The present invention relates to an amphibious vehicle having a decoupler
for coupling/decoupling a drive shaft of the vehicle, and more particularly to an
amphibious vehicle having a drive-shaft decoupler for engaging and disengaging a
drive shaft which driveably connects an output from a power train of the vehicle
with the wheels or marine propulsion system of the vehicle. Such an amphibious vehicle
is described in DE-A-1 530 577, for example.
It has been found convenient to drive the marine propulsion systems
of an amphibious vehicle through the transmission by which the wheels are also driven.
With this arrangement it is necessary to disengage the drive to the wheels while
the drive to the marine propulsion is engaged when the amphibious vehicle is in
water mode. It is also desirable to be able to decouple and couple the drive to
the wheels and marine propulsion system independently of one another as the vehicle
makes the transition between land and marine modes of travel.
In the case of a transmission which incorporates a final-drive and
differential unit as an integrated part of the whole transmission, it would only
be possible to incorporate a decoupler into the transmission by designing a new
internal arrangement. For amphibious vehicles, which are used in specialized applications
and are produced in relatively low volumes, a dedicated transmission would be prohibitively
Therefore, on an amphibious vehicle in which the engine drives the
road wheels and the marine propulsion system through an integrated transmission/differential,
it has been found necessary to provide external drive shaft decouplers to disconnect
the drive between the differential and the driven wheels, and between the transmission
and the marine propulsion system. Typically a decoupler is provided in the driveline
between the transmission and each driven wheel. However, it is possible to use a
decoupler in the driveline between the transmission and only one of the driven wheels,
since disconnecting drive to one of the driven wheels will effectively disengage
drive to both wheels due to the effects of the differential.
A problem with known external drive shaft decouplers is the amount
of extra space they require. This is a particular problem in amphibious vehicles
in which the wheels are designed to retract upwardly and inboard of the vehicle
for use of the vehicle in water. In such vehicles the provision of wheel retraction
systems and specialized suspension systems reduces the available space for external
drive shaft decouplers.
A further problem which arises is the need to synchronise the speeds
of the input and output means of the decoupler when drive is being coupled. This
problem arises, for example, when the vehicle is preparing to leave the water with
the wheels deployed. In these circumstances it is necessary for drive to be maintained
to the marine propulsion system, in order to push the vehicle towards the shore,
whilst drive to the road wheels is coupled. This enables the vehicle to propel itself
out of the water using a combination of drive from the marine propulsion system
and the road wheels. It is necessary, therefore, for the decoupler to have a clutch
means to progressively engage the drive between the differential output of the transmission
(which may be spinning at 1000 RPM), and a rotating assembly consisting of the drive
shaft, brake disc, hub and wheel (which initially will be stationary in the water)
representing the inertia to be overcome.
A similar problem arises when the vehicle enters the water, when it
is desirable to couple drive to the marine propulsion system whilst drive to the
road wheels is maintained. This enables a smooth transition from land to waterborne
use of the vehicle but requires a stationary marine propulsion system to be coupled
to a rotating power take-off shaft of the transmission.
Furthermore, where the decoupler is to be used in the driveline between
the transmission and a drive shaft for a wheel of an amphibious vehicle, the decoupler
must be capable of handling the high torque loads which are experienced by the drive
shaft. For example very high torque loads are experience in such drive shafts when
drive to the wheels is engaged, wherein engine torque (say 250 Nm) is multiplied
by a first gear ratio (say 4:1) times a final drive ratio (say 3.5:1) :
250 x 4 x 3.5 = 3500 Nm
When shock-loads from wheel/ground-contact torque reactions are factored
in, it is common to allow for 10-12,000 Nm peak torque loads for the drive shafts
of an average sized road vehicle.
It is an object of the invention to provide an amphibious vehicle
having a decoupler which is capable of meeting the above requirements and which
requires less space than known decouplers.
In accordance with the invention there is provided an amphibious vehicle
comprising a decoupler for coupling/decoupling drive between an output from a the
vehicle power train and a component to be driven, characterised in that the decoupler
comprises a synchroniser adapted to synchronise the speed of an input means and
an output means of the decoupler when drive is being coupled, and in that the decoupler
forms part of an integrated unit also comprising a constant velocity joint.
By integrating a decoupler with synchroniser and a constant velocity
joint into a single unit, the integrated unit can be positioned in the space usually
taken up by a conventional constant velocity joint. Thus, the integrated unit requires
less space than would be the case if a separate decoupler and constant velocity
joint were to be used. Furthermore, there is a reduction in the number of components
required and the mounting arrangements are simplified. This reduces the weight of
the vehicle, the manufacturing and assembly costs of the vehicle and improves reliability.
In a particularly preferred embodiment the synchroniser is a synchromesh
device comprising a baulk-ring and a cone, the baulk-ring and cone of the synchroniser
providing a graduated drive engagement means.
