, when calculating the target assist torque based on the normal mode, the target assist torque is obtained by adding the main assist torque and the compensation assist torque, by obtaining the steering torque of the steering wheel and vehicle speed signals to calculate the main assist torque, and to calculate the compensation assist torque by obtaining the steering angular velocity signal of the steering wheel.

Further, the vehicle electric power steering control method as described above, wherein when the power steering control is implemented based on the normal mode, the target power assist torque is set to increase with the increase of the steering torque of the steering wheel, and at a given steering wheel Under the steering torque, the target assist torque decreases with the increase of vehicle speed.

Further, the vehicle electric power steering control method as described above, wherein, when realizing the power steering control based on the abnormal mode, if it is judged that the steering torque of the steering wheel is within the dead zone of the power assist map in the abnormal mode, and the motor torque deviates from the target power assist torque map If the failure factor of the numerical value is related to the motor drive system or the current sensor, the power assist control device stops the power steering.

A vehicle electric power steering control device, comprising a torque sensor for detecting the steering torque applied by the driver to the steering wheel steering operation, and a vehicle speed sensor for detecting the speed of the vehicle, the torque sensor and the vehicle speed sensor are respectively connected to an electronic control unit, The electronic control unit is connected with a motor for power steering, and the motor is connected with the steering shaft through a transmission mechanism, wherein the electronic control unit includes:

a main assist torque calculation unit, configured to receive signals representing the steering torque of the steering wheel and the vehicle speed, and calculate the main assist torque using a normal mode assist map or an abnormal mode assist map;

a target assist torque calculation unit for further calculating the target assist torque;

A fault judging unit is used to judge whether there is a fault factor that causes the motor torque to deviate from the target assist torque mapping value;

An abnormal mode control change command unit is used to send a command to change the control mode and a fault identification signal indicating the type of fault according to the fault judgment signal and the vehicle speed signal;

The excitation voltage generation unit is used to calculate the excitation voltage to be applied to the motor according to the signal of the target assist torque.

Further, the vehicle electric power steering control device as described above, wherein the excitation voltage generation unit includes:

a target current calculation unit, configured to receive a signal of a target assist torque, and calculate a target current proportional to the target assist torque;

a current deviation calculation unit, configured to calculate the deviation between the target current and the actual current supplied by the power supply;

The differential control unit is used to calculate the target voltage according to the current deviation, so that the actual current is equal to the target current;

a PWM voltage generating unit, configured to send a signal representing a PWM control voltage corresponding to a target voltage;

The H-bridge drive circuit is used to generate an excitation voltage according to the PWM control voltage signal, and apply the excitation voltage to the motor.

Further, the vehicle electric power steering control device as described above, wherein, the electronic control unit further includes a compensation torque calculation unit, which is used to receive the steering angular velocity signal of the steering wheel to calculate the compensation assist torque, the main assist torque calculation unit and the compensation torque The calculation unit sends the calculation results of the main assist torque and the compensation torque to the target assist torque calculation unit for addition to calculate the target assist torque.

Furthermore, in the vehicle electric power steering control device as described above, a current sensor is provided between the power relay supplying power to the motor and the excitation voltage generating unit for detecting the current flowing through the motor.

The beneficial effects of the present invention are as follows: the vehicle electric power steering control method and device provided by the present invention, in the case of abnormal torque fluctuation or motor torque deviating from the target power assist torque mapping value, according to the need to reduce the uncomfortable feeling in the steering operation The drive control of the power steering motor is performed according to the degree of certainty and the degree of necessity to reduce the force required to perform the steering operation. When the vehicle speed is low and the necessity of steering assist is high, the drive motor generates steering assist torque to reduce the burden on the driver; when the vehicle speed is high and the necessity of steering assist is low, the operation of the motor is prohibited to Minimizes uncomfortable feeling during steering maneuvers. Compared with the existing power steering control method, the present invention is more scientific and reasonable, and the power steering effect is also more remarkable.

