Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to improvements in hydraulic systems for
agricultural implements and to control and drive systems for same.
Air seeders typically comprise a seeding implement and a product
carrying aircart. Sometimes additional implements such as a packer are
operated in combination with air seeders. Hydraulic systems for aircarts with
hydraulic fan drives have large power demands which can be in excess of what
a tractor hydraulic system can properly provide. This can be more of a problem
when the air seeder is used in combination with other implements having
hydraulic systems.
A boost system which provides additional fluid power for aircarts is
shown in U.S. Patent No. 6,170,412 "Hydraulic System Having Boost Pump in
Parallel with a Primary Pump And Boost Pump Drive Therefor" of Russell J.
Memory et al. In the Memory et al system the tractor primary pump and a
boost pump are arranged in parallel in a hydraulic circuit to supply an
aircart
fan motor. Flow controls for the system enable one pump to maintain at least a
minimum flow to the load when the flow provided by the other pump
diminishes. The boost system increases total fluid capacity so that reserve
capacity for serving other loads is maintained. In the Memory et al
specification prior art related to such hydraulic systems is presented and the
benefits of the Boost Pump parallel system are described. The parallel system,
however, has some shortcomings which the present invention overcomes.
As noted above, the Memory et al parallel boost system provides
additional fluid volume to maintain the aircart fan operation when the tractor
primary hydraulic system is insufficient. However, the speed at which the
aircart fan operates is also limited by the pressure provided to it. Demand
for
increased sizes of air seeders requires aircart fans to provide more airflow
to
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deliver the seeding products farther distances across the larger implements.
One prior art system is disclosed in the article titled "White Hydraulics
PTO Pump System" appearing in Design News, July 20, 1992. The system
shown in that article is one in which a tractor system operates as a charge
pump for a PTO driven hydraulic pump. The circuit shown is not a series boost
system but, rather, the tractor system provides only a charge pressure as is
required by gerotor pumps. The circuit shows that the pressure across the
motor is the difference between the charge pressure and the PTO pump
pressure and the circuit is not a series boost pressure circuit.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a hydraulic drive having
a boost series system which boosts the pressure provided by the tractor system
and delivers this boosted pressure to a hydraulic motor, e.g. an aircart fan
motor. This can provide pressure much higher than can be delivered by the
tractor hydraulic system alone and allows the tractor pump to operate at a
lower pressure, at which pressure it is capable of delivering more flow.
Accordingly, the invention in one aspect provides a hydraulic drive
system adapted to be connected to a primary or main source of hydraulic power
including a main pump and a reservoir; said hydraulic drive system comprising:
a hydraulic motor for driving a load, a high pressure supply line connected to
an inlet of said hydraulic motor and a low pressure return line connected to
an
outlet of said hydraulic motor, said supply and return lines adapted to be
connected to output and return ports respectively of said main source, and a
boost pump having an outlet and an inlet in communication with downstream
and upstream portions of said supply line respectively, such that when said
drive system is connected to said main source, said boost pump is in series
with
said main pump whereby the boost pump serves to boost the pressure of the
flow delivered thereto, a drive for said boost pump, and a fluid control means
disposed between the outlet of said boost pump and the inlet of said hydraulic
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motor to assist in controlling the speed of said hydraulic motor.
The present invention in one preferred form provides a hydraulic system
for boosting pressure to a hydraulic motor, e.g. an aircart fan motor and for
controlling flow pressure or volume delivered to the motor as a means of motor
fan speed control. Specifically, a boost pump is connected in series with an
aircart fan motor and tractor primary hydraulic system. The tractor primary
system supplies flow to the boost pump and the boost pump increases the
pressure. A flow control downstream of the boost pump is controlled to deliver
a portion of the boosted pressure flow to the aircart fan motor sufficient to
maintain a particular fan speed and any remaining portion is directed back to
the inlet side of the boost pump. The flow passing through the fan motor is
returned to the tractor hydraulic system where it is filtered and cooled.
Alternatively the invention can also include boost pumps driven by other
means, such as a PTO drive pump which is hydraulically connected in place of
the ground drive boost pump in the aircart circuit described above.
The control for the flow delivered from the boost pump is preferably a
pressure compensated adjustable flow control, or the control might
alternatively
be a form of pressure control to control the fan motor speed by maintaining or
varying the pressure delivered to the aircart fan. The control preferably
relieves
the excess flow to the inlet side of the boost pump to minimize power loss.
However the excess flow may otherwise be relieved to the tractor return
depending on the nature of the control valve that is used. Either type of
control
may be adjusted from a remote location to set the fan speed as desired.
