CN211001300U

CN211001300U - Vehicle control device

Info

Publication number: CN211001300U
Application number: CN201921343370.XU
Authority: CN
Inventors: 坂上恭平; 矢崎彻
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2018-10-25
Filing date: 2019-08-19
Publication date: 2020-07-14
Anticipated expiration: 2029-08-19
Also published as: JP7011998B2; JP2020066361A

Abstract

A vehicle control device is a vehicle control device having a control unit (U) that controls a vehicle (1) including a power transmission member (D) and tires (T) attached to front and rear wheels, wherein the control unit (U) determines that a slip state of the tires (T) is apparent from a road surface as a tire (T) that becomes a front wheel (WfR, Wf L) or a rear wheel (WrR, Wr L) due to elastic deformation of the tire (T)An elastic slip state in which the tire (T) is in a slip state or a slip state in which the tire (T) is actually slipping on the road surface, and when it is determined that the tire (T) has been shifted from the elastic slip state to the slip state, the rear wheel steering angle (WrR, Wr L) which is the steering angle of the rear wheels (WrR, Wr L) is changed so that the slip state of the tire (T) is changed to the elastic slip state₂)。

Description

Vehicle control device

Technical Field

The present invention relates to a vehicle control device that performs control for suppressing slippage of a drive wheel of a vehicle.

Background

A traction control device for a vehicle that controls the output of a drive source so that the drive wheels driven by the drive source generate an optimum traction force to cause the slip of the drive wheels to follow a reference slip is known, for example, as described in patent document 1 below.

However, in the traction control of the vehicle in the past, when the front wheel and the rear wheel are simultaneously slipping, the true value of the ground speed is unknown, so that an error becomes large, and it is difficult to detect a minute slip with high accuracy.

Even if slip can be detected with high accuracy, when a vehicle including front wheels and rear wheels as wheels turns, a turning force (force in a direction perpendicular to the traveling direction of the wheels when the vehicle is viewed from above) acts on the wheels on the side of the drive wheels in addition to the driving force or the braking force. As a result, the load on the drive wheels increases, and the slip amount of the drive wheels increases. In this case, control for stabilizing the behavior of the vehicle is required.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent No. 5945571 publication

SUMMERY OF THE UTILITY MODEL

[ problem to be solved by the utility model ]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a vehicle control device that performs control for stabilizing behavior of a vehicle during turning.

[ means for solving problems ]

In order to solve the above problem, the present invention provides a control device for a vehicle having a control unit U for transmitting power from a drive source E to at least one of front wheels WfR, Wf L or rear wheels WrR, Wr L for a vehicle having the drive source E, front wheels WfR, Wf L, rear wheels WrR, Wr LA force transmission member D, tires T attached to the front wheels WfR, Wf L and the rear wheels WrR, Wr L, and an operating element 9, and a front wheel rudder angle which is a rudder angle of the front wheels WfR, Wf L₁A vehicle 1 operated by an operation element 9 determines a slip state of a tire T and controls running of the vehicle 1, wherein a control unit U determines whether the slip state of the tire T is an elastic slip state in which the tire T of front wheels WfR and Wf L or rear wheels WrR and Wr L apparently slips against a road surface or a moving slip state in which the tire T actually slips against the road surface due to elastic deformation of the tire T, and changes a rear wheel rudder angle as a steering angle of the rear wheels WrR and Wr L so that the slip state of any one of the tires T attached to the front wheels WfR and Wf L and the rear wheels WrR and Wr L is changed from the elastic slip state to the moving slip state when it is determined that the slip state of the tire T is changed to the elastic slip state₂。

As such, when the slip state of the tire has been shifted from the elastic slip state to the moving slip state, it is preferable to reduce the slip of the tire that has been shifted to the moving slip state. In this case, the steering angle of the rear wheel is changed so that the slip state of the tire is changed to the elastic slip state, whereby the turning force of the front wheel and the turning force of the rear wheel can be distributed at an appropriate ratio. Thereby, the burden imposed on the drive wheels is reduced, and the slip of the tire that has been shifted to the slip state with respect to the road surface is reduced, whereby the energy consumption of the drive source required for running can be suppressed to a minimum. Further, by reducing the slip, an appropriate frictional resistance can be obtained from the road surface, and the behavior of the vehicle can be stabilized.

In the vehicle control device, the control unit U may detect the rotational fluctuation of the power transmission member D and the rotational fluctuation of the wheel W of the front wheels WfR and Wf L or the rear wheels WrR and Wr L when determining that the elastic slip state is shifted to the shift slip state, and may determine the phase delay Ψ based on the amplitude ratio m of the rotational fluctuation amplitude of the wheel W with respect to the rotational fluctuation amplitude of the power transmission member D and the phase delay Ψ of the rotational fluctuation of the wheel W with respect to the rotational fluctuation of the power transmission member D₁Calculating as a slip state of the tire TSlip recognition amount ζ of index₂By identifying the slip zeta₂And a reference value ζ corresponding to an elastic slip limit of the tire T_SComparing the displacement slip state with the slip recognition amount ζ₂Less than a reference value ζ_SIn the case of (2), it is determined that the vehicle is in a slip state.

Thus, the boundary between the elastic slip and the movement slip can be appropriately determined.

In the vehicle control device, the control unit U may calculate the center-of-gravity slip angle β of the slip angle (sideslip angle) determined as the center of gravity of the vehicle 1, and when the center-of-gravity slip angle β is out of the predetermined range, the rear wheel rudder angle may be fixed so as to be parallel to the front-rear direction of the vehicle 1₂Or limiting the rudder angle of the rear wheels from the state of becoming parallel₂The amount of change of (1).

In this way, when the center of gravity slip angle is out of the predetermined range, there is no room for increasing the center of gravity slip angle. In this case, the yaw rate is increased by fixing the rear wheel steering angle so as to be parallel to the front-rear direction of the vehicle or by limiting the amount of change in the rear wheel steering angle from the parallel state, and the center-of-gravity slip angle is reduced until the center-of-gravity slip angle falls within a predetermined range. Thus, the behavior of the vehicle can be stabilized by reducing the slip of the tire converted into the slip state with respect to the road surface, and the responsiveness of the vehicle behavior (turning) to the operation of the operation element can be improved by maintaining the center-of-gravity sideslip angle within a prescribed range.

In the vehicle control device, the front wheels WfR and Wf L may include a right front wheel WfR and a left front wheel Wf L, the rear wheels WrR and Wr L0 may include a right rear wheel WrR and a left rear wheel Wr L, the control unit U may calculate a center-of-gravity slip angle β which is a slip angle at the center of gravity of the vehicle 1, and when the center-of-gravity slip angle β appears in the left direction, the driving force of the left front wheel Wf L or the left rear wheel Wr L may be made smaller than the driving force of the right front wheel WfR or the right rear wheel WrR, and when the center-of-gravity slip angle β appears in the right direction, the driving force of the right front wheel WfR or the right rear wheel WrR may be made smaller than the driving force of the left front wheel Wf L or the left rear wheel Wr L.

In this way, when the center of gravity slip angle appears in the left direction, the driving force of the left front wheel or the left rear wheel is made smaller than that of the right front wheel or the right rear wheel, and when the center of gravity slip angle appears in the right direction, the driving force of the right front wheel or the right rear wheel is made smaller than that of the left front wheel or the left rear wheel, thereby suppressing an increase in the center of gravity slip angle. This stabilizes the behavior of the vehicle and improves the responsiveness of the vehicle behavior (turning) to the operation of the operation element.

