U.S. patent number 3,892,184 [Application Number 05/386,648] was granted by the patent office on 1975-07-01 for drive arrangements for mining machines.
This patent grant is currently assigned to Coal Industry (Patents) Limited. Invention is credited to Robert Charles Kenn, David Arthur Tate.
United States Patent |
3,892,184 |
Kenn , et al. |
July 1, 1975 |
DRIVE ARRANGEMENTS FOR MINING MACHINES
Abstract
A mining machine travels along a haulage chain by using a series
of toothed sprockets in a drive of the machine to engage the chain.
The drive is reversible and the drive arrangement causes the
currently leading sprocket to drive the machine irrespective of the
direction of travel. This reduces the risk of damage to the
chain.
Inventors: |
Kenn; Robert Charles
(Lichfield, EN), Tate; David Arthur (Burton Upon
Trent, EN) |
Assignee: |
Coal Industry (Patents) Limited
(London, EN)
|
Family
ID: |
23526473 |
Appl.
No.: |
05/386,648 |
Filed: |
August 8, 1973 |
Current U.S.
Class: |
104/287; 104/235;
104/172.3; 104/178 |
Current CPC
Class: |
B61C
11/02 (20130101); E21C 29/10 (20130101) |
Current International
Class: |
B61C
11/02 (20060101); B61C 11/00 (20060101); B61b
013/00 () |
Field of
Search: |
;104/172R,172C,172B,165,178,147R,236,237,172BT,172S,235
;74/245R,245C,217C,218,220,226,243R,243C,243H |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,091,886 |
|
Nov 1967 |
|
GB |
|
335,036 |
|
Sep 1930 |
|
GB |
|
Primary Examiner: Wood, Jr.; M. Henson
Assistant Examiner: Kashnikow; Andres
Attorney, Agent or Firm: Wray; James C.
Claims
We claim:
1. A drive arrangement for a machine adapted to haul itself to and
fro along a haulage chain extending along a machine's path,
comprising a machine, a plurality of sprockets mounted on the
machine and arranged for engagement with the chain, and drive means
connected to the sprockets and adapted to drive at least a
currently leading sprocket irrespective of direction of travel of
the machine along the chain.
2. The drive arrangement of claim 1 in which the sprockets are
mounted on respectively normally oriented axes.
3. A drive arrangement for a machine adapted to haul itself to and
fro along a haulage chain extending along a machine's path,
comprising a machine, a plurality of sprockets mounted on the
machine and arranged for engagement with the chain, and drive means
connected to the sprockets and adapted to drive at least the
currently leading and currently trailing sprockets irrespective of
direction of travel of the machine along the chain.
4. A drive arrangement as claimed in claim 3, in which the drive
means is adapted to drive the currently leading sprocket so that it
exerts substantially all the driving force required to haul the
machine along the chain while the currently trailing sprocket
exerts only sufficient force to haul the relatively slack chain
around the trailing sprocket.
5. A drive arrangement as claimed in claim 4, in which adjustment
means are provided for adjusting the proportion of the total thrust
exerted by each driven sprocket.
6. The drive arrangement of claim 3 wherein the drive means
comprise first and second driving means connected to sprockets
arranged for remote forward and rearward engagement with the
chain.
7. The drive arrangement of claim 6 further comprising first and
second power conduit means respectively connected to the first and
second driving means, and a reversible power source connected to
the power conduit means for supplying power to one conduit
means.
8. The drive arrangement of claim 7 further comprising a third
conduit interconnecting the driving means whereby exhaust power is
supplied to one driving means connected to the currently leading
sprocket through the one power conduit means, and exhaust from the
one driving means is supplied to the other driving means through
the third conduit means.
9. The drive arrangement of claim 8 further comprising relief means
connected to the third conduit and to an inlet of the power means
for releasing pressure above a predetermined level from the third
conduit.
10. The drive arrangement of claim 9, wherein the relief means is
adjustable, and further comprising booster power means connected to
the third conduit for increasing power in the third conduit to a
maximum permitted by adjustment of the relief means.
11. A drive arrangement for a mining maching adapted to haul itself
to and fro along a haulage chain extending along a machine's path,
comprising a machine, a plurality of sprockets mounted on the
machine and arranged for engagement with the chain, and drive means
connected to the sprockets and adapted to drive only the currently
leading sprocket irrespective of direction of travel of the machine
along the chain.
Description
This invention relates to drive arrangements for mining machines
and in particular to drive arrangements comprising sprockets which
in operation engage haulage chains extending along the paths of the
machines.
