JP2010081720A - Vehicular driving force controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicular driving force controller which secures running stability on an acceleration turn of a rear-wheel drive vehicle. <P>SOLUTION: Limit driving forces F<SB>XL_LIM</SB>, F<SB>XR_LIM</SB>are calculated from renewed slip ratio σ<SB>L_REF</SB>, σ<SB>R_REF</SB>existing near the intersection of L<SB>M</SB>=0, L<SB>CP</SB>=0 (S12). Process is shifted to S13 for comparison using a target driving force F<SB>REF</SB>obtained in S4 and the limit driving forces F<SB>XL_LIM</SB>, F<SB>XR_LIM</SB>. The smaller one is set as a final target driving force F<SB>REF</SB>. The process is shifted to S14. Because the driving force is limited so as not to exceed the limit driving forces F<SB>XL_LIM</SB>, F<SB>XR_LIM</SB>calculated from a rear wheel local part C<SB>rREF</SB>, which becomes the stability limit of the right and left rear wheel, an oversteer can be prevented on the acceleration turn of the rear-wheel drive vehicle while securing the driving force required by an occupant. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle driving force control device, and in particular, to ensure running stability during acceleration turning of a rear wheel drive vehicle.

  A motor-driven vehicle such as a hybrid vehicle has many advantages such as having an energy recovery function, easy distribution of drive devices, and fast torque response. Proposals have been made.

  Patent Document 1 is a hybrid vehicle that can independently control the driving force of the left and right rear wheels, and determines the required driving force of the occupant from the vehicle speed and the accelerator pedal opening, and determines the required turning amount of the occupant from the steering angle of the steering wheel and the vehicle speed. While determining, the technique which restrict | limits the maximum driving force according to turning request | requirement amount is proposed.

  In Patent Document 1, the maximum driving force change associated with the battery state change is reduced as the passenger's turn request amount increases, so that the maximum driving force change can be reduced without consuming battery energy. Further, since the required turning amount is any one of the lateral force, yaw rate, and slip angle of the vehicle, the maximum driving force can be limited by the same vehicle behavior parameter used for the determination without being affected by the vehicle speed or the like. it can.

JP 2008-74328 A

  By the way, in the case of a rear-wheel drive vehicle, an acceleration operation during turning, that is, a so-called accelerator on, may cause the vehicle to become unstable such as oversteer. In order to ensure running stability during turning, it is necessary to balance the yaw moment caused by the front wheel lateral force and the anti-yaw moment caused by the rear wheel lateral force. Two are possible.

  The first factor is saturation of the rear wheel lateral force limit. Since the rear wheel is a driving wheel, if the tire force of the rear wheel is saturated before the front wheel, the yaw moment caused by the front wheel lateral force cannot be canceled by the anti-yaw moment caused by the rear wheel lateral force. Then, since the yaw moment on the front wheel side remains, the turning speed further increases, and an increase in the yaw rate of the vehicle cannot be prevented.

  The second factor is that the rear wheel lateral force increase is lower than the front wheel lateral force increase. Generally, when the rear wheel lateral force increase rate obtained based on the ratio of the lateral force change to the tire slip angle is relatively larger than the front wheel lateral force increase rate, so-called understeer, the rear wheel lateral force can be secured. The turning behavior of the vehicle is stable. However, when the rear wheel is a driving wheel, a forward driving force is generated, so that the lateral force is relatively reduced, and as a result, the rear wheel lateral force increase rate may become smaller and unstable. .

  That is, when turning, as the slip angle of the front wheel decreases, the slip angle of the rear wheel increases and the centrifugal force increases, so the vehicle slip angle increases. As the vehicle slip angle increases, the front wheel lateral force increases more greatly because the front wheel lateral force increase rate is larger than the rear wheel lateral force increase rate. Therefore, when the front wheel lateral force is balanced with the rear wheel lateral force, the sum of the front wheel lateral force and the rear wheel lateral force balances with the centrifugal force, so that a steady turn is obtained, but the front wheel lateral force and the rear wheel lateral force When the sum is smaller than the centrifugal force, the slip angle of the vehicle body increases and diverges more and more.

  In Patent Document 1, although it is possible to reduce the maximum driving force change without consuming battery energy, it is a proposal on the assumption of steady turning, and there is no suggestion or examination about vehicle instability during accelerated turning. It has not been.

  An object of the present invention is to provide a vehicle driving force control device that ensures running stability during acceleration turning of a rear wheel drive vehicle.

  The invention according to claim 1 is a vehicle driving force control device for controlling the driving force of the driving wheel, wherein the vehicle is accelerated by the driving means capable of independently driving the left and right rear wheels, the accelerator depression amount and the steering angle. When the vehicle is in an accelerated turning state, the driving force of the left and right rear wheels is calculated from the stability limit of the left and right rear wheels obtained based on the ratio of the lateral force change to the tire slip angle. Output control means for limiting the driving force so as not to exceed the limit acceleration driving force.

