JP2009278770A - Vehicle and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of slips at front wheels and rear wheels even if improving traveling performance upon the instruction of low-friction coefficient road-surface traveling, in a vehicle equipped with a motor for the front wheels and a motor for the rear wheels. <P>SOLUTION: When rear-wheel distribution torque Tra generated when required torque T* is distributed according to load distribution exceeds a limit which is set by the rated maximum torque Tm2max of the motor for the rear wheels (S140), torque obtained by summing the torque exceeding the limit and front-wheel distribution torque Tfa is set as front wheel required torque Tf* in a range of the limit set by the rated maximum torque Tm1max of the motor for the front wheels (S190 to S210), and when low-μ road traveling is instructed (S220), torque limited by upper-limit torque based on an estimated friction coefficient μ* smaller than a friction coefficient which is estimated on a normal traveling road surface and a road surface gradient θ is outputted to the front and rear wheels (S240 to S310). By this, even if a larger amount of the required torque T* is distributed to the front wheel side and the rear wheel side, the occurrence of the slips of the front and rear wheels can be suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle and a control method therefor, and more specifically, a front wheel motor that outputs power to a front wheel, a rear wheel motor that outputs power to a rear wheel having a smaller rated maximum torque than the front wheel motor, and a front wheel motor. Further, the present invention relates to a vehicle including a power storage means for exchanging electric power with a rear wheel motor.

Conventionally, this type of vehicle has been proposed that includes an electric motor as a power source for traveling, a power storage device that supplies electric power to the electric motor, and a snow switch that instructs low-μ road traveling. (For example, refer to Patent Document 1). In this vehicle, when the snow switch is turned on, slip is prevented by traction control that limits the torque output from the electric motor.
JP-A-10-94110

  In vehicles equipped with two motors for front wheels and rear wheels as driving power sources, motors with different ratings can be used according to the characteristics of the vehicle, but each torque output from the two motors is rated. If it is limited by, the torque required for running may not be sufficiently output. Further, even in a vehicle equipped with these two traveling motors, when starting traveling on an uphill road, when a low μ road traveling is instructed as in the above-described vehicle, control is performed so that slip does not occur. Is desired.

  The vehicle according to the present invention and the control method thereof include a front wheel motor and a rear wheel motor, and slip occurs on the front wheels and the rear wheels even when the traveling performance is improved when low-friction coefficient road traveling is instructed. The main purpose is to suppress this.

  The vehicle and the control method thereof according to the present invention employ the following means in order to achieve at least the above-described main object.

The vehicle of the present invention
Electric power is exchanged between the front wheel motor that outputs power to the front wheels, the rear wheel motor that outputs power to the rear wheels with a rated maximum torque smaller than that of the front wheel motor, and the front wheel motor and the rear wheel motor. A vehicle comprising power storage means,
Road surface gradient acquisition means for acquiring a road surface gradient;
Instructing means for instructing low-friction-coefficient road running on a road surface having a small friction coefficient,
When the required driving force required for traveling is distributed according to the load on the front wheels and the rear wheels, the front wheel distributed driving force distributed to the front wheels is within the range of restriction by the rated maximum torque of the front wheel motor and When the rear wheel distribution driving force distributed to the rear wheels is within the limit of the rated maximum torque of the rear wheel motor, the front wheel distribution driving force and the rear wheel distribution driving force are required before the front wheels are requested. A wheel required driving force and a rear wheel required driving force required for the rear wheel, the front wheel distributing driving force is within a limit range by the rated maximum torque of the front wheel motor, and the rear wheel distributing driving force is When the rear wheel motor is out of the range limited by the rated maximum torque of the rear wheel motor, the driving force exceeding the driving force corresponding to the rated maximum torque of the rear wheel motor and the front of the rear wheel distribution driving force A driving force that is the sum of the front wheel distribution driving force is set as the required front wheel driving force within a range limited by the rated maximum torque of the front wheel motor, and a driving force corresponding to the rated maximum torque of the rear wheel motor is A required driving force setting means for setting the rear wheel required driving force;
When the low friction coefficient road traveling is not instructed, the set front wheel required driving force and rear wheel required driving force are set as a front wheel execution driving force and a rear wheel execution driving force, and the low friction coefficient road traveling is performed. When instructed, the low friction coefficient When the road surface is not instructed, the front wheel and the rear wheel are idled based on a predetermined estimated friction coefficient smaller than the road surface friction coefficient estimated when not instructed and the acquired road surface gradient. The front wheel execution driving force and the driving force for limiting the front wheel required driving force and the rear wheel required driving force set by the upper limit driving force of each of the front wheels and the rear wheels to prevent slippage due to An execution driving force setting means for setting as the rear wheel execution driving force;
Control means for controlling the electric motor for the front wheels and the electric motor for the rear wheels so that the set driving force for executing the front wheels and the driving force for executing the rear wheels are output to the front wheels and the rear wheels to travel.
It is a summary to provide.

