JP2006067733A - Electric vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric vehicle that can get the behavior of the vehicle close to a desirable movement by shortening a time until the direction of steering front wheels follows the directions to which the steering front wheels should advance, and that suppresses the phenomenon of continuous vibration in the steering direction caused by reaction force that the steering front wheels receive from a road surface. <P>SOLUTION: The electric vehicle is provided with rear wheels 2RL, 2RR that cause a driving force difference to occur to right and left wheels; front wheels 42FL, 42FR that change direction in the car body turning direction according to the turning of a car body; a variable drag means that varies the drag of the turning direction of the steering front wheels 42FL, 42FR; a steering-front-wheel target-direction-calculating means that calculates the direction to which the steering front wheels 42FL, 42FR should advance according to a turning target value; encoders 27FL, 27FR that detect the actual direction of the steering front wheels 42FL, 42FR; and a drag controlling means that outputs a drag-adjusting command to the variable drag means, in such a way that the larger the deviation between the direction to which the steering front wheels 42FL, 42FR should advance and the actual direction, the smaller the drag becomes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of an electric vehicle that uses an electric motor as a drive source and performs a turning operation by a difference in driving force between left and right wheels.

As a vehicle configuration with a simple configuration that does not have a tire steering mechanism, there is known a vehicle configuration in which the rear wheels of the vehicle are casters and the front wheels are independently motor-driven. In this electric vehicle, a turning operation with a small turning radius is realized by adjusting the motor output of the front wheels independently on the left and right (see, for example, Patent Document 1).
JP-A 48-44914

  However, in the above prior art, a phenomenon in which the rear wheel caster continuously vibrates in the turning direction may occur depending on the reaction force received from the road surface. As a measure for avoiding such a phenomenon, a method using a rotating damper that generates a drag force in a direction opposite to the direction in which the caster rotates is known.

  However, when a rotating damper is used to generate a drag in the direction opposite to the direction in which the caster rotates, the direction of the caster wheel is not the same as the direction in which the caster wheel should move. It takes a lot of time to follow the direction in which the vehicle should travel, and the caster wheel does not advance in the direction in which the vehicle should travel, leaving the problem that the behavior of the vehicle deviates from the desired behavior.

  In view of such a problem, the present invention can bring the behavior of the vehicle closer to a desired movement by shortening the time until the direction of the steered wheel (caster wheel) follows the direction in which the steered wheel should proceed. An object of the present invention is to provide an electric vehicle capable of suppressing a phenomenon in which a steered wheel continuously vibrates in a steered direction by a reaction force received from a road surface.

In order to achieve the above object, in the present invention,
A driving wheel that generates a driving force difference between the left and right wheels;
Steered wheels that change direction in the direction of turning of the vehicle according to the turning of the vehicle,
Drag variable means for varying the drag in the steered direction of the steered wheels,
Driving target value detecting means for detecting a driving target value of the vehicle;
A turning target value detecting means for detecting a turning target value of the vehicle;
Motor output adjusting means for adjusting the left and right driving force sum of the driving wheel according to the driving target value, and adjusting the left and right driving force difference of the driving wheel according to the turning target value;
A steered wheel target direction computing means for computing a direction in which the steered wheel should proceed according to the turning target value;
Steered wheel direction means for detecting the actual direction of the steered wheel;
Drag control means for outputting a drag adjustment command to the drag variable means so that the drag decreases as the deviation between the direction in which the steered wheel should travel and the actual direction increases,
It is characterized by providing.

  Therefore, in the electric vehicle according to the present invention, when the deviation between the direction of the steered wheels and the direction in which the steered wheels should travel is large, the direction of the steered wheels can be reduced by reducing the drag in the steered direction of the steered wheels. It is possible to shorten the time until the steered wheel follows the direction in which the steered wheels are to travel, and thus the behavior of the vehicle can be brought closer to a desired movement. At the same time, when the deviation between the direction of the steered wheel and the direction in which the steered wheel should proceed is small, the continuous vibration of the steered wheel in the steered direction can be suppressed by increasing the drag in the steered wheel.

  Hereinafter, the best mode for carrying out an electric vehicle of the present invention will be described based on Example 1 and Example 2 shown in the drawings.

First, the configuration will be described.
FIG. 1 is an overall system diagram illustrating an electric vehicle according to a first embodiment. As shown in FIG. 1, the electric vehicle according to the first embodiment includes electric motors 3RL and 3RR as driving force generation sources, and the rotation shafts of the electric motors 3RL and 3RR are connected to speed reducers 4RL and 4RR. The rear wheels (drive wheels) 2RL and 2RR are connected to the electric vehicle. Here, the output characteristics of the two electric motors 3RL and 3RR, the reduction ratios of the two reduction gears 4RL and 4RR, and the radii of the two left and right rear wheels 2RL and 2RR are all the same.

  Each of the electric 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 () in which the drive circuits 5RL and 5RR that control power transfer with the lithium ion battery 6 receive the power running and regenerative torque of the electric motors 3RL and 3RR from the integrated controller 30. Adjust to match the right rear wheel). However, in the situation where the rear wheels 2RL and 2RR run idle when output according to the torque command value, the torque is limited for each rear wheel 2RL and 2RR so that the rear wheels 2RL and 2RR corresponding to the drive circuits 5RL and RR do not run idle. And output. Then, the drive circuits 5RL and 5RR transmit the motor rotation speed detected by a rotation position sensor (not shown) attached to each motor rotation shaft to the integrated controller 30, respectively.

  Here, as a method of limiting and outputting the motor torque of each wheel so that the rear wheels 2RL and 2RR do not idle, for example, as disclosed in JP-A-6-98418, the wheels receive from the road surface. A method of estimating the reaction force and adjusting the motor torque of each wheel based on the estimated value, as disclosed in the document “Lateral Motion Stabilization with Feedback Controlled Wheels” (Sakai et al. 6th International Symposium on Advanced Vehicle Control, 2002) In addition, using a model that represents the wheel rotation speed characteristics with respect to the motor torque, and adjusting the motor torque independently for each wheel according to the difference between the wheel rotation speed output by the model and the actual rotation speed, There is a method of adjusting the torque of the motor independently so that the slip ratio falls within a predetermined range. However, since either method can be used, explanation is omitted here. To do.

  The front wheels (steered wheels) 42FL and 42FR are caster-type wheels provided on the turning shafts 41FL and 41FR of the front wheels 42FL and 42FR. Of the left and right front wheels 42FL and 42FR, one front wheel 42 is shown in FIG. A turning rotation shaft (vehicle body side turning support shaft) 41 of the front wheel 42 is inside a hollow support portion (steering wheel side turning support shaft) 45 of the front wheel 42, and is turned to 45 through a bearing 71 (FIG. 3). In contrast, it rotates. The rotation angle of the hollow support portion 45 relative to the turning shaft 41 (the rotation angle of the direction A of the hollow support portion 45 with respect to the vehicle front direction) is measured by the encoders (turning wheel direction detection means) 27FL and 27FR shown in FIG. The measurement signal is sent to the controller 30 described later.

  The parts 44 and 43 and the front wheel 42 are all supported so as to rotate integrally around the turning shaft 41. Here, the intersection point P with the ground surface when the center of the rotation shaft 41 is extended and the point Q directly below the rotation center point 43 of the tire are configured such that the distance is ζ (> 0). A so-called caster structure in which the tire naturally steers so that the traveling direction of the turning rotation shaft 41 of the front wheel 42 coincides with the tire orientation A by traveling resistance during traveling is employed. The hollow support portion 45 of the front wheel 42 has a support shaft (not shown) in the vehicle longitudinal direction and the vehicle lateral direction so that the hollow support portion 45 is not easily deformed in the vehicle longitudinal and lateral directions. Further, the hollow support portion 45 is provided with a spring and a damper (not shown) with respect to the vertical direction, making it difficult to transmit the vertical force received by the front wheel 42 from the road surface to the vehicle body.