Description of drawings

1 is a schematic diagram of a vehicle electric power steering device according to an embodiment of the present invention;

Fig. 2 is the functional diagram of each module of the electric control unit of the embodiment of the present invention;

Fig. 3 is the flow chart of assist control program;

Fig. 4 is the mapping relation of steering torque and basic assist torque;

FIG. 5 is a schematic diagram of an abnormal mode assist map for calculating basic assist torque when a fault occurs;

FIG. 6 is a schematic diagram of a compensation torque map for calculating compensation torque;

Fig. 7 is a schematic diagram of the signal offset of the steering torque sensor;

FIG. 8 is a schematic diagram of signal fluctuations of the steering torque sensor.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in FIG. 1 , the electric power steering device mainly includes: an electric power steering device 60 to provide auxiliary steering force (steering torque) to a steering shaft 21 connected to a steering wheel 61 . The steering shaft 21 includes: an upper steering shaft 21a whose top end is connected to the steering wheel 61, a spline shaft 88 is provided at the bottom end, and a universal joint 21c connecting the spline shaft 88 and the lower steering shaft 21b. The pinion shaft 48 of the lower steering shaft 21b has a rack shaft 89 with a rack 89a meshing with the pinion. A rack and pinion mechanism 84 is formed by the pinion shaft 48 and the rack shaft 89 (rack 89a). Tie rods 46 are provided at both ends of the rack shaft 89 and have outer ends to which the front wheels 62 are attached.

A power transmission mechanism 85 is formed by the worm gear 44 and the worm wheel 45 . The motor 42 outputs a rotational force (torque) that assists the steering torque, and applies the rotational force to the lower steering shaft 21 b through the power transmission mechanism 85 . A steering torque sensor 20 is provided to the lower steering shaft 21b. When the driver operates the steering wheel 61 and applies steering torque to the steering shaft 21 , the steering torque sensor 20 senses the steering torque applied to the steering shaft 21 .

Reference numeral 63 denotes a speed sensor for sensing the speed of the vehicle, and 64 denotes a control device constituted by a computer. The control device 64 receives the steering torque signal T output from the steering torque sensor 20 and the speed signal V output from the speed sensor 63, and outputs a drive control signal SG1 to Basically the control is the operation of the motor 42 .

Electric steering device 60 includes: steering torque sensor 20, speed sensor 63, control device 64, motor 42, rack and pinion mechanism 84 and other components that add to the device structure of a regular conventional steering system.

When the driver operates the steering wheel 61 to change the direction in which the vehicle travels, the rotational force based on the steering torque applied to the steering shaft 21 is converted into a linear motion in the axial direction of the rack shaft 89 through the rack and pinion mechanism 84, and The direction of travel of the front wheels 62 is changed by the tie rods 46 . At this time, the steering torque sensor 20 provided to the steering shaft 21a simultaneously senses the steering torque, converts the steering torque into an electric steering torque signal Th according to the steering of the steering wheel 61 by the driver, and transmits the steering rejection signal Th to the control device 64. The speed sensor 63 senses the speed of the vehicle, converts the speed into a speed signal V, and then outputs the speed signal V to the control device 64 . The control device 64 generates a motor current for driving the motor 42 on the basis of the steering torque signal Th and the speed signal V. The motor 42 driven by motor current applies assist steering force to the lower steering shaft 21c via the worm gear reducer mechanism 85 . As above, the steering force applied to the steering wheel 61 by the driver is reduced by the drive motor 42 .

The speed sensor 63 outputs two pulse signals with the same frequency. Among the two pulse signals, one pulse signal is used as the vehicle speed signal V, and the other pulse signal is used as the signal Ve for judging whether a fault has occurred in the sensor. If the steering speed sensor 63 is functioning normally, the two pulse signals represent the same value. On the other hand, if a malfunction has occurred in the speed sensor 63, the two pulse signals represent different values. Therefore, by comparing the values indicated by the two pulse signals with each other, it is judged whether or not a failure has occurred in the speed sensor 63 .

The direction in which the steering wheel 61 turns is identified based on whether the steering torque Th takes a positive value or a negative value. According to the embodiment of the present invention, when the steering wheel 61 is turned clockwise, the steering torque Th takes a positive value. In contrast, when the steering wheel 61 is turned counterclockwise, the steering torque Th takes a negative value. Accordingly, the magnitude of the steering torque Th represents the magnitude of the absolute value of the steering torque Th.

A sensor that changes reluctance according to the torsion angle of a torsion bar provided in the middle of the steering shaft 21 a and outputs a voltage signal based on the change in reluctance is used as the steering torque sensor 20 . The steering torque sensor 20 can output two independent voltage signals. Of the two voltage signals, one voltage signal is used as a detection signal representing the steering torque Th, and the other voltage signal is used as a signal Thc for judging whether a malfunction has occurred in the sensor. If the steering torque sensor 20 is functioning properly, both voltage signals represent the same value. On the other hand, if a malfunction has occurred in the steering torque sensor 20, the two voltage signals indicate different values. Therefore, by comparing the values indicated by the two voltage signals with each other, it is judged whether or not a malfunction has occurred in the steering torque sensor 20 .