  In the vehicle of the present invention, when the required driving force required for traveling is distributed according to the load on the front wheels and the rear wheels, the front wheel distributed driving force distributed to the front wheels is limited by the rated maximum torque of the front wheel motor. Front wheel required drive that requires the front wheel distributed drive force and the rear wheel distributed drive force for the front wheels when the rear wheel distributed drive force that is inward and distributed to the rear wheels is within the limit of the rated maximum torque of the rear wheel motor. This is set as the required rear wheel driving force required for the power and the rear wheel, the front wheel distributed driving force is within the limits of the rated maximum torque of the front wheel motor, and the rear wheel distributed driving force is the rated maximum torque of the rear wheel motor. Of the rear wheel distribution driving force, the sum of the driving force that exceeds the driving force corresponding to the rated maximum torque of the rear wheel motor and the front wheel distribution driving force of the rear wheel distribution driving force Setting the driving force corresponding to the rated maximum torque of the rear wheel electric motor and sets the required front wheel driving force within the limits according to rated maximum torque as required rear wheel driving force. As a result, more of the required driving force can be distributed to the front wheel side and the rear wheel side within the range of the rated maximum torque of each of the front wheel motor and the rear wheel motor. Then, when the low friction coefficient road traveling on the road surface having a small friction coefficient is not instructed, the set front wheel required driving force and rear wheel required driving force are set as the front wheel executing driving force and the rear wheel executing driving force. When the low friction coefficient road surface driving is instructed, the front wheel and the rear wheel are idled based on a predetermined estimated friction coefficient smaller than the road surface friction coefficient estimated when the low friction coefficient road surface driving is not instructed and the road surface gradient. The front wheel required drive force and the rear wheel required drive force that are set by the upper limit drive force of each of the front and rear wheels to prevent slippage due to the front wheel execution drive force and the rear wheel execution Set as driving force, and control the front wheel motor and rear wheel motor so that the set front wheel driving force and rear wheel driving force are output to the front and rear wheels That. Thereby, it can suppress that a slip generate | occur | produces on a front wheel and a rear wheel. As a result, it is possible to improve running performance such as startability when low friction coefficient road running is instructed, and to suppress occurrence of slip on the front wheels and the rear wheels.

  In such a vehicle according to the present invention, the execution driving force setting means is configured to perform the front wheel execution when slipping due to idling occurs in at least one of the front wheel and the rear wheel when the low friction coefficient road surface traveling is instructed. A means for setting the front wheel execution driving force and the rear wheel execution driving force so that at least the execution driving force on the wheel side where slip occurs is reduced among the driving force and the rear wheel execution driving force. It can also be. By so doing, it is possible to suppress the slip generated on the front wheel and the rear wheel. In this case, the execution driving force setting means is configured to cause the front wheel execution driving force and the at least one of the front wheels and the rear wheels to slip when slippage occurs due to slipping when at least one of the front wheels and the rear wheels is instructed. A means for setting at least the wheel-side execution driving force on the side where slip occurs in the rear-wheel execution driving force using a friction coefficient smaller than the predetermined estimated friction coefficient instead of the predetermined estimated friction coefficient It can also be. By so doing, it is possible to more reliably suppress the slip generated on the front wheel and the rear wheel.

  In the vehicle of the present invention, the execution driving force setting means may be configured such that, when the low friction coefficient road surface traveling is instructed, the road surface friction coefficient, the road surface gradient, and the upper limit driving force of each of the front wheels and the rear wheels. The upper limit driving force of each of the front wheel and the rear wheel is set based on the predetermined estimated friction coefficient and the acquired road gradient using the relationship between the upper limit driving force and the set upper limit driving force. The front wheel execution driving force and the rear wheel execution driving force may be set. In this way, the upper limit driving force for each of the front wheels and the rear wheels can be set more reliably.

  Further, in the vehicle of the present invention, three axes of an internal combustion engine, a generator for inputting / outputting power, a drive shaft connected to the front wheel axle, an output shaft of the internal combustion engine, and a rotating shaft of the generator. And a three-axis power input / output means for inputting / outputting power to / from the remaining shafts based on power input / output to / from any two of the three shafts. It can also be connected to the drive shaft.

The vehicle control method of the present invention includes:
Electric power is exchanged between the front wheel motor that outputs power to the front wheels, the rear wheel motor that outputs power to the rear wheels with a rated maximum torque smaller than that of the front wheel motor, and the front wheel motor and the rear wheel motor. A vehicle control method comprising:
When the required driving force required for traveling is distributed according to the load on the front wheels and the rear wheels, the front wheel distributed driving force distributed to the front wheels is within the range of restriction by the rated maximum torque of the front wheel motor and When the rear wheel distribution driving force distributed to the rear wheels is within the limit of the rated maximum torque of the rear wheel motor, the front wheel distribution driving force and the rear wheel distribution driving force are required before the front wheels are requested. A wheel required driving force and a rear wheel required driving force required for the rear wheel, the front wheel distributing driving force is within a limit range by the rated maximum torque of the front wheel motor, and the rear wheel distributing driving force is When the rear wheel motor is out of the range limited by the rated maximum torque of the rear wheel motor, the driving force exceeding the driving force corresponding to the rated maximum torque of the rear wheel motor and the front of the rear wheel distribution driving force A driving force that is the sum of the front wheel distribution driving force is set as the required front wheel driving force within a range limited by the rated maximum torque of the front wheel motor, and a driving force corresponding to the rated maximum torque of the rear wheel motor is Set as the rear wheel required driving force,
When the low friction coefficient road traveling that travels on the road surface with a small friction coefficient is not instructed, the set front wheel required driving force and the rear wheel required driving force are set as the front wheel executing driving force and the rear wheel executing driving force, When the low friction coefficient road surface traveling is instructed, the front wheel and the rear wheel based on a predetermined estimated friction coefficient and a road surface gradient smaller than the road surface friction coefficient estimated when the low friction coefficient road surface traveling is not instructed. A driving force for limiting the set front wheel required driving force and the rear wheel required driving force by the upper limit driving force of each of the front wheel and the rear wheel for preventing slippage due to idling in the wheel is for executing the front wheel. Set as driving force and driving force for executing the rear wheel,
Controlling the front-wheel motor and the rear-wheel motor so that the set front-wheel execution driving force and rear-wheel execution driving force are output to the front wheels and the rear wheels to travel.
It is characterized by that.