FIG. 3 shows an enlarged cross-sectional view of the coupling portion A between the turning rotation shaft 41 of the front wheel 42 and the hollow support portion 45.
The turning rotation shaft (steering wheel support shaft) 41 is provided inside the hollow support portion 45 and rotates with respect to the hollow support portion 45 via two sets of upper and lower bearings 71 and 71. Between the upper and lower bearings 71, 71, an electrorheological fluid 73 is sealed with a sealant 72, and the electrorheological fluid 73 has a positive electrode 77 formed in a cylindrical shape inside the hollow support portion 45, and a roller. It is also sandwiched between the negative electrodes of the rudder rotating shaft 41. A copper wire 76 with an insulating film is connected to the negative electrode of the turning shaft 41, and the positive electrode 77 is insulated from the hollow support portion 45 by an insulator 74, and a copper wire 75 with an insulating film is connected to it. Yes. Therefore, by applying a voltage from the outside to the copper wire 75 and the copper wire 76, a voltage is applied to the electrorheological fluid 73 to change the viscosity of the electrorheological fluid 73, and the hollow support portion 45 and the turning shaft 41 It is the structure which adjusts the drag of the steering direction with respect to the rotational speed difference (equivalent to a drag variable means). The voltage between the copper wire 75 and the copper wire 76 is adjusted by the viscosity adjusting controllers 31L and 31R of the electrorheological fluid and a booster circuit (not shown). The viscosity adjustment controllers 31L and 31R receive viscosity command values (corresponding to drag adjustment commands) transmitted from the integrated controller 30 described later, and the viscosity adjustment controllers 31L and 31R control the booster circuit so as to realize the viscosity, The voltage between the copper wire 75 and the copper wire 76 is adjusted.

  Further, the front wheel 42 is provided with a friction brake (braking means) by a hydraulic system (not shown) at a portion 44, and the hydraulic pressure of the brake system rises in response to the depression of the brake pedal by the driver. Accordingly, the brake pad fixed to the portion 44 sandwiches the disk that rotates together with the front wheel 42 to brake the front wheel 42.

  The rear wheels 2RL and 2RR are also provided with friction brakes (not shown), and the rear wheels 2RL and 2RR are braked in response to the driver's depression of the brake pedal, as with the front wheels 42. Furthermore, a link 51RL is connected to the rear wheel 2RL, and the rear wheel 2RL is steered by moving the link 51RL in the vehicle left-right direction by the steering motor 52RL. A motor drive circuit 53RL is connected to the steering motor 52RL, and the motor drive circuit 53RL receives the steering angle detection value from the actual steering angle sensor attached to the left rear wheel and the left rear wheel received from the integrated controller 30. Based on the steering angle target value tδrl, the torque of the steering motor 52RL is adjusted so that the actual left steering wheel actual turning angle matches the left rear wheel steering angle target value tδrl. Similarly, a link 51RR is connected to the rear wheel 2RR, and the rear wheel 2RR is steered by moving the link 51RR in the vehicle left-right direction by the steering motor 52RR. A motor drive circuit 53RR is connected to the steering motor 52RR, and the motor drive circuit 53RR receives the detected steering angle value from the actual steering angle sensor attached to the right rear wheel and the right rear wheel received from the integrated controller 30. Based on the steering angle target value tδrr, the torque of the steering motor 52RR is adjusted so that the actual right rear wheel steering angle matches the right rear wheel steering angle target value tδrr.

  In addition, electric motors 3RL, 3RR, batteries, and the like are arranged at front and rear positions of the rear wheels 2RL and 2RR so that the front and rear center of gravity of the electric vehicle in FIG. For example, the front-rear center of gravity position is designed so that the wheel load ratio between the front wheels 42FL and 42FR and the rear wheels 2RL and 2RR is 2: 8.

  The integrated controller 30 can be displaced left and right by an accelerator opening signal detected by an accelerator pedal sensor (driving target value detecting means) 23, a brake pedal force signal detected by a brake pedal sensor (braking force detecting means) 22, and right and left. The displacement angle signal of the steering wheel 11 detected by the displacement angle sensor 26 attached to the support point of the steering wheel 11 that can be detected, and the steering angle sensor (turn target value detection means) 21 attached to the rotating shaft of the steering wheel 11 are detected. A steering wheel 11 rotation angle signal, a vehicle body lateral acceleration (acceleration in the vehicle width direction) and longitudinal acceleration signals detected by an acceleration sensor 24 attached to the center of gravity of the vehicle, a yaw rate signal detected by the yaw rate sensor 8, and driving Operated by An encoder 27FL that detects the state signal of the shift lever 25, the angle formed by the rotation surface of the left front wheel 42FL and the front of the vehicle, the encoder 27FR that detects the angle formed by the rotation surface of the right front wheel 42FR and the vehicle front, and left and right front wheels Front wheel rotation speed signals detected by the front wheel rotation sensors 49 and 50 attached to the wheel rotation shafts 43FL and 43FR of the 42FL and 42FR, respectively, are input.

  As a shift position of the shift lever 25, a position “P” that can be selected only when the vehicle is stopped and used during parking, a position “D” that is used during normal forward travel, a position “A” that is used during forward travel in Mode A, There is a position “AR” that is used during reverse travel. Here, mode A is an operation mode in which the vehicle is rotated with the vicinity of the rear wheel of the turning inner wheel as the turning center, and mode B is an operation mode in which the vehicle is rotated with the point between the left and right rear wheels as the turning center. is there.

  These shift positions are selected by the driver by operating the shift lever 25. Based on these signals, the integrated controller 30 calculates a torque command value tTRL for the rear left wheel motor 3RL and a torque command value tTRR for the rear right wheel motor 3RR, and transmits them to the drive circuits 5RL and 5RR of the motors 3RL and 3RR. To do. Here, the torque command value tTRL to the rear left wheel motor 3RL and the torque command value tTRR to the rear right wheel motor 3RR are both in units of Nm, and the direction in which the vehicle is accelerated forward is positive. The integrated controller 30 also calculates rear wheel steering angle target values tδrl and tδrr and transmits them to the motor drive circuits 53RL and 53RR, respectively. The rear wheel rudder angle target values tδrl and tδrr have a unit of rad, and the direction to turn left is positive. Further, the integrated controller 30 calculates the viscosity command value tEl of the electrorheological fluid of the left front wheel and the viscosity command value tEr of the electrorheological fluid of the right front wheel, and transmits them to the viscosity adjustment controllers 31L and 31R of the electrorheological fluid, respectively.

Next, the operation will be described.
[Mode selection control processing]
FIG. 4 is a flowchart showing the flow of the mode selection control process executed by the integrated controller 30 according to the first embodiment. Each step will be described below. The integrated controller 30 includes peripheral components such as a RAM / ROM in addition to the microcomputer, and executes the flowchart of FIG. 4 at regular intervals, for example, every 5 ms.

  In step S401, each sensor signal and reception signals from the drive circuits 5RL and 5RR are stored in a RAM variable, and the process proceeds to step S402. Specifically, the accelerator opening signal is stored in a variable APS (unit is% and fully opened is 100%), the brake pedal force signal is stored in a variable BRK (unit is Pa), and the steering wheel 11 The displacement angle signal is stored in variable Win (unit is rad, left is positive), and the rotation angle signal of steering wheel 11 is stored in variable δ (unit is rad, counterclockwise is positive). The vehicle body lateral acceleration signal is stored in a variable YG (takes the direction when turning left in FIG. 1 is positive), and the vehicle body yaw rate signal is stored in the variable γ (takes the direction when turning left in FIG. 1 is positive). The vehicle body lateral acceleration signal is stored in the variable YG (the direction when turning left in FIG. 1 is positive), and the shift lever signal is stored in the variable SFT.

  Further, the angle formed by the encoder 27FL and the rotation surface of the left front wheel 42FL and the front of the vehicle is stored in a variable CFL (the unit is rad, and the rotation direction of the left front wheel 42FL is counterclockwise with respect to the vehicle front direction). And the angle between the rotation surface of the right front wheel 42FR and the front of the vehicle detected by the encoder 27FR is stored in the variable CFR (the unit is rad, and the rotation surface of the left front wheel 42FL is opposite to the vehicle front direction). Take the clockwise direction).

  The rotation speed signal from the left front wheel rotation sensor 49 is a variable NFL, and the rotation speed signal from the right front wheel rotation sensor 50 is a variable NFR (both units are rad / s, and the direction in which the vehicle moves forward is positive). ). Further, for the signals received from the drive circuits 5RL and 5RR, the rotational speeds of the respective motors are stored in variables NRL and NRR (both units are rad / s, and the direction in which the vehicle advances is positive).

In step S402, the vehicle speed V (unit is m / s and the direction in which the vehicle moves forward is positive) is calculated by the following equation, and the process proceeds to step S403 (corresponding to vehicle speed detection means).
V = (NFL * Rf + NFR * Rf + NRL / GG * Rr + NRR / GG * Rr) * R / 4
Here, Rf is the radius of the front wheel, Rr is the radius of the rear wheel, and GG is the reduction ratio of the reduction gear of the rear wheel.

  In step S403, it is determined whether or not the shift lever position is the position “P” used during parking. If “P”, the process proceeds to step S404, and this routine is executed with tTRL = tTRR = tδr1 = tδrr = 0. finish. Otherwise, the process proceeds to step S410.