FIG. 7 shows that the line showing the steering torque Th indicated by the detection signal of the faulty steering torque sensor 20 is shifted from the origin. That is, the detected steering torque deviates from the actual steering torque (indicated by the horizontal axis in FIG. 7 ). When the steering wheel 61 is turned in one of the clockwise and counterclockwise directions, if the steering wheel 61 is turned by a greater amount, the resulting steering torque is erroneously detected. This may cause torque clockwise/counterclockwise variation, which is a phenomenon in which the torque output of the motor 42 varies between clockwise and counterclockwise turning operations of the steering wheel 61 by the same steering torque. In Fig. 7, the solid line represents the torque detection characteristic under the normal state (the relationship between the actual steering torque and the steering torque detected by the sensor); the dotted line represents the torque detection characteristic under the fault state, in this fault state, when the steering wheel 61 When turning clockwise, if the steering wheel 61 is turned by a larger amount, the steering torque is erroneously detected; and the alternate long and short dotted lines represent torque detection characteristics in a fault state, in which, when the steering wheel 61 is turned counterclockwise, if the steering wheel 61 is turned by a greater amount, the steering torque is erroneously detected.

The electronic control unit 64 for controlling the operation of the electric motor 42 mainly includes a main CPU, an auxiliary CPU and their respective ROMs and RAMs, and receives detection signals from the steering torque sensor 20 and the vehicle speed sensor 63 respectively connected to the electronic control unit 64 . The vehicle speed sensor 63 outputs a vehicle speed signal indicating the traveling speed V of the vehicle. The electronic control unit 64 is also connected to the warning device 25 which is a warning light notifying the driver of the occurrence of a malfunction.

FIG. 2 is a functional block diagram of the entire electronic control unit 64, including the functional modules of the microcomputer. The functions shown in the functional blocks are realized by executing programs. The electronic control unit 64 includes a main assist torque calculation unit 31 for calculating main assist torque and a compensation torque calculation unit 32 for calculating compensation torque.

The main assist torque calculation unit 31 receives the signals representing the steering torque Th and the vehicle speed V, and calculates the basic assist torque based on the steering torque Th and the vehicle speed V, and uses the assist map to calculate the main assist torque Tas, and the corresponding relationship between Tas, Th and V varies with the vehicle model rather different. Two assist maps are prepared, that is, the normal mode assist map is used when the fault judgment unit 64 (described later) judges that there is no fault, and the abnormal mode assist map is used when the fault judgment unit 64 judges that a fault has occurred. These assist maps are stored in the ROM of the microcomputer.

As shown in Fig. 4, the power assist map in normal mode defines an approximate linear relationship between the main assist torque Tas and the steering torque Th for various vehicle speeds V, which can be calculated according to the formula of main assist torque Tas=Th*θ, where θ is the steering angle. According to the normal mode assist map, the main assist torque Tas is set to increase as the steering torque Th increases. As shown in FIG. 4, the relationship between the steering torque Th and the main assist torque Tas is set so that as the vehicle speed V increases, the main assist torque Tas decreases as a whole, that is, at a given steering torque Th, the main assist torque Tas decreases. The assist torque Tas decreases with the increase of the vehicle speed V, and the specific corresponding relationship can be determined according to the empirical value obtained from the specific test.

As shown in FIG. 5 , the dead band width of the steering torque Th is larger in the abnormal mode assist map than in the normal mode assist map. In the dead zone, the main assist torque Tas is set to zero. In the normal mode assist map, various relationships are set between the main assist torque Tas and the steering torque Th for various vehicle speeds. In contrast, the abnormal mode assist map does not provide various assist characteristic curves according to the vehicle speed V. However, the assist characteristic may be changed based on the vehicle speed V.

The assist map in the normal mode according to the embodiment of the present invention can be used as calculation data in the normal mode. The abnormal mode assist map according to the embodiment of the present invention can be used as abnormal mode calculation data. Instead of using such an assist map, it is possible to store a function defining the variation of the assist torque Tas with the steering torque Th, and use the function to calculate the main assist torque Tas.