  In the invention of claim 1, since the output control means limits the driving force of the left and right rear wheels, the lateral force of the left and right rear wheels can be artificially increased, and the tire slip angle can be reduced. In addition, the driving force of the left and right rear wheels is limited so as not to exceed the limit acceleration driving force calculated from the stability limit of the left and right rear wheels obtained based on the ratio of the lateral force change to the tire slip angle. Driving force can also be secured.

  According to a second aspect of the present invention, in the first aspect of the present invention, a target yaw moment is set according to the steering angle, the vehicle speed, and the yaw rate of the vehicle, and the difference in driving force between the left and right rear wheels is controlled so as to be the target yaw moment. Moment control means, acceleration control means that sets the target acceleration of the vehicle based on the amount of depression of the accelerator so that the maximum acceleration is achieved when the accelerator is fully opened, and traction that performs brake traction control for each wheel so that a driving force exceeding the friction circle is not generated Control means, and the output control means controls the driving force of the left and right rear wheels while maintaining the target yaw moment.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, there is provided a relationship model between a tire slip angle and a slip ratio and a tire generation force, and the output control means includes the lateral force increase rate and a target yaw. The limit acceleration driving force is calculated from a slip ratio calculated based on a moment and the relation model.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the output control means uses the stability discriminant that is the stability condition of the characteristic equation obtained from the equation of motion of the turning motion. Is calculated.

  The invention according to claim 5 is the invention according to claim 2 or 3, wherein the output control means slips from a first evaluation function obtained from the stability limit and a second evaluation function obtained from the target yaw moment. It is characterized by calculating a rate.

  The invention according to claim 6 is the invention according to claim 5, wherein the output control means sets, as an optimum slip ratio, a slip ratio at which the first evaluation function is zero and the second evaluation function is minimum. It is characterized by that.

  According to a seventh aspect of the present invention, in the second aspect of the present invention, the yaw moment control means includes a feedforward calculation means for setting the first target yaw moment by a feedforward based on the yaw rate, and a first feedback feedback based on the yaw rate. A tire for setting a target tire driving force for the left and right rear wheels, as well as setting a target yaw moment by a sum of the first target yaw moment and the second target yaw moment. It has a driving force setting means.

  According to the first aspect of the present invention, the driving means capable of independently driving the left and right rear wheels, the acceleration turning detection means for detecting the acceleration turning state based on the accelerator depression amount and the steering angle, and when the vehicle is in the acceleration turning state Output control means for limiting the driving force so that the driving force of the left and right rear wheels does not exceed the limit acceleration driving force calculated from the stability limit of the left and right rear wheels obtained based on the ratio of the lateral force change to the tire slip angle Therefore, traveling stability during acceleration turning of the rear wheel drive vehicle can be ensured.

  In other words, the driving characteristics and the wheel lateral force that tend to contradict each other, that is, the driving force and the wheel lateral force that tend to decrease when one increases, the physical characteristics that have a direct causal relationship to the behavior of the vehicle body, the ratio of the lateral force change to the tire slip angle Therefore, oversteer can be prevented while securing the driving force required by the occupant during acceleration turning of the rear wheel drive vehicle.

  According to the second aspect of the present invention, the yaw moment control means for setting the target yaw moment according to the steering angle, the vehicle speed, and the yaw rate of the vehicle, and controlling the driving force difference between the left and right rear wheels so as to be the target yaw moment, Acceleration control means for setting the target acceleration of the vehicle based on the amount of depression of the accelerator so as to achieve maximum acceleration, and traction control means for performing brake traction control for each wheel so that a driving force exceeding the friction circle does not come out, Since the output control means controls the driving force of the left and right rear wheels while maintaining the target yaw moment, it is possible to ensure the running stability of the vehicle while maintaining the turning characteristics during acceleration turning.

  According to a third aspect of the present invention, there is provided a relationship model between a tire slip angle and a slip ratio and a tire generating force, and the output control means calculates a slip ratio calculated based on the lateral force increase rate and a target yaw moment. Since the limit acceleration driving force is calculated from the relationship model and the relationship model, stable acceleration turning can be performed while satisfying the target yaw moment.

  According to the invention of claim 4, the output control means calculates the stability limit by a stability discriminant that is a stability condition of the characteristic equation obtained from the equation of motion of the turning motion, thereby ensuring the stability of the system. be able to.

  According to the invention of claim 5, the output control means calculates the slip ratio from the first evaluation function obtained from the stability limit and the second evaluation function obtained from the target yaw moment. Accelerated turning that satisfies

  According to a sixth aspect of the present invention, the output control means satisfies the target yaw moment in order to set the slip ratio at which the first evaluation function is zero and the second evaluation function is minimum as the optimum slip ratio. And stable turning control becomes possible. Moreover, even if the solution is theoretically a solution that satisfies both evaluation functions, that is, a calculation that does not include a solution that is both zero, a suitable slip ratio can be obtained.

  According to the invention of claim 7, the yaw moment control means sets the first target yaw moment by feedforward based on the yaw rate, and sets the second target yaw moment by feedback based on the yaw rate. And a tire driving force setting means for setting a target tire driving force for the left and right rear wheels, as well as setting a target yaw moment by the sum of the first target yaw moment and the second target yaw moment. The target yaw moment can be easily obtained regardless of changes in vehicle body characteristics.