  In step S410, it is determined whether or not the shift lever position is “D” or “A”. If the shift lever position is “D” or “A”, the process proceeds to step S413; Control goes to step S421.

  In step S413, it is determined whether or not the shift lever position is “A” and the vehicle speed V is less than a first vehicle speed threshold value Va (eg, 3 m / s). If YES, the process proceeds to step S414. Then, the calculation routine in mode A, which will be described later, is executed, and this routine ends. If not, the process proceeds to step S415, an arithmetic routine in mode D described later is executed, and this routine is terminated.

  When the process proceeds from step S410 to step S421, a calculation routine in mode AR described later is executed, and this routine is terminated.

[Mode selection control action]
When the shift position of the shift lever 25 can be selected only when the vehicle is stopped and the “P” position used for parking is selected, the flow proceeds from step S401 to step S402 to step S403 to step S404 in the flowchart of FIG. In step S404, the torque command value tTRL to the rear left wheel motor 3RL, the torque command value tTRR to the rear right wheel motor 3RR, and the rear wheel steering angle target values tδrl and tδrr are set to tTRL = tTRR = tδrl = tδrr = 0. This routine ends.

  When the position “D” or “A” is selected as the shift position of the shift lever 25 and the “A” position selection condition is not satisfied, step S401 → step S402 → The flow proceeds from step S403 to step S410 to step S413 to step S415. In step S415, the calculation routine for mode D used during normal forward travel is executed, and this routine is terminated.

When the position “D” or “A” is selected as the shift position of the shift lever 25 and the “A” position is selected and the A position selection condition of V <Va is satisfied, FIG. In the flowchart of FIG. 4, the process proceeds from step S401 to step S402, step S403, step S410, step S413, and step S414. In step S414, the calculation routine for mode A used during extremely low-speed forward travel is executed, End the routine.
That is, even when the “A” position is selected, when the vehicle speed V is equal to or higher than the first set threshold value Va, the process proceeds to step S415, and the calculation routine for mode D is executed. Migration is prohibited. For this reason, it is possible to suppress instability of vehicle behavior due to abrupt transition to driving mode A while the vehicle is traveling.

  When the “AR” position used during reverse travel is selected as the shift position of the shift lever 25, the flow proceeds to step S401 → step S402 → step S403 → step S410 → step S421 in the flowchart of FIG. In S421, the calculation routine for the mode AR used during reverse running is executed, and this routine is terminated.

[About the design principle and operation form of the controller that realizes the reference model response]
Next, in the calculation routine (FIG. 6) in mode D in step S415, the calculation routine in mode A (step 9) in step S414, and the calculation routine (FIG. 14) in mode AR in step S421, the rear left wheel motor A method for calculating the torque command value tTRL to 3RL, the torque command value tTRR to the rear right wheel motor 3RR, the rear wheel steering angle target values tδrl and tδrr, and the viscosity command values tEl and tEr of the electrorheological fluid of the front wheels will be sequentially described. However, before describing the calculation process in each calculation routine, first, the calculation principle and method of realizing the motor torque command value and the rear wheel steering angle target value in mode D will be described.

  “Motor motion and control” (Sankaido) shows the equation of motion of the vehicle behavior for steering the front and rear wheels. For example, in p194, the front wheel rudder angle δf [rad] and the rear wheel rudder angle δr [rad] (the rear wheel left and right rudder angles are the same) are manipulated variables, and the vehicle yaw rate γ [rad / s] and the vehicle body The equation of motion is shown with the vehicle body slip angle β [rad] at the center of gravity as the state quantity. This equation of motion shows that the vehicle speed V [m / s] is constant (dV = 0), V ≠ 0, and the slip angle (β [rad]) is very small (| β | << 1, sinβ ≒ β, cosβ ≒ 1). Derived on the premise of.

ここで、Lrは後輪軸と重心との距離[m]、Ltは後輪のトレッドベース距離/2[m]、mは車重[kg]、Iγはヨー慣性モーメント[Nmss]である。また、Krは後輪タイヤコーナリングスティッフネス[N/rad] であり、後輪ステアリング剛性の影響によるステアリング角に対するコーナリングパワーの低下分も加味した値である。Ｖは車速[m/s]であり、γはヨーレート[rad/s]、βは車体重心位置の車体すべり角[rad]である。
「自動車の運動と制御」（山海堂）p52に記されているように横力Ｙ[N]とヨーレートγ[rad/s]と滑り角β[rad]は次の関係にある。
Ｙ＝mＶ(dβ/dt＋γ) …(A2) The concept of this equation of motion can be extended to the electric vehicle of the first embodiment. That is, an operation amount with the right wheel driving force u [N] and the left wheel driving force -u [N] is added, the steering angle of the rear wheel is set to the same value δr [rad], and the front wheel of FIG. As a function of the caster type, the lateral force generated at the front wheels is almost zero, and the equation of motion can be derived as follows.
(Formula 1)

Here, Lr is the distance [m] between the rear wheel shaft and the center of gravity, Lt is the tread base distance / 2 [m] of the rear wheel, m is the vehicle weight [kg], and Iγ is the yaw moment of inertia [Nmss]. Kr is the rear wheel tire cornering stiffness [N / rad], which takes into account the decrease in cornering power with respect to the steering angle due to the influence of the rear wheel steering stiffness. V is the vehicle speed [m / s], γ is the yaw rate [rad / s], and β is the vehicle slip angle [rad] at the center of gravity of the vehicle.
As described in “Vehicle Movement and Control” (Sankaido) p52, the lateral force Y [N], the yaw rate γ [rad / s], and the slip angle β [rad] have the following relationship.
Y = mV (dβ / dt + γ) (A2)

These equations of motion can be rewritten into the following form using the differential operator s.
β = {Q ₁₂ (s) / Qden (s)} · δr + {Q ₁₃ (s) / Qden (s)} · u
γ = {Q ₂₂ (s) / Qden (s)} · δr + {Q ₂₃ (s) / Qden (s)} · u
Y = {Q ₃₂ (s) / Qden (s)} · δr + {Q ₃₃ (s) / Qden (s)} · u (A3)
Q ₁₂ (s), Q ₁₃ (s), Q ₂₂ (s), Q ₂₃ (s), Q ₃₂ (s), Q ₃₃ (s), and Qden (s) are all functions of the vehicle speed V. It is expressed by the following formula.
Q ₁₂ (s) = 2VKr (I _γ s + mVLr)
Q ₁₃ (s) = -2Lt (mV ² -2LrKr)
Q ₂₂ (s) = -2mV ² KrLrs
Q ₂₃ (s) = 2VLt (mVs + 2Kr)
Q ₃₂ (s) = 2mV ² KrI _γ s ²
Q ₃₃ (s) = 4mVLtKr (Lrs + V)
Qden (s) = mV ² I _γ s ² +2 VKr (mLr ² + I _γ ) s + 2 mV ² LrKr (A4)

“Automotive motion and control” (Sankaido) p203-p207, the front wheel rudder angle is adjusted so that the response of the vehicle yaw rate γ and slip angle β to the steering operation amount δ is a desirable transfer characteristic (reference model). A controller derivation method for generating the command value δf ^* and the rear wheel steering angle command value δr ^* is also shown. According to this method, in the first embodiment of the present invention, the response of the yaw rate γ and the slip angle β to the steering operation amount δ is a desirable transfer characteristic (reference model), and the yaw rate γ and the slip to the steering displacement angle Win. A controller (P1 in FIG. 5 (a)) that calculates the command value u * of the driving force difference between the left and right wheels and the command value δr ^* of the rear wheel steering angle so that the response of the angle β becomes a desirable transfer characteristic (reference model). (s), P2 (s), P3 (s), and P4 (s)) can be derived as follows.

Now, the desired transfer characteristic (reference model) of yaw rate γ with respect to the steering operation amount δ is G _γδ , the desired transfer characteristic (reference model) of slip angle β with respect to the steering operation amount δ is G _βδ , and the desired yaw rate γ with respect to the steering displacement angle Win. The transfer characteristic (normative model) is G _γw , and the desired transfer characteristic (normative model) of the slip angle β with respect to the steering displacement angle Win is G _βw .
G _γδ = m ₂ / (s ² + 2wns + wn ² )
G _βδ = 0
G _γw = 0
G _βw = m ₁ / (s ² + 2wns + wn ² )… (A5)

That is, desired response smooth second order response of the yaw rate γ for steering operation amount [delta] _{(e.g., wn = 4π, m 2 =} wn 2/4) and a smooth and desired response of the slip angle β with respect to steering wheel lateral displacement Win The secondary response characteristics are set (for example, wn = 4π, m ₁ = wn ² ). The slip angle β is set so that it is not affected by the steering operation amount δ, and the yaw rate γ is not affected by the steering displacement angle Win.

