Vehicle drive force control device

Abstract

Vehicle drive force control device with: a tire force estimation device (2m) suitable for estimating a tire force generated on a tire; a friction circle limit estimation device (2k) that is suitable for estimating a friction circle limit as the maximum tire force that the tire can exert against an actual road surface; a slip rate calculation device (3b) suitable for calculating a slip rate of the tire; a first torque reduction value calculation device (2) that is suitable for calculating a first torque reduction value (TTCS1) on the basis of a relationship between the tire force and the friction circle limit value; a second torque reduction value calculation device (3) capable of calculating a second torque reduction value (TTCS2) based on at least the slip rate; and a control value setting device (4) which is suitable for comparing the first torque reduction value (TTCS1) with the second torque reduction value (TTCS2) and for setting the smaller of the two values ​​as the control value (TTCS) for controlling a driving force of the vehicle.

Description

[0001] The present invention relates to a vehicle driving force control device for controlling a driving force to appropriately maintain an adhesion force of a vehicle wheel in various traveling states, for example, during a starting mode, a straight-ahead traveling mode, or a cornering mode of a vehicle.

[0002] Various traction control devices for limiting the driving force to reduce slip of the vehicle wheel have been proposed and put into practice.

[0003] For example, patent document JP-A-5-214974 describes a technique according to which a slip rate of a drive wheel is calculated based on the speed of the drive wheel and the speed of the vehicle body, and the engine output torque is reduced when the slip rate has exceeded a predetermined threshold to perform feedback control with respect to the throttle valve and prevent excessive slip of the drive wheel.

[0004] During cornering of a vehicle, a lateral force acting on a tire increases, whereas an allowable longitudinal driving force and a slip rate for maintaining stable vehicle behavior decrease. Therefore, in a traction control device such as the traction control device described in JP-A-5-214974, although a very small amount of tire slip must be detected during cornering to stabilize vehicle behavior, such detection is difficult because the computational accuracy for estimating the ground speed of the vehicle body is limited. This makes it difficult to reduce the driving force to maintain vehicle stability by determining a torque reduction value with high accuracy.

[0005] DE 101 60 049 B4 relates to a system and a method for monitoring the driving behavior of a motor vehicle with at least one wheel. A sensor device assigned to the at least one wheel detects at least one wheel-related variable and outputs a signal representing this wheel variable, which is fed to an assessment device that processes this signal and determines at least one characteristic value characterizing the power transmission capacity of the at least one wheel. In particular, it is proposed to combine a friction coefficient determined from the wheel contact force and the wheel circumferential force and a wheel slip determined from the wheel speed into a friction coefficient-wheel slip value pair and to use this value in a vehicle dynamics control system.

[0006] DE 198 44 467 A1 relates to a vehicle driving force control device comprising a tire force estimator adapted to estimate a tire force generated at a tire, a friction circle limit estimator adapted to estimate a friction circle limit as the maximum tire force that the tire can exert against a current road surface, a slip rate calculator adapted to calculate a slip rate of the tire, and a torque reduction value calculator adapted to calculate a torque reduction value based at least on the slip rate.

[0007] The present invention was developed under these circumstances, and it is an object of the present invention to provide a vehicle driving force control device that can control the driving force with high accuracy to improve the stability of the vehicle in all driving conditions, for example, when the vehicle is operating in a cornering mode, a straight-ahead mode, or a starting mode. This object is achieved by the features of the claims.

[0008] According to the vehicle driving force control device of the present invention, the driving force can be controlled with high accuracy, so that the stability of the vehicle can be improved in all traveling conditions, for example, when the vehicle is performing a cornering mode, a straight-ahead traveling mode, or a starting mode.

[0009] Embodiments of the present invention will be described below with reference to the drawings. Fig. 1 shows a functional block diagram of a driving force control device; Fig. 2 shows a flowchart of a driving force control program; Fig. 3A and Fig. 3B shows a functional block diagram of a first traction control unit; Fig. 4 shows a flowchart of a first tax value calculation program; Fig. 5 shows a continuation of the flow chart of Fig. 4; Fig. 6 shows an example of engine torque set based on engine speed and throttle opening; Fig. 7 shows an example of a relationship between an accelerator pedal operation degree and a throttle opening for generating a requested engine torque; Fig. 8 shows a flowchart of a routine for calculating an additional yaw moment; Fig. 9A and Fig. 9B show a lateral or lateral acceleration saturation coefficient; Fig. 10 shows a map of a vehicle speed feedback gain; Fig. 11 shows a difference in the additional yaw moment value between a road with a low friction coefficient µ and a road with a high friction coefficient µ; Fig. 12 shows an excessive or excessive tire force to be minimized; Fig. 13 shows a functional block diagram of a second traction control unit; and Fig. 14 shows a flowchart of a second tax value calculation program.

[0010] The Fig. 1 to 14 show an embodiment of the present invention. In this embodiment, the vehicle is, for example, a four-wheel drive vehicle equipped with a center differential. In this vehicle, the wheelbase is limited by a slip differential clutch (tightening torque T LSD ) enables the center differential to distribute the longitudinal drive force on the basis of a basic torque distribution R f_cd is adjustable.

[0011] In Fig. 1, reference numeral 1 denotes a vehicle driving force control device installed in a vehicle for appropriately controlling a driving force. The driving force control device 1 is connected to a throttle opening sensor 11, an engine speed sensor 12, an accelerator pedal depression sensor 13, a transmission control unit 14, a lateral acceleration sensor 15, a yaw rate sensor 16, a steering wheel angle sensor 17, wheel speed sensors 18 for the individual wheels, a longitudinal acceleration sensor 19, and a road surface friction coefficient estimation unit 20, and receives a throttle opening degree θ from these devices. th , an engine speed N e , an actuation level θ ACC an accelerator pedal, a main gear ratio i, a turbine speed N t a torque converter, a tightening torque T LSDa slip limiting differential clutch, a lateral acceleration (d 2 y / dt 2 ), a yaw rate γ, a steering angle θ H , wheel speeds ω fl , ω fr , ω rl and ω rr of the individual wheels (where the indices “fl”, “fr”, “rl” and “rr” denote a left front wheel, a right front wheel, a left rear wheel and a right rear wheel, respectively), a longitudinal acceleration (d 2 x / dt 2 ) and a road surface friction coefficient µ.

[0012] Based on these input signals, the driving force control device 1 calculates an appropriate driving force value according to a driving force control program described below and outputs the driving force value to an engine control unit 5. The engine control unit 5 outputs a control signal to a throttle control unit (not shown), thereby causing a motor to be driven, which actuates a throttle valve.

[0013] As in Fig. 1, the driving force control device 1 essentially comprises a first traction control unit 2, a second traction control unit 3 and a control value setting unit 4.

