JP4645343B2 - Vehicle steering assist device - Google Patents

Description

  The present invention relates to a vehicle steering assist device that assists a steering operation of a steering wheel using an electric motor.

Conventionally, in this type of device, for example, as disclosed in Patent Document 1 below, in order to avoid collision with an obstacle on the condition of the presence of an obstacle in front of the vehicle, a sudden steering operation of a steering wheel, and the like The collision avoidance steering by the driver is determined, and when the collision avoidance steering is determined, the amount of current flowing through the electric motor is increased according to the turning operation of the steering handle. And it makes it easier to avoid the collision of the vehicle with the obstacle by making the steering operation of the steering wheel easier by the driver. Further, for example, as shown in Patent Document 2 below, the magnitude of the current that is determined according to the steering operation of the steering wheel by the driver and flows to the electric motor is avoided to avoid an abnormality associated with the temperature rise of the electric motor. There is also known a steering assist device for a vehicle which is restricted to be performed.
JP 2000-43741 A Japanese Patent Laid-Open No. 2001-171540

  However, in the former conventional device, a large current flows excessively in the electric motor, and there is a possibility that an abnormality occurs in the electric motor due to overheating. In the latter conventional apparatus, no consideration is given to collision avoidance steering for avoiding collision with an obstacle.

  The present invention has been made to address both of the above problems, and it is an object of the present invention to provide a steering assist device for a vehicle that can achieve both protection of an electric motor and collision avoidance steering.

In order to achieve the above object, the present invention is characterized in that an electric motor for assisting a steering operation of a steering wheel and a target assist current determining means for determining a target assist current to be supplied to the electric motor according to a driving state of the vehicle. Current limiting means for limiting the determined magnitude of the target assist current for overheating protection of the electric motor or a circuit device for controlling the electric motor, and the target assist current limited by the current limiting means. In a vehicle steering assist device having a drive control means for controlling the electric motor by flowing it through the electric motor, the collision avoidance steering by the driver for avoiding the collision of the obstacle is performed by the differential value of the steering speed or the steering torque. current system time and determines the collision avoidance steering judging means based on the differential value, the collision avoidance steering by the collision avoidance steering determining means is determined In the provision and restriction releasing means for mitigating the magnitude of limit conditions of the target assist current by means.

In this case, the collision avoidance steering determination unit includes, for example, an obstacle detection unit that detects an obstacle, and the obstacle detection unit detects the obstacle and the differential value of the steering speed or the differential value of the steering torque is a predetermined value. The collision avoidance steering is determined on the condition that it is above . Further, the current limiting means has, for example, a temperature detection means for detecting the temperature of the electric motor or the temperature of the circuit device for controlling the electric motor, and limits the target assist current as the detected temperature becomes higher. To do.

  In the present invention configured as described above, when the driver suddenly steers the steering wheel to avoid a collision with an obstacle, the collision avoidance steering determination means determines this collision avoidance steering and The relaxing means relaxes the restriction condition of the target assist current magnitude by the current limiting means. Therefore, the driver can easily steer the steering wheel, and it is easy to avoid the vehicle colliding with the obstacle. On the other hand, the limit relaxation means only relaxes the current limit flowing to the electric motor, and does not increase the current flowing to the electric motor indefinitely. Therefore, the extreme overheating of the circuit device for controlling the electric motor or the electric motor is not possible. The electric motor or the circuit device for controlling the electric motor does not become abnormal due to overheating.

  Another feature of the present invention is that when the restriction mitigation means further determines the collision avoidance steering by the collision avoidance steering judgment means in a state where the restriction condition of the magnitude of the target assist current is already relaxed. This is because the limiting condition of the magnitude of the target assist current is relaxed under stricter limiting conditions than those already relaxed. According to this, even when the collision avoidance steering is performed again without the obstacle being avoided by one collision avoidance steering, the electric current flowing through the electric motor is not greatly relieved, and the electric motor Alternatively, excessive overheating of the circuit device for controlling the electric motor is appropriately prevented.

  In addition, another feature of the present invention is that a travel restriction unit is provided that restricts vehicle travel when the number of times collision avoidance steering is determined by the collision avoidance steering determination unit exceeds a predetermined number. In this case, for example, the travel restricting means brakes the vehicle or reduces the driving force of the vehicle. According to this, when the collision avoidance steering by the driver cannot avoid the collision between the vehicle and the obstacle, the traveling of the vehicle is limited, so that the collision between the vehicle and the obstacle is more easily avoided. At the same time, overheating of the electric motor or the circuit device for controlling the electric motor is avoided, and occurrence of an abnormality due to overheating of the electric motor or the circuit device for controlling the electric motor is surely avoided.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an entire vehicle steering apparatus including a steering assist apparatus according to the present invention.

  The vehicle steering apparatus includes a steering shaft 12 connected to a steering handle 11 so that an upper end thereof is integrally rotated. A pinion gear 13 is connected to a lower end of the shaft 12 so as to be integrally rotated. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1, FW2 are steerably connected to both ends of the rack bar 14 via tie rods and knuckle arms (not shown). The left and right front wheels FW1 and FW2 are steered left and right in accordance with the axial displacement of the rack bar 14 accompanying the rotation of the steering shaft 12 around the axis.