In the vehicle control device, the control unit U may change the rear wheel rudder angle₂In the case of (2), corresponding to the rear wheel rudder angle₂Operation amount theta of operation element 9_HAnd an operation amount theta_HThe control gain i between the yaw rate γ of the vehicle 1 and the corrected front wheel rudder angle₁。

In this way, when the rear wheel steering angle is changed, the amount of operation of the operation element becomes constant even when the rear wheel steering angle is changed, and the steering wheel is easily operated by the driver, by correcting the front wheel steering angle in accordance with the rear wheel steering angle, the amount of steering wheel operation, and the value of the control gain between the amount of steering wheel operation and the yaw rate.

The reference numerals are those for corresponding constituent elements of the embodiments described below, and are given as examples of the present invention.

[ effects of the utility model ]

According to the utility model discloses a controlling means for vehicle can make the behavior of the vehicle when turning stable.

Drawings

Fig. 1 is a diagram showing a driving member and a braking member of a vehicle including a vehicle control device according to a first embodiment.

Fig. 2 is a diagram showing a modeled wheel.

Fig. 3 (a) to 3 (D) are diagrams illustrating elastic slip accompanying rotation of the tire.

Fig. 4 is a graph showing static torsion (static torque) characteristics of a tire.

Fig. 5 is a graph showing the elastic slip characteristic of the tire.

Fig. 6 is a graph showing a relationship between a slip ratio of a tire and a driving torque.

Fig. 7 is a graph showing a relationship between a slip ratio of a tire and a friction coefficient between the tire and a road surface.

Fig. 8 is a diagram showing a mechanical model of the drive wheel.

Fig. 9 (a) and 9 (B) are graphs showing rotation fluctuation transmission characteristics between the differential device and the drive wheels.

Fig. 10 is a diagram showing a relationship between a slip state of a tire and a vibration mode.

Fig. 11 is a diagram showing the root locus of the elastic slip mode and the traveling slip mode.

Fig. 12 is a diagram showing a wheel steering structure and various detection members of a vehicle including a vehicle control device.

Fig. 13 is a view showing angles formed by the wheel and the center of gravity of the vehicle with respect to the traveling direction of the vehicle.

Fig. 14 is a block diagram showing a schematic configuration of the electronic control unit.

Fig. 15 is a flowchart illustrating an outline of control in the first embodiment.

Fig. 16 is a flowchart showing fig. 15 in more detail.

Fig. 17 is a diagram showing the relationship between the front wheel turning force, the yaw angular acceleration, and the rear wheel turning force.

Fig. 18 is a flowchart illustrating control of the second embodiment.

Fig. 19 is a flowchart illustrating control of the third embodiment.

[ description of symbols ]

1: vehicle with a steering wheel

9: steering wheel (steering wheel: operating element)

D: differential gear (Power transmission component)

E: internal combustion engine (Driving source)

m: amplitude ratio

T: tyre for vehicle wheels

U: electronic control unit (control component)

W: wheel of vehicle

Wf, wfR, Wf L front wheel

Wr, WrR, Wr L rear wheel

β side slip angle of center of gravity

β_S: permissible value of center of gravity sideslip angle (specified value)

γ: yaw rate

₁: front wheel rudder angle

₂: rear wheel rudder angle

ζ₂: dimensionless quantity (slippage identification quantity)

ζ_S: reference value

θ_H: amount of steering wheel operation

Ψ₁: phase delay

Detailed Description

[ first embodiment ]

Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. In the following description, first, a method of determining the slip state of the tire T, specifically, the slip state identifier ID, which is an index of the control performed by the vehicle control device according to the present embodiment is described_Slip(＝ζ_S/ζ₂) The following describes a method of estimating the center-of-gravity slip angle β, which is an index of control performed by the vehicle control device of the present embodiment, and thereafter uses the slip state identifier ID_Slip(＝ζ_S/ζ₂) And the index of the center-of-gravity sideslip angle β, a specific method of slip suppression control of the front wheels as the drive wheels by the vehicle control device will be described.

For example, the characters are denoted by the left front wheel Wf L, the right front wheel WfR, the left rear wheel Wr L, and the right rear wheel wrr, and when the characters are collectively referred to, L and R are omitted as necessary, such as the front wheel Wf and the rear wheel Wr.

[ slip status identifier ID_SlipBy means of]

As shown in fig. 1, a four-wheeled vehicle having an internal combustion engine E as a driving source for running includes a pair of left and right front wheels Wf, Wf (specifically, a left front wheel Wf L, a right front wheel WfR) as driving wheels, and a pair of left and right rear wheels Wr, Wr (specifically, a left rear wheel Wr L, a right rear wheel WrR) as driven wheels, and the driving force of the internal combustion engine E is transmitted to the left and right front wheels Wf, Wf via a transmission M, a differential device D, and left and right driving shafts Sd, Sd.

The master cylinder Cm that generates brake hydraulic pressure by operating the brake pedal P1 is connected to the left and right front wheel brake calipers Cf, Cf and the left and right rear wheel brake calipers Cr, Cr via a hydraulic regulator H incorporating an electric oil pump. The hydraulic modulator H can arbitrarily increase or decrease the brake fluid pressure generated by the master cylinder Cm and supply the brake fluid pressure to the left and right front wheel brake calipers Cf, Cf and the left and right rear wheel brake calipers Cr, thereby individually controlling the braking force of the four wheels, and performing an anti-lock brake control for suppressing the locking of the wheels during deceleration or a sideslip control for suppressing the sideslip during cornering.

An Electronic control unit U (ECU) as a control unit including a microcomputer is connected to a brake operation amount detecting unit S1 that detects a brake hydraulic pressure generated by the master cylinder Cm by a depression force of a brake pedal P1, an accelerator opening degree detecting unit S2 that detects an operation amount of an accelerator pedal P2, a differential device rotational speed detecting unit S3 that detects a rotational speed of a differential device D, front wheel speed detecting units S4, S4 that detect wheel speeds of left and right front wheels Wf, and rear wheel speed detecting units S5, S5 that detect wheel speeds of left and right rear wheels Wr, Wr.

When the driver operates the brake pedal P1 to generate brake fluid pressure in the master cylinder Cm, the brake fluid pressure is transmitted to the front wheel brake calipers Cf, Cf and the rear wheel brake calipers Cr, Cr via the hydraulic modulator H, and brakes the front wheels Wf, Wf and the rear wheels Wr, Wr. When the antilock brake control is performed, the hydraulic modulator H operates in response to a command from the electronic control unit U, and arbitrarily adjusts the brake hydraulic pressure transmitted to the front wheel brake calipers Cf, Cf and the rear wheel brake calipers Cr, Cr.

The electronic control unit U operates the throttle valve in accordance with the accelerator opening detected by the accelerator opening detecting means S2, and performs not only Drive-by-wire control (Drive-by-wire) for generating a predetermined driving force in the internal combustion engine E, but also traction control for reducing the driving force of the internal combustion engine E and suppressing slipping of the front wheels Wf, Wf as driving wheels.

Next, the friction characteristics of the tire T will be described using a simple model shown in fig. 2. Generally, the wheel W is made of metal such as aluminum or steel and has a circular ring structure, and therefore is sufficiently rigid compared to the tire T made of rubber. That is, when the driving torque is applied to the wheel W, the sidewall portion and the tread portion of the tire T are deformed. In order to express this elastic deformation, the tread surface (including the ring of the ground contact surface) of the wheel W and the tire T is represented by a rigid mass, and a state in which the spring force acts in a direction to suppress the torsion of both is considered. In a land portion between the tire T and the road surface, the tire T is deformed by the mass of the vehicle, and the tire T and the road surface are brought into contact with each other (contact surface) by a certain fixed width (contact width). In the ground contact surface, a frictional force F acts between the rubber and the road surface, which is represented by the following formula.