With a known mining machine, the drive arrangement comprises a
drive sprocket and at least one idler sprocket around which the
haulage chain passes in sequence.
In operation substantially all wear and damage to the links of the
chain occurs when the chain engages or disengages a sprocket, the
amount of wear or damage increasing rapidly as the chain tension
increases. Thus, it follows that if relatively highly tensioned
chain is passed around a sprocket the wear and damage caused to the
chain is greater than if relatively low tensioned chain is passed
around the sprocket.
Unfortunately, with the known drive arrangement it is necessary
when the machine is travelling in one direction that the drive
sprocket pulls on the section of chain passing around the idler
sprocket. Thus this section of chain has a relatively high tension
causing the chain links to wear quickly and become damaged and the
operational life of the chain to be reduced. This is especially so
when relatively highly tensioned chain is wound in a clockwise
direction around one of the sprockets and in a counter clockwise
direction around the other sprocket. Further, each chain link which
is made continuous by welding is subjected to reverse bending which
at relatively high tension tends to cause failure at the weld due
to fatigue.
An object of the present invention is to provide a drive
arrangement for a mining machine which reduces the tendency of the
chain to become worn or damaged.
According to the present invention a drive arrangement for a mining
machine adapted to haul itself to and fro along a haulage chain
extending along the machine's path comprises a plurality of
sprockets arranged for engagement with the chain, and means adapted
to drive at least the currently leading sprocket irrespective of
the direction of travel of the machine along the chain.
Preferably, the drive means enables the drive of at least two of
the sprockets to be driven simultaneously.
The drive means may be such that the currently leading sprocket
exerts substantially all the driving force required to haul the
machine along the chain while the currently trailing sprocket
exerts only sufficient force to haul the relatively slack chain
around the trailing sprocket.
Alternatively, the drive means may selectively control said drives
so that only the currently leading sprocket is driven.
Preferably, two of the sprockets are mounted for rotation about
axes arranged normal to one another so that the two sprockets
drivably engage alternate links of the chain, respectively.
Preferably, each of said drives comprises a hydraulic motor.
Advantageously, both the hydraulic motors are fed with pressure
fluid from a single pump.
Gearing may be provided between each motor and its associated drive
sprocket and the gearing may include an epicyclic gear.
By way of example only, seven embodiments of the invention will be
described with reference to the accompanying drawings, in
which:
FIG. 1 is a diagrammatic plan of a part of a first embodiment of a
drive arrangement for a mining machine, constructed in accordance
with the present invention;
FIG. 2 is a diagrammatic plan of a part of a second embodiment of a
drive arrangement for a mining machine, also constructed in
accordance with the present invention;
FIG. 3 is an incomplete plan of a third embodiment of drive
arrangement for a mining machine, also constructed in accordance
with the present invention;
FIG. 4 is a section along the line IV -- IV of FIG. 3;
FIG. 5 is a hydraulic circuit for the third embodiment of drive
arrangement;
FIG. 6 is a diagrammatic view of a part of a fourth embodiment of
drive arrangement for a mining machine constructed in accordance
with the present invention;
FIG. 7 is a hydraulic circuit diagram circuit for a fifth
embodiment of drive arrangement; and
FIG. 8 is a hydraulic circuit for a sixth embodiment of drive
arrangement.
FIG. 1 shows a part of the haulage drive arrangement of a well
known shearer type mining machine for winning coal from the face by
repeatedly hauling itself to and fro along a flexible round link
chain 2 extending along the path of the machine, the ends of the
chain 2 being attached to anchored chain tensioning devices with
the chain initially at a relatively low tension e.g. 2 tons. As the
machine hauls itself along the face a rotary cutter drum (not
shown) mounted on the machine engages the coal face and wins the
coal which is loaded onto an armoured face conveyor (not shown) in
well known manner.
The haulage drive arrangement comprises a motor 4 (only a part of
which is shown) drivably engaging gears within a gearbox 6, and two
sprockets 8, and 10 mounted on the gearbox 6. The sprockets 8, 10
are arranged so as to sequentially engage the chain 2.
