JP4814128B2 - Vehicle driving force distribution control device - Google Patents

Description

  The present invention relates to a driving force distribution control device in a vehicle that can distribute driving force between front and rear wheels, and in particular, controls driving force distribution including left and right wheels in a vehicle that can distribute driving force independently between left and right wheels. The present invention relates to a vehicle driving force distribution control device.

  As a vehicle such as an automobile capable of independently controlling the driving force of the front wheels and the rear wheels and distributing the driving force between the front and rear wheels, for example, the front wheels are driven by an internal combustion engine (engine) and the rear wheels are driven by an electric motor (motor). There is something to drive. In this vehicle, the engine output shaft and the motor output shaft are not mechanically joined, and each can output torque independently.

  In addition, there is a vehicle in which the front left and right wheels are driven by a single engine, and the rear left and right wheels each output torque, but in this vehicle, in addition to determining the front and rear wheel driving force distribution ratio, By determining the driving force distribution ratio in the wheels, the yaw moment can be appropriately generated in the vehicle.

  As such driving force distribution control in a vehicle, there is one that switches traveling modes such as front wheel shaft driving, rear wheel shaft driving, and four wheel driving according to the vehicle state quantity. As such a driving force distribution control device, the driving force of different power sources such as an engine and a motor is distributed so that the front and rear wheel driving force distribution ratio is the distribution with the least fuel consumption, and the vehicle according to the traveling state or traveling condition. There is one that suppresses fuel consumption as much as possible within a range in which the movement is stable (for example, Patent Document 1).

JP 2005-53317 A

  In the prior art described in Patent Document 1, when the driver's required driving force is distributed to the front and rear wheels, the range excluding the front wheel driving force distribution ratio that exceeds the maximum frictional force of one of the front and rear wheels is excluded. Therefore, only the distribution ratio with the smallest fuel consumption is calculated. For this reason, although a wheel does not slip, since the distribution ratio itself in which a vehicle is most stable is not calculated, it may be weak to a disturbance. In addition, there is only one piece of information that determines that the vehicle is destabilized, and it cannot necessarily be said that the best driving force distribution including the stabilization of the vehicle is achieved.

  The present invention has been made in view of the above-mentioned problems, and the object thereof is a trade-off relationship between the front and rear wheel driving force distribution ratio that suppresses fuel consumption and the front and rear wheel driving force distribution ratio that stabilizes the vehicle. It is an object of the present invention to provide a vehicle driving force distribution control device that achieves the best driving force distribution including the stabilization of the vehicle by resolving the above problem, more appropriately achieving better fuel efficiency and vehicle stabilization.

  In order to achieve the above object, a vehicle driving force distribution control device according to the present invention is a vehicle capable of independently controlling the driving force of the front wheels and the rear wheels, with respect to the overall target driving force of the vehicle. A driving force distribution control device for determining a target driving force and a rear wheel target driving force, wherein the first front and rear wheels calculate a first front and rear wheel driving force distribution ratio in consideration of turning stability or straight running stability of the vehicle. Calculated by the driving force distribution ratio calculating means, the second front and rear wheel driving force distribution ratio calculating means for calculating the second front and rear wheel driving force distribution ratio in consideration of the fuel consumption, and the first front and rear wheel driving force distribution ratio calculating means. A specific value between the calculated first front / rear wheel driving force distribution ratio and the second front / rear wheel driving force distribution ratio calculated by the second front / rear wheel driving force distribution ratio is calculated as the final front / rear wheel driving force distribution ratio. A final front and rear wheel driving force distribution ratio calculating means Based on the closing front-rear wheel driving force distribution ratio, it is characterized by setting a target driving force of the front wheel target driving force and the rear wheel.

  The vehicle driving force distribution control device according to the present invention preferably has a vehicle stability index for judging the turning stability or straight running stability of the vehicle, and the final front and rear wheel driving force distribution ratio calculating means includes the vehicle stability The final front and rear wheel driving force distribution ratio approaches the second front and rear wheel driving force distribution ratio as the stability index indicates high stability, and the final front and rear wheel driving force distribution ratio as the vehicle stability index indicates low stability. Is close to the first front and rear wheel driving force distribution ratio.

  The vehicle driving force distribution control device according to the present invention further includes the front and rear wheel driving in a vehicle capable of controlling the driving forces of the left and right wheels of the front wheel, the left and right wheels of the rear wheel, and the left and right wheels of both the front and rear wheels to different driving forces. The left and right wheel target driving force is set in advance according to the force distribution ratio, the steering amount, and the speed, and the first front and rear wheel driving force distribution ratio and the second front and rear wheel drive are set in consideration of the left and right wheel target driving force. It is characterized by determining the power distribution ratio.

