A driving force control unit between the transmission and a driven axle of a 4-wheel drive vehicle

Abstract: A differential control unit (1) for a 4-wheel drive vehicle is disposed between a transmission (5) and a propeller shaft (3), controls the speed differential between front and rear wheels generated when turning the 4-wheel drive vehicle, limits the torsion stress due to the speed differential so that it can improve driving performance and keep the vehicle stable. The differential control unit (1) for limiting a differential includes a screw shaft (6) connected to the transfer case and transmitting turning effect, a piston (14P) for moving forward and backward the shaft portion, a multiple disc clutch (15C) for differential control according to existence and non-existence of friction occurred by forward and backward motion of the piston, a spline gear (16) forming the spline gear on the outer circumference to pass through the inner circumference of the multiple disc clutch (15C), and a housing (9) connected and fixed to the propeller shaft (3) to equip components of a third stopper disposed for supporting the spline gear (16).

Description: The present invention relates to a driving force control unit for front and rear wheels of a 4-wheel drive vehicle which is disposed on a propeller shaft for connecting a transmission and a differential gear of the 4-wheel drive vehicle so as to improve driving performance and keep the vehicle stable by absorbing and controlling the speed difference generated between the front and rear wheels and by limiting the torsion stress when its turning. In general, because speed difference is generated between front wheels and rear wheels when turning of the 4-wheel drive vehicle, it causes a spin of wheels and a torsion driving system so that it affects driving performance. A specific tight corner braking phenomena occurs in the 4-wheel drive vehicle due to a difference of radius of gyration between the front and rear wheels, and more particularly due to the difference of the number of rotations according to the big radius of gyration for the front wheel and the small radius of gyration for the rear wheel when turning the vehicle. The difference of radius of gyration causes forced slipping of the wheels or torsion stress of the driving system like a propeller shaft. This results in locking the driving system and thereby braking the vehicle. The braking phenomena of the driving system exerts a harmful influence upon rigidity of the propeller shaft and also on smooth turning of the vehicle, and causes loss of power. As the propeller shaft of the 4-wheel drive vehicle is a direct connecting type, the rear wheels having small rotative velocity are slipped by the speed difference between the front and rear wheels when turning the vehicle. Accordingly, driving performance and stability of the vehicle drops. In addition, because torsion stress occurred by turning of the vehicle causes the vehicle body to vibrate when designing the vehicle, the size and weight of the propeller shaft should be increased to reduce vibration. In recent years, a viscose coupling has been used to solve the problem. However the viscose coupling has a complex structure and increases manufacturing costs. It is an object to provide a driving force control unit of a 4-wheel drive vehicle which is disposed between a transmission and a propeller shaft, and improves running performance and stability of the vehicle by preventing occurrence of torsion stress by absorbing a violator of the speed regulations and controlling differential between front and rear wheels. According to the invention, this is achieved by the features of claim 1. Advantageous further embodiments are described in the subclaims 2 to 5. The driving force control unit is disposed on a propeller shaft for connecting a transmission and a differential gear so as to prevent occurrence of torsion stress and a differential limits and at the same time, absorb the speed difference between front and rear wheels when turning the 4-wheel drive vehicle. The driving force control unit includes a screw shaft for connecting to the transfer case and transmitting turning effect, a piston for moving forward and backward the shaft portion, a multiple disc clutch for differential control according to existence and non-existence of friction occurred by forward and backward motion of the piston, a spline gear forming spline gear on the outer circumference to move straight the multiple disc clutch, and a housing connected and fixed to the propeller shaft so as to equip components of a stopper disposed for supporting the spline gear. