JP5007549B2 - Tire lateral force calculation device - Google Patents

Description

  The present invention relates to a tire lateral force calculation device that calculates tire lateral force.

  As this type of technology, the technology described in Patent Document 1 is disclosed.

In Patent Document 1, as a technique for controlling vehicle motion in consideration of tire friction circle characteristics, a feedforward controller based on an inverse model of a linear vehicle model is used to calculate an operation amount for realizing a target yaw rate. Is disclosed. Here, the linear vehicle model is obtained by linearly approximating the tire lateral force characteristics in the vicinity of the tire slip angle at the current time in order to cope with the nonlinearity of the tire lateral force with respect to the tire slip angle.
JP-A-5-193510

  However, in the above prior art, the frictional circle characteristic of the tire including the tire longitudinal force is not considered. For this reason, an accurate control result cannot be obtained at the time of braking / driving, and there is a possibility that the rider feels uncomfortable in ride comfort and maneuverability.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a tire lateral force calculation device capable of suppressing the discomfort of ride comfort and maneuverability given to the occupant.

In order to achieve the above object, a tire slip angle estimating means for estimating or detecting a tire slip angle, a wheel load estimating means for estimating or detecting a wheel load, and a tire slip ratio from a tire longitudinal force within a predetermined tire slip ratio range. The tire lateral force to obtain the tire lateral force from the tire slip angle estimated value, the wheel load estimated value, and the tire longitudinal force using the approximate expression that approximated the relationship to the tire and the relationship between the tire slip ratio and the tire lateral force An approximation means, an approximate expression is an expression using a tire slip ratio κ, a tire longitudinal force Fx _i, and coefficients B ₀ , C ₀ , D ₀ determined from wheel load and tire slip angle ,
κ = tan (sin-1 (Fx _i / D ₀ ) / C ₀ ) / B ₀
It was decided that.

  In the calculation of the tire lateral force, it is not necessary to detect the actual tire slip rate with a fast response speed, so that the calculation accuracy of the tire slip rate can be improved without shortening the calculation cycle. In addition, since the relationship between the tire longitudinal force and the tire slip rate within a predetermined tire slip rate range is used, it is possible to calculate the tire force with high accuracy in consideration of the friction circle without using the convergence calculation, and the calculation load is reduced. Be lowered.

  Therefore, the control considering the friction circle can be realized at a low cost, and the calculation accuracy is improved, so that the ride comfort and the maneuverability are improved, and the uncomfortable feeling is suppressed. In addition, since a feedforward controller that performs yaw rate control can be designed in consideration of the tire friction circle, the target yaw rate can be realized with high accuracy, and riding comfort and operability are improved.

  Hereinafter, the best mode for realizing the tire lateral force calculation device of the present invention will be described based on Example 1 and Example 2.

  First, the configuration will be described.

  FIG. 1 is a configuration diagram of an electric vehicle to which the left and right rear wheels are independently driven by separate electric motors, to which the tire lateral force calculation device of the present invention is applied.

  The electric vehicle includes electric motors 3RL and 3RR as driving force generation sources, and the rotation shafts of the respective motors are connected to the rear wheels 2RL and 2RR of the electric vehicle via speed reducers 4RL and 4RR. . The output characteristics of the two motors, the reduction ratio of the two reduction gears, and the radius of the two wheels are all the same.

  Each of the motors 3RL and 3RR is a three-phase synchronous motor in which a permanent magnet is embedded in a rotor. Torque command values tTRL (left rear wheel), tTRR (right rear wheel) that drive circuits 5RL and 5RR that control power transfer to and from the lithium ion battery 6 receive the power running and regenerative torque of those motors from the integrated controller 30. And adjust to match each. Then, the drive circuits 5RL and 5RR transmit the output torque of each motor and the motor rotation speed detected by a rotation position sensor (not shown) attached to the motor rotation shaft to the integrated controller 30, respectively.

  The front wheels 2FL and 2FR are mechanically steered mechanically through the steering gear 14 by the rotational movement of the steering wheel 11 operated by the driver, and the steering gear 14 is entirely moved in the vehicle width direction by the auxiliary steering motor 12. Auxiliary steering is performed by displacing to. That is, the steering angles of the front wheels 2FL and 2FR are the sum of the main steering angle by the steering wheel 11 and the auxiliary steering angle by the auxiliary steering motor 12. The front wheel rudder angle is controlled to match the target front wheel rudder angle transmitted by the integrated controller 30 by adjusting the output of the auxiliary steering motor 12 by the control circuit 13. The front wheels 2FL and 2FR are provided with rotation sensors 25 and 26 for detecting the rotation speed, and each rotation speed is detected and transmitted to the integrated controller 30.

  The rear wheels 2RL and 2RR are steered by displacing the steering gear 15 as a whole in the vehicle width direction by a steering motor (not shown). The rear wheel steering angle is controlled so as to coincide with the target rear wheel steering angle transmitted by the integrated controller 30 by the control circuit 13 adjusting the output of the steering motor.