Incidentally, in FIG. 5A, the relationship among the steering operation amount δ and the steering displacement angle Win, the yaw rate γ, and the slip angle β is as follows. Here, 1 / Td (s) is the servo delay of the rear wheel steering system.
_{β = ({Q 13 (s} ) / Qden (s)} p1 (s) + {Q 12 (s) / Qden (s)} · {p2 (s) / Td (s)}) δ +
_{({Q 13 (s) /} Qden (s)} p3 (s) + {Q 12 (s) / Qden (s)} · {p4 (s) / Td (s)}) Win
_{γ = ({Q 23 (s} ) / Qden (s)} p1 (s) + {Q 22 (s) / Qden (s)} · {p2 (s) / Td (s)}) δ +
_{({Q 23 (s) /} Qden (s)} p3 (s) + {Q 22 (s) / Qden (s)} · {p4 (s) / Td (s)}) Win ... (A6)
Accordingly, the transfer characteristics, respectively desired transfer characteristic _{G βw, G γδ, G βδ} , from the condition that match the G _{Ganmadaburyu,} formula (A7) is guided,
G _βw = m ₁ / (s ² + 2wns + wn ² ) = {Q ₁₃ (s) / Qden (s)} p3 (s) + {Q ₁₂ (s) / Qden (s)} · {p4 (s) / Td (s)}
_{G βδ = 0 = {Q 13} (s) / Qden (s)} p1 (s) + {Q 12 (s) / Qden (s)} · {p2 (s) / Td (s)}
_{G γδ = m 2 / (s} 2 + 2wns + wn 2) = {Q 23 (s) / Qden (s)} p1 (s) + {Q 22 (s) / Qden (s)} · {p2 (s) / Td (s)}
_{G γw = 0 = {Q 23} (s) / Qden (s)} p3 (s) + {Q 22 (s) / Qden (s)} · {p4 (s) / Td (s)} ... (A7)
By solving these simultaneous equations and using the relational expression (A4), the controllers P1 (s), P2 (s), P3 (s) and P4 (s) can be derived as shown in the expression (A8). Here, the servo delay of the rear wheel steering is a first-order delay of a time constant τ (for example, τ = 0.1 [s]), that is, Td = τs + 1.
p1 (s) = {m ₂ / (2Lt)} {(I _γ s + mVLr) / (s ² + 2wns + wn ² )}
p2 (s) = {m ₂ (mV ² -2LrKr) / (2VKr)} {(τs + 1) / (s ² + 2wns + wn ² )}
p3 (s) = {m ₁ mVLr / (2 * Lt)} {s / (s ² + 2wns + wn ² )}
p4 (s) = {m ₁ (mVs + 2Kr) / (2Kr)} {(τs + 1) / (s ² + 2wns + wn ² )}… (A8)

As described above, in the first embodiment of the present invention, the difference in driving force between the left and right wheels so that the responses of the yaw rate γ and the slip angle β to the steering operation amount δ and the steering displacement angle Win are respectively desirable transmission characteristics (reference model). The controller (P1 (s), P2 (s), P3 (s) and P4 (s) in Fig. 5 (a)) to calculate the command value u ^* and the rear wheel steering angle command value δr ^* Can do.

Next, a method for realizing the controllers P1 (s), P2 (s), P3 (s), and P4 (s) in the equation (A8) will be described. Since P1 (s), P2 (s), P3 (s), and P4 (s) can be rewritten by the following equation (A9), a method for realizing the equation (A9) will be described. b0, b1, and b2 are functions such as the vehicle speed V.
yx = (b2s ² + b1s + b0) / (s ² + 2wns + wn ² )… (A9)
Equation (A9) can be rewritten as shown in FIG. Therefore, at every predetermined time (for example, every 5 ms), first, X2 and X1 are updated by performing the integration calculation in FIG. 5B by Euler approximation, for example, and then b0, b1, and b2 are changed. This is realized by sequentially updating the output yx from X2, X1, b0, b1, b2, and ux from moment to moment after updating sequentially according to the vehicle speed V.

[Calculation routine in mode D]
In the calculation routine in mode D of step S415 in FIG. 3, the flowchart of FIG. 6 is executed.

  In step S501, the target driving force tTD of the vehicle is calculated. The calculation is performed by referring to a map MAP_tTD (V, APS) stored in advance in the ROM (corresponding to motor output adjusting means). The map MAP_tTD (V, APS) is characteristic data with the vehicle speed V and the accelerator opening APS as axes, and is set as shown in FIG. 7, for example.

At step S502, it calculates a steady-state value m ₁ of the vehicle body slip angle to steering wheel lateral displacement Win. For example, a fixed value of m ₁ = wn ² (wn is 4π, for example). Alternatively, in order to realize characteristics according to the vehicle speed V and the steering operation amount δ, a method of multiplying the steering displacement angle Win by a value obtained by table map MAP_m1 (V, δ) stored in advance in ROM is used. May be.

  In steps S503 to S512, the target torque tU [Nm] and the rear wheel steering command values tδrl and tδrr of the driving force difference generated in the rear wheel left and right motors according to the steering wheel rotation angle δ, the steering displacement angle Win and the vehicle speed V are calculated. Calculate. Based on the above design principle, the calculation is such that the response of the yaw rate γ and the slip angle β to the steering operation amount δ is a desirable transfer characteristic (reference model), and the response of the yaw rate γ and the slip angle β to the steering displacement angle Win. Is calculated to have a desirable transfer characteristic (normative model).

G _{γδ is} the desired transfer characteristic (reference model) of yaw rate γ with respect to the steering operation amount δ, G _{βδ is} the desired transfer characteristic (reference model) of slip angle β with respect to the steering operation amount δ, and the desired transfer characteristic of yaw rate γ with respect to the steering displacement angle Win. The (reference model) is described as G _γw , and the desirable transfer characteristic (reference model) of the slip angle β with respect to the steering displacement angle Win is described as G _βw as a characteristic represented by the equation (A5).

In step S503, the vehicle speed V calculated in step S420 is used to calculate the values corresponding to b0, b1, and b2 in equation (A9) for the first equation in equation (A8) as follows.
b2 = 0
b1 ＝ (m ₂ Ir) / (2Lt)
b0 = (V * m ₂ * m * Lr) / (2Lt) ... (B1)
Here, m ₂ is such that the steady value of the yaw rate with respect to the steering wheel rotation angle δ is, for example, δ / 4.
m ^₂ = wn _2/4
Keep it as Vehicle design values are used for m, Ir, Lr, and Lt.

  In step S504, X2 and X1 are updated by Euler approximation of the integration calculation of FIG. 5B using X2 and X1 obtained when the previous step S504 is executed. In FIG. 5B, ux is the steering wheel rotation angle δ, and the output yx is substituted into the variable yx1. In the calculation, variables X2a and X1a are used as variables used in step S504 as X2 and X1 in FIG. After updating X2 and X1 in FIG. 5 (b), the output yx is calculated from the relational expression shown in FIG. 5 (b) according to those values and b0, b1 and b2 obtained in step S503, and assigned to yx1. To do.

In step S505, using the vehicle speed V calculated in step S420, the values corresponding to b0, b1, and b2 in equation (A9) are calculated as follows for the equation in the second stage of equation (A8). In order to prevent 0%, the vehicle speed V is calculated by limiting the minimum value to Vmin (for example, 1 m / s).
b2 = 0
b1 ＝ m ₂ (mV ² -2LrKr) τ / (2VKr)
b0 ＝ m ₂ (mV ² -2LrKr) / (2VKr)… (B2)
Vehicle design values are used for m, Lr, and Kr. Also, τ is set to, for example, about 0.1 in accordance with the servo delay of the rear wheel steering system.

  In step S506, X2 and X1 obtained by executing the previous step S506 are used, and X2 and X1 are updated by Euler approximation of the integral calculation of FIG. In FIG. 5B, ux is the steering wheel rotation angle δ, and the output yx is substituted into the variable yx2. In the calculation, variables X2b and X1b are used as variables used in step S506 as X2 and X1 in FIG. After updating X2 and X1 in FIG. 5 (b), the output yx is calculated from the relational expression shown in FIG. 5 (b) according to those values and b0, b1 and b2 obtained in step S505, and assigned to yx2. To do.

