JP2006137268A - Device for controlling front and rear wheel torque distribution for four-wheel drive vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for controlling a front and rear wheel torque distribution for four-wheel drive vehicles, capable of easily achieving tight corner braking restriction performance and start/acceleration performance simultaneously by executing front and rear wheel torque distribution control based on a power ratio as a substitutional property. <P>SOLUTION: This device for controlling the front and rear wheel torque distribution for four-wheel drive vehicles is provided with a front and a rear wheel torque distribution control means provided with a transfer clutch 9 at a distribution position for output torque from a power source to front wheels 14 and 15 and rear wheels 7 and 8 for executing front and rear wheel torque distribution control by clutch torque control to the transfer clutch 9. The torque distribution control means is a means to determine a clutch torque control command value based on the power ratio Lc/Ltm between a power Ltm of power output of the power source and differential power Lc of the transfer clutch 9. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a front and rear wheel torque distribution control device for a four-wheel drive vehicle that controls a torque distribution ratio to front and rear wheels by electronic control.

Conventionally, the following enumeration devices are known as front and rear wheel torque distribution control devices for four-wheel drive vehicles that control the torque distribution ratio to the front and rear wheels by electronic control.
(1) Front and rear wheel torque distribution method based on front and rear wheel rotational speed difference (ΔN) + vehicle acceleration (α) (see, for example, Patent Document 1).
(2) Front-rear wheel torque distribution method based on front-rear wheel rotational speed difference (ΔN) + acceleration of front-rear wheel rotational speed difference (dΔN / dt) (see, for example, Patent Document 2).
(3) Front and rear wheel torque distribution method based on front and rear wheel rotational speed difference (ΔN) + lateral G (YG) + vehicle speed (V) (see, for example, Patent Document 3).
JP 2001-71781 A JP 2001-71775 A Japanese Patent Laid-Open No. 7-17282

  However, since these conventional front and rear wheel torque distribution control devices are front and rear wheel torque distribution control systems that use the front and rear wheel rotational speed difference (ΔN) as common control information, in order to improve start / acceleration performance. If the front-rear wheel torque distribution ratio is controlled in the direction of equal torque distribution to the four wheels with good response to the occurrence of the front-rear wheel rotational speed difference, tight corner braking is likely to occur and smooth turning is difficult. On the other hand, if the front and rear wheel torque distribution ratio is slowly controlled in the four-wheel torque distribution direction with respect to the occurrence of the front and rear wheel rotational speed difference in order to suppress tight corner braking, the start / acceleration performance is improved by allowing drive slip. It will decline. That is, there is a trade-off between the tight corner braking phenomenon suppressing performance and the start / acceleration performance securing, and it is difficult to achieve both performances.

  The present invention has been made paying attention to the above problem, and by adopting front and rear wheel torque distribution control based on a substitute characteristic called a power ratio, it is easy to achieve both tight corner braking suppression performance and start / acceleration performance. An object of the present invention is to provide a front and rear wheel torque distribution control device for a four-wheel drive vehicle that can be achieved.

In order to achieve the above object, in the present invention, a transfer clutch is provided at a position where the output torque from the power source is distributed to the front wheels and the rear wheels, and front and rear wheel torque distribution control is performed by clutch torque control of the transfer clutch. In a front and rear wheel torque distribution control device for a four-wheel drive vehicle equipped with wheel torque distribution control means,
The front and rear wheel torque distribution control means determines a clutch torque control command value based on a power ratio between a power source output power of the power source and a differential power of the transfer clutch. .

