JP2009293719A - Lateral driving force distribution control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain driving performance from being reduced and vehicle behavior from becoming unstable by a slip, by performing driving force distribution control, before right-left rear wheels actually slip. <P>SOLUTION: In a driving source front end type four-wheel drive vehicle 10 for arranging an engine 12 on the vehicle front side, since a driving force transmission passage to the rear wheels 30L and 30R is relatively longer than front wheels 20L and 20R, there is a delay time up to transmitting driving force to the rear wheels 30L and 30R from being rotated by transmitting the driving force to the front wheels 20L and 20R, and before transmitting the driving force to the rear wheels 30L and 30R by using its time difference, the driving force distribution control to the right-left rear wheels 30L and 30R can be performed by a driving force distribution adjusting means based on a rotation state (a rotating speed difference Δω<SB>f</SB>) of the right-left front wheels 20L and 20R, and a slip of the rear wheels 30L and 30R is restrained when the vehicle starts on a low μ road such as a snow road, and the vehicle behavior is stabilized, and excellent starting performance is provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a left / right driving force distribution control method for controlling the distribution of driving force to the left and right rear wheels, and in particular, the driving force distribution control is performed before the left and right rear wheels actually slip (spin). It is about technology.

2. Description of the Related Art A left / right driving force distribution control device that controls driving force distribution for left and right wheels is known. The device described in Patent Document 1 is one example, and the driving force distribution transmitted from the driving source to the left and right wheels via the differential gear mechanism is adjusted by driving force distribution adjusting means such as a hydraulic motor. By determining the start of the distribution control based on the actual slip ratio of the left and right wheels, the vehicle speed, the yaw moment of inertia of the wheels, etc., the driving force distribution is controlled before the actual idling occurs.
JP 2001-18777 A

  However, in such conventional left / right driving force distribution control, since the driving force distribution control is performed based on the actual slip ratio of the left and right wheels for which the driving force distribution is to be controlled, a slip state is avoided to some extent. However, there is still room for improvement, for example, the driving performance at the time of starting or the like is impaired due to the slip or the behavior of the vehicle becomes unstable. Input rotation that restricts differential rotation by the differential gear mechanism by mechanically moving the torque quickly according to the slip of the left and right wheels in order to improve drive performance degradation and instability of vehicle behavior due to single wheel slip It is conceivable to provide a mechanical differential limiting mechanism such as a proportional type, torque sensitive type, or disc spring type, but due to the differential limitation, a driving force difference occurs between the left and right wheels, and a moment is generated around the center of gravity, causing the vehicle to deflect. there's a possibility that.

  The present invention has been made in the background of the above circumstances, and the object of the present invention is that the driving performance distribution control is performed before the left and right rear wheels actually slip, so that the driving performance by the slip is improved. The object is to suppress the lowering or the behavior of the vehicle from becoming unstable, or to suppress the deflection of the vehicle due to the differential limitation of the mechanical differential limiting mechanism.

  In order to achieve such an object, the first invention is characterized in that in the front-rear wheel drive vehicle that travels by driving the front and rear wheels, the driving force distribution to the left and right rear wheels is controlled based on the rotation state of the left and right front wheels. .

  The second invention includes (a) a center differential gear mechanism that distributes and transmits the driving force of a drive source disposed on the front side of the vehicle to the front and rear wheels, and (b) to the rear wheel side via the center differential gear mechanism. (D) a rear wheel differential gear mechanism that distributes and transmits the transmitted driving force to the left and right rear wheels; and (c) a drive that is provided in the rear wheel differential gear mechanism and adjusts the driving force distribution to the left and right rear wheels. (D) The driving force distribution for the left and right rear wheels is controlled by the driving force distribution adjusting means based on the rotational state of the left and right front wheels.

  According to a third aspect of the present invention, in the left / right driving force distribution control method according to the first or second aspect of the invention, (a) a rotational speed difference calculating step for calculating a rotational speed difference between the left and right front wheels; And a slip suppression driving force distribution step for increasing the driving force distribution of the rear wheel on the side where the rotational speed is low.

According to a fourth aspect of the invention, in the left / right driving force distribution control method according to the first or second aspect of the invention, (a) a road surface friction coefficient estimating step for estimating left and right road surface friction coefficients μ _l and μ _r from the rotational speed fluctuations of the left and right front wheels. And (b) a slip suppression driving force distribution step of increasing the driving force distribution of the rear wheel on the higher side of the left and right road surface friction coefficients μ _l and μ _r .

5th invention is the left-right driving force distribution control method of 2nd invention, (a) The said front-and-rear wheel drive vehicle is provided in the said differential gear mechanism for rear wheels, and performs the differential rotation of the said right-and-left rear wheel mechanically. (B) a road surface friction coefficient estimating step for estimating left and right road surface friction coefficients μ _l and μ _r from fluctuations in rotational speed of the left and right front wheels; and (c) the machine In the road surface friction coefficient estimating step, a vehicle deflection direction caused by a difference in driving force between the left and right rear wheels caused by limiting the differential rotation of the left and right rear wheels by the differential differential limiting mechanism is obtained. A deflection direction determination step determined based on the road surface friction coefficients μ _l and μ _r , and (d) the driving force so as to suppress the deflection of the vehicle in the deflection direction determined in the deflection direction determination step. Deflection for controlling distribution of driving force to the left and right rear wheels by distribution adjusting means And a restraining driving force distribution step.

  In the left and right driving force distribution control method according to the first aspect of the invention, the driving force distribution for the left and right rear wheels is controlled based on the rotation state of the left and right front wheels. In the event of a change, it is possible to start driving force distribution control for the left and right rear wheels before the left and right rear wheels have slipped. Is prevented from becoming unstable. In addition, when a mechanical differential limiting mechanism is used together to improve drive performance degradation and vehicle behavior instability due to single-wheel slip, drive force distribution to the left and right rear wheels is based on the rotation state of the left and right front wheels. By appropriately controlling the above, it is possible to suppress the deflection of the vehicle due to the differential limitation of the mechanical differential limiting mechanism.