F＝μN…(1)

μ is a friction coefficient between rubber and a road surface (which varies depending on aged change of the tire T, road surface, environmental conditions, and the like), and N is a ground contact load of the tire T. The magnitude of the resultant of the frictional forces F must be balanced with the driving force, which is the force required to run the vehicle against the running resistance (acceleration, deceleration, constant speed running).

Next, from fig. 3 (a) to 3 (D), a state is considered in which the vehicle travels by applying a driving torque to the wheel W to rotate the tire T.

At the moment when the driving torque is applied to the wheel W, the torque is not transmitted to the tire T, and the tire T is not rotated yet. At this time, the tire T is elastically deformed, and a torsion angle is generated between the wheel W and the tire T (see fig. 3 a). In this state, the tire T is in a static torsion state in which a torsion angle is generated in proportion to the driving torque of the wheel W, and exhibits the characteristics as shown in fig. 4 (for simplicity, nonlinearity such as viscoelasticity is not considered).

When the torsion angle is generated, the torque is transmitted to the tire T as a reaction force thereof, and the tire T starts to rotate (see fig. 3B). As the tire T rotates, one element of the tire T, which has been elastically deformed, leaves the ground contact surface, and the elastic strain is released. At this time, the reaction force of the portion corresponding to the released elastic strain is not sufficient for the magnitude required for transmitting the driving torque of the wheel W, and therefore the rotation of the tire T is temporarily stopped. However, the new element takes over an element of the tire T that has left the ground contact surface to come into contact with the road surface and elastically strain, whereby the reaction force that has been lost is restored and the tire T rotates again. As described above, the boundary condition relating to each element is not unique to each element, and a case where the element moves in accordance with the movement of the element is particularly referred to as a movement boundary. When the actual tire T continues to rotate, the phenomenon described above continues to occur (see fig. 3C), and therefore the rotation angle of the tire T decreases at a fixed rate with respect to the rotation angle of the wheel W. Since the rotation angle of the wheel W per unit time is proportional to the rotation speed (rotation angular velocity), the rotation angle of the tire T is also reduced in proportion to the rotation speed of the wheel W, and a constant rotation transmission loss occurs (see fig. 3D). This phenomenon is referred to as elastic slip because the apparent slip occurs between the wheel W and the road surface due to elastic deformation. However, the amount of elastic slip is generated at a fixed ratio to the rotation speed of the wheel W, and therefore the rotation speed loss Δ ω caused by the slip and the rotation speed ω of the wheel W are utilized_wheelRatio of (S)_r＝Δω/ω_wheelTo indicate more convenience. The ratio Sr is referred to as a slip ratio.

S_r＝Δω/ω_wheel…(2)

When the elastic slip characteristic of the tire T is illustrated, the friction coefficient between the tire T and the road surface is sufficiently high (or the ground contact load of the tire T is sufficiently large) as shown in fig. 5. Of course, since there is a limit to the frictional force between the tire T and the road surface, if the driving torque of the wheel W is increased, eventually, the contact surface of the tire T and the road surface start to slip. This is distinguished from elastic slippage and is called movement slippage. That is, when the driving torque of the wheel W is increased, as shown in fig. 6, the elastic slip first progresses, and finally the traveling slip is reached, and the driving wheel loses its grip.

In general, a friction coefficient obtained by non-dimensionalizing (nondimensionalization) the driving torque shown in fig. 6 using equation (1) is used as the friction characteristic of the tire T (see the broken line in fig. 7). However, these characteristics are ideal, and when considering that the ground contact surface is once in a slip friction state in addition to nonlinearity of elastic deformation due to the structure of the tire T or the viscoelasticity of rubber, the friction coefficient is generally lowered, and the actual friction characteristics are as shown by the solid line in fig. 7. However, the friction mechanism and physical properties resulting from a state change from elastic slip to movement slip (referred to as slip state) are the same.

As described above, in order to obtain the maximum grip force of the tire T, it is desirable to maintain the slip state at the boundary between the elastic slip state and the moving slip state. Further, since no slip occurs in the ground contact surface in the elastic slip state, it is also desirable to maintain the slip state within the limit (boundary with the movement slip state) of the elastic slip state from the viewpoint of enhancing the wear resistance. However, since the characteristics (slip ratio and friction coefficient) of the solid line in fig. 7 change due to individual differences and aging of the tire T and changes in environmental conditions such as the road surface, in the conventional method for detecting the slip ratio, even if the progress of the slip ratio is grasped, the boundary (elastic slip limit) cannot be determined, and only a clear moving slip state can be determined. Therefore, in order to solve the problem, a slip state detection method is required.

Right the principle of the present invention for detecting the sliding state is explained. It is considered that in the elastic slip state shown in fig. 3 (a) to 3 (D), a torsion angle is generated between the wheel W and the tire T due to the elastic deformation

And the contact surface is moved only by the contact length (the tire T is rotated only by the contact length, and the contact surface is just replaced). At this time, in rotationThe ground surface before movement stores strain energy generated by elastic deformation

The strain energy is released by rotation. The strain energy does not perform work for the running of the vehicle, and therefore can be considered as a state in which the driving energy imparted from the wheel W is dissipated in the cycle of generation and release of the strain. If it is understood that such energy dissipation occurs due to apparent slip (elastic slip), the frictional force acting on the ground surface is F, which can be written as follows.

That is, energy dissipation can be replaced by a virtual work generated by friction and apparent slippage as in equation (3). k is a radical of_TIs the torsional rigidity of the tire T, R is the dynamic radius of the tire T, T_fCorresponding to the frictional torque generated in the ground plane. On the other hand, when the tire T has corresponded to the twist angle

When rotating, if the angle of torsion is included

And the rotation angle of the wheel W is set as

Slip ratio S_rAccording to a geometric relationship, become

According to the formula (2) and the formula (4), the following becomes

If it is substituted into formula (3), the reaction system is changed to

Friction torque T_fIs represented by a viscous resistance proportional to a slip (loss of rotation speed) Δ ω generated between the wheel W and the road surface. Here, c_TCorresponding to the coefficient of viscosity, and the tire rigidity k_TAnd (4) in proportion. Therefore, as shown in fig. 8, a dynamic model from the differential device D to the tire contact surface can be shown.

When the driving shaft Sd is driven at a constant rotation speed from the differential device D and is now in a state of being balanced with the driving force of the tire T, the displacements (angles) from the balance point of the rigid body particles corresponding to the differential device D, the wheel W, and the tire T are represented by θ₁、θ₂、θ₃Then, the variation equation becomes the following formula.

[ mathematical formula 1]

Here, if pass through

[ mathematical formula 2]

x₁＝θ₁，x₂＝θ₂，x₃＝θ₃

Is used to make the formula (7) non-dimensionalized and to express the state variable x (vector) as

[ mathematical formula 3]

Then, the expression of the equation of state of the formula (7) becomes the following formula.