  The vehicle driving force distribution control device according to the present invention preferably generates a yaw moment for the vehicle to have a predetermined yaw rate as the left and right wheel target driving force set in advance according to the front and rear wheel driving force distribution ratio. In this way, the target driving force is distributed to the left and right wheels.

  In the vehicle driving force distribution control device according to the present invention, preferably, the first front and rear wheel driving force distribution ratio calculating means applies the vehicle stability index to the tires of the four wheels when the front and rear wheel driving force distribution ratio is a certain value. The first front-and-rear wheel driving force distribution ratio is calculated based on the index.

  In the vehicle driving force distribution control device according to the present invention, preferably, the second front and rear wheel driving force distribution ratio calculation means uses the vehicle fuel consumption index as a vehicle power configuration, or a power configuration and an energy storage medium. It is calculated according to both efficiency, and the second front and rear wheel driving force distribution ratio is calculated based on the index.

  According to the vehicle driving force distribution control device of the present invention, when the vehicle is unstable, the first front and rear wheel driving force distribution ratio is output when the vehicle is stable, and when the vehicle continues to travel stably, the fuel consumption is increased. When the second front / rear wheel driving force distribution ratio that suppresses the amount is output and the vehicle state quantity is between the two, the final value of the front / rear wheel driving force distribution ratio can be output according to the vehicle state quantity.

  As a result, appropriate driving force distribution according to the state of the vehicle can be performed, eliminating the trade-off relationship between the front and rear wheel driving force distribution ratio that suppresses fuel consumption and the front and rear wheel driving force distribution ratio that stabilizes the vehicle. Therefore, it is possible to achieve both front and rear wheel driving force distribution that balances fuel consumption improvement and vehicle stabilization more appropriately, and stabilizes the vehicle before spinning or drifting out.

Embodiments of a vehicle driving force distribution control apparatus according to the present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of a standard configuration of a vehicle to which a driving force distribution control device according to the present invention is applied. The vehicle has an engine (internal combustion engine) 105 and a front motor (electric motor) 104 as drive sources for the left and right front wheels (tires) 1, and a rear motor (drive motor for the left and right rear wheels 3 and 4). Electric motor) 109.

  The engine 105 may be a fuel-efficient engine that can suppress fuel consumption, such as a direct injection internal combustion engine. The front motor 104 and the rear motor 109 are electric motors capable of power running and regeneration, and employ a three-phase synchronous motor, a three-phase induction motor, or the like.

  The output shaft of the engine 105 is connected to the power split mechanism 112 via the clutch 111b in a torque transmission relationship. The output shaft of the front motor 104 is connected to the power split mechanism 112 via the clutch 111a in a torque transmission relationship. The power split mechanism 112 adds the output torque of the front motor 104 and the output torque of the engine 105 and transmits the power to the torque converter 103.

  In this mechanism, the vehicle can travel only with the power of the front motor 104 by engaging the clutch 111a and disengaging the clutch 111b. Further, if the clutch 111 a is not engaged and the clutch 111 b is engaged, the vehicle can travel only with the power of the engine 105. In addition, the power split mechanism 112 can share the torque to be output to the front wheels 1 and 2 between the front motor 104 and the engine 105, so that the power of both can be used efficiently.

  The output torque of the torque converter 103 is transmitted to the transmission (automatic transmission) 102, and is thereby transmitted to the front wheel shaft 100a via the differential 101. Thereby, the left and right front wheels 1 and 2 are rotationally driven.

  A rear wheel shaft 100 b is drivingly connected to the rear motor 109, and the rear wheels 3 and 4 are rotationally driven by the output torque of the rear motor 109.

  A power source for operating the front motor 104 and the rear motor 109 is a battery 107. As the battery 107, a lithium ion battery or a nickel metal hydride battery is used. However, any battery other than a battery that can input and output energy reversibly may be used.

  An inverter 106 for the front motor 104 and an inverter 108 for the rear motor 109 are connected to the battery 107. The inverters 106 and 108 have a function of converting the direct current output from the battery 107 into alternating current and converting the alternating current generated by the front motor 104 and the rear motor 109 into direct current.

  When the front motor 104 and the rear motor 109 perform a power running operation, the direct current stored in the battery 107 is converted into alternating current by the inverters 106 and 108, respectively, and the alternating current is supplied to the front motor 104 and the rear motor 109. . Here, a configuration in which the direct current of the battery 107 is boosted by a DC / DC converter or the like and sent to the inverters 106 and 108 is also conceivable.

  When the front motor 104 and the rear motor 109 perform regenerative operations, the alternating currents generated by the motors 104 and 109 are converted into direct currents by the inverters 106 and 108, and the direct currents are stored in the battery 107.

