WO2003089812A1

WO2003089812A1 - Friction plate type limited slip differential for vehicle

Info

Publication number: WO2003089812A1
Application number: PCT/KR2003/000748
Authority: WO
Inventors: S. Choi
Original assignee: M & Tec Corp.
Priority date: 2002-04-16
Filing date: 2003-04-14
Publication date: 2003-10-30
Also published as: AU2003219602A1; KR100477515B1; KR20030082047A

Abstract

The present invention relates to a friction plate type Limited Slip Differential (LSD) for transmission of the vehicle. When a vehicle is stuck in mud or snow, one drive wheel spins while the other remains stationary, the differential is transferring all the torque and rotary motion to the drive wheel with the least resistance. A LSD provides more driving force to the wheel with traction when one wheel begins to spin. With the addition of clutch plates to differential case, differential action can be restricted so if one drive wheel has no traction, the other wheel that has some traction will at least receive some torque. LSD is used on motor-sports vehicle for increased traction while cornering and off-road vehicle where the wheels are constantly losing traction.

Description

DESCRIPTION

TITLE OF THE INVENTION

FRICTION PLATE TYPE LIMITED SLIP DIFFERENTIAL FOR VEHICLE

FIELD OF THE INVENTION

The invention is termed the "Friction Plate Type Limited Slip

Differential for transmissions of vehicles" as it allows appropriate

distribution of traction force in both driving wheels through limiting

the differential action. Such limitation of the differential action is

required in several conditions, particularly for motor-sports vehicles

and when enhanced traction force is required in driving. For

example, in motor sports vehicles improvements in the stability of

straight-forward driving or in the stability of cornering are often

required as quick start, accelerating, and quick turning often occur

frequently and repeatedly. The enhanced traction force is required

when driving off-roads or getting out of rugged roads.

The invention is called friction plate type Limited Slip

Differential (LSD) where limitation of differential action in vehicles is created through using the friction resistance which occur between

the friction plates. The device is following structures: front and

rear differential case which support gears and friction plates; 2-side

gears and 4-pinion gears for vehicles with the same size of torque

distribution; case plates which are fixed along the splines of the

differential case; clutch plates constrained to the splines of the side

gear and thus able to rotate exactly same with the side gear; cross-

shaped pinion shaft which supports four pinion gears; cam which

transmits the limited differential torque to clutch plate; and plurality

of coil springs which provides regulated pre-load to generate

friction torque on the friction plates.

DESCRIPTION OF RELEATED ART

In general the differential in transmission for vehicles allows the

smooth driving such as cornering or even driving forward with one

wheel on a flat road while the wheel on the other side on a rugged

road or when the difference occur in the radius of dynamic load

between the tires or friction coefficient on the roads.

However, such differential possesses a number of weaknesses

as^~ the following illustrates. If one wheel falls into mud and skids, then the transmittal of the driving force may not occur, and thus

resulting incapacity to drive. Also, when making quick turns, the

occurrence of load movement in inner wheels can block the

transmitting of driving force thus may result in the decrease of

accelerating tendency of the vehicle. Even on normal road condition,

the stability aspect in straight-forward driving can be decreased

under quick start.

Therefore, the purpose of the invention is to maintain the

stability and acceleration of the forward driving of vehicles when

facing repeated quick start or quick turn and to increase the traction

force of vehicles when driving under rugged roads where skidding

occur frequently due to the falling of wheels on one side by adding

the friction plate type clutch structure onto the differential of

generally-used transmissions allowing appropriate limited in

differential action of vehicles.

The existing friction plate type limited differential used the dish

spring as a mechanism to apply pre-load to the friction plates. The

application of dish-spring is advantageous under a small space

where spatial limitation is accompanied. However, as seen in Fig. 10 regarding an example of unique characteristics of dish spring

curve, the dish spring posses a number of problems such as the

occurrence of instability in friction characteristic or decrease in

differential limitation effect due to abrasion of friction plates in

accordance to duration of use due to non-linear relationship in the

applying force according to displacement requiring regular

readjustment of friction plate clearance. Another weakness would

be the difficult in achieving the appropriate spring constant

adjustment in accordance to the usage of vehicles.

