Note: Descriptions are shown in the official language in which they were submitted.
Field of the Invent _
The present invention relates to street sweepers or
the like and more particularly relates to such sweepers
with a hydrostatic propulsion system and method of
operation having an inching throttle and a hydrostatic
brake incorporated therein.
Description of the Prior Art
Street sweepers with mechanical drives to the
propulsion wheels are illustrated in United States patent
3r316,578 to Tawny dated May 2, 1967; and Woolworth
patent 3/636~580 which issued on January 25, 1982
Summary of the Invention
According to an aspect of the invention, a
hydrostatic propulsion system for a vehicle, such as a
mobile sweeper or the like having driven wheels,
comprises:
means which define a main power driven positive
displacement swish plate pump including pistons and has
forward and reverse pump stroking means for varying the
position of the swish plate between zero piston
displacement to full forward or full reverse piston
displacement;
means which defines at least one swish plate motor
operatively connected to the pump and to at least one
driven wheel and has low speed and high speed motor
stroking means for varying the position of the motor
swish plate between an initial high piston displacement
low speed position and a low piston displacement high
speed position;
means which defines a pump stroking valve;
means which provides and maintains hydraulic fluid
in the main pump and in the motor;
operator controlled shift means moves the stroking
valve between a neutral position and at least one pump
selected operative position;
inching throttle valve means which is movable
between a fully open position and a fully closed position
and in fluid communication with both of the pump stroking
means and the stroking valve;
operator controlled accelerator means moves the
throttle valve means between a fully open position and
the fully closed position for progressively moving the
pump stroking means between zero piston displacement and
a positive piston displacement when the pump stroking
valve is in -the selected operative position for driving
the vehicle in the selected direction;
a hydrostatic brake valve is connected in parallel
with the inching valve and movable between a normal fully
lo closed position and an open position; and
a manually operated brake pedal is operatively
connected to the brake valve for shifting the valve to
the open position upon initial movement of the pedal for
balancing the fluid pressure acting on both of the pump
stroking means for providing a hydrostatic braking force
to the vehicle.
According to another aspect of the invention, a
hydrostatic propulsion system for a vehicle, such as a
mobile sweeper or the like having driven wheels,
comprises
means which defines a main power driven positive
displacement swish plate pump including pistons and has
forward and reverse pump stroking means for varying the
position of the swish plate between zero piston
displacement to full forward or full reverse piston
displacement;
means which define at least one swish plate motor
operatively connected to the pump and to at least one
driven wheel and has low speed and high speed motor
stroking means for varying the position of the motor
swish plate between an initial high piston displacement
low speed position and a low piston displacement high
speed position;
means which defines a pump stroking valve;
means which provides and maintains hydraulic fluid
in the main pump and in the motor;
operator controlled shift means moves the stroking
valve between a neutral position and at least one pump
selected operative position;
({I
inching throttle valve means which is movable
between a fully open position and a fully closed position
and in fluid communication with both ox the pump stroking
means and the stroking valve;
operator controlled accelerator means moves the
throttle valve means between a fully open position and
the sully closed position for progressively moving the
pump stroking means between zero piston displacement and
a positive piston displacement when the pump stroking
valve is in the selected operative position for driving
the vehicle in the selected direction;
the shifting means includes a manually operated
lever, a quadrant adjacent the lever and has reverse,
neutral, low and high speed positions thereon with the
reverse, low and high speed positions being the selected
operative positions, and a plurality of detent means
positioned between the lever and the quadrant for
maintaining the lever in specific ones of the selected
positions until the lever is manually moved to a
different position;
the accelerator means includes an accelerator pedal
controlled by the foot of an operator for moving the
throttle valve from a fully opened position to a fully
closed position for progressively increasing the speed of
the vehicle until the throttle valve is fully closed;
and additionally comprises a high speed motor valve
operatively connected to the high speed motor stroking
means, switch means operatively connected to the high
motor speed valve and responsive to the lever hying in
its high speed position to open the high speed valve; and
when the throttle valve is in its open position to
establish equal pressure on the forward and reverse pump
stroking means, when the lever is in the high speed
position to prepare the vehicle for movement in a forward
direction in a high speed range, and when the accelerator
pedal is actuated to progressively close the throttle
valve, the high pressure fluid is directed into the high
speed motor stroking means Jo shift or maintain the motor
swish plate in its high speed position for driving the
I
pa
vehicle in a forward direction in a high speed range at
speeds proportional to the degree of closure of the
throttle valve.