  The controller 110 is an ECU by a microcomputer that controls each component mounted on the vehicle. The controller 110 stores the amount of power SOC (State Of Charge) stored in the battery 107, the torque output from the engine 105, the current value flowing through the battery 107, the rotation of the front wheels 1, 2, and the rear wheels 3, 4. Sensor values such as speed, accelerator pedal (not shown), amount of brake pedal depression, vehicle longitudinal and lateral acceleration, vehicle yaw rate, and gear ratio of transmission 102 are taken in, and based on these values A command value for operating each drive source is output.

Here, for convenience, a distribution step number i of the driving force distribution is introduced. i is a number assigned to each front wheel driving force distribution rate α when the front wheel driving force distribution rate α is engraved at an appropriate interval. When driver required driving force is divided into n equal parts, α i is expressed by the following equation (1). Can be defined as
αi = 1 / n · i (1)
αi (α0, ... αi, ... αn)

The front / rear wheel driving force distribution ratio is expressed by equation (2).
Front wheel driving force distribution ratio: Rear wheel driving force distribution ratio = αi: (1-αi) (2)

  As shown in FIG. 1, for a vehicle capable of distributing driving force between front and rear wheels, the torque command value to each driving source can be determined by determining the front wheel driving force distribution rate α. In the present embodiment, the front wheel driving force distribution ratio α is calculated, and the torque command value (target driving force) of each driving source is set based on this.

  FIG. 2 shows an embodiment of the driving force distribution control apparatus embodied by the controller 110. The driving force distribution control device of the present embodiment includes a driver required driving force calculation unit 200, a front and rear wheel driving force distribution ratio calculation unit 201 corresponding to the maximum frictional force, and a first front and rear wheel driving force distribution ratio calculation that emphasizes vehicle stability. Unit 202, second front and rear wheel driving force distribution ratio calculation unit 203 that emphasizes fuel consumption, and final front and rear wheel driving force distribution ratio calculation unit 204.

  The driver required driving force calculation unit 200 sets the maximum vehicle torque that can be output at the current vehicle speed V from the motor output map and the engine output map as 100, and calculates the driver required driving force (torque) Treq from the accelerator depression amount Ap (0 to 100). Is calculated. The current vehicle speed V is calculated as an average value of the rotation speed of each wheel.

When the maximum output torque of the front motor 104 at the current vehicle speed V is Tmfmax, the maximum output torque of the rear motor 109 is Tmrmax, and the maximum output torque of the engine 105 is Tenmax, the driver request torque Treq can be calculated by the following equation (3).
Treq = (Tmfmax + Tmrmax + Tenmax) Ap (3)

  The front / rear wheel driving force distribution ratio calculation unit 201 calculates a front / rear wheel driving force distribution ratio (in this embodiment, a front wheel driving force distribution ratio) that does not exceed the maximum frictional force.

The front-rear wheel driving force distribution ratio calculation unit 201 inputs the current vehicle longitudinal acceleration ax and the current vehicle lateral acceleration ay from an acceleration sensor mounted on the vehicle, and considers the driving resistance Fres due to the vehicle speed from the driver required torque Treq. The road surface friction coefficient μ is defined as in the following equation (4), where Rt is the tire radius and W is the vehicle weight.
μ = 1− (Treq / Rt−Fres) / W / g−ax−ay (4)
Where g: gravity acceleration

Here, the driver requested drive force Treq is divided into n, the front wheel drive force distribution ratio α when the maximum friction force of the front wheels 1 and 2 is not exceeded is αmax (i = max), and the maximum friction force of the rear wheels 3 and 4 is set. Is set to αmin (i = min) (αmin,... Αi,... Α_max).
The step width n at this time may be appropriately changed within a sufficiently accurate range.

αmax and αmin can be defined as the following equations (5) to (8), where Wf is the front wheel load and Wr is the rear wheel load.
(When Treq / Rt ≦ μWf)
αmax = 1 (5)
(When Treq / Rt> μWf)
αmax = μWf / Treq (6)
(When Treq / Rt ≦ μWr)
αmin = 1 (7)
(When Treq / Rt> μWr)
αmin = μWr / Treq (8)

  Therefore, the front and rear wheel driving force distribution ratio calculation unit 201 that calculates the front and rear wheel driving force distribution ratio that does not exceed the maximum frictional force outputs two values of αmax and αmin as the front wheel driving force distribution ratio α.

  Next, the first front and rear wheel driving force distribution ratio calculation unit 202 will be described. The first front / rear wheel driving force distribution ratio calculation unit 202 uses the standard deviation of the four wheels as a driving force distribution ratio for stabilizing the vehicle to determine whether the force generated in the tire four wheels is used uniformly. Calculate and use the front and rear wheel driving force distribution ratio when the deviation is the smallest.