  Therefore, in the front and rear wheel torque distribution control device of the four-wheel drive vehicle of the present invention, the front and rear wheel torque distribution control means performs the work of the power source output power of the power source and the differential power of the transfer clutch. A clutch torque control command value is determined based on the ratio. That is, “power source output power” means the power source output energy, and “differential power” means the loss energy in the transfer clutch, and this loss energy is the difference between the clutch torque and the differential rotation. Calculated by product with number. Therefore, for example, when control is performed to reduce the power ratio to a low value, the clutch torque is reduced to reduce energy loss in the transfer clutch during turning where a differential rotation speed is generated due to the difference in turning radius of each wheel. Thus, the drive torque distribution shifts to the two-wheel distribution direction, and the tight corner braking suppression performance can be enhanced. In addition, when control is performed to keep the power ratio to a low value, the energy in the transfer clutch is increased by increasing the clutch torque and decreasing the differential rotation speed at the time of starting when the differential rotation speed is generated by the drive slip. Loss is suppressed, and the drive torque distribution shifts to the four-wheel distribution direction, and the start / acceleration performance can be improved. As a result, by adopting front and rear wheel torque distribution control based on the substitute characteristic of the power ratio, it is possible to easily achieve both tight corner braking suppression performance and start / acceleration performance.

  Hereinafter, the best mode for realizing a front and rear wheel torque distribution control device for a four-wheel drive vehicle according to the present invention will be described based on a first embodiment shown in the drawings.

First, the configuration will be described.
FIG. 1 is an overall system diagram showing a rear wheel drive-based four-wheel drive vehicle to which the front and rear wheel torque distribution control device of the first embodiment is applied.

  As shown in FIG. 1, the drive system of the four-wheel drive vehicle includes an engine 1, an automatic transmission 2, a rear propeller shaft 3, a rear differential 4, rear drive shafts 5 and 6, a left rear wheel 7, a right rear wheel 8, A truss clutch 9, a front propeller shaft 10, a front differential 11, front drive shafts 12 and 13, a left front wheel 14, and a right front wheel 15 are provided. The left and right rear wheels 7 and 8 correspond to main drive wheels, and the left and right front wheels 14 and 15 correspond to driven wheels.

  The engine 1 is subjected to fuel injection control or the like according to a command from the engine controller 16, and the automatic transmission 2 is subjected to gear shift control or the like according to a command from the automatic transmission controller 17.

  The front / rear differential limiting system that controls the engagement of the transfer clutch 9 includes a front / rear differential limiting actuator 19 and a differential limiting controller 20 that outputs a fastening command or a release command to the front / rear differential limiting actuator 19. Configured.

  As the transfer clutch 9, for example, a hydraulic multi-plate clutch, an electromagnetic multi-plate clutch, or the like is applied, and it has a front-rear differential limiting function that limits the differential between the left and right rear wheels 7 and 8 and the left and right front wheels 14 and 15 by fastening. . That is, when the transfer clutch 9 is engaged, the drive torque is transmitted from the left and right rear wheels 7 and 8 to the left and right front wheels 14 and 15 via the transfer clutch 9, and thereby the left and right rear wheels 7 and 8 and the left and right front wheels 14 are transmitted. , 15 is limited.

  Information from the accelerator opening sensor 21, the longitudinal acceleration sensor 22, the mode changeover switch 23, and the like is input to the differential limiting controller 20. The mode changeover switch 23 is means for manually switching between the 2WD fixed mode, the 4WD fixed mode, and the auto mode. When the 4WD fixed mode of the mode switch 23 is selected, the differential limiting action for the front and rear wheels is strongest. Further, when the auto mode of the mode switch 23 is selected, front and rear wheel torque distribution control based on the substitute characteristics (Lc / Ltm) of the first embodiment is executed.

  As shown in FIG. 1, an anti-skid brake system (hereinafter referred to as “ABS”) that brakes the wheels 7, 8, 14, 15 with brake hydraulic pressure includes a brake pedal 30, a booster 31, a master cylinder 32, Master cylinder hydraulic pipes 33, 34, ABS actuator 35, left rear wheel wheel cylinder hydraulic pipe 36, right rear wheel wheel cylinder hydraulic pipe 37, left front wheel wheel cylinder hydraulic pipe 38, right front wheel wheel cylinder hydraulic pipe 39 A left rear wheel wheel cylinder 40, a right rear wheel wheel cylinder 41, a left front wheel wheel cylinder 42, a right front wheel wheel cylinder 43, and a brake controller 44.

  The ABS actuator 35 is constituted by an oil pump, a hydraulic pressure control valve, and the like, and during normal braking, each wheel 7, via two brake hydraulic pressure systems divided corresponding to the master cylinder hydraulic pressure pipes 33, 34. Brake fluid pressure is supplied to 8,14,15. At the time of ABS operation, the brake fluid pressure is controlled by three modes of pressure reduction, holding, and pressure increase so as to suppress braking lock of each wheel 7, 8, 14, and 15.

