U.S. patent application number 09/767869 was filed with the patent office on 2001-08-16 for vehicle transmission apparatus.
Invention is credited to Szymkowiak, Zbigniew.
Application Number | 20010013433 09/767869 |
Document ID | / |
Family ID | 26243470 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013433 |
Kind Code |
A1 |
Szymkowiak, Zbigniew |
August 16, 2001 |
Vehicle transmission apparatus
Abstract
The ATV transmission includes an epicyclic arrangement, which
serves as a drive-differential. One road wheel is geared to the
planet-carrier or spider, and the other to the ring gear, while the
engine drives the sun. An idler-gear between the ring and its road
wheel means that the ring and the spider rotate in opposite senses,
whereby a large gear ratio between the sun and the road wheels can
be provided. Steering of the vehicle is provided, by driving the
road wheels at different speeds. This is accomplished using a
steer-differential, which is identical to the drive-differential;
rotating the sun of the steer-differential imposes a corresponding
differential speed on the road wheels.
Inventors: |
Szymkowiak, Zbigniew;
(Waterloo, CA) |
Correspondence
Address: |
Anthony ASQUITH
173 Westvale Drive
Waterloo
ON
N2T 1B7
CA
|
Family ID: |
26243470 |
Appl. No.: |
09/767869 |
Filed: |
January 24, 2001 |
Current U.S.
Class: |
180/6.2 |
Current CPC
Class: |
B60K 17/34 20130101;
F16H 2048/106 20130101; B62D 11/16 20130101; B62D 11/18 20130101;
F16H 48/10 20130101; B60K 17/16 20130101; F16H 48/11 20130101 |
Class at
Publication: |
180/6.2 |
International
Class: |
B62D 011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2000 |
GB |
0001605.5 |
Nov 29, 2000 |
GB |
0029118.7 |
Claims
1. An all-terrain vehicle, having left and right co-axial road
wheels, wherein: the vehicle includes a drive-transmission; the
drive-transmission includes: a drive-sun-gear; a
drive-planet-carrier, or drive-spider; at least one
drive-planet-gear; a drive-ring-gear; a drive-idler-gear; all of
which are rotatable, for operation of the vehicle, about respective
axes of rotation; the drive-spider is mounted co-axially with the
drive-sun-gear, and is rotatable relative to the drive-sun-gear;
the drive-planet-gear is in mesh with the drive-sun-gear; the axis
of the drive-planet-gear is parallel to, and spaced from, the axis
of the drive-sun-gear; the axis of rotation of the
drive-planet-gear is fixed in the drive-spider; the drive-ring-gear
is mounted co-axially with the drive-sun-gear, and is rotatable
relative to the drive-sun-gear; the drive-ring-gear is internal,
and is in mesh with the drive-planet-gear; the drive-transmission
includes a left-output-shaft, and a right-output-shaft; the
left-output-shaft and the right-output-shaft are adapted to drive
the respective road-wheels of the vehicle; the structure and
arrangement of the vehicle is such that the left road-wheel and the
right road-wheel are coaxial, and, in forwards motion of the
vehicle, rotate in the same sense; the drive-transmission includes
a drive-spider-gear-train and a drive-ring-gear-train; the
drive-spider-gear-train is effective to force the drive-spider and
the left-output-shaft to rotate at a drive-spider-train-ratio; the
drive-ring-gear-train is effective to force the drive-ring-gear and
the right-output-shaft to rotate at a drive-ring-train-ratio; the
drive-idler-gear is included in one of the said drive-gear-trains,
and is so arranged that the left-output-shaft and the
right-output-shaft, and hence the road wheels, rotate in the same
sense; and the vehicle includes an engine, and includes structure
that is effective to transmit motive power from the engine to the
drive-sun-gear.
2. Vehicle of claim 1, wherein the structure of the vehicle is such
that the ratio of the left road-wheel to the left-output-shaft is
fixed, and is such that the ratio of the right road-wheel to the
right-output-shaft is fixed.
3. Vehicle of claim 2, wherein the fixed ratio of the left
road-wheel to the left-output-shaft is the same as the fixed ratio
of the right road wheel to the right-output-shaft.
4. Vehicle of claim 3, wherein the left road wheel is mounted
directly on the left-output-shaft and the right road wheel is
mounted directly on the right-output-shaft.
5. Vehicle of claim 1, wherein: the drive-spider-train-ratio and
the drive-ring-train-ratio are unequal; Nsun is the number of teeth
on the drive-sun-gear and Nring is the number of teeth on the
drive-ring-gear; the drive-ring-train-ratio and the
drive-spider-train-ratio are so geared that the ratio of the
drive-ring-train-ratio to the drive-spider-train-ratio is
(1+Nsun/Nring) to one.