  The control flow of the first front / rear wheel driving force distribution ratio calculation unit 202 will be described with reference to the flowchart shown in FIG.

  First, the longitudinal acceleration ax and the lateral acceleration ay currently applied to the vehicle are input from the vehicle acceleration sensor (step S301). Due to this acceleration, the vehicle is swung back and forth and left and right, and the load of each wheel moves between the wheels.

  Next, the load movement amount of each wheel is calculated based on this (step S302). If the initial wheel load of each wheel is W1, W2, W3, W4, the vehicle tread is t, the height of the center of gravity of the vehicle is h, and the gravitational acceleration is g, the wheel load W1t, W2t, W3t, W4t of each wheel after the load is moved. Is expressed by the following equations (9) to (12) in a steady state.

The subscripts 1 to 4 of the wheel load W correspond to the wheel numbers in FIG. 1, W1 is the right front wheel load, W2 is the left front wheel load, W3 is the right rear wheel load, and W4 is the left front wheel load.
W1t = W1-W / g.ax.h / L + W / g.ay.h / t (9)
W2t = W2-W / g.ax.h / L-W / g.ay.h / t (10)
W3t = W3 + W / g.ax.h / L + W / g.ay.h / t (11)
W4t = W4 + W / g.ax.h / L-W / g.ay.h / t (12)

  Next, the maximum frictional forces Ffmax1, Ffmax2, Ffmax3, Ffmax4 of each wheel (1, 2, 3, 4) are calculated (step S303). Since the road surface friction coefficient μ is calculated by the equation (4), the maximum frictional force Ffmaxj (j = 1, 2, 3, 4) of each wheel can be calculated based on this.

  Next, the usage rate of the frictional force is calculated to determine how much of the frictional force is currently occupied by the tire (step S304).

Here, a method of calculating the frictional force usage rate will be described with reference to FIGS. 4 and 5.
FIG. 4 shows the maximum frictional force Ffmax1 that can be generated by each wheel (1, 2, 3, 4) by changing the load of each wheel (1, 2, 3, 4) depending on the longitudinal acceleration and lateral acceleration applied to the vehicle. , Ffmax2, Ffmax3, and Ffmax4 are different in size.

As shown in FIG. 5, generally, the resultant force Frj of the driving force Fxj and the lateral force Fyj generated in each tire is suppressed within the range of the maximum friction force Ffmaxj. The lateral force Fyg applied to the center of gravity G of the vehicle is obtained by Expression (13).
Fyg = 1 / (1 + A · V2) · V2 / L · W / g (13)
However, V is a vehicle speed, A is a vehicle-specific constant called a stability factor, and is a value corresponding to the vehicle speed.

Further, the longitudinal force Fxg applied to the center of gravity G of the vehicle is estimated by the following equation (14) from the driver request tire shaft torque Treqf in consideration of the running resistance Wres.
Fxg = W / g · Treqf · Rt + Wres (14)

Next, the driving forces Fx1 and Fx2 for the front wheels 1 and 2 and the driving forces Fx3 and Fx4 for the rear wheels 3 and 4 are calculated for each distribution step number i. That is, the driving force of the four wheels is defined as in the equations (15) to (18).
Fx1 = Fx · αi / 2 (15)
Fx2 = Fx · αi / 2 (16)
Fx3 = Fx · (1-αi) / 2 (17)
Fx4 = Fx · (1-αi) / 2 (18)

Since the lateral force Fyg applied to the center of gravity G of the vehicle is applied to each wheel in the same manner as the load distribution ratio, the lateral force Fyj applied to each wheel (j = 1 to 4) can be defined by the following equation (19).
Fyj = Fyj · Wj / W (19)

Accordingly, the frictional force usage rate Uj (j = 1 to 4) of each wheel when the front wheel driving force distribution rate αi (i: distribution step number, min ≦ i ≦ max) is obtained by the following equation (20).
Uj = √ (Fxj2 + Fyj2) / μ · Wj (20)
However, 0 ≦ Uj ≦ 1

Next, the standard deviation Adisi of the frictional force usage rate is calculated from the minimum front wheel driving force distribution rate αmin not exceeding the maximum frictional force to the maximum front wheel driving force distribution rate αmax not exceeding the maximum frictional force (step S305). Since the frictional force usage rate Uj of each wheel is calculated, first, an average value Ai of the frictional force usage rate Uj of each wheel at the distribution step number i is obtained by the following equation (21).
Ai = ΣUj / 4 (21)
However, j = 1-4

Subsequently, the standard deviation Adisi of the frictional force usage rate is obtained by (Expression) 22.
Addi = √ (1/4 · Σ (Uj−Ai) 2) (22)
However, j = 1-4

  Thus, Min (Adisi) having the smallest standard deviation at a certain front and rear wheel driving force distribution ratio indicates that the frictional force of each wheel is used most uniformly.

