Plunging shaft coupling which permits both pivoting and plunging

A coupling for connecting two shafts to each other. The coupling allows one shaft to pivot about transverse axes and plunge toward and away from the other shaft. The coupling is well suited for use as the inboard plunging unit of a constant velocity joint for a front wheel drive vehicle. The shaft end is received in a splined opening formed in a trunnion. The trunnion is pivotably supported in a trunnion support body. The trunnion support body is in turn pivotably supported in slider blocks and the slider blocks are slidable within a drive canister or can. The sliding surfaces preferably include bearings formed of a high PV plastic material such as VESPEL.TM..

FIELD OF THE INVENTION 
The present invention relates to a coupling for use in a constant velocity 
joint for connecting two shafts so that rotation of one shaft about its 
own axis results in rotation of the other shaft about its axis. The 
present invention is particularly directed to a coupling for use as the 
inboard plunging joint of a constant velocity joint used in a front wheel 
drive of a motor vehicle. 
BACKGROUND OF THE INVENTION 
Constant velocity joints connect shafts such that the speeds of the shafts 
connected by the joint are absolutely equal at every instant throughout 
each revolution. This distinguishes constant velocity joints from simple 
universal joints. Specifically, if one of the shafts connected by a 
universal joint is revolving at an absolutely constant speed, then the 
other shaft will revolve at a speed that is, during two parts of each 
revolution, slightly greater and, during the other two parts of the 
revolution, slightly less than the constant speed of the first shaft. The 
magnitude of this fluctuation in speed increases as the angle between the 
axes of the two shafts increases. This disadvantage becomes of practical 
importance in applications requiring constant velocity such as front wheel 
driven vehicles and in the drives to independently sprung wheels where the 
angles between the shafts may be as large as 40.degree.. 
It is known that the speed variation problem can be solved by using two 
universal joints in series. If the joints are properly arranged, the 
irregularity introduced by one joint will be cancelled out by the equal 
and opposite irregularity introduced by the second joint. Constant 
velocity joints include such double universal joints as well as any joint 
in which the speeds of the shafts connected by the joint are absolutely 
equal at every instant throughout each revolution. Typically a constant 
velocity joint includes a shaft with a universal-type coupling at each 
end. This arrangement is sometimes referred to as a constant velocity 
shaft. 
In a front wheel drive vehicle, constant velocity drive shafts are always 
used in pairs. One shaft is located on the left (driver) side of the 
vehicle and the other is placed on the right (passenger) side. Each shaft 
has an inboard or plunge coupling that connects the constant velocity 
shaft to the engine/transaxle and an outboard or fixed coupling that 
connects the shaft to a left or right wheel. The inboard and outboard 
couplings and shaft together comprise a constant velocity joint or drive 
shaft which couples the engine/transaxle shaft to the wheel shaft. In 
operation, the outboard coupling turns with the wheel around a "fixed" 
center, while the inboard coupling "telescopes" or plunges and turns at an 
angle sufficient to allow required movement of the car's suspension 
system. 
Each coupling must be capable of pivoting at least about two transverse 
axes to the extent required by the specific application. For example, a 
compact constant velocity joint that provides power to the wheels 
typically must operate at angles of 40.degree. or more to meet the car's 
requirements for steering and suspension movements. Thus, each end of the 
joint must be able to move at least 20.degree.. 
Various constant velocity joints have been developed for use in motor 
vehicles. These include the Tracta joint manufactured in England by Bendix 
Limited, the so called Weiss joint manufactured in America by Bendix 
Products Corporation and a joint developed by Birfield Transmissions 
Limited. Today, there are two basic outboard joint designs and three basic 
inboard joint designs commonly in use. 
The two basic outboard front wheel drive couplings are the Rzeppa and the 
fixed tripod design. The Rzeppa design includes a cage, inner and outer 
races and a matched set of six balls guided by the cage. The fixed tripod 
design includes a three legged cross or trunnion fixed in a housing, a 
shaft end having a tulip shape, and tracks of circular cross-section to 
match the rollers. 