  An electric motor 15 for steering assist is assembled to the rack bar 14. The electric motor 15 is connected to the rack bar 14 via the ball screw mechanism 16 so that power can be transmitted, and assists the steering of the left and right front wheels FW1, FW2 by the rotation thereof. The electric motor 15 is a DC motor in the present embodiment, but a three-phase AC motor can also be used. The ball screw mechanism 16 functions as a speed reducer and a rotation-linear converter. The ball screw mechanism 16 reduces the rotation of the electric motor 15 and converts it into a linear motion and transmits it to the rack bar 14. Instead of assembling the electric motor 15 to the rack bar 14, the electric motor 15 is assembled to the steering shaft 12, and the rotation of the electric motor 15 is transmitted to the steering shaft 12 via the speed reducer so that the shaft 12 is axially connected. You may comprise so that it may drive around.

  Next, an electric control device that controls the operation of the electric motor 15 will be described. The electrical control device includes a steering angle sensor 21, a steering torque sensor 22, an environmental temperature sensor 23, a substrate temperature sensor 24, and a vehicle speed sensor 25. The steering angle sensor 21 is assembled to the steering shaft 12 and detects the steering angle θ of the steering handle 11 by detecting the rotation angle of the shaft 12. The steering angle θ represents the magnitude of the steering angle θ when the steering handle 11 is steered in the right direction and the left direction by positive and negative values, respectively. The steering torque sensor 22 is assembled to the steering shaft 12 and detects the steering torque Tr acting on the steering shaft 12 by the turning operation of the steering handle 11. The steering torque Tr also represents the magnitude of the steering torque Tr when the right and left front wheels FW1, FW2 are steered in the right direction and the left direction by positive and negative values, respectively. Further, instead of assembling the steering angle sensor 21 and the steering torque sensor 22 to the steering shaft 12, the steering angle θ and the steering torque Tr are determined from the amount of displacement and strain in the axial direction of the rack bar 14 by assembling the rack bar 14. May be detected respectively.

  The environmental temperature sensor 23 is assembled to the housing of the electric motor 15 and detects the temperature of the housing as the environmental temperature Tc. Further, the environmental temperature sensor 23 may be arranged in the vicinity of the electric motor 15 other than the housing of the electric motor 15 to detect the environmental temperature Tc of the electric motor 15. The substrate temperature sensor 24 detects the temperature Tb of the substrate on which the steering assist electronic control unit 30 (hereinafter referred to as the steering assist ECU 30), the drive circuit 31, and the booster circuit 33 are arranged. The vehicle speed sensor 25 detects the vehicle speed V. These sensors 21 to 25 are connected to the steering assist ECU 30.

  The steering assist ECU 30 includes a microcomputer including a CPU, a ROM, a RAM, and the like as main components and includes an A / D converter. The assist control program shown in FIG. 2, the boost control program shown in FIG. 4 is repeatedly executed in parallel every predetermined short time. By repeatedly executing these programs, the steering assist ECU 30 drives and controls the electric motor 15 via the drive circuit 31. The drive circuit 31 is configured by an inverter circuit, and is controlled by the steering assist ECU 30 to flow the target output current Iout * to the electric motor 15. The drive circuit 31 also includes a current sensor 31a, which detects the motor actual current Im flowing through the electric motor 15 and supplies it to the steering assist ECU 30.

  The drive circuit 31 receives DC power from the battery 32 via the booster circuit 33. The booster circuit 33 is controlled by the steering assist ECU 30 to boost the input power supply voltage Ein from the battery 32 in accordance with the boost ratio Ep and supply it to the drive circuit 31. The input power supply voltage Ein supplied from the battery 32 to the booster circuit 33 is supplied to the steering assist ECU 30 for boost control.

  The steering assist ECU 30 includes a peripheral monitoring electronic control unit 41 (hereinafter referred to as peripheral monitoring ECU 41), an engine control electronic control unit 42 (hereinafter referred to as engine control ECU 42), and a brake control electronic control unit 43 (hereinafter referred to as brake control ECU 43). It is connected.

  The peripheral monitoring ECU 41 inputs a detection signal of a front obstacle from a peripheral monitoring sensor 44 including a laser radar, an ultrasonic sensor, etc., and a distance to the front obstacle and a yaw angle shift of the front obstacle with respect to the vehicle center line. Calculate the quantity. The engine control ECU 42 controls the output of the engine device 45, and controls the engine output by the engine device 45 to be reduced in order to reduce the driving force to the vehicle in response to an instruction from the steering assist ECU 30. The brake control ECU 43 controls the brake device 46, and operates the brake device 46 in order to generate a braking force for the vehicle according to an instruction from the steering assist ECU 30. Note that both the engine control ECU 42 and the brake control ECU 43 constitute a travel restriction unit of the present invention that restricts the travel of the vehicle.

  Next, the operation of the embodiment configured as described above will be described. The steering assist ECU 30 repeatedly executes the assist control program shown in FIG. 2 every predetermined short time after the ignition switch is turned on. This assist control program is started in step S10, and the steering assist ECU 30 in step S11, the steering torque Tr detected by the steering torque sensor 22, the environmental temperature Tc detected by the environmental temperature sensor 23, and the substrate temperature sensor 24. The substrate temperature Tb detected by the vehicle speed V, the vehicle speed V detected by the vehicle speed sensor 25, and the motor actual current Im detected by the current sensor 31a are input.