The sprockets 8, 10 are connected to the gearbox 6 so that when the
machine is travelling in one direction, the sprockets 8, 10 i.e.
the currently leading sprocket, is selected to be the drive
sprocket while the other sprocket 10, 8 is an idler sprocket. When
the machine is travelling in the opposite direction the sprocket 8,
10 which was initially the drive sprocket now becomes the idler
sprocket and the other sprocket 10, 8 i.e. the now leading
sprocket, is selected as the drive sprocket. A gear control lever 7
is provided on the gearbox 6 to enable an operator to select which
of the sprockets 8 or 10 is the driven. The sprockets 8, 10 are
arranged so that in both directions of machine travel the chain
links passing around the idler sprocket are at a relatively low
tension determined by the initial tension applied to the chain and
by the component of the weight of the chain acting at the machine.
The tension need be only sufficient to ensure that the chain is
pulled around the idler sprocket away from the drive sprocket.
When the machine operator starts the machine for movement in the
direction indicated by arrow A, operation of the machine control
selects sprocket 8 as the drive sprocket and sprocket 10 as the
idler sprocket. The drive sprocket 8 is rotated in a clockwise
direction as seen in FIG. 1 so that the section of chain in advance
of the machine becomes subjected to a relatively high tension e.g.
twelve tons. The tensioned links of the chain are engaged by the
teeth of the drive sprocket 8 and wound around the sprocket until
they are fed towards the idler sprocket 10. By the time the links
of the chain disengage the drive sprocket 8 they have a relatively
low tension which is due to the tensioning devices at the end of
the chain and which is maintained throughout the engagement of the
links with the idler sprocket 10. Thus the wear and damage caused
to the links of the chain as they pass around the idler sprocket
tend to be small leading to a prolonged operational chain life.
In order for the machine to travel in the opposite direction to
that indicated by arrow A, the operator moves the controls such
that the sprocket 10 now becomes the drive sprocket and is driven
in a clockwise direction as seen in FIG. 1. Again as the machine is
hauled along the face, relatively low tensioned chain is fed from
the drive sprocket 10 towards the idler sprocket 8.
In modified drive arrangements the selection of the drive sprocket
is achieved by hydraulic control means which replace the mechanical
gear control lever. An example of such hydraulic control means is
described with reference to the fourth embodiment of drive
arrangement (see later in this specification).
FIG. 2 shows a second embodiment of drive arrangement for a shearer
type of mining machine which is similar to that described above
with reference to FIG. 1, the major difference being that the axis
of the sprocket 10 is turned through 90.degree. so that it is
substantially horizontal. With this second embodiment the teeth of
the two sprockets 8 and 10 drivably engage alternate links of the
chain, respectively i.e. sprocket 8 drivably engages only the
vertical links, the horizontal links forming only tie links and the
sprocket 10 drivably engages only the horizontal links, the
vertical links now forming the tie links. During the passage of the
links around a sprocket it is only the drivably engaged links which
tend to wear and become damaged, the tie links being relatively
unaffected. Thus it will be seen that with the axes of the
sprockets 8 and 10 mounted at right angles with respect to each
other, the wear and damage suffered by the chain links will be
spread evenly over all the links resulting in a prolonged
operational life of the chain.
With this second embodiment of drive arrangement the links are not
subjected to reverse bending as they sequentially pass around the
sprockets. Thus the operational life of the chain is further
prolonged.
In modifications of the first and second embodiment control means
may be provided which control the drive mechanism so that the
currently leading sprocket exerts substantially all the driving
force required to haul the machine along the chain while the
currently trailing sprocket exerts only sufficient forces to haul
the relatively slack or low tensioned chain around the trailing
sprocket. One example of such control means is described with
reference to the fourth embodiment of drive arrangement (see later
in this specification).
When the direction of movement of the machine along the face is
reversed the control means reverses the operation of the drive
mechanisms so that the now leading sprocket exerts substantially
all the driving force. Thus in both directions of travel of the
machine along the face the chain passing around the currently
trailing sprocket is relatively slack or at a relatively low
tension just sufficient to haul the chain around the sprocket and
prevent jamming.
FIGS. 3, 4 and 5 of the drawings show a third embodiment of haulage
drive arrangement of a well known shearer type mining machine 21
(only a part of which is shown) for winning coal from a longwall
face by repeatedly hauling itself to and fro along a flexible round
link chain 22 extending along the path of the machine, the ends of
the chain 22 being anchored with the chain initially slack or at a
relatively low tension e.g. less than 1 ton. As the machine 21
hauls itself along the face a rotary cutter drum (not shown)
mounted on the machine engages the coal face and wins the coal
which is loaded onto an armoured face conveyor (not shown) in well
known manner.