[0014] The first traction control unit 2 is provided as the first torque reduction value calculation means. The first traction control unit 2 is connected to the throttle opening sensor 11, the engine speed sensor 12, the accelerator pedal depression sensor 13, the transmission control unit 14, the lateral acceleration sensor 15, the yaw rate sensor 16, the steering angle sensor 17, the wheel speed sensors 18 for the individual wheels, and the road surface friction coefficient estimation unit 20, and receives a throttle opening degree θ from these devices. th , an engine speed N e , an actuation level θ ACC of the accelerator pedal, a main gear ratio i, a turbine speed N t of the torque converter, a tightening torque T LSD the slip limiting differential clutch, a lateral acceleration (d 2 y / dt 2), a yaw rate γ, a steering angle θ H , wheel speeds ω fl , ω fr , ω rl and ω rr of the individual wheels (where the indices “fl”, “fr”, “rl” and “rr” denote a left front wheel, a right front wheel, a left rear wheel and a right rear wheel, respectively) and a road surface friction coefficient µ.

[0015] According to the Fig. 3A and Fig. 3B, the first traction control unit essentially comprises: an engine torque calculation section 2a, a section 2b for calculating a requested engine torque, a transmission output torque calculation section 2c, a total driving force calculation section 2d, a section 2e for calculating the front / rear ground force, a section 2f for calculating the load distribution for the left wheels, a section 2g for calculating the ground forces for the individual wheels, a section 2h for calculating the longitudinal forces for the individual wheels, a section 2i for calculating the requested lateral forces for the individual wheels, a section 2j for calculating the lateral forces for the individual wheels, a section 2k for calculating friction circle limits for the individual wheels, a section 2l for calculating requested resultant tire forces for the individual wheels,a section 2m for calculating resulting tire forces for the individual wheels, a section 2n for calculating requested excessive tire forces for the individual wheels, a section 2o for calculating excessive tire forces for the individual wheels, a section 2p for calculating an excessive tire force, an excess torque calculation section 2q, and a section 2r for calculating a first control value.

[0016] The engine torque calculation section 2a receives a throttle opening θ th from the throttle opening sensor 11 and an engine speed N e from the engine speed sensor 12. The engine torque calculation section 2a refers to a map (e.g. the one shown in Fig. 6) reference created in advance based on engine characteristics to obtain a currently generated engine torque T egThe engine torque calculation section 2a then outputs the determined engine torque T eg to the transmission output torque calculation section 2c. The engine torque T eg can alternatively be read by the engine control unit 5.

[0017] The transmission output torque calculation section 2c receives the engine speed N e from the engine speed sensor 12, a main gear ratio i and a turbine speed N t a torque converter from the transmission control unit 14 and an engine torque T eg from the engine torque calculation section 21a.

[0018] The transmission output torque calculation section 1c calculates a transmission output torque T t for example, according to the following equation (1) and gives the calculated transmission output torque T tto the total driving force calculation section 2d and the section 2h for calculating longitudinal forces for the individual wheels. Tt=Teg⋅t⋅i

[0019] Here, t denotes a torque ratio of the torque converter, which is determined by reference to a map prepared in advance, which shows a relationship between a speed ratio e (= N t / N e ) of the torque converter and a torque ratio of the torque converter.

[0020] The total driving force calculation section 2d receives the transmission output torque T t from the transmission output torque calculation section 1c.

[0021] The total driving force calculation section 2d calculates a total driving force F x for example, according to the following equation (2) and gives the calculated total driving force F xto section 2e to calculate the front / rear ground force and section 2h to calculate the longitudinal forces for the individual wheels. Fx=Tt⋅η⋅if / Rt

[0022] Here, η denotes a transmission efficiency of a drive system, i f a final gear ratio and R t a tire radius.

[0023] The front / rear ground force calculation section 2e receives the total driving force F x from the total driving force calculation section 2d. The front / rear ground force calculation section 2e then calculates a front wheel ground force F according to the following equation (3). zf and gives the calculated front wheel ground force F zfto section 2g for calculating ground forces for the individual wheels and section 2h for calculating longitudinal forces for the individual wheels. In addition, section 2e for calculating front / rear ground forces calculates a rear-wheel ground force F according to the following equation (4). zr and gives the calculated rear wheel ground force F zr to section 2g to calculate ground forces for the individual wheels. F2f=Wf−((m⋅(d2× / dt2)⋅h) / L) F2r=W−Fzf

[0024] Here, W f a static front wheel force, m a vehicle mass, (d 2 x / dt 2 ) a longitudinal acceleration (= F x / m), h is the height of the center of gravity, L is a wheel or axle base and W is a vehicle mass (gravitational force) (= m·g; where g is the acceleration due to gravity).

[0025] The section 2f for calculating a load ratio for the left wheels receives a lateral acceleration (d 2 y / dt 2 ) from the lateral acceleration sensor 15. The left wheel load ratio calculation section 2f calculates a load ratio WR according to the following equation (5) _l for the left wheels and gives the calculated load ratio WR _l for the left wheels to section 2g for calculating ground forces for the individual wheels, section 2i for calculating requested lateral forces for the individual wheels and section 1j for calculating lateral forces for the individual wheels. WR_1=0.5−((d2y / dt2) / G)⋅(h / Ltred)

[0026] Here, L tred an average tread value of the front and rear wheels.

[0027] The section 2g for calculating ground forces for the individual wheels receives the front wheel ground force F zf and the rear wheel ground force F zr from section 2e to calculate the front / rear ground force and also receives the load ratio WR _l for the left wheels from section 2f for calculating a load ratio for the left wheels. Section 2g for calculating ground forces for the individual wheels calculates a ground force F according to the following equations (6), (7), (8) and (9), respectively. zf_l for the left front wheel, a ground force F zf_r for the right front wheel, a ground force F zr_l for the left rear wheel and a ground force F zr_r for the right rear wheel and outputs these calculated values ​​to section 2k for calculating friction circle limits for the individual wheels. F2f_1=Fzf⋅WR_1 F2f_r=Fzf⋅(1−WR_1) Fzr_1=Fzr⋅WR_1 F2r_r=Fzr⋅(1−WR_1)

[0028] Section 2h for calculating longitudinal forces for the individual wheels receives a tightening torque T LSD the slip limiting differential clutch of the center differential from the transmission control unit 14, the transmission output torque T t from the transmission output torque calculation section 2c, the total drive force F x from the total driving force calculation section 2d and the front wheel ground force F zf from section 2e for calculating the front / rear ground force. According to a procedure described below, section 2h for calculating the longitudinal forces calculates a longitudinal force F for the individual wheels. xf_l for the left front wheel, a longitudinal force F xf_r for the right front wheel, a longitudinal force F xr_l for the left rear wheel and a longitudinal force F xr_rfor the right rear wheel and outputs these calculated values ​​to section 21 for calculating requested resultant tire forces for the individual wheels and section 2m for calculating resultant tire forces for the individual wheels.

[0029] An example of a procedure for calculating the longitudinal force F xf_l for the left front wheel, the longitudinal force F xf_r for the right front wheel, the longitudinal force F xr_l for the left rear wheel and the longitudinal force F xr_r for the right rear wheel is described below.