  The second invention substantially corresponds to one embodiment of the first invention, and the same effects as the first invention can be obtained. In that case, the second invention relates to a front and rear wheel drive vehicle having a drive source disposed on the front side of the vehicle, and the driving force transmission path to the rear wheels is longer than that of the front wheels. There is a delay time from when the driving force is transmitted to the rotational drive until the driving force is transmitted to the rear wheel, and the driving force is transmitted to the rear wheel in advance using the time difference. Before, it is possible to control the driving force distribution to the left and right rear wheels by the driving force distribution adjusting means based on the rotation state of the left and right front wheels. For example, when the vehicle starts on a low μ road such as a snowy road, Suppressed, the vehicle behavior is stabilized, and excellent start performance can be obtained.

  According to the third aspect of the present invention, when the difference in rotational speed between the left and right front wheels is calculated and the rotational speed difference is equal to or greater than a predetermined value, the driving force distribution on the rear wheel on the side where the rotational speed is low, that is, the side where the possibility of slipping is low is increased. As a result, the slip of the rear wheel on the opposite side, which has a high possibility of slipping, is suppressed, the driving performance at the time of starting and the like is improved, and the vehicle behavior is stabilized. In that case, it is only necessary to calculate the difference between the rotational speeds of the left and right front wheels and compare it with a predetermined value, so that signal processing is simple and processing time is short, and driving force distribution control can be performed with excellent responsiveness. .

The fourth invention is the left and right front wheel rotational speed road surface friction coefficient of the left and right from the variation mu _l, mu _r to estimate, its right and left road surface friction coefficient mu _l, mu higher side i.e. slip possibilities smaller side of the _r By increasing the driving force distribution of the rear wheels, the slip of the opposite rear wheel, which has a high possibility of slipping, is suppressed, and the driving performance at the time of starting and the like is improved and the vehicle behavior is stabilized.

The fifth invention includes a mechanical differential limiting mechanism that mechanically limits the differential rotation of the left and right rear wheels, and estimates the left and right road surface friction coefficients μ _l and μ _r from fluctuations in the rotational speed of the left and right front wheels. Does the above-mentioned mechanical differential limiting mechanism tend to cause a vehicle deflection direction, that is, a clockwise direction, due to a difference in driving force between the left and right rear wheels caused by limiting the differential rotation of the left and right rear wheels? It is determined whether it tends to turn counterclockwise based on the road surface friction coefficients μ _l and μ _r , and the driving force distribution to the left and right rear wheels is controlled by the driving force distribution adjusting means so as to suppress the deflection of the vehicle in the deflection direction. By being controlled, the deflection of the vehicle due to the differential limitation of the mechanical differential limiting mechanism is suppressed.

  The present invention includes a front-rear wheel drive vehicle that travels by driving front and rear wheels, and in particular, a center differential gear mechanism that distributes the drive force of a drive source disposed on the front side of the vehicle to the front and rear wheels, and a drive force transmission path The rear wheel side has a longer driving time than the front wheel, and the time difference can be used to perform the driving force distribution control for the left and right rear wheels in advance before the rear wheel side generates the driving force. The present invention is suitably applied to a front-and-rear wheel drive vehicle of a drive source front type. That is, using the time difference from when the driving force is transmitted to the front wheels to be rotationally driven until the driving force is transmitted to the rear wheels, in advance, that is, before the driving force is transmitted to the rear wheels. By controlling the driving force distribution for the left and right rear wheels, the start performance can be improved by suppressing the slip of the left and right rear wheels when the vehicle starts on a low μ road such as a snowy road. However, if the driving force distribution control for the left and right rear wheels can be performed based on the rotation state of the left and right front wheels, the left and right rear wheels before the left and right rear wheels actually generate a slip due to, for example, a change in the road surface condition during traveling. It is possible to start the driving force distribution control for the vehicle, to suppress the deterioration of driving performance and vehicle instability due to slip, or to suppress the deflection of the vehicle due to the differential limitation of the mechanical differential limiting mechanism Therefore, the present invention can also be applied to other front and rear wheel drive vehicles such as a front and rear wheel independent drive type in which front and rear wheels are driven by separate drive sources and a drive source rear type. As the drive source, various power sources suitable for the vehicle such as an internal combustion engine such as a gasoline engine or a diesel engine, or an electric motor can be adopted.

  For example, a driving force transmitted from a common driving source is transmitted to the left and right rear wheels via a rear wheel differential gear mechanism, and the driving force distribution is adjusted by a driving force distribution adjusting means provided in the differential gear mechanism. Although it is configured to be adjusted, a driving source such as an electric motor may be provided separately for the left and right wheels, and the driving force distribution may be adjusted by individually controlling the output of these driving sources. As the differential gear mechanism, a planetary gear type or a bevel gear type is preferably used. For example, in Patent Document 1, the driving force distribution adjusting means is configured to increase or decrease the speed of one wheel by a hydraulic motor, but to increase or decrease the speed of one wheel by a combination of a speed change mechanism and a clutch. Various modes are possible, such as.

In the third aspect of the invention, the driving force distribution of the rear wheel on the side where the rotational speed is slow, that is, the side on which the grip force with the road surface is high and difficult to slip is increased, but the driving force distribution is a predetermined constant distribution ratio. It is also possible to change the distribution ratio stepwise or continuously according to the rotational speed difference. The same applies to the fourth invention. When the difference between the left and right road surface friction coefficients μ _l and μ _r is equal to or greater than a predetermined value, the left and right driving force distribution may be set to a predetermined constant distribution ratio. The driving force distribution ratio may be changed stepwise or continuously according to the road surface friction coefficients μ _l and μ _r .