This invention has solved the above mentioned problems in the

following skills were applied: First, for setting-up differential torque

and to realize delicate adjustment of torque, the structure to apply

plurality of coil springs were installed instead of the dish spring.

Plurality of coil springs are characterized by the displacement

to change linearly in according to the spring force. Second, for

setting-up the initial torque in according to the vehicle usage, the

structure was invented to control the number of springs or to allow

installation of plurality of springs with different spring constant.

Third, for stabilized friction characteristics of friction plates and optimization of friction coefficent, the shape of lubricant groove of

the friction plate was invented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view for illustrating limited

slip differential;

FIG. 2 is a sectional view for illustrating installed shape of

limited slip differential in transmission;

FIG. 3 is a plan view of the limited slip differential;

FIG. 4 is a sectional view taken along line C-C of FIG. 3;

FIG. 5 is a sectional view taken along line D-D of FIG. 4;

FIG. 4 is a front view for illustrating applying forces to groove

of cam;

FIG. 7 is a plane view of case plate and shape of lubrication

groove;

FIG. 8 is a plane view of clutch plate and shape of

lubrication groove;

FIG. 9 is a perspective view of rear case for illustrating shape

of case spline and holes for installing the coil springs;

^• FIG. 10 is a ^"graph for illustrating dish characteristics, the prior art;

1 : front case;

1 a : front case spline;

1 b : holes of front case for installing coil springs;

2 : rear case;

2a : rear case spline;

2b : holes of rear case for installing coil springs;

3 : case plate;

3a : protrusion of case plate;

3b : lubricant groove of case plate;

4 : clutch plate;

4a : protrusion of clutch plate;

4b : lubricant groove of clutch plate;

5 : coil spring;

6 : side gear;

6a : external spline of side gear;

6b : internal spline of side gear;

7 : front cam;

8 : rear cam;

8a : protrusion of cam; 9 : pinion gear;

10 : pinion shaft;

1 1 : spacer;

12 : speedometer drive gear;

13 : bearing ;

14 : bolt;

15 : limited slip differential assembly;

16 : differential drive gear;

17 : transmission case;

18 : drive shaft;

19 : cam groove;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

features of the present invention will become apparent to

those skilled in the art upon consideration of the following detailed

description of the invention. The detailed description particularly

refer to the accompanying figures.

Fig. 2 shows the installed condition of limited slip differential

in the transmission of vehicle.

^• This invention, as seen on Fig. 1 and Fig 3, is comprised of case, clutch packs, differential and springs.

Gears, plates and coil springs can be built inside the cases (1 )

(2), and for the ease of assembly, the cases are made as a front-&-

rear separation types. This means the cases are comprised of the

Front Cased ) and the Rear Case(2), and the Front Cased ) and the

Rear Case(2) are connected through the Bolts. Both ends of the

above mentioned cases (1 ),(2) are being supported by transmission

case (17) through bearing (13), and as in the case of prior art, they

are also connected to the differential drive gear(16) which is driven

by the engine and transmit driving force to the vehicle wheels

through drive shaft(18).

Clutch packs are comprised of the Case Plates(3) and the

Clutch Plates(4). The Case Plates(3), a number of protrusions(3) are

formed in external circumference of plate and is constrained at the

cases (1 ), (2) along the internal spline (1 a), (2a) of the case. The

Clutch Plate(4) is located in-between the Case Plate(3). The Clutch

Plate(4), a number of protrusions(4a) are formed in internal

circumference of plate, and are constrained along the external

spline(δa) of the side gear; they transmit the torque which acts on

the side gear. Clutch packs, Multiple Case PlatesO) and the Clutch Plates(4), are symmetrically placed at both ends in between CAM

(7), (8) and cased ) (2) datum for the center line of the pinion

shaft(10). As the friction between the Case Plate(3) and the Clutch

Plate(4) characteristically directly effect the differential limiting

capability, in order to provide sufficient lubrication to stabilize the

friction characteristics and friction coefficent change lubricant

groove (3b), (4b) have been set-up on both sides of the Case

Plate(3) and the Clutch Plate(4) as shown on Fig. 8. The lubricant

groove(3a), which is placed through optional degree for even

distribution of the circumference from the center of the plate at both

sides of the Case Plate(3), is constrained onto cases (1 ),(2) and is

designed to maximize the lubrication under the rotating condition.