[0030] First, a front wheel load distribution ratio W R_f calculated according to the following equation (10). WR_f=Fzf / W

[0031] Then a minimum front wheel longitudinal torque T fmin and a maximum front wheel longitudinal torque T fmax calculated according to the following equations (11) and (12). Tfmin=Tt⋅Rf_cd−TLSD(≥0) Tfmax=Tt⋅Rf_cd+TLSD(≥0)

[0032] A minimum front wheel longitudinal force F xfmin and a maximum front wheel longitudinal force F xfmax calculated according to the following equations (13) and (14). Fxfmin=Tfmin⋅η⋅if / Rt Fxfmax=Tfmax⋅η⋅if / Rt

[0033] Then a determination value I is calculated in the following way.

[0034] If W R_f ≤ F xfmin / F x is, it is decided that the slip limiting differential torque at the rear wheels is increasing, so the determination value I is set to 1.

[0035] If W R_f ≥ F xfmax / F x is, it is decided that the slip limiting differential torque at the front wheels is increasing, so the determination value I is set to 3.

[0036] In cases other than those above (ie, where Fxfmin / F x < W R_f < F xfmax / F x is), a normal condition is confirmed, so that the determination value I is set to 2.

[0037] According to the determination value I, a front wheel longitudinal force F xf calculated as follows: If I=1:Fxf=Tfmin⋅η⋅if / Rt If I=2: Fxf=Fx⋅WR_f If I=3: Fxf=Tfmax⋅η⋅if / Rt

[0038] Based on the front wheel longitudinal force F calculated according to equation (15), (16) or (17) xf a rear wheel longitudinal force F xr calculated according to the following equation (18): Fxr=Fx−Fxf

[0039] Using the front wheel longitudinal force F xf and the rear wheel longitudinal force F xr the longitudinal force F xf_l for the left front wheel, the longitudinal force F xf_r for the right front wheel, the longitudinal force F xr_lfor the left rear wheel and the longitudinal force F xr_r for the right rear wheel according to the following equations (19) to (22): Fxf_l=Fxf / 2 Fxf_r=Fxf_l Fxf_l=Fxr / 2 Fxr_r=Fxr_l

[0040] The calculations of the longitudinal forces of the individual wheels in the first embodiment described above are merely examples and can be appropriately selected according to the driving method or the driving mechanism of the vehicle.

[0041] Section 2i for calculating requested lateral forces for the individual wheels receives the lateral acceleration (d 2 y / dt 2 ) from the lateral acceleration sensor 15, a yaw rate γ from the yaw rate sensor 16, a steering wheel angle θ H from the steering wheel angle sensor 17, wheel speeds ω fl , ω fr , ω rl and ω rrof the four wheels from the wheel speed sensors 18 for the respective (four) wheels and the load ratio WR _l for the left wheels from section 2f to calculate a load ratio for the left wheels.

[0042] According to a procedure described below (ie according to the procedure described in Fig. 8 shown flow diagram) an additional yaw moment M z θ is calculated. Based on this additional yaw moment, a requested front wheel lateral force F yf_FF calculated according to the following equation (23), and a requested rear wheel lateral force F yr_FF is calculated according to the following equation (24). Based on the requested front wheel lateral force F yf_FF and the requested rear wheel lateral force F yr_FF according to the following equations (25) to (28) a requested lateral force F yf_l_FF for the left front wheel, a requested lateral force F yf_r_FFfor the right front wheel, a requested lateral force F yr_l_FF for the left rear wheel and a requested lateral force F yr_r_FF for the right rear wheel and output to section 21 to calculate requested resultant tire forces for the individual wheels. Fyf_FF=Mzθ / L Fyr_FF=(−I2⋅(dγ / dt)+m⋅(d2y / dt2)⋅Lf) / L

[0043] Here, I z an inertial yaw moment of the vehicle and L f a distance between the front axle and the center of gravity. Fyf_l_FF=Fyf_FF⋅WR_l Fyf_r_FF=Fyf_FF⋅(1−WR_l) Fyr_l_FF=Fyr_FF⋅WR_l Fyr_r_FF=Fyr_FF⋅(1−WR_l)

[0044] Then, as in Fig. 8, the additional yaw moment M z θ is determined. First, in step S301, a vehicle speed V is calculated (e.g., V = (ω fl + ω fr + ω rl + ω rr) / 4), and then in step S302, a lateral acceleration / steering wheel angle gain G is calculated using the following equation (29). y calculated: Gy=(1 / (1+A⋅V2))⋅(V2 / L)⋅(1 / n)

[0045] Here, A denotes a stability factor and n a steering gear ratio.

[0046] Then, the processing proceeds to step S303, in which reference is made to a map generated according to a value (G y ·θ H ) is created in advance by multiplying the lateral acceleration / steering wheel angle gain G y with the steering wheel angle θ H and the lateral acceleration (d 2 y / dt 2 ) to calculate a lateral acceleration saturation coefficient Kµ. According to Fig. 9A, this map used to determine a lateral acceleration saturation coefficient Kµ is calculated according to a value (G y ·θ H) is created in advance, which is calculated by multiplying the lateral acceleration / steering wheel angle gain G y with the steering wheel angle θ H and the lateral acceleration (d 2 y / dt 2 ), which value increases with increasing lateral acceleration (d 2 y / dt 2 ) decreases in a state where the steering wheel angle θ H is greater than or equal to a given value. This means that if G y ·θ H has a large value, the lateral acceleration (d 2 y / dt 2 ) increases with increasing road surface friction coefficient µ, but on a road with low friction coefficient µ, the lateral acceleration (d 2 y / dt 2 ) are less likely to occur. Therefore, according to Fig. 9B a lateral acceleration reference value described below (d 2 yr / dt 2 ) based on the fact that G y ·θ Hhas a large value and the lateral acceleration (d 2 y / dt 2 ) has a large value, is set to a low value if it is assumed that the vehicle is driving on a road with a high friction coefficient µ, so that the correction value regarding the additional yaw moment M z θ is set to a small value.

[0047] In step S304, a lateral acceleration deviation feedback gain K y calculated according to the following equation (30): Ky=Kθ / Gy

[0048] Here, Kθ denotes a steering angle feedback gain, which is calculated according to the following equation (31): Kθ=(Lf⋅Kf) / n

[0049] Here, K f an equivalent cornering force of the front axle.

[0050] In particular, the lateral acceleration deviation feedback gain K yaccording to equation (30) as the target value (maximum value) with regard to the case according to which the additional yaw moment M z θ (stationary value) becomes zero in a state where the steering is absolutely ineffective on a road with a very low friction coefficient µ (γ = 0, (d 2 y / dt 2 ) = 0)

[0051] Subsequently, in step S305, a lateral acceleration reference value (d 2 yr / dt 2 ) is calculated according to the following equation (32): (d2yr / dt2)=Kμ⋅Gy⋅(1 / (1+Ty⋅s))⋅θH

[0052] Here s denotes a differential operator and T y a first-order delay time constant of the lateral acceleration. The delay time constant T y first order, for example, according to the following equation (33) with a value given by K r The equivalent cornering force of the rear axle is calculated. Ty=Iz / (L⋅Kr)

[0053] In step S306, a lateral acceleration deviation (d 2 ye / dt 2 ) is calculated according to the following equation (34): (d2ye / dt2)=(d2y / dt2)−(d2yr / dt2)

[0054] Subsequently, in step S307, a yaw rate / steering wheel angle gain Gγ is calculated according to the following equation (35). Gγ=(1 / 1+A⋅V2))⋅(V / L)⋅(1 / n)

[0055] In step S308, a yaw rate feedback gain Kγ is calculated according to the following equation (36) with respect to a case where, for example, the additional yaw moment M z θ (stationary value) during a ride with adhesion (when (d 2 ye / dt 2 ) = 0) takes the value zero. Kγ=Kθ / Gγ

[0056] In step S309, a vehicle speed feedback gain K vcalculated based on a pre-created map. This map is created in such a way that an undesirable additional yaw moment M z θ is avoided in a low-speed range, such as in Fig. 10. In Fig. 10 denotes V cl for example a speed of 40 km / h.