  Hereinafter, the best mode for carrying out the present invention will be described.

  Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is an example in which the present invention is applied to an electrically driven vehicle equipped with an electrically driven system and independently driving left and right rear wheels with respective electric motors.

  As shown in FIG. 1, in this vehicle 1, left and right front wheels 2L and 2R are driven wheels, and left and right rear wheels 3L and 3R are drive wheels, and left and right electric motors 4L and 4R mounted on the rear part of the vehicle 1 The rear wheels 3L and 3R can be independently driven. That is, the driving force of the vehicle 1 is transmitted from the electric motors 4L and 4R to the rear wheel axles 5L and 5R through a reduction gear (not shown), and is transmitted to the left and right rear wheels 3L and 3R connected to each other. A battery 6 is disposed in front of the electric motors 4L and 4R in the vehicle 1, and is connected to each of the electric motors 4L and 4R so that electric power can be supplied.

  The left and right front wheels 2L, 2R and rear wheels 3L, 3R include discs 7a to 10a that rotate integrally with the wheels, and calipers 7b to 10b that receive the supply of brake hydraulic pressure and brake the rotation of these discs 7a to 10a. Brake devices 7 to 10 are provided, and a braking system 11 for operating these brake devices 7 to 10 is provided.

  The braking system 11 includes a tandem master cylinder 13 that is operated by a brake pedal 12, wheel cylinders (not shown) provided in the calipers 7b to 10b, and hydraulic passages that connect the cylinders. Further, the braking system 11 is shared by the rear wheel ABS hydraulic system and the front wheel ABS hydraulic system for anti-skid brake control, the rear wheel TRC hydraulic system for brake traction control, and these hydraulic systems. And a pump drive motor. The configuration of the braking system is well known and will not be described in detail.

  The control unit 14 of the vehicle 1 is turned on when the brake pedal 12 is operated, the wheel speed sensors 15 to 18 for detecting the wheel speeds of the left and right front and rear wheels, the steering angle sensor 20 for detecting the steering angle of the steering handle 19, respectively. Detection signals are input from the brake switch 21, an accelerator sensor 23 that detects the amount of depression of the accelerator pedal 22, a vehicle speed sensor 24 that detects the traveling speed of the vehicle 1, and a yaw rate sensor 25 that detects the yaw rate of the vehicle 1. It is configured to be.

  Next, a control system of the driving force control apparatus according to the present embodiment will be described with reference to FIGS. The control system of the driving force control device is stored inside the control unit 14, and for convenience, in FIG. 2, the other mechanism of the vehicle 1 and the control system of the driving force control device are shown separately.

As shown in the block diagram of FIG. 2, the control system of the driving force control device controls the left and right rear wheels 3L, 3R so as to achieve a target yaw moment (hereinafter referred to as M _REF ) set by the steering angle, the vehicle speed, and the yaw rate. A yaw moment control unit 30 (yaw moment control means) that controls the driving force difference, and an acceleration control unit 31 (acceleration control) that sets the target acceleration of the vehicle 1 based on the amount of depression of the accelerator 22 so that the accelerator 22 is fully opened when the accelerator 22 is fully opened. Means), a traction control unit 32 (traction control means) that performs brake traction control for each wheel so that a driving force exceeding the friction circle set from the tire force of each wheel is not generated, and M _REF is maintained and calculated The output control unit 33 (output control means) controls the driving force of the left and right rear wheels so as not to exceed the limit acceleration driving force.

(Yaw moment control)
The yaw moment control unit 30 obtains a target yaw rate setting unit 34 that sets a target yaw rate from the detected steering angle and vehicle speed, and feedforward (hereinafter referred to as FF) processing from the steering angle, vehicle speed, and current yaw rate γ. A feedforward calculation unit 35 (feedforward calculation means) for calculating the obtained target yaw moment, so-called _{MREF_FF} , and a target yaw moment obtained by feedback (hereinafter referred to as FB) processing from the target yaw rate and the current yaw rate, so-called a feedback calculation unit 36 for calculating the M _{REF_FB} (feedback arithmetic _unit), and the target yaw moment setting unit 37 calculates the _{M REF} from the sum of the _{M REF_FF} and _{M REF_FB,} target driving force of the left and right rear wheels 3L, 3R to be described later _{(hereinafter, F REF} indicating a) from and _{M REF} Target driving force of the people right rear wheel respectively consist driving force distribution unit 38. which is calculated _{(hereinafter, F XL_REF, F XR_REF} denoted). The target yaw moment setting unit 37 and the driving force distribution unit 38 correspond to tire driving force setting means.

  The target yaw rate setting unit 34 calculates a target yaw rate gain using a map of the vehicle speed and yaw rate gain stored in advance, and uses a first-order lag-based vehicle speed-sensitive reference model of steering angle input to calculate the target yaw rate gain. The target yaw rate is calculated.