BRIEF DESCRIPTION OF FIGURES
Fig. 1. shows a schematic circuit of the boost pump series system in
accordance with an embodiment of the invention;
Fig.2. shows a chart of the tractor pump and aircart fan motor
pressure-volume operating curves for the boost pump series pressure boost
system;
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Fig. 3 is a schematic diagram of a control system for the hydraulic
circuit;
Fig. 4 shows portions of the hydraulic circuit and boost pump ground
drive superimposed on an outline of an aircart frame;
Fig. 5 is a perspective view of the boost pump and its mechanical drive
assembly;
Fig. 6 is an exploded view of the boost pump and drive assembly shown
in Fig. 5;
Fig. 7 is an exploded view of the boost pump mounting assembly and
drive coupling;
Figs. 8 and 9 are side and rear elevation views of the boost pump and its
mechanical drive assembly;
Fig. 10 is a side elevation view of the boost pump drive sprocket and
associated assemblies showing the forces exerted by and on it during use.
i 5 DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Fig. 1 shows a preferred form of series boost system hydraulic circuit
20. Hydraulic circuit 20 is connected to a tractor primary hydraulic power
source 22 which includes a main pump 24, a reservoir 25 and other components
to be noted hereafter. A high pressure supply line 26 extends from the output
of primary source 22 to the inlet port of a hydraulic motor 28 which drives an
aircart fan (not shown). A low pressure return line 30 extends from the outlet
port of motor 28 to the return port and reservoir of primary source 22.
A boost pump 32 is connected in the supply lines 26 in series with the
primary source 22. The inlet port of boost pump 32 is connected to the high
pressure supply from primary source 22 and the high pressure output side of
boost pump 32 is connected to supply line portion 26a which leads into a boost
flow control 38 in the form of a pressure compensated adjustable flow control,
the latter having one outlet connected to a supply line portion 26b connected
to
the inlet of fan motor 28 and another outlet connected to return line 40 which
is
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connected at junction 42 to the inlet side of boost pump 32. A by-pass line 43
having check valve 44 can by-pass flow from the primary source 22 around the
boost pump 32 as described hereafter. Line 43 is connected to supply line 26,
26a at junctions 45, 46 at the inlet and outlet sides of boost pump 32
respectively. Although the mechanical ground drive for the boost pump 32 will
be described hereafter, mention is made here of single-acting hydraulic ram
50,
the inlet of which is connected to supply line 26 via ram supply line 52 in
which is disposed a pressure reducing valve 54. Ram 50 is connected to engage
the boost pump with its ground drive when the (tractor) hydraulic primary
source 22 is energized.
Now that the hydraulic circuit of Fig. 1 has been described in general
terms, some of the major components of same will be described in further
detail, beginning with the primary source 22.
Primary Source (22)
The primary hydraulic power source 22, as noted above, is provided by
the tractor. This includes a fluid reservoir, filter, pump, tractor flow
controls,
and provides for the dissipation of heat from the hydraulic fluid. These
components (all well known per se) do not need to be duplicated in the boost
system which is connected to the tractor system to obtain that advantage. The
tractor main source 22 supply is typically controlled by a relief valve set at
2300-2900 psi.
Boost Pump (32)
The boost pump 32 is a pump such as an Eaton Model 2000 series disc
valve geroler-type having a displacement of 18.7 cubic inches/rev. with a
pressure rating of 3000 psi continuous.
The boost pump 32 is driven by an aircart ground wheel via a
mechanical drive to be described hereafter with reference to Figs. 4-10. One
or
more boost pumps (see second pump in phantom in Fig. 1) may be connected
in parallel, each driven by separate aircart ground engaging wheels, to
provide
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adequate boost flow. By having pumps connected to two aircart wheels on
either side of the aircart one could minimize variation in total boost pump
flow
as when the aircart travels in a turn in which the wheel on the inside of the
turn
has reduced rotational speed.
The boost pump 32 may, alternatively, be driven by a tractor power take
off (PTO) drive (not shown).
Boost Flow Control (38)
The pressure compensated adjustable flow control 38, as noted above, is
used to control the volume of the hydraulic flow Which is directed to the fan
motor 28. The control 38 is set to give the desired hydraulic motor and fan
speed and any excess flow is returned via line 40 to the inlet side of the
boost
pump. A preferred boost flow control valve is supplied by Brand Hydraulics
Model FCR-55-NO. The flow control 38 has an adjustment lever which can be
set manually or can be adjusted by an actuator controlled from the tractor cab
to
set the maximum amount of boost flow that will be directed to the fan motor
28. In this way the operator can control the aircart fan speed on the go. The
aircart fan speed is sensed and indicated in the tractor cab by conventional
means (not shown) to provide information to the operator for adjusting the
flow
controls.