The haulage drive arrangement comprises two drive sprockets 23, 24
arranged to drivably engage the chain 22 in sequence; which
sprocket is the leading sprocket and which is the trailing sprocket
at any one time depends upon the direction of machine travel. The
sprockets 23, 24 are provided with teeth 41 which engage the chain
22 in well known manner. The sprockets 23, 24 are driven by
identical independent drive mechanisms 25, 26 respectively. FIG. 3
shows only parts of the drive mechanisms 25 and 26, FIG. 4 shows a
section through the sprocket 23 and the drive mechanism 25 and FIG.
5 is a hydraulic circuit diagram of the drive arrangement. Each
drive mechanism includes an epicyclic gear 27, a train of spur
gears 28 and a hydraulic motor 29. Both the hydraulic motors 29 are
fed simultaneously by pressure fluid supplied from a single
variable delivery pump 42 (see FIG. 5) housed in the machine body
and driven by the machine's electric motor 4. As can be seen from
FIG. 5 the flow of pressure fluid from the pump 42 is fed to the
two motors 29 which are arranged in parallel, the flow being
controlled by a control handle 43 capable of being moved from a
central "Off" position to "Forward" or "Reverse" positions. The
amount of movement of the handle away from the "Off" position
determines the quantity of pressure fluid fed to the motors and,
therefore, determines the speed of the machine along the chain.
Each epicyclic gear 27 comprises a planet carrier 30 rigid with the
associated drive sprocket 23 or 24, three planets 31 arranged to
engage an outer fixed annulus 42 and a sun 32 which is fixedly
mounted on a shaft 33 with a gear wheel 34 arranged to engage the
associated train of spur gears 28 comprising gear wheels 35, 36,
37, 38 and 39. The gear wheel 39 is engaged by a pinion wheel 40
fixedly mounted on the associated motor 29.
In operation, the operator starts the pump 42 which upon actuation
of the control handle 43 simultaneously feeds pressure fluid to
both the hydraulic motors 29 so that they rotate in opposite
directions and cause both the drive sprockets 23, 24 to rotate and
drivably engage the chain 22. Since the drive arrangement comprises
two drive sprockets 23, 24 the pull exerted by each sprocket for a
given machine pull is approximately one half the pull which would
be exerted by a single sprocket for the same machine pull. For
example, if a machine pull of 20 tons is desired, with a drive
arrangement as shown in FIG. 3 the pull exerted by each sprocket
23, 24 would be 10 tons.
As both sprockets 23, 24 are driven it is not necessary for the
section of the chain 22 on the trailing side of the machine 21 to
be tensioned in order to rotate the sprocket. With a drive
arrangement constructed in accordance with the present invention
the chain 22 is not required to rotate sprocket 23 or 24 and thus
the section of the chain 22 on the trailing side of the machine 21
can be slack or at a very low tension. As previously explained this
means for a given machine pull the tension in the section of the
chain 22 in advance of the machine 21 is kept to a minimum. Thus
the operation life of the chain 22 is prolonged and danger and
delays arising through chain breakage are reduced.
Another advantage of a drive arrangement constructed in accordance
with the present invention is that because the drive mechanism 27
for the sprockets 23 and 24 are independent of each other, the
sprockets can momentarily rotate at different speeds so that if the
links of the chain 22 fed from the leading drive sprocket 23 or 24
are of varying length, the trailing sprocket 24 or 23 will
momentarily rotate at a different speed so that the section of the
chain 22 between the two sprockets 23, 24 is kept at a constant
tension. This ensures that bunching of the chain 22 between the
sprockets 23, 24 is prevented and no resultant jamming of the chain
can occur.
Chain guide plates (not shown) may be provided to ensure that the
section of the chain 22 on the trailing side of the machine 21 is
guided off the sprocket 23 or 24.
In modification, the gearing may be dispensed with and relatively
slow speed motors may be directly connected to the drive
sprockets.
In further modification, means are provided so that the pull
exerted by the trailing sprocket is less than that exerted by the
leading sprocket. The pull exerted by the trailing sprocket may be
only sufficient to guide the chain away from the leading sprocket.
One example of hydraulic means for achieving such a further
modification is described with reference to the fourth embodiment
described later in the specification.
Referring now to FIG. 6 of the drawing which shows a part of the
fourth embodiment of drive arrangement for a mining machine.
The drawing shows a part of the haulage drive arrangement of a well
known shearer type mining machine for winning coal from the face by
repeatedly hauling itself to and fro along a flexible round link
chain 2 extending along the path of the machine, the ends of the
chain 2 being anchored with the chain initially at a relatively low
tension e.g. two tons. As the machine hauls itself along the face a
rotary cutter drum (not shown) mounted on the machine engages the
coal face and wins the coal which is loaded onto an armoured face
conveyor (not shown) in well known manner.
