JPH0729553B2 - Four-wheel drive control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive device used in a vehicle such as an automobile, and more particularly to a control method for a full-time four-wheel drive device having a center differential device.

2. Description of the Related Art As one of four-wheel drive devices used in vehicles such as automobiles, a center differential device that performs a differential action between a rear wheel and a front wheel, and a difference that limits the differential action of the center differential device. A full-time type four-wheel drive device having a motion limiting device has already been proposed, and a four-wheel drive device of this type is disclosed in, for example, Japanese Utility Model Laid-Open No. 47-203 and Japanese Patent Laid-Open No. 50-1.
47027 and JP-A-55-72420.

In the four-wheel drive system as described above, the differential action of the center differential device avoids the occurrence of the tight corner braking phenomenon due to the difference in the radius of gyration between the front wheels and the rear wheels when the vehicle turns, but on the other hand, If any one of the multiple wheels slips and loses driving force,
The phenomenon that the driving force of all the wheels is reduced due to the differential action of the center differential device occurs. Therefore, in a four-wheel drive system having a center differential device, a differential limiting device that limits the differential action of the center differential device is provided. A so-called viscous fluid type coupling or a friction engagement type clutch is used.

Problems to be Solved by the Invention In a differential limiting device using a viscous fluid type coupling, the differential limiting effect is determined by the rotational speed difference between the front wheel and the rear wheel, and the rotational speed difference is determined by the viscous fluid coupling action. When it is larger, the torque transmission capacity is increased to increase the differential limiting effect, but the front wheels and the rear wheels cannot be completely connected to each other. That is, the front wheels and the rear wheels cannot be completely locked up. The viscous fluid type coupling can cause a state close to a lockup state as its capacity increases, but the torque transmission capacity is relatively large even in a region where the difference in rotational speed between the front wheels and the rear wheels is small as the capacity increases. As a result, the differential limiting action becomes excessive and the occurrence of the tight corner braking phenomenon cannot be satisfactorily avoided. On the contrary, if a small capacity viscous fluid type coupling is selected, the tight corner braking phenomenon can be avoided when the vehicle turns, but the tire slip amount becomes considerably large and the rotation speed difference between the front wheel and the rear wheel becomes large. If it becomes large, the necessary differential limiting effect cannot be obtained when the tire slips, and it is possible to avoid losing the driving force of all the wheels, but an increase in the driving force of the slipped tire cannot be expected. Further, in a viscous fluid type coupling, the torque transmission capacity thereof has a large temperature dependency, and it is difficult to select and maintain an appropriate torque capacity under all use conditions.

In the differential limiting device using a friction engagement type clutch, if this is an on-off type of complete engagement and complete disengagement, the four-wheel drive state changes abruptly due to the switching, especially the manual switching type However, it is difficult to judge the switching, and it is difficult to actually use it properly.

In four-wheel drive, when the difference between the rear wheel rotation speed and the front wheel rotation speed is more than a predetermined value, that is, when one tire is slipping on the road surface, the clutch is engaged and the rear wheel and the front wheel are rotated. Japanese Unexamined Patent Publication (Kokai) No. 55-72420 discloses a four-wheel drive system in which the clutch is disengaged during the other four-wheel drive to allow the differential action of the center differential device. In the four-wheel drive system, the above-mentioned problems are solved. Speaking of whether the clutch may be released when one tire is not slipping on the road surface, that is not the case, and in order for the engagement of the next clutch to be quickly performed without requiring a long time lag. The clutch may be engaged even when one of the tires does not slip on the road surface within a range where the tight corner braking phenomenon does not occur. Further, in the four-wheel drive system as described above, when one of the tires is not slipping on the road surface, the clutch is released, so that the distribution ratio of the input torque to the rear wheels and the front wheels is unique to the center differential device. The drive torque applied to the rear wheels and the front wheels may not be an appropriate value for driving the vehicle with the maximum drive force, depending on the magnitude of the input torque. Especially when the center differential device is of the non-uniform torque distribution type, the difference between the drive torques applied to the rear wheels and the front wheels increases as the input torque increases, and this difference becomes too large. In some cases, a vehicle running drive state may not be obtained, and the tires of the wheels on the larger torque distribution amount may easily slip.