  In addition, the integrated controller 30 includes an accelerator opening signal APO detected by an accelerator pedal sensor 23, a steering wheel rotation angle signal STR detected by a steering angle sensor 21 attached to the rotation shaft of the steering wheel 11, and The yaw rate signal γ detected by the yaw rate sensor 8, the front wheel longitudinal acceleration signal axf detected by the acceleration sensor 27 attached at the center of the front wheel axis, the front wheel lateral acceleration signal ayf, and the acceleration sensor attached at the center of the rear wheel axis. The rear wheel longitudinal acceleration signal axr detected by the vehicle 28, the rear wheel lateral acceleration signal ayr, and the vehicle slip angle signal β output from the slip angle sensor 29 attached to the position of the center of gravity are input.

  Next, processing executed in the integrated controller 30 will be described.

In the electric vehicle to which the tire lateral force calculation apparatus according to the first embodiment is applied, a target for realizing the target tire slip angle β ₀ ^* and the target yaw rate γ ₀ ^* using a vehicle motion model in accordance with input signals from various sensors. The front and rear wheel steering angles δ _f ^* , δ _r ^* are calculated.

  As a conventional technique, there is known a technique that controls the vehicle motion in consideration of the tire friction circle characteristic (for example, JP-A-5-193510). In this prior art, an operation amount for realizing a target yaw rate is calculated using a feedforward controller based on an inverse model of a linear vehicle model. Here, the linear vehicle model is obtained by linearly approximating the tire lateral force characteristics in the vicinity of the tire slip angle at the current time in order to cope with the nonlinearity of the tire lateral force with respect to the tire slip angle.

  However, in this prior art, the frictional circle characteristic of the tire including the tire longitudinal force is not taken into consideration. For this reason, an accurate control result cannot be obtained at the time of braking / driving, and there is a possibility that the rider may feel uncomfortable in ride comfort and operability.

  As another conventional technique, a brush model that is a well-known tire model is used, and a target tire slip ratio that achieves a desired tire longitudinal force and tire lateral force is obtained by convergence calculation (for example, JP 2004-25996 A). In this prior art, the desired vehicle state is realized by using a deviation between the obtained target tire slip ratio and the actual slip ratio obtained from the wheel speed and the vehicle body speed.

  However, this conventional technique requires a convergence calculation to calculate the target tire slip ratio. Further, in order to accurately detect the actual slip rate with a fast response speed, a high-speed detection cycle is required. For these reasons, if the control accuracy is to be ensured, the calculation load increases and the calculation device may become expensive. In addition, since the actual slip rate has a limit in detection accuracy, the control accuracy may be lowered, and as a result, the rider may feel uncomfortable in ride comfort and maneuverability.

  In the first embodiment, the calculation accuracy of the tire slip ratio is improved without detecting the actual tire slip ratio with a fast response speed, and the tire force is accurately calculated in consideration of the friction circle without using the convergence calculation. It is something to try.

  First, a method for calculating the tire lateral force from the tire longitudinal force without using the slip ratio detection value, which is a feature of the tire lateral force calculating device of the present invention, will be described.

  FIG. 2 is a graph showing the relationship between the tire longitudinal force and the tire slip ratio. The tire longitudinal force and the tire slip ratio take positive and negative values, respectively, but are shown as absolute values in FIG.

  As shown in the hatched range in FIG. 2, in the absolute value range of a certain tire slip ratio, the absolute value of the tire longitudinal force increases as the absolute value of the tire slip ratio increases (solid line in FIG. 2). Then, the absolute value of the tire longitudinal force takes a peak value at an absolute value of a certain tire slip rate, and the absolute value of the tire longitudinal force decreases as the absolute value of the tire slip rate further increases (dotted line in FIG. 2).

  Therefore, conventionally, the relationship between the tire slip rate and the tire longitudinal force has not been uniquely determined, and there has been no method for easily obtaining the tire slip rate from the tire longitudinal force. Therefore, when calculating the tire slip ratio from the tire longitudinal force, it is necessary to use a method such as a convergence calculation.

  The absolute value of the tire longitudinal force takes a peak value with the absolute value of the tire slip ratio, and the absolute value of the tire longitudinal force starts to decrease at the peak value. The tire slips over the entire contact surface with the road surface. Because. However, when slip is suppressed by ABS control, traction control, etc., the range where the tire slips across the entire contact surface with the road surface is not used.

  In Example 1, the use range of the tire slip ratio is limited from the tire slip ratio at which the tire longitudinal force is minimized to the tire slip ratio at which the tire longitudinal force is maximized, and the relationship between the tire longitudinal force and the tire slip ratio is Made it unique.

  Next, the correspondence between the tire longitudinal force and the tire slip rate will be described.