6. Vehicle of claim 1, wherein: the vehicle also includes a
steer-transmission: the steer-transmission includes: a
steer-sun-gear; a steer-planet-carrier, or steer-spider; at least
one steer-planet-gear; a steer-ring-gear; a steer-idler-gear; all
of which are rotatable, for operation of the vehicle, about
respective axes of rotation; the steer-spider is mounted co-axially
with the steer-sun-gear, and is rotatable relative to the
steer-sun-gear; the steer-planet-gear is in mesh with the
steer-sun-gear; the axis of the steer-planet-gear is parallel to,
and spaced from, the axis of the steer-sun-gear; the axis of
rotation of the steer-planet-gear is fixed in the steer-spider; the
steer-ring-gear is mounted co-axially with the steer-sun-gear, and
is rotatable relative to the steer-sun-gear; the steer-ring-gear is
internal, and is in mesh with the steer-planet-gear; the
steer-transmission includes a steer-spider-gear-train and a
steer-ring-gear-train; the steer-spider-gear-train is effective to
force the steer-spider and one of the left- and right-output-shafts
to rotate at a steer-spider-train-ratio; the steer-ring-gear-train
is effective to force the steer-ring-gear and the other of the
left- and right-output-shafts to rotate at a
steer-ring-train-ratio; the arrangement of the drive-transmission
and the steer-transmission is such that the difference between the
rotational speed of the left-output-shaft from the rotational speed
of the right-output-shaft is determined by the speed of rotation of
the steer-sun-gear; and the steer-transmission includes an operable
steering-means, which is effective, when operated, to drive the
steer-sun-gear to rotate at a rotational speed proportional to the
steering needs of the vehicle.
7. Vehicle of claim 6, wherein the steer-transmission is in
substance identical to the drive-transmission.
8. Vehicle of claim 7, wherein the arrangement of the vehicle is
such that, when the steering-means is operated to steer the vehicle
in the straight-ahead direction, the speed of rotation of the
speed-sun-gear is zero.
9. Vehicle of claim 6, wherein: the steer-spider-gear-train
connects the steer-spider to the left-output-shaft; the
steer-ring-gear-train connects the steer-ring to the
right-output-shaft; the drive-spider-gear-train connects the
drive-spider to the left-output-shaft; the drive-ring-gear-train
connects the drive-ring to the right-output-shaft.
10. Vehicle of claim 9, wherein: the steer-spider-gear-train
includes gear teeth on the steer-spider which are in direct mesh
with gear teeth on the left-output-shaft; and the
drive-spider-gear-train includes gear teeth on the drive-spider
which are in direct mesh with the said gear teeth on the
left-output-shaft.
11. Vehicle of claim 10, wherein: the steer-ring-gear-train
includes gear teeth on the steer-ring which are geared to gear
teeth on the right-output-shaft; the drive-ring-gear-train includes
gear teeth on the drive-ring which are geared to the said gear
teeth on the right-output-shaft.
12. Apparatus of claim 6, wherein: the drive-idler-gear is included
in the drive-spider-gear-train; the steer-idler-gear is included in
the steer-spider-gear-train; the drive-spider-gear-train and the
steer-spider-gear-train are so arranged that the drive-idler-gear
and the steer-idler-gear are one and the same gear.
13. Apparatus of claim 6, wherein: the drive-idler-gear is included
in the drive-ring-gear-train; the steer-idler-gear is included in
the steer-ring-gear-train; the drive-ring-gear-train and the
steer-ring-gear-train are so arranged that the drive-idler-gear and
the steer-idler-gear are one and the same gear.
14. Vehicle of claim 6, wherein: the drive-ring-gear-train includes
the drive-idler-gear; the steer-ring-gear-train includes the
steer-idler-gear; the drive-idler-gear and the steer-idler-gear are
formed as one and the same idler-gear-component; the
drive-ring-gear is in direct mesh with gear teeth on the said
idler-gear-component; the steer-ring-gear is in direct mesh with
gear teeth on the said idler-gear-component; and the
idler-gear-component is in direct mesh with the gear-teeth on the
right-output-shaft.
15. Vehicle of claim 14, wherein the axes of rotation of the
steer-sun-gear, the steer-spider, the steer-planet-gear, the
steer-ring-gear, the drive-sun-gear, the drive-spider, the
drive-planet-gear, the drive-ring-gear, the idler-gear-component,
and the left- and right-output-shafts, are all parallel.
16. Vehicle of claim 15, wherein: the components recited in claim
15 are housed in a common transmission housing; the transmission
housing is in two halves, which are bolted together; respective
abutment faces on the two halves are thereby brought into contact;
the split plane defined by the abutment faces is perpendicular to
the said axes.
17. Vehicle of claim 6, wherein: NSS is the number of teeth on the
steer-sun-gear and NSR is the number of teeth on the
steer-ring-gear; the steer-ring-train-ratio and the
steer-spider-train-ratio are so geared that the ratio of the
steer-ring-train-ratio to the steer-spider-train-ratio is
(1+NSS/NSR) to one.
18. Vehicle of claim 6, wherein the drive-ring-train-ratio, the
drive-spider-train-ratio, the steer-ring-train-ratio, and the
steer-spider-train-ratio remain constant during operation of the
apparatus.
19. Apparatus of claim 6, wherein the ratio of the
drive-ring-train-ratio to the steer-ring-train-ratio is the same as
the ratio of the drive-spider-train-ratio to the
steer-spider-train-ratio.
20. Apparatus of claim 19, wherein the drive-ring-train-ratio is
equal to the steer-ring-train-ratio.
21. Vehicle of claim 6, wherein: the vehicle includes two or more
left-side wheels which are drive-coupled together to rotate in
unison with the left-output-shaft; the vehicle includes two or more
right-side wheels, which are drive-coupled together to rotate in
unison with the right-output-shaft.