  After step S11, the steering assist ECU 30 calculates a target assist current Ias * corresponding to the input steering torque Tr and vehicle speed V with reference to the target assist current table in step S12. The target assist current table is provided in the ROM of the steering assist ECU 30, and stores a target assist current Ias * that increases as the steering torque Tr increases, as shown in FIG. Further, the target assist current Ias * shows a larger value as the vehicle speed V decreases with respect to the same steering torque Tr. Instead of using this target assist current table, a function that prescribes a target assist current Ias * that changes according to the steering torque Tr and the vehicle speed V is stored in advance, and an operation using this function is executed. The target assist current Ias * corresponding to the steering torque Tr and the vehicle speed V may be calculated.

  Next, in step S13, the steering assist ECU 30 estimates and calculates the temperature Tm of the electric motor 15 (hereinafter simply referred to as the motor temperature Tm) using the environmental temperature Tc and the motor actual current Im. The motor temperature Tm is specifically the temperature of the coil of the electric motor 15 and causes a failure (for example, disconnection, short circuit, etc.) of the electric motor 15. The estimation calculation of the motor temperature Tm will be briefly described. Basically, the heat generation amount of the coil is time integrated using the square value of the motor actual current Im, and at the same time, the heat dissipation of the coil and the environmental temperature Tc are calculated. The motor temperature Tm is estimated in consideration.

  After the process of step S13, the steering assist ECU 30 refers to the first current limit table in step S14, and performs the first operation according to the calculated motor temperature Tm and the collision avoidance count value N (= 0 to Nmax). The maximum allowable current Imax1 is calculated. The first current limit table is provided in the ROM of the steering assist ECU 30, and can flow to the electric motor 15 for each collision avoidance count value N (= 0 to Nmax) as shown in FIG. 1st maximum allowable current Imax1 is specified. That is, the first maximum allowable current Imax1 is set to a predetermined large value if the motor temperature Tm is equal to or less than the limit start temperatures Tmo (0), Tmo (1), Tmo (2) ·· Tmo (Nmax). When the motor temperature Tm exceeds the limit start temperatures Tmo (0), Tmo (1), Tmo (2)... Tmo (Nmax), the motor temperature Tm is set to gradually decrease. At the limit start temperatures Tmo (0), Tmo (1), Tmo (2) ·· Tmo (Nmax), Tmo (1) is the largest and decreases in the order of Tmo (2) ·· Tmo (Nmax). , Tmo (0) is minimum. The collision avoidance count value N, which will be described in detail later, represents the number of times the driver has steered the steering wheel 11 in an emergency to avoid a collision with an obstacle, and is initially set to “0”. ing.

  Therefore, when the collision avoidance steering is not performed by the driver, the collision avoidance count value N is set to “0”, and the first maximum allowable current Imax1 is calculated in the calculation of the first maximum allowable current Imax1. Is set to a current value corresponding to the motor temperature Tm in accordance with a characteristic line defined by normal steering (N = 0) in the graph of FIG. Instead of using the first current limit table, a function defining the first maximum allowable current Imax1 that changes according to the motor temperature Tm and the collision avoidance count value N (= 0 to Nmax) is stored in advance. The first maximum allowable current Imax1 corresponding to the motor temperature Tm and the collision avoidance count value N may be calculated by executing a calculation using this function.

  Next, in step S15, the steering assist ECU 30 refers to the second current limit table, and determines the second maximum allowable value according to the input substrate temperature Tb and the collision avoidance count value N (= 0 to Nmax) described above. The current Imax2 is calculated. The second current limit table is provided in the ROM of the steering assist ECU 30, and as shown in FIG. 7, the second current limit table can flow to the electric motor 15 for each collision avoidance count value N (= 0 to Nmax). A second maximum allowable current Imax2 is specified. That is, the second maximum allowable current Imax2 is set to a predetermined large value if the substrate temperature Tb is equal to or lower than the limit start temperatures Tbo (0), Tbo (1), Tbo (2) ·· Tbo (Nmax). When the substrate temperature Tb exceeds the limit start temperatures Tbo (0), Tbo (1), Tbo (2)... Tbo (Nmax), the substrate temperature Tb is set to gradually decrease. Tbo (1) is the maximum at the limit start temperatures Tbo (0), Tbo (1), Tbo (2) ·· Tbo (Nmax), and decreases in the order of Tbo (2) ·· Tbo (Nmax). , Tbo (0) is minimum.

  Therefore, also in this case, when the collision avoidance steering is not performed by the driver, the collision avoidance count N is set to “0”, and the second maximum allowable current Imax2 is calculated in the second maximum allowable current Imax2. The maximum allowable current Imax2 is set to a current value corresponding to the substrate temperature Tb in accordance with a characteristic line defined by normal steering (N = 0) in the graph of FIG. Instead of using the second current limit table, a function defining the second maximum allowable current Imax2 that changes according to the substrate temperature Tb and the collision avoidance count value N (= 0 to Nmax) is stored in advance. The second maximum allowable current Imax2 corresponding to the substrate temperature Tb and the collision avoidance count value N may be calculated by executing a calculation using this function.