In view of the above-mentioned problems in the conventional four-wheel drive system, the present invention appropriately distributes the driving torque to the front wheels and the rear wheels to maximize the driving force in the motion state at that time. It is an object of the present invention to provide a four-wheel drive system control method capable of causing a vehicle to travel with the use of the vehicle, and at the same time avoiding the loss of the driving force of all wheels due to slip and the occurrence of a tight corner braking phenomenon.

Means for Solving the Problems According to the present invention, the above-mentioned object has one input member and two output members for the rear wheel and the front wheel, and has a difference between the rear wheel and the front wheel. A center differential device for operation, and a differential for connecting two members of the input member and the two output members of the center differential device to each other with a variable torque transmission capacity to limit the differential action of the center differential device. A four-wheel drive control method including a control device and a control device for controlling the torque transmission capacity of the differential limiting device, comprising: (a) relative rotation between a rear wheel rotation speed and a front wheel rotation speed; Detecting a dynamic change, (b) setting the torque transmission capacity of the differential limiting device to a relatively low first value when the relative change is less than or equal to a predetermined value, and (c) ) Process Sometimes, returning to the above step (a), and (d) when the relative change becomes equal to or more than the predetermined value, the torque transmission capacity of the limited slip differential device is set to a second value larger than the first value. And (e) a step of gradually reducing the torque transmission capacity of the differential limiting device from the second predetermined value to the first predetermined value when performing the step (d). ) When the torque transmission capacity of the differential limiting device is reduced to the first value by the step (e), the step (e) is ended and the step (a) is returned to. It is achieved by a method for controlling a four-wheel drive system, which includes:

The difference amount between the rear wheel rotation speed and the front wheel rotation speed may be a rotation speed difference or a rotation speed ratio.

Further, the torque transmission capacity of the differential limiting device may be controlled according to the input torque.

The differential control device used in the four-wheel drive system according to the present invention may be any one as long as the torque transmission capacity can be freely changed by a control signal from the outside.
A hydraulic servo-type wet multi-plate clutch, an electromagnetic powder clutch, or the like may be used.

According to the control method of the four-wheel drive system according to the present invention as described above, when the state in which the relative change between the rear wheel rotation speed and the front wheel rotation speed is equal to or less than the predetermined value continues, The torque transmission capacity of the limited slip differential is set to a relatively low first value, and the vehicle is operated under a certain limited slip differential to avoid the occurrence of the tight corner braking phenomenon. It is possible to obtain an appropriate distribution of the driving torque between the front and rear wheels by the differential device and a wheel drive characteristic that appropriately copes with the slip of the wheels at the front wheels or the rear wheels. Further, once it is detected that the relative change between the rear wheel rotation speed and the front wheel rotation speed has increased above the predetermined value, the torque transmission capacity of the differential limiting device once becomes the above-mentioned relatively low first value. The torque transmission capacity of the limited slip differential is then increased to a higher second value and then gradually reduced from the second value to the first value over a period of time, whereby the rear wheel speed and When an operating state occurs in which the relative change between the front wheel rotational speeds exceeds the above-mentioned predetermined value, the torque transmission capacity of the limited slip differential is increased in anticipation that it will continue for at least a certain time. Therefore, the vehicle drive system is controlled so as to eliminate the slip generated on the front wheels or the rear wheels. At this time, the torque transmission capacity of the limited slip differential is changed from the first value to the second value in order to promptly deal with the occurrence of a large slip on the front wheels or the rear wheels. However, since the process of returning it from the second value to the first value is gradually performed over a certain time, the magnitude of the torque transmission capacity of the limited slip differential device may be increased. It does not change too frequently between the first value and the second value, and there is no risk of undesired instability in the drive characteristics of the vehicle drive system.

Example Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a skeleton diagram showing a four-wheel drive system used for carrying out the control method according to the present invention. In the drawing, reference numeral 1 denotes an internal combustion engine, which is vertically installed in the front part of a vehicle, and at the rear part of the internal combustion engine, an automatic transmission 2 for a vehicle.
And the four-wheel drive transfer device 3 are sequentially connected.