This arrangement has the added advantage that a known synchromesh
device from a conventional gearbox can be adopted for use in the decoupler. This
enables the synchroniser device of the decoupler to be manufactured using commercially
available components at much lower cost than would be the case if the components
were to be purpose designed and manufactured.
Whilst known synchromesh devices, as found in a conventional manual
gearbox, perform the tasks of clutching and coupling/decoupling in a combined operation
as an integrated mechanism, such devices have not previously been employed for other
than their designed purpose of manual gear selection inside the conventional gearbox.
In this respect it should be noted that the inertia loads residual in gearbox internal
shafting are very much lower than those of a drive shaft and wheel submerged in
water. Also drive torque in a gearbox is not subject to final-drive multiplication
and extreme wheel-to-ground shock-loading.
However, extensive analysis and tests have indicated that the clutching
requirement of a drive shaft decoupler for an amphibious vehicle could be sustained
by a synchromesh comprising a baulk-ring and synchro-cone, provided it is subjected
to a greatly reduced number of application cycles than that normally experienced
in the life of a gearbox.
Subsequent extensive testing based on the precise requirements of
a drive shaft decoupler for an amphibious vehicle with regard to inertia loadings,
road-load inputs, torsional vibration frequencies, and amphibious duty-cycles, have
proved that a heavy goods vehicle gearbox synchromesh is capable of performing these
unaccustomed tasks of high-inertia clutching and high-torque coupling, while fitting
within the cost and space specifications when designed into a dedicated decoupler
casing as shown herewith.
An embodiment of the present invention will now be described by way
of example only with reference to the accompanying drawings in which:
- Figure 1 is a section through a decoupler of an amphibious vehicle in accordance
with the invention, the decoupler is shown in the position in which drive is disengaged
- Figure 2 is view similar to that of Figure 1 but showing the decoupler in the
position in which drive is engaged or coupled; and
- Figure 3 is a schematic plan view in section of an amphibious vehicle in accordance
with the invention, showing a drive train including an engine, gearbox and three
decouplers of the type shown in Figures 1 and 2.
Referring firstly to Figure 1, a decoupler incorporating a constant
velocity CV joint is indicated generally at 10. The decoupler 10 is of the form
of an integrated unit, which is housed in a casing 12. A driving shaft 14, which
may be from the output stage of a gearbox or from a differential (not shown), enters
the casing 12 through a circular aperture 16 to the left hand side of the casing
12 (as viewed), and is free to rotate within the casing. An oil seal 18 seals between
the driving shaft 14 and the aperture 16. The driving shaft 14 comprises an input
of the decoupler 10.
The driving shaft 14 terminates inside the casing 12 in a flange 20,
the periphery of which is splined 22. A drive ring 24, which is correspondingly
internally splined, is in permanent driving engagement with the spline 22 and rotates
with the driving shaft 14. A circumferential slot 26 is provided in the periphery
of the drive ring 24, and a selector arm 28 locates in the slot 26. A rod 30, which
is mounted for reciprocating movement, indicated by arrow A, in a bore 32 of the
casing 12, mounts the selector arm 28 at one end. A linkage (not shown) is provided
to enable an operator of an associated vehicle (80, Figure 3) to selectively slide
the rod 30 and selector arm 28 to a required position. Alternatively the movement
of the rod 30 can be remotely controlled by means of a pneumatic or hydraulic cylinder
A CV joint indicated generally at 34 is rotatably mounted in ball
bearings 36 in the right hand side of the casing 12 (as viewed). An oil seal 38
seals between the casing 12 and the CV joint 34, with the roller bearings 36 sealed
in a protected position inside the casing 12. The oil seal 38 and the roller bearings
36 are positionally aligned and supported in the casing 12 by a pair of circlips
The end of the CV joint 34 facing the flange 20 of the driving shaft
14 is stepped at 42. A stepped cap 44 is rigidly mounted on the stepped end 42.
The periphery of the outer step of the cap 44 is splined at 46, and the periphery
of the inner step is provided with a synchro-cone 48. The spline 46 has the same
form as the spline 22.
A baulk ring 50 formed as a truncated cone extending into a flange,
is located between the stepped cap 44 of the CV joint 34, and the flange 20 of the
driving shaft 14. The periphery of the flange of the baulk ring 50 is splined at
52, and the spline 52 also has the same form as the splines 22 and 46. The flange
20, the baulk ring 50 and the outer step of the cap 44 are of the same diameter
and are concentric.
The CV joint 34 is of the "RZEPPA" type, and comprises splines 54,
a plurality of roller balls 56, and a driven shaft 58 which comprises an output
of the decoupler. Typically there are three or four roller balls 56 mounted in equally
spaced arrangement about the periphery of the end of the drive shaft 58. The CV
joint 34 is capable of an articulation of up to 45° away from the axis of the driving
shaft 14 and includes a conventional dust gaiter (not shown) which extends between
the drive shaft 58 and a groove 59 provided in the body of the CV joint 54.