[0057] In step S310, an additional yaw moment M z θ is calculated according to the following equation (37): Mzθ=Kv⋅(−Kγ⋅γ+Ky⋅(d2ye / dt2)+Kθ⋅θH)

[0058] In equation (37), the term -Kγ·γ corresponds to a yaw moment corresponding to a yaw rate γ, the term Kθ·θ H a steering wheel angle θ H corresponding yaw moment and the expression K y · (d 2 ye / dt 2 ) a yaw moment correction value. Therefore, when the vehicle is traveling with a large lateral acceleration (d 2 y / dt 2) on a road with a high friction coefficient µ, as in Fig. 11, the additional yaw moment M z θ a large value, which improves the handling. On the other hand, when the vehicle is driving on a road with a low friction coefficient µ, the additional yaw moment M z θ increases because the additional yaw moment M z θ is reduced by the effect of the correction value, so that stable driving behavior is ensured.

[0059] Section 2j for calculating lateral forces for the individual wheels receives the lateral acceleration (d 2 y / dt 2 ) from the lateral acceleration sensor 15, the yaw rate γ from the yaw rate sensor 16 and the load ratio WR _lfor the left wheels from section 2f to calculate a load ratio for the left wheels. Then, section 2j to calculate lateral forces for the individual wheels calculates a front-wheel lateral force F yf_FB and a rear wheel lateral force F yr_FB according to the following equations (38) and (39). Based on the front wheel lateral force F yf_FB and the rear wheel lateral force F yr_FB Section 2j calculates a lateral force F for the individual wheels according to the following equations (40) to (43) yf_l_FB for the left front wheel, a lateral force F yf_r_FB for the right front wheel, a lateral force F yr_l_FB for the left rear wheel and a lateral force F yr_r_FB for the right rear wheel and outputs these calculated values ​​to section 2m to calculate resulting tire forces for the individual wheels. Fyf_FB=(Iz⋅(dγ / dt)+m⋅(d2y / dt2)⋅Lr) / L Fyr_FB=(−Iz⋅(dγ / dt)+m⋅(d2y / dt2)⋅Lf) / L

[0060] Here, L r a distance between the rear axle and the center of gravity. Fyf_l_FB=Fyf_FB⋅WR_l Fyf_r_FB=Fyf_FB⋅(1−WR_l) Fyr_l_FB=Fyr_FB⋅WR_l Fyr_r_FB=Fyr_FB⋅(1−WR_l)

[0061] The individual wheel friction circle limit value calculation section 2k receives a road surface friction coefficient µ from the road surface friction coefficient estimation unit 19 and the ground force F zf_l for the left front wheel, the ground force F zf_r for the right front wheel, the ground force F zr_l for the left rear wheel and the ground force F zr_r for the right rear wheel from section 2g for calculating ground forces for the individual wheels.

[0062] Then, the friction circle limit value calculation section 2k calculates a friction circle limit value µ_F for the individual wheels according to the following equations (44) to (47) zfl for the left front wheel, a friction circle limit value µ_F zfr for the right front wheel, a friction circle limit value µ_F zrl for the left rear wheel and a friction circle limit value µ_F zrr for the right rear wheel and outputs the calculated values ​​to section 2n for calculating requested excess tire forces for the individual wheels and section 2o for calculating excess tire forces for the individual wheels.

[0063] That is, the section 2k for calculating friction circle limits for the individual wheels is provided as a friction circle limit estimator that estimates a maximum tire force that a tire can exert on a current road surface. μ_Fzfl=μ⋅Fzf_l μ_Fzfr=μ⋅Fzf_r μ_Fzrl=μ⋅Fzr_l μ_Fzrr=μ⋅Fzr_r

[0064] Section 21 for calculating requested resultant tire forces for the individual wheels receives the longitudinal force F xf_l for the left front wheel, the longitudinal force F xf_r for the right front wheel, the longitudinal force F xr_l for the left rear wheel and the longitudinal force F xr_r for the right rear wheel from section 2h to calculate longitudinal forces for the individual wheels and also receives the requested lateral force F yf_l_FF for the left front wheel, the requested lateral force F yf_r_FF for the right front wheel, the requested lateral force F yr_l_FF for the left rear wheel and the requested lateral force F yr_r_FFfor the right rear wheel from section 2i for calculating requested lateral forces for the individual wheels. Section 21 for calculating requested resultant tire forces for the individual wheels calculates a requested resultant tire force F according to the following equations (48) to (51). _fl_FF for the left front wheel, a requested resulting tire force F _fr_FF for the right front wheel, a requested resulting tire force F _rl_FF for the left rear wheel and a requested resulting tire force F _rr_FF for the right rear wheel and outputs these calculated values ​​to section 2n for calculating requested excess tire forces for the individual wheels. That is, section 21 for calculating requested resultant tire forces for the individual wheels is provided as a means for estimating a first tire force. F_fl_FF=(Fxf_l2+Fyf_l_FF2)1 / 2 F_fr_FF=(Fxf_r2+Fyf_r_FF2)1 / 2 F_rl_FF=(Fxr_l2+Fyr_l_FF2)1 / 2 F_rr_FF=(Fxr_r2+Fyr_r_FF2)1 / 2

[0065] The section 2m for calculating resulting tire forces for the individual wheels receives the longitudinal force F xf_l for the left front wheel, the longitudinal force F xf_r for the right front wheel, the longitudinal force F xr_l for the left rear wheel and the longitudinal force F xr_r for the right rear wheel from section 2h to calculate longitudinal forces for the individual wheels and also receives the lateral force F yf_l_FB for the left front wheel, the lateral force F yf_r_FB for the right front wheel, the lateral force F yr_l_FB for the left rear wheel and the lateral force F yr_r_FBfor the right rear wheel from section 2j for calculating lateral forces for the individual wheels. Section 2m for calculating resulting tire forces for the individual wheels calculates a resulting tire force F according to the following equations (52) to (55). _fl_FB for the left front wheel, a resulting tire force F _fr_FB for the right front wheel, a resulting tire force F _rl_FB for the left rear wheel and a resulting tire force F _rr_FB for the right rear wheel and outputs these calculated values ​​to section 2o for calculating excess tire forces for the individual wheels. That is, section 2m for calculating resultant tire forces for the individual wheels is provided as a means for estimating a secondary tire force. F_fl_FB=(Fxf_l2+Fyf_l_FB2)1 / 2 F_fr_FB=(Fxf_r2+Fyf_r_FB2)1 / 2 F_rl_FB=(Fxr_l2+Fyr_l_FB2)1 / 2 F_rr_FB=(Fxr_r2+Fyr_r_FB2)1 / 2

