U.S. patent application number 10/669730 was filed with the patent office on 2004-05-27 for dual-path, single-pump hydrostatic drive for mower.
Invention is credited to Bednar, Richard D..
Application Number | 20040099464 10/669730 |
Document ID | / |
Family ID | 22485682 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040099464 |
Kind Code |
A1 |
Bednar, Richard D. |
May 27, 2004 |
Dual-path, single-pump hydrostatic drive for mower
Abstract
A turf care machine includes a base mounted on a plurality of
wheels, a support structure affixed to and extending from the base
for supporting a turf machine operator interface, and a hydraulic
control system for regulating the speed and direction of the mower.
The hydraulic system includes: an engine with a drive shaft; a
single hydraulic pump driven by the engine; a first valve set
having an inlet connected to the pump outlet; a first hydraulic
wheel motor connected to the first valve set; a second valve set
connected to the first valve set and to second hydraulic wheel
motor. This drive system has the advantage of using only one pump
for driving both drive wheels in a seemingly independent dual path
mode of operation, thereby minimizing cost and the number of fluid
linkages and parts in such a system.
Inventors: |
Bednar, Richard D.; (Lake
Mills, WI) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
22485682 |
Appl. No.: |
10/669730 |
Filed: |
September 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10669730 |
Sep 24, 2003 |
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09594830 |
Jun 14, 2000 |
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6662895 |
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60139231 |
Jun 14, 1999 |
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Current U.S.
Class: |
180/306 |
Current CPC
Class: |
F16H 61/42 20130101;
F16H 61/461 20130101; F16H 61/44 20130101; F16H 61/452
20130101 |
Class at
Publication: |
180/306 |
International
Class: |
B60K 017/14 |
Claims
What is claimed is:
1. In a turf machine including a base mounted on a plurality of
wheels and having a turf machine operator interface, a hydraulic
control system for regulating the speed and direction of the turf
machine, comprising: an engine; a hydraulic pump, driven by the
engine, having an inlet and an outlet providing a source of
unidirectional pressurized hydraulic fluid useful for driving
hydraulic motors; a first valve set having an inlet connected to
the hydraulic pump outlet and a first and second outlet; a first
hydraulic motor having an inlet connected to the first outlet of
the first valve set and an outlet; a second valve set having an
inlet connected to the second outlet of the first valve set,
further having a first and second outlet, the second outlet being
connected to the inlet of the hydraulic pump; and a second
hydraulic motor having an inlet connected to the first outlet of
the second valve set, wherein the first and second hydraulic motors
are coupled to the hydraulic pump in series.
2. The system of claim 1, wherein said first valve set contains a
first variable volume control valve which regulates volume and
direction of fluid flow to the first hydraulic motor; and wherein
the second valve set contains a second variable volume control
valve which regulates volume and direction of the fluid flow to the
second hydraulic motor.
3. The system of claim 1, wherein the pump is a variable volume
pump.
4. The system of claim 2, wherein the first variable volume control
valve contains a first forward setting for driving the first
hydraulic motor in a forward direction, a neutral position for not
allowing fluid to flow to the first hydraulic motor, a reverse
setting for providing flow for driving the first hydraulic motor in
a reverse direction and; a second variable volume control valve
contains a first forward setting for driving the second hydraulic
motor in a forward direction, a neutral position for not allowing
fluid to flow to the second hydraulic motor, a reverse setting for
providing a flow for driving the second hydraulic motor in a
reverse direction.
5. The system of claim 4, further having a left operable control
coupled to the first valve; a first operable control coupled to the
second valve; and a second operable control coupled to the
hydraulic pump.
6. The system of claim 3 having a first clutch disposed between the
engine and the hydraulic pump.
7. In a turf machine including a base mounted on a plurality of
wheels, a hydraulic control system for regulating the speed and
direction of the mower comprising: a hydraulic pump, having an
outlet and an inlet, for controlling hydraulic fluid flow; a first
valve set having a first and second inlet connected to the
hydraulic pump outlet and a first and second outlet; a first
hydraulic motor having an inlet connected to the first outlet of
the first valve set and an outlet connected to the second inlet of
the first valve set; a second valve set having a first and second
inlet, the first inlet being connected to the second outlet of the
first valve set, and further having a first and second outlet, the
second outlet being connected to the inlet of the hydraulic pump; a
second hydraulic motor having an inlet connected to the first
outlet of the second valve set and an outlet connected to the
second inlet of the second valve set, wherein the first and second
hydraulic motors are coupled to the hydraulic pump in series.
8. The system of claim 7, wherein said first valve set contains a
first variable volume control valve which regulates volume and
direction of fluid flow to the first hydraulic motor; and wherein
the second valve set contains a second variable volume control
valve which regulates volume and direction of the fluid flow to the
second hydraulic motor.
9. The system of claim 7, wherein the pump is a single direction
variable volume pump.
10. The system of claim 9, wherein the first variable control valve
contains a first forward setting for driving the first hydraulic
motor in a forward direction, a neutral position for not allowing
fluid to flow to the first hydraulic motor, a reverse setting for
providing flow for driving the first hydraulic motor in a reverse
direction and; a second variable control valve contains a first
forward setting for driving the second hydraulic motor in a forward
direction, a neutral position for not allowing fluid to flow to the
second hydraulic motor, a reverse setting for providing a flow for
driving the second hydraulic motor in a reverse direction.