Although in the preferred embodiment the CV joint is of the Rzeppa
type, it should be understood that any suitable type of CV joint could be used.
For example, the CV joint could be any of the following: Tracta, Weiss, Tripode,
AC, VL, UF, UFC, GI, GE, GIC, ARR or Triplan type.
The operation of the decoupler 10 will now be described with reference
also to Figure 2. In Figure 1 the decoupler 10 is shown uncoupled and coupling is
effected by movement of the rod 30 to the right as viewed. As the rod 30 is moved,
for example, by a hydraulic cylinder, (not shown) the selector arm 28, which is
engaged in the circumferential slot 26 of the drive ring 24, moves the drive ring
24 in the spline 22 towards the CV joint 34. The internal spline of the drive ring
24 engages the spline 52 of the baulk ring 50, and pushes the baulk ring 50 onto
the synchro-cone 48. The baulk ring 50 rotates at the speed of the driving shaft
14 and the frictional contact between the conical part of the baulk ring 50 and
the synchro-cone 48, synchronises the speed of the stepped cap 44 and the CV joint
34 with the speed of the driving shaft 14. The arrangement of the baulk ring 50
synchro-cone 48 and drive ring 24 is commonly known as a synchromesh device.
Further movement of the drive ring 24 by the selector arm 28 causes
the drive ring 24 to slide to a position engaging both the spline 46 of the cap
44 and the spline 22 of the driving shaft flange 20, as shown in Figure 2. The full
torque of the driving shaft 14 can then be passed through the drive ring 24 to the
driven shaft 58 of the CV joint 34.
Referring now to Figure 3, an amphibious vehicle, indicated generally
at 80, has a transverse power train 60. The power train 60 comprises an engine 62,
an in-line gear box 64, a differential unit 66 driven from the gearbox and a transfer
gearbox 67 driven from the differential. Drive is provided from the differential
to a pair of drive shafts 68 which drive the rear wheels 69 of the vehicle, and
from the transfer gearbox 67 to a third shaft 70 which drives a marine propulsion
system in the form of a water jet 71. A decoupler 10, of the kind described above
in relation to Figures 1 and 2, is provided between each of the rear wheel drive
shafts 68 and the differential 66 and between the drive shaft 70 and the transfer
gearbox 67. The decouplers 10 allow drive to be selectively and independently connected
between the differential 66 and each of the rear wheel drive shafts 68 and between
the transfer gearbox and the water jet drive shaft 70. In the arrangement shown,
the drive shafts 68, 70 comprise the same part as the drive shaft referenced 58
in Figures 1 and 2.
In the embodiment shown in Figure 3, a decoupler 10 is provided for
each of the rear wheel drive shafts 68. However, in an alternative embodiment, a
decoupler 10 may be provided for only one of the rear wheel drive shafts 68, the
other drive shaft 68 being provided with a conventional CV joint or the like. Those
skilled in the art will readily understand that decoupling drive to one of the rear
wheels will effectively disengage drive to both of the rear wheels, due to the effects
of the differential 66.
Similarly, it may not be considered essential to provide a decoupler
in the marine propulsion system drive, as it is feasible to allow the marine propulsion
unit to freewheel when the amphibious vehicle is driven in road mode. This entails
a small loss of power, which is undesirable; but allows simplification of the marine
Some amphibious vehicle power trains do not require any road wheel
decouplers. These include power trains where the marine power takeoff is upstream
of the road wheel transmission. For example, a sandwich power takeoff may be used
between the engine and transmission, as shown in Figure 1 of our co-pending application
no. GB0020887.6. In this case, road wheel decouplers are not required, because drive
to the road wheels can be decoupled simply by placing the gearbox in neutral gear.
Road wheel decouplers are also not required where the marine power
takeoff is from the timing end of the crankshaft, for example according to Figure
2 of our co-pending application no. GB0021007.0.
It will be understood from the above that although Figure 3 shows
an amphibious vehicle with a transverse engined power train, the decoupler 10 is
equally suitable for use with a longitudinally engined power train or indeed any
power train arrangement suitable for use in an amphibious vehicle.
The decoupler 10 is especially suitable for use in an amphibious vehicle
because of the limited space around the engine and drive shafts, and the need to
keep the weight of the vehicle to a minimum.
It is not intended that the decoupler 10 be used to couple drive between
the transmission and the wheels when the vehicle is on land when the torques to
be coupled would be high. Rather, it is intended that the decoupler 10 will be used
to couple drive to the wheels when the vehicle is afloat in water and the wheels
(not shown) are able to spin almost unimpeded. By the time that the wheels reach
land, the driving ring 24 of the decoupler 10 is fully engaged with the spline 46
of the CV joint. Furthermore, coupling of the drive shaft 70 and of the wheel drive
shafts 68 will occur when the gearbox is in low gear, with the engine running at
low speed. This reduces the inertia to be overcome in synchronising speeds of the
drive shafts 68, 70 with the driving shaft 14.