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention: Fig. 1 is a schematic view illustrating a driving force control unit between front and rear wheels in accordance with a preferred embodiment of the present invention; Fig. 2 is an exploded perspective view illustrating a driving force control unit in accordance with a preferred embodiment of the present invention; Fig. 3 is a sectional side view illustrating a driving force control unit between front and rear wheels in accordance with a preferred embodiment of the present invention; Fig. 4 is a view illustrating differential operation of a driving force control unit for front and rear wheels in accordance with a preferred embodiment of the present invention. Fig. 5 is a partially cutaway perspective view illustrating a piston in accordance with a preferred embodiment of the present invention. A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Referring first to Fig. 1, there is illustrated a front-rear driving force control unit between front and rear wheels according to an embodiment of the present invention, and reference numeral 1 refers to the driving force control unit. The driving force control unit 1 is a device for absorbing a violator of speed regulations so as to prevent torsion stress and for controlling a differential between the front and rear wheels when turning of a 4-wheel drive vehicle. The driving force control unit 1 is disposed on a propeller shaft 3 for connecting a differential gear 2 with a transfer-case of a transmission 5. The driving force control unit 1 includes a screw shaft 6 disposed on a connecting shaft of the transfer-case so as to be rotated by the power of the transmission. Figs. 2 and 3, respectively illustrate a perspective view disassembling the front and the rear driving force control unit and a sectional side view illustrating a front-rear driving force control unit in accordance with a preferred embodiment of the present invention. In the driving force control unit 1, the screw shaft 6 is formed with a head portion 7 and a shaft portion 8. A sealing member 10 is inserted in an inner circumference groove of a housing 9 in which the head portion 7 is displaced. The housing 9 is provided with a first stopper 11 and a plurality of needle bearings 12 are disposed between the first stopper 11 and the head portion 7 for smooth rotation therebetween. A spiral groove 14 is formed on an outer circumference of the shaft portion 8 of the screw shaft 6 so that metal balls 13 can move along the groove when the shaft 6 rotates. A piston 14P having circumferential grooves which act as a passageway for the metal balls 13 with the groove of the screen shaft 6 is disposed around the shaft portion 8 of the screw shaft. As the metal ball 13 moves in a direction guided along the spiral groove 14 according to the rotation of the screw shaft 6, the piston 14P is disposed so as to move forward and backward the shaft portion 8. A multiple disc clutch 15C is formed with brake plates 17 and brake discs 19, and it can move sideways. The brake plates 17 are combined with the spline gear 16 which is formed in the inner circumference of the housing 9 and the brake discs 19 are disposed on the outer circumference of the gear 18 so as to contact and add friction to the brake plates 17. As the multiple disc clutch 15C is pressed by moving forward of the piston 14P, contact friction is generated between the brake plates 17 and the brake discs 19. Accordingly, the housing 9 is rotated by the contact friction, whereby the differential is done. A third stopper 20 is fixed to an end of the spline gear 18 by a bolt 22. The bolt 22 passes through a coupling hole 23 formed around the inner circumference of the spline gear 8, and a screw hole 21 is formed around the inner circumference of the third stopper 20 corresponding to the coupling hole 23 so as to fix the spline gear 18 and the third stopper 20. A plurality of needle bearings 12' are disposed between the third stopper 20 and the second stopper 11' formed around the inner circumference of the housing 9 so as to decrease friction generated between them. A sealing member 10 is inserted in the outer circumference of the third stopper 20 so as to seal with the housing 9. The differential of the 4-wheel drive vehicle is accomplished by connecting the housing 9 to the propeller shaft 3. Fig. 5 illustrates a partially cutaway perspective view of a piston 14P in accordance with a preferred embodiment of the present invention. A spiral-type guide groove 15 is formed in the inner circumference of the piston 14P. Because a number of metal balls 13 are inserted in the guide groove 15, the metal balls absorb the transmitted power so as to not allow transmission of the power when the piston 14P which moves left or right is displaced on one end. The operation of the above is due to the metal balls 13 having a structure that can infinitely move along the guide groove 15. In the above described driving force control unit, the rotative velocity of the front wheel is equal to the rotative velocity of the rear wheel when driving in a straight line. Accordingly, when the driving force is distributed from a transmission 4, the screw shaft 6 rotates faster than the piston 14P, and then the piston 14P moves along the spiral type groove 14 and presses the multiple disc clutch 15C so that the driving force control unit 1 operates as one body and transmits the driving force to the rear wheels. When the vehicle turns, the radius of gyration of the front wheel is bigger than the radius of gyration of the rear wheel. Accordingly, the screw shaft 6 connected to the front wheel rotates faster than the housing 9 connected to the rear wheel. As a result, the piston 14P for