Fluid coupling

Herein disclosed is a fluid coupling which comprises: a pump impeller connected to the output shaft of an engine; and a turbine runner for transferring a working fluid to and from the pump impeller. On the pump impeller and the turbine runner, respectively, there are arranged a pump blade and a turbine blade without any inner core for guiding the flow of the working fluid inside of the pump impeller and the turbine runner. By bending at least one of the working fluid outlet side of the pump blade and the working fluid inlet side of the turbine blade, there is formed transfer limit means for limiting the transfer of the working fluid when the fluid coupling is in a stalling state.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fluid coupling and, more particularly, 
to a fluid coupling having no inner core and suited for use with a 
continuously variable transmission. 
2. Description of the Prior Art 
A fluid coupling (hereinafter referred to as "coupling") operates to 
transfer power through a working fluid between a pump impeller and a 
turbine runner, which are opposed to each other. The coupling does not 
function to increase input torque, and is different from a torque 
converter in this regard; rather, a coupling simply functions as a power 
transmitting junction. Since a coupling can be made smaller and lighter 
that a torque converter, due to absence of a stator, it is well suited for 
use as a coupler in a vehicle having a V-belt type continuously variable 
transmission (referred to hereinafter as "CVT"). 
Couplings of two types are known. One type of coupling is equipped with an 
inner core for guiding the flow of a working fluid therein and the other 
type is not equipped with such an inner core. The coupling of the type 
having no inner core offers the advantage of low weight, although its 
fluid passage varies in accordance with slippage between the pump and the 
turbine. In not having a fixed flow passage, it differs from the type of 
coupling having an inner core, and flow analysis for such a coupling is 
difficult, as is designing for predictable performance. An "inner core" is 
shown, for example, as member 8 in U.S. Pat. No. 5,005,356 issued to 
Saunders and as elements 10b in U.S. Pat. No. 4,866,935 issued to 
Hayabuchi et. al. 
If a coupling without an inner core is to be used in an automobile to 
exploit its advantages, in order to improve the starting acceleration of a 
vehicle having a torque converter, especially a CVT, the engine r.p.m. at 
the start is desirably raised to increase torque, by reducing the capacity 
coefficient of the coupling at stalling (at a velocity ratio of 0) time. 
On the other hand, the capacity coefficient in an intermediate velocity 
ratio range has to be high to provide good mileage in steady running, good 
passing acceleration and good responsiveness. 
The conventional approach to adjusting the capacity coefficient in a 
coupling having no inner core is by changing the blade angle. If the 
capacity coefficient at stalling is decreased in such a manner, the 
capacity coefficient in the intermediate velocity ratio range decreases 
with an increase in the velocity ratio, but the maximum capacity 
coefficient range is not in the intermediate velocity ratio range. In 
short, the characteristics cannot be finely adjusted by changing the blade 
angle although the capacity coefficient can be changed. 
It is known in the prior art to provide a baffle plate for setting the 
capacity coefficient to a low value at stalling, while suppressing 
reduction in the capacity coefficient in the intermediate velocity ratio 
range. With a baffle plate, the flow of the working fluid in the coupling 
is blocked over a range extending from the time of stalling to the low 
velocity ratio and is offset from the blocked path in an intermediate or 
higher range so that the blocking action may be reduced or eliminated. 
However, in attaching a baffle plate to the blade, the number of parts, the 
weight and the production cost are increased accordingly. This prior art 
approach also creates a problem in that the baffle board is difficult to 
fix, thereby endangering the reliability of the structure. 
SUMMARY OF THE INVENTION 
In view of the background thus far described, one objective of the present 
invention is to provide a fluid coupling, without an inner core, which 
gives improved performance without an increase in the number of parts. 
Another object of the present invention is to provide a fluid coupling 
having a sufficiently small capacity coefficient at the time of stalling 
with minimal reduction of the capacity coefficient at an intermediate 
velocity ratio. 
Accordingly, the present invention provides a fluid coupling including a 
pump impeller connected to the output shaft of an engine and a turbine 
runner. A pump blade and a turbine blade are provided on the pump impeller 
and turbine runner, respectively. The fluid coupling of the present 
invention has no inner core for guiding the flow of said working fluid 
inside of the pump impeller and turbine runner. The coupling of the 
present invention is provided with transfer limit means formed by bending 
either the working fluid outlet side of the pump blade or the working 
fluid inlet side of the turbine blade, for limiting the transfer of 
working fluid from pump to turbine when the fluid coupling is in a 
stalling state. 
In the coupling thus constructed according to the present invention, the 
transfer limit means formed in the pump blade and/or the turbine blade is 
disposed in the passage of the working fluid in the stalling range, i.e., 
in the vicinity of the average streamline, to limit the transfer of the 
working fluid so that it acts to reduce the capacity coefficient in the 
stalling range. However, in the intermediate velocity ratio range, some 
inertia force is established in the flow of the working fluid so that the 
action of the transfer limit means, limiting the transfer of the working 
fluid, is reduced and, accordingly, the reduction in the capacity 
coefficient in the intermediate velocity ratio range is less than in the 
stalling range. 