On the Clutch Plate(4), there is the spiral Lubricant groove(4b),

which is centered eccentrically in an optional distance from the

center of the plate, is constrained on the Side Gear(6) and is

designed to maximize the inflow and outflow of lubricant under the

rotating condition. The structure considered to maintain the stable

lubricating layer to prevent plate seizing and to stabilize friction

characteristics.

The differential of the limited slip differential is -comprised of a couple of Side Gears(6), four Pinion Gears(9), cross-shaped Pinion

Shaft(10), which supports four Pinion Gears(9), and Front CAM(7)

and Rear CAM(8), which support the Pinion Shaft(10). The internal

spline(6b) of the Side Gear is connected with the Drive Shaft(18) to

transmit the driving force to the wheels of vehicle. There are

Spacers(1 1 ) at the both ends of Side Gear(6) supporting cases

(1 ),(2). The Pinion Gears(9), which are installed at each level of

cross-shaped Pinion Shaft(I O), rotate datum for the Pinion Shaft(I O)

and are geared with the Side Gear(6) to rotate around the Side

Gear(6). Also, the Pinion Gear(9) was optionally designed in a

four pinion structure for minimizing the size and maximizing torque

capacity which allows ease of application without any changes

within the open differential of the vehicle. As shown on Fig. 6, the

Front CAM(7) and the Rear CAM(8) are structured in a symmetrical

formation and are constrained to Case spline(1 a),(2a) to support the

rotation of the Pinion Gear(6) and the Pinion Shaft(10) by forming a

similar shape of protrusions (8a) as the Case Plate in external

circumference. Four grooves (19) are formed to support the Pinion

Shaftd O) on the cylinder of CAM(7),(8). The formation of CAM

grooved 9) is structured in such a way that when ttie vehicle speeds-up, the Pinion Shaft(10) moves along the incline of CAM

grooved 0) and differential action is restricted as the clearance

between the Front CAM(7) and the Rear CAM(8) gets bigger while

the Case Plate(3) and the Clutch Plate(4) are pressed to each other.

However, when the vehicle slows-down, the CAM grooved 9) is

structured to restrict the movement of the Pinion Shaft to allow

differential action.

The spring, which is comprised of plurality of Coil Springs(5),

are set-up on the holes (1 b), (2b) of case and are able to generate

differential limiting torque through applying pre-load on the Case

Plates(30) and the Clutch Plates(4). The springs are structured to

easily adjust the differential limiting torque by decrease the number

of the Coil Spring(5) or to optionally select springs with different

spring constant in accordance to the purpose of vehicle usage.

The operating principles of this invention, limited slip

differential, is as follows:

If different sizes of reaction force act onto the right and the

left driving wheels due to the road condition or the spinning action

and the differences in torque are generated at both of the Side Gears(6), the torque is transmitted to the Pinion Gears(9) which is

geared with both of the Side Gears(6), the Pinion Gears(9) and the

Pinion Shaft(10) are rotated around the Side Gear(6) datum for the

rotatiing axis of the Side gears(6). As Shown on Fig. 6, reaction

force(Fn) is generated on the inclined plane of the Front CAM(7) and

the Rear CAM(8) in an vertical direction with the inclined plane,

which is connected to the Pinion Shaft through the inclined plane at

the CAM grooved 9). The reaction force (Fn) at the inclined plane

is divided into circumferential direction force (Fr) and axial direction

force (Fx). Circumferential direction force(Fr) tries to rotate the CAM

(7), (8), but the it is constrained to the Rear Case spline(2a), and

thus not allowed for rotation. Axial direction force (Fx) operates

CAM(7),(8) in the direction to pressing the Case Plate(3) and the

Clutch Plate(4) along the Case spline.

When the Front CAM(7) and the Rear CAM(8) overcomes the

pre-load from the Coil Spring(5) and move along the Case

spline(1 a),(2a), the clearance between the two CAMs (7), (8) gets

bigger and press the Case Plate(3) and the Clutch Plate(4). When

the Case Plates(3) and the Clutch Plates(4) are pressed by the

CAMs (7), (8), the torsional friction is generated due to the relative movement between the Case Plates(3), which is constrained to the

Case spline(1 a),(2a), and the Clutch Plates, which tends to rotate by

the torque of the Side Gear(6). At this moment, if the size of torque,

which is generated by the torsional friction between the Case

Plates(3) and the Clutch Plates(4), is bigger than the torque acting

upon the Side Gear(6), the differential action is restricted; whereas if

the size of torque acting upon the Side Gear(6) gradually increases

and becomes bigger than the torsional friction, then the differential

action begins to be generated finally.