  In the range of the tire slip ratio shown in the hatched portion of FIG. 2, when the tire slip ratio and the rate of change of the tire slip ratio increase as the tire longitudinal force increases, the tire slip ratio becomes maximum when the absolute value of the tire longitudinal force becomes maximum. So that the rate of change is infinite. As a result, when the tire frictional circle characteristic is taken into account, it is possible to perform an accurate calculation regarding the tire longitudinal force.

  Further, as will be described below, the change in the relationship between the tire longitudinal force and the slip ratio according to the wheel load and the tire slip angle is also associated.

  FIG. 3 is a graph showing the relationship between the wheel load and the rate of change of the absolute value of the tire slip ratio with respect to the tire longitudinal force when the absolute value of the tire slip ratio is near zero.

  When the absolute value of the tire slip rate is near zero, the change rate of the tire slip rate with respect to the absolute value of the tire longitudinal force is a tendency of a downwardly convex curve as shown in FIG. 3 according to the increase in wheel load. Set as shown. Thereby, when the vehicle performs acceleration / deceleration while turning, the accuracy of the tire force calculation is improved.

  FIG. 4 is a graph showing the relationship between the tire longitudinal force and the tire slip ratio according to the wheel load.

  For an arbitrary tire longitudinal force, the tire slip ratio is set to decrease as the wheel load increases. By setting the coefficient in this way, the tire force calculation accuracy when turning during braking / driving is improved.

  FIG. 5 is a graph showing the relationship between the tire longitudinal force and the tire slip ratio according to the tire slip angle.

  For an arbitrary tire longitudinal force, the tire slip ratio is set to increase as the tire slip angle increases. By having such a relationship, the tire force calculation accuracy when the tire slip angle changes is improved.

For example, the formula for obtaining the tire slip ratio κ of tire longitudinal force Fx _i is a tire slip angle alpha, the wheel load by using the Fz, it is expressed as follows.
κ = tan (sin ^-1 (Fx _i / D ₀ ) / C ₀ ) / B ₀ … (1)
B ₀ (α, Fz) = exp (-| kBx · α |) · Bx (Fz) (2)
C ₀ (α, Fz) = exp (-| kCx · α |) · Cx (3)
D ₀ (α, Fz) = exp (-| kDx · α |) · Dx (Fz) (4)

Here, Bx, Cx, Dx is a parameter determined by the magic formula tire model, kBx, kCx, kDx are parameters determined by the wheel load Fz _i. Expression (1) is an approximate expression based on a tire model of a magic formula.

  The tire lateral force can be calculated from the slip ratio calculated value κ and an equation for calculating the tire force using a slip ratio such as a known magic formula or brush model.

  FIG. 6 is a diagram showing a result of comparing the frictional circle characteristics of a tire calculated by changing the wheel load and the tire slip angle by the tire lateral force calculation device used in Example 1 with a magic formula. ) Shows the results when the tire slip angle is small, and (b) shows the results when the tire slip angle is large. As shown in FIG. 6, even when the wheel load or the tire slip angle is changed by the tire lateral force calculation method of the first embodiment, the tire friction circle characteristic can be accurately simulated.

  Although ignored in the present embodiment, the coefficient of friction between the tire and the road surface may be corrected. Further, the method for obtaining the tire slip ratio from the tire longitudinal force is not limited to the approximate expression as long as the relationship between the tire longitudinal force, the tire slip ratio, the wheel load, and the tire slip angle is set so as to show the above-described tendency. A map or the like may be used instead.

  FIG. 7 is a block diagram of the integrated controller 30.

  In the integrated controller 30, control with respect to the target tire slip angle and the target yaw rate is executed, for example, every 20 ms.

ただし、ω_β、ω_γは設計時に決定する規範応答の時定数である。 The normative input calculator 101 inputs a target vehicle slip angle β ₀ ^* and a target yaw rate γ ₀ ^* calculated by a host controller not shown here, and a current vehicle slip angle β and yaw rate γ. 5) Calculate the normative input using equation (6).

However, ω _β and ω _γ are time constants of normative responses determined at the time of design.

The tire slip angle calculator 102 uses the following equations (7) and (8) from the vehicle slip angle β, the vehicle speed V, the yaw rate γ, the front wheel rudder angle δ _f, and the rear wheel rudder angle δ _r. The tire slip angle α _i (i = fl, fr, rl, rr) of each wheel is calculated. Fl, fr, rl, and rr represent the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively.
α _fl = α _fr = β + (L _f / V) · γ-δ _f (7)
α _rl = α _rr = β- (L _r / V) · γ-δ _r (8)
However, L _f is the front wheel axis center of gravity distance, and L _r is the rear wheel axis center of gravity distance. The tire slip angle calculator 102 corresponds to the tire slip angle estimating means of the present invention.