γ _REF = (K _yaw (V) × δ _f ) / (T _CV × s + 1)
Γ _REF is a target yaw rate, K _yaw is a target yaw rate gain, V is a vehicle speed, δ _f is a steering angle, T _CV is a target yaw rate time constant, and s is a Laplace operator. For convenience, as shown in FIG. 3, the vehicle 1 has a tread length of lt, a center of gravity and a front wheel axle distance of l _f , a center of gravity and a rear wheel axle distance of l _r , a vehicle speed V, a steering angle δ _f , a slip A model is set in which the vehicle is turning at an angle β, a yaw rate γ, and a yaw moment M, the left rear wheel driving force is F _XL , and the right rear wheel driving force is F _XR .

The feedforward calculation unit 35 calculates using the following equation in order to compensate only for the rising of the steering response.
M _REF — _FF = K _FF × ((K _yaw (V) × δ _f ) −γ)
_KFF is an FF control gain. The controller outputs the largest value immediately after the start of steering, and converges to zero as the yaw rate approaches the steady yaw rate. Since the yaw rate is used as an argument, it is not a general FF control, but it ignores the latest behavior of γ _REF and predicts and uses values in the future. This is called FF control.

  The feedback calculation unit 36 uses a general PI controller to calculate according to the following formula.

Note that K _{P — FB} and K _{I — FB} are an FB control P gain and an FB control I gain.

Since the driving force distribution unit 38 uniquely determines the driving force that satisfies the target driving force F _REF and the target yaw moment M _REF calculated by the target yaw moment setting unit 37, the target driving of each of the left and right rear wheels is determined. The forces F _{XL_REF} and F _{XR_REF} are calculated by the following equations.
F _{XL_REF} = −M _REF / lt + F _REF / 2
F _{XR_REF} = + M _REF / lt + F _REF / 2

(Acceleration control)
The acceleration control unit 31 is configured to be able to proportionally apply a driving force that achieves a maximum speed when the accelerator pedal 22 is fully opened, and applies a target driving force F _REF (F _{XL_REF} , F _{XR_REF} ) to the accelerator pedal 22. Using the opening degree θ and the wheel speeds ω _RL and ω _{RR of the} left and right rear wheels, the following formula is used.

F _REF = mK _AC θ: θ = 0 to 1
Here, m is the vehicle weight, and _KAC is the acceleration gain. The effect of wheel rotation compensation is compensated by traction control described later.

(Traction control)
The traction control unit 32 _obtains a target after traction from F _{XL_REF} , F _{XR_REF} calculated by the driving force distribution unit 38, wheel lateral forces F _YL , F _YR , and friction circle radii F _{MAX — L} , F _{MAX — R.} The driving forces F _{XL_REF2} and F _{XR_REF2} are calculated. The friction circle radius F _{MAX — L} of the left rear wheel can be obtained by the following equation.

Similarly, the friction circle radius F _{MAX — R} of the right rear wheel is obtained.

Using the friction circle radii F _{MAX — L} and F _{MAX — R} , the target driving force F _{XL — REF2} of the left rear wheel is calculated by the following equation.

Here, sign (•) indicates the sign of the argument, and min (•) indicates the minimum value of the argument. Similarly, the target driving force F _{XR_REF2} for the right rear wheel is calculated. Further, correction amounts ΔF _{XL_REF} and ΔF _{XR_REF} are calculated using the following equations.
ΔF _{XL_REF} = F _{XL_REF2} -F _{XL_REF}
ΔF _{XR_REF} = F _{XR_REF2} -F _{XR_REF}

Next, the traction control unit 32 calculates driving force commands F _{XL_CMD} and F _{XR_CMD} for compensating the yaw moment using the correction amounts ΔF _{XL_REF} and ΔF _{XR_REF} . Since the traction control is performed on each of the left and right rear wheels 3L and 3R, the target yaw moment M _REF may not be satisfied if the driving force is limited by a predetermined wheel. Accordingly, when the driving force is limited at a specific wheel, processing for reducing the driving force of the opposite wheel is performed so as to satisfy the target yaw moment M _REF . First, the direction of the moment due to the limitation of the driving force is calculated by the following equation.
ΔM = −ΔF _{XL_REF} + ΔF _{XR_REF}

Next, based on the calculation results using the correction amounts ΔF _{XL_REF} and ΔF _{XR_REF} , F _{XL_CMD} , F _{XR_CMD for} each of three cases where the driving force is not limited, the yaw moment increases, and the yaw moment decreases. Ask for. First, when the driving force is not limited, that is, when ΔM is zero,

When the yaw moment increases, that is, when ΔM exceeds zero,

When the yaw moment decreases, that is, when ΔM is less than zero,

Can be expressed as

Next, the driving force is converted into torque, and processing relating to inertia compensation of each wheel is performed. The tire torque commands T _{L — CMD} and T _{R — CMD} are calculated by substituting the previously calculated driving force commands F _{XL — CMD} and F _{XR — CMD} into the following equation.

The wheel angular acceleration is obtained by pseudo-differentiating the wheel speed, and is used as a low-pass filter for suppressing noise through a first-order lag filter with _TCW as a time constant.
As shown in FIG. 4, since the rear wheel lateral force can be set based on the friction circle radius, the rear wheel lateral force limit can be prevented from being saturated. That is, the yaw moment caused by the front wheel lateral force can be effectively canceled by the anti-yaw moment caused by the rear wheel lateral force.