moving the screw shaft 6 moves left along the spiral groove 14 because the power is transmitted by the metal balls 13. The multiple disc clutch 15C is unpressed by the moving left of the piston 14P. A slip occurring to the unpressed multiple disc clutch 15C and the multiple disc clutch 15C absorbs the power transmitted to the rear wheels within the limit. At this time, the piston 14P that is moved left cannot move any more by the first stopper 11 and the transmitted power is absorbed by the metal balls 13 moving along the guide so that they allow easy operation. Accordingly, the driving force control unit 1 can absorb the torsion stress generated by rotatory difference between the screw shaft 6 and the housing 9. The piston 14P moves left again and returns to the initial state when the vehicle is driven in a straight line after its turning. Therefore, the driving force control unit 1 is directly connected and it rotates as one body. For example, if the rear wheels are stuck in a puddle and they lose driving force, the piston 14P moves left and it diminishes pressure applied to the multiple disc clutch 15C so that a slip occurs with the result of velocity difference between the front wheel and the rear wheel. When the transmission of power is intercepted through the multiple disc clutch 15C, the vehicle can easily escape from a rough road or a puddle or an icy road because maximum power is transmitted to the front wheels. The invention can absorb in itself the velocity difference between the front wheel and the rear wheel, transmit stable driving force to the front wheel and the rear wheel, improve driving performance and keep the vehicle stable by absorbing and controlling a violator of the speed regulations generated between the front and the rear wheel and by limiting the torsion stress when its turning. Also, because the invention is lower in weight than the prior propeller shaft and can be manufactured so as to be compact, it can decrease manufacturing costs and reduce fuel consumption. In addition, the invention can distribute the driving force of the front and rear wheels corresponding to road conditions so that it can improve driving performance and keep the vehicle stable. While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiment, but, on the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims: A driving force control unit (1) between the transmission and a driven axle of a 4-wheel drive vehicle, disposed on a propeller shaft (3) for connecting a transmission (5) to a differential gear (2) so as to control rotational differences and torsion stress between the front and rear wheels when turning the vehicle, the driving force control unit comprising: a first rotating element connected to the transmission (5); a second rotating element connected to the differential gear (2); and means for transmitting rotating force of the first rotating element to the second rotating element without slippage when the vehicle is driven in a straight line and generating slippage between the first and second rotating element when turning the vehicle, wherein the first rotating element is a screw shaft (6) having a spline gear (18) formed on its one end, and wherein the second rotating element is a housing (9) disposed around the screw shaft. The driving force control unit according to claim 1, wherein the means comprises: a piston (14P) disposed between the screw shaft (6) and the housing (9), and movable along an outer circumference of the screw shaft (6) in a longitudinal direction in accordance with the running condition of the vehicle and a plurality of first discs each splined on an outer circumference of the spline gear (18); and a plurality of second discs each splined on an inner circumference of the housing (9), whereby the first discs and the second discs are selectively engaged through friction with each other in response to the movement of the piston (14P). The driving force control unit according to claim 1, wherein the screw shaft (6) comprises a head portion (7) connected and equipped to the transmission (5), a spiral groove (14) for inserting a metal ball (13), and a shaft portion (8) inserted in the inner circumference of the piston (14P) so as to move the piston (14P) forward and backward. The driving force control unit according to claim 1, wherein the piston (14P) forms a spline gear (18) for rectilinear alternating motion in the inner circumference of the housing (9), inserts the metal ball (13) for transmitting power to its inner circumference between a groove and a guide groove (15) so that the multiple disc clutch (15C) is pressed by the piston (14P) moving forward, and the power is transmitted or intercepted. A driving force control unit according to claim 1, wherein a third stopper (20) is nob type, and a bolt (22) combines a screw hole (21) penetrating the center of the third stopper (20) and a coupling hole (23) of the spline gear (18) so that the internal components can be stabilized when power transmitting.

Inventors: PARK BYONG KYUN, PARK, BYONG KYUN
Applicants: HYUNDAI MOTOR CO LTD, HYUNDAI MOTOR COMPANY
Application year: 1996
Main classification: B60K17
IPC codes: B60K23, B60K17, F16H48