In the wheel load calculator 103, from the front wheel longitudinal acceleration signal axf, the front wheel lateral acceleration signal ayf, the rear wheel longitudinal acceleration signal axr, and the rear wheel lateral acceleration signal ayr, the following equations (9) and ( 10), Formula (11), and Formula (12) are used to determine the wheel load Fz _i (i = fl, fr, rl, rr) of each vehicle wheel.
Fz _fl = Zf-ΔZd-2ΔZc ・ (Zf-ΔZd) / (Zf + Zr) (9)
Fz _fr = Zf-ΔZd + 2ΔZc ・ (Zf-ΔZd) / (Zf + Zr) (10)
Fz _rl = Zr + ΔZd-2ΔZc · (Zr + ΔZd) / (Zf + Zr) (11)
Fz _rr = Zr + ΔZd + 2ΔZc · (Zr + ΔZd) / (Zf + Zr) (12)
Zf = m · g · Lr / L (13)
Zr = m · g · Lf / L (14)
ΔZd = m · ax · hcg / 2L (15)
ΔZc = m · ay · hcg / 2Lt (16)
ax = (axf + axr) / 2 (17)
ay = (Lr · ayf + Lf · ayr) / L (18)
Where m is the vehicle weight, Lf is the front wheel shaft center of gravity distance, Lr is the rear wheel shaft center of gravity distance, Lt is the tread base distance / 2, L is the wheel base length, and hcg is the center of gravity height.

  Although ignored in the first embodiment, a delay in load change due to the suspension may be considered. Further, the wheel load of each wheel may be substituted with the target values of the longitudinal acceleration and the lateral acceleration without using the acceleration sensor. In this case, the acceleration sensor 28 may not be provided.

  The wheel load calculator 103 corresponds to the wheel load estimating means of the present invention.

The tire longitudinal force calculator 104 calculates the tire longitudinal force Fx _i (i = fl, fr, rl, rr) from the output torque tT of the driving force generator. Note that when the tire longitudinal force is given as the target value of the vehicle motion, the target tire longitudinal force Fx _i ^* may be used.

The tire lateral force calculator 105 uses the tire slip angle α _i , the wheel load Fz _i , and the tire longitudinal force Fx _i obtained from the tire slip angle calculator 102, the wheel load calculator 103, and the tire longitudinal force calculator 104. Thus, the tire lateral force Fy _i is calculated based on the above-described tire lateral force calculating method. The tire lateral force calculator 105 corresponds to the tire lateral force estimating means of the present invention.

  FIG. 8 is a block diagram of calculations performed in the tire lateral force calculator interior 105.

As shown in FIG. 8, the coefficient calculator 201 calculates the coefficients B ₀ , C ₀ , D from the above-described equations (2), (3), and (4) from the tire slip angle α _i and the wheel load Fz _i. Determine ₀ .

The tire slip ratio calculator 202 uses the coefficients B ₀ , C ₀ , D ₀ obtained by the coefficient calculator 201 to determine the tire slip ratio estimated value κ from the equation (1). The tire slip ratio calculator 202 corresponds to the tire slip ratio calculator of the present invention.

The frictional circle characteristic calculator 203 calculates the tire force correction amount based on the frictional circle characteristic based on the equation (19) from the calculation result of the tire slip ratio calculator 202 and the tire slip angle α _i .
Fy ₀ = cos (CG ・ tan ⁻¹・ (BG ・ (κ-am ₁ ))) (19)
CG = am ₀ … (20)
BG = am ₂・ cos (tan ^-1 (am ₃ α)) (21)

Equation (19) is a magic formula model, and am _i (i = 0,1,2,3) is a constant determined by the tire specifications.

In the tire model 204, the tire lateral force Fy _i is calculated from the tire slip angle α _i , the wheel load Fz _i, and the result of the frictional circle characteristic calculator 203 by the formula (22) based on the magic formula.
Fy _i = (Dy · sin (cy · tan ^-1 (By · (α + shy))) + svy) · Fy ₀ … (22)
Dy = μ (a ₁ · Fz + a ₂ ) · Fz (23)
Cy = a ₀ (24)
BCDy = a ₃ · sin (2 · tan ^-1 (Fz / a ₄ )) (25)
By = BCDy / (Dy / Cy) (26)
shy = a ₈・ γ (27)
svy = a ₁₁・ Fz ・ γ (28)
Here, a _i (i = 0,1,2,3,4,8,11) is a constant determined by the tire specifications. The tire model 204 corresponds to the tire lateral force calculation means of the present invention.