22. Vehicle of claim 6, wherein: the operable steering means
includes a steering-actuator, which is manually operable from a
straight-ahead position progressively to a steer-to-the-left
position, and progressively to a steer-to-the-right position; the
operable steering means includes a means for driving the
steer-sun-gear to rotate clockwise when the steering actuator is
moved to the steer-to-the-left position, and to rotate
anti-clockwise when the steering actuator is moved to the
steer-to-the-right position.
23. Vehicle of claim 22, wherein the steering means includes a
hydraulic motor coupled to the steer-sun-gear, and the
steering-actuator includes a means for supplying hydraulic fluid to
the motor at a flow rate that varies progressively in proportion to
the progressive operation of the steering-actuator.
Description
[0001] This invention relates to a transmission apparatus for a
vehicle. The apparatus is primarily intended for an all-terrain
vehicle, and for other vehicles in which the ratio between the
engine speed and the size of the road wheels tends towards the
high-engine-speed, low-wheel-speed end of the scale. The apparatus
is intended for use on vehicles of the kind in which skid-steering
has traditionally been employed, including tracked vehicles, and
vehicles in which a line of wheels on the right side are all
chained together and a line of wheels on the left side are all
chained together.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0002] Exemplary embodiments of the invention will now be described
with reference to the accompanying drawings, in which:
[0003] FIG. 1 is a cross-section of a transmission apparatus for a
vehicle;
[0004] FIG. 1a is a diagrammatic cross-section of the apparatus of
FIG. 1, showing the manner of interaction of some of the gears of
the apparatus;
[0005] FIG. 2 is a cross-section of a transmission apparatus, which
includes the apparatus of FIG. 1 as a component thereof;
[0006] FIG. 3 comprises the view of FIG. 2 in conjunction with an
end elevation of the apparatus.
[0007] FIG. 4a is a diagrammatic side-elevation of another
transmission apparatus that embodies the invention.
[0008] FIG. 5b is a diagrammatic plan-view of the apparatus of FIG.
4a.
[0009] The apparatuses shown in the accompanying drawings and
described below are examples which embody the invention. It should
be noted that the scope of the invention is defined by the
accompanying claims, and not necessarily by specific features of
exemplary embodiments.
[0010] FIG. 1 is a diagram of a differential unit 20 for a vehicle.
The power input to the differential is at input shaft 23, and the
outputs to the road-wheels of the vehicle are at left and right
output shafts 24,25. The unit 20 serves to allow the road-wheels to
adopt the different speeds relative to each other that the wheels
undergo when the vehicle is being steered around a curve. The
differential unit 20 of FIG. 1 is a "free" differential; that is to
say, if one road-wheel should lock, the other road-wheel is free to
rotate at twice the speed.
[0011] The input shaft 23 takes drive from either 1st drive gear 26
or 2nd drive gear 27, depending which has been selected by a
gear-selection mechanism (not shown in FIG. 1). (The extension 28
of the input shaft shown in FIG. 1 is for a brake.) The input shaft
carries teeth, which serve to define a sun-gear 29. Meshing with
the sun-gear 29 are a number of planet gears 30, carried on
respective spindles 32, the spindles being mounted in a spider 34.
The spider 34 is guided by needle-bearings 35 for rotation about
the input shaft 23. The spider 34 carries spider-output-teeth 36,
which mesh with the left-output-gear 37, which is unitary with the
left-output-shaft 24.
[0012] The planet gears 30 also mesh internally with the internal
gear-teeth of ring 38. The ring 38, like the spider 34, is guided
by bearings 39 for rotation about the input shaft 23. The ring 38
carries ring-output-teeth 40. The ring-output-teeth 40 mesh with a
right-output-idler-gear, which is not shown in FIG. 1, but which is
carried in the differential housing. FIG. 1 a shows the disposition
of the right-output-idler-gear 42, diagrammatically, as to its
manner of location. The right-output-idler-gear 42 also meshes with
the right-output-gear 43 on the right output shaft 25.
[0013] The spider 34 drives the left-output-shaft 24, and the ring
38 drives the right-output-shaft 25. The vehicle requirement is
that the two output shafts must rotate in the same sense.
Therefore, since the spider 34 and the ring 38 rotate in opposite
senses, the drive to one of the output shafts 24,25 must go through
an idler gear, whereby the rotation of that one output shaft is
reversed. This condition is met in the apparatus of FIG. 1, in that
the drive between the spider 34 and the left-drive-gear 37 is
direct, as shown, whereas the drive between the ring 38 and the
right-output-gear 43 goes through the right-output-idler-gear 42,
and is thereby made to rotate in the same sense as the
left-drive-gear 37.
[0014] As a result, since the ring and the spider rotate in
opposite senses, the two output shafts rotate in the same sense. It
should be understood that FIGS. 1 and la are diagrammatic:
naturally, the designer must see to it that the various gears can
lie in mesh with each other, and of course can be assembled. Also,
in most vehicles, the left and right output shafts have to be
co-axial. Thus, it may be required that both the left drive and the
right drive must go through intermediate gears: in that case, to
ensure that both output shafts turn in the same sense, whatever the
number of intermediate gears going to the left-output-shaft, there
must be one more, or one less, intermediate gears going to the
right-output-shaft.