  Information from a brake lamp switch 45, a left front wheel speed sensor 46, a right front wheel speed sensor 47, a left rear wheel speed sensor 48, a right rear wheel speed sensor 49, and the like is input to the brake controller 44.

  The engine controller 16, the automatic transmission controller 17, the differential limit controller 20, and the brake controller 44 are connected to each other by a bidirectional communication line 50 for exchanging information. It is supplied to the differential limiting controller 20 via the directional communication line 50.

Next, the operation will be described.
[Front and rear wheel torque distribution control processing]
FIG. 2 is a flowchart showing a flow of front and rear wheel torque distribution control processing executed at predetermined control cycles by the differential limiting controller 20 of the first embodiment. Each step will be described below (front and rear wheel torque distribution control means). .

  In step S1, four wheel rotation speeds (left front wheel rotation speed FrLrev, right front wheel rotation speed FrRrev, left rear wheel rotation speed RrLrev, right rear wheel rotation speed ReRrev) are read from the brake controller 44 based on the wheel speed information. The process proceeds to S2.

  In step S2, following the reading of the rotational speeds of the four wheels in step S1, the main driving wheel rotational speed Ave (RrLrev, ReRrev) based on the average rotational speed of the left and right rear wheels 7, 8 and the average rotational speed of the left and right front wheels 14, 15 The driven wheel rotational speed Ave (FrLrev, FrRrev) based on the value is calculated, and the process proceeds to step S3.

In step S3, following the calculation of the main wheel rotation speed and the driven wheel rotation speed in step S2, the differential rotation speed of the left and right rear wheels 7, 8 and the left and right front wheels 14, 15 is changed to the rotation speed difference in the transfer clutch 9. Replaced differential rotation speed ΔN,
ΔN = (Ave (RrLrev, ReRrev) −Ave (FrLrev, FrRrev)) × if
However, if is calculated by the formula of the final drive gear ratio, and the process proceeds to step S4.

  In step S4, following the calculation of the differential rotational speed ΔN in step S4, information on the engine torque Teng and the engine rotational speed Engrev is fetched from the engine controller 16, and the transmission input rotational speed ATinrev and the transmission are transmitted from the automatic transmission controller 17. Information on the output rotational speed AToutrev and the AT gear position GearPosition is captured, and the process proceeds to step S5.

  In step S5, following the capturing of various information in step S4, the speed ratio of the torque converter is calculated from the engine speed Engrev and the transmission input speed Atinrev (turbine speed), and the process proceeds to step S6. The transmission input rotational speed Atinrev may be obtained from the transmission output rotational speed AToutrev and the AT gear position GearPosition.

  In step S6, following the speed ratio calculation in step S5, the torque ratio of the torque converter is calculated by the torque converter characteristic (Map) in which the characteristic of the torque ratio with respect to the speed ratio is set, and the process proceeds to step S7.

In step S7, following the torque ratio calculation in step S6, engine torque Teng, torque ratio, and AT gear position GearPosition were used.
Transmission output torque = Teng x torque ratio x GearPosition
The transmission output torque is calculated by the following formula, and the process proceeds to step S8.

In step S8, following the calculation of the transmission output torque in step S7, the transmission output torque and the transmission output rotational speed Atoutrev were used.
Transmission output power Ltm = Transmission output torque x Atoutrev
The transmission output power Ltm is calculated by the following equation, and the process proceeds to step S9.

In step S9, following the calculation of the transmission output power Ltm in step S8, the work which is the ratio of the differential power Lc to the transmission output power Ltm, where Lc is the differential power of the transfer clutch 9. The target clutch torque is calculated so that the rate ratio Lc / Ltm is equal to or less than the predetermined value α, and the process proceeds to step S10.
Here, as shown in FIG. 3, the “predetermined value α” is obtained when the control using the power ratio Lc / Ltm as a substitute characteristic is performed, when the sensitivity evaluation of the driver with respect to the tight corner brake is performed, As the ratio ratio Lc / Ltm was increased, the steering feeling was lowered and the sensitivity evaluation was worsened. Therefore, when the value of the power ratio Lc / Ltm is varied in various ways, the limit value obtained as a good evaluation as the sensitivity evaluation of the driver is set as the predetermined value α. And this predetermined value (alpha) does not give the same value with all the vehicle types, but sets an optimal value with vehicle specifications (a weight, a wheel base, a tire characteristic, etc.) and a vehicle state.