In step S507, the vehicle speed V calculated in step S420 and m ₁ calculated in step S502 are used, and the values corresponding to b0, b1, and b2 in equation (A9) are expressed as follows for equation (A8) in the third stage: Calculate as follows.
b2 = 0
b1 ＝ m ₁ mVLr / (2Lt)
b0 = 0 ... (B1 ')
Vehicle design values are used for m, Lr, and Lt.

  In step S508, X2 and X1 obtained by executing the previous step S508 are used, and X2 and X1 are updated by Euler approximation of the integral calculation of FIG. In FIG. 5B, ux is the steering displacement angle Win, and the output yx is substituted into the variable yx3. When calculating, variables X2c and X1c are used as variables used in step S508 as X2 and X1 in FIG. After updating X2 and X1 in FIG. 5 (b), the output yx is calculated from the relational expression shown in FIG. 5 (b) according to those values and b0, b1 and b2 obtained in step S507, and substituted into yx3. To do. Thus, by setting b0 = 0, it is possible to realize an operation in which the left / right driving force difference operation is not constantly performed with respect to the steering displacement angle Win (the same as the steady gain of p3 (s) being 0). is there).

At step S509, the use of a m ₁ computed by the vehicle speed V and the step S502 calculated in step S420, for formula of formula (A8) the fourth stage, the formula (A9) of b0, b1, the value of the next corresponding to b2 Calculate as follows.
b2 ＝ Vm ₁ mτ / (2Kr)
b1 ＝ (m ₁ mV + 2 * m ₁ τKr) / 2
b0 ＝ m ₁ … (B2 ')
m and Kr use vehicle design values. Τ is set to the same value as described above.

  In step S510, X2 and X1 obtained by executing the previous step S510 are used, and X2 and X1 are updated by Euler approximation of the integral calculation of FIG. In FIG. 5B, ux is the steering displacement angle Win, and the output yx is substituted into the variable yx4. In the calculation, variables X2d and X1d are used as variables used in step S510 as X2 and X1 in FIG. After updating X2 and X1 in FIG. 5 (b), the output yx is calculated from the relational expression shown in FIG. 5 (b) according to those values and b0, b1 and b2 obtained in step S509 and substituted into yx4. To do.

In step S511, the rear wheel steering command values tδrl and tδrr are calculated as the sum of the yx2 value calculated in step S506 and the yx4 value calculated in step S510.
tδrl = tδrr = yx2 + yx4

In step S512, the target left / right driving force difference tU is calculated as the sum of the yx1 value calculated in step S504 and the yx3 value calculated in step S508 (corresponding to the motor output adjusting means).
tU = yx1 + yx3

Subsequently, in step S513, the direction βf to which the front wheels should travel is calculated (corresponding to the steered wheel target direction calculation means). The direction βf that the front wheel should travel is calculated by the following equation as βf of the vehicle body slip angle at the front wheel position when the responses of the yaw rate γ and the slip angle β each have desirable transfer characteristics (reference model).
βf = (β + (L-Lr) γ / V)
= {m ₁ / (s ² + 2wns + wn ² )} Win + {(L-Lr) m ₂ / (s ² + 2wns + wn ² ) / V} δ… (E1)
Here, L is the distance (wheelbase length) between the front wheel and the rear wheel. In addition, this calculation uses the terms {m ₁ / (s ² + 2wns + wn ² )} Win and {(L-Lr) m ₂ / (s ² + 2wns + wn ² ) / V} δ as described above for yx1, yx2 , yx3, yx4, etc., respectively, and calculating by adding the sum of the terms. In order to prevent 0%, the vehicle speed V is calculated by limiting the minimum value to Vmin (for example, 1 m / s).

Subsequently, in step S514, a viscosity command value tEl for the electrorheological fluid of the left front wheel is calculated. The viscosity command value tEl is calculated by the following equation according to the difference between βf calculated in step S513 and the rotation angle of the left front wheel, the vehicle speed V, and the brake pedaling force BRK.
tEl = DM x COEF1x COEF2… (E2)
Here, DM, COEF1, and COEF2 are calculated from the relationship shown in FIG. In other words, DM is calculated by drawing the ROM data (FIG. 8A) related to the absolute value of the difference between βf and the rotation angle CFL of the left front wheel, and COEF1 is related to the vehicle speed V. The calculated ROM data (FIG. 8 (b)) is calculated by drawing, and COEF2 is calculated by drawing the ROM data (FIG. 8 (c)) related to the brake pedaling force BRK. Here, FIG. 8 (a) is a right-down characteristic, and FIG. 8 (b) and FIG. 8 (c) are a right-up characteristic. By doing so, the greater the difference between the direction in which the front wheels should travel and the direction of the front wheels, the smaller the drag in the steering direction of the front wheels, and the higher the vehicle speed, the greater the drag in the steering direction of the front wheels, The larger the value, the greater the drag in the steering direction of the front wheels.

Subsequently, in step S515, the viscosity command value tEr of the electrorheological fluid of the right front wheel is calculated. The viscosity command value tEr is calculated by the following equation according to the difference between βf calculated in step S513 and the rotation angle CFR of the right front wheel, the vehicle speed V, and the brake pedaling force BRK.
tEr = DMx COEF1 x COEF2… (E3)
The calculation method is the same as in step S514.

  In step S516, tEl and tEr calculated in steps S514 and S515 are corrected (corresponding to drag control means). The correction is performed based on the difference between βf and the rotation angle of the left front wheel (βf−CFL) and the difference between βf and the rotation angle of the right front wheel (βf−CFR). When (βf−CFL) and (βf−CFR) are both positive values, both negative values, or one of them is 0, no correction is performed. When either (βf−CFL) or (βf−CFR) is a positive value and either one is a negative value, correction is performed according to the absolute value of both. The correction is performed so as to increase the viscosity command value of the wheel having a small absolute value so as to decrease the viscosity command value of the wheel having a large absolute value. For example, in the case of (βf−CFL) <0, (βf−CFR)> 0, | βf−CFL |> | βf−CFR |, tEL = 0.9 tEL, tER = 1.1 tER, and correction calculation is performed.

In step S517, the target left / right driving force difference tU is corrected. The correction is performed by the following equation according to the sum of (βf−CFL) and (βf−CFR).
tU = tU + Ku (βf−CFL + βf−CFR) (E4)
Here, Ku is a positive constant and corresponds to the gain of the correction amount. For example, when the rotation angle CFL of the left front wheel and the rotation angle CFR of the right front wheel are larger than βf (when CFL and CFR are counterclockwise with respect to βf), tU is corrected to a negative direction.

In step S518, torque command values tTRL and tTRR for the rear wheels are calculated from the target driving force tTD and the target left / right driving force difference tU by the following equation.
TTRL = tTD * Rr / GG / 2-tU * Rr / GG
TTRR = tTD * Rr / GG / 2 + tU * Rr / GG… (B3)
After the calculation in step S518, this routine ends.

[Calculation routine in mode A]
In the calculation routine in mode A of step S414 in FIG. 3, the flowchart of FIG. 9 is executed.

  In step S801, a target speed tV at the center position of the rear wheel shaft is calculated. For example, when the accelerator calculation APS is 0, tV = 0, and when the APS is 100%, tV = 3 [m / s] is assigned proportionally.

  In step S802, a target value tρ that is an inverse value of the turning radius of the center position of the rear wheel shaft (point P in FIG. 10) is calculated. The target value tρ is a positive value when turning left, that is, when the vehicle's turning center is on the left, and negative when turning right, that is, when the vehicle's turning center is on the right. For example, the characteristics shown in FIG. 11 are set according to δ. Here, for example, when Wt is the half length of the tire width and Lt is the half length of the tread base distance of the rear wheel, the target value tρ is -1 / (Lt + Wt) and 1 / (Lt + Wt).

  In step S803, the target slip angle βc of the center position of the rear wheel shaft (point P in FIG. 10) (the angle of the direction in which the point P advances with respect to the direction of the vehicle body, with the counterclockwise direction being positive. The unit is [rad ].) The calculation is performed with reference to the table previously stored in the ROM as shown in FIG. 12 according to tρ and the steering displacement angle Win.