[0066] The section 2n for calculating requested excessive tire forces for the individual wheels receives the friction circle limit value µ_F zfl for the left front wheel, the friction circle limit value µ_F zfr for the right front wheel, the friction circle limit value µ_F zrl for the left rear wheel and the friction circle limit value µ_F zrr for the right rear wheel from section 2k to calculate friction circle limits for the individual wheels, and also receives the requested resultant tire force F _fl_FF for the left front wheel, the requested resulting tire force F _fr_FF for the right front wheel, the requested resulting tire force F _rl_FF for the left rear wheel and the requested resulting tire force F _rr_FFfor the right rear wheel from section 21 for calculating requested resultant tire forces for the individual wheels. Subsequently, section 2n for calculating requested excessive tire forces for the individual wheels calculates a requested excessive tire force ΔF according to the following equations (56) to (59). _fl_FF for the left front wheel, a requested excessive tire force ΔF _fr_FF for the right front wheel, a requested excessive tire force ΔF _rl_FF for the left rear wheel and a requested excessive tire force ΔF _rr_FF for the right rear wheel and outputs these calculated values ​​to the excess tire force calculation section 2p. That is, the requested excess tire force calculation section 2n for the individual wheels is provided as a means for estimating a first excess tire force. ΔF_fl_FF=F_fl_FF−μ_Fzfl ΔF_fr_FF=F_fr_FF−μ_Fzfr ΔF_rl_FF=F_rl_FF−μ_Fzrl ΔF_rr_FF=F_rr_FF−μ_Fzrr

[0067] Section 2o for calculating excessive tire forces for the individual wheels receives the friction circle limit value µ_F zfl for the left front wheel, the friction circle limit value µ_F zfr for the right front wheel, the friction circle limit value µ_F zrl for the left rear wheel and the friction circle limit value µ_F zrr for the right rear wheel from section 2k to calculate friction circle limits for the individual wheels and also receives the resulting tire force F _fl_FB for the left front wheel, the resulting tire force F _fr_FB for the right front wheel, the resulting tire force F _rl_FB for the left rear wheel and the resulting tire force F _rr_FBfor the right rear wheel from section 2m for calculating resulting tire forces for the individual wheels. Section 2o for calculating excessive tire forces for the individual wheels calculates an excessive tire force ΔF according to the following equations (60) to (63). _fl_FB for the left front wheel, an excessive tire force ΔF _fr_FB for the right front wheel, an excessive tire force ΔF _rl_FB for the left rear wheel and an excessive tire force ΔF _rr_FB for the right rear wheel and outputs these calculated values ​​to the excess tire force calculation section 2p. That is, the excess tire force calculation section 2o for the individual wheels is provided as a means for estimating a second excess tire force. ΔF_fl_FB=F_fl_FB−μFzfl ΔF_fr_FB=F_fr_FB−μFzfr ΔF_rl_FB=F_rl_FB−μFzrl ΔF_rr_FB=F_rr_FB−μFzrr

[0068] The excess tire force calculation section 2p receives the requested excess tire force ΔF _fl_FF for the left front wheel, the requested excessive tire force ΔF _fr_FF for the right front wheel, the requested excessive tire force ΔF _rl_FF for the left rear wheel and the requested excessive tire force ΔF _rr_FF for the right rear wheel from section 2n to calculate requested excess tire forces for the individual wheels and also receives the excess tire force ΔF _f1_FB for the left front wheel, the excessive tire force ΔF _fr_FB for the right front wheel, the excessive tire force ΔF _rl_FB for the left rear wheel and the excessive tire force ΔF _rr_FBfor the right rear wheel from section 2o for calculating excess tire forces for the individual wheels. Section 2p for calculating an excess tire force then compares a total value of the requested excess tire forces ΔF _fl_FF , ΔF _fr_FF , ΔF _rl_2F and ΔF _rr_FF with a total value of excessive tire forces ΔF _fl_FB , ΔF _fr_FB , ΔF _rl_FB and ΔF _rr_FB and sets the larger of these two values ​​as the excessive tire force F over . Fover=MAX((ΔF_fl_FF+ΔF_fr_FF+ΔF_rl_FF+ΔF_rr_FF),(ΔF_fl_FB+ΔF_fr_FB+ΔF_rl_FB+ΔF_rr_FB))

[0069] The overtorque calculation section 2q receives the engine speed N e from the engine speed sensor 12, the main gear ratio i and the turbine speed N t of the torque converter from the transmission control unit 14 and the excessive tire force F overfrom the section 2p for calculating an excessive tire force. The excess torque calculation section 1q calculates an excess torque T according to the following equation (65). over and outputs the calculated value to the tax value calculation section 2r. Tover=Fover⋅Rt / (t⋅i⋅η⋅if)

[0070] The control value calculation section 2r receives the requested engine torque T drv from section 2b to calculate a requested engine torque and also receives the excess torque T over from the overtorque calculation section 2q. The control value calculation section 2r calculates a first control value (a first torque reduction value) TTCS1 according to the following equation (66) and outputs the calculated value to the control value setting unit 4. TTCS1=Tdrv−Tover

[0071] Therefore, in the first embodiment, the excessive tire force calculating section 2p, the excess torque calculating section 2q, and the control value calculating section 2r constitute a driving force setting means that corrects a driving force requested by a driver.

[0072] Next, a first control value setting program executed by the driving force control device 2 will be described with reference to the Fig. 4 and Fig. 5 described flowcharts.

[0073] In step S201, required parameters are read, which specify a throttle opening degree θ th , an engine speed N e , an actuation level θ ACC of the accelerator pedal, a main gear ratio i, a turbine speed N t a torque converter, a tightening torque T LSD a slip limiting differential clutch, a lateral acceleration (d 2 y / dt2 ), a yaw rate γ, a steering angle θ H , wheel speeds ω fl , ω fr , ω rl and ω rr of the individual wheels and a road surface friction coefficient µ.

[0074] In step S202, the engine torque calculation section 2a refers to a map (e.g., the one shown in Fig. 7), which was created in advance based on engine characteristics to determine a currently generated engine torque T eg to determine.

[0075] In step S203, the requested engine torque calculating section 2b determines a throttle opening degree θ th based on a map created in advance (e.g. the one in Fig. 7, which shows a relationship between θ ACC and θ th Based on the throttle opening degree θ thSection 2b determines an engine torque T to calculate a requested engine torque eg as requested engine torque T drv based on the Fig. 6 shown map.

[0076] In step S204, the transmission output torque calculating section 2c calculates a transmission output torque T t according to the above equation (1).

[0077] In step S205, the total driving force calculating section 2d calculates a total driving force F x according to the above equation (2).

[0078] In step S206, the front / rear ground force calculating section 2e calculates a front wheel ground force F according to equation (3). zf and according to equation (4) a rear wheel ground force F zr .

