192 clutches and power-stop control – Clutches – Fluent material
Reexamination Certificate
2000-04-20
2001-09-04
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Fluent material
C464S027000
Reexamination Certificate
active
06283264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a hydraulic power transmission joint for use in distribution of the driving force of a motor vehicle, and more particularly to a hydraulic power transmission joint capable of changing over the torque transmission characteristics in response to rotational-speed differences between two power shafts through the coupling thereof.
2. Description of the Related Arts
Conventional hydraulic power transmission joints are known from, e.g., U.S. Pat. Nos. 5,706,658 and 5,983,635.
To transmit torque in response to rotational-speed differences between two shafts, the hydraulic power transmission joint comprises:
a cam housing interposed between the input and output shafts and coupled to one of the shafts, the cam housing being provided with a cam face having two or more raised portions formed on its internal side;
a rotor coupled to the other of the shafts and rotatably housed in the cam housing, the rotor having a plurality of axially extending plunger chambers;
a plurality of plungers each reciprocatively accommodated in each of the plurality of plunger chambers under a pressing force of a return spring, the plurality of plungers being operated by the cam face upon the relative rotations of the two shafts;
an intake/discharge hole formed in the rotor and leading to the plurality of plunger chambers;
a rotary valve being in rotatable sliding contact with an end face of the rotor, the rotary valve being positioned relative to the rotor in a predetermined relationship, the rotary valve having on its surface a plurality of intake ports and a plurality of discharge ports acting respectively as intake valves and discharge valves depending on a positional relationship relative to the intake/discharge hole;
flow resistance generating means for generating flow resistance as a result of flow of oil discharged by the operation of the plungers.
In the event that tires having different diameters are mounted on the front and rear shafts with use of such a hydraulic power transmission joint, the rotational-speed difference and torque will increase accordingly as the vehicle velocity rises, and resultant cumulation of the vehicle front and rear differential torque may cause an increase in the running resistance. To solve such a problem, a torque characteristic shifting mechanism of
FIG. 1
is proposed which includes therein a weight portion which is displaced against a retainer spring force in response to a vehicle velocity (centrifugal force) to thereby relieve the internal pressure to change over the transmission torque.
FIG. 1
is a partial sectional view of a rotary valve of the hydraulic power transmission joint provided with the torque characteristic shifting mechanism. A rotary valve
102
is rotatably housed in a cam housing
101
. The rotary valve
102
has on its outer periphery a positioning protrusion
102
A which engages with a notch
101
A formed in the inner periphery of the cam housing
101
. The rotary valve
102
is provided with discharge ports
103
and intake ports
104
which are formed alternately in the circumferential direction, with the intake ports
104
leading to intake passages
105
extending to the outer peripheral surface of the rotary valve
102
. An accommodation hole
106
is formed at the outer periphery of the rotary valve
102
outside the discharge ports
104
. The accommodation hole
106
is in the shape of a circumferentially elongated hole having a raised portion formed on its bottom. The accommodation hole
106
accommodates a weight member
107
in such a manner as to be displaceable in the radial direction (centrifugal direction). The weight member
107
has a bottom which is shaped so as to correspond to the bottom of the accommodation hole
106
and which is provided with a recessed portion. The top of the weight member
107
is provided with spring accommodation holes
110
and
111
accommodating therein springs
108
and
109
, respectively. A drain hole
112
is interposed between the accommodation hole
106
and the discharge port
103
so that the accommodation hole
106
and the discharge port
133
can communicate with each other by way of the drain hole
112
. The drain hole
112
has at its exit an accommodation groove
114
for receiving a ball
113
. The ball
113
is received in the accommodation groove
114
and normally blocks the drain hole
112
. A predetermined gap is formed between the weight member
107
and the accommodation hole
106
. The springs
108
and
109
press the weight member
107
by a given spring force. The ball
113
received in the accommodation groove
114
formed at the exit of the drain hole
112
blocks the drain hole
112
by the spring force of the springs
108
and
109
, and when a predetermined vehicle velocity is reached and the weight member
107
is displaced in the centrifugal direction by the centrifugal force, the ball
113
opens the drain hole
112
. In this manner, the conventional torque characteristic shifting mechanism allows the weight member
107
to be displaced against the springs
108
and
109
in response to the vehicle velocity (centrifugal force) so that the ball
113
opens the drain hole
112
to relieve the internal pressure, thereby rendering the torque &Dgr;T variable as seen in FIG.
2
.
In
FIG. 2
, a curve a represents a torque characteristic obtained when the vehicle velocity V has reached a predetermined vehicle velocity, and a curve b represents a torque characteristic obtained when the vehicle velocity V has reached a predetermined vehicle velocity V2. The transmission torque lowers depending on the vehicle velocity V as indicated by an arrow c, thereby preventing the running resistance from increasing.
Referring then to
FIG. 3
, description will be made of the balance at a point where the torque characteristic is shifted. Arrows d and e denote a spring force P of the springs
108
and
109
, an arrow f denotes a centrifugal force (mr &ohgr;
2
) acting on the weight member
107
, and an arrow g denotes a thrust-up force (&Dgr;P·A) by the internal oil pressure thrusting up the weight member
107
via the ball
113
in the centrifugal direction. A represents the area of contact of the ball
113
with the drain hole
112
, and &Dgr;P represents a discharge pressure. The discharge pressure &Dgr;P is proportional to a transmission torque &Dgr;T (&Dgr;P∝&Dgr;T). The balance at the point (indicated by the vehicle velocity) at which the torque characteristic is changed over is therefore given as
2P−m·r·&ohgr;
2
−&Dgr;P·A=0, &ohgr;
2
∝V
2
where m is a mass of the weight member;
r·&ohgr;
2
is an acceleration; and
V is a vehicle velocity.
Such a conventional hydraulic power transmission joint allowed the springs to press the opposed ends of the weight member, with the balance at the torque characteristic shifting point being given as
2P−m·r·&ohgr;
2
−&Dgr;P·A=0
hence it suffered deficiencies which follow.
First, although the balance expression results in 2P=&Dgr;P·A when the vehicle velocity V is zero, a condition &Dgr;P≧P
0
(P
0
is a predetermined pressure required for keeping the drain hole closed) needs to be satisfied in order to prevent any early drain, and it is also desirable to increase the area of contact A as much as possible with the aim of improving the fuel efficiency after shifting and of preventing any increase in the running resistance.
To acquire a larger contact area, the spring force has also to be increased. Due to the relationship that the spring force balances directly with the area of contact A, however, larger spring accommodation spaces are needed, resulting in the joint having a larger external diameter.
In the condition that &Dgr;P·A is constant (&Dgr;P·A=C), the balance expression is given as
2P=m·r·&ohgr;
2
+C
namely,
&ohgr;
2
=(2P·C)/m·r
For the purpose of improving the fuel efficiency after shifting and of suppressing any increase in the running resistance as described here
Hirao Kiyonori
Kato Tadahiko
Kusukawa Hirotaka
Murata Shigeo
Nakano Hiroyuki
Fujiunivance Co.
Lorence Richard M.
Wenderoth , Lind & Ponack, L.L.P.
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