  Next, the standard deviation of the frictional force usage rate is used as a vehicle stability index, and the front wheel driving force distribution rate αd that is the minimum value Min (Adisi) is obtained. Accordingly, the front wheel driving force distribution ratio αd output by the first front and rear wheel driving force distribution ratio calculating unit 202 is αd = αi, i is the distribution number in Min (Adisi), and this is the first front wheel driving force distribution ratio αd. (Step S306).

  The first rear wheel driving force distribution ratio at this time is (1−αd), and the first front and rear wheel driving force distribution ratio is αd: (1−αd).

  That is, the first front / rear wheel driving force distribution ratio calculation unit 202 calculates a vehicle stability index according to the force applied to the tires of the four wheels at a certain front / rear wheel driving force distribution ratio. Based on this, the first front / rear wheel drive force distribution ratio is output. Specifically, it is determined whether the force generated in the tires is uniformly used as the drive force distribution ratio that stabilizes the vehicle. Therefore, the standard deviation of the four wheels is calculated, and the front / rear wheel driving force distribution ratio when the deviation is the smallest is used.

 As described above, in the present embodiment, the standard deviation of the tire friction force usage rate is calculated and the distribution ratio with the smallest deviation is set. However, the physical quantity indicating the stability of the vehicle is not limited to this and is the tire speed. A slip ratio representing a ratio to the vehicle speed may be used. Further, in turning stability and turning stability, the vehicle front and rear wheel load distribution ratio at that time may be adopted as the first front and rear wheel driving force distribution ratio.

  For example, as shown in FIG. 6, based on some index that considers the stability of the vehicle, (i) that obtains the best evaluation is searched for that index, and the front wheel driving force distribution ratio αi at that time is determined as the first front wheel. The driving force distribution rate αd may be used.

  That is, the first front / rear wheel driving force distribution ratio calculation unit 202 calculates a vehicle stability index according to the force applied to the tires of the four wheels at a certain front / rear wheel driving force distribution ratio. Based on this, the first front and rear wheel driving force distribution ratio (first front wheel driving force distribution ratio αd) is calculated.

  Next, the second front / rear wheel driving force distribution ratio calculation unit 203 will be described. The second front / rear wheel driving force distribution ratio calculation unit 203 calculates a front / rear wheel driving force distribution ratio for reducing fuel consumption as a front / rear wheel driving force distribution ratio with an emphasis on fuel consumption.

  The control flow of the second front / rear wheel driving force distribution ratio calculation unit 203 will be described with reference to the flowchart shown in FIG.

  First, the range αmin and αmax of the front wheel driving force distribution ratio α are input from the front and rear wheel driving force distribution ratio calculation unit 201 (step S401).

Next, the rear motor burden torque Trm at a certain front wheel driving force distribution ratio αi (i: distribution step number, min ≦ i ≦ max) is calculated by the following equation (23), and the rear wheel burden torque Trm is shown in FIG. The required rear motor current Arm is calculated based on the output characteristics of the rear motor 109 as described above (step S402).
Trm = Treq · (1-αi) (23)

  Next, the front motor required power generation amount is calculated from the battery charge / discharge request amount (step S403). Here, the power generation amount Creq required by the battery 107 is calculated from the remaining battery charge SOC using a map as shown in FIG. In this map, the smaller the remaining battery charge SOC is, the more the required charge amount is increased. The more the remaining battery charge SOC is, the more the battery 107 is discharged.

  In this embodiment, the power generation amount Creq is obtained by power generation by the front motor 104. Here, for example, when the remaining battery charge SOC is less than 50%, the front motor 104 generates power (regeneration) in order to make a power generation request to the front motor 104. Conversely, the remaining battery charge SOC is 50%. If the value exceeds the value, the front motor 104 performs power running.

Next, a method for calculating the power running torque and power generation torque of the front motor 104 will be described. As an example, it is assumed that a power generation request is issued in a state where the remaining battery charge SOC is 50% or less, and the magnitude of the torque is Tpreq. The torque Tfm borne by the front motor 104 is calculated by the following equation (24).
Tfm = Treq · αi (24)

  Next, the torque distribution amount between the front motor 104 and the engine 105 is calculated with reference to the engine optimum fuel consumption line (step S404). Here, the optimal fuel consumption line S is calculated in the engine torque map as shown in FIG. 10, and the engine torque according to the optimal fuel consumption line S at a certain engine speed Neng is defined as Tenopt, and according to the following states. The power generation request torque Tprep is calculated.

(When Tfm <Tenopt and Tfm + Tpreq ≧ Tenopt)
Tprep = Tfm-Tenopt (25)
Thereby, the power generation amount is suppressed.