An automatic transmission 2 for a vehicle includes a hydraulic torque converter 5 having a general structure provided in a converter case 4 and a gear type transmission 7 provided in a transmission case 6.
And an output member (crankshaft) (not shown) of the internal combustion engine 1 by an input member 8 of the hydraulic torque converter 5 for rotationally driving the internal combustion engine 1 via the hydraulic torque converter 5 to a transmission. It is given to 7. The speed change device 7 is a speed change device which is known per se and is composed of a planetary gear mechanism or the like, and is switched between a plurality of speed stages, and the speed change control is performed by a hydraulic control device 9.

The four-wheel drive transfer device 3 has a planetary gear type center differential device 10 for full-time 4WD. The center differential device 10 includes a carrier 11 as an input member to which rotational power is applied from a transmission device 7 and Planetary pinion supported on the carrier
12 and a sun gear 13 and a ring gear 14 meshing with the planetary pinion 12, the ring gear 14 is connected to the rear wheel drive shaft 15, and the sun gear 13 is a sleeve-like front wheel drive that is concentric with the rear wheel drive shaft 15. Is connected to the intermediate shaft 16. The four-wheel drive transfer device 3 is provided with a front-wheel drive shaft 17 in parallel with the front-wheel drive intermediate shaft 16, and the front-wheel drive intermediate shaft 16 and the front-wheel drive shaft 17 are mounted on their respective sprockets 18.
And 19 are driven and connected by an endless chain 20 that meshes.

The four-wheel drive transfer device 3 is provided with a hydraulically actuated differential control clutch 21 that selectively connects the sun gear 13 and the ring gear 14, and the differential of the differential control clutch is the four-wheel drive transfer. Hydraulic control device provided in the device 3
It is supposed to be done by 22.

The differential control clutch 21 is a hydraulic servo-type wet multi-plate clutch as shown in FIG.
By the servo hydraulic pressure supplied to the oil chamber 36 of 35, the servo piston 37 moves to the right in the figure against the spring force of the return spring 38, so that the sun gear 13 and the ring gear 14 of the center differential device 10 have a torque transmission relationship. Are connected, and the torque transmission capacity is proportionally increased as the servo hydraulic pressure supplied to the oil chamber 36 increases.

The hydraulic control device 22 is a pressure regulator valve 40 that receives hydraulic pressure from an oil pump 39 incorporated in the automatic transmission 2 for a vehicle to regulate the hydraulic pressure to a predetermined hydraulic pressure, and an electromagnetic type that receives hydraulic pressure from the pressure regulator valve 40. It has a servo hydraulic control valve 41. The servo hydraulic control valve 41 has a port a connected to the oil chamber 36 of the hydraulic servo device 35, a hydraulic port b to which hydraulic pressure is supplied from the pressure regulator valve 40, and a drain port c. The port a is connected to the hydraulic port b, while the port a is connected to the drain port c when the power is not supplied. A pulse signal having a predetermined duty ratio is given to the servo hydraulic control valve 41 from the control device 45, and the servo hydraulic control valve 41 supplies the servo hydraulic pressure having a magnitude corresponding to the duty ratio to the oil chamber 36 of the hydraulic servo device 35. Will be supplied.

One end of a rear propeller shaft 24 is drivingly connected to the rear wheel drive shaft 15 by a universal joint 23.

Front propeller shaft with universal joint 25 for front wheel drive shaft 17
One end of 26 is connected. The front propeller shaft 26
One side of the automatic transmission 2 for a vehicle extends substantially parallel to its axis, and at the other end, a universal joint 27 and an intermediate connecting shaft 28 form a drive pinion shaft 31 which is an input shaft of a front differential device 30. Is connected to one end of. The drive pinion shaft 31 is rotatably supported by a differential case 32 integrally formed with an oil pan 29 made of cast iron of the internal combustion engine 1.

A drive pinion 33 composed of a bevel gear is provided at an end of the drive pinion shaft 31, and the drive pinion meshes with a ring gear 34 of the front differential device 30.