11. The system of claim 9 having a first clutch disposed between
the internal combustion engine and the variable volume pump.
12. The system of claim 11 further having cutter blades and a
second clutch disposed between the engine and the cutter blades.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/594,830 filed on Jun. 14, 2000 which claims
the benefit of U.S. Provisional Application No. 60/139,231 filed
Jun. 14, 1999. The disclosures of the above applications are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to hydraulic drive systems for
self-propelled turf care equipment, and more particularly to a
dual-path reversible hydrostatic drive system for a steerable turf
care machine having a single variable volume hydraulic pump as a
source of hydraulic drive power.
BACKGROUND OF THE INVENTION
[0003] Commercial turf care machines are typically self-propelled
and are often equipped with drive mechanisms for both driving and
steering the wheels of the machines. These drive mechanisms
typically include a mechanism for transferring the driving torque
from a source of power such as an internal combustion engine to at
least two of the machine wheels, thereby turning the machine wheels
and assisting the machine operator in both propelling and
maneuvering the piece of equipment.
[0004] While both hydraulic and mechanical drive mechanisms have
been commonly used in the past, hydraulic drive mechanisms are
being implemented in turf care machines on an ever increasing basis
due to decreases in the price of such systems. Specifically,
hydrostatic drive mechanisms have long been known to exhibit
desirable characteristics such as allowing a machine operator to
quickly switch between forward, neutral and reverse modes of
operation, and to provide for efficient steering of the machines as
well. Dual path hydrostatic drives are used on both zero-turn
riding mowers and zero-turn walk-behind mowers for a number of
years, as is shown in U.S. Pat. No. 3,616,869 to Rilling and U.S.
Pat. No. 4,920,733 to Berrios, which are both hereby incorporated
by reference. These drive systems feature a dedicated hydraulic
pump and hydraulic motor combination for each of the two driving
wheels. Typically, the pumps and motors are located near the
driving wheels, and the two pumps are driven by a belt powered by a
pulley mounted to the output shaft of the internal combustion
engine.
[0005] One desirable feature of these dual path machines is their
ability to turn and maneuver with considerable agility. This is a
direct result of each driving wheel being controlled by the
operator independently of the other driving wheel. So, while one
wheel is being driven forward at a desired speed, the other wheel
can be driven, for example, in the opposite direction at the same
speed, thereby allowing the turf care machine to turn on its own
axis. Commercial riding and walk-behind mowers having a dual path
hydrostatic drive system are available from more than a half-dozen
different companies.
[0006] A turf care machine operator manipulates a typical dual path
hydrostatic drive mechanism through a plurality of levers located
on an operator/turf machine interface such as a handle bar
structure. These operator control systems typically include both
traction controls and speed controls to enhance machine operability
and maneuverability. A typical traction control for a dual path
hydrostatically-driven machine provides the machine operator with
selective control between forward, neutral and reverse modes of
operation for each driven wheel, while a typical speed control
provides the operator with an overall control for regulating the
maximum forward speed at which the machine can be operated.
State-of-the art traction and speed controls are disclosed in U.S.
Pat. No. 5,343,678 to Stuart and U.S. Pat. No. 5,651,241 to Wegner,
which are both hereby incorporated by reference. They are also
available on various mid-size commercial mowers including those
from Textron Turf Care & Specialty Products of Johnson Creek,
Wis., such as the Ransomes.RTM.) Bob-Cat.RTM. mid-size mowers Model
No. 942215 (a riding mower) and Model No. 930301 (a walk-behind
mower), the operations and details of which are respectively
described in publicly available Ransomes operator and service
manuals.
[0007] While the present dual path hydrostatic drive systems that
are presently available on commercial turf care machines typically
exhibit sufficient performance characteristics, such systems
normally require a hydraulic fluid reservoir as well as a pair of
reversible variable displacement pumps, thus increasing turf care
machine cost. It would therefore be desirable to provide more
economic arrangements for the hydraulic drive system which
facilitates ease of operation, improves efficiency and/or reduces
manufacturing costs.
[0008] As such, a first object of the present invention is to
provide an improved system for regulating/controlling a hydrostatic
drive mechanism of a conventional turf care machine.
[0009] A second object of the present invention is to provide an
improved system for regulating/controlling the hydrostatic drive
system of a turf care machine that allows the operator to adjust
the power to the drive system in a way which helps reduce heating
of the hydraulic fluid and improves system efficiency.
[0010] A third object of the present invention is to provide a
system and method for regulating/controlling the hydrostatic drive
of a turf care machine that requires only one single pump for
driving both drive wheels in a seemingly independent dual path mode
of operation, thereby minimizing cost and the number of fluid
linkages and parts in such a system.
[0011] A fourth object of the present invention is to provide an
economically efficient dual-path hydrostatic drive system which has
a reduced number of external hydraulic connections for improved
system reliability.