[0015] In a sun and planet gear arrangement, in addition to the
fact that the spider and the ring rotate in opposite senses when
the sun is driven, the ratio between the sun and the spider is not
the same as the ratio between the sun and the ring. The ratios may
be determined as follows:
[0016] the sun rotates at Vsun, the ring at Vring, the spider at
Vspider;
[0017] the sun gear has Nsun teeth, and the ring gear has Nring
teeth;
[0018] if the spider 34 is held stationary (Vspider=0), the ring 38
rotates at a speed of Vring=Vsun*Nsun/Nring (in the opposite
rotational sense to the sun gear);
[0019] if the ring 38 is held stationary (Vring=0), the spider 34
rotates at a speed of Vspider=Vsun*Nsun/(Nring+Nsun) (in the same
rotational sense as the sun gear).
[0020] Generally, what is required in a vehicle is that, when the
left and right output shafts are rotating at the same speed, the
output shafts are then being driven with nominally the same torque.
In fact, during light driving, it would not really matter if the
left wheel were being driven with more torque than the right wheel.
But, if the vehicle is being driven in a heavy manner, it does
matter, because the more-vigorously driven wheel might tend to
spin. If more torque is being fed to the left wheel than to the
right wheel, the left wheel would be more likely to overcome its
frictional grip on the ground, and spin. But if both wheels are
being driven with the same torque, both have the same tendency to
spin, whereby the overall tendency for the wheels to spin is
minimised.
[0021] So, the designer should see to it that the overall gear
ratio between the sun gear 29 and the left shaft 24, via the spider
34, is the same as the overall gear ratio between the sun gear 29
and the right shaft 25, via the ring 38. When that is so, the
available torque is divided equally between the output shafts. That
is to say, in order for the available torque from the sun gear to
be divided equally between the two output shafts, when the two
output shafts are rotating at the same speeds, the overall ratio
between the sun and the left shaft, via the spider, must be the
same as the overall ratio between the sun and the right shaft, via
the ring.
[0022] Consider the case where the number of teeth in the ring
gear, Nring, is three times the number of teeth in the sun gear,
Nsun. Now, if the left shaft were driven at the same speed as the
spider, i.e if the gear ratio between the spider and the left shaft
is 1:1, the ratio between the ring and the right shaft would have
to be 4:3 (i.e the right shaft rotates slower than the ring), in
order for the left shaft and the right shaft to receive equal
torques. Similarly, if, instead, the right shaft and the ring were
geared 1:1, the spider and the left shaft would have to be geared
3:4 (i.e the left shaft rotates faster than the spider) in order
for the left and right shafts to receive equal torques.
Alternatively, if the left shaft and the spider were geared at say
3:2 (as is the case in FIG. 1), the right shaft and the ring have
to be geared at 2:1, for the shafts to receive equal torques.
[0023] In FIG. 1, the sun gear 29 has twenty-three teeth and the
ring 38 has sixty-nine internal teeth (for a 3:1 ratio between ring
and sun). The spider 34 has thirty teeth at 36 and the left output
gear 37 has forty-five teeth (for a 3:2 ratio between spider and
left shaft). The ring 38 carries fifty-six external teeth at 40,
which mesh with fifty-six teeth on the idler 42; the twenty-five
teeth 45 on the idler 42 mesh with the fifty teeth on the
right-output-gear 43 (for a 2:1 ratio between ring and right
shaft).
[0024] Thus, in the differential transmission unit of FIG. 1, when
the vehicle is moving straight ahead, and the road wheels are
therefore rotating at equal speeds, the overall gear ratio between
the sun 29 and the left shaft 24 is the same as the overall ratio
between the sun 29 and the right shaft 25; plus, the idler gear 42
between the ring 38 and the right shaft 25 ensures that the shafts
24,25 rotate in the same sense. Therefore, the unit behaves, in one
sense, like a traditional free differential: the two output shafts
24,25 divide the torque received from the input shaft 23 equally
between them. If one output shaft should speed up, e.g by being the
outside wheel as the vehicle turns a corner, the shafts are free to
adopt the relative speeds imposed by the cornering manoeuvre, and
the available torque is still fed to each wheel equally.
[0025] However, the unit 20 of FIG. 1 is unlike a traditional
differential, in the sense that the unit itself contains an overall
or aggregate gear ratio. In a normal differential, during straight
ahead motion (i.e when the output shafts are rotating both at the
same speed), the differential itself, as a unit, rotates as a
complete unit in unison with the output shafts. That is to say, the
gears inside the differential do not move relative to each other.
In a normal differential, relative movements of the gears within
the differential occurs only when the output shafts are rotating at
different speeds, i.e when the vehicle is being steered. In the
apparatus of FIG. 1, the gears within the apparatus are rotating
relative to each other all the time, whether the vehicle is going
straight ahead, or is being steered.
[0026] This overall ratio of the epicyclic or planetary
differential unit 20 depicted in FIG. 1 may be assessed as
follows.
[0027] The speed ratio between the sun 29 and the ring 38, with
spider 34 fixed, is Nring/Nsun. In the particular FIG. 1 case, this
ratio is 3:1. That is to say, for every one rev of the ring, the
sun completes three revs; or, when the spider is fixed, the ring
rotates at one-third the speed of the sun, and in the opposite
direction.
[0028] The speed ratio between the sun 29 and the spider 34, with
ring 38 fixed, is Nring/Nsun+1. Thus, for every one rev of the
spider, the sun completes four revs. That is to say: when the ring
is fixed, the spider rotates at one-quarter the speed of the sun,
and in the same direction.