  In step S10, following the calculation of the target clutch torque in step S9, a control signal for obtaining the calculated target clutch torque is output, and the process proceeds to return.

[Front and rear wheel torque distribution control]
This system recognizes the vehicle running state based on information from other in-vehicle controllers 16, 17, 44, and suppresses tight corner braking phenomenon that improves running stability and steering feeling in a turning state. This is a front and rear wheel torque distribution control device for achieving both start / acceleration performance at a high level.

  That is, when starting or running, as shown in the flowchart of FIG. 2, go to step S1, step S2, step S3, step S4, step S5, step S6, step S7, step S8, step S9, and step S10. It will be a flow that goes forward.

Then, when the target clutch torque in step S9 describes the calculation process in detail, the differential power Lc is obtained by using the clutch torque and the differential rotational speed ΔN obtained in step S3.
Differential power Lc = Clutch torque × ΔN (1)
Is given by
In addition, the control condition in step S9 is
Lc / Ltm ≦ α (2)
It is. Therefore, according to equations (1) and (2),
Clutch torque ≦ (α × Ltm) / ΔN (3)
Thus, the target clutch torque can be calculated by replacing the clutch torque in equation (3) with the target clutch torque.
Therefore, the target clutch torque is calculated so that the above expression (3) is satisfied, and it is possible to finely control the optimum clutch torque with respect to the transmission output power Ltm and the differential rotation speed ΔN.

  Therefore, when the control for suppressing the power ratio Lc / Ltm to a predetermined value α or less is executed, the value on the right side of the above equation (3) at the time of turning in which the generation of the differential rotational speed ΔN increases due to the difference in turning radius of each wheel. As the value becomes smaller, the clutch torque on the left side of the above equation (3) is decreased in accordance with the value on the right side, thereby establishing the equation (3). That is, at the time of turning where the generation of the differential rotational speed ΔN is inevitable, the energy loss of the transfer clutch 9 is suppressed by reducing the clutch torque itself transmitted through the transfer clutch 9. With the release operation, the drive torque distribution is further shifted in the rear wheel distribution direction, and the tight corner braking suppression performance can be enhanced.

  Further, when the control for reducing the power ratio Lc / Ltm to a predetermined value α or less is executed, a differential rotational speed ΔN is generated by a drive slip at the time of starting or during intermediate acceleration. On the other hand, when the clutch torque is decreased as in turning, the drive torque distribution is further shifted in the rear wheel distribution direction, and the differential rotational speed ΔN is increased. The value on the right side of the above equation (3) May become smaller and control may not converge. Therefore, when the differential rotational speed ΔN is generated by the drive slip, the differential rotational speed ΔN caused by the drive slip is kept low by increasing the clutch torque, and the right side of the above equation (3) is reduced. By increasing the value, formula (3) is established. In other words, energy loss of the transfer clutch 9 is suppressed by lowering the differential rotational speed ΔN by increasing the clutch torque of the transfer clutch 9, and drive torque distribution increases torque distribution to the left and right front wheels 14, 15. Shifting to the four-wheel distribution direction can improve start / acceleration performance.

  As described above, in order to establish the expression (3), both reduction and increase of the clutch torque of the transfer clutch 9 are required. For this reason, for example, it may be determined whether the vehicle is traveling straight or turning, and logic for selecting an increase in the clutch torque of the transfer clutch 9 when traveling straight and selecting a decrease in the clutch torque of the transfer clutch 9 during turning may be added. .