In the fourth aspect of the invention, it is only necessary to compare the road surface friction coefficients μ _l and μ _r and increase the driving force distribution of the rear wheel on the higher side. However, the left and right rear sides are based on the road surface friction coefficients μ _l and μ _r. A rear wheel differential rotation prediction process for predicting the wheel rotation speed difference is provided, and the driving force distribution is continuously changed according to the rotation speed difference so as to suppress the differential rotation of the rotation speed difference. good. In implementing the third aspect of the invention, the driving force distribution control is performed by estimating the road surface friction coefficients μ _l and μ _r based on the difference between the rotational speeds of the left and right front wheels and predicting the difference in the rotational speed of the rear wheels. It can also be done.

  In the fifth aspect of the invention, the deflection direction of the vehicle due to the differential limitation of the mechanical differential limiting mechanism is determined, and the left / right driving force distribution is adjusted so as to suppress the deflection, for example, a predetermined constant according to the deflection direction However, it is possible to calculate not only the deflection direction but also the deflection strength (eg generated yaw rate), and change the allocation ratio stepwise or continuously according to the deflection strength. It is. The mechanical differential limiting mechanism automatically suppresses the differential rotation by moving the torque to the slow rotation side. For example, the input rotation proportional type, the torque sensitive type, the disc spring type, etc. are widely known. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a four-wheel drive vehicle 10 to which the present invention is preferably applied, and is based on front engine front wheel drive (FF) in which an engine 12 as a drive source is disposed on the front side of the vehicle. This is a front and rear wheel drive vehicle with a drive source in front. In FIG. 1, the driving force generated by the engine 12 as a driving source is generated by a pair of left and right front wheels 20L via an automatic transmission 14, a front wheel differential gear mechanism 16, and a pair of left and right front wheel axles 18L and 18R. , 20R, a center differential gear mechanism (center differential) 22, a propeller shaft 24 serving as a driving force transmission shaft, a left and right driving force distribution device 26, and a pair of left and right rear wheel axles 28L and 28R. To the pair of left and right rear wheels 30L, 30R.

  The engine 12 is, for example, an internal combustion engine such as a gasoline engine or a diesel engine that generates a driving force by combustion of fuel injected in a cylinder. The automatic transmission 14 is, for example, a stepped automatic transmission (automatic transmission) that outputs the rotation input from the engine 12 by decelerating or increasing the rotation at a predetermined speed ratio, and is a forward shift stage, a reverse shift stage. , And neutral are selectively established, and speed conversion corresponding to the gear ratio is performed. The input shaft of the automatic transmission 14 is connected to the output shaft of the engine 12 via a torque converter (not shown).

  FIG. 2 is a skeleton diagram illustrating the configuration of the left / right driving force distribution device 26. As shown in FIG. 2, the left and right driving force distribution device 26 has a drive pinion (bevel gear) 38 provided at the end of the propeller shaft 24 that is rotationally driven from the engine 12 via the center differential gear mechanism 22. And a driving force is transmitted through a driven gear 40 meshing with the drive pinion 38. The left and right driving force distribution device 26 is arranged adjacent to the rear wheel differential gear mechanism 42 and the rear wheel differential gear mechanism 42 that distributes and transmits the driving force to the left and right rear wheels 30L and 30R. A transmission gear device 44 disposed coaxially with the wheel axle 28R, and a first clutch C1 and a second clutch C2 that selectively transmit the output of the transmission gear device 44 to the rear wheel axles 28L, 28R. ing.

  The rear wheel differential gear mechanism 42 includes a ring gear R1, a plurality of pairs of pinions P1-1 and P1-2 that mesh with each other, and a carrier CA1 that supports the pinions P1-1 and P1-2 such that they can rotate and revolve, respectively. And a double pinion type planetary gear device having a sun gear S1 meshing with the ring gear R1 via the plurality of pairs of pinions P1-1 and P1-2, and its gear ratio ρ (= the number of teeth of the sun gear S1 / The number of teeth) is set to 0.5, for example. The ring gear R1 is provided integrally with the case 46 in the case 46 of the rear wheel differential gear mechanism 42, and the driven gear 40 is integrally fixed to the case 46. The rotation of the shaft 24 is decelerated by the drive pinion 38 and the driven gear 40 and transmitted from the case 46 to the ring gear R1. The carrier CA1 is connected to the left rear wheel 30L via the left rear wheel axle 28L, and the sun gear S1 is connected to the right rear wheel 30R via the right rear wheel axle 28R. The carrier CA1 may be connected to the right rear wheel 30R, and the sun gear S1 may be connected to the left rear wheel 30L.

  The transmission gear unit 44 is a single pinion type planetary gear unit including a sun gear S2, a pinion P2, a carrier CA2 that supports the pinion P2 so as to be capable of rotating and revolving, and a ring gear R2 that meshes with the sun gear S2 via the pinion P2. Configured. The sun gear S2 is integrally connected to the case 46 of the rear wheel differential gear mechanism 42, and functions as an input member of the transmission gear device 44. The carrier CA2 is connected to the torque movement switching brake B, and is selectively connected to the non-rotating member 48 and stopped. The ring gear R2 functions as an output member of the transmission gear device 44, and is engaged (including slip) with the carrier CA1 of the rear wheel differential gear mechanism 42 via the first clutch C1, and the left rear wheel. While being selectively connected to the axle 28L, it is engaged (including slip) and selectively connected to the right rear wheel axle 28R via the second clutch C2. The torque transfer switching brake B, the first clutch C1, and the second clutch C2 are each a multi-plate hydraulic friction engagement device that can be slip-engaged. The hydraulic control circuit 34 is operated by the electronic control device 36 shown in FIG. Is switched to engage or disengage, and hydraulic control is performed to control transmission torque during slip engagement.