[0029] With the ring 38 fixed, four clockwise revs of the sun 29
turn the spider 34 one rev clockwise; with the spider 34 fixed,
three clockwise revs of the sun 29 turn the ring 38 one rev
anticlockwise. Thus, one complete clockwise rev of the spider,
added to one complete anticlockwise rev of the ring, takes seven
clockwise revs of the sun. If the sun 29 were to rotate at 4900 rpm
clockwise, and if the ring 38 and the spider 34 were to be
constrained to rotate both at the same speed (in opposite
directions), that speed would be 700 rpm each--the spider at 700
rpm clockwise and the ring at 700 rpm anti-clockwise. However,
preferably, the spider should be geared to rotate 3/4 times the
speed of the ring, and that is what has been done in the unit 20 of
FIG. 1. Consequently, in FIG. 1, if the sun rotates at 4900 rpm
clockwise, the spider rotates at 600 rpm clockwise, and the ring
rotates at 800 rpm anti-clockwise. Given that the sun 29 is turning
at 4900 rpm clockwise, it follows that when the vehicle is being
driven forwards in a straight line, whereby the two road wheels
(and the two output shafts which carry the road wheels) are turning
at equal speeds, both anticlockwise, the spider rotates at 600 rpm
clockwise and the ring rotates at 800 rpm anticlockwise.
[0030] As explained, the unit 20 includes an overall gear
reduction. This is unlike a conventional differential, which does
not provide a gear reduction, in itself. If, in the conventional
unit, a reduction is required (as it usually is) between the input
shaft and the output shafts, the reduction has to come from some
arrangement outside the differential itself. Thus it is common for
a conventional differential to be driven through e.g a crown wheel
and pinion, which has a ratio in the region of e.g 3:1 or 4:1. The
conventional differential does not itself provide any speed
reduction, i.e it has a ratio of 1:1.
[0031] It is recognised that in some types of vehicle, it would be
advantageous to provide a gear ratio actually in the differential,
which, as explained, is the case with the differential unit 20 of
FIG. 1. In ordinary vehicles, the running speed of the engine and
the size of the tires traditionally are such that the 1:1 ratio in
the differential is ideal. Indeed, the 1:1 ratio is so well-suited
to traditional road vehicles that if the differential did have a
ratio, a corresponding set of gears would have to be provided, to
compensate, and to restore the overall ratio. As a result, the
differential as depicted in FIG. 1 is not ideally suitable for a
vehicle such as a traditional automobile.
[0032] However, some other types of vehicle have a different set of
parameters as to the overall ratio between the engine and the road
wheels. All-terrain vehicles, for example, generally have
comparatively high-rewing engines for the size of wheels. The need
arises, in such a vehicle, for the transmission to have a
considerably larger overall ratio than is common in an ordinary
road vehicle. Traditionally, this has meant that in such vehicles a
reduction gear has had to be provided. The differential as depicted
in FIG. 1 avoids that need. It provides a unit that not only
divides the torque between the two output shafts, but imposes an
overall ratio, typically of 7:1 or thereabouts, between the input
shaft and the two output shafts. It may be noted that it would be
very difficult to arrange for a crown-wheel and pinion, as
traditionally associated with the differential on an automobile, to
have a gear ratio as high as 7:1.
[0033] The apparatus as described in FIG. 1 may be used as it
stands, simply as a "free" differential. However, the apparatus can
also serve as an element in a steering control system for the
vehicle. Now, instead of the two output shafts 24,25 of the
differential being free as to their relative speeds, the two output
shafts are driven to rotate, either at the same speed (for straight
ahead), or at different speeds, when it is desired to steer the
vehicle to the left or right. The magnitude of the imposed
difference between the speeds of the left and right wheels serves
to define the radius of the turning circle the vehicle
undergoes.
[0034] (It is noted that the idea is known, of driving the left and
right road wheels at different speeds, as a way of steering a
vehicle. That is to say, it is known to apply engine power to the
left and right wheels of the vehicle through a differential, and
then to steer the vehicle by the use of a means for imposing a
pre-determined velocity difference on the two wheels.)
[0035] FIG. 2 shows a combined transmission/steering apparatus 46.
It may be noted that the portion of the apparatus indicated by
numeral 20 is a differential, and in fact is the differential 20
depicted in FIG. 1. But now, the drive gears 37,43 on the left and
right shafts 24,25 are in mesh with gears 47,48 respectively,
whereby the output shafts 24,25 are not simply free to adopt their
own speeds, relative to each other. Rather, any constraints on the
gears 47,48 will now act as constraints on the relative speeds of
the two output shafts. As will be explained, the gears 47,48 are
constrained in such manner as to force the two output shafts 24,25
to rotate at the same speeds for straight ahead steering, or at
different speeds for steering to left or right.
[0036] As shown in FIG. 2, the means for imposing the required
speed difference between the left and right output shafts 24,25
takes the form of a second epicyclic or planetary unit 49, which is
more or less identical to the parallel unit 20 which, as described,
serves as the differential. In the unit 49, again, the sun 50 has
twenty-three teeth and the ring 52 has sixty-nine internal teeth.
The spider 53 carries thirty teeth, at 47, in mesh with the
forty-five teeth of the left output gear 37. The ring 52 carries
twenty-five (external) teeth, at 48, which mesh with the fifty
teeth of the right output gear 43.