SUMMARY OF THE INVENTION
[0012] To achieve one or more of the foregoing objects, and in
accordance with the teachings of the present invention, a
single-pump hydraulic drive system for a steerable, self-propelled
wheeled vehicle is provided that is designed and adapted for
regulating the operation of a self-propelled mower or other piece
of turf care equipment or similar kind of the machine. The system
of the present invention finds particular utility for midsize
commercial mowers and similar kinds of steerable self-propelled
wheeled equipment, typically having a net weight of about 140 kg
(about 310 pounds) to about 500 kg (about 1100 pounds), which are
manually steered and must often be manipulated around obstacles
during operation.
[0013] A manually-steered self-propelled wheeled vehicle, such as a
commercial mower, according to one embodiment of the present
invention, is implemented with a single-pump hydraulic drive system
having a pair of control valve sets for controlling the volume and
direction of fluid from the single hydrostatic pump to a pair of
wheel drive motors. The single hydraulic pump, which is preferably
a variable volume pump, functions to provide hydraulic fluid power
required to drive the wheels. The pump preferably includes a
manually-operated maximum volume adjustment mechanism, such as a
movable machine speed lever connected to a rotatable trunnion shaft
or other volume control input means on the pump, for selectively
setting the desired maximum pump displacement at any desired level,
from a fraction of the pump's output, such 20%, all the way up to
100%. Via this machine speed lever, an operator can select the
maximum drive speed at which the mower will operate. If desired,
this speed control mechanism can be operatively connected in a
combined manner on the turf machine so that the speed control lever
limits the top speed of the traction controls. The operator
traction controls typically include independently-actuated left and
right control levers, typically operated by the user's left and
right hands, which are mechanically connected via independent
linkages to the conventional control valve operators mounted on the
first and second valve sets, which valve sets will shortly be
described.
[0014] The hydraulic pump is connected to a first valve set, which
regulates the volume and direction of fluid to the left hydraulic
wheel motor. The left wheel motor mechanically drives the mower's
left driving wheel, and thus controls the direction and speed of
rotation of the left driving wheel. Hydraulic fluid may also be
partially or completely shunted or bypassed around the left
hydraulic wheel motor by the first valve set, in those operating
situations where the left driving wheel is not to be driven at all
or is not to be driven at a speed as great as the speed of the
right driving wheel. The hydraulic fluid, after traveling back from
the left wheel motor into the first valve set, or after being
shunted through the first valve set, is then transferred through a
suitable fluid conduit to a second valve set. The second valve set
regulates the direction and flow of the fluid to the lawn mower's
right wheel drive motor. This motor is turn mechanically drives the
mower's right driving wheel, and thus controls the direction and
speed of rotation of the right driving wheel. Hydraulic fluid may
also be partially or completely shunted around the right hydraulic
wheel motor by the second valve set, in those situations where the
right driving wheel is not to be driven at all or is not to be
driven at a speed as great as the speed of the left driving wheel.
After the hydraulic fluid leaves the second valve set, it
recirculates through a suitable fluid conduct back to the inlet
side of the single hydraulic pump.
[0015] The first and second valve sets preferably each contain at
least one control valve for regulating the volume and direction of
hydraulic fluid discharged therefrom. Preferably each control valve
has two outlet ports which are directly piped to the associated
wheel drive motor. Each control valve also preferably has a
pressure inlet port, a pilot bypass port, and a discharge port. One
preferred control valve is an infinitely-adjustable five-port
three-position proportional directional control valve for
selectively directing fluid to its associated wheel motor. The
control valve also preferably has a three-position closed center
valve spool arrangement. In the forward and reverse positions, the
control valve directs hydraulic fluid to the wheel motor in order
to respectively run the wheel motor in the forward or reverse
direction. Because the control valve is proportional and infinitely
positionable, the flow of hydraulic fluid can be adjusted as
desired to achieve any desired rate of speed of the associated
wheel, including no speed (that is no rotation), which occurs when
the valve spool is in its closed center position.
[0016] The left and right operator traction control levers and
linkages provided on the mower may take on any conventional or
suitable form for providing independent mechanical movements to the
control operators of the first and second valve sets. Typically,
the control operators of the valve sets will be adjustable between
full forward, neutral and full reverse positions. As a first
example, on a walk-behind mower employing a single-pump hydrostatic
drive system of the present invention, these control levers may be
hand grip levers of the type conventionally found on walk-behind
mowers having a two-pump dual-path hydraulic drive system. As a
second example, on a riding mower where the operator is seated, the
control levers may be a pair of hand-operable, pivotally mounted,
spring-returned-to-neutral levers positioned along side of, or in
between the knees of, the seated operator. As a third example, on a
stand-up riding or platform mower, the operator traction control
levers may be a pair of hand levers or coupling members that are
independently movable and preferably are arranged to pivot about a
single axis. The control levers may also be limited in their
pivotal movement in at least one direction by a lawn mower handle
structure upon which they are mounted. As a fourth example, left
and right foot-operated control pedals may be provided. In all of
these examples, the control operator of the first valve set
receives its command as to the desired direction and volume of the
fluid flow into the left wheel drive motor from the left-hand (or
left foot) traction control lever through the left-hand linkage.