The compensation torque calculation unit 32 receives a signal representing the steering angular velocity ω of the driver's steering wheel 61 obtained by the driver's operation, and calculates the compensation torque Tc based on the steering angular velocity ω to be added to the operation of the steering wheel 61 by the driver. Some heaviness. Compensation torque Tc is calculated using the compensation torque map shown in FIG. 6 , Tc=Ke*ω, Ke is the motor damping torque constant. As can be seen from the compensation torque map, the compensation torque applied in the direction opposite to the direction in which the steering wheel 61 is turned is set to increase as the steering angular velocity ω increases. The compensating torque is not limited to the torque used to add some heavy feeling to the operation of the steering wheel 61 . For example, a return torque applied based on the steering angle θ to return the steering wheel 61 to the neutral position, or a cooperative control torque generated according to commands from other control systems. Alternatively, the device may not use compensating torque.

The electronic control unit 64 includes the target torque calculation unit 33 . The target assist torque calculation unit 33 receives signals representing the main assist torque Tas calculated by the main assist torque calculation unit 31 and the compensation torque Tc calculated by the compensation torque calculation unit 32 . The target assist torque calculation unit 33 then calculates the target assist torque T*=(Tas+Tc) by adding together the main assist torque Tas and the compensation assist torque Tc. Then, the motor 42 is controlled by the following units based on the target assist torque T*.

The electronic control unit 64 includes an excitation voltage generation unit 30, and the excitation voltage generation unit 30 is composed of a target current calculation unit 34, a current deviation calculation unit 35, a differential control unit (D control unit) 36, a PWM voltage generation unit 37, and an H bridge drive circuit 38. composition.

The target current calculation unit 34 receives a signal representing the target assist torque T* calculated by the target assist torque calculation unit 33, and calculates a target current I* proportional to the target assist torque T*. The target current satisfies the following relationship: K _T I*=Tas+J _M *(dω _M /dt)+D _M ω _M +F _M sgn(ω _M ),

Among them, K _T is the motor torque coefficient, Tas is the main booster torque, J _M is the moment of inertia coefficient, D _M is the viscosity coefficient, F _M is the damping torque, ω _M is the motor speed, and sgn() is a sign function.

The target deviation calculation unit 35 receives signals representing the target current I* calculated by the target current calculation unit 34 and the actual current Ix flowing to the motor 42, and calculates a deviation ΔI (=I*− Ix). The current sensor 71 is provided between the power relay and the PWM voltage generating unit 37 , and detects the current (Ix) flowing through the motor 42 . The power relay 72 is provided on the power line. The power relay 72 allows or prevents the supply of current to the motor 42 .

The deviation ΔI representing the calculation by the current deviation calculation unit 35 is sent to the differential control unit (D control unit) 36 . The differential control unit 36 calculates the target voltage V* based on the deviation ΔI so that the actual current Ix is equal to the target current I*, that is, the deviation ΔI is equal to zero. The formula for calculating the target voltage is as follows:

V*=Kh I*+K _M (dω _M /dt)+K _D ω _M +K _F sgn(ω _M ),

Among them, Kh is the motor impedance constant, K _M is the motor inertia coefficient, K _D is the viscosity coefficient, K _F is the damping coefficient, ω _M is the motor speed, and sgn() is a sign function.

A signal representing the target voltage V* calculated by the differential control unit 36 is sent to the PWM voltage generation unit 37 . In this way, the signal of the target voltage calculated by the differential control unit 36 is sent to the PWM voltage generation unit 37 . The PWM voltage generating unit 37 sends a signal representing a PWM control voltage corresponding to the target voltage V* to the H-bridge driving circuit 38 . The H-bridge driving circuit 38 generates an excitation voltage based on the PWM control voltage signal, and applies the excitation voltage to the motor 42 through the power line. Accordingly, the front wheels 62 are steered with the assistance of the driving power generated by the motor 42 .

The electronic control unit 64 also includes a failure judging unit 64 . The failure judging unit 64 judges whether a failure has occurred which is a factor causing the motor torque to deviate from the target assist torque map value. That is, the failure judging unit 64 judges whether a deviation has occurred in the output of the steering torque sensor 20, that is, whether the numerical value detected by the steering torque sensor 20 deviates from the actual value; whether the current sensor 71 signal fluctuates abnormally; Whether there is fluctuation in the motor driving system of the H-bridge driving circuit 38; and whether at least one of the power line leading to the motor 42 or the internal circuit of the motor 42 is damaged.