[ mathematical formula 4]

When the frequency response of the rotation speed of the wheel W with respect to the rotation speed variation of the differential device D is obtained from the equation (8), the frequency response is as shown in fig. 9 (a) and 9 (B). Fig. 9 (a) is an amplification ratio (amplitude ratio m) of the rotational fluctuation amplitude of the wheel W with respect to the rotational fluctuation amplitude of the differential device D, and fig. 9 (B) is a phase delay (Ψ) of the rotational fluctuation of the wheel W with respect to the rotational fluctuation of the differential device D₁)。

Coefficient of Friction viscosity c according to equation (6)_TThe smaller the value of (b), the closer the slip state is to the moving slip state. In fig. 9 (a) and 9 (B), (a) shows a response of the elastic slip state, and (c) shows a response of the shift slip state. Further, (b) corresponds to a boundary (elastic slip limit) between the two slip states. When (a) and (c) in fig. 9 (a) and 9 (B) are compared, it is found that the peak value (amplitude ratio) of the response shifts to the low frequency side with the shift slip state. The vibration modes in which the response at this time becomes a peak are referred to as an elastic slip mode (a) and a slip mode (c), and the difference between the respective vibration modes is shown in fig. 10.

In the elastic slip mode, the driving force is transmitted to the road surface by the elastic deformation of the tire T, and hence the tire rigidity (k)_T) The generated elastic force acts on the wheel W as a reaction force. Therefore, the wheel W is subjected to the rigidity (k) of the drive shaft₁) And tire rigidity (k)_T) The resultant of the generated elastic forces vibrates.

In the traveling slip mode, the tire T dynamically slips with the road surface, and is therefore determined by the tire stiffness (k)_T) The generated elastic force is released by the slip, and the reaction force acting on the wheel W also disappears. Therefore, the wheel W is integrated with the tire T and is subjected to only the rigidity (k) by the drive shaft₁) The generated elastic force vibrates in the same phase.

According to the above, the elastic sliding is accompanied by the transition from the elastic sliding state to the movement sliding stateThe shift mode disappears, and the shift glide mode appears. Therefore, the slip state can be determined by monitoring the rotational fluctuation of the differential device D and the rotational fluctuation of the wheel W in accordance with the frequency band of the slip pattern. In the shift slip mode, the amplitude ratio sharply increases, and the phase delay approaches 90deg from 0deg according to fig. 9 (a) and 9 (B). Therefore, the shift slip state can be determined at least either by a sharp increase in the amplitude ratio in the frequency band corresponding to the shift slip pattern or by a phase delay close to 90 deg. The frequency corresponding to the shift slip mode is determined by various design factors of the model shown in FIG. 8, i.e., the drive shaft stiffness (k)₁) Tire rigidity (k)_T) Moment of inertia (I) of wheel W₂) Moment of inertia (I) of tire T₃) The determination can be made by calculating the eigenvalues and eigenvectors of jacobian matrix (jacobian matrix) a shown in equation (8).

However, torque fluctuations are usually generated in the internal combustion engine E, which is a drive source of the vehicle, and these torque fluctuations are also transmitted from the differential device D to the tires T. As a factor of torque fluctuation, there is fluctuation of the cylinder internal pressure in the case of the internal combustion engine E, and there is cogging torque (cogging torque) due to the number of poles in the case of the electric motor. The differential device D generates rotational fluctuations due to the torque fluctuations that have been input. At this time, if the rotation of the differential device D varies

[ math figure 5]

It is shown that equation (8) can be grasped as forced excitation under the boundary conditions. A. the₁The amplitude of the rotational fluctuation of the differential device D is Ω is an angular frequency (angular frequency) of an exciting force (torque fluctuation of the internal combustion engine E), and t is time. In such a forced excitation state, the state equation shown in equation (8) becomes the following equation.

[ mathematical formula 6]

From equation (9), B represents an external force (excitation input), and the natural vibration mode (hereinafter referred to as the natural mode) of the original system is determined by the jacobian matrix a. The parameters for determining the Jacobian matrix A are rho and omega₁、ω₂、ζ₂But where ρ, ω₁、ω₂For various design factors (known numbers), the eigenmode is finally represented by a dimensionless quantity ζ corresponding to the slip recognition quantity of the present invention₂To determine (which of the eigenmodes is excited differs depending on the excitation input B). Therefore, as long as the dimensionless quantity ζ can be known by some method₂Then the slip state should be indexable. Here, the periodic solution (periodic solution) of the equation (9) is assumed as follows.

[ math figure 7]

τ＝Ωt

When the coefficient is determined by the galierkin method (galerkin method) by substituting the formula (9), the following relational expression is obtained.

[ mathematical formula 8]

m is an amplification ratio (amplitude ratio) of the rotational fluctuation amplitude of the wheel W to the rotational fluctuation amplitude of the differential device D, Ψ₁Since the phase of the rotational fluctuation of the wheel W is delayed with respect to the rotational fluctuation of the differential device D, the dimensionless amount ζ can be obtained from the equation (10) by measuring the rotational fluctuation of the differential device D and the rotational fluctuation of the wheel W₂. Here, the number of the first and second electrodes,since the relational expression of expression (10) is two, two unknowns can be obtained at maximum. Thus, except for dimensionless quantity ζ₂In addition, ω can be simultaneously obtained₂Even if the rigidity or friction coefficient of the tire changes due to individual differences, aging, road surface conditions, or the like, a value suitable for the current situation can be obtained.

Then, for the dimensionless quantity ζ₂The relationship with the eigenmode will be explained. The operation of the eigenmode can be described by obtaining an eigen value λ of the jacobian matrix a. Fig. 11 shows the behavior (root locus) of the eigenvalue λ corresponding to the shift slip pattern. Fig. 11 (a) to (c) correspond to fig. 9 (a) and 9 (B) and fig. 10 (a) and (c).

In fig. 11, the horizontal axis represents the real axis, the vertical axis represents the imaginary axis, and the imaginary part represents the vibration solution (vibration solution). In the elastic slip state (see fig. 11 (a)), the root is located on the real axis and no vibration solution is present. On the other hand, in the shift slip state (see fig. 11 (c)), the root has an imaginary part and generates vibration. That is, it is known that the dimensionless quantity ζ is obtained₂If < 0.86 (see fig. 11 (b)), the shift slip mode appears. Therefore, it can be based on a dimensionless quantity ζ₂The slip state is determined as follows.

Dimensionless quantity ζ₂Elastic slip state when the pressure is higher than 0.86

Dimensionless quantity ζ₂When the value is 0.86, the elastic slip limit (grip limit)

Dimensionless quantity ζ₂The state is a moving slip state at the time of < 0.86

Wherein a dimensionless quantity ζ which becomes an elastic slip limit₂Becomes ζ₂0.86 is the case of the present embodiment, and the value differs depending on various design factors.

From the above, the dimensionless amount ζ is obtained by measuring the rotational fluctuation of the differential device D and the rotational fluctuation of the wheel W₂And for dimensionless quantity ζ₂Value of (d) and ζ as a reference value_SThe magnitude relationship of (2) is compared, whereby the slip state can be determined. Zeta_SIs ζ in the elastic slip limit₂In the examples describedZeta formation_S＝0.86。

In the vehicle shown in fig. 1, the electronic control unit U monitors the dimensionless amount ζ based on the rotation variation of the differential D detected by the differential rotation speed detecting means S3 and the rotation variation of the wheels W of the front wheels Wf, Wf detected by the front wheel rotation speed detecting means S4, S4₂When has become ζ₂＜ζ_SIn the case of (3), transition to the shift slip state is determined, and traction control for limiting the driving force of the internal combustion engine E via an electronically controlled throttle valve or anti-lock brake control for limiting the braking force of the front wheel brakes Cf, Cf via a hydraulic modulator H is performed. Instead of limiting the driving force of the internal combustion engine E, it is also possible to limit the driving force by limiting the downshift of the transmission M. This makes it possible to obtain acceleration and deceleration that maximizes the grip performance of the tire T, and to prevent unnecessary wheel spin, thereby avoiding a situation in which the behavior of the vehicle becomes unstable. Further, by minimizing the occurrence of the movement slip, the wear of the tire T can be suppressed.