The three basic types of inboard front wheel drive couplings are the cross 
groove design, the double offset design and the tripod-plunge design. The 
cross groove design includes a cage, angled inner and outer races, and a 
matched set of six balls, guided by the cage for movement in the races. 
The double offset design is similar to the Rzeppa design and includes a 
cage, inner and outer races having grooves formed therein, and six balls 
guided by the cage. The tripod plunge design includes a three legged cross 
or trunnion and a bearing assembly fixed in place on a splined shaft. The 
assembly slides in a grooved tulip shaped housing. 
One of the basic requirements of the inboard plunging joint or coupling is 
that it must be able to transmit torque into the wheel axle. The 
previously mentioned inboard plunging couplings have performed 
satisfactorily in small cars with relatively low torque engines. However, 
such couplings have not performed well when applied to larger cars with 
higher torque engines. Accordingly, there have been attempts to increase 
the torque carrying capacity of known inboard plunging joints. 
One inboard plunging Joint: designed by General Motors to minimize ride 
disturbance induced by high angulation under high torque, known as 
"shudder", is shown in FIGS. 1 and 1A. This joint is called the S-plan 
joint and is said to provide shudderless operation. 
As shown in FIG. 1, the S-plan joint is a modified version of the tripod 
plunge design inboard joint. The S-plan joint typically includes a drive 
canister or housing 10 having axial grooves formed therein, a trunnion 30' 
having a splined shaft receiving opening and three legs, a bearing 
assembly 60 supporting each leg in an axial groove and a flexible boot 
assembly including a boot 40, sealing ring 41 and clamp 42 for sealing the 
interior of the joint. Snap rings 6 are provided to retain an 
engine/transaxle shaft 1 in the splined opening of the trunnion 30'. The 
principal difference between the S-plan joint and a conventional tripod 
plunge design PV joint is that the bearing assemblies 60 of the S-plan 
joint are square so that the torque transmitting surface area is increased 
significantly. The increased torque carrying capacity of this joint 
eliminates angulation under high torque (shudder). 
The principal disadvantage of the S-plan joint is that the square bearing 
assemblies 60 responsible for the improved torque capacity results are 
very intricate and expensive. As best shown in FIG. 1A, each square 
bearing assembly 60 includes an outer housing 62, outer races 61 and inner 
races 64 and a series of tiny needle bearings 63 between the outer race 61 
and inner race 64. This complex multi-part structure is quite expensive 
both in terms of cost of the parts and assembly time. This expense is 
significant since each vehicle requires six such bearing assemblies. 
Thus, there is a need for an inexpensive, easily assembled inboard plunging 
coupling capable of transmitting high torque. 
The present invention also relates to the use of bearing sleeves instead of 
rolling element bearings. 
This application relates, in part, to the use of sleeve bearings which can 
be used instead of expensive ball bearings. The principal limitation in a 
sleeve bearing's performance is the so-called PV limit. For instance, high 
edge loading causes a sleeve bearing to reach its PV limit. PV is the 
product of load or pressure (P) and sliding velocity (V). A sleeve bearing 
subjected to increasing PV loading will eventually reach a point of 
failure known as the PV limit. The failure point is usually manifested by 
an abrupt increase in the wear rate of the bearing material. 
As long as the mechanical strength of the bearing material is not exceeded, 
the temperature of the bearing surface is generally the most important 
factor in determining PV limit. Therefore, anything that affects surface 
temperature--coefficient of friction, thermal conductivity, lubrication, 
ambient temperature, running clearance, hardness and surface finish of 
mating materials--will also affect the PV limit of the bearing. 
Thus, the first step in selecting and evaluating a sleeve bearing is 
determining the PV limit required by the intended application. It is 
usually prudent to allow a generous safety margin in determining PV 
limits, because real operating conditions often are more rigorous than 
experimental conditions. 
Determining the PV requirements of any application is a three step process. 
First, the static loading per unit area (P) that the bearing must 
withstand in operation must be determined. For journal bearing 
configurations, the calculation is as follows: 
EQU P=W/(d.times.b) 
P=pressure, psi (kg/cm.sup.2) 
W=static load, lb (kg) 
d=bearing surface ID, in. (cm) 
b=bearing length, in. (cm) 
Pressure (P) should not exceed certain maximum values at room temperature. 