In step S804, the left rear wheel motor and the right rear wheel are obtained from the target speed tV of the center position of the rear wheel shaft (point P in FIG. 10), the target value tρ of the reciprocal value of the turning radius of the center position of the rear wheel shaft, and the target slip angle βc. The target rotational speeds tNRL and tNRR of the wheel motor are calculated by the following formula. At that time, pay attention to the following relationship. That is, when the vehicle turns so as to realize tρ obtained in step S802 and the target slip angle βc obtained in step S803, the rotation center of the vehicle is point Q in FIG. 10, and therefore the moving speed of point P is tV. The moving speed of the left rear wheel is tV * R1 / R0 (R1 is the distance between the left rear wheel and point Q, R0 is the distance between point P and point Q), and the moving speed of the right rear wheel is tV * R2 / R0 (R2 is the distance between the right rear wheel and point Q). Using this relationship, the target rotational speeds tNRL and tNRR of the left rear wheel motor and the right rear wheel motor are calculated by the following equations.
tNRL = tV / Rr * GG * sqrt (1-2tρLt cos (βc) + tρ ² Lt ² )
tNRR = tV / Rr * GG * sqrt (1 + 2tρLt cos (βc) + tρ ² Lt ² )… (C1)
Here, it is utilized that the values of R1 / R0 and R2 / R0 can be derived as follows from the geometric relationship shown in FIG.
R1 / R0 = sqrt (1-2tρLt cos (βc) + tρ ² Lt ² )
R2 / R0 = sqrt (1 + 2tρLt cos (βc) + tρ ² Lt ² ) * sqrt means a square root function.

In step S805, feedback control is performed so that the rotation speed NRL of the left rear wheel motor approaches the target rotation speed tNRL of the left rear wheel motor. For example, proportional control is performed as in the following equation to calculate a torque command value tTRL for the left rear wheel motor. Kp1 is a proportional gain.
tTRL = Kp1 * (tNRL-NRL)

In step S806, feedback control is performed so that the rotational speed NRR of the right rear wheel motor approaches the target rotational speed tNRR of the right rear wheel motor. For example, proportional control is performed as in the following equation to calculate a torque command value tTRR for the right rear wheel motor. Kp1 is the same proportional gain as in step S805.
tTRR = Kp1 * (tNRR−NRR)

The method of step S805 and step S806 is a method of calculating the torque command value to the motor only by feedback, but using the direction βfl that the left front wheel should advance and the direction βfr that the left front wheel should advance, for example, ( The following equation may be used to correct the feed forward according to the sum of (βfl−CFL) and (βfr−CFR).
tTRL = Kp1 * (tNRL-NRL)-Kq (βfl-CFL + βfr-CFR)
tTRR = Kp1 * (tNRR-NRR) + Kq (βfl−CFL + βfr−CFR)… (F1)
Here, Kq is a positive constant and corresponds to the gain of the correction amount. For example, when the rotation angle CFL of the left front wheel is larger than βfl and the rotation angle CFR of the right front wheel is larger than βfr (CFL is counterclockwise with respect to βfl, and CFR is counterclockwise with respect to βfr) TTRL and tTRR are corrected so as to generate a clockwise yaw moment that counteracts the counterclockwise yaw moment generated by the rotation angle of the front wheel. In this case, step S808 is executed before S805 and step S806.

In step S807, rear wheel steering command values tδrl and tδrr are calculated. The rear wheel steering command values tδrl and tδrr are calculated based on the vehicle rotation center (point Q in FIG. 10) corresponding to tρ obtained in step S802 and the target slip angle βc obtained in step S803. The left rear wheel turning angle tδrl is calculated by the following equation so that the line connecting the rotation center point Q and the left rear wheel center is perpendicular to the rolling direction of the tire.
tδrl = tan ⁻¹ {sin (βc) / (cos (βc) -tρLt)}
The right rear wheel turning angle tδrr is calculated by the following equation so that the line connecting the rotation center point Q and the right rear wheel center is perpendicular to the rolling direction of the tire.
tδrr = tan ^-1 {sin (βc) / (cos (βc) + tρLt)}

Subsequently, in step S808, the direction βfl that the left front wheel should travel and the direction βfr that the left front wheel should travel are calculated (corresponding to target steered wheel direction calculation means). βfl and βfr are calculated as the angles of C and D shown in FIG.
βfl = tan ^-1 {tρL + sin (βc) / (cos (βc) −tρLt)}
βfr = tan ⁻¹ {tρL + sin (βc) / (cos (βc) + tρLt)}

Subsequently, in step S809, a viscosity command value tEl for the electrorheological fluid of the left front wheel is calculated. The viscosity command value tEl is calculated by the following equation according to the difference between βfl calculated in step S808 and the rotation angle of the left front wheel, the vehicle speed V, and the brake pedaling force BRK.
tEl = DM × COEF1 × COEF2
This calculation is as shown in step S514.

Subsequently, in step S810, the viscosity command value tEr of the electrorheological fluid of the right front wheel is calculated by the following equation.
tEr = DM × COEF1 × COEF2
The calculation method is the same as that in step S809.

In step S811, tEl and tEr calculated in steps S809 and S810 are corrected (corresponding to drag control means). The correction is performed based on the difference between βfl and the rotation angle of the left front wheel (βfl−CFL) and the difference between βfr and the rotation angle of the right front wheel (βfr−CFR). When (βfl−CFL) and (βfr−CFR) are both positive values, both negative values, or one of them is 0, no correction is performed. When either (βfl−CFL) or (βfr−CFR) is a positive value and either one is a negative value, correction is performed according to the absolute value of both. The correction is performed so as to increase the viscosity command value of the wheel having a small absolute value so as to decrease the viscosity command value of the wheel having a large absolute value. For example, in the case of (βfl−CFL) <0, (βfr−CFR)> 0, | βfl−CFL |> | βfr−CFR |, tEL = 0.9 tEL, tER = 1.1 tER.
After the calculation in step S811, this routine ends.

  By performing the above calculation, as shown in FIG. 13 (a), it is possible to perform an operation of turning the vehicle in a small turn with the vicinity of the rear wheel of the turning inner wheel (excluding the tire width) as the turning center. In addition, the left and right turning amount of the rear wheel is adjusted so that the straight line connecting the center of rotation determined by the turning radius and turning posture and the rear wheel is perpendicular to the tire direction. The tire can roll smoothly. This effect can be achieved in the same way during the AR mode driving described later.

[Calculation routine in mode AR]
In the calculation routine in the mode AR of step S421 in FIG. 3, the flowchart of FIG. 14 is executed.

  In step S1501, a target speed tV at the center position of the rear wheel shaft is calculated. For example, when the accelerator calculation APS is 0, tV = 0, and when the APS is 100%, tV = −3 [m / s] is assigned proportionally.

  In step S1502, a target value tρ that is an inverse value of the turning radius of the center position of the rear wheel shaft (point P in FIG. 10) is calculated. The calculation method is the same as that in step S802.

  In step S1503, the target slip angle βc of the center position of the rear wheel axle (point P in FIG. 10) (the angle of the direction in which the point P advances with respect to the direction of the vehicle body, with the counterclockwise direction taken positively. The unit is [rad ].) The calculation is the same method as in step S803.

In step S1504, the left rear wheel motor and the right rear wheel are obtained from the target speed tV of the center position of the rear wheel shaft (point P in FIG. 10), the target value tρ of the reciprocal value of the turning radius of the center position of the rear wheel shaft, and the target slip angle βc. The target rotational speeds tNRL and tNRR of the wheel motor are calculated by the following formula. Since the calculation method is the same as that in step S804, description thereof is omitted.
tNRL = tV / Rr * GG * sqrt (1-2tρLt cos (βc) + tρ ² Lt ² )
tNRR = tV / Rr * GG * sqrt (1 + 2tρLt cos (βc) + tρ ² Lt ² )… (D1)

In step S1505, feedback control is performed so that the rotation speed NRL of the left rear wheel motor approaches the target rotation speed tNRL of the left rear wheel motor. For example, proportional control is performed as in the following equation to calculate a torque command value tTRL for the left rear wheel motor. Kp3 is a proportional gain.
tTRL = Kp3 * (tNRL-NRL)

  In step S1506, feedback control is performed so that the rotational speed NRR of the right rear wheel motor approaches the target rotational speed tNRR of the right rear wheel motor. For example, proportional control is performed as in the following equation to calculate a torque command value tTRR for the right rear wheel motor. Kp3 is the same proportional gain as in step S1505. tTRR = Kp3 * (tNRR-NRR)

The method of step S1505 and step S1506 is a method of calculating the torque command value to the motor only by feedback, but using the direction βfl that the left front wheel should advance and the direction βfr that the right front wheel should advance, for example, ( The following equation may be used to correct the feed forward according to the sum of (βfl−CFL) and (βfr−CFR).
tTRL = Kp1 * (tNRL-NRL) + Kq (βfl−CFL + βfr−CFR)
tTRR = Kp1 * (tNRR-NRR)-Kq (βfl-CFL + βfr-CFR)… (F2)
Here, Kq is a positive constant and corresponds to the gain of the correction amount. For example, when the rotation angle CFL of the left front wheel is larger than βfl and the rotation angle CFR of the right front wheel is larger than βfr (CFL is counterclockwise with respect to βfl, and CFR is counterclockwise with respect to βfr) TTRL and tTRR are corrected so as to generate a counterclockwise yaw moment that counteracts the clockwise yaw moment generated by the rotation angle of the front wheels. In this case, step S1508 is executed before S1505 and step S1506.