When the relations of the formulae (4) to (6) are used, the result is

The slip Δ ω generated between the wheel W and the road surface can be expressed using a dimensionless quantity.

If the elastic slip limit is present and Δ ω is Δ ω ═ Δ ω_SThen, then

Therefore, according to the formula (11) and the formula (12), the process becomes

Δω/Δω_S＝ζ_S/ζ₂…(13)，

By finding the dimensionless quantity ζ₂The ratio of the current slip to the elastic slip limit can be determined. Thus, in addition to the determination of the slip state, the allowance of the current slip with respect to the elastic slip limit can be quantitatively expressedAnd (4) degree.

Therefore, the driving force or the braking force can be increased or decreased (feedback control) so that the dimensionless amount ζ obtained by measuring the rotational fluctuation of the differential device D and the rotational fluctuation of the wheel W can be made₂And ζ_SRatio of (i.e.. zeta.)_S/ζ₂Value of (slip state identifier ID)_Slip) Becomes 1. Accordingly, the control of the current driving force or braking force corresponding to the excessive or insufficient amount can be performed with respect to the elastic slip limit, and the grip limit of the tire T can be maintained with high accuracy, and the behavior of the vehicle can be stabilized while the maximum acceleration and deceleration is obtained. Further, by minimizing the occurrence of the movement slip, the wear of the tire T can be suppressed.

[ method of estimating center of gravity sideslip angle β ]

Next, a method of estimating the center of gravity slip angle β of the vehicle 1 will be described, first, a configuration necessary for estimating the center of gravity slip angle β of the vehicle 1 will be described, and fig. 12 is a diagram showing a wheel steering structure and various detection means of the vehicle 1 including a vehicle control device.

As shown in fig. 12, the vehicle 1 is a steer-by-wire (steer-by-wire) four-wheel steering vehicle, the vehicle 1 includes a front wheel steering control device 4 for steering front wheels Wf, a rear wheel steering control device 5R for steering rear wheels Wr, and a rear wheel steering control device 5L, the front wheels Wf, Wf and the rear wheels Wr, Wr are rotatably supported by respective knuckles (knuckle)6, and the knuckles 6 are supported by suspensions 7 including suspension arms, springs, shock absorbers, and the like.

On the driver's seat side of the vehicle 1, a steering shaft 11 is provided to which a steering wheel 9 (steering wheel: operation element) is attached at a rear end thereof. The steering shaft 11 is provided with a reaction force actuator 13 that gives a steering reaction force to the driver.

The front-wheel steering control device 4 includes a steering gear (steering gear)15 having a front-wheel-side knuckle 6fR and a front-wheel-side knuckle 6f L coupled to both ends thereof, a front-wheel steering actuator 16 for driving the steering gear 15, and the like.

The rear wheel steering control device 5R and the rear wheel steering control device 5L include a rear wheel steering actuator 8R and a rear wheel steering actuator 8L, respectively, between the vehicle 1 and the knuckle 6rR and the knuckle 6R L, the rear wheel steering actuator 8R and the rear wheel steering actuator 8L are linear-motion electric actuators each including an output rod driven in the axial direction by a motor, the front end of each output rod is connected to the knuckle 6rR and the knuckle 6R L, the rear wheel steering actuator 8R and the rear wheel steering actuator 8L perform telescopic operations, and thereby the steering angle (toe angle) of the rear wheel WrR and the rear wheel Wr L is changed, and the rear wheel steering control device 5R and the rear wheel steering control device 5L extend one of the left and right rear wheel steering actuators 8R and the rear wheel steering actuator 8L and shorten the other, and thereby the left and right rear wheels WrR and the rear wheels L are steered in phase with each other.

The front wheel steering actuator 16, the rear wheel steering actuator 8R, the rear wheel steering actuator 8L, the reaction force actuator 13, and the like are connected to an electronic control Unit U including a Central Processing Unit (CPU) or a Read Only Memory (ROM), a Random Access Memory (RAM), a peripheral circuit, an input/output interface, various drivers, and the like.

In the vehicle 1, various sensors for transmitting detection signals to the electronic control unit U are disposed and connected. Specifically, the brake operation amount detection means S1, the accelerator opening degree detection means S2, the differential rotation speed detection means S3, the front wheel speed detection means S4, S4, and the rear wheel speed detection means S5, S5 are connected to the electronic control unit U.

Further, in the vehicle 1, an operation amount θ of the detection steering wheel 9 is arranged_HA steering angle detecting means S6 for detecting a steering angle of a steering wheel, a vehicle speed detecting means S7 for detecting a vehicle speed V which is a traveling speed of a center of gravity point of the vehicle 1, and a lateral acceleration a_yLateral acceleration detecting means S8 for (lateral G), yaw rate detecting means S9 for detecting yaw rate γ (yaw rate), and front wheel rudder angle₁The front wheel rudder angle detecting means S10 and S10 for detecting the rear wheel rudder angle₂The rear wheel steering angle detection means S11, S11, and the stroke detection means S12, S12 for detecting the stroke positions of the rear wheel steering actuator 8R and the rear wheel steering actuator 8L, and the like, are provided as various kinds of transmission mechanismsA sensor is provided. Further, a not-shown detection front-rear acceleration G is arranged_xThe forward/backward acceleration detecting means of (1).

A method of estimating the center of gravity sideslip angle β in the vehicle 1 having the detection means as described above will be described with reference to fig. 13, fig. 13 is a diagram showing an angle formed by the wheel and the center of gravity of the vehicle with respect to the traveling direction of the vehicle, in fig. 13, the front-rear direction of the vehicle 1 is the x direction, and the direction orthogonal thereto is the y direction, and in the present embodiment, as described above, an example is shown in which the front wheel Wf is used as the driving wheel and the rear wheel Wr is used as the driven wheel.

As shown in FIG. 13, the front wheels Wf are separated from the center of gravity toward the front of the vehicle by a distance l₁The rear wheel Wr is separated from the center of gravity only by a distance l toward the rear of the vehicle₂. In addition, this figure shows a case where the vehicle 1 makes a left turn, and the state quantity on the front wheel Wf side in this case is the front wheel travel speed V which is the travel speed of the front wheel Wf_fFront wheel steering angle as steering angle of front wheel Wf₁Front wheel slip angle α as the slip angle of front wheel Wf₁. Front wheel rudder angle₁Is an angle formed by the front-rear direction of the front wheel Wf with respect to the front-rear direction (x-direction) of the vehicle 1 when the vehicle 1 is viewed from above, and is a front wheel slip angle α₁Is an angle formed by a vector of the front wheel traveling speed with respect to the front-rear direction of the front wheel Wf when the vehicle 1 is viewed from above. The state quantity on the rear wheel Wr side is a rear wheel travel speed V as a travel speed of the rear wheel Wr_rAnd a rear wheel steering angle as a steering angle of the rear wheel Wr₂Rear wheel slip angle α as the slip angle of rear wheel Wr₂. Rear wheel rudder angle₂Is an angle formed by the front-rear direction of the rear wheel Wr with respect to the front-rear direction (x-direction) of the vehicle 1 when the vehicle 1 is viewed from above, and is a rear wheel slip angle α₂Is an angle formed by a vector of a rear wheel traveling speed with respect to the front-rear direction of the rear wheel Wr when the vehicle 1 is viewed from above, and the state quantities at the center of gravity point of the vehicle 1 are a vehicle speed V as a traveling speed at the center of gravity point of the vehicle 1, a center of gravity slip angle β as a slip angle at the center of gravity point of the vehicle 1, and a yaw angle γ, the center of gravity slip angle β is an angle formed by a vector of a vehicle speed with respect to the front-rear direction (x-direction) of the vehicle 1 when the vehicle 1 is viewed from above, and the state quantities at the center of gravity point are the vehicle speed VIn the following description, these state quantities are used for description.