[0079] In step S207, the left wheel load ratio calculating section 2f calculates a load ratio WR according to equation (5)_l for the left wheels.

[0080] In step S208, the ground force calculating section 2g calculates a ground force F for the individual wheels according to equations (6), (7), (8) and (9), respectively. zf_l for the left front wheel, a ground force F zf_r for the right front wheel, a ground force F zr_l for the left rear wheel and a ground force F zr_r for the right rear wheel.

[0081] In step S209, the longitudinal force calculation section 2h calculates a longitudinal force F for the individual wheels according to equations (19) to (22). xf_l for the left front wheel, a longitudinal force F xf_r for the right front wheel, a longitudinal force F xr_l for the left rear wheel and a longitudinal force F xr_rfor the right rear wheel. Subsequently, the section 2i for calculating requested lateral forces for the individual wheels calculates a requested lateral force F in step S210 according to equations (25) to (28). yf_l_FF for the left front wheel, a requested lateral force F yf_r_FF for the right front wheel, a requested lateral force F yr_l_FF for the left rear wheel and a requested lateral force F yr_r_FF for the right rear wheel.

[0082] In step S211, the lateral force calculating section 2j calculates a lateral force F for the individual wheels according to equations (40) to (43). yf_l_FB for the left front wheel, a lateral force F yf_r_FB for the right front wheel, a lateral force F yr_l_FB for the left rear wheel and a lateral force F yr_r_FB for the right rear wheel.

[0083] In step S212, the friction circle limit value calculating section 2k calculates a friction circle limit value µ_F for the individual wheels according to equations (44) to (47). zfl for the left front wheel, a friction circle limit value µ_F zfr for the right front wheel, a friction circle limit value µ_F zrl for the left rear wheel and a friction circle limit value µ_F zrr for the right rear wheel.

[0084] In step S213, the requested resultant tire force calculating section 21 calculates a requested resultant tire force F for the individual wheels according to equations (48) to (51). _fl_FF for the left front wheel, a requested resulting tire force F _fr_FF for the right front wheel, a requested resulting tire force F _rl_FF for the left rear wheel and a requested resulting tire force F _22_FF for the right rear wheel.

[0085] In step S214, the resulting tire force calculating section 2m calculates a resulting tire force F for the individual wheels according to equations (52) to (55). _fl_FB for the left front wheel, a resulting tire force F _fr_FB for the right front wheel, a resulting tire force F _rl_FB for the left rear wheel and a resulting tire force F _rr_FB for the right rear wheel.

[0086] In step S215, the requested excessive tire force calculating section 2n calculates a requested excessive tire force ΔF for the individual wheels according to equations (56) to (59) _fl_FF for the left front wheel, a requested excessive tire force ΔF _fr_FF for the right front wheel, a requested excessive tire force ΔF _rl_FF for the left rear wheel and a requested excessive tire force ΔF _rr_FF for the right rear wheel.

[0087] In step S216, the excessive tire force calculating section 2o calculates an excessive tire force ΔF for the individual wheels according to equations (60) to (63). _fl_FB for the left front wheel, an excessive tire force ΔF _fr_FB for the right front wheel, an excessive tire force ΔF _rl_FB for the left rear wheel and an excessive tire force ΔF _rr_FB for the right rear wheel.

[0088] In step S217, the excessive tire force calculating section 2p calculates an excessive tire force F according to equation (64). over .

[0089] In step S218, the overtorque calculation section 2q calculates an overtorque T according to equation (65) over .

[0090] In step S219, the control value calculation section 2r calculates a first control value (a first torque reduction value) TTCS1 according to equation (66) and outputs the calculated value to the control value setting unit 4. Finally, the processing exits the program.

[0091] According to the first embodiment of the present invention, in the first traction control unit 2, a torque value at which a tire force to be generated at each wheel based on a driver's request exceeds a friction circle limit is compared with a torque value at which a tire force currently generated at the wheel exceeds the friction circle limit, and the driving force is corrected by subtracting the larger of the two values ​​from a driver-requested driving force. This allows an overtorque condition to be appropriately corrected not only now but also in the future, so that appropriate control for preventing oversteer and understeer conditions can be implemented. As a result, the grip forces of the tires can be appropriately maintained, so that the driving stability of the vehicle can be improved.

[0092] Because the correction value to be subtracted from the driving force requested by the driver is simply a torque value at which a tire force exceeds the friction circle limit, a sudden reduction in the driving force in the longitudinal direction is prevented. This prevents the driver from experiencing an unpleasant feeling or an unsatisfactory feeling due to a lack of acceleration (i.e., the driving force is Fig. 12 only by a measure F xa reduced).

[0093] Alternatively, the grip forces of the tires can be maintained by appropriately reducing the driving force in the longitudinal direction (i.e., the driving force can be Fig. 12 only by a measure F xb In this case, the control is achieved by adding Fig. 3A and Fig. 3B by dashed lines and changing the calculations performed by the section 2n for calculating requested excessive tire forces for the individual wheels and the section 2o for calculating excessive tire forces for the individual wheels in the following manner.

[0094] The section 2n for calculating requested excessive tire forces for the individual wheels receives the friction circle limit value µ_F zfl for the left front wheel, the friction circle limit value µ_F zfr for the right front wheel, the friction circle limit value µ_F zrl for the left rear wheel and the friction circle limit value µ_F zrr for the right rear wheel from section 2k for calculating friction circle limits for the individual wheels, receives the requested lateral force F yf_l_FF for the left front wheel, the requested lateral force F yf_r_FFfor the right front wheel, the requested lateral force F yr_l_FF for the left rear wheel and the requested lateral force F yr_r_FF for the right rear wheel from section 2i to calculate requested lateral forces for the individual wheels and receives the longitudinal force F xf_l for the left front wheel, the longitudinal force F xf_r for the right front wheel, the longitudinal force F xr_l for the left rear wheel and the longitudinal force F xr_r for the right rear wheel from section 2h to calculate longitudinal forces for the individual wheels.

[0095] The section 2n for calculating requested excessive tire forces for the individual wheels calculates a requested excessive tire force ΔF according to the following equations (67) to (70) _fl_FF for the left front wheel, a requested excessive tire force ΔF _fr_FF for the right front wheel, a requested excessive tire force ΔF _rl_FFfor the left rear wheel and a requested excessive tire force ΔF _rr_FF for the right rear wheel and outputs these calculated values ​​to section 2p for calculating an excessive tire force. ΔF_fl_FF=Fxf_l−(μ_Fzfl2−Fyf_l_FF2)1 / 2 ΔF_fr_FF=Fxf_r−(μ_Fzfr2−Fyf_r_FF2)1 / 2 ΔF_rl_FF=Fxr_l−(μ_Fzrl2−Fyr_l_FF2)1 / 2 ΔF_rr_FF=Fxr_r−(μ_Fzrr2−Fyr_r_FF2)1 / 2

[0096] Section 2o for calculating excessive tire forces for the individual wheels receives the friction circle limit value µ_F zfl for the left front wheel, the friction circle limit value µ_F zfr for the right front wheel, the friction circle limit value µ_F zrl for the left rear wheel and the friction circle limit value µ_F zrr for the right rear wheel from section 2k for calculating friction circle limits for the individual wheels, receives the lateral force F yf_l_FB for the left front wheel, the lateral force Fyf_r_FB for the right front wheel, the lateral force F yr_l_FB for the left rear wheel and the lateral force F yr_r_FB for the right rear wheel from section 2j to calculate lateral forces for the individual wheels and receives the longitudinal force F xf_l for the left front wheel, the longitudinal force F xf_r for the right front wheel, the longitudinal force F xr_l for the left rear wheel and the longitudinal force F xr_r for the right rear wheel from section 2h to calculate longitudinal forces for the individual wheels.