[0037] In FIG. 2, the speed of the sun gear 50 is determined by the
speed of a steering shaft 54. If the steering shaft is stationary,
then the sun gear 50 is also stationary. When that is so, the
spider 53 carrying the planetary gears 56 rotates at a fixed ratio
relative to the ring 52, with its internal gear. For example, when
the output shafts 24,25 are both rotating at the same speed of 400
rpm, the spider 53, being geared to the left shaft 24 at a ratio of
3:2, rotates at 600 rpm. The ring 52, being geared to the right
output shaft 25 at a ratio of 2:1, rotates at 800 rpm.
[0038] As shown in FIG. 2, the right output shaft 25 is geared
directly to the ring 52, and the left output shaft 24 is geared
directly to the spider 53, and therefore, since the left and right
shafts rotate in the same sense, the ring and the spider are also
constrained to rotate both in the same sense. That is to say, when
the output shafts 24,25 are both rotating at 400 rpm, the spider 53
is rotating at 600 rpm and the ring 52 is rotating at 800 rpm, both
in the same sense.
[0039] The speed ratios of the epicyclic unit 49 can be assessed in
the same manner as those of the differential unit 20. Thus, it may
be noted that the condition required for the steer-sun 50 to be
stationary, is that the steer-ring 52 and the steer-spider 53
rotate at a speed ratio of 4:3. Thus, with the ratios in the unit
of FIG. 2, when the steering shaft 54 is not rotating, the output
shafts 24,25 are constrained to rotate both at the same speed.
[0040] To repeat: if the output shafts 24,25 are rotating both at
400 rpm clockwise, the steer-spider 53 is rotating at 600 rpm
anti-clockwise, the steer-ring 52 is rotating at 800 rpm
anti-clockwise, and the steer-sun 50 (plus the steering shaft 54)
is stationary. At the same time, in the differential unit 20, the
drive-ring 38 is rotating at 800 rpm clockwise, the drive-spider 34
is rotating at 600 rpm anti-clockwise, and the drive-sun 29 is
rotating at 4900 rpm anti-clockwise.
[0041] Again, it will be understood that in the planetary
differential unit 20, the drive-spider 34 and the drive-ring 38
rotate in opposite senses at a 4:3 ratio, and the drive-sun 29
rotates at high speed; whereas in the planetary steering unit 49,
the steer-spider 53 and the steer-ring 52 rotate both in the same
sense at a 4:3 ratio, and the steer-sun 50 is stationary.
[0042] The ratio between the speed of the drive-sun-gear 29 and the
speed of the output-shafts 24,25 is 4900:400, when both shafts are
turning at the same speed. Similarly for steering purposes, it will
be understood that, whatever speed is imposed on the steer-sun-gear
50 by the steering shaft 54, the ratio between that speed and the
difference between the speeds of the output-shafts also is
4900:400. It may be noted that this speed difference between the
output shafts has the same 4900:400 ratio to the speed of the
steer-sun-gear, throughout the range of actual speeds of the output
shafts.
[0043] It may be inferred, indeed, that if the vehicle is
stationary when the steering shaft 54 is set in rotation, the
tendency will be for the vehicle to simply go round in a circle.
Whether the vehicle actually does so depends on the disposition of
the other wheels on the vehicle. Vehicles for which the kind of
drive as described herein might be considered are often tracked, or
have several linked wheels arranged in a line along the sides of
the vehicle. In those cases, it would be inadvisable to try to make
the vehicle spin without moving forwards, because doing so would
impose potentially damaging side loads on the tracks or wheels.
However, the fact that the steering system makes such a manoeuvre
even possible is an indication of the degree with which the
steering of such vehicles can be controlled, by the steering system
as described. The steering of tracked vehicles is notoriously
highly inefficient and crude, whereas the system as described
herein permits the steering to be delicately and closely controlled
and coordinated with the forwards motion.
[0044] Attention is directed to the right-output-idler-gear 42 in
FIG. 1a. This component has two sets of gear teeth, one set 57
having fifty-six teeth, and the other set 45 having twenty-five
teeth. The fifty-six teeth at 57 mesh with the fifty-six teeth at
40 of the ring 38, and the twenty-five teeth at 45 mesh with the
fifty teeth at 43 on the right output shaft 25. Thus, there is a
2:1 ratio between the ring 38 and the right output shaft 25.
[0045] It is recognised that the idler 42 need not be a separate
component, but can be the same component as the ring 52 of the
steering unit 49. As shown in FIG. 2, ring 52 carries fifty-six
teeth, at 59; and ring 52 also carries twenty-five teeth, at 48.
Thus, the idler 42 in FIG. 1a and the ring 52 in FIG. 2 can be, and
in FIG. 2 are, one and the same component.
[0046] That is to say, the fifty-six teeth 40 on the ring 38 of the
differential unit 20 mesh directly with the fifty-six teeth 59 on
the ring 52 of the steering unit 49. This condition is not apparent
from FIG. 2. This is because, in FIG. 2, the various shafts are
shown as if they were all in a line. FIG. 3 shows how the end-on
arrangement of the shafts corresponds with the view of FIG. 2, from
which it will be understood that the teeth 40 on the ring 38 do
indeed mesh with the teeth 59 on the ring 52.
[0047] Thus, the rings 38 and 52 are constrained always to rotate
at the same speeds, but in the opposite sense. It will be
understood that this manner of linking the differential unit 20 and
the steering unit 49 leads to a very economical and compact
arrangement of gears. It may be noted especially that all the gear
shafts are parallel, and the number of shafts is small in number,
given the fact that the overall apparatus combines the complete
transmission, differential, final drive, and steering functions of
the vehicle. The apparatus is arranged so that the engine is
coupled to the input shaft 23, and the road wheels are coupled to
the output shafts 24,25, and that is all that need be done to
secure the several functions just mentioned.