  In the vehicle control method according to the present invention, when the required driving force required for traveling is distributed according to the load on the front wheels and the rear wheels, the front wheel distributed driving force distributed to the front wheels depends on the rated maximum torque of the front wheel motor. When the rear wheel distribution driving force distributed to the rear wheels is within the limitation range based on the rated maximum torque of the rear wheel motor, the front wheel distribution driving force and the rear wheel distribution driving force are required for the front wheels. The front wheel required driving force and the rear wheel required driving force required for the rear wheel are set so that the front wheel distributed driving force is within the limits of the rated maximum torque of the front wheel motor and the rear wheel distributed driving force is equal to that of the rear wheel motor. When it is out of the range of the limit by the rated maximum torque, the driving force that is the sum of the driving force that exceeds the driving force corresponding to the rated maximum torque of the rear wheel motor and the front wheel distributing driving force out of the rear wheel distributing driving force Setting the driving force corresponding to the rated maximum torque of the rear wheel electric motor and sets the required front wheel driving force within the limits according to the rated maximum torque of the motor as required rear wheel driving force. As a result, more of the required driving force can be distributed to the front wheel side and the rear wheel side within the range of the rated maximum torque of each of the front wheel motor and the rear wheel motor. Then, when the low friction coefficient road traveling on the road surface having a small friction coefficient is not instructed, the set front wheel required driving force and rear wheel required driving force are set as the front wheel executing driving force and the rear wheel executing driving force. When the low friction coefficient road surface driving is instructed, the front wheel and the rear wheel are idled based on a predetermined estimated friction coefficient smaller than the road surface friction coefficient estimated when the low friction coefficient road surface driving is not instructed and the road surface gradient. The front wheel required drive force and the rear wheel required drive force that are set by the upper limit drive force of each of the front and rear wheels to prevent slippage due to the front wheel execution drive force and the rear wheel execution Set as driving force, and control the front wheel motor and rear wheel motor so that the set front wheel driving force and rear wheel driving force are output to the front and rear wheels That. Thereby, it can suppress that a slip generate | occur | produces on a front wheel and a rear wheel. As a result, it is possible to improve running performance such as startability when low friction coefficient road running is instructed, and to suppress occurrence of slip on the front wheels and the rear wheels.

  Next, the best mode for carrying out the present invention will be described using examples.

  FIG. 1 is a configuration diagram showing an outline of the configuration of an electric vehicle 20 according to an embodiment of the present invention. As shown in the drawing, the electric vehicle 20 according to the embodiment includes a motor MG1 connected to front wheels 30a and 30b via a differential gear 32 and configured as a known synchronous generator motor, and rear wheels 34a and 34b via a differential gear 36. A motor MG2 configured as a well-known synchronous generator motor and a battery 44 as a secondary battery electrically connected to the motor MG1 and the motor MG2 via inverters 40 and 42 for driving the motors MG1 and MG2. And an electronic control unit 50 for controlling the entire vehicle. Here, a motor having a rated maximum torque that is sufficiently smaller than that of the front wheel motor MG1 is used as the rear wheel motor MG2 in consideration of mountability in a vehicle.

  The electronic control unit 50 is configured as a microprocessor centered on the CPU 52. In addition to the CPU 52, a ROM 54 that stores processing programs, a RAM 56 that temporarily stores data, input / output ports and communication ports (not shown), and the like. Is provided. The electronic control unit 50 is applied to, for example, signals from two rotational position detection sensors (not shown) that detect the rotational positions of the rotors of the motors MG1 and MG2, and motors MG1 and MG2 detected by a current sensor (not shown). Signals necessary for driving and controlling the motors MG1 and MG2, such as phase current, voltage between terminals from a voltage sensor (not shown) installed between terminals of the battery 44, and power line connected to the output terminal of the battery 44 In addition to signals necessary for managing the battery 44, such as a charge / discharge current from a current sensor (not shown) attached to the battery, a battery temperature from a temperature sensor (not shown) attached to the battery 44, an ignition signal from the ignition switch 60 The shift position sensor 62 detects the operation position of the shift lever 61. The shift position SP, the accelerator opening Acc from the accelerator pedal position sensor 64 for detecting the depression amount of the accelerator pedal 63, the brake pedal position BP from the brake pedal position sensor 66 for detecting the depression amount of the brake pedal 65, a vehicle speed sensor The vehicle speed V from 67, the road surface gradient θ from the gradient sensor 68 that detects the road surface gradient in the front-rear direction of the vehicle, and a low μ road that is attached to the installation panel in front of the driver's seat and has a small friction coefficient such as a wet road surface or snowy road. The low μ road switch signal SW from the low μ road switch 69 for instructing the low μ road traveling is input via the input port. Further, the electronic control unit 50 outputs a switching control signal to the inverters 40 and 42. The electronic control unit 50 also calculates the rotational speeds Nm1 and Nm2 of the motors MG1 and MG2 based on a signal from a rotational position detection sensor (not shown).

  Next, the operation of the electric vehicle 20 according to the embodiment thus configured will be described. FIG. 2 is a flowchart showing an example of a drive control routine executed by the electronic control unit 50. This routine is repeatedly executed every predetermined time (for example, every several msec).

  When the drive control routine is executed, first, the CPU 52 of the electronic control unit 50 first determines the accelerator opening Acc from the accelerator pedal position sensor 64, the vehicle speed V from the vehicle speed sensor 67, the road surface gradient θ from the gradient sensor 68, and the low μ. A process of inputting data necessary for control, such as the low μ road switch signal SW from the road switch 69 and the rotation speeds Nm1, Nm2 of the motors MG1, MG2, is executed (step S100). Here, the rotational speeds Nm1 and Nm2 of the motors MG1 and MG2 are input based on the rotational positions of the rotors of the motors MG1 and MG2 detected by a rotational position detection sensor (not shown). In the embodiment, the road surface gradient θ is assumed to be a positive value on an uphill road and a negative value on a downhill road.

  When the data is input in this way, the required torque T * to be output in accordance with the front and rear wheels is set as the torque required for the vehicle based on the input accelerator opening Acc and the vehicle speed V (step S110). In the embodiment, the required torque T * is determined in advance by storing the relationship among the accelerator opening Acc, the vehicle speed V, and the required torque T * in the ROM 54 as a required torque setting map. , The corresponding required torque T * is derived from the stored map and set. FIG. 3 shows an example of the required torque setting map.