The hydraulic control circuit 34 includes a solenoid valve that controls an oil passage and a hydraulic pressure, and the solenoid valve is controlled by an electronic control unit 36, whereby the torque movement switching brake B, the first clutch C1, and the first The engagement and disengagement states of the two clutches C2 are switched, and the transmission torque at the time of slip engagement of the first clutch C1 and the second clutch C2 is adjusted, whereby the driving force distribution state for the left and right rear wheels 30L, 30R is adjusted. Be controlled. The transmission gear unit 44 and the brake B correspond to a transmission mechanism. The transmission gear unit 44, the brake B, and the clutches C1 and C2 constitute a driving force distribution adjusting unit 50. The electronic control device 36 receives signals representing the rotational speeds ω _fl and ω _fr from the rotational speed sensors 32L and 32R that detect the rotational speeds (wheel speeds) ω _fl and ω _fr of the left and right front wheels 20L and 20R. It comes to be supplied.

  The electronic control unit 36 includes a CPU, ROM, RAM, an input / output interface, and the like, and includes a so-called microcomputer that executes signal processing according to a program stored in advance in the ROM while using a temporary storage function of the RAM. The torque movement switching brake B, the first clutch C1, and the second clutch C2 are engaged by controlling the command value of the excitation current supplied to the solenoid valve provided in the hydraulic control circuit 34. The disengaged state is switched, and the transmission torque at the time of slip engagement of the first clutch C1 and the second clutch C2 is adjusted. As a result, it is possible to control the driving force distribution for the left and right rear wheels 30L, 30R, or to limit the differential by the rear wheel differential gear mechanism 42.

  That is, the driving force generated by the engine 12 is a driving force that rotationally drives the case 46 of the rear-wheel differential gear mechanism 42 via the automatic transmission 14, the center differential gear mechanism 22, the propeller shaft 24, and the like. Is entered as Since the ring gear R1 of the rear wheel differential gear mechanism 42 is provided integrally with the case 46, the driving force from the propeller shaft 24 is input from the case 46 to the rear wheel differential gear mechanism 42. 3 (a) to 3 (d) are collinear diagrams in which the rotational speeds of the three rotating elements (sun gear S1, carrier CA1, and ring gear R1) of the rear wheel differential gear mechanism 42 can be connected by a straight line. The left vertical axis shows the rotational speed Nl of the carrier CA1 connected to the left rear wheel 30L, and the right vertical axis shows the rotational speed Nr of the sun gear S1 connected to the right rear wheel 30R. The central vertical axis indicates the rotational speed of the ring gear R1 that is rotated integrally with the case 46, that is, the input rotational speed Ni. The central vertical axis also shows the rotational speed of the ring gear R2 of the transmission gear unit 44, that is, the rotational speed Nc of the first clutch C1 and the second clutch C2.

  On the other hand, the table shown on the right side of each of FIGS. 3A to 3D shows the states of the torque transfer switching brake B, the first clutch C1, and the second clutch C2. Indicates an engaged state (including slip), and “x” indicates a released state. The straight line between the rotational speeds Nl and Nc indicates the state of the first clutch C1, the solid line indicates the slip engagement state, and the broken line indicates the released state. The straight line between the rotational speed Nc and the rotational speed Nr indicates the state of the second clutch C2, the solid line indicates the slip engagement state, and the broken line indicates the disengaged state.

FIG. 3A is an alignment chart when the left and right driving force distribution device 26 is not controlled. During non-control, the torque transfer switching brake B, the first clutch C1, and the second clutch C2 are all in a released state. In this state, only the rear wheel differential gear mechanism 42 functions, and the transmission gear unit 44 is in an idling state, and the driving force is distributed substantially evenly to the left and right rear wheels 30L, 30R. Thereby, the left and right driving force distribution device 26 functions as a normal open differential without performing torque movement and differential limitation. Therefore, if the friction coefficients μ _l and μ _r of the left and right rear wheels 30L and 30R are substantially the same, for example, when traveling straight, the rear wheel differential gear mechanism 42 is shown in FIG. rotated integrally, left and right rear wheels 30L, 30R of the rotational speed Nl, although Nr becomes substantially the same, turning or when the left and right rear wheels 30L, the friction coefficient mu _l of 30R, when mu _r are different and the like Are allowed to perform differential rotation with their rotational speeds Nl and Nr being different.

  FIG. 3B is a collinear diagram when the driving force distribution of the right rear wheel 30R is increased (increased) by the left / right driving force distribution control. The torque movement switching brake B is engaged and the first The clutch C1 is slip-engaged and the second clutch C2 is released. Here, when the torque movement switching brake B is engaged, the carrier CA2 of the transmission gear unit 44 is locked, and the rotation speed Nc of the ring gear R2 is decelerated and rotated in the reverse rotation direction. Further, as the first clutch C1 is slip-engaged, the rotation of the ring gear R2 is transmitted to the left rear wheel axle 28L via the carrier CA1 of the rear wheel differential gear mechanism 42. Here, since the rotational speed Nc of the ring gear R2 is in the reverse rotation direction, when the first clutch C1 is slip-engaged, the driving force of the left rear wheel 30L is reduced via the carrier CA1 and the left rear wheel axle 28L. Thus, the driving force of the right rear wheel 30R is relatively increased. Further, since the rotational speed Nl of the left rear wheel 30L is reduced by slip engagement of the first clutch C1, the rotational speed Nr of the right rear wheel 30R is increased by the rear wheel differential gear mechanism 42.