If the value detected by the steering torque sensor 20 deviates from the actual value, the detected torque Th deviates from the true steering torque. That is, when the steering wheel 61 is turned in one of the clockwise direction and the counterclockwise direction, if the steering wheel 61 is turned by a smaller amount, the generated steering torque is erroneously detected. Therefore, even if the same operating force is used to turn the steering wheel 61 clockwise or counterclockwise, the magnitude of the steering assist torque supplied varies between when the steering wheel 61 is turned clockwise or when the steering wheel 61 is turned counterclockwise. Accordingly, the operating force required by the driver changes according to the turning direction of the steering wheel 61 . Therefore, the driver may feel an uncomfortable feeling in the turning operation of the steering wheel 61 . Therefore, the failure judging unit 64 compares the signals Th and Thc sent from the steering torque sensor 20 with each other, and if the deviation between the voltage values represented by these signals Th and Thc is equal to or larger than the reference value, judges that the steering torque sensor 20 A failure has occurred in .

In FIG. 2, the voltages of the two phases are collectively referred to as Vx. If any of the power supply lines 42U, 42V of the motor 42 is damaged, although the motor can rotate, the torque output of the motor 42 will fluctuate. When such a sudden change occurs in the power line, the current deviation value calculated by the current feedback control is not equal to zero. Therefore, when the deviation current value calculated by the current deviation calculation unit 35 and represented by the deviation signal ΔI is not equal to zero, the failure judging unit 64 judges that one of the power lines is damaged.

When it is judged that an offset has occurred in the output of the steering torque sensor 20, that is, the value detected by the steering torque sensor 20 deviates from the actual value, and this offset is a factor causing abnormal torque fluctuations or motor torque deviation from the target assist torque map value ; Current sensor 71 has broken down; In the motor drive system (for example, PWM voltage generating unit 37 or H bridge drive circuit 38) has broken down; Or lead to at least one in the power line 42U, 42V of motor 42 damaged, then failure The judgment unit 64 sends a failure judgment signal indicating the type of failure to the abnormal mode control change command unit 40 . When a main failure other than the above is detected, or when an assist stop command is received from another control system, the electronic control unit 64 stops the operation of the entire control system using a failure processing function unit (not shown).

The abnormal mode control change command unit 40 receives a signal representing the vehicle speed V from the vehicle speed sensor 63 in addition to the failure judgment signal. When the failure judgment signal is output from the failure judgment unit 64 and the vehicle speed V is higher than the set value (20 km/h), the abnormal mode control change command unit 40 outputs a command to stop the steering assist. In response to this stop command, the steering assist is stopped. For example, the power relay is closed to cut off the power supply to the motor 42 . When the failure judgment signal is output from the failure judgment unit 64 and the vehicle speed is equal to or lower than the set value (20 km/h), the abnormal mode control change command unit 40 sends the change control to the main assist torque calculation unit 31 and the compensation torque calculation unit 32 mode, and send a fault identification signal indicating the type of fault to the main assist torque calculation unit 31.

The main assist torque calculation unit 31 sets the assist map to be used as the abnormal mode assist map according to the control mode change command received from the abnormal mode control change command unit 40 and calculates the assist torque Tas using the abnormal mode assist map. When the failure identification signal received from the abnormal mode control change command unit 40 indicates that one of the current sensors 71 has failed, the main assist torque calculation unit 31 outputs a stop command PWM OFF for stopping the slave PWM when the steering torque Th enters a dead zone. The output of the voltage generating unit 37. When the failure identification signal indicates that one of the phases in the motor drive system has failed, the main assist torque calculation unit 31 outputs an OFF signal MR OFF to the power relay.

The compensation torque calculation unit 32 stops calculation of the compensation torque when receiving the control mode change command from the abnormal mode control change command unit 40 . The compensation torque calculation unit 32 then sets the value of the compensation torque Tc to zero, and then sends a signal indicating that the compensation torque Tc is zero to the target assist torque calculation unit 33 .

Information such as torque Th, Tas, Tc, and T*, current Ix, I*, IUx, IVx, and ΔI, voltage Vx, steering angular velocity ω, steering angle θ, and vehicle speed V represent their magnitude and direction.

FIG. 3 shows the assist control program executed by the electronic control unit 64 and stored in the ROM of the electronic control unit 64 as a control program. The assist control program is prepared by combining the respective units 31 - 40 of the electronic control unit 64 to perform processing in association with each other and arranging the processing in chronological order. The control program is executed periodically at predetermined time intervals when the ignition switch is turned on.