According to a further aspect of the invention, a
method is provided for controlling the speed of a mobile
vehicle, such mobile vehicle is driven by a hydrostatic
pump in fluid communication with a hydrostatic motor
drivingly connected to at least one wheel of the vehicle,
the pump and motor each includes a pivotal swish plate
for varying the displacement of associated pistons in
response to actuation of forward and reverse pump
stroking means and low speed and high speed motor
stroking means and includes a pump stroking valve. The
pump stroking valve is connected to a shift lever and an
inching valve is connected to the accelerator pedal. The
method comprises the steps of:
maintaining a supply of hydraulic fluid for the
hydrostatic pump and the motor;
selectively positioning the lever -to a position
which opens the pump stroking valve to a position which
initially communicates high pressure fluid to one ox the
pump stroking means and to thereafter equalize the
pressure on both pump stroking means; and
progressively moving the accelerator pedal to a
position which closes the inching throttle valve which
communicates with the forward and reverse pump stroking
means between a fully open position and a fully closed
position for progressively varying the pressure acting on
the forward and reverse pump stroking means from an equal
pressure and zero pump displacement to a position wherein
one of the pump stroking means is at maximum pressure and
the pump pistons are at maximum displacement for
directing fluid to the motor for slowly and smoothly
increasing the speed of the vehicle in the selected
direction as determined by thy degree of closure of the
throttle valve, when moving the shift lever into a high
forward speed setting the lever position is responsive
for directing the high pressure fluid into the high speed
motor stroking means for providing minimum motor piston
4b
displacement and a high forward speed range of between
about 0-20 miles per hour.
Brief Description of the Drawings
Preferred embodiments of the invention are shown in
S the drawings, wherein:
Figure 1 is a diagrammatic perspective of a three
wheel street sweeper powered by the hydrostatic drive
system of the present invention;
Figure 2 is a hydraulic diagram of the hydrostatic
drive system of the mobile street sweeper of Figure l;
Figure 3 is a diagrammatic illustration of one of
the stash plate propulsion drive motors;
Figure 4 is a diagrammatic side elevation of a shift
control lever connected to the stroking valve of a
lo traction pump;
Figure 5 is a diagrammatic plan of the stroking
valve of the traction pump connected to an accelerator
pedal which is shown in elevation; and
Figure 6 is a diagrammatic elevation of a brake
pedal shown in inoperative position and adjacent a switch
which pedal when depressed first actuates the hydrostatic
braking system and thereafter actuates the master
cylinder of a standard hydraulic brake system.
Description of the Preferred Embodiments
The hydrostatic propulsion system 10 fig. 2) of -the
present invention includes an inching drive and brake and
is intended for use with a vehicle such as a street
sweeper 12 fig. 1).
The street sweeper 12 comprises a chassis I mounted
on a steerable front wheel 16 and two rear wheels 18
(only one being shown) drive by hydraulic motors 22 and
24 foe. 2). The sweeper includes a hopper 25 which
receives debris from a main broom 26 and a pair of gutter
brooms 27 (only one being shown. The debris swept by
the brooms is elevated into the hopper 25 by an elevator
(not shown) disposed within a housing 28 for discharge
into the hopper 25. All of the above components are
driven by power from an engine 29 which drives a
hydraulic control system and the hydrostatic propulsion
system 10 of the
I
present invention. The rear wheels 18 are driven and
controlled by the hydrostatic propulsion system 1.0, An
operator in a cab 30 is provided with the controls to
operate the sweeper
The hydrostatic propulsion system 10 (Fig. 2) is
similar to that disclosed in cop ending Canadian patent
application SUN. 438,Q00, filed September 29, 1983,
except that certain pilot operated components have been
changed to manually operated components; and an inching
throttle valve 31, an orifice 32, and a hydrostatic brake
valve 33 have been added to the system thereby
considerably improving the performance of the vehicle.