Control System
Fig. 3 shows the control system which allows the operator to make
boost flow adjustments from a remote location such as a tractor cab. A three-
way switch 60 feeds control signals to controller 62 which has an output
connected to linear actuator 64. This in turn moves the control lever of the
boost flow control 38 as described previously. Fan speed display 66 coupled
with the operator's knowledge of the type and size of equipment and the nature
of the operation, e.g. seeding and/or fertilizing, enables the correct setting
to be
made.
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OPERATION
The operator sets the tractor primary system 22 to provide a base flow
to the aircart fan motor circuit. Operation of the aircart fan circuit also
engages
the boost pump 32 with the ground drive by activating ram 50. Preferably this
is done before the air seeding system is in motion to prevent shock to the
boost
pump drive components which would result from engaging the drive while in
motion. The force with which the hydraulic ram 50 engages the boost drive is
limited by the above-noted pressure control 54.
The hydraulic flow provided by the tractor primary source 22 bypasses
the boost pump 32 through a by-pass line 43 and check valve 44 when the
aircart ground speed is less than that which is needed to operate the boost
pump
32 at base speed. The tractor source 22 thereby maintains a minimum base fan
speed which prevents line blockage when the aircart is moving slow or is
stopped. The check valve 44 closes to prevent the boost pump flow from
circulating back to the pump inlet when the boost pump speed increases to
boost the pressure in supply line 26 above that pressure supplied by the
tractor
primary source. The boosted pressure flow is controlled by the flow control
38. The flow contro138, as noted above, is a pressure compensated adjustable
flow control which is adjusted to deliver a portion of the flow to the aircart
fan
motor 28, and the remaining portion is returned via return line 40 to junction
42 in line 26 on the inlet side of the boost pump 32. The flow control 38 is
adjusted so the portion of flow volume delivered to aircart fan motor 28
operates the fan at the desired speed.
A key advantage of returning the excess boost flow back to the boost
pump inlet is that power loss and heat is build up is minimized. The excess
flow
could alternatively be returned back to the tractor primary source 22;
however,
the full potential energy in the boosted pressure would be lost in relieving
the
flow to the return line 30 and much heat would be generated. The flow is thus
advantageously returned via the junction 42 connected to the inlet side of the
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boost pump 32 where the pressure is that provided by the tractor primary
source
22. Only part of the total pressure is lost as the flow is relieved and
returned to
the supply line 26 and much of the energy is retained in the remaining non-
returned fluid.
After the flow delivered to the aircart fan motor 28 applies work in
operating the motor, the exhaust flow from the fan motor returns back to the
tractor primary system via the return line 30. This amount of flow is replaced
by the tractor system and delivered to the aircart fan circuit again via the
supply
line 26. The tractor primary system provides components (well known per se)
for cooling and filtration of the fluid in the circuit and those components do
not
need to be duplicated in the aircart fan motor hydraulic circuit.
Fig.2. demonstrates the advantage of this boost series system. Without a
boost pump, an aircart fan may be operated with a flow volume V 1 at pressure
P 1 shown on the tractor pump curve. The tractor system is incapable of
operating the fan at the desired speed which requires flow and pressure at
Vfan
and Pfan. The total tractor pump capacity is required to operate the fan at
flow
vi.
The boost pump series circuit described above provides additional
pressure so the fan may be operated at a higher speed which requires flow Vfan
and pressure Pfan. The portion of the required pressure which is delivered by
the tractor(P2) is reduced by addition of the boost pump which provides
pressure nP boost. At the lower pressure P2, the tractor is able to provide
more
than enough flow volume V2 and the amount of volume in excess of the
required volume Vfan, can be used to operate other circuits in the various
implements (not shown) attached to the tractor. Thus the advantages of the
boost pump series circuit can be easily recognized.
Reference will now be had to Figs. 4-10 which illustrate the mechanical
drive for the boost pump 32. In Fig. 4, a portion of an aircart is shown in
phantom with certain of the hydraulic lines. An aircart ground engaging wheel
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70 is mounted to axle 72 via wheel hub 74 (Figs 5 and 6) and a primary drive
sprocket 76 is fixed to wheel hub 74. Axle 72 is journalled in support housing
78 which is bolted to the aircart frame. A dual race roller drive chain 80 is
attached snugly around the perimeter of primary sprocket 76 so that the second
race extends inwardly from the inner face of sprocket 76 (Figs. 5 and 6).
A boost pump 32 and its carrier assembly 82 are pivotally mounted to
housing 78 by way of a pivot mount 84 fixed to housing 78 and bolted via pivot
bolts 87 to upstanding pivot lugs 88 on the boost pump carrier housing 86.
Referring to Fig. 7, the boost pump 32 is mounted in one end of carrier
housing 86 and serves to rotate a pump drive sprocket 90 mounted at the
opposing end of housing 86 via drive shaft 92 journalled in housing 86 by
bearings 88 and via coupling sprockets 94.