  FIG. 3C is a collinear diagram when the driving force distribution of the left rear wheel 30L is increased (increased) by the left / right driving force distribution control. The torque movement switching brake B is engaged and the second The clutch C2 is slip-engaged and the first clutch C1 is released. As in FIG. 3B, when the torque movement switching brake B is engaged, the carrier CA2 of the transmission gear unit 44 is locked, and the rotational speed Nc of the ring gear R2 is decelerated and rotated in the reverse rotation direction. Further, as the second clutch C2 is slip-engaged, the rotation of the ring gear R2 is transmitted to the right rear wheel axle 28R. Here, since the rotation speed Nc of the ring gear R2 is in the reverse rotation direction, when the second clutch C2 is slip-engaged, the driving force of the right rear wheel 30R is reduced via the right rear wheel axle 28R, and the left The driving force of the rear wheel 30L is relatively increased. Further, since the rotational speed Nr of the right rear wheel 30R is decelerated by slip engagement of the second clutch C2, the rotational speed Nl of the left rear wheel 30L is increased by the rear wheel differential gear mechanism 42.

  FIG. 3D is a collinear diagram at the time of differential limitation. At the time of this differential limitation, the torque movement switching brake B is released and the first clutch C1 and the second clutch C2 are both engaged. When the first clutch C1 and the second clutch C2 are engaged, the left and right rear wheel axles 28L and 28R are respectively connected to the rear wheel differential gear mechanism 42 via the first clutch C1 and the second clutch C2. In this case, the differential rotation of the left and right rear wheels 30L, 30R is limited. In this case, when the clutches C1 and C2 are fully engaged, the left and right rear wheel axles 28L and 28R function as rear wheel differential gears via the first clutch C1 and the second clutch C2, respectively. It is directly connected to the case 46 of the mechanism 42 and can be rotated integrally, and the left and right rear wheels 30L, 30R are rotated in the same direction. The differential limiting force is proportional to the transmission torque of the first clutch C1 and the second clutch C2, that is, the engagement hydraulic pressure, and can be set arbitrarily.

  The flowchart of FIG. 4 is a diagram for specifically explaining the control of the driving force distribution for the left and right rear wheels 30L, 30R, and is executed by signal processing by the electronic control unit 36. This flowchart is repeatedly executed at a predetermined cycle time. Steps S1 and S2 are rotation speed difference calculation steps and function as rotation speed difference calculation means, while steps S3 to S6 are slip suppression driving force distribution steps. It functions as a slip suppression driving force distribution means.

In step S1 of FIG. 4, detection signals are read from the rotational speed sensors 32L and 32R to measure the rotational speeds (wheel speeds) ω _fl and ω _fr of the left and right front wheels 20L and 20R. In step S2, the following formula (1 ) To calculate their rotational speed difference Δω _f . In step S3, it is determined whether or not the rotational speed difference Δω _f is smaller than a predetermined constant slip determination value −X. If Δω _f <−X, that is, the rotational speed ω _{fr of the} right front wheel 20R. Is higher than the value obtained by adding X to the rotational speed ω _fl of the left front wheel 20L, and if the right front wheel 20R is slipping or is likely to slip, step S4 is executed to distribute the driving force. The adjustment means 50 increases the driving force distribution on the opposite side, that is, the left rear wheel 30L side where the wheel grip force is estimated to be relatively large. Specifically, as shown in FIG. 3C, the torque transfer switching brake B is engaged, the second clutch C2 is slip-engaged, the driving force of the right rear wheel 30R is reduced, and the left rear The driving force of the wheel 30L is relatively increased, and thereby the slip of the right rear wheel 30R is suppressed. The driving force distribution ratio at this time, that is, the engagement hydraulic pressure of the second clutch C2 may be a predetermined constant value, or may be increased stepwise or continuously according to the rotational speed difference Δω _f. good.
Δω _f = ω _fl −ω _fr・ ・ ・ (1)

If the determination in step S3 is NO (No), that is, if Δω _f <−X, step S5 is executed to determine whether the rotational speed difference Δω _f is greater than the slip determination value X, that is, the left front wheel 20L. of the rotation speed omega _fl is higher than the value obtained by adding X to the rotational speed omega _fr of the front right wheel 20R, the left front wheel 20L has slipped, or it is determined whether a high state likely to slip. The slip determination value X at this time is the same as the slip determination value -X in step S3 except that the sign is different. If Δω _f > X, step S6 is executed, and the driving force distribution adjusting means 50 increases the driving force distribution on the opposite side, that is, the right rear wheel 30R side where the wheel grip force is estimated to be relatively large. . Specifically, as shown in FIG. 3B, the torque movement switching brake B is engaged, the first clutch C1 is slip-engaged, the driving force of the left rear wheel 30L is reduced, and the right rear The driving force of the wheel 30R is relatively increased, and thereby the slip of the left rear wheel 30L is suppressed. Driving force distribution ratio when this, i.e. the engagement oil pressure of the first clutch C1 may be a predetermined constant value, but also be stepwise or continuously increased in accordance with the rotational speed difference [Delta] [omega _f good.

Here, the four-wheel drive vehicle 10 of the present embodiment is a front-and-rear wheel drive vehicle with a drive source in front, and the driving force transmission path from the engine 12 to the rear wheels 30L and 30R is longer than the front wheels 20L and 20R. , There is a delay time from when the driving force is transmitted to the front wheels 20L and 20R to be rotationally driven until the driving force is transmitted to the rear wheels 30L and 30R, and in advance using the time difference, that is, Before the driving force is transmitted to the rear wheels 30L, 30R, the driving force distribution adjusting means 50 can control the driving force distribution to the left and right rear wheels 30L, 30R. When the vehicle starts, the left and right rear wheels 30L and 30R are prevented from slipping, so that the vehicle behavior is stabilized and excellent start performance is obtained. Further, during vehicle traveling, the left and right front wheels 20L due to changes in the road surface condition (friction coefficient mu), the 20R slip is determined in step S3 or S5 on the basis of the rotational speed difference [Delta] [omega _f, step S4 or By controlling the driving force distribution to the left and right rear wheels 30L, 30R in S6, the driving force distribution control is started before the left and right rear wheels 30L, 30R actually slip, and the left and right rear wheels 30L, 30R are controlled. A decrease in driving performance and instability of vehicle behavior due to one slip are preferably suppressed. It is also possible to change the slip determination values X and -X depending on whether the vehicle starts at a predetermined vehicle speed or less or is running.