  Subsequently, the front wheel distribution distributed to the front wheels 30a, 30b is multiplied by the required torque T * set to the load distribution ratio Kf to the front wheels when the vehicle load is distributed to the front wheels 30a, 30b and the rear wheels 34a, 34b. The torque Tfa is set, and the rear wheel distribution torque Tra distributed to the rear wheels 34a and 34b is set by multiplying the value 1 obtained by subtracting the load distribution ratio Kf to the front wheel side by the required torque T * (step S120). ). Here, in the embodiment, the load distribution ratio Kf to the front wheel side is the distribution to the front wheel side when the weight of one person or two persons in the stopped state is distributed to the front wheel side and the rear wheel side. A ratio previously determined as a ratio and stored in the ROM 54 (for example, 55% or 60%) is used.

  Next, the value obtained by multiplying the rated maximum torque Tm1max of the motor MG1 by the gear ratio Gf of the differential gear 32 so as to be converted into the torque to the front wheels 30a, 30b is compared with the set front wheel distribution torque Tfa (step S130). The rear wheel distribution torque Tra set by multiplying the rated maximum torque Tm2max of the motor MG2 by the gear ratio Gr of the differential gear 36 so as to be converted into the torque to the rear wheels 34a, 34b is compared (step S140). When the torque Tfa is equal to or smaller than the rated maximum torque Tm1max multiplied by the gear ratio Gf and the rear wheel distributed torque Tra is equal to or smaller than the rated maximum torque Tm2max multiplied by the gear Gr, the front wheel distributed torque Tfa is applied to the front wheels 30a and 30b. If the required front wheel required torque Tf * is set as it is, (Step S150), it sets the wheel requested torque Tr * After the required rear wheel distribution torque Tra rear wheels 34a, to 34b (step S160). Here, as the rated maximum torques Tm1max and Tm2max of the motors MG1 and MG2, those set based on a map stored in the ROM 54 in which the relationship between the vehicle speed V and each of the rated maximum torques Tm1max and Tm2max is determined in advance are used. The gear ratios Gf and Gr that are stored in the ROM 54 in advance can also be used. In the embodiment, the rated maximum torque Tm2max of the motor MG2 is sufficiently smaller than the rated maximum torque Tm1max of the motor MG1, and specifically, the gear ratio Gf is equal to the rated maximum torque Tm1max of the motor MG1 in the entire vehicle speed range. The ratio of the product of Tm1max · Gf to the rated maximum torque Tm2max of the motor MG2 and the product of the gear ratio Gr (Tm2max · Gr) is the load distribution ratio Kf to the front wheels and the load to the rear wheels It was assumed that the front and rear wheels differed significantly from the ratio with the distribution ratio (1-Kf) (for example, (Tm1max · Gf) :( Tm2max · Gr) = 7: 3, etc.). Therefore, when the front wheel distribution torque Tfa is larger than the rated maximum torque Tm1max multiplied by the gear ratio Gf in step S130, it can be determined that the rear wheel distribution torque Tra is also larger than the rated maximum torque Tm2max multiplied by the gear Gr. A value obtained by multiplying the rated maximum torque Tm1max by the gear ratio Gf is set as the front wheel required torque Tf * (step S170), and a value obtained by multiplying the rated maximum torque Tm2max by the gear ratio Gr is set as the rear wheel required torque Tr * ( Step S180).

  In steps S130 and S140, when the front wheel distribution torque Tfa is equal to or less than the maximum rated torque Tm1max multiplied by the gear ratio Gf and the rear wheel distribution torque Tra is greater than the maximum rated torque Tm2max multiplied by the gear ratio Gr, this rating A value obtained by multiplying the maximum torque Tm2max by the gear ratio Gr is set as the rear wheel required torque Tr * (step S190), and a value obtained by subtracting the rear wheel required torque Tr * from the rear wheel distributed torque Tra is added to the front wheel distributed torque Tfa. A provisional torque Tftmp, which is a provisional value of torque required for the front wheels 30a and 30b, is calculated by the following equation (1) (step S200), and is calculated by multiplying the rated maximum torque Tm1max of the motor MG1 by the gear ratio Gf. The provisional torque Tftmp is limited by the equation (2) to set the front wheel required torque Tf * ( Step S210). As described above, when the rear wheel distribution torque Tra exceeds the range of the limit by the rated maximum torque Tm2max of the motor MG2, the torque (Tra-Tr *), that is, the torque (Tra-Tm2max ·) exceeding the torque corresponding to the rated maximum torque Tm2max. Gr) and the front wheel distribution torque Tfa are set as the front wheel required torque Tf * within the range limited by the rated maximum torque Tm1max of the motor MG1, so the range of the rated maximum torques Tm1max and Tm2max of the motors MG1 and MG2 Within this, more of the required torque T * can be distributed to the front wheel side and the rear wheel side.

Tftmp = Tfa + (Tra-Tr *) (1)
Tf * = min (Tftmp, Tm1max ・ Gf) (2)

  When the front wheel required torque Tf * and the rear wheel required torque Tr * are thus set, the input low μ road switch signal SW is checked (step S220), and the low μ road switch signal SW is off and no low μ road traveling is instructed. Sometimes, the set front wheel required torque Tf * and the rear wheel required torque Tr * are divided by the gear ratios Gf and Gr, respectively, to set the torque commands Tm1 * and Tm2 * for the motors MG1 and MG2 (step S230). Switching control of the switching elements of the inverters 40 and 42 is performed so that the motors MG1 and MG2 are driven by Tm1 * and Tm2 * (step S310). By such control, when the low μ road running is not instructed, the required torque T * is output to the front wheels 30a, 30b and the rear wheels 34a, 34b within the range limited by the rated maximum torques Tm1max, Tm2max of the motors MG1, MG2. Can drive.