Therefore, if the size of differential torque, i.e. the torque

difference generated on the both driving wheels, is smaller than the

differential limiting torque, then there will be no relative movement

between the Case Plates(3) and the Clutch Plates(4), the internal

parts rotate together with the cases (1 ),(2) and the same size of

driving force is transmitted to the both of the wheels. If torque

difference of both of the wheels gradually increase and become

bigger than the torsional friction, the relative movement is generated

between the Case Plates(3) and the Clutch Plates(4), and finally the

differential action is allowed. Hence, the differential limiting torque

is determined by the size of pre-load of the Coil Springs(5> and the torsional friction of the Case Plates(3) and the Clutch Plates(4)

through the pressing by two CAMs (7), (8).

Vehicles should be able to fully utilize the driving force through

the appropriate differential limitation to get out of driving conditions

such as rugged roads. At the same time, under conditions such as

cornering and general driving, the differential action should be

allowed for smooth driving. This means that the size of differential

limiting torque needs to be changed according to the purpose of

vehicle usage or the driving condition. Therefore, determining the

size of differential limiting torque of the limited slip differential

becomes significant.

This invention, friction plate type limited slip differential, is

able to fully utilize the driving force of vehicles while at the same

time allowing smooth differential action. It has limited change in

differential limiting torque in accordance to duration of the use and it

allow easiness in adjusting differential limiting torque fitting with the

usage purpose of the vehicle without any internal structural change

since it is able to either control the number of Springs(5) or adapt to

the different spring constant optionally. As shown on Fig. 7 and Fig. 8, it also has other unique characteristics such as preventing seizing

due to smooth lubricating action and has lubricant groove

formation(3b),(4b) on surface of the Case Plate(3) and the Clutch

Plate(4) to secure friction characteristics and to maintain friction

coefficent.

REPRESENTATIVE DRAWING

FIG. 1

INDEX

friction plate, limited slip differential, LSD, differential, side

gear, pinion gear, pinion shaft, cam, case plate, clutch plate, coil

spring

Claims

What is claimed is:

.A Limited SI ip Different ial comprising:

The multi-Case Plates(3) which is constrained in the Cases

(1),(2) along the spl ine(1a),(2a) inside the Case where a

number of protrusions(4a) are formed in the external

circumference of the plate;

The Clutch Plate(4) which is located in-between the Case

Plates(3) and transmits torque by acting upon the Side

Gear(6) through the external spline(βa) of the Side Gear(6)

where a number of protrusions(3a) are formed in the internal

circumference of the plate;

A couple of the Side Gears(6);

Four Pinion Gears(9) and cross-shaped Pinion ShaftdO)

supporting the Pinion Gears;

The Front CAM(7) and the Rear CAM(8) which support the

Pinion ShaftdO) and transmit the torque to the Case Plate(3)

and the Clutch Plate(4) through the inclined plane formed at the

cylinder; - The plurality of Coil Springs(5) which generate differential action

limiting torque through applying pre-load on the Case Plates(4)

and the Clutch Plates(4) mentioned above;;

The Case Spring installation holes(1 b),(2b) which accommodate

the above mentioned Coil Spring(5);

Front-and-rear Separating Type Cases (1 ),(2) which form spline

(1 a), (2a) inside that accommodate the protrusions(3a) of the

above mentioned Case Plates

2. Case p l ate :

The limited slip differential as defined in claim 1, wherein

the above mentioned Case Plate(3) is characterized by the

shape of lubricant groove (3b) which evenly divides the

circumference at an optionally chosen angle from the center

of the plate.

3. Clutch plate:

The limited slip differential as defined in claim 1, or 2,

- the above mentioned Clutch Plate(4) is characterized by the shape of Lubricant groove(4b) in spiral form with

eccentrically centered in relation to the optionally chosen

range from the plate center.