Figure 3 diagrammatically illustrates motor 22 which
is identical to motor 24 and includes a non-rotatable
swish plate 34 ~ournaled on a rotatable motor shaft 35
and illustrated in its low speed, high capacity starting
position. Main pistons 36 and cylinders 37 are secured
to and rotate with the shaft 35 in response to receiving
high pressure fluid in one cylinder and discharging the
fluid from the other cylinder. The pistons include feet
38 which slide against the non-rotatable swish plate thus
imparting rotation to the shaft 35 and the main piston
and cylinder units slid ably connected thereto. A
"forward" non-rotatable stroking control piston 39 and
cylinder 40, and a "reverse" stroking control piston 41
and cylinder 42 are provided for controlling the angle of
the swish plate 34 and thus the speed ranges of the
motors. The pistons 39, 41 are connected to the swish
plate 34. Stationary abutments 44 and 46 limit the
pivotal movement of the swish plate between a maximum
displacement, low speed 18 position and a minimum
displacement high speed 8 position.
I-lydrostatic Propulsion Drive
The hydrostatic propulsion drive system 10
(Fig. 2) comprises a pump assembly 50 which includes
the companionways located within a housing illu~rate~ by
phantom lines 52; left and right motor assemblies
54,56 that include the components located within the
housings illustrated by phantom lines 58,60, respect-
lively; a valve assembly 62 illustrated between the
motor assembly and outlined within phantom fine Go; a
two-speed shift control assembly 68 illustrated within
phantom line 70; the inching throttle valve 31, the
orifice 32, and the hydrostatic brake valve 33; and a
conventional sup or tank T.
The pump assembly 50 includes a main positive
displacement, swish plate pump 80 and an auxiliary pump
82, both of which are of conventional design and are
driven by the vehicle engine 29 (Fig. 1) in a counter-
clockwise direction indicated by the arrow OW (Fig. 2).
The auxiliary pump 82 draws hydraulic fluid through
conduit 83 from the tank T and circulates the fluid
into the main pump 80 to first corrigenda thereafter
maintain top main pump charged. The auxiliary pump 82
also circulates the fluid through a conventional screen
S and provides make-up fluid for the main pump 80.
It will be understood that the pump 80 is
similar to the motors disclosed in Figure 3 except the
swish plate is movable to both sides of the zero degree
position, and the shaft is driven by the engine 29
fig. 1) rather than being driven by fluid from the
pump 80.
The left hydrostatic wheel motor 22 Fix 1
and I and the right hydraulic motor 24 (Fig. 2) are
conventional positive displacement, swish plate motors
which receive hydraulic fluid from the main pump 80 and
receive control fluid from the auxiliary pump 82. As is
well known in the art, when the pump 80 is being
started, the pump swish plate will be positioned sub-
staunchly normal to its axis of rotation and thus -the
pistons of the pump will be at low displacement and
will pump very little, if any, fluid. Conversely, the
Sicily Lowe I J. i) or each motor 2~,~4 will be
positioned at the maximum angle relative to its axis of
rotation, thus the piston of the motor 22,24 will be
at maximum displacement at start up.
With main pump 80 (Fig. 2) and auxiliary pump
82 started, hydraulic fluid will be drawn by ho Audi-
fiery pump 82 from the tank T through the suction con-
dull 83 which directs fluid into the conduits 84 and
86. When the pressure in conduit 84 exceeds 22~ psi.,
a pilot pressure operated relief valve 88 is opened
against the urging of a spring 90, thereby directing
fluid into pilot lines 92 and 94. The pressure in line
92 is directed through a mechanically operated four-way
stroking valve 100 in the pump assembly 50 when in its
illustrated neutral position. Fluid at equal pressure
is thus directed through the pilot lines 102 and 104 to
the forward swish plate control unit 106 and to the
reverse swish plate control unit 108 of the main
hydraulic pump 80, thus maintaining the main pump at or
near zero displacement.