  After the process of step S15, the steering assist ECU 30 compares the first maximum allowable current Imax1 and the second maximum allowable current Imax2 in step S16. If the first maximum allowable current Imax1 is less than or equal to the second maximum allowable current Imax2, the maximum allowable current Imax is set to the first maximum allowable current Imax1 and the table flag TBL is set to “1” in step S17. On the other hand, if the first maximum allowable current Imax1 is larger than the second maximum allowable current Imax2, the maximum allowable current Imax is set to the second maximum allowable current Imax2 and the table flag TBL is set to “2” in step S18. To do. The table flag TBL indicates that the first maximum allowable current Imax1 defined by the first current limit table by “1” is adopted as the maximum allowable current Imax, and is defined by the second current limit table by “2”. This indicates that the second maximum allowable current Imax2 is adopted as the maximum allowable current Imax. By the processing of these steps S16 to S18, the maximum allowable current Imax is set to a smaller value of the first maximum allowable current Imax1 and the second maximum allowable current Imax2, and the maximum allowable current Imax is specified. The type of the current limit table currently used is indicated by a table flag TBL.

  After the processing of steps S17 and S18, the steering assist ECU 30 limits the current flowing through the electric motor 15 to the maximum allowable current Imax or less by the processing of steps S19 to S21. That is, if the target assist current Ias * is equal to or less than the maximum allowable current Imax, the target assist current Ias * is set as the target output current Iout * as it is. On the other hand, when the target assist current Ias * is larger than the maximum allowable current Imax, the maximum allowable current Imax is set as the target output current Iout *.

  Next, the steering assist ECU 30 controls the drive circuit 31 so that the target output current Iout * flows through the electric motor 15 in step S22, and temporarily ends the execution of the assist control program in step S23. In the control of the drive circuit 31, a boosted voltage Eout (target boosted voltage Eout *) boosted by the booster circuit 33 and supplied to the drive circuit 31 by boosting control described later is taken into consideration. By driving control of the electric motor 15 according to the target output current Iout *, the electric motor 15 drives the rack bar 14 in the axial direction through the ball screw mechanism 16 with a driving force according to the target output current Iout *. On the other hand, the turning operation of the steering handle 11 by the driver is transmitted to the rack bar 14 via the steering shaft 12 and the pinion gear 13 to drive the rack bar 14 in the axial direction. Thus, when the driver tries to turn the steering handle 11 to steer the left and right front wheels FW1 and FW2, the electric motor 15 assists the driver in turning the steering handle 11.

  With such steering assist control, the target output current Iout * (target assist current Ias *) increases as the steering torque Tr increases, so that the driver can steer the left and right front wheels FW1, FW2 with a small steering force. . Further, as the vehicle speed V decreases, the target output current Iout * (target assist current Ias *) increases, so that the running stability of the vehicle during high speed running is maintained well, and the vehicle turning performance during low speed running is maintained. Will also be good. Further, the current flowing through the electric motor 15 is defined by the target output current Iout *, and the target output current Iout * is limited according to the motor temperature Tm and the substrate temperature Tb. Therefore, the electric motor 15, the steering assist ECU 30, An abnormality due to overheating does not occur in the drive circuit 31, the booster circuit 33, and the like.

  In parallel with the execution of the assist control program, the steering assist ECU 30 repeatedly executes the boost control program of FIG. 3 every predetermined short time. This step-up control program is started in step S30, and the steering assist ECU 30 inputs the input power supply voltage Ein supplied from the battery 32 to the step-up circuit 33 in step S31 and the steering detected by the steering angle sensor 21. Enter the angle θ. The input power supply voltage Ein is A / D converted by an A / D converter in the steering assist ECU.

  Next, the steering assist ECU 30 calculates the steering speed ω by time-differentiating the steering angle θ in step S32. If the calculated steering speed ω is less than the predetermined steering speed ω1, the high speed steering flag FSF is set to “0”, and if the steering speed ω is equal to or higher than the predetermined steering speed ω1, the processing proceeds to steps S33 to S35. The steering flag FSF is set to “1”. Next, the determination process of steps S36 and S37 is executed. The determination process of step S36 determines whether or not the steering handle 11 is in a collision avoidance steering state for avoiding a collision with an obstacle by the current collision avoidance steering flag KSFnew. The current collision avoidance steering flag KSFnew is set to “1” or “0” by the execution of a collision avoidance steering determination program, which will be described later. "" Indicates that it is in any other state. The determination process in step S37 is to determine whether the steering handle 11 is in a high-speed steering state based on the set high-speed steering flag FSF.

  If the current collision avoidance steering flag KSFnew and the high speed steering flag FSF are both “0” and the steering handle 11 is in the normal steering state, it is determined as “No” in steps S36 and S37, and the process proceeds to step S38. The target boost voltage Eout * corresponding to the input power supply voltage Ein is calculated with reference to the first target boost table (solid line in FIG. 8) defining the target boost voltage Eout * with respect to the input power supply voltage Ein during normal steering. If the collision avoidance steering flag KSFnew and the high speed steering flag FSF are “0” and “1” respectively and the steering handle 11 is in the high speed steering state at this time, “No” and “Yes” are determined in steps S36 and S37, respectively. In step S39, the second target boosting table (broken line in FIG. 8) defining the target boosted voltage Eout * with respect to the input power supply voltage Ein at the time of high speed steering is referred to, and the target boosted voltage according to the input power supply voltage Ein. Eout * is calculated.