(Tfm <Tenopt and Tfm + Tpreq <Tenopt)
Tprep = Tenopt−Tfm (26)

  Further, even when the power generation request torque Tprep is negative (discharge request), the battery charge remaining SOC can be kept near 50% and the engine can be operated at the best engine efficiency by following the same procedure.

  Next, how much energy is actually consumed (fuel consumption and power consumption) is calculated (step S405). The engine 105 can calculate the amount of energy Conseng actually consumed by the engine 105 from the required torque and the rotation speed at that time. For this, an output characteristic of the engine 105 is obtained in advance by experiments or the like, and a map of the fuel consumption characteristic at that time is used.

On the other hand, the energy consumed or produced by the front motor 104 can be calculated from the value of the current flowing through the battery 107 and the battery voltage, and obtained as the power consumption (production amount) Consmo. Based on these, the total energy consumption Consum for a given i is expressed by the following equation (27).
Conssum (i) = Conseng + Consmo (27)

  At this time, as shown in FIG. 11, (i) at which the fuel consumption is reduced is calculated (step S406), and the front wheel driving force distribution rate αi at that time is output as the second front wheel driving force distribution rate αf. (Step S470).

  The second rear wheel driving force distribution ratio at this time is (1-αf), and the second front and rear wheel driving force distribution ratio is αf: (1-αf).

  As described above, in this embodiment, the torque of the front motor 104 is calculated so that the required amount of battery power generation is kept near 50%, and the front motor 104 and the engine 105 are driven so as to match the optimum fuel consumption line of the engine 105. The front wheel driving force distribution rate at which the sum of the fuel consumption and the power consumption is minimized is defined as the second front wheel driving force distribution rate αf.

  That is, the second front / rear wheel driving force distribution ratio calculation unit 203 calculates a fuel consumption index of the vehicle according to the power configuration of the vehicle or the efficiency of both the power configuration and the energy storage medium, and based on the index. The second front and rear wheel driving force distribution ratio (second front wheel driving force distribution ratio αf) is calculated.

  The torque distribution ratio between the front motor 104 and the engine 105 at this time is provided with an index relating to energy use, as shown in FIG. 11, as in a method of distributing based on the battery charge / discharge request amount and the engine optimum fuel efficiency line. Thus, the front and rear wheel driving force distribution ratio is determined according to the index. There are various control methods for reducing the fuel consumption by the second front / rear wheel driving force distribution ratio including known examples.

  Since the first front / rear driving force distribution ratio and the second front / rear driving force distribution ratio can be realized by providing an output that can be regarded as the front / rear wheel driving force distribution ratio, the first front / rear driving force distribution ratio and the second front / rear driving force distribution ratio are It is not limited to the embodiment.

  Next, the final front and rear wheel driving force distribution ratio calculation unit 204 will be described. The final front and rear wheel driving force distribution ratio calculating unit 204 calculates the first front wheel driving force distribution ratio αd calculated by the first front and rear wheel driving force distribution ratio calculating unit 202 and the second front and rear wheel driving force distribution ratio calculating unit 203. The second front wheel driving force distribution rate αf and the vehicle state quantity are input, and the final front wheel driving force distribution rate αm is output.

In the input of the vehicle state quantity, a necessary amount of information to be used as an index of the motion state of the vehicle is inputted as a matrix. In this embodiment, the yaw rate is input. A deviation amount Δ between the yaw rate and the reference yaw rate obtained from the steering angle and the vehicle speed is calculated, and an evaluation amount (weight) Ev is set according to the deviation amount Δ using a map as shown in FIG. The final front wheel driving force distribution ratio αm is calculated and output according to (28).
αm = αf · Ev + αd (1-Ev) (28)

  In this case, if the deviation amount Δ from the reference yaw rate is small, the evaluation amount Ev approaches 1, and as a result, the final front and rear wheel driving force distribution ratio calculating unit 204 sets the second front wheel driving force as the final front wheel driving force distribution rate αm. The distribution rate αf is output. On the other hand, when the yaw rate deviation amount Δ increases and the evaluation amount EV becomes 0, the final front and rear wheel driving force distribution ratio calculation unit 204 sets the first front wheel driving force distribution as the final front wheel driving force distribution rate αm. The rate αd is output.

  If 0 <Ev1 <, an intermediate value between the first front wheel driving force distribution rate αd and the second front wheel driving force distribution rate αf is output as the final front wheel driving force distribution rate αm according to the equation (28). That is, an intermediate value αm (including end points) between the first front and rear wheel driving force distribution ratio αd and the second front and rear wheel driving force distribution ratio αf of the first front wheel driving force distribution ratio αd and the second front wheel driving force distribution ratio αf. Output according to an index called vehicle state quantity.