[0097] Section 2o for calculating excessive tire forces for the individual wheels then calculates an excessive tire force ΔF according to the following equations (71) to (74) _fl_FB for the left front wheel, an excessive tire force ΔF _fr_FB for the right front wheel, an excessive tire force ΔF _rl_FB for the left rear wheel and an excessive tire force ΔF _rr_FBfor the right rear wheel and outputs these calculated values ​​to section 2p for calculating an excessive tire force. ΔF_fl_FB=Fxf_l−(μ_Fzfl2−Fyf_l_FB2)1 / 2 ΔF_fr_FB=Fxf_r−(μ_Fzfr2−Fyf_r_FB2)1 / 2 ΔF_rl_FB=Fxr_l−(μ_Fzrl2−Fyr_l_FB2)1 / 2 ΔF_rr_FB=Fxr_r−(μ_Fzrr2−Fyr_r_FB2)1 / 2

[0098] On the other hand, the second traction control unit 3, as shown in Fig. 1, is provided as a second torque reduction value calculation device. The second traction control unit 3 is connected to the throttle opening sensor 11, the engine speed sensor 12, the transmission control unit 14, the lateral acceleration sensor 15, the four wheel speed sensors 18, and the longitudinal acceleration sensor 19, and receives signals from these components indicating a throttle opening degree θ th , an engine speed N e, a main gear ratio i, a lateral acceleration (d 2 y / dt 2 ), wheel speeds ω fl , ω fr , ω rl and ω rr of the individual wheels and a longitudinal acceleration (d 2 x / dt 2 ) show.

[0099] According to Fig. 13, the second traction control unit 3 essentially includes a vehicle speed calculation section 3a, a slip rate calculation section 3b, a total grip force calculation section 3c, a motor torque calculation section 3d, a running resistance torque calculation section 3e, and a second control value calculation section 3f.

[0100] The vehicle speed calculation section 3a receives the wheel speeds ω fl , ω fr , ω rl and ω rrof the four individual wheels from the four respective wheel speed sensors 18 and calculates an average of the wheel speeds to obtain a vehicle speed V (= (ω fl + ω fr + ω rl + ω rr ) / 4). The vehicle speed calculation section 3a then outputs the vehicle speed V to the slip rate calculation section 3b and the running resistance torque calculation section 3e.

[0101] The slip rate calculation section 3b receives the wheel speeds ω fl , ω fr , ω rl and ω rrof the four individual wheels from the four respective wheel speed sensors 18 and also receives the vehicle speed V from the vehicle speed calculation section 3a. The slip rate calculation section 3b then calculates a slip rate of the respective wheels using the following equation (75) and outputs the highest slip rate value as a slip rate λ to the second control value calculation section 3f. λ=(ω−V) / ω⋅100

[0102] In this case, ω ω fl to ω rr represents.

[0103] The total adhesion force calculation section 3c receives the lateral acceleration (d 2 y / dt 2 ) from the lateral acceleration sensor 15 and also receives the longitudinal acceleration (d 2 x / dt 2) from the longitudinal acceleration sensor 19. The total grip force calculating section 3c then calculates a total grip force TG corresponding to the acceleration of the vehicle body, for example, according to the following equation (76), and outputs the calculated value to the second control value calculating section 3f. TG=((K1⋅(d2x / dt2))2+(K2⋅(d2y / dt2))2)1 / 2

[0104] In this case, K1 and K2 denote correction coefficients.

[0105] Similar to the engine torque calculation section 2a in the first traction control unit 2, the engine torque calculation section 3d receives the throttle opening degree θ th from the throttle opening sensor 11 and the engine speed N e from the engine speed sensor 12. The engine torque calculation section 3d refers to a map (e.g. to the one shown in Fig. 6), which was created in advance based on engine characteristics to determine a currently generated engine torque T eg Then, the motor torque calculation section 3d outputs the determined motor torque T eg to the second control value calculation section 3f. The engine torque T eg can alternatively be read by the engine control unit 5.

[0106] The running resistance torque calculation section 3e receives the main transmission gear ratio i from the transmission control unit 14 and the vehicle speed V from the vehicle speed calculation section 3a. The running resistance torque calculation section 3e then calculates a running resistance T p, which consists of a rolling resistance of the tires and an air resistance of the vehicle body, for example, according to the following equation (77) and outputs the calculated value to the second control value calculating section 3f. Tp=(K3+K4⋅V2)⋅i

[0107] In this case, K3 and K4 denote correction coefficients.

[0108] The second control value calculation section 3f receives the main transmission gear ratio i from the transmission control unit 14, the slip rate λ from the slip rate calculation section 3b, the total grip force TG from the total grip force calculation section 3c, the engine torque T eg from the engine torque calculation section 3d and the driving resistance T p from the driving resistance torque calculation section 3e. Then, the second control value calculation section 3f calculates a second control value T TCS2which is used when the engine torque is reduced, and outputs the calculated value to the control value setting unit 4.

[0109] That is, based on the following equation (78), a value by which a first-order time delay filtering with respect to the engine torque T eg is obtained, as the first initially required engine torque T EF calculated. TEF=(1−K)⋅TEF(k−1)+K⋅Teg(k)

[0110] In addition, an initially required base torque T ii from a pre-created map based on the main transmission ratio i and the total grip force TG. The initially required base torque T ii and the driving resistance T p are added to obtain a second initially required engine torque T ED to determine. TED=Tii+Tp

[0111] The second initially required engine torque T ED is a sum of the initially required base torque T ii , which represents a torque that is transferred to the road without being consumed by excessive slip of the drive wheels, and the driving resistance T p , which consists of the rolling resistance of the tires and the air resistance of the vehicle body. Therefore, the second initially required engine torque T ED a value obtained by subtracting an ineffective torque consumed by excessive slip of the drive wheels from the actual engine torque T eg is received.

[0112] As mentioned in connection with a second control value calculation program described below, when the slip rate λ exceeds predetermined threshold values ​​L C1 and L C2 exceeds either the first initially required engine torque T EFor the second initially required engine torque T ED selected and as the second control value (second torque reduction value) T TCS2 and output to the control value setting unit 4. On the other hand, if the slip rate λ exceeds the predetermined threshold values ​​L C1 and L C2 does not exceed, the second tax value T TCS2 to the current engine torque T eg set because in this case no torque reduction is carried out.