  If the collision avoidance steering flag KSFnew is “1” this time and the steering handle 11 is in the collision avoidance steering state, “Yes” is determined in step S36, and in step S40, the input power supply voltage during the collision avoidance steering is determined. A target boost voltage Eout * corresponding to the input power supply voltage Ein is calculated with reference to a third target boost table (one-dot chain line in FIG. 8) defining the target boost voltage Eout * with respect to Ein. Instead of using these first to third target boost tables, a function defining each target boost voltage Eout * that changes according to the input power supply voltage Ein is stored in advance, and this function is used. The target boost voltage Eout * corresponding to the input power supply voltage Ein may be calculated by executing the calculation.

  After the processes of steps S38 to S40, the steering assist ECU 30 calculates the boost ratio Ep (= Eout * / Ein) by dividing the calculated target boost voltage Eout * by the input power supply voltage Ein in step S41. To do. Then, the steering assist ECU 30 controls the boost ratio in the boost circuit 33 to the calculated boost ratio Ep in step S42, and once ends the boost control program in step S43. When the input power supply voltage Ein is equal to or lower than a predetermined small voltage Eo (see FIG. 8), both the target boost voltage Eout * and the boost ratio Ep are “0”. In this case, the boost control of the booster circuit 33 is performed. Not done.

  In such boost control, the boost ratio Ep increases in the order of the normal steering state, the high speed steering state, and the collision avoidance steering state of the steering handle 11, and the output power supply voltage supplied from the booster circuit 33 to the drive circuit 31 is in this order. Get higher. Therefore, it is possible to cope with an increase in the amount of current that flows to the electric motor 15 during high-speed steering of the steering handle 11 and during collision avoidance steering.

  Further, in parallel with the execution of the assist control program and the boost control program as described above, the steering assist ECU 30 executes the collision avoidance determination program of FIG. 4 every predetermined short time. The execution of the collision avoidance program is started in step S50, and the steering assist ECU 30 in step S51, the steering angle θ detected by the steering angle sensor 21, the steering torque Tr detected by the steering torque sensor 22, and the calculation. Motor temperature Tm detected, substrate temperature Tb detected by the substrate temperature sensor 24, vehicle speed V detected by the vehicle speed sensor 25, distance to the front obstacle calculated by the peripheral monitoring ECU 41 and the center of the front obstacle Enter the yaw angle deviation for the line. In step S52, it is determined whether the driver is performing a collision avoidance steering operation for avoiding a collision with the front obstacle based on the detection of the front obstacle and the steering operation status of the steering wheel.

  In determining the collision avoidance steering operation, first, the following determination elements are calculated. That is, the steering assist ECU 30 calculates the relative speed of the front obstacle with respect to the host vehicle by differentiating the distance to the front obstacle inputted from the surrounding monitoring ECU 41 with respect to time, and automatically calculates from the relative speed and the distance to the front obstacle. Calculate the collision margin time until the vehicle collides with an obstacle ahead. Further, the predicted course of the host vehicle is estimated using the input steering angle θ and the vehicle speed V, and the predicted path, the distance to the front obstacle, and the yaw angle deviation amount of the front obstacle are used to A lateral deviation amount of the obstacle with respect to the predicted course of the vehicle is calculated. In view of the fact that the lateral deviation amount increases during collision avoidance steering of the steering handle 11 by the driver, the lateral deviation amount is time-differentiated to calculate the rate of change of the lateral deviation amount. Further, in view of the fact that the driver steers the steering handle 11 suddenly during collision avoidance steering, the driver calculates the differential values of the steering speed ω and the steering torque Tr by differentially calculating the input steering angle θ and the steering torque Tr. calculate.

  In step S52, the steering assist ECU 30 determines that the steering operation of the steering handle 11 by the driver is collision avoidance steering for avoiding a collision with a front obstacle based on the calculation result. . For example, when the calculated predicted collision time and the lateral deviation amount are each less than a predetermined value, and the calculated change rate of the lateral deviation amount, the steering speed ω, and the differential values of the steering torque Tr are each greater than or equal to the predetermined value, the driver Thus, it is determined that the steering handle 11 has been subjected to collision avoidance steering. Note that all these determination elements may not be satisfied at the same time, but may be determined that the collision avoidance steering is present when some of the conditions are satisfied. Further, the collision avoidance steering may be determined by omitting some of all the determination elements. In step S52, when the collision avoidance steering determination is made, the current collision avoidance steering flag KSFnew is set to “1”, and when the collision avoidance steering determination is not made, the current collision avoidance steering is performed. The steering flag KSFnew is set to “0”.

  After step S52, the steering assist ECU 30 determines in step S53 whether the current collision avoidance steering flag KSFnew is “1”. If collision avoidance steering is not determined and the current collision avoidance steering flag KSFnew is “0”, “No” is determined in step S53, and the process proceeds to steps S54 to S57. In step S54, it is determined whether or not the table flag TBL set by the process of step S17 in FIG. 2 is “1”. If the table flag TBL is “1”, the determination process of step S55 is executed. To do. If the table flag TBL is not “1”, the determination process of step S56 is executed. In this case, the table flag TBL indicates which of the motor temperature Tm and the substrate temperature Tb currently defines the maximum allowable current Imax, and the motor temperature Tm does not currently specify the maximum allowable current Imax. In this case, the determination process in step S55 is executed. On the other hand, if the substrate temperature Tb currently defines the maximum allowable current Imax, the determination process of step S56 is executed.