When the center-of-gravity sideslip angle β is estimated, the rear wheel rudder angle is first obtained₂Yaw angular velocity gamma, rear wheel speed V_rwThe detection value of (3). Rear wheel speed V_rwIs the rotational speed of the rear wheel Wr (the circumferential speed of the rear wheel Wr in the contact surface between the tire and the road surface), and when the rear wheel Wr rotates without slipping with respect to the road surface, the rear wheel running speed V is set to be equal to the rear wheel running speed V_rSpeed V of rear wheel_rwAnd (5) the consistency is achieved. In general, the relationships of the expressions (14) and (15) are geometrically established between the velocities in the x-direction and the y-direction. Speed V in x direction_xIs the x-direction component of the vehicle speed V, the y-direction speed V_yIs the y-direction component of the vehicle speed V.

[ mathematical formula 9]

[ mathematical formula 10]

When formula (14) is substituted for formula (15), formula (16) can be obtained.

[ mathematical formula 11]

Here, since the rear wheel Wr is a driven wheel, if it is assumed that the influence of the slip is negligible, (V)_rcosα₂≒V_rw，α₂About 0) to obtain the formula (17) approximately.

[ mathematical formula 12]

Thus, according to the rudder angle of the rear wheel₂Yaw angular velocity gamma, rear wheel speed V_rwDistance l from the center of gravity of vehicle 1 to rear wheel Wr₂To infer (calculate) the center of gravity sideslip angle β.

[ slip suppression control of drive wheels ]

Then, the slip state identifier ID is obtained from the two indexes obtained in the above manner_Slip(＝ζ_S/ζ₂) And the estimated value of the center-of-gravity sideslip angle β, the electronic control unit U of the vehicle 1 performs the slip suppression control of the front wheels Wf, and fig. 14 is a block diagram showing a schematic configuration of the electronic control unit U.

As shown in fig. 14, the electronic control unit U of the present embodiment includes: the tire slip state determination unit 21 determines whether or not the tire slip state identifier ID is present_SlipA slip angle estimation unit 22 for estimating the center of gravity slip angle β, a target turning force setting unit 23 for setting the target turning force based on the slip state identifier ID_Slip(＝ζ_S/ζ₂) And a calculated value (estimated value) of the center-of-gravity sideslip angle β, and a target front wheel turning force CF of the front wheels Wf as the drive wheels is set_1t(ii) a The target steering angle setting unit 24 uses the target front wheel turning force CF_1tThe target rudder angle of the front wheel Wf or the rear wheel Wr is set according to the value of the steering angle; and a drive current setting unit 25 for setting a drive current corresponding to the target steering angle. Further, detection signals from various sensors are input to the tire slip state determination unit 21, the slip angle estimation unit 22, the target steering angle setting unit 24, and the drive current setting unit 25, respectively, as necessary. Details will be described later.

With this configuration, the set values of the drive currents set by the drive current setting unit 25 are output to the front wheel steering actuator 16, the right rear wheel steering actuator 8R, and the left rear wheel steering actuator 8L.

First, an outline of control in the first embodiment will be described. Fig. 15 is a flowchart illustrating an outline of control in the first embodiment. As shown in fig. 15, the electronic control unit U calculates the steady slip state by the method described above while the vehicle 1 is runningIdentifier ID_Slip(＝ζ_S/ζ₂) And the center of gravity sideslip angle β (step s 1).

Then, it is judged that the slip state identifier ID is present_SlipThe gravity center slip angle β is a permissible value β of the gravity center slip angle when the shift slip occurs and is greater than 1_SIn the range of (i β | ≦ β |)_S，β_S≧ 0), the center of gravity side slip angle β is again the center of gravity side slip angle permissible value β_SOutside of the range (| β | > β)_S，β_S≧ 0) (step s2, step s 3).

Furthermore, it can be said that the slip condition of the front wheels produces a shifting slip and that there is a margin in the center of gravity sideslip angle β, provided that all the conditions are met, in which case the electronic control unit U proceeds to increase the rear wheel rudder angle₂Control of the value of (step s 10). Increase the rudder angle of the rear wheel₂A rear wheel turning force CF of a rear wheel Wr as a driven wheel₂Increase, on the other hand, reduce the front wheel turning force CF of the front wheels Wf as the driving wheels₁. This suppresses the slip of the front wheels Wf.

On the other hand, when any of the above conditions is not satisfied, the slip state of the front wheels can be said to be an elastic slip state or a state in which there is no margin in the center-of-gravity slip angle β₂Control of the value of (step s 20). Thus, by reducing the rudder angle of the rear wheels₂While suppressing an increase in the center-of-gravity slip angle β.

Further, the center of gravity slip angle β becomes the center of gravity slip angle permissible value β_SIs out of range (out of predetermined range), as a reduction of the rear wheel rudder angle₂Control of the value of (1), the rear wheel rudder angle₂The rear wheel rudder angle may be limited by fixing the rear wheel rudder angle to 0 (parallel to the front-rear direction of the vehicle 1)₂A rear wheel rudder angle from a parallel position (a position of the rear wheel Wr parallel to the front-rear direction of the vehicle 1) at which the rudder angle becomes 0₂The amount of change of (1).

Thereafter, the electronic control unit U sets the rear wheel rudder angle as in step s10 or step s20₂Is reflected toThe wheels Wr, and the running of the vehicle 1 is performed (step s 4).

Next, the rear wheel rudder angle in step s10 and step s20 will be described in more detail with reference to fig. 16 and 17₂The method of determining (2). Fig. 16 is a flowchart showing fig. 15 in more detail. FIG. 17 shows a front wheel turning force CF₁With yaw angular acceleration and rear wheel turning force CF₂A graph of the relationship of (1).

When both of the following conditions are satisfied in step s2, step s3 shown in fig. 16, transition is made to step s10, the condition being that the slip state identifier ID is satisfied_SlipA condition of > 1 and a center of gravity slip angle β of a center of gravity slip angle allowance value β_SIn the range of (i β | ≦ β |)_S，β_S≧0)。

In step s10, the target front wheel turning force CF is first reduced_1tThe absolute value of (step s 11). Target front wheel turning force CF_1tThe absolute value of (A) is as shown in the upper graph of FIG. 17, in the total turning force CF_AOn the line of absolute value of (c), one side is opposite to the front wheel turning force CF₁Absolute value of (C) and rear wheel turning force CF₂Is set to the front wheel turning force CF while comparing the absolute values of₁Becomes a smaller value.