(Output control)
The output control unit 33 at a predetermined slip angle, a local C _P setting unit 39 for setting a stability limit to ensure the stability of the vehicle rear wheels based on the stable discriminant (hereinafter, referred to as local C _P), the limit driving It is comprised from the force setting part 40 and the driving force restriction | limiting part 41 which restrict | limits a target driving force with a limit driving force. As shown in FIG. 5, the local C _P in the present embodiment, the wheel side force change rate at predetermined slip angle is defined by the so-called local tangent slope. Accordingly, those originally a topical C _P represented by dashed line A, as shown in FIG. 6, if the reduced [Delta] F _X driving force, because the lateral force increases, as indicated by the solid line B in FIG. 5 , it is possible to obtain a large local C _P of the inclination angle than the local C _P indicated by a broken line.

The local _CP setting unit 39 has a characteristic equation (2) that can be obtained from the theoretical equation of motion (1) in a turning motion at a constant speed.

Incidentally, I _Z yaw inertia moment, C _f is the front wheel lateral force variation rate (one wheel portion of cornering power) in the slip angle of, C _r is the cornering power of the wheels lateral force variation rate (one wheel min in slip angle of the rear wheels ).

Here, equation (2) is that it can be predetermined turning state origin and the C _f, the Cr and local C _P at that time, the saturation of the wheel is suppressed by the traction control, tire curve Is constant, the constant term in equation (2) is positive. That is, the turning stability condition of the vehicle 1 can be expressed by Expression (3). Further, based on the equation (3), the rear wheel local C _P (hereinafter referred to as C _rREF ) that becomes the stability limit can be expressed by the equation (4).

In Formula (4), there is a front wheel local _CP (hereinafter referred to as C _f ), and this local C _f is a deviation of the lateral force formula of the physical model Brush Model by a slip angle. It is obtained by differentiating. Accordingly, the local C _f can be calculated using a formula similar to formula (9) described later. Since the front wheel is a driven wheel, the slip rate σ is calculated as zero.

In the limit driving force setting unit 40 will be described _later, since _{the C Rref} sets the limit driving force in a range satisfying the equation (3), the local _{C P} setting unit 39 is required relation between the driving force and the _{C Rref.} This relational expression is obtained using a Brush Model, which is a physical model of the slip angle and slip ratio and the tire generation force. The tire model in the case where the range where the adhesive zone exists in Formula (5) and Formula (6), that is, not so-called total slip is shown.

Note that μ road surface friction coefficient, F _Z is the vertical load, sigma is around the slip ratio, the λ tire adhesive zone length ξs and composite slip ratio is respectively equations (7) and (8).

Incidentally, K _beta tire longitudinal stiffness, K _s indicates the tire lateral stiffness. Further, cos θ and sin θ are set as follows by approximating the input angle.
cos θ = σ / λ
sin θ = (K _β (1 + σ) tan β) / K _s λ
The following equation (9) of local C _P (C _rREF ) is set by partial differentiation of equation (6) with the slip angle.

The local _CP setting unit 39 obtains the local C _P (C _f ) of the front wheel by assuming that the slip ratio σ of the front wheel, which is the driven wheel, is zero, and substituting it into the formula (4) according to equation (9). It has set a stability limit rear of the local _C P _{(C rREF).}

The limit driving force setting unit 40 satisfies the driving force difference (target yaw moment M _REF ) required by the yaw moment control unit 25 for the purpose of limiting the driving force, and (b) the rear wheel local _CP is stable. A process of calculating a driving force that is a stability limit of the vehicle 1 when the vehicle is below the limit is performed. Per processing, for erasing the slip ratio σ from the aforementioned equations (5) and equation (9), it is mathematically is difficult to expression and the driving force F _X and local C _P, the limit driving force In the setting unit 40, the driving force _{FX_REF} is set by first _{obtaining the} slip rate σ by numerical approach and substituting the slip rate into the equation (5). First, based on the above (a) and (b), expressions (5) and (9) are expressed as follows.

Since M _{REF in} Expression (10) is set by the yaw moment control unit 30 and _{Cr REF} in Expression (11) is determined by Expression (4), the limit driving force setting unit 40 has Expression (10) and Expression (10). Slip ratios σ _L and σ _R satisfying both of (11) are obtained by convergence calculation, and converted into driving force _{FX_REF} using equation (5). The subscripts L and R indicate the left wheel and the right wheel, respectively, and the road surface friction coefficient μ, the contact load F _Z , and the slip angle β of each wheel can be substituted with experimental values.

First, in order to examine the slip ratios σ _L and σ _R satisfying the expression (10), the following expression is set.
L _M = W _M (M _REF −M (σ _L , σ _R )) ² (12)
W _M is a moment weighting factor, and M (σ _L , σ _R ) is a yaw moment at a predetermined left-right slip ratio. That is, Expression (12) is a function that becomes zero when the target yaw moment M _REF and the yaw moment calculated from the slip ratio coincide with each other, and increases as the distance increases.