  In step S1507, rear wheel steering command values tδrl and tδrr are calculated. The calculation method is the same as that in step S807.

Subsequently, in step S1508, the direction βfl that the left front wheel should travel and the direction βfr that the right front wheel should travel are calculated (corresponding to the steered wheel target direction calculation means). .beta.fl and .beta.fr are calculated from the geometrical relationship as the 180.degree. inversion angles of C and D shown in FIG.
βfl = tan ^-1 {tρL + sin (βc) / (cos (βc) -tρLt)} + π
βfr = tan ⁻¹ {tρL + sin (βc) / (cos (βc) + tρLt)} + π

Subsequently, in step S1509, the viscosity command value tEl of the electrorheological fluid of the left front wheel is calculated. The viscosity command value tEl is calculated by the following equation according to the difference between βfl calculated in step S1508 and the rotation angle of the left front wheel, the vehicle speed V, and the brake pedaling force BRK.
tEl = DM x COEF1 x COEF2
This calculation is as shown in step S514.

Subsequently, in step S1510, the viscosity command value tEr of the electrorheological fluid of the right front wheel is calculated by the following equation.
tEr = DM x COEF1 x COEF2
The calculation method is the same as that in step S1509.

In step S1511, tEl and tEr calculated in steps S1509 and S1510 are corrected (corresponding to drag control means). The correction is performed based on the difference between βfl and the rotation angle of the left front wheel (βfl−CFL) and the difference between βfr and the rotation angle of the right front wheel (βfr−CFR). When (βfl−CFL) and (βfr−CFR) are both positive values, both negative values, or one of them is 0, no correction is performed. When either (βfl−CFL) or (βfr−CFR) is a positive value and either one is a negative value, correction is performed according to the absolute value of both. The correction is performed so as to increase the viscosity command value of the wheel having a small absolute value so as to decrease the viscosity command value of the wheel having a large absolute value. For example, in the case of (βfl−CFL) <0, (βfr−CFR)> 0, | βfl−CFL |> | βfr−CFR |, tEL = 0.9 tEL, tER = 1.1 tER.
After the calculation of step S1511, this routine is finished.

  By performing the above calculation, as shown in FIG. 13 (b), the vehicle can be rotated slightly while moving backward.

Next, the effect will be described.
In the electric vehicle according to the first embodiment, the following effects can be obtained.

(1) Rear wheels 2RL and 2RR that generate a difference in driving force between the left and right wheels, front wheels 42FL and 42FR that change the direction of the vehicle body according to the turning of the vehicle body, and drag in the steering direction of the front wheels 42FL and 42FR The drag variable means for varying the vehicle, the drive target value detection means for detecting the drive target value of the vehicle, the turn target value detection means for detecting the turn target value of the vehicle, and the rear wheels 2RL and 2RR according to the drive target value Motor output adjustment means that adjusts the left and right driving force sum and adjusts the left and right driving force difference between the rear wheels 2RL and 2RR according to the turning target value, and calculates the direction in which the front wheels 42FL and 42FR should proceed according to the turning target value The drag becomes smaller as the deviation between the steered wheel target direction calculating means, the encoders 27FL and 27FR for detecting the actual directions of the front wheels 42FL and 42FR, and the direction in which the front wheels 42FL and 42FR should move and the actual direction is larger. The drag variable means And a drag control means for outputting a drag adjustment command.
Thereby, when the deviation is large, by reducing the drag in the steering direction of the front wheels 42FL, 42FR, it is possible to shorten the time until the direction of the front wheels 42FL, 42FR follows the direction in which the front wheels 42FL, 42FR should travel, Therefore, the behavior of the vehicle can be brought close to a desired movement. At the same time, when the deviation is small, the continuous vibration in the turning direction of the front wheels 42FL, 42FR can be suppressed by increasing the drag in the turning direction of the front wheels 42FL, 42FR.

  (2) A vehicle speed detecting means for detecting the vehicle speed V is provided, and the drag control means increases the drag as the detected vehicle speed V is higher. That is, based on the fact that the vibration speed of the front wheels 42FL and 42FR tends to increase as the vehicle speed V increases, the controller 30 adjusts the viscosity of the electrorheological fluid to increase as the vehicle speed V increases (steps S514 and S515). , S809, S810, S1509, S1510). Thereby, when the vehicle speed V is low, the vibration of the front wheels 42FL and 42FR is effectively suppressed according to the vehicle speed V without increasing the time until the direction of the front wheels 42FL and 42FR follows the direction in which the front wheels 42FL and 42FR should travel. can do.

  (3) A friction brake that brakes the front wheels 42FL and 42FR and a brake pedal sensor 23 that detects the braking force of the friction brake are provided, and the drag control means increases the drag as the detected braking force increases. . That is, based on the fact that the vibration speed of the front wheels 42FL, 42FR tends to increase as the braking force of the front wheels 42FL, 42FR increases, the controller 30 adjusts the viscosity of the electrorheological fluid to increase as the brake pedal force increases. (Steps S514, S515, S809, S810, S1509, S1510). Thereby, when the brake pedal force is small, the vibration of the front wheels 42FL and 42FR is effectively suppressed according to the brake pedal force without increasing the time until the direction of the front wheels 42FL and 42FR follows the direction in which the front wheels 42FL and 42FR should travel. it can.

  (4) Two left and right front wheels (42FL, 42FR) are provided, and the drag control means adjusts the drag for each front wheel 42FL, 42FR so that the sum of the vehicle yaw moments generated by the deviation is reduced. That is, when the deviation is positive or negative in the two front wheels 42FL and 42FR, the viscosity of the electrorheological fluid is adjusted so that the yaw moments that affect the vehicle cancel each other according to the difference (step S516). , Correction of viscosity command values tEl, tEr in S811, S1511). Thereby, the effect which reduces the influence which the yaw moment according to each difference has on a vehicle motion can be acquired. In adjusting the viscosity, it is utilized that the yaw moment is increased as the deviation is increased, and the yaw moment is increased as the viscosity of the electrorheological fluid is increased. When the deviation is large, the electrorheological fluid viscosity is reduced, and when the deviation is small, the electrorheological fluid viscosity is increased, thereby bringing the absolute values of the reverse yaw moments generated by the two front wheels 42FL and 42FR closer to each other, Reduce the impact on vehicle motion.

  (5) The drag variable means includes an electrorheological fluid 73 enclosed between the turning shaft 41 and the hollow support 45, and the drag control means adjusts the voltage applied to the electrorheological fluid 73. The drag force can be continuously adjusted by an electrical command, and the adjustment according to the state of the vehicle and the front wheels 42FL and 42FR can be electrically performed.

  (6) When there is a difference between the direction of the front wheels 42FL and 42FR and the direction in which the front wheel should travel, a configuration for correcting the left and right torque difference of the rear wheels so as to cancel the yaw moment that the vehicle is affected according to the deviation did. Specifically, the correction amount is calculated in step S517 (step formula (F1) for mode A and formula (F2) for mode AR) in the controller 30. Thereby, even when the deviations are both positive or negative in the plurality of front wheels, it is possible to obtain an effect of reducing the influence of the yaw moment according to the deviations on the vehicle motion.

  The second embodiment is an example in which a magnetorheological fluid is used as a drag varying unit that varies the drag in the steering direction of the front wheels.

First, the configuration will be described.
FIG. 15 is a cross-sectional view illustrating a main part of a front wheel applied to the electric vehicle according to the second embodiment. In addition, the same code | symbol is attached | subjected to the part same as the structure of Example 1 shown in FIG. 2, and description is abbreviate | omitted.
As shown in FIG. 15, a magnetorheological fluid 85 is sealed with a sealant 72 between the upper and lower bearings 71. By passing a current through a plurality of coils 83 embedded along the inner circumference of the hollow support portion 45, a magnetic flux is generated in the member 86 made of iron, thereby forming an electromagnetic circuit indicated by an arrow in the figure. The viscosity of the magnetorheological fluid 85 is changed.

  Thus, the viscosity of the magnetorheological fluid 85 is changed, and the drag in the turning direction against the rotational speed difference between the hollow support portion 45 and the turning shaft 41 is adjusted. The coil 83 is configured to supply current from the outside through copper wires 81 and 82 with insulating films, and according to the viscosity command value from the integrated controller 30, the viscosity adjustment controllers 31L and 31R (see FIG. 1) have their current values. Adjust.