After starting the control program, the electronic control unit 64 first checks the status of each component (step S11). Next, the electronic control unit 64 judges in step S12 whether a failure has occurred. If it is judged in step S12 that there is no malfunction ("NO" in step S12), the electronic control unit 64 executes the normal mode steering assist control in step S13. That is, the electronic control unit 64 uses the main assist torque calculation unit 32 to calculate the main assist torque Tas, and adds it to the compensation torque Tc to obtain the target assist torque T*, and controls the motor 42 through the above-mentioned current feedback. Such normal mode steering assist is performed periodically unless a malfunction is detected.

If it is determined in step S12 that a failure has occurred, the electronic control unit 64 executes step S14, in which the alarm device 25 is turned on. Next, in step S15 , the ECU 64 judges whether the detected fault is a factor causing abnormal torque fluctuation or motor torque deviating from the target assist torque map value. If such a malfunction has been detected, there is no need to deactivate the power steering control. An affirmative judgment is made in step S15 if the fault judging unit 64 judges that: when an offset has occurred in the output of the steering torque sensor 20; when the current sensor 71 has failed; or when the power line of the motor 42 has been damaged. If the fault judging unit 64 judges that a fault other than the above-mentioned fault has occurred, a negative judgment is made in step S15.

If a negative judgment is made in step S15 , then in step S16 , the electronic control unit 64 prohibits the drive control of the motor 42 . Therefore, the power steering is stopped. On the other hand, if an affirmative judgment is made in step S15, ie, if it is judged that the detected fault is a fault of a factor causing the motor torque to deviate from the target assist torque map value, the steering assist function is operated although incorrect. Therefore, the drive control of the motor 42 is allowed according to the degree of necessity of the steering assist.

The electronic control unit 64 reads the vehicle speed V detected by the vehicle speed sensor 63 in step S17, and determines whether the vehicle speed is higher than a predetermined 20 km/h (step S18). When driving at high speeds, steering assistance is less necessary. Therefore, when the vehicle speed V is higher than 20 km/h, the ECU 64 prohibits the drive control of the motor 42 to stop the power steering (step S16).

On the other hand, when the vehicle is running at a low speed, the driver has a heavy burden of turning the steering wheel 61 . Therefore, if it is judged that the vehicle speed V is equal to or lower than 20 km/h ("NO" in S18), the ECU 64 permits the drive control of the motor 42 to perform the abnormal mode assist control (step S19). That is, the ECU 64 uses the main assist torque calculation unit 31 to calculate the main assist torque with reference to the abnormal mode assist map, uses the main assist torque Tas to set the target assist torque T*, and controls the operation of the motor 42 through the above-mentioned current feedback control. In this way, since the compensation torque Tc corresponding to the steering angular velocity ω is set to zero, the target assist torque T* is equal to the main assist torque Tas.

In the abnormal mode assist control, the main assist rotation Tas(=T*) is calculated using the abnormal mode assist map shown in FIG. 5 . As can be seen from the map, the width of the steering torque dead zone in which the main steering torque Tas is set to zero is large. Therefore, when the driver performs the steering operation with a torque of less than 3 Nm, the detected steering torque Th is within the dead zone. Thus, the target assist torque T* is set to zero, and no command to drive the motor 42 is issued. On the other hand, when the driver performs a steering operation with a torque greater than 4 Nm, the detected steering torque is outside the dead zone, a predetermined target assist torque T* is set, and drive control of the motor 42 is performed. That is, if it is judged that a failure has occurred that is a factor causing the motor torque to deviate from the target assist torque map value, the motor 42 provides steering assist to the driver's intentional steering wheel 61 operation with a torque greater than 4Nm. On the other hand, the motor 42 is prohibited from providing steering assist to the driver's unintentional operation of the steering wheel 61 with a torque of less than 3 Nm. Therefore, when the degree of necessity of steering assist is high, the motor 42 is driven to reduce the driver's burden. On the other hand, when the degree of necessity of the steering assist of the electric motor 42 is low, the operation of the electric motor 42 is stopped to prevent the occurrence of the motor torque deviating from the target assist torque map value.

