Hydraulic system for reel mower vehicles

A hydraulic system for a vehicle adapted for operating a plurality of reel mower cutting units and for driving at least one vehicle component such as drive wheels or power steering. The vehicle carries an engine near the front of the vehicle which generates heat. The system includes a fluid reservoir located remote from the engine and near the rear of the vehicle. An input line is coupled with the reservoir, and a first pump is operatively coupled with the input line. A first motor receives fluid from the first pump for driving a reel mower, and a branched line having first and second branches receives fluid from the first motor. The first branch is a first return line extending to the reservoir. A second pump having a lower capacity than the first pump is operatively coupled with the second branch, and a second motor receives fluid from the second pump for driving the vehicle component. A second return line receives fluid from the second motor and is coupled with the input line for allowing fluid from the second motor to flow to the first pump without first flowing to the reservoir.

BACKGROUND OF THE INVENTION 
This invention relates to hydraulic systems for vehicles having reel mower 
cutting units. 
Reel mowers are typically used to mow grass in well groomed areas such as 
golf courses. Some vehicles which are adapted for operating reel mowers 
include a hydraulic system which powers the reel mowers and also the 
vehicle's drive wheels. These hydraulic systems typically include a fluid 
reservoir which stores and recirculates hydraulic fluid. The reservoir can 
generally cool the fluid stored therein and thereby maintain fluid in the 
system at sufficiently low temperatures during operation. 
One type of conventional reel mower vehicle includes reel mower cutting 
units located at the front of the vehicle, which allows the cutting units 
to mow grass before the vehicle wheels trample or compress the grass. A 
hydraulic gear pump is positioned near the front portion of the vehicle 
for powering the cutting units. A charge pump, hydraulic pump and 
hydrostatic system are also carried near the front portion of the vehicle 
for powering the vehicle's ground engaging drive wheels. Fluid within the 
hydraulic system becomes heated under operational loads. Also, many of the 
hydraulic components and lines are positioned within or relatively close 
to the warm engine compartment located near the front portion of the 
vehicle, which further heats the hydraulic fluid flowing in the system. 
Once the hydraulic fluid has passed through the pumps and other hydraulic 
componentry it is routed back to the reservoir via a common return line. 
Conventional hydraulic systems typically position the reservoir near the 
front portion of the vehicle, and relatively close to or within the engine 
compartment in order to make the vehicle relatively compact. The 
reservoir's close proximity to the warm engine can generally hinder the 
fluid within the reservoir from cooling. A hydraulic fluid cooler may 
therefore be necessary, adding further expense to the vehicle. 
The gear pump which operates the reel mowers, and the hydrostatic pump 
which operates the drive wheels have different operating flow rates or 
capacities, and operate different vehicle components. The two pumps and 
their respective motors therefore generally act as separate systems. Many 
conventional systems connect the two pumps in parallel such that the two 
pumps draw fluid from the reservoir via a common input line. The parallel 
configuration of the two pumps allows each pump to draw the proper amount 
of fluid it requires from the reservoir via the common input line even 
though the pumps draw in fluid at different rates. Since the input line 
supplies both pumps with fluid, a relatively large amount of fluid must be 
drawn in from the reservoir through the input line. 
Cavitation is a phenomenon which can occur when the pressure head in a 
hydraulic system is insufficient and the fluid is allowed to reach its 
vapor pressure. The combination of a long suction line and a pump with a 
marginal inlet vacuum is an ideal environment for cavitation to occur. 
When the hydraulic fluid is relatively cold, the fluid viscocity 
increases, making it more difficult for a pump to draw in fluid. 
Cavitation causes fluid to vaporize into vapor cavities which are carried 
with the flowing liquid. As cavities encounter a region of high pressure, 
they may collapse as the vapor condenses. This collapse is accompanied by 
intense pressures caused by fluid rushing in to fill the cavity where its 
momentum is converted into pressure from the impact of the walls of the 
cavity as they meet. Any boundry or wall containing the fluid in the 
vacinity of the collapse will be subjected to repeated and intense 
localized pressures, which may cause damage to components, pumps or fluid 
lines. Conventional reel mower hydraulic systems generally do not 
experience many pump cavitation problems. Most conventional reel mower 
hydraulic systems are relatively compact, and therefore do not include 
long hydraulic lines which would significantly contribute to problems of 
cavitation. 