The haulage drive arrangement comprises a motor 4 (only a part of
which is shown) drivably engaging gears within a gearbox 6, and
three sprockets 8, 9 and 10 are arranged so as to sequentially
engage the chain 2, the middle sprocket 9 being an idler
sprocket.
The sprockets 8, 10 are driven sprockets connected to the gearbox 6
so that when the machine is travelling in one direction, the
currently leading sprocket 8 or 10 is selected to be the drive
sprocket while the other sprocket 10, 8 is an idler sprocket. When
the machine is travelling in the opposite direction the sprocket 8,
10 which was initially the drive sprocket now becomes the idler
sprocket and the other sprocket 10, 8 is selected as the drive
sprocket. The sprockets 8, 10 are driven sprockets connected to the
gearbox 6 so that when the machine is travelling in one direction,
the currently leading sprocket 8 or 10 is selected to be the drive
sprocket while the other sprocket 10, 8 is an idler sprocket. When
the machine is travelling in the opposite direction the sprocket 8,
10 which was initially the drive sprocket now becomes the idler
sprocket and the other sprocket 10, 8 is selected as the drive
sprocket. A gear control lever 7 is provided on the gearbox 6 to
enable an operator to select which of the sprockets 8 or 10 is
driven. The sprockets 8, 9 and are arec arranged so that in both
directions of machine travel the chain links passing around the
idler sprockets are at a relatively low tension determined by the
initial tension applied to the chain by the tensioning devices
attached to the end of the chain and by the component of the weight
of the chain acting at the machine. The tension need be only
sufficient to ensure that the chain is pulled around the idler
sprocket away from the drive sprocket.
When the machine operator starts the machine for movement in the
direction indicated by arrow A, operation of the machine gear
control lever 7 selects sprocket 8 as the drive sprocket and
sprocket 10 as an idler sprocket along with idler sprocket 9. The
drive sprocket 8 is rotated in a clockwise direction as seen in the
drawing so that the section of chain in advance of the machine
becomes subject to a relatively high tension e.g. twelve tons. The
tensioned links of the chain are engaged by the teeth of the drive
sprocket 8 and wound around the sprocket until they are fed towards
the idler sprockets 9 and 10. By the time the links of the chain
disengage the drive sprocket 8 they have a relatively low tension,
which tension is maintained throughout the engagement of the links
with the idler sprockets 9 and 10. Thus the wear and damage caused
to the links of the chain as they pass around the idler sprocket
tend to be small leading to a prolonged operational chain life.
In order for the machine to travel in the opposite direction to
that indicated by arrow A, the operator moves the gear control
lever 7 such that the sprocket 10 becomes the drive sprocket and is
driven in a clockwise direction as seen in the drawings. Again as
the machine is hauled along the face, relatively low tensioned
chain is fed from the drive sprocket 10 towards the idler sprocket
9 and 8.
In modifications, mechanical gear control means may be provided
which control the drive mechanisms so that the currently leading
sprocket 8 or 10 exerts substantially all the driving force
required to haul the machine along the chain while the currently
trailing sprocket 10 or 8 exerts only sufficient forces to haul the
relatively slack or low tensioned chain around the trailing
sprockets 9 and 10 or 9 and 8.
When the direction of movement of the machine along the face is
reversed the gear control means reverses the operation of the drive
mechanisms so that the now leading sprocket exerts substantially
all the driving force. Thus in both directions of travel of the
machine along the face the chain passing around the currently
trailing sprocket is relatively slack or at a relatively low
tension just sufficient to haul the chain around the sprocket and
prevent jamming.
Referring now to FIG. 7 which shows a hydraulic circuit of a fifth
embodiment of drive arrangement constructed in accordance with the
present invention.
The fifth embodiment of drive arrangement is described with
reference to a three sprocket arrangement similar to that shown in
FIG. 6 although it is to be understood that the drive arrangement
is suitable for driving any configuration of sprockets e.g. two
sprockets as shown in FIGS. 1 or 2 or configurations where more
than one intermediate idler sprocket is provided, e.g. to guide the
chain along a preselected path.
The fifth embodiment of drive arrangement drives only the currently
leading sprocket.