The hydraulic control devices 9 and 22 operate on the basis of a control signal from the electric control device 45 to perform the switching control of the shift stage of the transmission 7 and the transmission torque control of the differential control clutch 21. The control device 45 includes a microcomputer having a general structure, the rear wheel rotation speed sensor 46r outputs information about the rear wheel rotation speed, the front wheel rotation speed sensor 46f receives information about the front wheel rotation speed, and the throttle opening sensor 47 sends information about the internal combustion engine. The information about the throttle opening of No. 1 is given by the manual shift position sensor 48, the information about the manual shift range, and the input torque sensor 49 gives the information about the input torque given to the four-wheel drive transfer device 3, respectively. A control signal for switching control of the shift stage of the transmission 7 is sent to the hydraulic control device 9 in accordance with a predetermined shift pattern according to the vehicle speed and the throttle opening determined by the manual shift range and the rear wheel rotation speed or the front wheel rotation speed. The differential control clutch is output according to the difference between the rear wheel speed and the front wheel speed and the input torque. A pulse signal of a predetermined duty ratio for controlling the torque transmission capacity of 21 and outputs to the servo hydraulic pressure control valve 41.

The torque transmission capacity Tc of the differential control clutch 21 is specifically controlled according to the flowchart shown in FIG.

That is, the difference between the rear wheel rotation speed Nr and the front wheel rotation speed Nf is a predetermined value Nset.
In the following cases, the torque transmission capacity Tc is determined according to the following formula so that the torque transmission capacity Tc increases in accordance with the increase of the input torque Ti within the range where the differential control clutch 21 is not in the completely engaged state.

Tc = k ₁ · Ti k ₁ is a coefficient, and this coefficient k ₁ determines the rate of increase of the torque transmission capacity Tc with respect to the input torque Ti, which is less than 1 at which the differential control clutch 21 does not enter the fully engaged state. It is set to a positive value. It should be noted that this torque transmission capacity Tc does not have to be in a proportional relationship with respect to the input torque Ti, as long as it has a functional relationship with respect to the input torque Ti.

As a result, when the difference between the rear wheel rotational speed and the front wheel rotational speed is less than or equal to a predetermined value, the torque transmission capacity Tc of the differential control clutch 21 increases the input torque Ti within a range in which the differential control clutch 21 does not enter the fully engaged state. It is prevented that the difference between the distributed torque amounts of the rear wheels and the front wheels exceeds a predetermined value while allowing the differential action of the center differential device 10 to increase.
While avoiding the occurrence of the tight corner braking phenomenon, the distribution amount of the input torque to the rear wheels and the front wheels is appropriately maintained,
The vehicle will always run with the maximum driving force.

On the other hand, when the difference between the rear wheel rotation speed Nr and the front wheel rotation speed Nf is greater than or equal to a predetermined value Nset, that is, when either the rear wheel or the front wheel slips on the road surface, the differential control clutch twenty one
The torque transmission capacity Tc is determined according to the following equation so that the torque transmission capacity Tc increases in accordance with the increase of the input torque Ti so that the torque transmission capacity Tc becomes a completely engaged state.

Tc = k ₂ · Ti k ₂ is a coefficient, and this coefficient k ₂ is larger than the coefficient k ₁ , which is set to a numerical value at which the differential control clutch 21 is in the fully engaged state. It should be noted that the torque transmission capacity Tc at this time may also have a functional relationship with the input torque Ti.

As a result, when the difference between the rear wheel rotational speed and the front wheel rotational speed is equal to or greater than a predetermined value, the differential control clutch 21 is fully engaged and the differential action of the center differential device 10 is blocked, and the rear wheel and the front wheel are separated from each other. Is completely locked up, and it is possible to prevent the driving force of all wheels from being reduced when the tire slips due to the differential action of the center differential device 10.

The torque transmission capacity Tc of the differential control clutch 21 at the time of tire slip may be fixedly set to the maximum value irrespective of the input torque Ti.
Even when Ti is small, it is necessary to set it to a high value that is necessary when the input torque Ti is large, and wasteful power loss due to the hydraulic pump increases.