Similarly, the control operator of the second valve set receives
its command as to the desired direction and volume of fluid flow
into the right wheel drive motor from the right-hand (or
right-foot) traction control lever through the right-hand linkage.
In this manner, the direction and speed of the rotation of the left
and right driving wheels may be accurately controlled. Through
manipulation of this pair of controls, the left wheel can go in a
forward direction at any desired speed while the right wheel is
going in a rearward direction at any desired speed (or vice versa).
This functionality enables the operator to turn the mower at an
effective zero turning radius, if so desired, just like in
traditional dual-path machines.
[0017] At least two further variations of the first embodiment of
the present invention are contemplated. The control valve of each
valve set that determines fluid volume and direction may be a
spring-returned to closed-center neutral position valve, meaning
the hydraulic flow to the associated wheel motor is zero in the
absence of external forces applied to shift the valve away from its
centered neutral position. Preferably, suitable spring members are
provided internally within the control valve to shift its spool to
a closed-center neutral position. Alternatively, the control valve
may be spring-returned to one of its full open positions. In either
variation, the traction control levers and/or their associated
linkages may also be provided with spring members to return the
control valve to a neutral position when the mower operator
releases the traction control levers. Alternatively, as is common
with some commercial walk-behind mowers, the traction control
levers and/or their associated linkages may be provided with spring
members to return the control valve to a full open position, such
as full forward, when the mower operator releases the traction
control levers.
[0018] A second embodiment or aspect of the single-pump hydrostatic
drive system of the present invention for steerable self-propelled
wheeled vehicles is provided. This second aspect includes all of
the same components found in the first embodiment of the invention.
It also includes, within each control valve set, a
pressure-operated bypass valve, which is also sometimes called a
slave-operated volume compensation valve. These bypass valves are
preferably infinitely-adjustable three-port two-position
pilot-operated control valves that are spring-returned to an open
position in the absence of back pressure in a pilot fluid line
typically connected to normal outlet port of the bypass valve. Each
bypass valve functions to divert all or a portion of the fluid
around its respective control valve within its valve set when a
particular wheel is not being driven at all or is not being driven
at its near maximum rate of speed so as to match the particular
pump output flow. These slave-operated bypass valves include
opposed pilot lines connected respectively to the inlet port and
the pilot bypass port of the associated control valve. Thus, the
nearly instantaneous pressures experienced within the fluid
conduits connected to the inlet port and the bypass port serve to
control the position of the slave-operated bypass valve. When a
sufficient pressure backup is detected in the conduit leading to
the inlet port of the control valve, the bypass valve diverts part
or all of the fluid flow to the discharge port of its valve set. In
this manner, the energy-wasting, heat-generating circulation of the
hydraulic fluid through the bypass passages and bypass port of the
directional control valve is avoided, and the overall speed of
response of the hydraulic drive system as a whole is improved.
According to this aspect of the present invention, the bypass
valves are preferably mounted directly to or adjacent to their
associated control valve. Or both valves can be mounted adjacent to
one another on a common pre-ported valve mounting plate or manifold
block to achieve a single integrated valve set that minimizes the
number of external fluid connections that have to be made to each
valve set. In addition, if desired, the single pump and the first
and second valve sets may be mounted upon a larger common hydraulic
manifold block, base or mounting plate to further minimize the
number of external fluid connections between these three sets of
hydraulic components within the hydrostatic drive system of the
present invention. In all versions of the present invention, the
valve sets are preferably positioned in relatively close proximity
to the hydraulic wheel motors, which typically directly drive the
axles of the driving wheels of the turf care machine.
[0019] Additional aspects, features, objects and advantages of the
present invention will become apparent from a reading of the
following detailed description of the preferred embodiments taken
in conjunction with the accompanying drawings and appended
claims.
[0020] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0022] The drawings form an integral part of the description of the
preferred embodiments and are to be read in conjunction therewith.
Like reference numerals designate the same or similar components or
features in the various Figures, where:
[0023] FIG. 1 is a perspective view of a typical walk-behind turf
machine incorporating the single-pump hydrostatic drive system of
the present invention;
[0024] FIG. 2 is an elevational view of the FIG. 1 walk-behind turf
machine as viewed from the rear, showing the single hydraulic pump
and two valve sets mounted on a common hydraulic manifold bolted to
the rear deck of the mower;
[0025] FIG. 3 is an enlarged perspective view of the operator
control area of the handle bar structure showing the T-bar engine
speed control lever and the centrally located speed control lever
for drive pump to set the maximum drive speed;
[0026] FIG. 4 is a diagrammatic plan view showing one possible
lay-out of the various hydraulic and mechanical components of the
single-pump dual-path hydrostatic drive system of the present
invention generally located on the rear deck of a commercial
mower;
[0027] FIG. 5 is a detailed hydraulic diagram of the hydrostatic
drive system of the present invention particularly useful for a
dual-path walk-behind commercial mower showing the spools of the
two control valves being spring-returned to their full-forward open
position, and also showing the hydraulic interconnections among the
various hydraulic components; and
[0028] FIG. 6 is a hydraulic drawing of the hydrostatic drive
system of the present invention, just like that of FIG. 5, except
that the directional control valves of the valve sets are
spring-returned to a center position, which is particularly useful
for riding mowers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The following description of the preferred embodiment(s) is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0030] Referring now to the drawings, FIG. 1 shows a typical piece
of turf care equipment, namely a zero-turn walk-behind mower,
generally at 2 upon which the hydrostatic drive control system of
the present invention is implemented. Conventional elements of the
turf care equipment 2 are fully described in publicly available
Ransomes Hydro Mid-Size Power Units Parts Manual, P/N-2308093 dated
March 1995. Although the present invention is described as being
implemented in association with a hydrostatic drive mechanism in a
turf care machine, it should be understood and appreciated that the
hydrostatic drive control mechanism of the present invention is
also adaptable for use in any piece of machinery in which a
hydrostatic drive mechanism is implemented or may be used.