The smaller boost pump drive sprocket 90 engages with the second race
of the drive chain 80 trained around primary sprocket 76 on the inside of the
1.5 base circle defined by the drive chain 80 (Figs. 8-10). In order to
provide for
engagement between the pump drive sprocket 90 and the drive chain 80 on the
primary sprocket, an actuating device is provided in the form of the
aforementioned hydraulic ram 50 which is connected to the hydraulic circuit
described above with reference to Fig. 1. Referring to Fig. 10, the hydraulic
ram 50 is interconnected between bracket 92 fixed to housing 78 and a pivot
point 94 on a lower extremity of boost carrier housing 86. Hence as hydraulic
ram 50 extends and retracts, carrier housing 86 rotates back and forth about
the
pivot bolts 87 (pivot P) in the direction of arrows A-A thus bringing drive
sprocket 90 toward and away from the drive chain 80. Since ram 50 is a single
acting ram, a coil tension spring 96 (Fig. 8) is also connected between fixed
bracket 92 and the further point 98 on the lower extremity of boost carrier
housing 86. Thus, when the hydraulic pressure in the system drops, the spring
96 rotates the boost carrier housing 86 clockwise as seen in Fig. 10 bringing
boost pump drive sprocket 90 away from the drive chain 80. When the tractor
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hydraulics are engaged (see operator step 2 above) the hydraulic pressure
extends ram 50 thus bringing sprocket 90 into engagement with the drive chain
80 to rotate the boost pump 32 once the operator puts the tractor and the
aircart
which it is towing into motion. A "clutching" action is thus provided by the
drive system described above. The drive is engaged when the tractor hydraulic
system supplies pressure to ram 50 and vice versa. The maximum force exerted
by ram 50 is of course determined by the setting of the pressure reducing
valve
54.
A key to the boost systems' ability to operate at the proper pressures and
flow rates is the selection of size and operating speed of the boost pump 32.
Limits to the choices of drive sprocket combinations between the aircart wheel
and the pump require high torque forces in driving the pump 32 at the design
conditions. The resulting forces can cause high wear in the pump drive
component, e.g. sprocket 90 and drive chain 80, and the forces cause the pump
is drive sprocket 90 to be repelled by the drive chain 80. The pivot mount of
the
boost pump carrier housing 86 has been positioned to alleviate these problems
so that a self-engaging force results to oppose the repelling force. The drive
sprocket 90 is then held in engagement with the drive chain 80 with a
relatively
smaller force from the pump drive activating ram 50. This action is best
illustrated in Fig. 10 which shows a side view of the boost pump drive
sprocket
90 with the torque force vector F torque offset a distance "C" from the
reaction
torque vector R torque passing through the pivot P defined by pivot bolts 87.
A
reaction couple is thus produced about pivot P in a direction which assists
the
drive sprocket 90's engagement with the drive chain 80, and in the same
direction as shown by force vector F cylinder. This self engaging reaction
between the drive sprocket 90 and drive chain 80 minimizes operating wear and
provides optimum life of the chain and sprocket drive components.
It is seen from the above that the forces which maintain the pump drive
sprocket 90 in engagement with chain 80 vary with the drive torque being
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transmitted so there is little excessive force which would otherwise
contribute
to wearing of the drive components leading to failure. The life of the drive
is
extended by the design of the drive because the drive engaging forces are no
larger than needed at any time. This is further described below.
The pump drive sprocket 90 is placed in and out of engagement with
drive chain 80 by operation of the hydraulic ram 50. However, the ram 50
typically contributes only a minor part of the force necessary to maintain the
drive engagement when the drive is operating under maximum load. The
majority of the force to maintain the engagement is a resultant of the
reaction
on the drive carrier housing 86. The pivotal connection of the drive carrier
housing 87 is located such that the reaction from the driving forces on the
sprocket 90 causes a moment force on the carrier housing 86 to maintain the
drive engagement. The new design provides for the engaging force to be
contributed in 2 parts, i.e. part from the hydraulic ram 50 and part from the
moment reaction on the carrier housing 86. The moment reaction is due to the
carrier pivot 87 being located a distance "C" offset from the directional
vector
F torque which acts on the sprocket as described above.
When the drive is operating at less than peak load, the driving forces are
decreased, the reaction is equally decreased and the moment engaging force is
decreased. The design thus provides reduced drive engaging forces at off-peak
loads so that the drive components wear at a reduced rate, thus extending the
life of the boost pump drive.
Preferred embodiments of the invention have been described by way of
example. Those skilled in the art will realize that various modifications and
changes may be made while remaining within the spirit and scope of the
invention. Hence the invention is not to be limited to the embodiments as
described but, rather, the invention encompasses the full range of
equivalencies
as defined by the appended claims.