These can be derived from a table of allowable static bearing pressure for 
most known materials. Next, the velocity (V) of the bearing relative to 
the mating surface must be calculated. For a journal bearing experiencing 
continuous rotation, as opposed to oscillatory motion, velocity is 
calculated as follows: 
EQU V=(dN) 
where: 
V=surface velocity, in/rain (cm/min) 
N=speed of rotation, rpm of cycles/min 
d=bearing surface ID, in. (cm) 
Finally, calculate PV as follows: 
EQU PV(psi-ft/min)=P(psi).times.V(in/min)12 
or, in metric units: 
EQU PV(kg/cm.sup.2 -m/sec)=P(kg/cm.sup.2).times.V(cm/min)/6000 
The PV limits of unlubricated bearing materials are generally available 
from the manufacturer of the material or from technical literature. Since 
PV limits for any material vary with different combinations of pressure 
and velocity as well as with other test conditions, it is prudent to 
consult the manufacturer for detailed information. 
One material which is particularly well suited to bearing applications is 
the polyimide thermoset material sold by Dupont under the trademark 
VESPEL.TM.. Properly lubricated VESPEL.TM. parts can withstand 
approximately 1 million psi-ft/min. 
SUMMARY OF THE INVENTION 
The present invention obviates the problems experienced with prior designs 
by providing a high torque plunging coupling which is much less expensive 
than the S-Plan-type coupling. Accordingly, it is expected that results 
equal to or better than the S-plan joint or coupling can be achieved at 
much lower cost. The coupling is useful in any environment requiring a 
plunging coupling, but is believed particularly useful as the inboard 
plunging coupling in a front wheel drive vehicle. 
The coupling of the present invention includes a drive canister, a trunnion 
and a trunnion support member. The drive canister includes a housing 
having a plurality of axial grooves formed therein. (The grooves 
preferably include planar surfaces). If desired, these grooves may include 
linings or coatings of a low friction, high PV plastic material such as 
VESPEL.TM.. The grooves are arranged in the drive canister so as to 
provide a cruciform-shaped opening extending axially inward from one end 
of the drive cannister to define an open end. The open end of the drive 
canister is adapted to receive the trunnion and trunnion support member 
for plunging movement in the axial grooves. The drive canister may have 
either a male spline or female spline end cap at the other end thereof. 
The trunnion comprises a substantially cylindrical body and spherical ends. 
The cylindrical body has bearing surfaces at its distal ends and a central 
cylindrical portion having a splined bore formed therein. The splined bore 
has an axis which is transverse to the longitudinal axis of the 
cylindrical body. Preferably, the bearings are simple cylindrical sleeves 
formed of a plastic material such as VESPEL.TM. having a high PV. 
Alternatively, rolling element bearings can also be used, but this 
increases cost and complexity. 
The trunnion support member comprises a body having a cross-sectional shape 
substantially complimentary to the shape of the open end of the drive 
canister so that the trunnion support member can slide axially within the 
axial grooves in the drive canister. The trunnion support member comprises 
a central body portion, a pair of coaxial cylindrical stub portions 
extending from opposite sides of the central body portion, and a pair of 
slider bearing blocks mounted on the cylindrical stub portions of the 
trunnion support member. 
The slider bearing blocks have cylindrical openings formed therein so that 
the blocks can be mounted on the cylindrical stub portions of the trunnion 
support member. The blocks also have outer surfaces which are 
complimentary to grooves formed in the drive canister such that the outer 
portion of the slider bearing blocks are slidable along the axial grooves 
formed in the drive canister. 
Preferably, the outer surfaces are planar so as to slide along 
corresponding planar surfaces of the axial grooves. The planar contact of 
the slider block with the planar surface of the groove allows such sliding 
but precludes rotation of the slider block in the grooves. The cylindrical 
stub portions are pivotable with respect to the slider bearing block to 
allow pivoting of the trunnion support member within the drive canister 
about the axis of the cylindrical stub portion. 