[0031] With reference to FIGS. 1, 2 and 3, the turf machine 2
includes a rear deck frame or base 54 having a handlebar support
structure 196 rigidly mounted to and extending upwardly from the
base 54. A front frame or mower deck 212 under which belts and
cutting blades (not shown) are located extends forwardly from the
rear deck or base. The cutter drive belts and rotary grass-cutting
blades are implemented under the mower deck as shown and described
in publicly available Ransomes Mid-Size Cutter Decks Parts Manual,
P/N-2308096. A power source, such as a conventional internal
combustion engine shown generally at 200, is mounted to base 54 and
provides power to the various components of the machine in any
conventional or suitable manner including those well known in the
art, such as flexible belt drives or hydraulic pump and motor
drives. Turf care machine 2 also includes a fuel tank 198 mounted
on the handlebar support structure 196 for storing fuel used by
engine 200. In addition a master pump speed control lever 199 is
provided near the top of handle bar structure 196 for setting
and/or adjusting the maximum displacement of variable volume 10.
Lever 199 is connected via a conventional mechanical linkage 203 to
the displacement control operator 205 projecting from pump 10. Also
provided on the top plate 209 of handlebar structure 196 is a motor
speed control lever 211 connected by a conventional mechanical
linkage, such as a Bowden cable arrangement (not shown), to the
throttle lever (not shown) of motor 200.
[0032] Turf care machine 2 includes left rear and right rear
driving wheels 62, 82 rotatably attached to base 54 and two front
caster-style non-driven wheels 198 attached to mower deck 212.
Specifically, rear wheels 62, 82 are preferably attached to and
driven by drive mechanisms, including hydraulic drive wheel motors
60, 80 shown in FIG. 3, in a manner that will be described in more
detail below. Associated with each hydraulic wheel motor is a valve
set 20, 64. Each valve set 20, 64 is mechanically coupled to
control levers 190 found on handle bar structure 174. Also
associated with these handle bars 174 are lockable, thumb-operated
neutral latch mechanisms 84. These conventional neutral latch
mechanisms are of the type as that disclosed in the aforementioned
Ransomes Hydro Mid-Size Power Unit Parts Manual. Alternatively, an
operator control arrangement of the type described in U.S. Pat. No.
5,343,678 to Stuart may be utilized, and the disclosure of that
patent is hereby incorporated herein by reference. The Stuart
patent discloses a pair of hand levers or coupling members that are
independently movable and preferably are arranged to pivot about a
single axis.
[0033] Referring to FIG. 4, turf machine 2 includes an internal
combustion engine 200, typically having a vertical output shaft,
coupled to an concentrically-mounted optional first clutch assembly
204. Assembly 204 may be an electrical or mechanical clutch. Engine
200 is drivingly connected to a variable volume hydraulic pump 10
via first flexible drive belt 208. Alternatively first flexible
belt 208 may be driven with conventional tensioner pulley and/or
idler pulley arrangement. Either arrangement may be utilized to
translate the mechanical rotary power of the output shaft of the
engine to a pulley concentrically mounted to the input shaft of
pump 10. Also shown concentrically mounted on the engine output
shaft is the second optional clutch assembly 206. Assembly 206 is
coupled to the cutter blade assembly 210 by drive belt 209. As a
first alternative, belt 209 may be coupled via a tensioner pulley
and idler pulley arrangement to provide selectively applied
mechanical rotary power to the rotary mower blades. As a second
alternative, a second hydraulic pump (not shown), driven directly
or by belt from the mechanical rotary power of the output shaft of
the engine, may be used to power one or more hydraulic motors to
drive conventional rotary cutting blades or conventional reel or
cylindrical-style cutting blades (not shown). These cutter drive
alternatives are well-known and need not be further described.
[0034] As shown in FIGS. 2 and 4, variable volume pump 10 is
preferably centrally mounted on the rear portion of deck 54, and
first and second valve sets 20, 64 are preferably mounted on deck
54 on either side of pump 10. Pump 10 and valve sets 20, 64 are
preferably mounted on a common hydraulic manifold 21 to minimize
external hydraulic connections between the various ports of pump 10
and the various ports of the individual valves within and between
valve sets 20, 64. In this manner, the possibility of leakage from
external fittings and lines is minimized, as is required assembly
time. Appropriate internal passages for main and pilot fluid flows
through the manifold can readily be provided using techniques well
known in the art of hydraulic valving and hydraulic manufacture.