  As described above, by using the front and rear wheel torque distribution control based on the substitute characteristic of the power ratio Lc / Ltm, it is possible to easily achieve both tight corner braking suppression performance and start / acceleration performance. In particular, in the front and rear wheel torque distribution control device according to the first embodiment, the predetermined value α, which is the target value of the power ratio Lc / Ltm, is set so as to ensure a region in which the sensitivity evaluation with respect to the tight corner brake is favorable. Turn (improvement of steering feeling) is possible.

Next, the effect will be described.
In the front and rear wheel torque distribution control device for the four-wheel drive vehicle of the first embodiment, the following effects can be obtained.

  (1) A transfer clutch 9 is provided at a position where the output torque from the power source is distributed to the front wheels 14 and 15 and the rear wheels 7 and 8, and the front and rear wheel torque distribution control is performed by clutch torque control of the transfer clutch 9. In the front and rear wheel torque distribution control device for a four-wheel drive vehicle provided with wheel torque distribution control means, the front and rear wheel torque distribution control means includes a power source output power Ltm of the power source and a differential work of the transfer clutch 9. In order to determine the clutch torque control command value based on the power ratio Lc / Ltm and the power ratio Lc / Ltm, the front and rear wheel torque distribution control based on the substitute characteristic of the power ratio Lc / Ltm is used to suppress tight corner braking. It is possible to easily achieve both performance and start / acceleration performance.

  (2) The front and rear wheel torque distribution control means uses a ratio of differential power Lc to power source output power Ltm as a power ratio Lc / Ltm, and clutch torque control increases as the value of the power ratio Lc / Ltm increases. Since the command value is lowered, the transmission loss (loss) of the transfer clutch 9 can be reduced.

  (3) The four-wheel drive vehicle is a vehicle in which a wheel to which driving torque from a power source is directly transmitted is a main driving wheel, and a wheel to which driving torque from the power source is transmitted via a transfer clutch 9 is a driven wheel. The front and rear wheel torque distribution control means determines the ratio of the differential power Lc to the power source output power Ltm and determines the clutch torque control command value so that the power ratio Lc / Ltm is equal to or less than a predetermined value α. Therefore, it is possible to achieve both tight corner braking suppression performance and start / acceleration performance that ensure smooth turning.

  (4) The front and rear wheel torque distribution control means sets the predetermined value α according to vehicle specifications (weight, wheelbase, tire characteristics, etc.) and vehicle conditions, so that a tight corner brake can be used regardless of vehicle type or vehicle condition. It is possible to set an optimum value that achieves a balance between running suppression performance and start / acceleration performance.

  (5) The four-wheel drive vehicle is a vehicle having an engine 1 and an automatic transmission 2 as a power source, and the front and rear wheel torque distribution control means uses a transmission output power Ltm as a power source output power, Since the transmission output torque based on the engine output torque Teng, the torque ratio and the AT gear position GearPosition is calculated by the product of the transmission output rotational speed AToutrev, the transmission output power Ltm can be calculated in real time.

  (6) The front and rear wheel torque distribution control means calculates the differential power Lc by the product of the clutch torque of the transfer clutch 9 and the differential rotational speed ΔN, so that the differential work in the transfer clutch 9 is performed in real time. The rate Lc can be calculated.

  The front and rear wheel torque distribution control device for a four-wheel drive vehicle of the present invention has been described based on the first embodiment. However, the specific configuration is not limited to the first embodiment, and the scope of the claims is as follows. Design changes and additions are allowed without departing from the spirit of the invention according to each claim.

  For example, in the first embodiment, the predetermined value α, which is the control target value of the power ratio Lc / Ltm, is a value that secures a region in which the sensitivity evaluation with respect to the tight corner brake is good, and the vehicle specifications (weight, wheel) Although the example set according to the base, tire characteristics, etc.) and the vehicle state is shown, the predetermined value α may be given as a variable value depending on the traveling situation such as when turning or starting.

  The front-rear wheel torque distribution control device for a four-wheel drive vehicle according to the present invention is not limited to an application example to a rear-wheel drive base four-wheel drive vehicle, and can of course be applied to a front-wheel drive base four-wheel drive vehicle. Furthermore, the applicable vehicle is not limited to an engine vehicle having an engine and a transmission as a power source, but of course applies to an electric vehicle using an electric motor as a power source, and a hybrid vehicle using an electric motor and an engine as a power source. Can do.