When a failure has occurred in the motor drive system, even if the steering torque Th is within the dead zone, erroneous operation of the motor 42 cannot be prevented only by changing the assist map. For example, if a malfunction occurs in the PWM voltage generating unit 37 or the H-bridge drive circuit 38, the motor 42 may be erroneously driven even if the target assist torque T* is set to zero. When a failure occurs in one of the current sensors 71, then only by changing the assist map, the erroneous operation of the motor 42 cannot be prevented. Therefore, when the abnormal mode steering assist control is performed, the following steps are additionally performed.

The electronic control unit 64 judges in step S20 whether the steering torque Th is within the dead zone of the abnormal mode assist map. If it is judged that the steering torque Th is within the dead zone ("YES" in step S20), the electronic control unit 64 judges in step S21 whether the fault is related to the motor drive system. If the fault is related to the motor drive system ("YES" in step S21), the electronic control unit 64 closes the power relay to cut off the power supply of the motor 42 (step S22). If the failure is not related to the motor drive system ("NO" in step S21), the electronic control unit 64 judges whether the failure is related to one of the current sensors 71 (step S23). If it is judged that the fault is related to one of the current sensors 71 ("YES" in the step S23), the ECU 64 stops sending the PWM control signal to the H bridge drive circuit 38 (step S24).

Therefore, when the steering torque Th is within the dead zone in the abnormal mode assist map, even if a detected malfunction is related to the motor drive system or the current sensor 71, the operation of the motor 42 is reliably stopped. On the other hand, when the steering assist torque Th is outside the dead zone or when the detected fault has nothing to do with the motor drive system and the current sensor 71, the ECU 64 controls the steering assist torque T* based on the target assist torque T* set using the abnormal mode assist map. The amount of current flowing through the motor 42 without performing steps S22 and S24.

In the above-mentioned assist control routine, the steering assist is prohibited or permitted based on whether the vehicle speed is higher than 20 km/h (step S18). 20 km/h can allow hysteresis. For example, when the vehicle speed V exceeds 22 km/h, the power steering can be prohibited, and when the speed V decreases and is equal to or less than 18 km/h, the power steering can be allowed. Alternatively, the determination of whether the vehicle speed V is higher than 20 km/h may be continuously performed for a predetermined length of time. When it is judged that a predetermined length of time has elapsed, the steering assist may be prohibited or permitted.

According to the electric power steering apparatus of the embodiment of the present invention, in the case where abnormal torque fluctuation occurs or the motor torque deviates from the target power assist torque map value, according to the degree of necessity of reducing the uncomfortable feeling in the steering operation and reducing the time required for steering operation The driving control of the motor 42 is performed according to the degree of necessity of the required force. That is, when the vehicle speed is low and the degree of necessity of the steering assist is high, the electric motor 42 is driven to generate the steering assist torque to reduce the driver's burden. On the other hand, when the vehicle speed is high and the degree of necessity of the steering assist is low, the operation of the electric motor is prohibited to minimize the uncomfortable feeling in the steering operation.

In addition, in such a failure state, the assist map is changed to an abnormal mode assist map in which the dead band width of the steering torque is larger than that in the normal state. Therefore, even when the vehicle is running at a low speed, if the degree of necessity of the steering assist is low, that is, the driver performs an intentional steering operation with relatively weak force, the operation of the motor 42 is prohibited. Therefore, the driver does not feel uncomfortable sensations such as abnormal torque fluctuations or deviation of the motor torque from the target assist torque map value. On the other hand, when the driver performs a steering operation with greater force, for example, when the driver turns the vehicle, the steering torque falls outside the dead zone, and the steering assist torque generated by the operation of the motor 42 reduces the driver's burden.

When the steering torque is low, the driver is more likely to feel uncomfortable sensations, such as abnormal torque or motor torque deviating from the target assist torque map value. Even in the case where the steering torque dead zone is set using the assist map, when a failure (a failure in the motor drive system or a current sensor) that does not cause the necessity to stop the operation of the motor 42 has occurred, the power line to the motor 42 is cut off or The issuance of the PWM control signal is stopped, thereby reliably stopping the operation of the motor 42 . In addition, since the alarm device 25 is also turned on when such an abnormal mode steering assist control is performed, the driver can be aware of the occurrence of a malfunction before stopping the steering assist control, thus making it possible to perform maintenance work on the steering assist system at an earlier stage.

The methods and devices described in the present invention are not limited to the examples described in the specific implementation modes. Other implementation modes obtained by those skilled in the art according to the technical solutions of the present invention also belong to the technical innovation scope of the present invention.