  When the low μ road switch signal SW is on and the low μ road traveling is instructed, it is determined whether or not there is a history of slippage due to idling in the front wheels 30a, 30b or the rear wheels 34a, 34b (step S240). When there is no slip history in the front wheels 30a, 30b and the rear wheels 34a, 34b, the estimated friction coefficient μ * estimated as the friction coefficient of the traveling road surface with respect to the front and rear wheels is set to a value μ1 for low μ road running (step) S250). Here, the slip history is reset to a value of 0 when the ignition is turned on, and is determined using a flag that is set to a value of 1 and stored in the RAM 56 when the occurrence of a slip is subsequently determined. it can. The occurrence of slip is caused by the rotational acceleration ΔNm1, which is obtained by dividing the difference between the rotational speeds Nm1, Nm2 of the motors MG1, MG2 and the rotational speeds Nm1, Nm2 input when the routine was executed last time by the execution interval of the routine. ΔNm2 can be determined by comparing the thresholds ΔNm1ref and ΔNm2ref that determine that the front wheels 30a and 30b and the rear wheels 34a and 34b have slipped from the grip state. Further, in the embodiment, the value μ1 is sufficiently smaller than the value estimated as the friction coefficient of the normal traveling road surface with respect to the front and rear wheels when the low μ road traveling is not instructed, and is estimated on a wet road surface or a snow road. The friction coefficient (for example, the value 0.3 or the value 0.4) is used.

  When the low μ road switch signal SW is on and the low μ road traveling is instructed, if there is a slip history in the front wheels 30a, 30b or the rear wheels 34a, 34b, the front wheels 30a, 30b or the rear wheels 34a, 34b slip. Is determined (step S260). When slip is not occurring, it is determined that the friction coefficient estimated up to the previous time is appropriate and this routine is executed last time. The set estimated friction coefficient μ * (previous μ *) is set to the estimated friction coefficient μ * (step S270). When slip is occurring, it is determined that the friction coefficient estimated up to the previous time is larger than the actual, A value obtained by subtracting the deviation Δμ from the previous μ * is set as the estimated friction coefficient μ * (step S280). Here, the deviation Δμ is determined in advance as a value indicating the degree to which the estimated friction coefficient μ * is reduced and stored in the ROM 54. For example, a value of 0.03 or a value of 0.05 can be used. . Therefore, when a low μ road traveling is instructed, first, a value μ1 is set to the estimated friction coefficient μ *. After that, when slip occurs in the front wheels 30a, 30b or the rear wheels 34a, 34b, until the slip converges. The estimated friction coefficient μ * is set smaller by a deviation Δμ.

  When the estimated friction coefficient μ * is set when the low μ road traveling is instructed in this way, the front wheels 30a, 30b and the rear wheels 34a, based on the input road surface gradient θ and the set estimated friction coefficient μ *. A front wheel upper limit torque Tflim and a rear wheel upper limit torque Trlim are set to prevent slippage due to idling in 34b (step S290). In the embodiment, the front wheel upper limit torque Tflim and the rear wheel upper limit torque Trlim are used for setting the front wheel upper limit torque by previously determining the relationship between the road surface gradient θ, the estimated friction coefficient μ *, and the front wheel upper limit torque Tflim and the rear wheel upper limit torque Trlim. A map and a rear wheel upper limit torque setting map are stored in the ROM 54. When the road surface gradient θ and the estimated friction coefficient μ * are given, the corresponding front wheel upper limit torque Tflim and rear wheel upper limit torque Trlim are derived from the stored maps. And set it. FIG. 4 shows an example of the front wheel upper limit torque setting map with a solid line. FIG. 4 also shows an example of a rear wheel upper limit torque setting map together with a broken line. As shown in the figure, the front wheel upper limit torque Tflim increases when the road surface gradient θ is large and the slope of the uphill road becomes steep, and the front wheel upper limit torque Tflim increases when the estimated friction coefficient μ * increases. Such a tendency can be determined by the following equation (3) obtained from an example of the relationship of balance of forces acting on the vehicle with respect to the road surface gradient shown in FIG. In FIG. 5 and equation (3), the conversion coefficient k1 for converting the vehicle mass mf to the front wheel side by the above-described load distribution, the gravitational acceleration g, and the force acting on the vehicle into the torque acting on the front wheels 30a and 30b, A predetermined constant can be used. Further, the rear wheel upper limit torque Trlim has the same tendency as the front wheel upper limit torque Tflim with respect to the road surface gradient θ and the estimated friction coefficient μ *, and the vehicle mass mf on the front wheel side in Expression (3) is shifted to the rear wheel side. The vehicle mass mr can be determined by replacing the front wheel upper limit torque Tflim in the entire region. This corresponds to the relationship between the load distribution ratio Kf to the front wheel side and the load distribution ratio (1-Kf) to the rear wheel side in the embodiment.

  Tflim = mf ・ g ・ k1 ・ (sinθ + μ * ・ cosθ) (3)

  When the front wheel upper limit torque Tflim and the rear wheel upper limit torque Trlim are thus set, the torque command Tm1 * of the motor MG1 is divided by the gear ratio Gf obtained by dividing the front wheel required torque Tf * by the set front wheel upper limit torque Tflim as follows: ), And a torque command Tm2 * of the motor MG2 is set by the equation (5) by dividing the rear wheel upper limit torque Trlim limited by the rear wheel upper limit torque Trlim by the gear ratio Gr (step S300). Then, switching control of the switching elements of the inverters 40 and 42 is performed so that the motors MG1 and MG2 are driven by the set torque commands Tm1 * and Tm2 * (step S310). With this control, when low μ road traveling is instructed, a torque limited by the upper limit torque based on the estimated friction coefficient μ * set smaller than the friction coefficient estimated on the normal traveling road surface and the road surface gradient θ is applied to the front wheels. 30a and 30b and the rear wheels 34a and 34b, it is possible to suppress slippage due to idling in the front wheels 30a and 30b and the rear wheels 34a and 34b. Travelability can be improved. As a result, the front wheels 30a and 30b and the rear wheels 34a and 34b are slipped even if the driving performance when the low-μ road driving is instructed is improved in the case of having two motors for the front wheels and the rear wheels. Can be suppressed.