The central body portion of the trunnion support member includes a 
cylindrical trunnion receiving bore having an axis which is transverse to 
the axis of the cylindrical stub portions. The central body portion 
further includes an elongated opening shaped to allow swinging motion of a 
shaft supported in the splined opening of the trunnion in the plane of the 
axis of the cylindrical stubs but a point located on the axis of the 
trunnion receiving bore. In this way, the elongated opening acts as a 
cylindrical bore with a range of axes all of which are coplanar with the 
axes of the cylindrical stubs and transverse to the axis of the trunnion 
receiving bore. This elongated opening allows the splined receiving 
opening to remain uncovered during a predetermined angular motion of about 
25 degrees. It follows that a shaft received in this opening has a freedom 
of movement of about 25 degrees in each direction for a total of roughly 
50 degrees. 
Preferably, bearings are provided at each surface where there is movement, 
i.e., rotation or sliding movement. The most suitable such bearing appears 
to be simple sleeves or lining of a plastic material having a low 
coefficient of friction and a high PV. Of course, other bearings such as 
rolling element bearings could be provided, but that would increase cost 
and complexity. 
In the assembled state, the splined opening of the trunnion receives a 
shaft end. The shaft end extends through the elongated opening formed in 
the trunnion support member. The elongated opening allows the shaft to 
pivot with the trunnion about the axis of the trunnion to the degree 
permitted by the elongated opening. Preferably the range of pivoting 
between the edges of the elongated opening is about 25 degrees in each 
direction for a total of 50 degrees. The shaft is also pivotable with the 
trunnion support member about the axes of the cylindrical stub. In this 
case, the pivoting movement occurs between the cylindrical stub and the 
cylindrical bores of the slider blocks. Finally, the shaft can plunge 
axially with the slider bearing blocks relative to the drive canister. In 
this case, the motion is between the outer surfaces, preferably planar, of 
the sliding bearing blocks and the axial grooves formed in the drive 
canister. Thus, collectively, the coupling allows pivoting about 
transverse axes and plunging relative to the drive canister. This 
satisfies the requirements of an inboard plunging coupling used in a CV 
joint in a front wheel drive vehicle. Of course, the coupling may have 
other applications for which it is well suited. Finally, since the 
coupling is constructed of relatively few components, it can be 
inexpensively produced on a large scale.

DETAILED DESCRIPTION OF THE INVENTION 
FIGS. 2, 2A, 3 and 3A illustrate the coupling of the present invention in 
an assembled state. The coupling of FIGS. 2 and 3 and the coupling of 
FIGS. 2A and 3A are identical except that the end cap 13 of the coupling 
in FIGS. 2A and 3A is formed with a female spline, whereas the end cap 13 
of the coupling of FIGS. 2 and 3 is formed with a male spline. The 
couplings are in all other respects identical and are discussed 
hereinafter together. 
As shown in the side views of FIGS. 2 and 2A, the coupling includes a drive 
canister or can 10 having an outer housing or shell 12 which, as best 
shown in FIGS. 7 and 7A, has two open ends. One end of the housing 12 is 
closed by an end cap 13. The end cap 13 is formed with a shaft connection 
in the form of a spline which may be either a male spline (FIG. 2) or a 
female spline (FIG. 2A). The drive canister 10 is formed with a plurality 
of axial grooves 11. In the illustrated embodiment, one pair of opposed 
axial grooves 11 have planar faces 11p. Preferably, the planar faces 11p 
include linings of a plastic material such as VESPEL.TM., having a low 
coefficient of sliding friction. The grooves may, as shown in FIG. 7A, 
define a cruciform shaped opening in the end of the canister outer housing 
or shell 12. 
The coupling also includes a trunnion 30 of the type depicted separately in 
FIGS. 4 and 4A. The trunnion has a cylindrical body and rounded ends 35 
which can be seen in FIGS. 2 and 2A. The cylindrical body of the trunnion 
includes a central cylindrical body portion and sleeve bearings at its 
distal ends. The trunnion 30 has a splined opening 37 formed in the 
central cylindrical body portion. As best seen in FIGS. 3 and 3A, the 
splined opening 37 is accessible through an elongated opening formed in 
the trunnion support member discussed below. 