Claims (9)

1. A vehicle electric power steering control method, characterized in that: the method stores normal mode calculation data and abnormal mode calculation data in the power assist control device, and calculates the target power assist torque by obtaining signals of steering torque and vehicle speed of the steering wheel; The detection device detects whether there is a fault factor that causes the motor torque to deviate from the target power assist torque mapping value. If the fault factor does not exist, the power assist control device calculates the target power assist torque based on the normal mode to realize power steering control; if there is a fault factor that causes the motor torque to deviate from the target power assist torque mapping If there is a fault factor that causes the motor torque to deviate from the target assist torque mapping value and the vehicle speed is greater than the set value , the power assist control device stops the steering power assist. 2. The vehicle electric power steering control method according to claim 1, characterized in that: the fault factors causing the motor torque to deviate from the target power assist torque mapping value include: the value detected by the steering torque sensor deviates from the actual value; the current sensor signal Abnormal fluctuations occur; abnormal fluctuations occur in the motor drive system; the power line leading to the motor or the internal circuit of the motor is damaged. 3. The vehicle electric power steering control method according to claim 1, characterized in that: when calculating the target assist torque based on the normal mode, the target assist torque is obtained by adding the main assist torque and the compensation assist torque, by The steering torque and vehicle speed signals of the steering wheel are obtained to calculate the main assist torque, and the compensation assist torque is calculated by obtaining the steering angular velocity signal of the steering wheel. 4. The vehicle electric power steering control method according to claim 1, 2 or 3, characterized in that: when the power steering control is realized based on the normal mode, the target power steering torque is set to increase as the steering torque of the steering wheel increases. is large, and under a given steering torque, the target assist torque decreases with the increase of vehicle speed. 5. The vehicle electric power steering control method according to claim 1, 2 or 3, characterized in that: when realizing the power steering control based on the abnormal mode, if it is judged that the steering torque of the steering wheel is within the dead zone of the power assist map of the abnormal mode, And if the fault factor causing the motor torque to deviate from the target assist torque mapping value is related to the motor drive system or the current sensor, the assist control device stops the steering assist. 6. A vehicle electric power steering control device, including a torque sensor for detecting the steering torque applied by the driver to the steering wheel steering operation, and a vehicle speed sensor for detecting the vehicle speed, the torque sensor and the vehicle speed sensor are respectively connected with the electronic control unit connection, the electronic control unit is connected to the motor for power steering, the motor is connected to the steering shaft through the transmission mechanism, and it is characterized in that: the electronic control unit includes: a main assist torque calculation unit, configured to receive signals representing the steering torque of the steering wheel and the vehicle speed, and calculate the main assist torque using a normal mode assist map or an abnormal mode assist map; a target assist torque calculation unit for further calculating the target assist torque; A fault judging unit is used to judge whether there is a fault factor that causes the motor torque to deviate from the target assist torque mapping value; An abnormal mode control change command unit is used to send a command to change the control mode and a fault identification signal indicating the type of fault according to the fault judgment signal and the vehicle speed signal; The excitation voltage generation unit is used to calculate the excitation voltage to be applied to the motor according to the signal of the target assist torque. 7. The vehicle electric power steering control device according to claim 6, wherein the excitation voltage generation unit comprises: a target current calculation unit, configured to receive a signal of a target assist torque, and calculate a target current proportional to the target assist torque; a current deviation calculation unit, configured to calculate the deviation between the target current and the actual current supplied by the power supply; The differential control unit is used to calculate the target voltage according to the current deviation, so that the actual current is equal to the target current; a PWM voltage generating unit, configured to send a signal representing a PWM control voltage corresponding to a target voltage; The H-bridge drive circuit is used to generate an excitation voltage according to the PWM control voltage signal, and apply the excitation voltage to the motor. 8. The vehicle electric power steering control device according to claim 6 or 7, characterized in that: the electronic control unit further includes a compensation torque calculation unit, which is used to receive the steering angular velocity signal of the steering wheel to calculate the compensation power steering torque, the main The assist torque calculation unit and the compensation torque calculation unit respectively send the calculation results of the main assist torque and the compensation torque to the target assist torque calculation unit for addition to calculate the target assist torque. 9. The vehicle electric power steering control device according to claim 6, characterized in that a current sensor is provided between the power relay supplying power to the motor and the excitation voltage generating unit for detecting the current flowing through the motor.

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