FIG. 7 shows an example in which σ _L and σ _R in Expression (12) are changed parametrically. Figure 7a, the horizontal axis sigma _L, the vertical axis sigma _R, the height axis is _{L M.} When a realistic moment is considered from the characteristics of the tire curve, the line of L _M = 0 has a simple shape as shown in FIG.

Next, consider the local _{C P.} FIG. 8A shows the equation (9) with the horizontal axis representing the slip angle, the vertical axis representing the local _CP , and the slip ratio as a parameter. As shown in FIG. 8 (a), when a high slip angle, to increase the local C _P, increases the slip rate, it will increase the so-called driving force. However, in regions of high slip angle, as well as increased stability due to local C _P, it is not necessary to consider the local C _P an increase occurs in the lateral forces decrease and the slip angle increases due to increased driving force, the vehicle control is difficult Become. Therefore, in the limit driving force setting unit 40 in the present embodiment, the expression (9) is replaced with the following expression that is a safer approximation.

As shown in FIG. 8 (b), the equation (13) can be a function in which the local _CP is increased by reducing the driving force even in a region where the slip angle is large. Since a small local _CP (that is, a small driving force) can be calculated as compared with the equation (9), the driving safety is excellent. Next, in order to examine the slip ratios σ _L and σ _R that satisfy Expression (13), the following expression is set.

L _CP = W _CP (C _rREF −C _r (σ _L , σ _R )) ² (14)
W _CP weighting factor _{moment, C r (σ L, σ} R) is local _{C P} at a given lateral slip rate. In other words, equation (14) is zero if the local C _P which is calculated from the target local C _P and the slip rate match, and a larger function with distance.

FIG. 9 shows an example in which σ _L and σ _R in Expression (14) are changed parametrically. In FIG. 9, the horizontal axis is σ _L , the vertical axis is σ _R , and the height axis is L _CP . FIG. 9A shows a typical shape when the turning lateral acceleration is small. FIG. 9B shows a case where the turning lateral acceleration becomes large and the driving force needs to be significantly limited. In the case of FIG. 9B, the line with L _CP = 0 appears in a very small slip ratio and a large slip ratio. However, the slip ratio converges to a small value as long as it is limited to the range of the adhesion region. A solution can be obtained.

In the limit driving force setting unit 40, using equation (12) and (14), the rear wheel topical C _P is numerically calculated upper limit slip rate not less than the stability limit C _Rref. As a method for calculating the slip ratio, the adhesive zone, on the line of L _{M =} 0 satisfying the equation (10), it is performed convergence calculation for obtaining a slip rate pair to minimize the local C _P. The reason for adopting the convergence calculation is that there is a possibility that the convergence is made at a point deviating from the point satisfying the equation (10) due to the difference in the slip rate change amount between the equation (13) and the equation (14). b) for topical C _P, you may not need to drive force limit, because not necessarily have to converge to the target local C _P.

Next, a specific convergence calculation method will be described. As shown in FIG. 10, from the characteristics of the tire force curve, a slip ratio pair that satisfies L _M = 0 satisfying the equation (10) of the target yaw moment M _REF can be expressed as a line L1. The inclination toward the line L1 has a shape as indicated by each arrow C.

For topical C _P, in the adhesive area, the local C _P higher the slip ratio increases is reduced, a small local C _P as a stability limit from equation (13), as shown in FIG. 9 (a), a large slip It can be expressed as an arc-shaped line centering on the rate. This is shown together with the line of L _M = 0 as the line L2 in FIG. As a calculation step,
As shown in FIG. 11, a direction toward the line L1 is a vector A, and a direction toward the line L2 is a vector B.
A component perpendicular to the vector A of the vector B is a vector C.
The vector A + vector C is the moving direction in the convergence calculation.

By said calculation step, the movement direction to meet the target yaw moment M _REF is not hindered, can be moved in a direction to reduce the local C _P, finally L _{M =} 0, the local C _P of on so-called line L1 It becomes possible to obtain the limited slip ratios σ _{L_REF} and σ _{R_REF} that converge to the minimum value. The vectors A and B can be obtained by partially differentiating the equations (12) and (14) with the slip rates σ _L and σ _R. By substituting the limited slip ratios σ _{L_REF} and σ _{R_REF} calculated by the above calculation into the equation (5), the limited driving forces F _{XL_LIM} and F _{XR_LIM} for the left and right rear wheels are set. The search range related to the left rear wheel is limited to the drive-side range with the magnitude of the slip ratio obtained by the equation (15) for calculating the slip ratio that leaves the adhesion area as the upper limit. Similarly, the range is set for the right rear wheel.

The driving force limiting unit 41 _compares the sum of the target driving force F _REF set by the acceleration control unit 31 and the limiting driving forces F _{XL_LIM} and F _{XR_LIM} set by the limit driving force setting unit 40 using the equation (16). The smaller one is set as the final target driving force F _REF .
F _REF = min (F _{XL_LIM} + F _{XR_LIM} , F _REF ) (16)
However, min (•) is a function that outputs the minimum value among the arguments. The final target driving force F _REF is sent to the traction control unit 32 and becomes the target driving force of the motors 4L and 4R.