The two end sprockets (not shown in FIG. 7) are drivably connected
to drive shafts 50 and 51 of two fixed displacement hydraulic
motors 52 and 53. The displacement of each of the motors is
selected to give the same chain speed on each sprocket for a given
flow rate of pressure fluid. As can be seen in FIG. 7 the motors 52
and 53 are hydraulically connected and a variable delivery pump 54
supplies pressure fluid to the two motors arranged in series. A
fixed displacement pump 55 is provided to make up leakage through
two check valves 56 and 57 and to maintain a desired pressure at
the inlet of the pump 54, the inlet pressure being regulated at the
desired pressure by a relief valve 58 regardless of the direction
of flow of pressure fluid which is controlled by a handle 59
provided on the variable delivery pump 54.
The pumps 54 and 55 are drivably connected to the machine's
electric motor via gearing 60.
In operation, the handle 59 is moved so that pressure fluid is fed
to rotate the desired motor 52 or 53 so that the machine is driven
in the desired direction, the driven motor being associated with
the currently leading drive sprocket. The pressure fluid supplied
from the pump 54 will drive the currently leading motor and
associated sprocket and will then exhaust to the currently trailing
motor before returning to the pump 54. Leakage and compressibility
due to load in the currently leading motor will reduce the flow of
pressure fluid supplied to the currently trailing motor which will,
therefore, tend to run at a lower speed when compared to the
currently leading motor. However, since the two motors 52 and 53
are interconnected by the chain which is kept tight by the
tensioning devices they will rotate at substantially the same speed
with the currently trailing motor rotated through the chain
interconnection, i.e. the currently trailing motor will be rotated
at a speed faster than the speed associated with the pressure fluid
exhausted from the currently leading motor. Thus, the currently
trailing motor will not generate any torque or back-pressure.
A second relief valve 61 is provided to by-pass excess pressure
fluid past the trailing motor and thus, limit the inter-motor
pressure to a low value in those cases where leakage and
compressibility affects are relatively small e.g. when the machine
is travelling along the face without cutting. The pressure fluid
from the relief valve 61 is fed through check valve 56 or 57 to the
feed for the pump 54.
When the direction of machine travel is reversed by movement of the
handle 59 the flow of pressure fluid will be reversed to drive only
the currently leading motor and associated sprocket.
Referring now to FIG. 8 which shows a hydraulic circuit for a sixth
embodiment of drive arrangement constructed in accordance with the
present invention.
The sixth embodiment of drive arrangement is described with
reference to a three sprocket arrangement similar to that shown in
FIG. 6 although it is to be understood that the drive is suitable
for driving any configuration of sprockets e.g. the two sprockets
as shown in FIGS. 1 or 2 or configuration of more than one
intermediate idler sprocket.
The sixth embodiment of drive arrangement drives both the currently
leading and trailing sprockets and can be adjusted so that the
currently trailing sprocket exerts a preselected thrust. This
preselected thrust exerted by the currently trailing sprocket may
vary from one half the total driving thrust exerted by the drive
arrangement. Alternatively, the thrust exerted by the currently
trailing sprocket may be only sufficient to haul the relatively
slack chain around the currently trailing and idler sprocket.
The sixth embodiment of drive arrangement is similar to the fifth
embodiment of drive arrangement previously described with reference
to FIG. 8. However, in the sixth embodiment of drive arrangement a
second variable displacement pump 62 is provided. The control
handle 59 is arranged to simultaneously control both pumps 54 and
62. The pump 62 is drivably connected by gears 63 to the machine's
electric motor and is hydraulically connected to the main pipe
interconnecting the two motors 52 and 53. A pressure relief valve
64, provided to limit the maximum pressure to a preselected value,
is hydraulically connected through check valves 56 and 57 to the
flow pipes on either part of the main pump 54 and to the low
pressure relief valve 58.
In operation of the sixth embodiment of drive arrangement, the pump
62 makes up for the leakage and compressibility losses in the
currently leading motor circuit and provides a desired fluid
pressure and flow at the intake of the currently trailing motor
which is thereby driven to exert the desired thrust. The proportion
of the total driving thrust exerted by the trailing sprocket can be
adjusted by adjustment of the setting of the relief valve 64. The
distribution of the total driving thrust exerted by the currently
leading and trailing sprockets is independent of the direction of
rotation for any particular setting of the relief valve 64.
The speed of the machine is controlled by the handle 59 and the
delivery of fluid from pump 62 is automatically controlled to zero
when the drive is idling so that power wastage and chain tension
are minimized while the machine is stationary.
From the above description is will be seen that the present
invention provides a drive arrangement for a mineral mining machine
which requires only relatively low tensioned chain to be passed
around the current trailing sprocket.
* * * * *