4Wd System - Subaru XT 1988 Service Manual

3-4 4WD SYSTEM
The conventional differential always delivers the same amount
of torque to each wheel. If one wheel slips, the other wheel
loses driving torque.
On the other hand, in the I imited slip differential, if the right
wheel slips, as shown in Fig. 6, the right side gear tends to
turn faster than the differential case. However, because the
clutch holds the right side gear in a braked state, a portion of
torque is transmitted from the right side gear to the differ·
ential case through the clutch, as shown by the broken line.
In the other nonslipping wheel, while the left side gear rotates
at low speed, the differential case turns at high speed. Thus,
torque is delivered from the differential case to the left side
gear through the clutch.
A14·103
Fig.
6
As a result, in addition to the torque delivered to the left side
gear from the pinions, an additional amount of torque is
transmitted to the left side gear which flows from the right
side gear via the clutch, differential case, left clutch and left
side gear in the order named. Given that torque in the direc-
tion in which the differential case turns is plus and that in the
reverse direction is minus, the amount of torque delivered to
the low-speed wheel, T
L,
is calculated by:
T
L
=
(+ Side gear torque) + (+ Clutch torque)
=
To + T c
The amount of torque delivered to the high-speed wheel, T s ,
is given by:
Ts
=
(+ Side gear torque) + (- Clutch torque)
=
To - Tc
6
Therefore, more torque is transmitted to the slower turning
wheel than to the faster wheel.
Torque Ratio of Right to Left Wheels
If one wheel slips, it causes a difference between the slipping
and non-slipping wheels in the amount of torque transmitted
to them. However, the torque ratio between the two wheels in
this case is constant and called a "transfer ratio". This transfer
ratio is expressed by the following equation:
Rt
=
..!.h..
Ts
Rt: Transfer ratio
T
L :
Low-speed wheel torque
T s: High-speed wheel torque
Transfer ratio is indicated by a value based on the ratio of the
low-speed wheel torque to the high-speed wheel torque.
Because the conventional differential delivers an equal amount
of torque to each wheel, the transfer ratio Rt is 1.
In LSD, the transfer ratio, 1
<
Rt
<
00,
can be obtained by
selecting the clutch coefficient that determines the torque
amount of the clutch .
Fig. 7
Oil
..
~
~
o
...
II
1
1
~t<--t--+-r-
oJ
High-speed wheel torque T
s
A14-104
Use only genuine SUBARU LSD oil to obtain the best per-
formance from the LSD.
SUBARU LSD oil
(Showa Sekiyu LSD oil #90)
Part No. 003304300
Service Procedures for LSD
The component parts of LSD kit (See Fig. 3) are not available
as piece parts.
Therefore, it is not recommended to disassemble LSD kit.