[0048] The drive to the input shaft 23 comes from the pre-input
shaft 62. Selector rods 63 are used to move the sliding gear 64 to
left or right along the pre-input shaft 62, and the reverse gear 65
along the shaft 67, whereby the sliding gear 64 meshes either with
the 1st gear 26 or the second gear 27, for different drive ratios,
and for reverse. The vehicle's engine (not shown) drives the
pre-input shaft 62 via a clutch (not shown).
[0049] The vehicle is steered by setting the steering shaft 54 to
rotate. As mentioned, a constant speed of rotation imposed on the
steering shaft 54 gives rise to a corresponding constant difference
between the speed of the left wheels and the speed of the right
wheels. To restore the vehicle to straight ahead motion, the
rotation of the steering shaft is cancelled, whereby the difference
between the speed of the left wheels and the speed of the right
wheels is cancelled.
[0050] The steering shaft 54 may be rotated by any appropriate
means. For example, an electric motor might be provided, and the
driver of the vehicle steers the vehicle by supplying power to the
said motor, causing it to rotate, clockwise or anti-clockwise, at
the speed appropriate to the desired steering effect, left or
right.
[0051] Alternatively, the steering shaft 54 may be rotated by means
of a hydraulic pump and motor. Suitable pump/motor units are
readily available, in which the speed of the shaft is controlled by
the swash-plate of the pump/motor unit. The swash-plate lever is
simply operated from the vehicle's steering tiller or wheel.
[0052] When the speed of the steering shaft is controlled by a
hydraulic pump/motor unit, it can be simply arranged that the
hydraulic oil for the pump/motor unit is the same as the
lubricating oil used in the transmission apparatus.
[0053] On the subject of lubrication of the gears and bearings in
the apparatus, attention is directed to the various oil passageways
as illustrated in FIG. 2. For example, oil collects in the
compartment 68. From there, the oil flows along the centre of the
shaft 23, and out of the radial ducts 69 to the needle bearings 70.
Centrifugal force from the rotating shaft serves to ensure a
vigorous circulation of oil. Ducts 72 also convey oil through the
planet gears to the needle bearings by which the planet gears are
mounted on their spindles. The remainder of the gears and bearings
are lubricated by splash. It should be noted that the arrangement
of the gears as herein depicted lends itself to this manner of
supplying pressurised oil to the needle bearings, even the needle
bearings in the planet gears, and there is no need for a
lubrication pump, complex pipework, etc.
[0054] As mentioned, the steering shaft 54 is held stationary when
the vehicle is being driven straight ahead. That arises because the
ring 52 and the spider 53 are constrained to rotate at a speed
ratio of 4:3. However, if some other ratio were imposed between the
ring 52 and the spider 53, the steering shaft would then have to be
rotated at some actual speed for straight ahead motion.
[0055] For example, the gearing between the ring and the spider
might be arranged such that: a speed of 200 rpm on the steering
shaft corresponds to straight ahead motion; a speed of 400 rpm on
the steering shaft corresponds to a full-steering-lock to the left;
and a speed of zero rpm at the steering shaft corresponds to
fullsteering-lock to the right. In that case, the driver-control
would be a control for changing the speed of the steering shaft,
and thus the driver-control need not include a provision for
driving the steering shaft into selectably either forwards or
reverse rotation.
[0056] In some cases, it can be easier to engineer a system in
which the steering shaft is always rotating, and always in the same
direction, than a system in which the steering shaft has to be made
to rotate in either sense, from a base of zero rotation. For
example, if it is desired to take some power from the vehicle's
engine to drive (or to assist in driving) the steering shaft, in
that case it would be simpler to engineer the system if the
steering shaft were set to rotate only in the one direction.
[0057] As mentioned, the transmission/steering apparatus of FIG. 2
is highly suitable for use on a tracked vehicle, or a vehicle that
uses two lines of wheels, all the left wheels being chained
together, and all the right wheels being chained together. However,
even when the vehicle has normal steering, the apparatus of FIG. 2
can still be used. In this case, the means for applying a
rotational speed to the steering shaft serves also to apply normal
steering movement to the front wheels of the vehicle--and the
designer then arranges that the differential speeds of the driven,
non-steered, rear wheels are coordinated with the steering angles
of the non-driven (or driven), steered, front wheels.
[0058] It will be understood that the actual assembly of the
apparatus as depicted in FIG. 2 poses some difficulties. The
"gears-within-gears" aspect of the design means that the bearings
cannot just simply be pressed each into place, since the other
components impede the assembly operation.
[0059] In particular, it is recognised that it would be difficult
to install means for preventing the bearings 72 that hold the
output shafts 24,25 in position, if that means had to be installed
on the bearings themselves. It is recognised, however, that the
provision of a means to hold the bearings 72 from wandering inwards
can be avoided; this is done, as shown in FIG. 2, by the provision
of a thrust washer 73 between the inner ends of the shafts 24,25.
The shafts 24,25, and the bearings 72, are held apart by means of
the thrust washer 73. Such a thrust washer is very easily
assembled, upon the two halves of the transmission housing being
brought together.