FIG. 5 shows that when the vehicle starts on a low μ road such as a snowy road, the rotational speed ω _fl of the left front wheel 20L is larger than the rotational speed ω _fr of the right front wheel 20R, and the rotational speed difference Δω _f is FIG. 4 is an example of a time chart when the slip determination value X is greater than the slip determination value X and the driving force distribution of the right rear wheel 30R is increased according to the flowchart of FIG. 4, and the time t ₁ becomes Δω _f > X and step S5 Is the time when step S6 is executed and the driving force distribution of the right rear wheel 30R is increased. This driving force distribution control is an excellent response when the engagement hydraulic pressure of the first clutch C1 is increased stepwise to a predetermined constant hydraulic pressure value, that is, when the driving force distribution ratio is changed stepwise. The driving force distribution can be controlled with.

If the determination in step S5 is NO, that is, if −X ≦ Δω _f ≦ X, step S7 is executed, and if the driving force distribution control in step S4 or S6 is being executed, the driving is performed. End processing of force distribution control is performed, and if driving force distribution control is not being executed, the processing is ended as it is. The end process of the driving force distribution control is to release all of the torque movement switching brake B, the first clutch C1, and the second clutch C2 as shown in FIG. 3 (a). The oil pressure is smoothly lowered at a predetermined rate of change and released.

As described above, in the left / right driving force distribution control method of this embodiment, the driving force distribution control for the left and right rear wheels 30L, 30R is performed based on the rotation state (rotational speed difference Δω _f ) of the left and right front wheels 20L, 20R. For example, when the rotation state of the left and right front wheels 20L and 20R changes due to, for example, a change in road surface condition while the vehicle is running, the driving force is distributed to the rear wheels 30L and 30R before the left and right rear wheels 30L and 30R slip. It is possible to start the control, and it is possible to suppress a decrease in driving performance or an unstable behavior of the vehicle due to one of the left and right rear wheels 30L and 30R slipping.

Further, the present embodiment relates to a front and rear wheel drive vehicle of a drive source front type in which an engine 12 as a drive source is disposed on the front side of the vehicle, and a driving force transmission path to the rear wheels 30L and 30R is provided to the front wheels 20L and 20R. Since the driving force is transmitted to the front wheels 20L and 20R to be rotated and driven, there is a delay time from when the driving force is transmitted to the rear wheels 30L and 30R. Therefore, before the driving force is transmitted to the rear wheels 30L and 30R, the left and right rear wheels 30L are driven by the driving force distribution adjusting means 50 based on the rotational state (rotational speed difference Δω _f ) of the left and right front wheels 20L and 20R. Since the driving force distribution control for 30R can be performed, the slip of the rear wheels 30L, 30R is suppressed when starting the vehicle on a low μ road such as a snowy road, the vehicle behavior is stabilized and the excellent starting performance is obtained. .

In this embodiment, the rotational speed difference Δω _f between the left and right front wheels 20L and 20R is calculated, and when the rotational speed difference Δω _f is smaller than the slip determination value −X or larger than the slip determination value X, Since the driving force distribution of the rear wheel 30L or 30R on the side where the rotational speed is slow, that is, the grip force is large and the possibility of slipping is large, the slip of the rear wheel 30R or 30L on the opposite side is highly likely to slip. Is suppressed, driving performance at the time of starting and the like is improved, and vehicle behavior is stabilized. In that case, it is only necessary to calculate the rotational speed difference Δω _f between the left and right front wheels 20L, 20R and compare with the predetermined slip determination values -X, X, so that the signal processing is simple and the processing time is short, Driving force distribution control can be performed with excellent responsiveness. In particular, when the driving force distribution ratio is changed in a stepwise manner as shown in FIG. 5, a more excellent response can be obtained and the driving force distribution can be changed efficiently.

  Next, another embodiment of the present invention will be described. In the following embodiments, parts that are substantially the same as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 6 is executed by the electronic control unit 36 instead of the flow chart of FIG. 4. Steps R1 and R2 are road surface friction coefficient estimating steps, which function as road surface friction coefficient estimating means, and steps R3 to R6 are performed. In the slip suppression driving force distribution step, it functions as a slip suppression driving force distribution means.

In Step R1 of FIG. 6, the detection signals are read from the rotational speed sensors 32L and 32R as in Step S1, and the rotational speeds (wheel speeds) ω _fl and ω _fr of the left and right front wheels 20L and 20R are measured. In Step R2, The left and right road surface friction coefficients μ _l and μ _r are calculated according to the following equations (2) and (3). The road surface friction coefficients μ _l and μ _r represent the left and right road surface conditions. In the next step R3, it is assumed that the left and right rear wheels 30L and 30R are in the same road surface state or the same road surface state if the vehicle is running, and the left and right rear wheels 30L and 30R are rotated according to the following equation (4). The speed difference Δω _r is calculated (predicted). In step R4, a rear wheel differential restraining force (moment) M for preventing differential rotation of the left and right rear wheels 30L and 30R having the rotational speed difference Δω _r is calculated according to the following equation (5). These calculation formulas are only examples, and are calculated with higher accuracy using other parameters such as the steering angle of the steering wheel (steering wheel angle), the gradient of the road surface, and the difference in grip force between the tires of the front and rear wheels. It is determined as appropriate according to the characteristics of the vehicle and the required accuracy.