Returning to FIG. 7, in the cornering power calculator 106, the tire slip angle α _i , the wheel load Fz _i , the tire longitudinal force obtained from the tire slip angle calculator 102, the wheel load calculator 103, and the tire longitudinal force calculator 104 are obtained. calculating a cornering power of each wheel using the fx _i. The cornering power of each wheel is obtained by partial differentiation of the tire lateral force Fy _i calculated based on the tire lateral force calculation method described above around the tire slip angle obtained by the tire slip angle calculator 102 with the tire slip angle. Is expressed as in equation (29). Note that the subscript i is fl, fr, rl, and rr indicating the left front wheel, right front wheel, left rear wheel, and right rear wheel.
Cp = ∂Fy _i / ∂α (i = fl, fr, rl, rr)… (29)

In the linear vehicle inverse model 107, the target tire slip angle α ^* _i (i = fl, fr, rl, rr) is calculated based on the inverse model of the equation of motion expressed in the horizontal direction and the yaw rotation direction. Calculate.

Note that the linear vehicle motion equation is such that the slip angle α _{i of} each wheel and the rudder angle δ _i of the front and rear wheels are linearly approximated as | α _i | << 1, | δ _i | << 1. It is expressed as (31).
mV (dβ ^* / dt + γ ^* ) = Fy _fl ^* + Fy _fr ^* + Fy _rl ^* + Fy _rr ^* … (30)
I _γ (dγ ^* / dt) = Lf (Fy _fl ^* + Fy _fr ^* ) -Lr (Fy _rl ^* + Fy _rr ^* )… (31)
Where m is the vehicle weight, V is the vehicle speed, β ^* is the target vehicle slip angle, γ ^* is the target yaw rate, Fx _i is the tire longitudinal force, Fy ^* _i is the target tire lateral force, I _γ is the yaw inertia moment, Lf Is the front wheel axle center point distance, Lr is the rear wheel axle center point distance, and Lt is the tread base distance / 2.

dβ ^* / dt (= β ^* ) and dγ ^* / dt (= γ ^* ) can be obtained from the reference input computing unit 101, for example.

Here, the target tire lateral force Fy _i ^x is the tire lateral force Fy _i , cornering power Cp _i , tire slip angle α obtained by the tire longitudinal force calculator 104, the cornering power calculator 106, and the tire slip angle calculator 102. _{Using i} , it is expressed as in equation (32).
Fy _i ^* = Fy _i + Cp (α _i ^* −α _i ) (32)
However, α _i ^* is a scaled tire slip angle.

Here, the target tire slip angle is expressed by equations (33) and (34) by linear approximation.
α _fl ^* = α _fr ^* … (33)
α _rl ^* = α _rr ^* … (34)

Therefore, the target tire slip angle α _i ^* is expressed by Expression (35) and Expression (36) from Expression (30), Expression (31), Expression (32), Expression (33), and Expression (34).

The rudder angle calculation unit 108 uses the target tire slip angle α _f ^* , α _r ^* , the target vehicle slip angle β ^*, and the target yaw rate γ ^* obtained by the linear vehicle inverse model 107 as a target front and rear wheel rudder. The angles δ _f ^* and δ _r ^* are calculated based on the equations (37) and (38).
δ _f ^* = β ^* + (L _f / V) γ ^* -α _f ^* (37)
^{_{δ r * = β * + (}} L r / V) γ * -α r * ... (38)
Expressions (37) and (38) are obtained from Expressions (7) and (8).

  FIG. 9 shows a case where the vehicle slip angle and yaw rate are controlled by the tire lateral force calculation device (the method of the present invention) of Example 1, and a controller based on a model that ignores wheel load and tire longitudinal force as in the conventional method. It is a simulation result at the time of controlling body slip angle and yaw rate. In this simulation, the result is when the tire longitudinal force is generated in the positive direction, that is, in the forward direction of the vehicle. 9A shows the result of the vehicle slip angle, FIG. 9B shows the result of the yaw rate, the solid line shows the target value, the broken line shows the conventional method, and the alternate long and short dash line shows the method of the present invention.

  As shown in FIG. 9, the target vehicle slip angle and the target yaw rate calculated by the integrated controller 30 of the first embodiment using the method of the present invention follow the target values. On the other hand, it can be seen that the target vehicle slip angle and the target yaw rate calculated by the controller using the conventional method both have an error with respect to the target value. From this result, it can be said that the technique of the present invention has a great effect on the response to changes in the tire longitudinal force and the wheel load compared to the conventional technique, and the ride comfort and the handling are improved.

  The effect of Example 1 is shown below.

  (1) In the tire lateral force calculation device according to the first embodiment, a tire slip angle calculator (tire slip angle estimating means) 102 for determining a tire slip angle, and a wheel load calculator (wheel load estimating means) 103 for determining a wheel load. Tire slip angle estimate and wheel load using an approximate expression that approximates the relationship between tire longitudinal force and tire slip rate within a predetermined tire slip rate range and the relationship between tire slip rate and tire lateral force. A tire lateral force calculator (tire lateral force estimating means) 105 for obtaining tire lateral force from the estimated value and tire longitudinal force is provided.