[0060] As mentioned, the various gear-shafts of the apparatus,
despite accomplishing so many different functions, are all
parallel. It is a simple enough task to assemble all the gears,
bearings, and shafts, into the gearbox housing, on a
production-line basis. Furthermore, it is recognised that the
gearbox housing itself can be structured on a
two-halves-that-simply-bolt-together basis. The castings for the
halves of the housing can be manufactured with a minimum of cores
and expensive mould features. This condition is most advantageous
in the case where, as here, the plane along which the two halves of
the gear box are bolted together lies at right angles to the
(parallel) axes of the various gear-shafts.
[0061] FIG. 4a is a diagrammatic end-view showing another
arrangement of gears that embodies the invention. FIG. 4b is a plan
view of the arrangement.
[0062] Here, the idler-gear is associated not with the outer-rings
of the epicyclic sets, but with the planet-carriers or spiders. The
idler-gear 60 meshes with teeth 62 on the drive-spider 63 and teeth
64 on the left-output-shaft 65. Teeth 67 on the drive-ring 68 mesh
directly with teeth 69 on the right-output-shaft 70.
[0063] As before, if the ring-to-sun ratio is 3:1, the correct
speeds and torques are realised at the output shafts if the
spider-to-left-shaft ratio is 2:3 and the ring-to-right-shaft ratio
is 1:2. Generalising, given that the ring-to-sun ratio is N:1, and
given that the spider-to-left-shaft ratio is 1:R, the speeds and
torques are equalised at the output shafts if the
ring-to-right-shaft ratio is 1:R*(N+1)/N. This applies whether the
idler is between the spider and the left shaft as in FIGS. 4a,4b,
or between the ring and the right shaft as in FIG. 2.
[0064] Similarly, the same idler-gear 60 meshes with teeth 72 on
the steer-spider 73, and teeth 74 on the steer-ring 75 mesh
directly with teeth 69 on the right-output-shaft 70.
[0065] In the diagrammatic view of FIG. 4b, the idler-gear 60 is
shown as two separate gears, but FIG. 4a shows they are one and the
same.
[0066] When the epicyclic drive-set and the epicyclic steer-set are
identical, and are connected to the left and right output shafts
identically, as in the examples depicted herein, the vehicle
steering is set to straight ahead when the steering-input-shaft is
stationary. Furthermore, a clockwise rotational velocity has the
same effect in steering the vehicle to the left as the same
magnitude of anti-clockwise rotational velocity has in steering the
vehicle to the right. If the steering-set and drive-set were not
identical, or were connected to the output shafts unequally, the
leftwards steering effect produced by a given change in the
clockwise rotational velocity might not be the same as the
rightwards steering effect produced by the same magnitude of change
in the anti-clockwise velocity (and/or the straight ahead steering
position might require some rotational velocity to be constantly
applied to the steering-input-shaft, although that can sometimes be
an advantage, as mentioned).
[0067] In its broadest scope, the invention provides a differential
having an inherent gear ratio, typically of the order of 7:1. Such
a differential finds application not so much on conventional
automobiles and trucks, but on all-terrain vehicles, in which it is
a simple matter to arrange that the input shaft from the
engine/gearbox into the differential is parallel to the output
shafts to the road wheels (so no bevel gears are required).
[0068] It is common, in ATVs, for all the left wheels of the
vehicle to be geared together, and for all the right wheels to be
geared together. The wheels may be tracked, either permanently, or
the tracks may be of the kind that can be mounted on and off the
wheels optionally/occasionally. Steering is done by driving the
right side wheels at a different speed from the left side wheels.
ATVs have been proposed which have included left and right sets of
driven-wheels, and left and right non-driven-but-steerable wheels,
and in some cases steering has been accomplished by a composite
system in which the non-driven-but-steerable wheels are steered
through an appropriate steering angle, and at the same time the
left side set of driven-wheels is driven to rotate at a different
speed from the right side set of driven-wheels, the difference
being a function of the steering angle.
[0069] When the ATV is arranged with a left side set of wheels
geared together and a right side set of wheels geared together, the
second aspect of the invention comes into its own, i.e of using a
corresponding epicyclic set to constrain the ratio between the two
sides, and thereby to steer the ATV. This system may be termed a
dual-differential drive/steering system, and it may be put to use
either in ATVs that have no other steering facility, or in ATVs in
which dual-differential drive/steering is used on the rear wheels,
or sets of rear wheels, to supplement the steering effect of
normally-steered front wheels.
[0070] In the case of ATVs with all the left wheels drive-coupled
together and all the right wheels drive-coupled together, ATVs with
the dual-differential drive/steering system as described herein can
be quite considerably better than ATVs with the conventional
skid-steering systems (and than ATVs with conventional steering).
The fineness and delicacy of control of the steering enables the
driver to carry out intricate manoeuvres, to apply power
judiciously in low-traction situations, and to escape being bogged
down in terrain that would halt a conventional vehicle.
[0071] The driven wheels may be drive-coupled together by virtue of
the fact that the wheels are tracked. Alternatively, the
drive-coupling of the left-side wheels may be done by mounting a
sprocket on each left wheel, and running a chain or chains between
the sprockets--the right side wheels being correspondingly
drive-coupled together.
[0072] In describing the embodiments, the terms left and right have
been used in the traditional sense, i.e relative to a person
driving the vehicle and facing forwards. When assessing the scope
of the patent, although the terms should be applied with
consistency, they should not be construed as being limited to that
traditional sense.
* * * * *