Next, the lateral acceleration a is confirmed_yWhether it is 0 or a positive value (step s 12). Here, at a lateral acceleration a_yWhen the value is 0 or positive, the turning force CF is applied to the target front wheel because the left turn is being performed_1tIs given a negative sign as the target front wheel turning force CF_1t(step s 13). On the other hand, at a lateral acceleration a_yWhen the value is negative, the target front wheel turning force CF is adjusted to make a right turn_1tIs directly taken as the target front wheel turning force CF_1t(step s 14).

Then, the determined target front wheel turning force CF is used_1tUsing equation (18) to calculate the rear wheel rudder angle₂Is detected (step s 15).

[ mathematical formula 13]

In the formula (18), except for the target front wheel turning force CF_1tBesides, the input lateral acceleration a_yCenter-of-gravity sideslip angle β, yaw angular velocity γ, vehicle speed V, and front wheel rudder angle₁. Here, the weight m of the vehicle 1 is used as the physical property value₁Elastic modulus K of tire T₂(by CF)₂＝K₂α₂To find the rear wheel side slip angle α₂As described above), the distance l from the center of gravity of the vehicle 1 to the rear wheels Wr₂. In addition, the driving force (or braking force) F of the front wheels Wf_fAnd a driving force (or a braking force (in the present embodiment, a braking force)) F of the rear wheel Wr_rThe estimation is based on the output torque and ratio of the drive source, or the brake fluid pressure. However, the influence may be small in a normal steering angle range, and in this case, 0 may be set.

In this way, in step s15, the rear wheel rudder angle is calculated by equation (18)₂A value of (1) then increasing the rear wheel rudder angle₂Is detected (step s 10).

On the other hand, when the slip state identifier ID is not satisfied in step s2, step s3 shown in fig. 16_SlipCondition > 1, or center of gravity slip angle β as center of gravity slip angle allowance value β_SIn the range of (i β | ≦ β |)_S，β_S≧ 0), the process proceeds to step s 20.

In step s20, the target front wheel turning force CF is first increased_1tThe absolute value of (step s 21). Target front wheel turning force CF_1tThe absolute value of (A) is as shown in the upper graph of FIG. 17, in the total turning force CF_AOn the line of absolute value of (c), one side is opposite to the front wheel turning force CF₁Absolute value of (C) and rear wheel turning force CF₂Is set to the front wheel turning force CF while comparing the absolute values of₁Becomes a larger value.

Next, the lateral acceleration a is confirmed_yWhether it is 0 or a positive value (step s 22). Here, at a lateral acceleration a_yWhen the value is 0 or positive, the turning force CF is applied to the target front wheel because the left turn is being performed_1tIs given a negative sign as the target front wheel turning force CF_1t(step s 23). On the other hand, at a lateral acceleration a_yWhen the value is negative, the target front wheel turning force CF is adjusted to make a right turn_1tIs directly taken as the target front wheel turning force CF_1t(step s 24).

Then, the determined target front wheel turning force CF is used_1tUsing equation (18) to calculate the rear wheel rudder angle₂Is detected (step s 25).

In this way, in step s25, the rear wheel rudder angle is calculated by equation (18)₂A value of (1), then the rear wheel rudder angle is reduced₂Is detected (step s 20).

As described above, according to the vehicle control device of the present embodiment, when the slip state has been shifted from the elastic slip state to the moving slip state, it is preferable to reduce the slip of the tire T shifted to the moving slip state. In this case, the rudder angle of the rear wheel is changed₂So that the front wheel turning force CF can be distributed in an appropriate ratio₁Force of rotation of rear wheel CF₂. Thereby, the burden imposed on the front wheels Wf as the drive wheels is reduced, and the slip of the tire T that has been shifted to the slip state with respect to the road surface is reduced, whereby the energy consumption of the internal combustion engine E as the drive source required for running can be suppressed to the minimum. Further, by reducing the slip, an appropriate frictional resistance can be obtained from the road surface, and the behavior of the vehicle 1 can be stabilized.

In the present embodiment, the slip state identifier ID is used_Slip(＝ζ_S/ζ₂) Is determined as the slip state, and when the slip state becomes the slip recognition amount (ζ)₂) < reference value (. zeta.)_S) In the case of a slip state identifier ID_SlipIf > 1, the tire T is judged to be in a moving slip state. Thus, the boundary between the elastic slip and the movement slip can be appropriately determined.

In the present embodiment, when the center-of-gravity slip angle β falls outside the predetermined range (the absolute value of the center-of-gravity slip angle β is not the center-of-gravity slip angle tolerance β)_SThe following case), there is no increase in the center of gravityMargin for sideslip angle β in this case, the rear wheel rudder angle is fixed so as to become parallel with respect to the front-rear direction of the vehicle 1₂Or limiting the rudder angle of the rear wheels from the state of becoming parallel₂The yaw rate γ is increased by the change amount of (a), and the center-of-gravity slip angle β is reduced until the center-of-gravity slip angle β falls within a predetermined range, whereby the behavior of the vehicle can be stabilized by reducing the slip of the tire T that has been shifted into the slip state with respect to the road surface, and the responsiveness of the vehicle behavior (turning) with respect to the operation of the steering wheel 9 can be improved by maintaining the center-of-gravity slip angle β within a predetermined range.

[ second embodiment ]

In the present embodiment, after the control of the first embodiment, the braking force of either the left front wheel Wf L or the right front wheel WfR is increased in accordance with the situation, and this is referred to as driving wheel braking force increase control (step s 30).

Next, the driving wheel braking force increase control will be specifically described. Fig. 18 is a flowchart illustrating control of the second embodiment. As shown in fig. 18, the electronic control unit U calculates the slip state identifier ID_Slip(＝ζ_S/ζ₂) And a center of gravity sideslip angle β (step s1), and determines whether or not the slip state identifier ID is present_SlipIf the center of gravity slip angle β is greater than 1, it is judged whether or not the center of gravity slip angle 8932 is the allowable center of gravity slip angle value β_S(step s2, step s 3). Thereafter, the rear wheel rudder angle is calculated by the same procedure as in the first embodiment₂(step s10, step s20), and reflection is performed (step s 4).

Then, the vehicle transitions to the driving wheel braking force increase control (step s 30). in step s30, the center of gravity slip angle β is first calculated, and it is confirmed whether the center of gravity slip angle β is 0 or a positive value (step s 31). here, when the center of gravity slip angle β is 0 or a positive value, if the vehicle is turning left, the vehicle front is in a state of turning the outside of the turning track toward the center of gravity (head out), and when the vehicle is turning right, the vehicle front is in a state of turning the inside of the turning track toward the center of gravity (head in). in this case, the vehicle front is adjusted so that the braking force of the left front wheel Wf L is increased (step s 32). thereby, the absolute value of the center of gravity slip angle β is decreased.

Thus, the increase in the center of gravity slip angle β can be suppressed by performing the driving wheel braking force increase control, and thus, in the first embodiment, the rear wheel turning force CF is increased₂This state can be continued, and even in a long-time turning state, the slip state of the front wheels Wf can be reduced, and further, by suppressing the center-of-gravity slip angle β, the responsiveness of the vehicle behavior (turning) to the operation of the steering wheel 9 can be improved.

In the second embodiment, the braking force of the left front wheel Wf L is adjusted to increase when the center-of-gravity slip angle β is 0 or a positive value, and the braking force of the right front wheel WfR is adjusted to increase when the center-of-gravity slip angle β is a negative value, but the present invention is not limited to this.

In the case where the driving wheels are the rear wheels Wr, the driving force of the left rear wheel Wr L may be made smaller than the driving force of the right rear wheel WrR when the center-of-gravity slip angle β appears in the left direction, and the driving force of the right rear wheel WrR may be made smaller than the driving force of the left rear wheel Wr L when the center-of-gravity slip angle β appears in the right direction.