It would be desirable to provide a hydraulic system which operates a 
plurality of components such as reel mower cutting units and vehicle drive 
wheels, and which generally cools the hydraulic fluid in a reservoir while 
hindering or preventing the occurance of pump cavitation, even when 
operating at relatively low ambient temperatures. 
SUMMARY OF THE INVENTION 
The preferred embodiment of the present invention provides a hydraulic 
system for a vehicle adapted for operating reel mower cutting units. The 
hydraulic system includes a fluid reservoir positioned at the rear of the 
vehicle such that heat from the engine mounted at the front of the vehicle 
is generally prevented from being transferred to the fluid in the 
reservoir. The ability of the reservoir to cool fluid is thereby enhanced 
by the reservoir's remote location with respect to the warm engine. 
According to the preferred embodiment, a gear pump for powering the reel 
mower units and a charge pump which feeds a plurality of vehicle 
components are located near the front portion of the vehicle. The gear 
pump and charge pump are operatively connected in series. An input line 
extends between the reservoir and the gear pump. The gear pump powers the 
reel mower motors. Fluid that has passed through the reel motors enters a 
branched line section. A first branch extends back to the reservoir for 
routing a portion of the fluid back to the reservoir. The second branch 
extends to the charge pump and serves to route a portion of the fluid 
thereto. The hydrostatic pump powers motors which drive the vehicle's 
ground engaging drive wheels. The hydrostatic pump operates as a generally 
seperate hydraulic circuit which the charge pump primes as fluid leaks 
from the hydrostatic pump's case drain. 
The return line from the vehicle components receives the fluid from the 
hydrostatic case drain, and is coupled in fluid communication with the 
input line at a location between the grear pump and the reservoir such 
that the return fluid is not routed all the way back to the reservoir at 
the rear of the vehicle. Since the return fluid is routed to the input 
line adjacent the gear pump, only a relatively small amount of fluid must 
be drawn from the reservoir via the input line which extends all the way 
to the reservoir at the rear of the vehicle. Therefore, cavitation at low 
ambient temperatures, and also cavitation due to pressure drop in the 
input line due to a relatively long input line, is generally reduced. 
The operating flow rates or capacities of the gear pump and charge pump are 
not equal. The gear pump has a higher operating flow rate than the charge 
pump, and therefore only a portion of the fluid which has passed through 
the reel motors will be accepted by the charge pump via the second branch. 
The remainder of the fluid will be directed through the first branch back 
to the reservoir. The difference in operating flow rates or capacities 
thereby generally insures that at least a portion of the fluid within the 
hydraulic circit is returning to the reservoir via the first branch to be 
cooled, and that at least some of the cooled fluid from the reservoir is 
being drawn into the hydraulic circuit for maintaining a sufficiently low 
fluid temperature in the circuit during operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is shown a circuit diagram of the hydraulic 
system 10 according to the preferred embodiment of the present invention. 
The hydraulic system 10 shown is used on a vehicle 12 (seen in FIG. 2) 
adapted for operating a plurality of reel mower cutting units 14 typically 
used for mowing golf courses. The hydraulic system 10 drives the reel 
mowers 14, the vehicle's wheels 16 and 26, and other vehicle components 
such as the power steering mechanism 18 and the lift mechanism 20 which 
raises the reel mowers 14 to a transport mode. The vehicle 12 includes an 
engine 22 and engine compartment 24 located near the front of the vehicle 
12 between the two front wheels 16. 
The vehicle 12 according to the preferred embodiment has two driven front 
wheels 16 and a single driven rear wheel 26 which is steerable. The 
operator seat 28 is located generally above the rear steerable wheel 26. A 
reservoir 30 is positioned at the rear of the vehicle 12 generally between 
the operator seat 28 and the single rear wheel 26. An input line 32 (seen 
schematically in FIG. 1) extends forward from the reservoir 30 and is 
operatively coupled with a hydraulic gear pump 34 which is positioned near 
the front of the vehicle 12. The gear pump 34 draws fluid from the 
reservoir 30 via the input line 32 for driving the reel motors 36. The 
reel motors receive fluid from and are driven by the gear pump 34 and are 
carried on the reel mower cutting units 14 operated in front of the wheels 
16 and 26. The fluid which has passed through the reel motors 36 flows 
into a branched line section 38. This branched line section 38 has first 
and second branches 40 and 42. The first branch 40 is a first return line 
which extends rearwardly to the reservoir 30 for returning a portion of 
the fluid to the reservoir 30 for cooling. The second branch line 42 
extends to a charge pump 44 which feeds a hydrostatic pump 46. The 
hydrostatic pump 46 powers the drive wheels 16. Other vehicle components 
such as the power steering mechanism 18 and the lift mechanism 20 receive 
fluid from the charge pump 44. The fluid which has passed through the 
power steering mechanism 18, the lift mechanism 20 and the hydrostatic 
pump's case drain 47 flows into a second return line 50. The second return 
line 50 is coupled in fluid communication with the input line 32 between 
the gear pump 34 and the reservoir 30. 
