Planetary gear transmission systems or components – Differential planetary gearing – Bevel gear differential
Reexamination Certificate
2001-04-04
2003-02-25
Parekh, Ankur (Department: 3681)
Planetary gear transmission systems or components
Differential planetary gearing
Bevel gear differential
C475S231000
Reexamination Certificate
active
06524211
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a differential gear having a differential limiting function.
2. Description of the Related Art
Differential gears with a differential limiting function (limited slip differential) are used as differential gears in automobiles, which, when the wheels on only one side of the automobile are slipping, transmit sufficient torque to the wheels on the other side via clutch means. This type of differential gear is used widely for the purpose of preventing, when wheels on one side from slipping on ice, snow, or mud, the hindered transmission of torque to the wheels on the other side, and preventing the swerve phenomenon from occurring when the automobile is turning or starting abruptly.
For example, the differential gear
100
as shown in
FIG. 11
is described in Japanese Patent Application Laid-Open No. S55-27980 and Japanese Patent Application Laid-Open No. 58-221046. This differential gear
100
comprises: a pair of pressure rings
103
accommodated in the differential case
101
such that they can move freely in the directions of axles
102
but cannot rotate relatively; a pinion shaft
104
that is placed at right angles to the axles
102
with the end thereof being held between the pressure rings
103
; a pinion gear
105
provided rotatably on the pinion shaft
104
; a pair of side gears
106
, provided at the ends of the left and right axles
102
such that they cannot rotate relatively, and that sandwich the pinion gear
105
between them and engage with the pinion gear on the opposite sides thereof; operation means
108
for operating the pressure rings
103
in such a direction as to increase the clearance
107
between the pressure rings
103
in accordance with an increase in relative torque between the pinion shaft
104
and differential case
101
in a differential state; and clutch means
109
that are provided on the opposite sides, in the directions of the axles, of the pressure rings
103
and that are operated by the pressure rings
103
to limit the differential between the left and right axles
102
as the clearance
107
becomes greater.
Various forms of the operating means
108
have been proposed. One of the means adopted is a means, for example, in which a square cam part
110
, one diagonal line of which is set in the directions of axles, is formed at the end of the pinion shaft, and in which a substantially V-shaped cam groove
111
is formed in the pressure rings
103
to engage with the cam part
110
.
Also, in this differential gear
100
, a relative torque arises between the pinion shaft
104
and differential case
101
and widening of the clearance
107
between the pressure rings
103
using the operating means
108
causes the clutch means
109
to operate and the differential between the left and right wheels to be limited. However, normally an elastic member
112
, such as a disc spring, is provided outside the clutch means
109
along the axis so that the clearance
107
between the pressure rings
103
returns to its set gap. The differential gear is also configured so that it exerts pressure that draws the pressure rings
103
close to each other via the multiplicity of clutch plates
113
in the clutch means
109
.
SUMMARY OF THE INVENTION
Basically, it is preferable that this type of differential gear
100
enters the differential state to enable a small turning circle when low speed circling is required such as when parking a car in a garage or at the side of the street, and enters the limited differential state to enable the desired functions to work with stability when the wheels on one side of the car are slipping, when the car is moving forward quickly, or when it is turning at high speed or under heavy loads.
However, in the elastic member
112
in the above differential gear
100
, because the pressure rings
103
are urged to come closer to each other through clutch plates
113
, when the urging force is weak, the clutch means
109
becomes easy to operate using the operation means
108
and the limited differential state occurs even when the automobile is turned at low speeds. This means that the differential state is not always stable. When the urging force is made stronger, the operation means
108
enables the differential state. However, because the clutch plates
113
are always frictionally abutted by the urging force exerted by the elastic member
112
and substantially is in a limited differential state, a stable differential state cannot be guaranteed when a automobile is made to turn a circle at low speeds. That is, there will be various problems such as that the automobile cannot make a sharp small turn when rotating at low speeds, or the so-called “chattering” phenomenon arises, in which there is alternate switching between the limited slip differential and differential state and, as a result, maneuverability deteriorates and the shocks that occur with chattering adversely affect the differential gear
100
and peripheral equipment.
Therefore, it is extremely difficult to specify the urging power that should be applied. For example, in racing automobiles used for sport, maneuverability during low speed rotation is sacrificed to some degree and the urging power exerted by the elastic member
112
is set higher so that a sufficient limited differential can be obtained at high speeds and under high loads.
Also, in automobiles with transverse engines, the layout demands of the engine and peripheral components mean that the shape and capacity of the differential case are greatly restricted compared to automobiles with vertical engines. For example, as in the differential gear
120
shown in
FIG. 12
, the right part of the differential case
121
has had to be narrowed. It is difficult to adequately increase the area of the frictionally abutting section of the clutch means
122
and if the pressure exerted on the elastic member
123
is increased to increase the friction abutting force, a differential state is not obtained when low speed rotation is required. This means that an adequate limited differential action cannot be obtained.
The present invention provides a differential gear that can switch, as appropriate, between differential and limited differential states.
The differential gear according to one embodiment of the invention comprises: a differential case that is rotated by a driving force from the engine, around the left and right axles; a pair of pressure rings accommodated in said differential case so as to be able to move freely in the direction of the axles but unable to rotate relatively; a pinion shaft provided at right angles to the axles with an end thereof held between said pressure rings; at least one pair of pinion gears provided rotatably on said pinion shaft; a pair of side gears, each being placed at the end of said left and right axles so as to be unable to rotate relatively, that sandwich the pinion gears and engage with the pinion gears on the opposite sides thereof; a set of clutch means arranged on the opposite sides, in the direction of the axles, of said pressure rings and that can limit the differential movement between the left and right axles by limiting the relative rotation of the differential case and side gears; urging means that urges the pressure rings in such directions as to decrease the clearance between the pressure rings without use of said clutch means; and operation means that operates the pressure rings against the urging force exerted by the urging means in such directions as to increase the clearance between the pressure rings in accordance with an increase in the relative rotation torque between the pinion shaft and differential case in a differential state.
In this differential gear, when the rotation resistance is the same for both the left and right wheels, the pinion gear, side gears, pinion shaft, and pressure rings all rotate integrally with the differential case and the left and right wheels rotate at the same speed. However, when the rotation resistance is different for the left an
Armstrong Westerman & Hattori, LLP
OS Giken Co., Ltd.
Parekh Ankur
LandOfFree
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