The meanings of the symbols used in the arithmetic expressions (2) to (5) are as follows. In this, the front distribution ratio a _f are the front wheels 20L, in the drive distribution ratio to 20R side, determined as appropriate depending on the front and rear are provided to the center differential gear mechanism 22 driving force distribution device, etc., electrically controlled The control value is used when possible. The engine driving force T is calculated based on, for example, the intake air amount, the fuel injection amount, and the like. The vertical loads W _fl , W _fr , W _rl , W _rr of the wheels may be determined in advance when the influence of the occupant or the load is small, but may be detected by a load sensor or calculated from acceleration, etc. You can also. Since the front differential ratio Df, the tire inertia moment I, the tire radius r, and the rear tread TDR hardly change, a predetermined value may be determined in advance.
a _f : front distribution ratio T: engine driving force Df: front differential ratio I: tire inertia moment ω _fl : left front wheel rotation speed ω _fr : right front wheel rotation speed Δω _r : rotation speed difference between left and right rear wheels μ _l : left road surface Friction coefficient μ _r : Right road surface friction coefficient W _fl : Left front wheel vertical load W _fr : Right front wheel vertical load W _rl : Left rear wheel vertical load W _rr : Right rear wheel vertical load r: Tire radius TDR: Rear tread

  In the next step R5, the driving force distribution of the left and right rear wheels 30L, 30R for generating the rear wheel differential restraining force M, that is, the engagement hydraulic pressure value of the clutch C1 or C2 is determined by a predetermined data map or calculation. It is calculated by an equation. The driving force distribution, that is, the engagement hydraulic pressure value at this time is continuously changed according to the rear wheel differential restraining force M. In step R6, the clutch C1 or C2 is slip-engaged with the hydraulic pressure obtained in step R5 and the brake B is completely engaged, and the driving force distribution for the left and right rear wheels 30L, 30R is distributed to the rear wheel differential restraining force. Change continuously according to M.

Also in this embodiment, the left and right road surface conditions, specifically, the friction coefficients μ _l and μ _r are estimated based on the rotation states of the left and right front wheels 20L and 20R, and the rear wheels are _calculated from the road surface friction coefficients μ _l and μ _r. 30L, calculates a rotation speed difference [Delta] [omega _r of 30R and (predicted), wheels 30L after it such as the differential rotation of the rotational speed difference [Delta] [omega _r is prevented, for controlling the driving force distribution for 30R, the Generation of the rotational speed difference Δω _r , that is, one slip of the rear wheels 30L and 30R is suppressed, and the same effect as in the above embodiment can be obtained. In addition, since the engagement pressure value of the driving force distribution i.e. the clutch C1 or C2 in the present embodiment, it is continuously varied in accordance with the suppressing rear wheel differential restraining force M of the occurrence of the rotational speed difference [Delta] [omega _r Even when the road surface condition changes while the vehicle is running, the driving force distribution to the rear wheels 30L and 30R is finely controlled to suppress the slip and further stabilize the vehicle behavior.

  The right and left driving force distribution device 60 of FIG. 7 mechanically limits the differential rotation of the left and right wheels 30L and 30R by the rear wheel differential gear mechanism 42 as compared to the left and right driving force distribution device 26 of the above embodiment. In the case where the mechanical differential limiting mechanism 62 is provided in the rear wheel differential gear mechanism 42, the differential rotation between the sun gear S1 and the carrier CA1 is limited. The mechanical differential limiting mechanism 62 automatically suppresses the differential rotation by moving the torque to the side where the rotational speed is slow, and has been widely known from the past such as an input rotation proportional type, a torque sensitive type and a disc spring type. It is what has been.

  FIG. 8 is executed by the electronic control unit 36 in place of the flowchart of FIG. 4 in the four-wheel drive vehicle 10 provided with the left / right driving force distribution device 60 of FIG. 7, and steps Q1 and Q2 are performed. In the road surface friction coefficient estimation step, it functions as a road surface friction coefficient estimation unit, steps Q3 and Q4 function as a deflection direction determination step and function as a deflection direction determination unit, and steps Q5 to Q7 are a deflection suppression driving force distribution step. It functions as a driving force distribution means. Note that steps Q1 to Q3, Q6, and Q7 in the flowchart of FIG. 8 perform the same signal processing as steps R1 to R3, R5, and R6 of the flowchart of FIG.

In step Q4 of FIG. 8, when the rotational speed difference Δω _r between the left and right rear wheels 30L and 30R calculated (predicted) in step Q3 occurs, the difference between the left and right rear wheels 30L and 30R is caused by the mechanical differential limiting mechanism 62. When the dynamic rotation is mechanically limited, a difference in driving force occurs between the left and right rear wheels 30L and 30R, and the yaw rate γ of the vehicle generated due to the driving force difference is calculated (predicted) according to the following equation (6). . This yaw rate γ represents the vehicle deflection direction (rightward or leftward of the center of gravity) and the strength of the deflection caused by the difference in driving force due to the differential limitation. In the next step Q5, the yaw rate γ The rear wheel differential restraining force (moment) M for canceling the generation is calculated according to the following equation (7). The symbol Iz in the equation (7) is a moment of inertia of the vehicle, a predetermined value is determined in advance, or when the vertical loads W _fl , W _fr , W _rl , W _{rr of the} wheels are detected by a load sensor or the like, It can also be calculated from the vertical loads W _fl , W _fr , W _rl , W _rr . These arithmetic expressions are merely examples, and can be appropriately determined according to vehicle characteristics, required accuracy, and the like, such as being able to calculate with higher accuracy using other parameters.

  Thereafter, Steps Q6 and Q7 are executed, and the driving force distribution of the left and right rear wheels 30L and 30R for generating the rear wheel differential restraining force M in the same manner as Steps R5 and R6, that is, the clutch C1 or C2 The engagement hydraulic pressure value is calculated by a predetermined data map, an arithmetic expression or the like, and the clutch C1 or C2 is slip-engaged by the engagement hydraulic pressure and the brake B is completely engaged, whereby the left and right rear wheels 30L. , 30R is continuously changed according to the rear wheel differential restraining force M.