Tm1 * = min (Tf *, Tflim) / Gf (4)
Tm2 * = min (Tr *, Trlim) / Gr (5)

  According to the electric vehicle 20 of the embodiment described above, when the rear wheel distribution torque Tra when the required torque T * is distributed according to the load distribution exceeds the limit by the rated maximum torque Tm2max of the rear wheel motor MG2, The front wheel required torque Tf is within the limit of the rated maximum torque Tm1max of the motor MG1 for the front wheel, with the sum of the torque exceeding the torque corresponding to the rated maximum torque Tm2max (Tra-Tm2max · Gr) and the front wheel distribution torque Tfa. Since it is set as *, more of the required torque T * can be distributed to the front wheel side and the rear wheel side within the limits of the rated maximum torques Tm1max and Tm2max of the motors MG1 and MG2. When the low μ road traveling is instructed, the front wheel 30a, the torque limited by the upper limit torque based on the estimated friction coefficient μ * set smaller than the friction coefficient estimated on the normal traveling road surface and the road surface gradient θ is provided. 30b and the rear wheels 34a and 34b, so that slippage due to idling can be suppressed in the front wheels 30a and 30b and the rear wheels 34a and 34b, and the running performance such as startability of the vehicle can be improved. it can.

  In the electric vehicle 20 of the embodiment, when slip occurs on the front wheels 30a, 30b or the rear wheels 34a, 34b when the low-μ road traveling is instructed, the setting is made based on the estimated friction coefficient μ * and the road surface gradient θ. The front wheel upper limit torque Tflim and the rear wheel upper limit torque Trlim are used to limit the front wheel required torque Tr * and the rear wheel required torque Tr * to set the torque commands Tm1 * and Tm2 * of the motors MG1 and MG2. Since the torque output from MG1 and MG2 only needs to be reduced, the front wheel required torque Tr * and the rear wheel required torque Tr * with the front wheel upper limit torque Tflim and the rear wheel upper limit torque Trlim set to be smaller by a predetermined torque than the upper limit torque as the previous value. To set torque commands Tm1 * and Tm2 * for motors MG1 and MG2 There.

  In the electric vehicle 20 of the embodiment, when slip occurs on the front wheels 30a, 30b or the rear wheels 34a, 34b when the low-μ road traveling is instructed, the front wheels are based on the estimated friction coefficient μ * that is uniformly set small. Although the upper limit torque Tflim and the rear wheel upper limit torque Trlim are set, only the upper limit torque on the wheel side where slip occurs is set based on the estimated friction coefficient μ * which is set small, and the wheel where no slip occurs The upper limit torque on the side may be set based on the estimated friction coefficient μ * (previous μ *) as the previous value.

  In the electric vehicle 20 of the embodiment, when slip is generated in the front wheels 30a, 30b or the rear wheels 34a, 34b when the low μ road traveling is instructed, the front wheels 30a, 30b and the rear wheels 34a from the motor MG1 and the motor MG2. , 34b is limited, but the value μ1 for low μ road travel used as the initial value of the estimated friction coefficient μ * set when low μ road travel is instructed is a sufficiently small value. Even if slip occurs, the torque output to the front wheels 30a, 30b and the rear wheels 34a, 34b is not limited even further by setting a sufficient torque limit (for example, value 0.2). Good.

  In the electric vehicle 20 of the embodiment, the road surface gradient θ detected by the gradient sensor 68 is used. However, in a vehicle including a navigation system, a road surface gradient acquired by the navigation system based on the current position may be used. Alternatively, the value from the gradient sensor may be used when the vehicle starts, and the road surface gradient estimated based on the value from the navigation system or the driving torque may be used when the vehicle is traveling.

  In the embodiment, the electric vehicle 20 including the motor MG1 that outputs power to the front wheels 30a and 30b and the motor MG2 that outputs power to the rear wheels 34a and 34b has been described, but instead of these motors MG1 and MG2, FIG. As illustrated in the hybrid vehicle 120 of the modified example, the engine 122 as an internal combustion engine and the motor MG1 and the motor MG2 are connected to the front wheels 30a and 30b via the planetary gear mechanism 124, and the motors are connected to the rear wheels 34a and 34b. The present invention may be applied to the hybrid vehicle 120 to which the MGR is connected.

  Moreover, it is not limited to what is applied to such a motor vehicle, It is good also as forms of vehicles, such as a train other than a motor vehicle, and it does not matter as a form of the control method of a vehicle.

  Here, the correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problems will be described. In the embodiment, the motor MG1 corresponds to the “front wheel motor”, the motor MG2 corresponds to the “rear wheel motor”, the battery 44 corresponds to the “power storage unit”, and the gradient sensor 68 corresponds to the “road surface gradient acquisition unit”. The low μ road switch 69 corresponds to “instruction means”, and the required torque T * is distributed to the front wheel side and the rear wheel side according to the load distribution, and the rated maximum torques Tm1max and Tm2max of the motors MG1 and MG2 are distributed. The electronic control unit 50 that executes the processing of steps S110 to S210 of the drive control routine of FIG. The torque command T of the motors MG1 and MG2 is based on whether or not low μ road traveling is instructed and the road surface gradient θ and the estimated friction coefficient μ * when low μ road traveling is instructed. The electronic control unit 50 that executes the processing of steps S220 to S300 of the drive control routine of FIG. 2 for setting m1 *, Tm2 * corresponds to “execution drive force setting means”, and torque commands Tm1 * for the motors MG1, MG2. , Tm2 *, the electronic control unit 50 that executes the process of step S310 of the drive control routine of FIG.