The hydraulic output from pump 10 is coupled through an
appropriately-sized and secured fluid conduit to inlet port 12 of
first valve set 20. This conduit, like most of the other fluid
lines in the hydraulic circuit diagram, may be an external fluid
line or may be an internally plumbed passage provided in manifold
21. First valve set 20 also has outlet ports 14 and 16 in the fluid
communication with hydraulic wheel motor 60, and a discharge port
18. The conduits between outlet ports 14 and 16 and motor 60 may be
plumbed with rigid hollow fluid-carrying lines, such as tubing or
pipe. Or all or part of these lines may be a flexible hydraulic
line, such as braided hydraulic hose with metallic pressure-crimped
end fittings with appropriate threaded fasteners.
[0035] Similarly, second valve set 64, which is identical in terms
of function to first valve set 20, has hydraulic output from port
18 coupled through an appropriately-sized and secured fluid conduit
to inlet port 66 of second valve set 20. Once again, this conduit,
like most of the other fluid lines in the hydraulic circuit
diagram, may be an external fluid line or may be an internally
plumbed passage provided in manifold 21. Second valve set 64 also
has outlet ports 68 and 70 in the fluid communication with
hydraulic wheel motor 80, and a discharge port 72. The fluid
connection between outlet ports 68 and 70 and wheel motor 80 may be
plumbed in the manner described for the fluid lines connected to
outlet ports 14 and 16.
[0036] As best seen in FIG. 5, first valve set 20, which functions
to regulate the amount and direction of fluid to left wheel drive
motor 60. Valve set 20 has a volume control valve 22 and an
optional slave-operated bypass valve 40. As shown, valve 22 is
preferably an infinitely-adjustable directional control valve
having three distinct internal valve spool positions, namely a
distinct full forward position represented by (rectangular)
envelope 24, a distinct neutral or blocked-center position
represented by envelope 26, and a distinct full reverse position,
represented by envelope 28. First control valve 22 has a first or
inlet port 30, a bypass port 38, and a discharge port 36. Valve 22
also has first and second outlet ports 32 and 34 which are in
respective fluid communication with and correspond to first and
second outlet ports 14 and 16. When optional slave-operated bypass
valve 40 is not provided, inlet port 30 normally is in fluid
communication with and may be regarded as corresponding to inlet
port 12. Discharge port 36 is in fluid communication with discharge
port 18 of first valve set 20. Directional control valve 22 is
connected to control lever 190 and return spring 50. The position
of the valve spool within valve 22 is determined by the position of
manual operator 190, which is connected to left-hand control lever.
Pilot bypass outlet 38 is connected to second pilot control inlet
48 of the optional slave-operated volume compensation control valve
40.
[0037] As can be seen in FIG. 5, the forward position represented
by envelope 24 of valve 20 connects (i.e., establishes open fluid
communication between) inlet port 30 to outlet port 32 and connects
outlet port 34 to discharge port 36. In addition, there is a fluid
path from inlet port 30 to pilot port 38 in envelope 24. In the
center position represented envelope 26, outlet ports 32 and 34 are
blocked, pilot port 38 is blocked, and inlet port 30 and discharge
port 36 are in fluid communication, all as shown. Accordingly, when
valve 22 is in its center position, the fluid flowing into inlet
port 38 will flow immediately out of outlet port 36 (subject to any
pressure drops caused by restricted size passages and orifices),
and the fluid will not be directed to or reach hydraulic motor 60.
Similarly, the fluid in the lines leading to motor 60 will be
blocked, and thus motor 60 and the left wheel connected thereto
will effectively be hydraulically braked. In the reverse position
represented by envelope 28, inlet port 30 is connected to outlet
port 34 and output port 32 is connected to discharge port 36. In
addition, pilot port 38 is in fluid communication with inlet port
30. Accordingly, when control valve 22 is in either its full
forward position 24 or its full reverse position 28, pilot line 38
will be at substantially the same pressure as is inlet port 30.
[0038] A slave-operated bypass or volume compensation valve 40 may
optionally be provided within first valve set 20. If valve 40 is
not provided, then inlet port 12 is piped directly to inlet port
30, as previously noted. As shown in Figure valve 40 is preferably
an infinitely-adjustable proportional control valve having two
basic positions or envelopes 47 and 49, three main ports 42, 44 and
45, two pilot ports 46 and 48, and a drain line port 52.
Specifically, valve 40 has a first inlet port 42, a first outlet
port 44, and second outlet port 45, and a first pilot inlet port 46
and a second pilot inlet port 48. In the first distinct or at-rest
position of valve 40, which is represented by envelope 47, inlet
port 12 is connected to first outlet port 44, and second outlet
port 45 is blocked, as shown. In the second distinct or fully
shifted position represented by envelope 49, inlet valve 12 is
connected to second output port 45, and first output port 44 is
blocked, as shown. Return spring 50 operates to bias valve 40 into
its nominal or at-rest position 47, as does sufficient hydraulic
pressure on second pilot port 48, provided that it is able to
overcome the hydraulic pressure if any being delivered to pilot
port 46. Hydraulic pressure on first pilot port 46 which is
sufficiently greater than the combined force of the hydraulic
pressure at pilot port 48 and the effective pressure generated by
return spring 50, causes valve 40 to shift from its at-rest
position or to the position represented by envelope 49. Thus, as
can be readily understood, pilot ports 46 and 48 function in
opposed relation to automatically actuate or bias the valve spool
of slave-operated compensation valve 40 to one position or the
other. In its first or fully at-rest position 47, bypass valve 40
functions to direct hydraulic fluid from pump 10 delivered to inlet
port 12 to outlet port 44 and onto inlet port 30 of valve 22. In
its second fully-actuated position 49, bypass valve 40 functions to
bypass hydraulic fluid being delivered to inlet port 12 to
discharge port 18, thus bypassing directional control valve 22 and
left wheel drive motor 60 altogether.