In this embodiment, the left and right road surface conditions, specifically, the friction coefficients μ _l and μ _r are estimated based on the rotation states of the left and right front wheels 20L and 20R, and the left and right rear wheels are determined from the road surface friction coefficients μ _l and μ _r. The rotation speed difference Δω _r between 30L and 30R is calculated (predicted), and the left and right rear wheels 30L generated by the mechanical differential limiting mechanism 62 mechanically limiting the differential rotation of the left and right rear wheels 30L and 30R. , The yaw rate γ of the vehicle generated due to the driving force difference of 30R is calculated (predicted), and driving force distribution control for the left and right rear wheels 30L, 30R is performed by the driving force distribution adjusting means 50 so as to cancel the generation of the yaw rate γ. Therefore, the deflection of the vehicle due to the differential limitation of the mechanical differential limiting mechanism 62 is suppressed. In particular, in this embodiment, the yaw rate γ representing not only the direction of deflection but also the strength of deflection is obtained, and the driving force distribution control is performed so as to cancel the generation of the yaw rate γ. Vehicle deflection due to differential limiting is adequately suppressed.

  As mentioned above, although the Example of this invention was described in detail based on drawing, these are one Embodiment to the last, This invention is implemented in the aspect which added the various change and improvement based on the knowledge of those skilled in the art. be able to.

It is a schematic block diagram explaining the four-wheel drive vehicle based on the front engine front wheel drive in which the driving force distribution control of the left and right rear wheels is performed according to the method of the present invention. FIG. 2 is a skeleton diagram specifically explaining a left / right driving force distribution device for rear wheels of the four-wheel drive vehicle of FIG. 1. 2 is a diagram for explaining the operation of the left and right driving force distribution device in association with the clutch and brake disengagement state, where (a) is not controlled, (b) is when driving force distribution of the right rear wheel is increased, (c) is when the driving force distribution of the left rear wheel is increased, and (d) is when differential is limited. 4 is a flowchart for specifically explaining left and right driving force distribution control executed by signal processing by the electronic control device of FIG. 1. FIG. 5 is an example of a time chart showing changes in rotational speed difference Δω _f and hydraulic pressures of clutches and brakes when left and right driving force distribution control is performed according to the flowchart of FIG. 4. It is a figure explaining the other Example of this invention, and is a flowchart corresponding to FIG. It is a figure explaining the Example in case the mechanical differential limiting mechanism is provided in the differential gear mechanism for rear wheels, and is a skeleton diagram corresponding to FIG. 8 is a flowchart for specifically explaining left and right driving force distribution control executed by signal processing by an electronic control unit in the embodiment of FIG.

Explanation of symbols

10: Four-wheel drive vehicle (front and rear wheel drive vehicle) 12: Engine (drive source) 20L, 20R: Front wheel 22: Center differential gear mechanism 26, 60: Left / right driving force distribution device 30L, 30R: Rear wheel 32L, 34R: Rotational speed sensor 42: Rear wheel differential gear mechanism 50: Driving force distribution adjusting means 62: Mechanical differential limiting mechanism Steps S1, S2: Rotational speed difference calculating step S3 to S6: Slip suppression driving force distributing step R1 , R2: Road surface friction coefficient estimation step R3 to R6: Slip suppression driving force distribution step Q1, Q2: Road friction coefficient estimation step Q3: Q4: Deflection direction determination step Q5 to Q7: Deflection suppression driving force distribution step

Claims (5)

In front and rear wheel drive vehicles that drive by driving front and rear wheels,
A left and right driving force distribution control method, wherein the driving force distribution to the left and right rear wheels is controlled based on a rotation state of the left and right front wheels. A center differential gear mechanism that distributes and transmits the driving force of a driving source disposed on the front side of the vehicle to the front and rear wheels;
A rear wheel differential gear mechanism that distributes and transmits the driving force transmitted to the rear wheel side via the center differential gear mechanism to the left and right rear wheels;
Driving force distribution adjusting means for adjusting the driving force distribution to the left and right rear wheels provided in the rear wheel differential gear mechanism;
In a front and rear wheel drive vehicle having
The left and right driving force distribution control method, wherein the driving force distribution adjusting means controls the driving force distribution to the left and right rear wheels based on the rotation state of the left and right front wheels. A rotational speed difference calculating step for calculating a rotational speed difference between the left and right front wheels;
A slip suppression driving force distribution step of increasing the driving force distribution of the rear wheels on the slow rotation side when the rotational speed difference is equal to or greater than a predetermined value;
The left and right driving force distribution control method according to claim 1, wherein: A road surface friction coefficient estimating step for estimating left and right road surface friction coefficients μ _l and μ _r from the rotational speed fluctuations of the left and right front wheels;
A slip suppression driving force distribution step of increasing the driving force distribution of the rear wheel on the higher side of the left and right road surface friction coefficients μ _l and μ _r ;
The left and right driving force distribution control method according to claim 1, wherein: The front and rear wheel drive vehicle includes a mechanical differential limiting mechanism that is provided in the differential gear mechanism for the rear wheel and mechanically limits the differential rotation of the left and right rear wheels,
A road surface friction coefficient estimating step for estimating left and right road surface friction coefficients μ _l and μ _r from the rotational speed fluctuations of the left and right front wheels;
In the road surface friction coefficient estimating step, a vehicle deflection direction generated due to a difference in driving force between the left and right rear wheels caused by limiting the differential rotation of the left and right rear wheels by the mechanical differential limiting mechanism. A deflection direction determination step for determining based on the obtained road surface friction coefficient μ _l , μ _r ;
A deflection suppression driving force distribution step of controlling the driving force distribution to the left and right rear wheels by the driving force distribution adjustment means so as to suppress the deflection of the vehicle in the deflection direction determined in the deflection direction determination step;
The left and right driving force distribution control method according to claim 2, wherein:

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