  In step S55, it is determined whether or not the input motor temperature Tm is lower than the limit start temperature Tmo (N) in FIG. In step S56, it is determined whether the input substrate temperature Tb is lower than the limit start temperature Tbo (N) in FIG. In this case, the variable “N” is the aforementioned collision avoidance count value. If the collision avoidance steering is not performed, the motor temperature Tm is less than the limit start temperature Tmo (N), or the substrate temperature Tb is less than the limit start temperature Tbo (N), and “Yes” is determined in step S55 or S56. In step S57, the collision avoidance count value N is cleared to “0”. If “No” is determined in step S55 or S56, the execution of the collision avoidance steering determination program is temporarily ended in step S66 after the process of step S65. In step S65, the previous collision avoidance steering flag KSFold representing the previous steering state is set to a value indicated by the current collision avoidance steering flag KSFnew in order to use the current steering state when the next collision avoidance steering determination program is executed. Keep it.

  On the other hand, when the steering handle 11 is subjected to collision avoidance steering and the current collision avoidance steering flag KSFnew is set to “1” in step S52 in order to avoid a collision with a front obstacle, the steering assist ECU 30 is set to step S53. It determines with "Yes" and progresses to step S58. In step S58, it is determined whether or not the previous collision avoidance steering flag KSFold is “0”. The determination process in step S58 is performed together with the determination process in step S53 to determine whether the collision avoidance steering of the steering handle 11 is continuing or newly started. That is, when the collision avoidance steering of the steering handle 11 is newly started, the current collision avoidance steering flag KSFnew is “1” and the previous collision avoidance steering flag KSFold is “0”. In S58, it is determined as “Yes”, and the determination processing in steps S59 to S61 is executed. When the collision avoidance steering is continuing, since the current collision avoidance steering flag KSFnew and the previous collision avoidance steering flag KSFold are both “1”, it is determined “No” in step S58, and the program is executed. The process proceeds to step S65.

  In the determination process in step S59, as in the determination process in step S54, the table flag TBL determines which of the motor temperature Tm and the substrate temperature Tb currently defines the maximum allowable current Imax. . If the motor temperature Tm defines the maximum allowable current Imax and the table flag TBL is “1”, “Yes” is determined in step S59, and the determination process of step S60 is executed. On the other hand, if the substrate temperature Tb defines the maximum allowable current Imax and the table flag TBL is “2”, “No” is determined in step S59, and the determination process of step S61 is executed. In step S60, it is determined whether the motor temperature Tm is equal to or higher than the limit start temperature Tmo (N). In step S61, it is determined whether the substrate temperature Tb is equal to or higher than the limit start temperature Tbo (N). If the motor temperature Tm is less than the limit start temperature Tmo (N) or the substrate temperature Tb is less than the limit start temperature Tbo (N), “No” is determined in step S60 or S61, and the above-described step S65 is performed. In step S66, the execution of this collision avoidance steering determination program is terminated. Therefore, in this case, the steering assist control described above continues.

  However, if the motor temperature Tm is equal to or higher than the limit start temperature Tmo (N) or the substrate temperature Tb is equal to or higher than the limit start temperature Tbo (N), the steering assist ECU 30 determines “Yes” in step S60 or S61. In step S62, “1” is added to the collision avoidance count value N. Then, “No” is determined in step S63 on condition that the collision avoidance count value N is equal to or less than the predetermined maximum value Nmax, and after execution of step S65, the collision avoidance steering determination program is executed in step S66. Exit.

  The collision avoidance count value N is increased when the first and second maximum allowable currents Imax1 and Imax2 are determined according to the motor temperature Tm and the substrate temperature Tb by the processing of steps S14 and S15 of the assist control program of FIG. It means switching of the characteristics of the first and second current limit tables used. Specifically, when the collision avoidance count value N changes from “0” to “1”, the characteristics of the maximum allowable current Imax (that is, the first and second maximum allowable currents Imax1, Imax2) are The characteristic line of N = 0) is switched to that according to the characteristic line at the time of initial collision avoidance steering (N = 1) (see FIGS. 6 and 7). As a result, the maximum allowable current Imax to the electric motor 15 is greatly relaxed, and a large rotational torque can be generated in the electric motor 15, so that the driver can steer the steering handle 11 easily. Makes it easier to avoid colliding with a forward obstacle.

  To further explain this point, when the steering handle 11 is steered rapidly in order to avoid a collision with a front obstacle, the target assist current Ias * is set to a large value as the steering torque Tr increases, and the motor is electrically operated. As a result of a large current flowing through the motor 15, the motor temperature Tm and the substrate temperature Tb rise. If the motor temperature Tm is less than the limit start temperature Tmo (N) or the substrate temperature Tb is less than the limit start temperature Tbo (N) due to the increase in the motor temperature Tm and the substrate temperature Tb, the process of step S62 is performed. Since this is not executed, the collision avoidance count value N does not increase, the characteristic line of the maximum allowable current Imax is not switched, and the maximum allowable current Imax is not relaxed. However, when the motor temperature Tm becomes equal to or higher than the limit start temperature Tmo (N) or the substrate temperature Tb becomes equal to or higher than the limit start temperature Tbo (N), the target assist current Ias *, that is, the current that needs to flow through the electric motor 15 is increased. When the limitation occurs, the collision avoidance count value N increases, the characteristic line of the maximum allowable current Imax is switched, and the maximum allowable current Imax is relaxed. Therefore, the driver can easily steer the steering handle 11, and it is easy to avoid the vehicle from colliding with an obstacle. On the other hand, the relaxation of the maximum allowable current Imax does not allow the current flowing through the electric motor 15 to be unlimitedly large, so that extreme overheating of the electric motor 15, the steering assist ECU 30, the drive circuit 31, the booster circuit 33, etc. is avoided. Thus, the electric motor 15, the steering assist ECU 30, the drive circuit 31, the booster circuit 33, and the like do not become abnormal due to overheating.