When the four-way valve 100 is in neutral as
US indicated in Figure 2, fluid in pilot line 116 flows
through a parallel passage in a pressure override valve
118 but is blocked from further flow by the centered
core of manual stroking control valve 100.
It will be noted that the fluid in line 94
normally flows through a cooler C to tank T. However
a spring loaded cooler by-pass check valve 12S is
opened when the pressure in conduit 94 exceeds 25 psi.
With the mechanically operated valve 100 in
the illustrated neutral position, pilot pressure from
conduit 92 is directed to the motor assemblies 54,56
through pilot lines 92,126. Pilot pressure and make-up
fluid from line 126 enters the right propulsion motor
12 Al 7
24 through line 128; rod cnt~rs tic for- proJJulsi~
motor 22 through lines 130 and 132.
When the operator wishes to drive the sweeper
in a forward dir~ctioll, Lowe slyly ox tile mechanically
operated pump stroking valve 100 is moved upwardly
(Fig. 2) to the parallel passage position by means to
be described hereinafter. The pilot fluid from line
116 then flows through the parallel passages in valves
118 and 100 and line 102 to the forward Sicily hate
displacement control unit 106 thus pumping propulsion
fluid at the desired capacity through a forward conduit
142 into the two hydraulic motors 22 and 24 to drive
the motors in a forward direction. Low pressure fluid
discharged from the motors 22 and 24 return through
"reverse" conduits 144 to the reverse outlet of the
variable displacement pump on.
In order to drive the sweeper in reverse, the
operator actuates controls to be described hereinafter,
to shift the mechanically operated valve 100 to the
cross-passage position Pilot fluid from line 116 then
flows into conduit 104 to the reverse swish plate con-
trot unit 108 which then pumps propulsion fluid into
the reverse ports of the two motors 22 and 24 through
"reverse" conduits 144 thereby driving the vehicle in
reverse direction with the return fluid returning to
the pump By through "forward" conduit 142.
The valve assembly 62 receives hydraulic
fluid from forward conduit 142 and reverse conduit 144
which directs fluid into the conduits 146 and 148,
respectively. Conduits 146 and 148 communicate with a
6,000 psi spring loaded pressure relief valve 150 and
152, respectively. The conduits 146 and 148 also
communicate with opposite ends of a three-position
pilot operated shuttle twelve 154. When driving the
vehicle in a forward direction, high pressure will be
present in l'forwardll conduits 142 and 146, and the
conduits 144 and 148 will be at a lower pressure thus
shifting the core of the shuttle valve 154 downwardly
(Fix. 2).
The components in the valve assembly 62 co-
operate with the coml~oncnts in -the tweezed shift con
trot assembly 68 in order to control the displacement
of the pistons 36 (I 3) in the motors 22,24 and thus
the output speed ranges of the motors.
When the motors 22,24 are being driven
forward in response to shifting the mechanically
operated valve 100 to the parallel passage position,
the shuttle valve 154 is piloted down (Fig. 2) with its
cross passage F communicating with a low pressure fine
148 and with a line 156 connected to a 165 psi relief
valve 158. When the pressure in line 156 is less than
165 psi, valve 158 remains closed and prevents flow of
fluid through motor cylinders 36 (Fig. 3).
When relief valve 158 is opened by the press-
use in excess of 165 psi, fluid flows through passage F
of shuttle valve 154 and through conduit 156 to the
shift control assembly 68. This fluid then flows
through conduit 159 and is blocked by closed solenoid
valve 160. This fluid further flows through conduit
162, a cross-passage and pilot operated valve 164,
through conduit 166 and into cylinder 40 (Fig. 3) of
low speed swish plate control unit 168 of each motor
22,24 thus urging the swish plate 34 toward the low
speed 18 position. Some fluid drains out of the cry-
finder 42 of reverse wash plate control unit 170 of
each motor for return to the two-speed shift assembly
68 through conduits 172 and 173. This return fluid
then flows through a cross-passage in valve 164 and
returns to the reverse control unit 108 of the pump 80
through conduits 174,130,126,92, a parallel passage in
valve 100 and conduit 104. It will be noted what
excess fluid in line 156 will pass through the open
relief valve 158 and flow into line 130 for return to
the reverse control unit 108 as above described. The
'Yo-yo
hydraulic motors 22,24 will drive the sweeper at a low
speed range of about 0-10 miles per hour when receiving
fluid through the last described circuits.