  As described above, by using the magnetorheological fluid instead of the electrorheological fluid, the same operation as that of the first embodiment can be obtained.

Next, the effect will be described.
In the electric vehicle according to the second embodiment, the following effects can be obtained.

  (7) A magnetorheological fluid 85 enclosed between the turning shaft 41 and the hollow support 45 and an electromagnet for adjusting the amount of magnetic flux passing through the magnetorheological fluid 85, and the drag control means is an electromagnet In order to adjust the current supplied to the vehicle, it is possible to continuously adjust the drag force according to the electrical command, and the adjustment according to the state of the vehicle and the front wheels 42FL and 42FR can be performed electrically.

(Other examples)
As mentioned above, although the electric vehicle of this invention has been demonstrated based on Example 1, 2, it is not restricted to this Example 1, 2 about a concrete structure, It concerns on each claim of a claim Design changes and additions are allowed without departing from the scope of the invention.

  For example, the drive system is not limited to the form shown in FIG. 1, and for example, the drive form of the rear wheels may be as shown in FIG. In FIG. 16, the rear wheel is a clutch motor 60 (both the inner and outer motors are rotatably supported, and torque is generated in the motor to apply reverse torque to the left and right wheels via the speed reducers 63R and 63L. This is a motor that is capable of generating a driving force difference between the left and right rear wheels according to Japanese Patent Application Laid-Open No. 4-332927, etc.), and is also controlled by the driving motor 61 via the differential gear 62. In this mode, a driving force is generated. As long as the left and right wheel torques of the rear wheels can be adjusted independently as described above, it is only necessary.

  In the first and second embodiments, the number of front wheels of the vehicle is two, but it may be one or more than three. As shown in the first embodiment, the direction in which each front wheel should proceed is calculated according to the number and position of the front wheels, and the drag of the rotation direction is adjusted according to the difference between the calculated value and the actual direction. good. Moreover, when applying Claim 7, it is realizable similarly by correct | amending the left-right torque difference of a motor so that the vehicle moment which generate | occur | produces by the difference may be negated. Alternatively, a configuration may be adopted in which a motor is connected to the front wheels to form driving wheels, and the two rear wheels are caster-type steered wheels.

  Further, as a method of not using an electroviscous fluid or a magnetorheological fluid in the drag variable means, a turning rotation shaft (vehicle-side turning support shaft) 41 and a hollow support portion (steering wheel-side turning support shaft) 45 are provided. There is also a method using an electromagnetic clutch or a friction brake that can adjust the coupling force between them. The rotation angle between the turning shaft 41 and the hollow support portion 45 is detected. The larger the rotation angle, the smaller the coupling force is adjusted. The higher the vehicle speed, the smaller the coupling force is adjusted. It is good also as a system adjusted small.

  Furthermore, it is good also as a structure provided with the actuator which drives a steered wheel. In other words, the steered wheels are not necessarily passively steered, and the steered wheels are steered by an actuator in accordance with a turning command, and the steered wheels are steered according to the vehicle body moment so as not to generate lateral force. Thus, this configuration can be achieved. In this case, the turning speed of the steered wheels is adjusted according to the turning response speed. That is, if the steered wheel is actively used as a steered device, the grip force is insufficient, so the function as a steered device cannot be achieved, but there is no problem if it is a driven operation, which is preferable in terms of straight running stability. Become. In addition, there is an effect that variations are increased in the handling method at low speed that does not expect grip force.

  In the first and second embodiments, the electric vehicle including the drive system that drives the left and right rear wheels with independent electric motors is shown. However, as described above, the drive system that can independently adjust the left and right wheel torques of the rear wheels is mounted. The present invention can also be applied to an electric vehicle.

1 is an overall system diagram illustrating an electric vehicle according to a first embodiment. It is the side view and top view which show the front wheel applied to the electric vehicle of Example 1. FIG. FIG. 3 is an enlarged cross-sectional portion of a coupling portion A in FIG. 2. 6 is a flowchart illustrating a flow of mode selection control processing executed by the integrated controller of the first embodiment. It is a figure explaining the calculation method at the time of mode D in the integrated controller of Example 1. FIG. 6 is a flowchart illustrating a calculation routine in mode D according to the first embodiment. 6 is a ROM data characteristic diagram of a target driving force tTD used in a calculation routine in mode D in Embodiment 1. FIG. 6 is a ROM data characteristic diagram for calculating a target viscosity of an electrorheological fluid in Example 1. FIG. 6 is a flowchart illustrating a calculation routine in mode A according to the first embodiment. It is a figure explaining the calculation method at the time of mode A and mode AR in Example 1. FIG. It is a ROM data characteristic view of the reciprocal value target value tρ of the turning radius used in the calculation routine in mode A and mode AR in the first embodiment. FIG. 6 is a ROM data characteristic diagram of a target slip angle βc used in a calculation routine in mode A in the first embodiment. It is a figure which shows the turning behavior example in Example 1. FIG. 7 is a flowchart illustrating a calculation routine in a mode AR in the first embodiment. It is sectional drawing which shows the principal part of the front wheel applied to the electric vehicle of Example 2. It is a figure which shows the other Example of a drive system.

Explanation of symbols

2RL, 2RR Rear wheel 3RL, 3RR Motor 4RL, 4RR Reducer 5RL, 5RR Drive circuit 6 Lithium ion battery 8 Yaw rate sensor 11 Steering wheel 21 Steering angle sensor 22 Brake pedal sensor 23 Accelerator pedal sensor 24 Acceleration sensor 25 Shift lever 26 Displacement angle Sensor 27FL, 27FR Encoder 30 Integrated controller 31L, 31R Viscosity controller 41FL, 41FR Steering rotation shaft 42FL, 42FR Front wheel 43FL, 43FR Wheel rotation shaft 44 Part 45 Hollow support 49, 50 Front wheel rotation sensor 51RL, 51RR Links 52RL, 52RR Steering motor 53RL, 53RR Motor drive circuit 71 Bearing 72 Sealing agent 73 Electrorheological fluid 74 Insulator 75, 76 Copper wire 77 Positive electrode

Claims (7)

A driving wheel that generates a driving force difference between the left and right wheels;
Steered wheels that change direction in the direction of turning of the vehicle according to the turning of the vehicle,
Drag variable means for varying the drag in the steered direction of the steered wheels,
Driving target value detecting means for detecting a driving target value of the vehicle;
A turning target value detecting means for detecting a turning target value of the vehicle;
Motor output adjusting means for adjusting the left and right driving force sum of the driving wheel according to the driving target value, and adjusting the left and right driving force difference of the driving wheel according to the turning target value;
A steered wheel target direction computing means for computing a direction in which the steered wheel should proceed according to the turning target value;
Steered wheel direction detection means for detecting the actual direction of the steered wheel;
Drag control means for outputting a drag adjustment command to the drag variable means so that the drag decreases as the deviation between the direction in which the steered wheel should travel and the actual direction increases,
An electric vehicle comprising: The electric vehicle according to claim 1,
Vehicle speed detecting means for detecting the vehicle speed is provided;
The electric vehicle characterized in that the drag control means increases the drag as the detected vehicle speed is higher. In the electric vehicle according to claim 1 or claim 2,
Braking means for braking the steered wheels;
Braking force detection means for detecting the braking force of the braking means;
Provided,
The electric vehicle according to claim 1, wherein the drag control means increases the drag as the detected braking force increases. The electric vehicle according to any one of claims 1 to 3,
A plurality of the steered wheels,
The electric vehicle characterized in that the drag control means adjusts the drag for each steered wheel so that a sum of vehicle yaw moments generated by the deviation becomes small. The electric vehicle according to any one of claims 1 to 4,
The drag variable means includes an electrorheological fluid sealed between a vehicle body side turning support shaft and a steered wheel side turning support shaft,
The electric vehicle characterized in that the drag control means adjusts a voltage applied to the electrorheological fluid. The electric vehicle according to any one of claims 1 to 4,
The drag variable means includes a magnetorheological fluid enclosed between a vehicle body side turning support shaft and a steered wheel side turning support shaft, and an electromagnet for adjusting the amount of magnetic flux passing through the magnetorheological fluid,
The electric vehicle characterized in that the drag control means adjusts a supply current to the electromagnet. The electric vehicle according to any one of claims 1 to 6,
A yaw moment estimating means for estimating a yaw moment that the vehicle receives due to the deviation is provided,
The electric motor according to claim 1, wherein the motor output adjusting means corrects the rear wheel left / right driving force difference so as to cancel the estimated yaw moment.

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