  In the state where the emergency collision avoidance steering is continued, “Yes” is determined in step S53 as described above, but “No” is determined in step S58. Therefore, steps S59 to S63 are performed. The collision avoidance count value N is not increased. On the other hand, once the emergency collision avoidance steering is finished, the current collision avoidance steering flag KSFnew is set to “1” in step S52. As a result of the determination of “No” in step S53, the program executes steps S54 to S54. The process proceeds to S57. In this case, as described above, if the motor temperature Tm is equal to or higher than the limit start temperature Tmo (N) or the substrate temperature Tb is equal to or higher than the limit start temperature Tbo (N), “No” is set in step S55 or S56. Thus, the collision avoidance count value N is maintained at the previous value. However, if the collision between the host vehicle and the front obstacle is avoided by the emergency collision avoidance steering and the steering handle 11 is not subjected to collision avoidance steering for a while, the motor temperature Tm and the substrate temperature Tb are The motor temperature Tm falls below the limit start temperature Tmo (N), or the substrate temperature Tb falls below the limit start temperature Tbo (N). In this case, the collision avoidance count value N in step S55. Is cleared to "0".

  In the collision avoidance steering described above, when the collision between the host vehicle and the front obstacle cannot be avoided, the driver performs the collision avoidance steering again on the steering handle 11. In this case, the collision avoidance count value N is not yet cleared to “0”. The collision avoidance steering again is detected by the processes of steps S52, S53, and S58, and the motor temperature Tm is equal to or higher than the limit start temperature Tmo (N), or the substrate temperature Tb is equal to or higher than the limit start temperature Tbo (N). As a result, the collision avoidance count value N increases until reaching the maximum value Nmax by the processing of steps S62 and S63. Therefore, the maximum allowable current Imax for the electric motor 15 is sequentially switched from the characteristic line at the first collision avoidance steering (N = 1) to the left characteristic line in FIGS. As a result, in this case, the maximum allowable current Imax of the electric motor 15 is reduced as compared with that during normal steering, but is switched to a side that is more severely limited than during previous collision avoidance steering.

  That is, when the limit of the maximum allowable current Imax for the electric motor 15 is already relaxed compared to that during normal steering by one collision avoidance steering, and when the collision avoidance steering is performed once or a plurality of times, The maximum allowable current Imax for the electric motor 15 is relaxed under the severer limit conditions than the already relaxed limit conditions. Therefore, even when a collision avoidance steering is performed again without an obstacle being avoided by one collision avoidance steering, the current flowing through the electric motor 15 is not greatly reduced, and the electric motor 15, Excessive overheating of the steering assist ECU, the drive circuit 31, the booster circuit 33, and the like is appropriately prevented.

  Even after the collision avoidance count value N continues to increase, the emergency collision avoidance steering is temporarily terminated and the motor temperature Tm becomes lower than the limit start temperature Tmo (N), or the substrate temperature Tb starts to be limited. If the temperature is lower than Tbo (N), the collision avoidance count value N is cleared to “0” by the processing of steps S52 to S57. However, when emergency collision avoidance steering is repeatedly performed and the collision avoidance count value N increases and exceeds the maximum value Nmax by the processes of steps S52, S53, and S58 to S62, "Yes" is determined in step S63. Determine and proceed to step S64. In step S64, the steering assist ECU 30 outputs a travel restriction instruction to the engine control ECU 42 and the brake control ECU 43.

  The engine control ECU 42 controls the output of the engine device 45 to reduce the engine output by the engine device 45 in order to reduce the driving force on the vehicle. The brake control ECU 43 controls the brake device 46 to operate the brake device 46 in order to generate a braking force for the vehicle. In this case, the characteristic of the maximum allowable current Imax for the electric motor 15 cannot be switched any more. Note that only one of the travel restrictions by the engine control ECU 42 and the brake control ECU 43 may be performed.

  As described above, in the case where the driver cannot avoid the collision with the front obstacle even though the steering handle 11 has been subjected to the collision avoidance steering many times, the vehicle travel is restricted when the collision avoidance steering is performed again. Is done. In this case, since the maximum allowable current Imax for the electric motor 15 is not further reduced, overheating of the electric motor 15, the steering assist ECU 30, the drive circuit 31, the booster circuit 33, etc. can be avoided, and the electric motor 15 The occurrence of abnormalities due to overheating of the steering assist ECU 30, the drive circuit 31, the booster circuit 33, and the like is reliably avoided.

  Furthermore, the present invention is not limited to the above-described embodiment and its modifications, and various modifications can be employed within the scope of the object of the present invention.