The hydrostatic pump 46 and wheel motors which drive the vehicle drive 
wheels 16 and 26 generally operate as a seperate system from the rest of 
the hydraulic circuit. The two systems are linked via the hydrostatic 
pump's case drain 47 which flows into the second return line, and also via 
the charge pump 44 which acts to force fluid into the hydrostatic pump's 
circuit to replace fluid which has leaked through case drain 47. 
The second return line 50 routes return fluid from the power steering 18, 
lift mechanism 20 and case drain 47 to the input line 32 generally 
adjacent the gear pump 34, and therefore fluid is routed generally 
directly to the gear pump 34 without first routing the fluid all the way 
back to the reservoir 30. Since the gear pump 34 receives a portion of the 
fluid it requires from the second return line 50, only a relatively small 
amount of fluid is being drawn through the long input line 32 from the 
remote reservoir 30. Since a relatively small amount of fluid is drawn 
through the input line 32, there is relatively little cavitation caused by 
pressure drop in the input line 32 due to the long input line 32. 
The system 10 is designed to route a portion of the fluid within the system 
back to the reservoir 30 to be cooled. The gear pump 34 has a higher 
operating flow rate or capacity than the charge pump 44. In other words, 
the gear pump 34 pumps a larger amount of fluid than the charge pump 44 is 
capable of pumping, such that the charge pump 44 can not accept all the 
fluid that the gear pump 34 is pumping. The charge pump 44 accepts a 
portion of the fluid pumped by the gear pump 34 via the second branch line 
42. The fluid that the charge pump 44 does not draw in is routed into the 
first branch line 40, which returns fluid to the reservoir 30. The 
difference in pump capacities thereby insures that a portion of the fluid 
in the system 10 is routed back to the reservoir 30 via the first return 
line 40 for cooling. 
Similarly, the difference in pump capacities insures that a portion of the 
fluid that the gear pump 34 draws in will come from the reservoir 30 via 
the input line 32. The charge pump 44 pumps a smaller amount of fluid than 
does the gear pump 34, and therefore the gear pump 34 requires more fluid 
than the charge pump 44 can supply via the second return line 50. Since 
only a portion of the fluid required by the gear pump 34 is supplied by 
the second return line 50, the remainder of the required fluid is drawn 
toward the gear pump 34 from the reservoir 30 via the input line 32. The 
difference in pump capacity therefore insures that at least a small amount 
of cool fluid from the remote reservoir 30 is being drawn in and 
circulated within the system 10 for maintaining a sufficiently low fluid 
temperature during operation. 
In the preferred embodiment of the present invention, the reservoir 30 is 
located about one meter from the gear pump 34, and therefore the input 
line 32 is about one meter in length. The gear pump 34 has an operating 
capacity of 5.76 gal/min, or 0.37 cu.in./rev at an engine speed of 3600 
rpm. The charge pump 44 has an output of 1.5 gal/min at 800 psi, and 4 
gal/min at 50 psi. The hydrostatic pump 46 has an operating capacity of 
12-18 gal/min. 
The preferred embodiment of the present invention therefore provides a 
hydraulic system 10 with a fluid reservoir 30 which is positioned remote 
from the warm engine compartment 24 such that the fluid within the 
reservoir 30 is allowed to cool more effectively. The routing of the 
hydraulic lines between the gear pump 34 which drives the reel motors 36 
and the charge pump 44 which drives the vehicle components 18, 20 acts to 
hinder cavitation by reducing the amount of fluid which must be drawn 
through the long input line 32 which extends to the reservoir 30. The 
hydraulic circuit of the present invention, in association with a gear 
pump 34 and charge pump 44 having different capacities as described above 
insures that a portion of the system's fluid is being directed into and 
drawn from the reservoir 30, such that the system 10 maintains a 
sufficiently low fluid temperature during operation, and insures that a 
positive hydraulic head is maintained at each pump inlet.