Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Fluid controlled mechanical clutch or brake
Reexamination Certificate
1999-12-01
2001-08-21
Estremsky, Sherry (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Fluid controlled mechanical clutch or brake
C475S144000, C475S297000, C477S143000
Reexamination Certificate
active
06277047
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic transmission, and more particularly, to an engagement control for a friction device of an automatic transmission.
2. Background Art
An automatic transmission for a motor vehicle has a planetary gear set constituted of sun gears, ring gears, pinions and the like. The speed change of the transmission is accomplished by engaging or releasing friction devices such as multiple-disc clutches or multiple-disc brakes. Generally, the friction devices comprise a plurality of drive plates connected to an input side and a plurality of driven plates connected to an output side disposed in an interleaving relation to the drive plates. When a pressure of a pressure plate is applied to those drive and driven plates, power is transmitted from the drive plates to the driven plates through a frictional contact therebetween.
Besides these multiple-disk type friction elements, a one-way clutch is used for engaging or releasing gears in some type of automatic transmissions. For example, in a sport-shift type automatic transmission whose gear selection can be performed manually, the one-way clutch is locked to engage a first speed gear together with an concurrent engagement of a multiple-disk brake.
FIG. 8
is a cross sectional view showing a construction of a one-way clutch with a multiple-disk friction element according to a prior art. The one-way clutch comprises an inner race
71
, a hub (outer race)
72
and a plurality of sprags
73
disposed between the inner race
71
and the hub
72
. When the sprags
73
are arranged as shown in
FIG. 8
, in case where the hub
72
rotates in a locking direction A (clockwise direction in the drawing), for example in case of acceleration at
1
st speed, the sprags
73
rise to engage the inner race
71
with the hub
72
, thereby the rotation of the hub
72
is locked. On the other hand, in case where the hub
72
rotates in a couterclockwise direction (in a contrary direction to A), for example in case of deceleration at
1
st speed, the sprags
73
fall sideways to allow the rotation of the hub
72
. Further, drive plates
75
and driven plates
76
are arranged interchangeably in an axial direction of the hub
72
. The drive plates
75
are spline-fitted to the hub
72
and the driven plates
76
are spline-fitted to a transmission housing
74
. Thus, a brake mechanism is formed by the hub
72
, the transmission housing
74
and the friction plates
75
,
76
. The inner race
71
is fixed to the transmission housing
74
.
Considering a case where the hub
72
rotates in the locking direction A in a condition of the brake applied, first when the hub
72
rotates in the locking direction A, the sprags
73
start rising. Note that the hub
72
is not locked unless the sprags
73
rise. That is, the locking force of the one-way clutch is generated by rotating the hub
72
by a rotation amount necessary for raising up the sprags
73
. Accordingly, the rotation of the hub
72
is restricted by either locking force of the one-way clutch or the one of the brake. As a result of this, sometimes the braking or locking force of the brake operates before the locking force of the one-way clutch is generated.
That is, as shown in
FIG. 8
, when the hub
72
rotates in the direction A, the clearance “a” (so-called backlash) in the fitting portions between the hub
72
and the drive plate
75
is closed so as to rotate the drive plate
75
in the direction A. At this moment, since the drive plate
75
is engaged with the driven plate
76
, the driven plate
76
is also rotated in the direction A. Accordingly, the clearance or backlash “b” in the fitting portions between the driven plate
76
and the transmission housing
74
is also closed and the protrusions of the driven plate
76
abut against the tooth face of the spline. Thus, a load according to the torque of the hub
72
and the degree of the engagement of the plates
75
and
76
is applied to the protrusions of the friction plates
75
,
76
. When the vehicle makes a sudden start, since this load becomes very large, the driven plate
76
is fatigued to lose endurance. On the other hand, in order to enhance the endurance or strength of the friction plates, the use of a material of high grade provides the automatic transmission with an increase in cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an automatic transmission having a friction device to which a reduced load is applied so that fatigues of the friction device are minimized.
To this object, the automatic transmission according to the present invention comprises a friction engaging means including a plurality of first plates spline-fitted to a hub and a plurality of second plates spline-fitted to a drum and disposed in an interleaving relation to the first plates, an one-way clutch provided in the hub and having a plurality of sprags for locking the rotation of the hub when the hub rotates in a locking direction and a control means for temporarily releasing the friction engaging means for a specified timespan when the friction engaging means is in an engagement condition and when the hub rotates in a locking direction.
Further, the timespan is established at a longer time than a time needed for locking the rotation of the hub. Further, the control means is designed to start to release the friction engaging means when a throttle opening angle exceeds a specified value.
REFERENCES:
patent: 4098148 (1978-07-01), Wayman
patent: 4747323 (1988-05-01), Kiuchi et al.
patent: 4864892 (1989-09-01), Ando et al.
patent: 4890512 (1990-01-01), Kano et al.
patent: 5730683 (1998-03-01), Usuki et al.
Fujisawa Tadao
Nakayama Jun
Sato Keiji
Sawaoka Masato
Suzuki Naoto
Estremsky Sherry
Farber Martin A.
Fuji Jukogyo Kabushiki Kaisha
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