  Next, a driving force control process according to the present embodiment will be described with reference to the flowchart of FIG. Si (i = 1, 2,...) Indicates each step.

In S1, various signals, road surface friction coefficient μ of each wheel, contact load F _Z , slip angle β, slip rate σ, vehicle speed V, etc. are read or estimated. After capturing various signals in S1, the output control unit 33 (S2), the yaw moment control unit 30 (S3), and the acceleration control unit 31 (S4) start processing in parallel.

In S3 following S1, the yaw moment control unit 30 calculates the target yaw moment M _REF based on the steering angle, the vehicle speed, and the yaw rate, and proceeds to S8. In S4 following S1, the acceleration control unit 31 calculates the target driving force F _REF based on the accelerator pedal opening and the wheel speed, and _proceeds to S13.

In S2, the left and right front wheels 2L, the state of the 2R, respectively By substituting the equation (9), to estimate the local C _P of the left and right front wheels, respectively, by the sum of both the local C _P obtains a front wheel local C _f. Next, the rear wheel local C which becomes the stability limit by substituting the front wheel local C _f into the stability discriminant (4) which is the stability condition of the equation (2) obtained from the equation (1) based on the yaw rate or the tire slip angle. _rREF is calculated (S5), and the process proceeds to the next.

Next, the upper limit of the slip ratio convergence calculation range is set by equation (15) (S6), and a temporary slip ratio, so-called initial value is set (S7). In the initial value setting, the previously determined slip rates s _L and s _R are set as temporary slip rates. Although the temporary slip ratio can be used as the origin, the previous value is used in this embodiment for the purpose of shortening the calculation time.

Next, the convergence calculation of the slip ratios σ _L and σ _R is started using the target yaw moment M _REF obtained in S3 and the target rear wheel local Cp C _rREF obtained in S5 (S8). In S8, the rear wheel topical C _P evaluation value and the yaw moment evaluation value of the rate of change, the slip rate evaluation function Tokoroishiki (12) and Equation (14) sigma _L, is partially differentiated by sigma _R. The rate of change of the rear wheel topical C _P is the vector B, the rate of change in yaw moment corresponds to the vector A.

Based on the change rate calculated in S8, the movement direction to meet the target yaw moment M _REF is not disturbed, the vector C which moves in a direction coming close to the local C _P to target local C _P, setting the update direction of the so-called temporary slip ratio (S9), and the temporary slip ratio set in S7 is updated (S10).

Next, it is determined whether or not to end the convergence calculation. (S11). As a result of the determination in S11, when it is determined that the values of the evaluation functions of Expression (12) and Expression (14) are both sufficiently small and exist near the intersection of L _M = 0 and L _CP = 0, the convergence calculation is performed. When finished, the process proceeds to S12. Incidentally, the end determination condition, if it exceeds convergence calculation range L _M is set at a sufficiently small and S6, or the number of times the predetermined number of convergence operation loop, it is possible to for example, when more than 100 times. If the result of determination in S11 is No, the process proceeds to S8.

Substituting the updated slip rates σ _{L_REF} and σ _{R_REF} existing near the intersection of L _M = 0 and L _CP = 0 into the equation (5) to obtain the limiting driving forces F _{XL_LIM} and F _{XR_LIM} (S12), The process proceeds to S13. In S13, the target driving force _{F REF} obtained in S4, the limiting drive force _{F XL_LIM,} by using the sum of _{F XR_LIM} comparison, set smaller as the final target driving force _{F REF,} the process proceeds to S14.

In S14, the traction control by the friction circle is executed for the final target driving force _FREF , and the process is terminated. That is, depending on the running state of the vehicle, rear wheel topical C _P be multiplied much driving force is present may not fall below the stability limit, to compensate the final safety in traction control by the friction circle Yes.

Next, operations and effects of the driving force control apparatus according to this embodiment will be described.
In _order to limit the driving force so as not to exceed the limit acceleration driving force F _{XL_LIM} , F _{XR_LIM} calculated from the rear wheel local _{Cr REF} that becomes the stability limit of the left and right rear wheels, Oversteer can be prevented while ensuring the maximum driving force required by the occupant. Further, since the driving forces F _XL and F _XR of the left and right rear wheels are controlled while maintaining the target yaw moment M _REF , it is possible to ensure the running stability of the vehicle while maintaining the turning characteristics during the acceleration turning. .

Further, in order to calculate the limit acceleration driving force from the slip ratios σ _{L_REF} , σ _{R_REF} calculated based on the rear wheel local _{Cr REF} and the target yaw moment M _REF that are the stability limits, and the tire model (5), Stable acceleration turning can be performed while satisfying the target yaw moment M _REF . In addition, the rear wheel local _{Cr REF} that is the stability limit is calculated by the stability discriminant (4), which is the stability condition of the characteristic equation (2) obtained based on the yaw rate or tire slip angle from the motion equation (1) of the turning motion. Therefore, the stability of the system can be ensured.