The trunnion 30 is received in a cylindrical bore 57 in the trunnion 
support member 50, the components of which are depicted in FIGS. 5, 5A, 
5B, 6, 6A, 10, 10A and 10B. The trunnion support member includes 
cylindrical stubs 53 mounted in slider bearing blocks 58 and a central 
body part 51 having a trunnion receiving bore formed therein. As best 
shown in FIGS. 3 and 3A, the trunnion support member 50 has an elongated 
opening 52 formed therein such that the portion of the trunnion in which 
the splined opening 37 is formed is accessible when the trunnion is turned 
through a predetermined angular range. 
In operation, the splined shaft receiving opening 37 formed in the trunnion 
receives the end of a shaft of the type shown in FIG. 1. A shaft so 
supported can pivot with the trunnion 30 about the longitudinal axis of 
the trunnion through the range of movement permitted by the elongated 
opening 52. Further, the shaft and trunnion can pivot with the trunnion 
support member about the axis of the cylindrical stubs 53 and the shaft, 
trunnion, and trunnion support member can slide with the slider bearing 
blocks 58 in the axial grooves 11 formed in the drive can or canister 10. 
Thus, a shaft received in the splined opening 37 in the trunnion can pivot 
about transverse axes and plunge relative to the drive canister or can as 
required for the inboard plunging joint of a constant velocity joint using 
a front wheel drive vehicle. 
Moreover, because of the planar contact between the slider bearing block 58 
and the axial grooves 11, this particular coupling has a very high torque 
capability. All of these advantageous operational results are achieved 
with a structure which has very few parts and in which the parts are 
relatively simple and easy to assemble. Thus, this coupling can be 
manufactured at a much lower cost than known couplings having similar 
capabilities. 
To enable a better understanding of the components of the present 
invention, a number of the important components will be discussed 
hereinafter with specific reference to FIGS. 4-10B. 
FIGS. 4 and 4A and 9 and 9A show the details of the components of the 
trunnion 30 of the present invention. Specifically, as shown in FIGS. 4 
and 4A, the trunnion body includes a central portion 32 having a splined 
bore 37 formed therein. The ends 35 of the trunnion are spherically shaped 
to facilitate the required pivoting motion of the trunnion support member 
50 as discussed above. The distal ends of the cylindrical portion of the 
trunnion 31 have a reduced diameter so as to allow a bearing, preferably a 
sleeve bearing, to be mounted on these distal ends 31. 
The construction of the sleeve bearings 38 provided on the distal ends of 
the trunnion 30 is shown in FIGS. 9 and 9A. As shown, the bearing is 
preferably a simple sleeve of a plastic material such as VESPEL.TM. having 
a low coefficient of sliding friction and a high PV. Naturally, if 
desired, rolling element bearings could be used instead, but this would 
dramatically increase the cost at assembly time involved in manufacturing 
the coupling. 
The configuration of the trunnion support member 50 is shown in FIGS. 5, 5A 
and 5B and in FIGS. 10, 10A and 10B. As shown in FIGS. 5, 5A and 5B, the 
trunnion supporting member 50 includes a body portion 51 having a trunnion 
receiving bore 58 formed therethrough. The trunnion receiving bore 58 is 
preferably cylindrical. The trunnion supporting member 50 further includes 
a pair of coaxial cylindrical stub portions 53 extending from the opposite 
sides of the body 51. An elongated opening 52 is formed in the body 51. 
The shape of the opening 52 is preferably constructed as the projection of 
a shaft which pivots about the axis of the trunnion receiving bore on a 
plane transverse to the axis of the trunnion receiving bore, which plane 
includes the axis of the cylindrical stub portions 53. In this way, the 
opening is shaped to permit angular movement of a shaft received in the 
shaft receiving opening 37 of the trunnion 30 for a predetermined angular 
movement (a) in either direction from the central direction for a shaft 
having diameter (d). In order to meet the requirements of a constant 
velocity joint for use in a front wheel drive vehicle, the range of 
movement should be about 50.degree. of total motion (25' in either 
direction). The range of angular motions (a) is best depicted in FIG. 5B. 