As described above, in the present embodiment, the electronic control unit U reduces the driving force of the left front wheel Wf L or the left rear wheel Wr L with respect to the right front wheel WfR or the right rear wheel WrR when the center of gravity sideslip angle β appears in the left direction, and reduces the driving force of the right front wheel WfR or the right rear wheel WrR with respect to the left front wheel Wf L or the left rear wheel Wr L when the center of gravity sideslip angle β appears in the right direction, whereby the center of gravity sideslip angle β can be suppressed, the behavior of the vehicle 1 can be stabilized, and the responsiveness of the vehicle behavior (turning) with respect to the operation of the steering wheel 9 can be improved.

[ third embodiment ]

A third embodiment of the present invention will be explained. The same or corresponding components as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted below. In the present embodiment, control is performed to correct the steering angle of the drive wheels after the control of the first embodiment and before the drive wheel braking force increase control of the second embodiment. This is referred to as drive wheel rudder angle correction control (step s 40).

Next, the drive wheel rudder angle correction control will be specifically described. Fig. 19 is a flowchart illustrating control of the third embodiment. As shown in fig. 19, the electronic control unit U calculates the slip state identifier ID_Slip(＝ζ_S/ζ₂) And a center of gravity sideslip angle β (step s1), and determines whether or not the slip state identifier ID is present_SlipIf the center of gravity slip angle β is greater than 1, it is judged whether or not the center of gravity slip angle 8932 is the allowable center of gravity slip angle value β_S(step s2, step s 3). Thereafter, the rear wheel rudder angle is calculated by the same procedure as in the first embodiment₂(step s10, step s20), and reflection is performed (step s 4).

Then, the rear wheel rudder angle is used₂Steering wheel operation amount theta_HSteering wheel operation amount theta_HThe value of the control gain i between the yaw rate γ and the front wheel rudder angle after the correction is obtained from the equation (19)₁. In addition, the steering wheel operation amount θ_HThis means the amount of operation of the steering wheel 9 by the driver.

[ mathematical formula 14]

Then, the corrected front wheel rudder angle obtained by the equation (19) is used₁To the front wheels Wf (step s 40). Thereafter, the transition is made to the driving wheel braking force increase control shown in the second embodiment (step s 30).

In the present embodiment, the steering system of the present embodiment is a steer-by-wire system, and the front wheels Wf and the rear wheels Wr can be independently controlled. Therefore, the front wheel rudder angle can be freely corrected as compared with the case where the steering wheel 9 is mechanically connected to the front wheels Wf₁。

As described above, in the present embodiment, when the rear wheel rudder angle is changed₂Corresponding to the rudder angle of the rear wheel₂Steering wheel operation amount θ as an operation amount of steering wheel 9_HAnd steering wheel operation amount theta_HThe control gain i between the yaw rate γ of the vehicle 1 and the corrected front wheel rudder angle₁. Therefore, even if the rear wheel rudder angle is performed₂The increase/decrease control of (2) changes the rear wheel rudder angle₂Using the steering wheel operation amount theta of the steering wheel 9_HThe steering wheel is also fixed, and the steering wheel can be easily operated by the driver.

While the embodiments of the present invention have been described above, the present invention is not limited to the embodiments, and various modifications can be made within the scope of the technical ideas described in the claims, the specification, and the drawings.

The application of the tire slip state determination method of the present invention is not limited to the traction control or the antilock brake control of the embodiments.

The drive source of the present invention is not limited to the internal combustion engine E of the embodiment, and may be another type of drive source such as an electric motor.

The drive wheels of the present invention are not limited to the front wheels Wf of the embodiment, and may be rear wheels Wr or four-wheel drive.

In addition, since the drive wheel braking force increase control of the present invention is intended to generate a drive force difference between the left and right drive wheels, in a vehicle having a left-right wheel drive force distribution mechanism or an in-wheel motor independent of the left and right wheels, the drive force difference may be generated between the left and right drive wheels by the drive force distribution without being limited to the increase in the braking force of the embodiment.

Claims

1. A vehicle control device that includes a control unit that determines a slip state of a tire and controls running of a vehicle that has a drive source, a front wheel, a rear wheel, a power transmission member that transmits power from the drive source to at least one of the front wheel or the rear wheel, the tire attached to the front wheel or the rear wheel, and an operation element, and in which a front wheel steering angle that is a steering angle of the front wheel is operated by the operation element,

the control means determines whether the slip state of the tire is an elastic slip state in which the tire of the front wheel or the rear wheel apparently slips with respect to a road surface due to elastic deformation of the tire or a moving slip state in which the tire actually slips with respect to the road surface,

when it is determined that the slip state of any one of the tires accompanying the front and rear wheels has transitioned from the elastic slip state to the moving slip state,

and a rear wheel steering angle that is a steering angle of the rear wheel is changed so that the slip state of the tire is changed to the elastic slip state.

2. The control device for a vehicle according to claim 1,

the control means, when determining that the shift slip state has been shifted from the spring slip state,

detecting a rotational fluctuation of the power transmission member and a rotational fluctuation of a wheel of the front wheel or the rear wheel, and calculating a slip recognition amount as an index of a slip state of the tire based on an amplitude ratio of a rotational fluctuation amplitude of the wheel with respect to a rotational fluctuation amplitude of the power transmission member and a phase delay of the rotational fluctuation of the wheel with respect to the rotational fluctuation of the power transmission member,

determining the movement slip state by comparing the slip recognition amount with a reference value corresponding to an elastic slip limit of the tire,

in a case where it has become that the slip recognition amount is smaller than the reference value, it is determined to be the movement slip state.

3. The control device for a vehicle according to claim 1 or 2,

the control means calculates a center-of-gravity slip angle as a slip angle of a center-of-gravity point of the vehicle,

in the case where the center of gravity slip angle becomes out of the prescribed range,

the rear wheel steering angle is fixed so as to be parallel to the front-rear direction of the vehicle, or the amount of change in the rear wheel steering angle from the parallel state is limited.

4. The control device for a vehicle according to claim 1 or 2,

the front wheels comprise a right front wheel and a left front wheel,

the rear wheel comprises a right rear wheel and a left rear wheel,

making the driving force of the left front wheel or the left rear wheel smaller with respect to the right front wheel or the right rear wheel when the center of gravity sideslip angle appears in the left direction,

when the center of gravity sideslip angle occurs in the right direction, the driving force of the right front wheel or the right rear wheel is made smaller with respect to the left front wheel or the left rear wheel.

5. The control device for a vehicle according to claim 3,

the front wheels comprise a right front wheel and a left front wheel,

the rear wheel comprises a right rear wheel and a left rear wheel,

the control means makes the driving force of the left front wheel or the left rear wheel smaller relative to the right front wheel or the right rear wheel when the center of gravity sideslip angle occurs in the left direction,

the control means makes the driving force of the right front wheel or the right rear wheel smaller relative to the left front wheel or the left rear wheel when the center-of-gravity sideslip angle occurs in the right direction.

6. The control device for a vehicle according to claim 1 or 2,

the control unit corrects the front wheel steering angle in accordance with the rear wheel steering angle, the operation amount of the operation element, and a control gain between the operation amount and the yaw rate of the vehicle when the rear wheel steering angle is changed.

7. The control device for a vehicle according to claim 3,

8. The control device for a vehicle according to claim 4,

9. The control device for a vehicle according to claim 5,