[0039] Valve 40 may also assume intermediate positions between
positions 47 and 49 if the combined hydraulic forces and its return
spring force are sufficiently closely balanced to permit the valve
spool to partially shift. In such a blended position, a portion of
the fluid being delivered from pump 10 to inlet 12 will be sent
through valve 22 hydraulic motor 60, while a portion will be
diverted to discharge ports 45 and 18 so as to go directly to inlet
port 66 of second valve set 64.
[0040] Control valve 22 and bypass valve 40 may each be provided
with a drain line to the low point 52 in the hydraulic system, as
shown, if needed. Low point 52 normally will be at the inlet or
suction side of pump 10. These optional drain connections help
recirculate fluid which has leaked past the valve spools of valve
20 and valve 40.
[0041] Also shown in FIG. 5, is an optional two-port, two-position
bypass valve 100 connected in parallel with pump 10. Bypass valve
100 is a manually operated valve that has two positions or
envelopes 104 and 108. During normal operation of the hydrostatic
system, valve 100 is closed, as shown by envelope 104. When opened,
as shown by envelope 108, valve 100 allows hydraulic fluid to flow
freely around pump 10. At times this may prove convenient when all
power on the mower is off, and the mower must be moved manually,
since this will allow hydraulic fluid in wheel motors 60 and 80 to
circulate in a complete loop through the hydraulic lines of
hydraulic drive system 5.
[0042] In operation, both valves 22 and 40 are capable of assuming
and an almost infinite number of intermediate positions between the
distinct valve spool positions. In such blended positions, there is
some fluid crossover between certain ports. Specifically, with
regard to valve 20, in an intermediate position between
fully-forward position 24 and center position 26, there is a
portion of the fluid flowing into inlet port 30 being passed to
outlet port 32 and thereafter to wheel motor 60, while another
portion of the fluid into inlet port 30 is being diverted to
discharge port 36. In a similar manner, when the valve 22 is in a
blended position partially between the center position 26 and full
reverse position 28, a portion of the fluid flow to inlet port 30
is sent to outlet port 34, and a portion of that fluid flow to
inlet port 30 is bypassed to discharge port 36. These two blended
positions just described are similar, except that the fluid flow
through wheel motor 60 is an opposite direction. In each of these
blended positions, the relative amount of fluid being directed to
wheel motor 60 versus the amount bypassed to discharge port 36 is
determined by the precise position of the valve spool, as control
by manual operator 190.
[0043] Those skilled in the art should appreciate that the energy
in the hydraulic fluid under pressure that is not being utilized in
wheel motor 60 or that is not being lost through pressure drops in
first valve set 20 or in its associated conduits is available to
drive wheel motor 80. Due to the substantially identical
construction of first valve set 20 and second valve set 64, the
fluid pressures between the two valve sets and their respective
hydraulic wheel motors tend to equalize very nicely in a reasonably
steady-state condition when the mower is traveling forward over
reasonably level ground in a substantially straight line. To the
extent that any unequal hydraulic pressures may exist that are
undesirable, the operator of the mower, by making minor manual
adjustments to the relative position of the traction control
levers, can easily make compensations so as to keep the mower
tracking in a substantially straight line. Such minor corrections
to the traction control levers will normally be made instinctively
without any real effort of a part of an experienced mower operator,
much like an experienced car driver will make slight changes to the
steering wheel in order to keep driving a car in a substantially
straight line down any given the road without having to think about
those steering corrections.
[0044] The operation of the FIG. 5 drive system will now be further
described to help further explain the functioning of the
single-pump, dual-path drive system which is inherently shown
therein. With reference to FIG. 5, consider operation of the mower
with the left-hand traction control lever for the left wheel drive
in its neutral position and the right-hand traction control lever
for the right wheel drive being in its full forward position shown.
The left traction control lever 190 is raised slightly to place the
first control valve 22 in the neutral position against biasing
spring 50. As a result, hydraulic pressure from inlet port 30 of
valve 22 is diverted to discharge outlet port 36, thereby bypassing
left drive motor 60. Also, with valve 22 in its neutral position
(envelope 26), hydraulic pressure on outlet port 38 and pilot port
48 will promptly be relieved via controlled leakage to drain 52. As
a result, pressure in inlet port 30 will be sufficient to shift
slave-operated valve 40 from its at-rest position 47 to full bypass
position 49. This shifting changes the flow of hydraulic fluid from
the variable volume pump 10 so as to divert the flow away from
valve 22, and subsequently the left drive wheel 60, directly to
discharge port 18 of valve set 20, where it then enters inlet port
66 or second valve set 64. With directional valve 74 in its full
forward position, the pressurized fluid is directed through bypass
valve 76 to port 86 of value 74, and onto and through second
hydraulic wheel motor 80.