  For example, in the above embodiment, the current flowing through the electric motor 15 is limited according to the estimated motor temperature Tm and the substrate temperature Tb. However, the current flowing through the electric motor 15 may be limited according to only one of the motor temperature Tm and the substrate temperature Tb. In this case, in the assist control program of FIG. 2, one of the processes of step S14 or S15 is omitted, and the process of step S16 is also omitted, and the maximum allowable current Imax is set by one of the processes of step S17 or S18. You can do it. Also, in the collision avoidance steering determination program of FIG. 4, the processing in steps S54 and S59 may be omitted, and one of steps S55 and S56 and one of steps S60 and S61 may be omitted.

  Further, instead of or in addition to the motor temperature Tm and the substrate temperature Tb, the current flowing through the electric motor 15 may be limited depending on the temperature of the circuit device for controlling the electric motor 15. That is, the current flowing through the electric motor 15 may be limited according to the temperature of the power transistor as the circuit element constituting the drive circuit 31, the boosting coil as the circuit element constituting the booster circuit 33, and the power transistor. In this case, a maximum allowable current table that is formed in the same manner as the first and second maximum allowable current tables of FIGS. 6 and 7 and that defines the maximum allowable current according to the temperature of these circuit elements is prepared. The temperature of these circuit elements is detected, and in the assist control program of FIG. 2, the maximum allowable current corresponding to the temperature of these circuit elements is calculated by the same processing as in steps S14 and S15. Then, by the same processing as in steps S16 to S18, the smallest maximum allowable current among the calculated maximum allowable currents is set as the maximum allowable current Imax, and a variable represented by the adopted maximum allowable table is set. . In the collision avoidance steering determination program shown in FIG. 4, the limit start temperature of the maximum allowable current table defined by the variable represented by the adopted maximum allowable current table is obtained by the same processing as steps S54 to S56 and steps S59 to S61. The clearing and counting up of the collision avoidance count value N may be controlled by comparing with the detected temperature related to the maximum allowable current table.

1 is an overall schematic diagram of a vehicle steering apparatus according to an embodiment of the present invention. It is a flowchart which shows the assist control program performed by steering assist ECU of FIG. It is a flowchart which shows the pressure | voltage rise control program performed by steering assist ECU of FIG. It is a flowchart which shows the collision avoidance steering determination program performed by steering assist ECU of FIG. 2 is a graph showing the relationship between steering torque, vehicle speed, and target assist current stored in a target assist current table provided in the steering assist ECU of FIG. 1. 3 is a graph showing a relationship between a motor temperature and a maximum allowable current stored in a first current limit table provided in the steering assist ECU of FIG. 1. 3 is a graph showing a relationship between a substrate temperature and a maximum allowable current stored in a second current limit table provided in the steering assist ECU of FIG. 1. 4 is a graph showing a relationship between an input power supply voltage and a target boosted voltage stored in first to third target boosting tables provided in the steering assist ECU of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Steering handle, 12 ... Steering shaft, 13 ... Pinion gear, 14 ... Rack bar, 15 ... Electric motor, 21 ... Steering angle sensor, 22 ... Steering torque sensor, 25 ... Vehicle speed sensor, 30 ... Steering assist ECU, 31 ... Drive Circuit, 41 ... Perimeter monitoring ECU, 42 ... Perimeter monitoring sensor, 42 ... Engine control ECU, 43 ... Brake control ECU

Claims (6)

An electric motor for assisting the steering operation of the steering wheel;
Target assist current determining means for determining a target assist current to flow to the electric motor in accordance with a driving state of the vehicle;
Current limiting means for limiting the magnitude of the determined target assist current for overheating protection of the electric motor or a circuit device for controlling the electric motor;
In a vehicle steering assist device, comprising: a drive control unit configured to drive and control the electric motor by causing a target assist current limited by the current limiting unit to flow through the electric motor;
Collision avoidance steering determination means for determining collision avoidance steering by a driver for avoiding a collision with an obstacle based on a differential value of a steering speed or a differential value of a steering torque ;
A vehicle steering assist device, comprising: a restriction mitigation unit for mitigating a restriction condition of a magnitude of a target assist current by the current limiting unit when collision avoidance steering is determined by the collision avoidance steering determination unit. The collision avoidance steering determination means is
Having obstacle detection means for detecting a front obstacle,
2. The vehicle according to claim 1 , wherein the collision avoidance steering is determined on the condition that a front obstacle is detected by the obstacle detection unit and a differential value of the steering speed or a differential value of the steering torque is equal to or greater than a predetermined value. Steering assist device. The current limiting means includes
Temperature detecting means for detecting the temperature of the electric motor or a circuit device for controlling the electric motor;
The vehicle steering assist device according to claim 1, wherein the target assist current is limited to be smaller as the detected temperature becomes higher.   The restriction mitigation means, when the restriction condition of the target assist current magnitude is already relaxed and the collision avoidance steering determination means further determines the collision avoidance steering, the already relaxed restriction The vehicle steering assist device according to any one of claims 1 to 3, wherein the restriction condition of the magnitude of the target assist current is relaxed under a restriction condition that is stricter than the condition. The vehicle steering assist device according to any one of claims 1 to 4, wherein when the number of times that the collision avoidance steering is determined by the collision avoidance steering determination means is a predetermined number or more, the vehicle travels. A steering assist device for a vehicle, characterized in that a travel limiting means for limiting is provided.   The vehicle steering assist device according to claim 5, wherein the travel restriction unit brakes the vehicle or reduces a driving force of the vehicle.

Images