  Here, the “front wheel motor” is not limited to the motor MG1 configured as a synchronous generator motor, and may be any type of motor that outputs power to the front wheels, such as an induction motor. I do not care. The “rear wheel motor” is not limited to the motor MG2 configured as a synchronous generator motor, and may be any type of motor that outputs power to the rear wheels, such as an induction motor. Absent. The “storage means” is not limited to the battery 44 as a secondary battery, and may be anything as long as it exchanges power with the front wheel motor and the rear wheel motor, such as a capacitor. The “road surface gradient acquisition means” is not limited to the gradient sensor 68, and any device that acquires a road surface gradient, such as a device that acquires a value from a navigation system, may be used. The “instruction means” is not limited to the low μ road switch 69, but may be one that instructs low-friction coefficient road running on a road surface having a small friction coefficient, such as one constituted by an electronic control unit. It doesn't matter what. As the “required driving force setting means”, the required torque T * is distributed to the front wheel side and the rear wheel side according to the load distribution, and the front wheel request is within the limits of the rated maximum torques Tm1max and Tm2max of the motors MG1 and MG2. The required driving force required for traveling is not limited to the electronic control unit 50 that executes processing for setting the torque Tf * and the rear wheel required torque Tr *. When the engine is distributed according to the load on the front wheels and the rear wheels, the distributed drive force distributed to the front wheels is within the limit of the rated maximum torque of the front wheel motor, and the rear wheel distributed drive force distributed to the rear wheels is When it is within the limits of the rated maximum torque of the wheel motor, the front wheel distribution drive force and the rear wheel distribution drive force are required for the front wheel required drive force and the rear wheel. The rear wheel distributed drive force is within the range of the limit by the rated maximum torque of the front wheel motor, and the rear wheel distributed drive force is outside the range of the limit by the rated maximum torque of the rear wheel motor. In this case, the sum of the driving force that exceeds the driving force corresponding to the rated maximum torque of the rear wheel motor and the driving force that is the sum of the front wheel distributing driving force within the rear wheel distributing driving force is within the limit by the rated maximum torque of the front wheel motor. As long as the driving force corresponding to the rated maximum torque of the electric motor for the rear wheels is set as the required driving force for the rear wheels, any driving force may be used. As the “execution driving force setting means”, the motors MG1, MG2 are based on whether or not low μ road traveling is instructed and the road surface gradient θ and the estimated friction coefficient μ * when low μ road traveling is instructed. Is not limited to the electronic control unit 50 that executes the process of setting the torque commands Tm1 * and Tm2 *, but is not instructed to run on the road surface with a low coefficient of friction, such as one constituted by a plurality of electronic control units. The set front wheel required driving force and rear wheel required driving force are set as the front wheel execution driving force and the rear wheel execution driving force. When low friction coefficient road traveling is instructed, low friction coefficient road traveling is instructed. Prevent slippage due to idling on the front and rear wheels based on a predetermined estimated friction coefficient smaller than the estimated road friction coefficient and the acquired road gradient. The front wheel required driving force set by the upper limit driving force of each of the front wheels and the rear wheel and the driving force limited to the rear wheel required driving force are set as the front wheel execution driving force and the rear wheel execution driving force. It does not matter as long as it is anything. The “control means” is not limited to the electronic control unit 50 that controls the motors MG1 and MG2 based on the torque commands Tm1 * and Tm2 * of the motors MG1 and MG2, and includes a plurality of electronic control units. As long as the front wheel motor and the rear wheel motor are controlled so that the set front wheel driving force and rear wheel driving force are output to the front wheels and the rear wheels for traveling. I do not care.

  The correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problems is the same as that of the embodiment described in the column of means for solving the problems. It is an example for specifically explaining the best mode for doing so, and does not limit the elements of the invention described in the column of means for solving the problems. In other words, the interpretation of the invention described in the column of means for solving the problem should be made based on the description of the column, and the examples are those of the invention described in the column of means for solving the problem. It is only a specific example.

  The best mode for carrying out the present invention has been described with reference to the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention. Of course, it can be implemented in the form.

  The present invention can be used in the vehicle manufacturing industry.

It is a block diagram which shows the outline of a structure of the electric vehicle 20 which is one Example of this invention. It is a flowchart which shows an example of the drive control routine performed by the electronic control unit 50 of an Example. It is explanatory drawing which shows an example of the map for request | requirement torque setting. It is explanatory drawing which shows an example of the map for front-wheel upper limit torque setting. It is explanatory drawing which shows an example of the relationship of the balance of the force which acts on the vehicle with respect to a road surface gradient. FIG. 11 is a configuration diagram showing an outline of a configuration of a hybrid vehicle 120 according to a modification.

Explanation of symbols

  20 Electric vehicle, 30a, 30b Front wheel, 32, 36 Differential gear, 34a, 34b Rear wheel, 40, 42 Inverter, 44 Battery, 50 Electronic control unit, 52 CPU, 54 ROM, 56 RAM, 60 Ignition switch, 61 Shift lever , 62 Shift position sensor, 63 Accelerator pedal, 64 Accelerator pedal position sensor, 65 Brake pedal, 66 Brake pedal position sensor, 67 Vehicle speed sensor, 68 Gradient sensor, 69 Low μ road switch, 120 Hybrid vehicle, 122 Engine, 124 Planetary gear Mechanism, MG1, MG2, MGR motor.