According to the present invention, therefore, the capacity coefficient can 
be reduced at stalling to a sufficiently low level, without provision of 
an inner core, and with minimal reduction in the capacity coefficient in 
the intermediate velocity ratio range. Moreover, the structure of this 
novel coupling simplifies the machining required in its production and 
provides a reliable product with no increase in the number of parts, 
weight or cost. 
An auxiliary advantage is that the acceleration of a vehicle having such a 
coupling can be improved while maintaining the mileage, passing 
acceleration and responsiveness.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One preferred embodiment of the present invention will be described with 
reference to the accompanying drawings. 
FIG. 1 shows a coupling having a pump impeller 1 and a turbine runner 2 
having a pump blade 11 and a turbine blade 21 arranged respectively 
thereon, without any inner core. In this embodiment, at the working fluid 
inlet side of the turbine blade 21, a transfer limit means 22, which is 
disposed in the passage of the working fluid in the stalling range to 
limit the transfer of the working fluid, is formed by bending the blade 
21. 
More specifically, the coupling shown in FIG. 1 is designed to be combined 
with a CVT (i.e., continuously variable transmission). The coupling 
includes a coupling cover 33 having a boss 31 engaged by and in alignment 
with the engine and attached to the drive plate of the engine through a 
spacer 32. A pump shell 12 is integrally welded to the coupling cover 33. 
A turbine hub 24 is splined to the input shaft of the CVT and has a 
turbine shell 23 riveted thereto. A lockup clutch piston 41 is supported 
axially and slidably on the turbine hub 24 and has a drive plate 42 
riveted thereto. A driven plate 44 is splined to the turbine hub 24 and, 
together with the drive plate 42, supports a damper spring 43. 
As shown in FIG. 3, each turbine blade 21 is attached to the turbine shell 
23 such that the major portion of its length is inclined at a 
predetermined angle .theta..sub.1, with respect to a radius of turbine 
shell 23 bisecting same (e.g., 30 degrees in the illustrated embodiment), 
in the direction of rotation of the turbine runner 2, as indicated by 
arrow in FIG. 3, i.e., with respect to a line normal to the turbine runner 
2 and bisecting blade 21. At the outer circumference of the turbine blade 
21, which opposes the outer circumference of the pump blade 11, there is 
provided a transfer limit means 22 which is partially bent with respect to 
the plane defined by the blade 21 that it starts from the position of a 
radius R, as shown in FIG. 2, and has its radially outerpoint located 
generally at the position of a radius r, as shown in FIG. 3. In this 
embodiment, the bending base line is inclined at an angle .theta..sub.2, 
(e.g., 30 degrees in the illustrated embodiment) with respect to the front 
edge 25 of the turbine blade 21, and the bent portion is inclined at a 
predetermined angle .theta..sub.3 (e.g., 30 degrees in the shown 
embodiment) with respect to the plane of the blade 21. 
In the coupling thus constructed, the working fluid discharged from the 
pump impeller 1 flows in stalling state (where the velocity ratio is 0) 
through the central portion of the transfer limit means 22, as indicated 
by the radius r in FIG. 3, so that the transfer limit means 22 formed in 
the turbine blade 21 is positioned in the passage of the working fluid, 
i.e., in the vicinity of the average streamline in the stalling state. As 
a result, the transfer of the working fluid is limited to reduce the 
capacity coefficient in the stalling state. Moreover, this transfer 
limiting action is decreased as the inertia force is established in the 
flow of the working fluid as a result of the rise in the velocity ratio, 
i.e., the reduction in relative velocity difference between the pump 
impeller 1 and the turbine runner 2. Thus, it is possible to suppress the 
reduction in the capacity coefficient in the intermediate velocity ratio 
range. 
FIG. 4 presents graphs plotting the change in the capacity coefficient (c) 
against the velocity ratio (e). A dotted line indicates a fundamental 
characteristic curve of .theta..sub.3 =0 degrees before the adjustment, 
i.e., without the transfer limit means 22. A solid line indicates a 
characteristic curve of .theta..sub.3 =30 degrees with provision for the 
transfer limit means 22. A double-dotted line indicates a characteristic 
curve of the corresponding case having a blade angle .theta..sub.1. In 
case the capacity coefficient (c) at the velocity ratio 0 is set to an 
equal value, as is apparent from the graphs, the capacity coefficient (c) 
will decrease with an increase in the velocity ratio (e) with blade angle 
.theta..sub.1. In contrast, where a transfer limit means 22 is provided, 
the characteristics are such that the maximum capacity coefficient range 
is present in the intermediate velocity ratio range as in the fundamental 
characteristic curve corresponding to the case in which the transfer limit 
means 22 is not provided. 
Accordingly, with the coupling of the embodiment described above, a CVT 
equipped vehicle can have improved mileage, passing acceleration and the 
responsiveness. 
The present invention has been illustrated above by an embodiment described 
in detail, in which the arrangement and shape of the transfer limit means 
are defined according to the starting position of the bending base line, 
the angle of inclination with respect to the front edge of the blade, and 
the bending angle with respect to the plane containing the blade. Despite 
the detail of the foregoing description, however, the arrangement and 
shape of the transfer limit means can be modified in various respects 
without departure from the scope of the appended claims so long as the 
intended function of the transfer limit means is retained.