[0045] As may be appreciated from FIG. 5, when control lever 190 is
further moved so as to place valve 22 into its full reverse
position represented by envelope 28, pressure is applied through
bypass port 38 so as to allow the slave-operated bypass valve 40 to
shift back into its first position 47. This allows fluid to once
again flow through first outlet port 44 of slave-operated valve 40
into inlet port 30 of control valve 22. As can be seen in FIG. 5,
in the full reverse position 28, the fluid flows from inlet 30
through second output port 16 so as to drive left wheel motor 60 in
a reverse direction. The flow leaves left drive motor 60 and enters
port 32 of control valve 22 at and is directed to the discharge
port 36. Subsequently, the fluid flows through discharge port 18 to
inlet port 66 of second valve set 64. The slave-operated valve 40
provides an efficient means to effectively divert fluid energies at
very low pressure drops away from control valve 22, and hence wheel
motor 60, to second volume control valve 74 and subsequently right
drive motor 80.
[0046] The functioning of the right valve set 64 is identical to
that described for left valve set 20, with the exception that
diverted fluids are not directed toward the left wheel 60, but
instead are directed back to variable volume pump 10.
[0047] FIG. 6 shows a hydraulic diagram for another embodiment of
the single pump hydrostatic drive system of the present invention.
FIG. 6 is similar to the FIG. 5 hydraulic diagram, except that
control valves 22 and 74 are spring-returned to a neutral position,
and an optional air-to-oil heat exchanger 215 is provided at the
inlet line leading to pump 10. By way of background, there are a
number of conventional mowers, including sit-down riding mowers and
standup platform mowers, which utilize control linkages and/or
reversible pumps which return to neutral to provide a braking
action upon the driving wheels with the control levers and linkages
have been released. For example, in the aforementioned '678 patent
to Stuart, left and right operator levers, called coupling members,
are independently pivotable control assemblies that the operator of
the mower can grasp with his left and right hands. These assemblies
or members are pivotably supported along a common axis by a lawn
mower handlebar structure that extends from the rear of a midsize
commercial mower.
[0048] The handle bar shown in that patent serves to limit the
forward movement of these coupling members. Pushing the right
coupling member or lever forward causes the right rear drive wheel
of the mower to be driven forwardly. Pushing the left coupling
member forward causes the left rear drive wheel of the mower to be
driven forwardly. Upon being released by the operator, the coupling
members are returned automatically by a spring force generated by
one or more coiled springs to a neutral configuration, wherein the
driving forces to the wheels are stopped. Simultaneously, a spring
force causes a brake arm to engage a brake band which tightens upon
a brake drum, thereby preventing movement of the lawn mower. The
braking force on either wheel can be increased by pivoting its
respective coupling member in a counterclockwise direction, When
the mower is placed in reverse, the lower bar of the coupling
member can be used to control the drive of the mower, so the
operator movement of the member will correspond to the direction of
desired movement. Using the hydraulic system of the present
invention, band brakes are not necessary since the hydraulic fluid,
once trapped in the lines by the closed center valves 22 and 74
shown in FIG. 5, will not permit the driving wheels to turn. Thus,
the control valves 22 and 74 shown in FIG. 5, with their
spring-returned to closed center configuration, will inherently
provide a braking action as is often desired for sit-down riding
mowers and stand-up riding platform mowers. Manually operated
shutoff valves shown in parallel with wheel motors 60 and 80 in
FIG. 5 are normally closed when the hydraulic system of FIG. 5 is
being operated as a self-propelled dual-path hydraulic drive
system. When a riding mower using the FIG. 5 system has all power
turned off, the mower can be manually moved by simply opening these
two manual shutoff valves. When opened, these shutoff valves allow
hydraulic fluid to recirculate freely in a loop through the shutoff
valve and its respective wheel motor.
[0049] While the above description discusses two embodiments of the
present invention, it will be understood that the description is
exemplary in nature and is not intended to limit the scope of the
invention. For example, the invention, while disclosed for use in a
commercial walk-behind lawn mower, may also be used for other
steerable self-propelled commercial lawn equipment, such as a
stand-up or platform mowers, aerators, spreaders and sprayers.
Also, other types of operator-controlled, steerable self-propelled
mobile equipment that traditionally has used a two-pump dual-path
hydrostatic drive system may also beneficially use the single-pump
system of the present invention. Such steerable self-propelled
mobile equipment includes but is not limited to large vacuum
cleaners, cement buggies, pipe and steel rod carriers, sweepers,
floor and pavement scrubbers, skid-steer loaders, and agricultural
equipment such as windrowers. The present invention, in its broader
aspects, will therefore be understood to be applicable for use with
such equipment, and also to be susceptible to modification,
alteration, and variation by those skilled in the art without
deviating from the fair scope of the invention as defined in the
following claims.
[0050] The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention.
* * * * *