  In the calculation of the tire lateral force, it is not necessary to detect the actual tire slip rate with a fast response speed, so that the calculation accuracy of the tire slip rate can be improved without shortening the calculation cycle. In addition, since the relationship between the tire longitudinal force and the tire slip rate within a predetermined tire slip rate range is used, it is possible to calculate the tire force with high accuracy in consideration of the friction circle without using the convergence calculation, and the calculation load is reduced. Be lowered.

  Due to the above effects, control considering the friction circle can be realized at low cost, and the calculation accuracy is improved, so that the ride comfort and the maneuverability are improved and the uncomfortable feeling is suppressed. In addition, since a feedforward controller that performs yaw rate control can be designed in consideration of the tire friction circle, the target yaw rate can be realized with high accuracy, and riding comfort and operability are improved.

  (2) The tire lateral force calculator (tire lateral force estimating means) 105 uses an approximate expression that approximates the relationship between the tire longitudinal force and the tire slip ratio within a predetermined tire slip ratio range, and estimates the tire slip angle. Tire slip ratio calculator (tire slip ratio calculating means) 202 for calculating a tire slip ratio from the tire load estimated value and the tire longitudinal force, tire slip angle estimated value, wheel load estimated value and tire slip ratio A tire model (tire lateral force calculation means) 204 for obtaining a force.

  Therefore, since it is not necessary to detect a tire slip rate with a fast response speed in the tire lateral force calculation, a calculation load can be reduced without requiring a short calculation cycle. For this reason, it is possible to realize control in consideration of the friction circle at a low cost.

  (3) The predetermined tire slip ratio range is a range from a tire slip ratio at which the tire longitudinal force is minimum to a tire slip ratio at which the tire vertical force is maximum in an arbitrary estimated wheel load value.

  Therefore, the relationship between the tire longitudinal force and the tire slip rate can be uniquely obtained. Therefore, an operation that could not be realized without performing a convergence operation or the like using an expensive arithmetic device can be realized with an inexpensive arithmetic device, and the cost can be reduced.

  (4) In a predetermined tire slip ratio range, the absolute value of the tire slip ratio increases as the absolute value of the tire longitudinal force increases, and the change rate of the absolute value of the tire slip ratio increases as the absolute value of the tire longitudinal force increases. When the absolute value of the tire longitudinal force increases, the rate of change in the absolute value of the tire slip ratio is infinite.

  Therefore, since the control considering the tire frictional circle characteristic with high accuracy can be realized, the ride comfort and the maneuverability are improved, and the uncomfortable feeling is suppressed.

  (5) An approximate expression that approximates the relationship between the tire longitudinal force and the tire slip ratio within a predetermined tire slip ratio range is the absolute value of the tire slip ratio relative to the tire longitudinal force when the tire slip ratio absolute value is near zero. The rate of change was set to a relationship represented by a downwardly convex curve in accordance with an increase in wheel load.

  Therefore, when the vehicle turns in an acceleration circle, the accuracy of the tire force calculation is improved, and accurate control can be realized, so that the ride comfort and the maneuverability are improved, and the uncomfortable feeling is suppressed.

  (6) An approximate expression that approximates the relationship between the tire longitudinal force and the tire slip rate within a predetermined tire slip rate range is set so as to decrease the tire slip rate with respect to the tire longitudinal force according to an increase in wheel load. .

  Therefore, tire force calculation can be performed with high accuracy during braking / driving while the vehicle is turning, and accurate control can be realized. Therefore, riding comfort and operability are improved, and a sense of incongruity is suppressed.

  (7) An approximate expression that approximates the relationship between the tire longitudinal force and the tire slip rate within a predetermined tire slip rate range is set so as to increase the tire slip rate with respect to the tire longitudinal force according to an increase in the slip angle. .

  Therefore, the accuracy of tire force calculation is improved during vehicle turning. Therefore, since accurate control can be realized, riding comfort and operability are improved, and a sense of incongruity is suppressed.

(8) An approximate expression that approximates the relationship between tire longitudinal force and tire slip rate within a predetermined tire slip rate range is determined from tire slip rate κ, tire longitudinal force Fx _i , wheel load and tire slip angle. Formula using the coefficients B ₀ , C ₀ , D ₀
κ = tan (sin ^-1 (Fx _i / D ₀ ) / C ₀ ) / B ₀
It was.

  Since the tire lateral force can be specifically calculated without detecting a tire slip rate with a fast response speed, the calculation load can be reduced without requiring a short calculation cycle. In addition, accurate calculation of the tire lateral force in consideration of the influence of the tire longitudinal force can be obtained with a low calculation load. Due to the above effects, a low-priced arithmetic device can realize control with high precision in consideration of the friction circle, so that ride comfort and handling are improved and a sense of incongruity is suppressed.

  Next, Example 2 will be described.