  That is, the final front / rear wheel driving force distribution ratio calculation unit 204 determines that the final front / rear wheel driving force distribution ratio (final front wheel driving force distribution distribution) increases as the vehicle stability index for determining the turning stability or straight-line stability of the vehicle shows high stability. Rate αm) approaches the second front and rear wheel driving force distribution ratio (second front wheel driving force distribution ratio αf), and the final front and rear wheel driving force distribution ratio (final front wheel driving force distribution ratio) as the vehicle stability index indicates low stability. αm) is made closer to the first front and rear wheel driving force distribution ratio (first front wheel driving force distribution ratio αd).

  Then, based on the final value front and rear wheel driving force distribution ratio αm, the front wheel target driving force and the rear wheel target driving force are set.

  As a result, appropriate driving force distribution according to the state of the vehicle can be performed, eliminating the trade-off relationship between the front and rear wheel driving force distribution ratio that suppresses fuel consumption and the front and rear wheel driving force distribution ratio that stabilizes the vehicle. Thus, it is possible to achieve both front and rear wheel driving force distribution that makes the vehicle unstabilized before achieving an inappropriate vehicle state such as spinning or drifting out more appropriately by improving fuel efficiency and stabilizing the vehicle.

  FIG. 13 shows an embodiment of a vehicle (rear wheel independent drive vehicle) to which the driving force distribution control device according to the present invention is applied. In FIG. 13, parts corresponding to those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and description thereof is omitted.

  In this embodiment, the left and right rear wheels 3 and 4 are configured to be independently driven by individual rear motors 109R and 109L. The rear motor 109R and the rear motor 109L are individually supplied with electric power from the inverters 108R and 108L for each motor, and are independently controlled independently.

  Here, the inverters 106, 108R, and 108L may be connected to the battery 107 via a converter.

  In such a vehicle, since the driving force distribution ratio between the front and rear wheels and the driving force distribution ratio between the left and right wheels of the rear wheel must be determined, the target driving force is more than the driving configuration of the vehicle shown in FIG. Increases the degree of freedom of decision.

  Therefore, the magnitude of the torque to be output by the left and right wheels with respect to the driving force distribution ratio of the front and rear wheels is set according to the steering angle and the vehicle speed. In a vehicle that can change the front-rear wheel driving force distribution ratio, if the distribution ratio is changed during a turn, the yaw rate generated in the vehicle changes. It is necessary to steer properly, which is a burden on the driver.

  On the other hand, in the rear wheel independent drive vehicle of the present embodiment, it is possible to compensate for a predetermined yaw rate by generating a yaw moment around the center of gravity of the vehicle due to a difference in driving force distribution between the left and right wheels.

  As shown in FIG. 14, the magnitude of the yaw moment ΔT to be generated at the center of gravity of the vehicle is calculated in accordance with the steering angle and vehicle speed at a certain front wheel driving force distribution rate α. Then, the yaw moment ΔT is output by generating a driving force so that the left and right wheels have the same size and opposite directions. In FIG. 13, ΔTmax is the magnitude of the yaw moment to be generated at the center of gravity at αmax, and ΔTmin is the magnitude of the yaw moment to be generated at the center of gravity at αmin.

  In this way, if the magnitude of the driving force that should be output by the left and right wheels is defined relative to the rear wheel driving force distribution ratio, two indicators (straight / turning stability, fuel consumption) are determined by the front / rear wheel driving force distribution ratio. ) Can be evaluated in the same procedure as in Example 1.

  The predetermined yaw rate at this time may be a yaw rate when passing a turning trajectory determined by a steering angle, a vehicle speed, and vehicle specifications. Alternatively, a driving force that averages the frictional force of each wheel during turning may be distributed to the left and right wheels.

  In other words, the left and right wheel target driving force is set in advance according to the front and rear wheel driving force distribution ratio, the steering amount, and the speed, and the first front and rear wheel driving force distribution ratio and the second front and rear wheel driving force are determined in consideration of the left and right wheel target driving force. Determine the wheel drive force distribution ratio. Then, the target driving force is distributed to the left and right wheels so as to generate a yaw moment for the vehicle to have a predetermined yaw rate as the left and right wheel target driving force set in advance according to the front and rear wheel driving force distribution ratio.

  The independent driving of the left and right wheels is not limited to the rear wheels, and may be front wheels.