As described above, since the difference between the rear wheel rotation speed Nr and the front wheel rotation speed Nf becomes equal to or greater than the predetermined value Nset, the differential control clutch 21 is completely engaged and the rear wheel and the front wheel are completely locked. In the up state, there is no difference in the number of revolutions, and at the same time, when the torque transmission capacity Tc is controlled based on the equation of Tc = K ₁ · Ti, the difference in the number of revolutions becomes the predetermined value Nset or more again. There is a risk that hunting will occur, so after this,
The transmission torque Tc determined based on the formula Tc = k ₂ · Ti is Tc
This is gradually reduced by ΔTc until it decreases to a value determined based on the formula of = k ₁ · Ti.

Incidentally, the differential control device such as the differential control clutch 21 is not limited to the one in which the two output members of the center differential device are connected with a variable torque transmission capacity as in the above-described embodiment, but the two of the center differential device are connected. One of the output members and the input member, that is, the carrier may be connected with a variable torque transmission capacity, and in this case, the same operational effect as that of the above-described embodiment can be obtained.

In the above, the present invention has been described in detail with reference to specific embodiments, but the present invention is not limited to these.
It will be apparent to those skilled in the art that various embodiments are possible within the scope of the invention.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a four-wheel drive device used for carrying out a control method for a four-wheel drive device according to the present invention, and FIG. 2 is a differential used for carrying out a control method for a four-wheel drive device according to the present invention. FIG. 3 is a schematic configuration diagram showing a control clutch control system, and FIG. 3 is a flow chart showing an embodiment of a control method for a four-wheel drive system according to the present invention. 1 …… internal combustion engine, 2 …… automatic transmission for vehicle, 3 …… transfer device for four-wheel drive, 4 …… converter case, 5 …… hydraulic torque converter, 6 …… transmission case, 7
...... Transmission, 8 …… Input member, 9 …… Hydraulic control device, 10 ・ ・ ・
… Center differential device, 11 …… Carrier, 12…
… Planetary pinion, 13 …… Sun gear, 14 …… Ring gear, 15 …… Rear wheel drive shaft, 16 …… Front wheel drive intermediate shaft, 17 ……
Front wheel drive shaft, 18, 19 …… sprocket, 20 …… endless chain, 21 …… differential control clutch, 22 …… hydraulic control device, 23…
… Universal joint, 24 …… Rear propeller shaft, 25 …… Universal joint, 26
...... Front propeller shaft, 27 …… Universal joint, 29 …… Oil pan, 30 …… Front differential device, 31 …… Drive pinion shaft, 32 …… Differential case, 33
...... Drive pinion, 34 …… Ring gear, 35 …… hydraulic servo device, 36 …… oil chamber, 37 …… servo piston, 39 …… oil pump, 40 …… pressure regulator valve, 41 ……
… Servo hydraulic control valve, 45 …… Control device, 46r
…… Rear wheel speed sensor, 46f …… Front wheel speed sensor, 47…
… Throttle opening sensor, 48 …… Manual shift position sensor, 49 …… Input torque sensor

Claims (1)

[Claims] 1. A center differential device having one input member and two output members for a rear wheel and a front wheel and performing a differential action between a rear wheel and a front wheel, and an input of the center differential device. Member and two of the two output members are connected to each other with a variable torque transmission capacity to limit the differential action of the center differential device, and a torque transmission capacity of the differential limiting device is controlled. In a method of controlling a four-wheel drive device including a control device for controlling the rotation speed of the vehicle, (a) a process of detecting a relative change between a rear wheel rotation speed and a front wheel rotation speed; and (b) the relative change. Is less than a predetermined value, the process of setting the torque transmission capacity of the differential limiting device to a relatively low first value, and (c) When the process of (b) is performed, the process returns to the process of (a). Process and (d) above When the relative change exceeds the predetermined value, the steps of setting the torque transmission capacity of the differential limiting device to a second value larger than the first value, and (e) the step (d) are performed. Sometimes, the torque transmission capacity of the differential limiting device is gradually reduced from the second predetermined value to the first predetermined value; and (f) the torque transmission of the differential limiting device by the process of (e). When the capacity is reduced to the first value, the step (e) is ended and the step (a) is returned to.