  The second embodiment is a calculation example of an internal vehicle model used in vehicle behavior prediction such as optimal route generation. The optimal route generation is to generate an optimal route of the vehicle by optimal control so that the result of the prediction calculation by the vehicle model held in the computer optimizes the specified evaluation function. For example, a method described in “Optimum route generation for automobiles” (Measurement and Control 2006 Vol.45 No.3 pp.209-215, Seirako (Nissan), Taketoshi Kawabuchi (Kyushu Univ.)) Is known. In order to generate an optimal route with high accuracy using a realistic controller, a vehicle model capable of performing high-precision calculation with a low calculation load is required.

  About the same structure as Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  FIG. 10 shows a block diagram of a vehicle model using the tire lateral force calculation device of the present invention.

  Here, the tire slip angle calculator 301 performs the same calculation as the tire slip angle calculator 102 of the first embodiment, and the wheel load calculator 302 performs the same calculation as the wheel load calculator 103 of the first embodiment.

The steer delay calculator 303 performs the calculations shown in the following equations (39) and (40) on the assumption that the front and rear wheel steering angles follow the first-order lag of the time constant 1 / ω _δ .

  Similar to the tire lateral force calculator 105 of the first embodiment, the tire lateral force calculator 304 calculates the tire lateral force based on the tire lateral force calculation method shown in the block diagram of FIG.

The tire force delay calculator 305 performs the calculations shown in equations (41) and (42) on the assumption that the tire longitudinal force Fx _i and the tire lateral force follow with the first order delay of the time constants 1 / ω _x and 1 / ω _y. Yes. Note that the subscript i is fl, fr, rl, and rr indicating the left front wheel, right front wheel, left rear wheel, and right rear wheel.
Fx _i '= -ω _x · Fx _i ' + ω _x · Fx _i (41)
Fy _i '= -ω _y · Fy _i ' + ω _y · Fy _i (42)

In the linear vehicle model 306, the motion equation shown in the equations (43), (44), and (45) is calculated with the vehicle motion in the plane as three degrees of freedom in the front and rear direction, the lateral direction, and the yaw rotation direction. Here, Equation (43), Equation (44), and Equation (45) are linear when the slip angle α _i of each wheel and the rudder angle δ _i of the front and rear wheels are set to | α _i | << 1, | δ _i | << 1. Approximate. The subscript i is fl, fr, rl, and rr indicating the left front wheel, right front wheel, left rear wheel, and right rear wheel.
m · (dV / dt) = Fx _fl + Fx _fr + Fx _rl + Fx _rr (43)
m ・ V ・ (dβ / dt + γ) = Fx _fl + Fx _fr + Fx _rl + Fx _rr (44)
I _γ (dγ / dt) = L _f (Fx _fl + Fx _fr ) -L _r (Fx _rl + Fx _rr ) + L _t {(Fx _fl + Fx _fr )-(Fx _rl + Fx _rr )} (45 )
Where m is the vehicle weight, V is the vehicle speed, β is the vehicle body slip angle, γ is the yaw rate, Fx _i is the tire longitudinal force, Fy _i is the tire lateral force, I _γ is the yaw moment of inertia, and L _f is the front wheel axle center of gravity. The point distance, _Lr is the rear wheel axle center point distance, and _Lt is the tread base distance / 2.

  Next, the result of calculating the vehicle motion by giving an input assuming the avoidance motion to the vehicle model is shown.

  FIG. 11 is a time chart showing a simulation result calculated using a magic formula as in the prior art and a simulation result calculated using the tire lateral force calculation device (the method of the present invention) of the present invention. In this simulation, the calculation cycle of the model using the conventional method is 1 ms, and the calculation cycle of the model using the method of the present invention is 20 ms. The inputs are the same front wheel steering angle and the rear wheel driving force given in pulses.

  11 (a) is a front wheel steering angle given as an input, (b) is a response of lateral force, (c) is a lateral position, (d) is a yaw rate, a solid line is a target value, a broken line is a conventional method, a one-dot chain line Shows the method of the present invention.

  From this result, it can be seen that the calculation result of the vehicle motion using the method of the present invention can simulate the vehicle motion calculation result of the conventional method.

  Further, in the conventional method, when the calculation cycle is set to 20 ms, the tire slip rate diverges and the vehicle motion cannot be calculated. On the other hand, it can be seen that the method of the present invention has a great effect on improving the calculation load without reducing the calculation accuracy.

  Next, effects of the second embodiment will be described.

  From the above results, when performing computations such as route generation using a vehicle model held inside the computer, by using the method of the present invention as a model, it is possible to control with high accuracy in consideration of the friction circle with an inexpensive computing device. Since it can be realized, ride comfort and handling are improved, and a sense of incongruity is suppressed.

  Although the best mode for carrying out the present invention has been described based on the first and second embodiments, the specific configuration of the present invention is not limited to the first and second embodiments. The present invention includes any design changes that do not depart from the spirit of the invention.