  Furthermore, in the first embodiment, a four-wheel drive vehicle in which a wheel to which driving torque from a power source is directly transmitted is a main driving wheel and a wheel to which driving torque from the power source is transmitted via a transfer clutch is a driven wheel. Although an example is shown, a four-wheel drive vehicle in which a transfer clutch is provided in each of the torque transmission paths of the front wheels and the rear wheels, and a four-wheel drive state base having a center differential or the like, the torque distribution is controlled by the transfer clutch. It can also be applied to wheel drive vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall system diagram illustrating a rear wheel drive-based four-wheel drive vehicle to which a front and rear wheel torque distribution control device according to a first embodiment is applied. 6 is a flowchart showing a flow of front and rear wheel torque distribution control processing executed by the differential limiting controller of the first embodiment. It is a figure which shows the result of the sensitivity evaluation with respect to the tight corner brake used when determining predetermined value (alpha) used for the front-and-rear wheel torque distribution control based on the substitute characteristic of Example 1. FIG.

Explanation of symbols

1 Engine 2 Automatic transmission 3 Rear propeller shaft 4 Rear differential 5, 6 Rear drive shaft 7 Left rear wheel 8 Right rear wheel 9 Truss clutch 10 Front propeller shaft 11 Front differential 12, 13 Front drive shaft 14 Left front wheel 15 Right front wheel 16 Engine controller 17 Automatic transmission controller 19 Front / rear differential limiting actuator 20 Differential limiting controller 21 Accelerator opening sensor 22 Front / rear acceleration sensor 23 Mode selector switch 44 Brake controller 46 Front left wheel speed sensor 47 Front right wheel speed sensor 48 Left rear wheel speed sensor 49 Right rear wheel speed sensor

Claims (6)

A four-wheel drive equipped with a front and rear wheel torque distribution control means provided with a transfer clutch at a position for distributing output torque from the power source to the front wheels and the rear wheels, and performing front and rear wheel torque distribution control by clutch torque control of the transfer clutch In the vehicle front and rear wheel torque distribution control device,
The front and rear wheel torque distribution control means determines a clutch torque control command value based on a power ratio between a power source output power of the power source and a differential power of the transfer clutch. Front and rear wheel torque distribution control device for four-wheel drive vehicles. In the front and rear wheel torque distribution control device for a four-wheel drive vehicle according to claim 1,
The front and rear wheel torque distribution control means uses the ratio of the differential power to the power source output power as the power ratio, and decreases the clutch torque control command value as the power ratio increases. Front and rear wheel torque distribution control device for wheel drive vehicles. In the front and rear wheel torque distribution control device for a four-wheel drive vehicle according to claim 1 or 2,
The four-wheel drive vehicle is a vehicle in which a wheel to which driving torque from a power source is directly transmitted is a main driving wheel, and a wheel to which driving torque from the power source is transmitted via a transfer clutch is a driven wheel.
The front and rear wheel torque distribution control means determines a clutch torque control command value so that a power ratio, which is a ratio of a differential power to a power source output power, is equal to or less than a predetermined value. Drive wheel front and rear wheel torque distribution control device. In the four-wheel drive vehicle front and rear wheel torque distribution control device according to claim 3,
The front / rear wheel torque distribution control unit is configured to set the predetermined value according to vehicle specifications and vehicle conditions, and a front / rear wheel torque distribution control device for a four-wheel drive vehicle. In the front and rear wheel torque distribution control device for a four-wheel drive vehicle according to any one of claims 1 to 4,
The four-wheel drive vehicle is a vehicle having an engine and a transmission as a power source,
The front and rear wheel torque distribution control means calculates a transmission output power as a power source output power by a product of a transmission output torque based on an engine output torque and a gear ratio and a transmission output rotation speed. A front and rear wheel torque distribution control device for a four-wheel drive vehicle. In the front-rear wheel torque distribution control device for a four-wheel drive vehicle according to any one of claims 1 to 5,
The front and rear wheel torque distribution control means calculates the differential power by a product of a clutch torque of the transfer clutch and a differential rotational speed, and a front and rear wheel torque distribution control device for a four-wheel drive vehicle.

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