[0113] The Fig. The flowchart shown in Figure 14 shows a second control value calculation program. In step S401, if the slip rate λ is less than or equal to the first threshold value L C1 is, ie while the slip rate λ is extremely small and the engine output torque is sufficiently transmitted to the road surface, proceed to step S402, where the second control value T TCS2 continues to the current engine torque Teg remains set and no torque reduction control is executed.

[0114] On the other hand, when the slip rate λ exceeds the first threshold value L in step S401, the processing proceeds to C1 exceeds, and if the slip rate λ in step S403 is less than or equal to the second threshold L C2 which is greater than the first threshold L C1 , ie in a range where the slip rate λ is relatively small, proceeds to step S404, where a first initially required engine torque T EF by filtering the second control value T TCS2 set engine torque T eg By setting the first initially required engine torque T EF and starting a feedback control in this way, a sudden change in the engine torque T egcan be prevented, thus avoiding any adverse effect on the vehicle's behavior. In addition, by using a filtered engine torque T eg certain, first initially required engine torque T EF a time delay that occurs until the engine torque T eg converges to a setpoint, thereby providing improved feedback characteristics.

[0115] In step S403, when the slip rate λ exceeds the second threshold L C2 exceeds, ie, when the slip rate λ is large, the processing proceeds to step S405, where a second initially required engine torque T ED , which is a sum of the initially required base torque T ii and the driving resistance T p represents, as a second control value T TCS2This causes feedback control to begin at a maximum initial torque at which the vehicle can potentially accelerate without excessive slip occurring at the drive wheels. This allows excessive slip to converge rapidly without having a significant impact on vehicle behavior.

[0116] According to Fig. 1, the control value setting unit 4 is provided as a driving force setting means and receives the first control value (the first torque reduction value) T TCS1 from the first traction control unit 2 and the second control value (the second torque reduction value) T TCS2 from the second traction control unit 3. The control value setting unit 4 then compares the first control value T TCS1 with the second control value T TCS2and sets the smaller value (ie, the value with a larger torque reduction value) as the control value (torque reduction value) T to be used by the driving force control device 1 TCS . The control value setting unit 4 then outputs the control value T TCS to the engine control unit 5. After receiving a control value T TCS indicating signal from the driving force control device 1, the engine control unit 5 carries out a control such that the driving force is limited to a value less than or equal to the control value T TCS is.

[0117] In particular, the driving force control device 1 according to Fig. 2 executes a driving force control program. In step S101, the first traction control unit 2 calculates a first control value T TCS1 , In step S102, the second traction control unit 3 calculates a second control value T TCS2 .

[0118] In step S103, the first control value T TCS1 and the second T TCS2 compared with each other. If the first control value T TCS1 less than or equal to the second control value T TCS2 is, the processing proceeds to step S104, where the first control value T TCS1 as tax value T TCS If, however, the first control value T TCS1 is greater than the second T TCS2 , the processing proceeds to step S105, where the second control value T TCS2 as tax value T TCS is set.

[0119] Subsequently, the control value T set in step S104 or S105 TCS output to the engine control unit 5 in step S106. Finally, the processing exits the program.

[0120] According to this embodiment, the first traction control unit 2 is provided, which is capable of estimating a tire force generated on a tire and estimating a friction circle limit as the maximum tire force that the tire can exert against a current road surface, and calculating a first torque reduction value based on a relationship between the tire force and the friction circle limit, and the second traction control unit 3 is capable of calculating a slip rate of the tire and calculating a second torque reduction value based on at least the slip rate. The control value setting unit 4 compares the first torque reduction value T TCS1 with the second torque reduction value T TCS2 and sets the smaller value (ie, the value with a larger torque reduction value) as a control value T to be used by the driving force control device 1 TCS. The control value setting unit 3 then outputs the control value T TCS to the engine control unit 5.

[0121] Therefore, in a driving state in which it is difficult to estimate a friction coefficient µ between the tires and the road surface, for example, when the vehicle is in a straight-ahead driving mode or in a starting mode, or in a driving state in which the adhesion forces of the tires in the lateral direction are not essential for the safety of the vehicle, the adhesion forces of the tires in the traveling direction can be appropriately used by the second traction control unit 3, which detects the slip rate of the tires and limits the drive torque. On the other hand, in a driving state in which the friction coefficient µ between the tires and the road surface can be estimated with high accuracy, for example,When the vehicle is in a cornering mode, tire slippage can be prevented by feedback control of the drive torque performed by the first traction control unit 2. This allows the tire grip forces in the lateral direction to be maintained at a high level, thereby increasing vehicle stability. For example, when the vehicle transitions from a cornering mode to a straight-ahead mode or a starting mode, or vice versa, the larger torque reduction value is set as the control value. This allows the vehicle to switch smoothly between modes without a sudden change in the control value, thereby achieving control according to which a driver feels a natural operating or functional feeling.

Claims

[1] Vehicle driving force control device comprising: a tire force estimator (2m) adapted to estimate a tire force generated on a tire; a friction circle limit estimator (2k) adapted to estimate a friction circle limit as a maximum tire force that the tire can exert against a current road surface; a slip rate calculating device (3b) adapted to calculate a slip rate of the tire; a first torque reduction value calculating means (2) adapted to calculate a first torque reduction value (TTCS1) based on a relationship between the tire force and the friction circle limit value; a second torque reduction value calculation device (3) adapted to calculate a second torque reduction value (TTCS2) based on at least the slip rate; and a control value setting device (4) which is suitable for comparing the first torque reduction value (TTCS1) with the second torque reduction value (TTCS2) and setting the smaller value as the control value (TTCS) for controlling a driving force of the vehicle. [2] The device of claim 1, further comprising: a road friction coefficient estimator (20) adapted to estimate a road surface friction coefficient (µ) of the current road surface; and a ground force estimation device (2e) adapted to estimate a ground force (Fzf, Fzr) acting on the tire; wherein the friction circle limit value estimating means (2k) estimates the friction circle limit value based on the road surface friction coefficient (µ) and the ground force (Fzf, Fzr). [3] The apparatus according to claim 1 or 2, wherein the tire force estimating means (2m) estimates a first tire force output from a motor to the tire and / or a second tire force actually generated between the tire and the road surface as the tire force. [4] The apparatus according to claim 3, wherein the first torque reduction value calculating means (2) comprises: a first excessive tire force estimating section (2n) adapted to estimate a tire force exceeding the friction circle limit value as a first excessive tire force based on the first tire force and the friction circle limit value; a second excessive tire force estimating section (2o) adapted to estimate a tire force exceeding the friction circle limit value as a second excessive tire force based on the second tire force and the friction circle limit value; and a first torque reduction value setting section (2r) adapted to set the first torque reduction value (TTCS1) based on the first excessive tire force and the second excessive tire force. [5] The apparatus according to claim 4, wherein the first torque reduction value setting section sets the first torque reduction value (TTCS1) based on the larger one of the first and second excessive tire forces. [6] Device according to one of claims 1 to 5, wherein the control value setting device (4) limits the driving force such that the driving force becomes less than or equal to a lower of the two torque reduction values ​​(TTCS1, TTCS2).

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