  For example, in Example 1 and Example 2, the tire lateral force calculation device of the present invention is applied to an electric vehicle. However, the vehicle is not limited to an electric vehicle as long as the vehicle can steer front and rear wheels. Applicable to vehicles.

It is a block diagram of the electric vehicle to which the left and right rear wheels are independently driven by separate electric motors, to which the tire lateral force calculation device of Example 1 is applied. It is a graph which shows the relationship between the tire longitudinal force of Example 1, and a tire slip ratio. It is a graph which shows the relationship between the change rate of the absolute value of the tire slip ratio with respect to a tire longitudinal force, and wheel load when the absolute value of the tire slip ratio of Example 1 is near zero. It is a graph which shows the relationship between the tire longitudinal force according to the wheel load of Example 1, and a tire slip ratio. It is a graph which shows the relationship between the tire longitudinal force according to the tire slip angle of Example 1, and a tire slip ratio. It is a figure which shows the result of having compared the frictional-circle characteristic of the tire calculated by changing the wheel load and the tire slip angle with the magic formula by the tire lateral force calculating apparatus of Example 1. 2 is a block diagram of an integrated controller according to Embodiment 1. FIG. It is a block diagram of the calculation performed inside the tire lateral force calculator of Example 1. The vehicle slip angle and yaw rate are controlled by the tire lateral force calculation device of the first embodiment, and the vehicle slip angle and yaw rate are controlled by a controller that ignores wheel load and tire longitudinal force as in the conventional method. It is a simulation result in the case of. The block diagram of the vehicle model using the tire lateral force calculating apparatus of Example 2 is shown. It is the time chart which showed the simulation result computed using the tire lateral force calculating apparatus of Example 2, and the simulation result computed using the conventional magic formula.

Explanation of symbols

102 Tire slip angle calculator
103 Wheel load calculator
104 Tire longitudinal force calculator
105 Tire lateral force calculator
107 Linear vehicle inverse model
108 Rudder angle calculator
201 Coefficient calculator
202 Tire slip ratio calculator
204 tire model

Claims (7)

Tire slip angle estimating means for estimating or detecting a tire slip angle;
A wheel load estimating means for estimating or detecting a wheel load;
Estimated tire slip angle and estimated wheel load using an approximate expression that approximates the relationship from tire longitudinal force to tire slip rate within a predetermined tire slip rate range and the relationship between tire slip rate and tire lateral force Tire lateral force estimating means for obtaining tire lateral force from tire longitudinal force and tire longitudinal force;
Equipped with a,
The approximate expression is an expression using the tire slip ratio κ, the tire longitudinal force Fx _i, and the coefficients B ₀ , C ₀ , D ₀ determined from the wheel load and the tire slip angle ,
κ = tan (sin-1 (Fx _i / D ₀ ) / C ₀ ) / B ₀
Tire lateral force calculating unit, characterized in that it. In the tire lateral force calculation device according to claim 1,
The tire lateral force estimating means includes
From the tire slip angle estimated value, the wheel load estimated value, and the tire longitudinal force, an approximate expression that approximates the relationship between the tire longitudinal force and the tire slip ratio within the range of the predetermined tire slip ratio is used. Tire slip ratio calculating means for calculating the slip ratio;
Tire lateral force calculation means for obtaining tire lateral force from the tire slip angle estimated value, the wheel load estimated value, and the tire slip rate;
A tire lateral force calculation device comprising: In the tire lateral force calculation device according to claim 1 or 2,
The predetermined tire slip ratio range is a range from a tire slip ratio at which the tire longitudinal force is minimum to a tire slip ratio at which the tire vertical force is maximum at an arbitrary estimated wheel load. Tire lateral force calculation device. In the tire lateral force calculation device according to any one of claims 1 to 3,
In the predetermined tire slip ratio range, the absolute value of the tire slip ratio increases as the absolute value of the tire longitudinal force increases, and the rate of change of the absolute value of the tire slip ratio as the absolute value of the tire longitudinal force increases. When the tire longitudinal force absolute value becomes maximum, the tire slip ratio absolute value change rate becomes infinite when the tire longitudinal force absolute value becomes maximum. In the tire lateral force calculation device according to any one of claims 1 to 4,
When the absolute value of the tire slip ratio is close to zero, the change rate of the absolute value of the tire slip ratio with respect to the tire longitudinal force is expressed by a downwardly convex curve as the wheel load increases. The tire lateral force calculation device is characterized in that the relationship is set to the relationship. In the tire lateral force calculation device according to any one of claims 1 to 5,
The tire lateral force calculation device according to claim 1, wherein the approximate expression is set so as to decrease the tire slip ratio with respect to the tire longitudinal force in accordance with an increase in the wheel load. In the tire lateral force calculation device according to any one of claims 1 to 6,
The tire lateral force calculation device according to claim 1, wherein the approximate expression is set so as to increase the tire slip ratio with respect to the tire longitudinal force in accordance with an increase in the slip angle.

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