The block diagram which shows one embodiment of the standard structure of the vehicle to which the driving force distribution control apparatus by this invention is applied. The block diagram which shows one Embodiment of the driving force distribution control apparatus by this invention. The flowchart which shows the control flow of the 1st front-and-rear wheel driving force distribution ratio calculation part of the driving force distribution control apparatus by this invention. Explanatory drawing which shows the force applied to the tire in each wheel during turning, and the maximum frictional force. Explanatory drawing which shows the relationship between the force concerning a tire, and the maximum frictional force. The conceptual diagram which searches (i) used as an optimal value with respect to the parameter | index which should be evaluated in calculation of 1st front-and-rear wheel driving force distribution ratio and 2nd front-and-rear wheel driving force distribution ratio, respectively. The flowchart which shows the control flow of the 2nd front-and-rear wheel drive force distribution ratio calculation part of the drive force distribution control apparatus by this invention. The graph which shows the output characteristic of a rear motor. The graph which shows the charging / discharging required characteristic of a battery. The graph which shows the example of a relationship between the optimal fuel consumption line of an engine, front motor burden torque, and front wheel burden torque. The conceptual diagram to search of (i) where the sum of fuel consumption and electric power consumption becomes the smallest. An evaluation map for calculating a value between the first front and rear wheel driving force distribution ratio and the second front and rear wheel driving force distribution ratio according to the vehicle state quantity. The block diagram which shows other embodiment of the standard structure of the vehicle to which the driving force distribution control apparatus by this invention is applied. A prescribed map of the amount of yaw moment that should be output by the left and right wheels relative to the front and rear wheel drive force distribution ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 12 Front wheel 13, 14 Rear wheel 101 Differential 102 Transmission 103 Torque converter 104 Front motor 105 Engine 106 Inverter 107 Battery 108 Inverter 109, 109R, 109L Rear motor 110 Controller 111a, 111b Clutch 200 Driver required driving force calculation part 201 Front-rear wheel drive Force distribution ratio calculation unit 202 First front and rear wheel driving force distribution ratio calculation unit 203 Second front and rear wheel driving force distribution ratio calculation unit 204 Final front and rear wheel driving force distribution ratio calculation unit

Claims (6)

A driving force distribution control device for determining a front wheel target driving force and a rear wheel target driving force with respect to a target driving force of the entire vehicle in a vehicle capable of independently controlling front and rear wheel driving forces. ,
First front and rear wheel driving force distribution ratio calculating means for calculating a first front and rear wheel driving force distribution ratio in consideration of turning stability or straight running stability of the vehicle;
Second front and rear wheel driving force distribution ratio calculating means for calculating a second front and rear wheel driving force distribution ratio in consideration of fuel consumption;
Between the first front and rear wheel driving force distribution ratio calculated by the first front and rear wheel driving force distribution ratio calculating means and the second front and rear wheel driving force distribution ratio calculated by the second front and rear wheel driving force distribution ratio calculating means. A final front and rear wheel driving force distribution ratio calculating means for calculating a specific value of
A vehicle driving force distribution control device that sets a front wheel target driving force and a rear wheel target driving force based on the final value front and rear wheel driving force distribution ratio.   The vehicle has a vehicle stability index for determining turning stability or straight running stability of the vehicle, and the final front and rear wheel driving force distribution ratio calculating means drives the final front and rear wheel as the vehicle stability index shows high stability. Bringing the force distribution ratio closer to the second front and rear wheel driving force distribution ratio, and bringing the final front and rear wheel driving force distribution ratio closer to the first front and rear wheel driving force distribution ratio as the vehicle stability index indicates low stability. The vehicle driving force distribution control device according to claim 1, wherein   In a vehicle that can control the driving force of the left and right wheels of the front wheel, the left and right wheels of the rear wheel, and the left and right wheels of the front and rear wheels to different driving forces, the right and left wheels according to the front and rear wheel driving force distribution ratio, the steering amount, and the speed The target driving force is set in advance, and the first front and rear wheel driving force distribution ratio and the second front and rear wheel driving force distribution ratio are determined in consideration of the left and right wheel target driving force. Alternatively, the driving force distribution control device for a vehicle according to claim 2.   The target driving force is distributed to the left and right wheels so as to generate a yaw moment for the vehicle to have a predetermined yaw rate as the left and right wheel target driving force set in advance according to the front and rear wheel driving force distribution ratio. The vehicle driving force distribution control device according to claim 3.   The first front and rear wheel driving force distribution ratio calculating means calculates a vehicle stability index according to the force applied to each tire of the four wheels at a certain front and rear wheel driving force distribution ratio, and based on the index The vehicle driving force distribution control device according to any one of claims 1 to 4, wherein a first front and rear wheel driving force distribution ratio is calculated.   The second front and rear wheel driving force distribution ratio calculating means calculates a fuel consumption index of the vehicle according to the power configuration of the vehicle or the efficiency of both the power configuration and the energy storage medium, and based on the index 6. The vehicle driving force distribution control device according to claim 1, wherein a two-front and rear wheel driving force distribution ratio is calculated.

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