As explained previously, a slider bearing block 58 is supported on each of 
the cylindrical stub portions 53. The construction of the slider bearing 
block is best shown in FIGS. 10, 10A and 10B. As shown therein, the slider 
bearing block 58 has a rectangular, preferably square, outer shape. The 
outer periphery includes planar surfaces 58p complimentary to the planar 
surfaces 11p of the axial grooves 11 formed in the drive canister 10 so 
that the outer surfaces 58p of the slider bearing block 58 can slide 
within the axial grooves 11. The slider bearing block 58 further includes 
a cylindrical bore formed therein to receive the cylindrical stub portion 
53. The cylindrical stub portions 53 are supported in the cylindrical bore 
such that both the trunnion support member 53 and the trunnion 30 are 
pivotable relative to the slider bearing block 58. To facilitate such 
pivoting, a bearing sleeve is mounted between the cylindrical stub portion 
53 and the cylindrical bore of the slider bearing block 58. Again, the 
preferred form of bearing is a sleeve of high PV plastic material such as 
VESPEL.TM.. 
An example of a suitable sleeve bearing is shown in FIGS. 6 and 6A. As 
shown therein, the sleeve bearing is a simple ring 72 of a high PV plastic 
material such as VESPEL.TM.. The ring is preferably secured by an adhesive 
or the like to either the cylindrical stub 53 or the cylindrical bore 
formed in the slider bearing block 58. Generally, it is better to secure 
the bearing ring 72 to the cylindrical stub 53 since this increases the 
sliding surface area (the outer surface of the bearing ring has a slightly 
greater surface area than the inner surface). 
Finally, the construction of the housing or shell portion 12 of the drive 
canister 10 is shown in FIGS. 7 and 7A. As shown in these figures, the 
shell 12 has a generally cylindrical outer peripheral shape and is formed 
with axial grooves 11 as best shown in FIG. 7A. The axial grooves define a 
generally cruciform opening in the end of the drive canister in which the 
assembled trunnion and trunnion support member fit. The axial grooves 11 
on which the slider bearing blocks 58 slide are planar so that planar 
contact is established between the slider bearing blocks 38 and the axial 
grooves 11. Such planar contact enables a great deal of torque to be 
transmitted between the two members. This contributes to the high torque 
capacity of this coupling. Moreover, the contact of these planar surfaces 
prevents rotation of the slider block 58 in the groove 11. 
To facilitate sliding between the slider bearing block 58 and the axial 
grooves 11 of the drive canister 10, a bearing is provided between the 
sliding surfaces. Again, a rolling element bearing could be used, but this 
is complicated and expensive. Instead, it is preferable to provide a layer 
or a sleeve of high PV plastic material between the sliding surfaces. 
Thus, a sleeve or insert 73 of high PV plastic material is preferably 
mounted on the planar surfaces of the axial grooves 11 of the drive 
canister on which the slider bearing blocks 58 slide. An example of such a 
sleeve or layer of high PV material is shown in FIG. 8. 
From the foregoing description, it should be apparent how the coupling of 
the present invention satisfies the operational requirements for a 
coupling used as an inboard plunging coupling of a front wheel drive 
vehicle constant velocity joint. Specifically, as previously noted, the 
requirements of such a coupling are a limited amount of pivoting about two 
transverse axes and a limited degree of plunging motion in the direction 
which is transverse to both of the axes about which pivoting occurs. In 
the case of the coupling of the present invention, the shaft receiving 
opening 37 of the trunnion 30 can receive a shaft. Once the shaft is 
received in the opening 37 it is pivotable about the axis of the trunnion 
30 and also pivotable about the axis of the cylindrical stubs 53. Further, 
the shaft can be plunged axially relative to the drive canister 10. In 
this way, the present invention provides a simple and inexpensive high 
torque coupling suitable for use as the inboard plunging unit of a 
constant velocity joint of a front wheel drive vehicle and in other 
applications where similar motion is required.