In order to calculate the slip ratio from the equation (12) that is the first evaluation function obtained from the target yaw moment M _REF and the equation (14) that is the second evaluation function obtained from the rear wheel local _{Cr REF} that is the stability limit. Accelerated turning that satisfies the target yaw moment M _REF is possible. Furthermore, since the slip ratio at which the first evaluation function is zero and the second evaluation function is the minimum is set as the optimum slip ratios σ _{L_REF} and σ _{R_REF} , a general positive definite function is used as the evaluation function and is minimized. More stable turning control is possible than the method for obtaining the slip ratio. Moreover, even when the calculation is theoretically free of a solution, a suitable slip ratio can be obtained.

Further, the expression rear wheel topical C _P (9) without, for using the equation (13) as a substitute formula, by reducing the slip ratio, the local C _P is increased, the driving force in order to ensure the local C _P It is possible to avoid a decrease in lateral force caused by an increase in so-called spin generation.

  In addition, various modifications can be added without departing from the spirit of the present invention. The electrically driven vehicle that is independently driven by the motor is not limited to the motor alone, and any control can be applied as long as the drive wheels are independently driven, such as a hybrid vehicle equipped with an engine.

It is a block diagram of the drive control apparatus for vehicles which concerns on an Example. 1 is a block diagram of a vehicle drive control device according to an embodiment. FIG. It is the turning model of the vehicle which concerns on an Example. It is explanatory drawing which shows the relationship between a driving force and a rear-wheel lateral force based on a friction circle. It is a relationship figure of the slip angle of a rear-wheel drive vehicle, and lateral force change rate. It is explanatory drawing which shows the relationship between the driving force and lateral force of a rear-wheel drive vehicle. An evaluation function according to the target yaw moment, the horizontal axis s _L, the vertical axis is s _R, height axis shows a relationship diagram of the L _M. It is an evaluation function related to the target yaw moment, and shows a relationship diagram in the case of considering a realistic moment from the characteristics of the tire curve. A relationship between the slip ratio and the local C _P, shows a relation diagram according to the equation (9). A relationship between the slip ratio and the local C _P, shows a relation diagram according to the equation (13). An evaluation function according to the local C _P, shows a relationship diagram when turning lateral acceleration is small. An evaluation function according to the local C _P, shows a relationship diagram when turning lateral acceleration is large. It is an evaluation function related to the target yaw moment, and is a diagram showing a slip ratio pair that satisfies the target yaw moment and the inclination of each point. It is a figure explaining the moving direction of a convergence calculation. It is a flowchart of the drive control which concerns on an Example.

Explanation of symbols

1 vehicle 3L left rear wheel 3R right rear wheel 4L left motor 4R right motor 14 control unit 20 steering angle sensor 23 accelerator sensor 30 yaw moment control unit 31 acceleration control unit 32 traction control unit 33 output control unit 35 feedforward calculation unit 36 feedback Calculation unit 37 Target yaw moment setting unit 38 Driving force distribution unit

Claims (7)

A vehicle driving force control device for controlling the driving force of a driving wheel,
Driving means capable of independently driving the left and right rear wheels;
Acceleration turning detection means for detecting an acceleration turning state based on an accelerator depression amount and a steering angle;
When the vehicle is in an accelerated turning state, the driving force of the left and right rear wheels is driven so as not to exceed the limit acceleration driving force calculated from the stability limit of the left and right rear wheels obtained based on the ratio of the lateral force change to the tire slip angle. An output control means for limiting the force; A yaw moment control means for setting a target yaw moment according to a steering angle, a vehicle speed, and a yaw rate of the vehicle, and controlling a driving force difference between left and right rear wheels so as to be the target yaw moment;
Acceleration control means for setting the target acceleration of the vehicle based on the amount of depression of the accelerator so that the maximum acceleration is obtained when the accelerator is fully opened;
Traction control means for performing brake traction control for each wheel so that a driving force exceeding the friction circle is not generated,
2. The vehicle driving force control device according to claim 1, wherein the output control means controls the driving force of the left and right rear wheels while maintaining the target yaw moment. It has a relationship model between tire slip angle and slip rate and tire generation force,
The said output control means calculates the said limit acceleration driving force from the slip rate calculated based on the said lateral force increase rate and the target yaw moment, and the said relationship model. Vehicle driving force control device.   The said output control means calculates the said stability limit by the stability discriminant which is a stability condition of the characteristic equation obtained from the equation of motion of turning motion, The vehicle use in any one of Claims 1-3 characterized by the above-mentioned. Driving force control device.   4. The vehicle according to claim 2, wherein the output control means calculates a slip ratio from a first evaluation function obtained from the stability limit and a second evaluation function obtained from the target yaw moment. Driving force control device.   6. The vehicle driving force control according to claim 5, wherein the output control means sets a slip ratio at which the first evaluation function is zero and the second evaluation function is minimum as an optimum slip ratio. apparatus. The yaw moment control means includes a feed forward calculation means for setting a first target yaw moment by feed forward based on a yaw rate;
Feedback calculation means for setting the second target yaw moment by feedback based on the yaw rate;
The tire driving force setting means for setting a target tire driving force for the left and right rear wheels, and setting a target yaw moment by a sum of the first target yaw moment and the second target yaw moment. The vehicle driving force control device according to claim 2.