Claims (6)

Electric power is exchanged between the front wheel motor that outputs power to the front wheels, the rear wheel motor that outputs power to the rear wheels with a rated maximum torque smaller than that of the front wheel motor, and the front wheel motor and the rear wheel motor. A vehicle comprising power storage means,
Road surface gradient acquisition means for acquiring a road surface gradient;
Instructing means for instructing low-friction-coefficient road running on a road surface having a small friction coefficient,
When the required driving force required for traveling is distributed according to the load on the front wheels and the rear wheels, the front wheel distributed driving force distributed to the front wheels is within the range of restriction by the rated maximum torque of the front wheel motor and When the rear wheel distribution driving force distributed to the rear wheels is within the limit of the rated maximum torque of the rear wheel motor, the front wheel distribution driving force and the rear wheel distribution driving force are required before the front wheels are requested. A wheel required driving force and a rear wheel required driving force required for the rear wheel, the front wheel distributing driving force is within a limit range by the rated maximum torque of the front wheel motor, and the rear wheel distributing driving force is When the rear wheel motor is out of the range limited by the rated maximum torque of the rear wheel motor, the driving force exceeding the driving force corresponding to the rated maximum torque of the rear wheel motor and the front of the rear wheel distribution driving force A driving force that is the sum of the front wheel distribution driving force is set as the required front wheel driving force within a range limited by the rated maximum torque of the front wheel motor, and a driving force corresponding to the rated maximum torque of the rear wheel motor is A required driving force setting means for setting the rear wheel required driving force;
When the low friction coefficient road traveling is not instructed, the set front wheel required driving force and rear wheel required driving force are set as a front wheel execution driving force and a rear wheel execution driving force, and the low friction coefficient road traveling is performed. When instructed, the low friction coefficient When the road surface is not instructed, the front wheel and the rear wheel are idled based on a predetermined estimated friction coefficient smaller than the road surface friction coefficient estimated when not instructed and the acquired road surface gradient. The front wheel execution driving force and the driving force for limiting the front wheel required driving force and the rear wheel required driving force set by the upper limit driving force of each of the front wheels and the rear wheels to prevent slippage due to An execution driving force setting means for setting as the rear wheel execution driving force;
Control means for controlling the electric motor for the front wheels and the electric motor for the rear wheels so that the set driving force for executing the front wheels and the driving force for executing the rear wheels are output to the front wheels and the rear wheels to travel.
A vehicle comprising:   The execution driving force setting means is configured to detect the front wheel execution driving force and the rear wheel execution when slippage due to idling occurs in at least one of the front wheel and the rear wheel when the low friction coefficient road traveling is instructed. 2. The vehicle according to claim 1, which is means for setting the front wheel execution driving force and the rear wheel execution driving force so that at least the execution driving force on the side of the wheel where slip occurs is reduced.   The execution driving force setting means is configured to detect the front wheel execution driving force and the rear wheel execution when slippage due to idling occurs in at least one of the front wheel and the rear wheel when the low friction coefficient road traveling is instructed. 3. The means for setting at least the effective driving force on the side of the wheel where slip occurs in the driving force for driving using a friction coefficient smaller than the predetermined estimated friction coefficient instead of the predetermined estimated friction coefficient. Vehicle.   The execution driving force setting means uses the relationship between the friction coefficient of the road surface, the road surface gradient, and the upper limit driving force of each of the front wheels and the rear wheels when the low friction coefficient road traveling is instructed. The upper limit driving force of each of the front wheels and the rear wheels is set based on the estimated friction coefficient and the acquired road surface gradient, and the front wheel execution driving force and the The vehicle according to any one of claims 1 to 3, which is means for setting a rear wheel execution driving force. A vehicle according to any one of claims 1 to 4,
An internal combustion engine;
A generator that inputs and outputs power;
Connected to three shafts of a drive shaft connected to the front wheel axle, the output shaft of the internal combustion engine, and the rotating shaft of the generator, and the power input to and output from any two of the three shafts 3-axis power input / output means for inputting / outputting power to the remaining shaft based on
With
The front wheel motor is connected to the drive shaft.
vehicle. Electric power is exchanged between the front wheel motor that outputs power to the front wheels, the rear wheel motor that outputs power to the rear wheels with a rated maximum torque smaller than that of the front wheel motor, and the front wheel motor and the rear wheel motor. A vehicle control method comprising:
When the required driving force required for traveling is distributed according to the load on the front wheels and the rear wheels, the front wheel distributed driving force distributed to the front wheels is within the range of restriction by the rated maximum torque of the front wheel motor and When the rear wheel distribution driving force distributed to the rear wheels is within the limit of the rated maximum torque of the rear wheel motor, the front wheel distribution driving force and the rear wheel distribution driving force are required before the front wheels are requested. A wheel required driving force and a rear wheel required driving force required for the rear wheel, the front wheel distributing driving force is within a limit range by the rated maximum torque of the front wheel motor, and the rear wheel distributing driving force is When the rear wheel motor is out of the range limited by the rated maximum torque of the rear wheel motor, the driving force exceeding the driving force corresponding to the rated maximum torque of the rear wheel motor and the front of the rear wheel distribution driving force A driving force that is the sum of the front wheel distribution driving force is set as the required front wheel driving force within a range limited by the rated maximum torque of the front wheel motor, and a driving force corresponding to the rated maximum torque of the rear wheel motor is Set as the rear wheel required driving force,
When the low friction coefficient road traveling that travels on the road surface with a small friction coefficient is not instructed, the set front wheel required driving force and the rear wheel required driving force are set as the front wheel executing driving force and the rear wheel executing driving force, When the low friction coefficient road surface traveling is instructed, the front wheel and the rear wheel based on a predetermined estimated friction coefficient and a road surface gradient smaller than the road surface friction coefficient estimated when the low friction coefficient road surface traveling is not instructed. A driving force for limiting the set front wheel required driving force and the rear wheel required driving force by the upper limit driving force of each of the front wheel and the rear wheel for preventing slippage due to idling in the wheel is for executing the front wheel. Set as driving force and driving force for executing the rear wheel,
Controlling the front-wheel motor and the rear-wheel motor so that the set front-wheel execution driving force and rear-wheel execution driving force are output to the front wheels and the rear wheels to travel.
A method for controlling a vehicle.

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