The solenoid valve 160 of the two-speed shift
assembly 68 is opened in response to the operator
closing a switch 176 in the cab 30 was will be de-
scribed later) when a speed range of between about 0-20
miles per hour in the forward direction is desired.
Lowe pressure fluid then flows from conduits 15G and
159, through open solenoid valve 160, and through
conduit 178 which pilots valve 164 to its parallel
passage position. Some of the high pressure fluid then
flows through a restructure 179 into return line 174,
while the bulk of the fluid flows from conduit 162
through a parallel passage in valve 164, through
previously described conduits to high speed control
cylinder 42 (Fig. 3) in each swish plate control unit
170 of motors 22,24 thus urging the swish plate 34
toward its high speed I position. Some fluid return
from the cylinder 40 of the low speed swish plate
control unit 168 of each motor 22,24, flows through
previously described conduits and the other parallel
passage in valve 164 for return to conduit 174 and the
tank T through conduits 130/126,92, 94 and cooler C as
previously described
It will be understood that springs are
provided in each motor for urging the swish plates
toward their low speed, maximum displacement 18 post-
lion relative to a plane perpendicular to the shaft of
the motor; and that high speed, minimum displacement
occurs at about 8 from said plane.
When driving the vehicle in reverse, the
operator actuates the mechanically operated pump
stroking valve 100 to its reverse or cross-passage
position to reverse the direction of flow of fluid into
the main pump 80 as previously described, thereby
directing high pressure fluid through conduit 144 into
I
--10--
the reverse conduits Jo of thwack valve awoke y Go
which pilots shuttle valve 154 upwardly after a press-
use of 6000 psi opens relief valves 150,152 causing
fluid from the conduit 146 to flow throucJh L~sacJe
R in shuttle valve 154 thereby driving motors 22,24 in
their reverse direction. Since the operations per-
formed by the valve azalea lye an the whelk I
control assembly 68 are substantially the same as that
described in regard to controlling the forward sluice Or
the sweeper, the description of this portion of the
circuit is considered unnecessary.
The circuit 10 Jig 2) also includes high
pressure protection components which protect the ho-
draulic components from damage. Assuming that the
mechanically operated stroking valve 100 is moved to
its parallel passage or forward position, and that
hydraulic pressure in conduits 142 and 146 exceed 6000
psi, relief valve 150 will first open thereby directing
6000 psi fluid through valve 150 into "reverse" conduit
148, thus piloting valve 152 open and balancing the
pressure on opposite sides of the two motors 22,24,
returning the shuttle valve 154 to its illustrated
central position thereby stopping the flow of fluid
through the motors. The 6000 psi pressure in conduit
142 and conduit 185 will also be directed into a pilot
operated 6000 psi override control valve 186 in the
pump unit 50 to shift override valve 186 to the left
twig. 2) thereby piloting valve 118 to its cross-
passage position. With valve 118 in its cross-passage
position, further slow from line 116 through the valve
118 is blocked and a conduit 102 communicating with the
forward swish plate unit 106 of main pump 80 is opened
through cross-passage in valve 118 to reverse line 92
thereby reducing the pressure in line 102~ Thus, the
pressure is reduced below 6000 psi in the hydraulic
system 10 of Figure 2 allowing the protective come
pennants to return to their illustrated positions
If the vehicle is being drivel in a reverse
direction and the pressure in conduit 148 exceeds 6000
psi, relief valve 152 will first open, rather than
or before relief valve 150 owns, thus opening the
pressure override control valve 186 and shifting pilot
operated valve 118 to reverse the flow of fluid to the
control units 1~8,106 ox the main pump 80 until the
maximum pressure drops to a save pressure below 6000
psi .
A pair of check valves 190,192 are included
in the circuit 10 to assure that a supply of hydraulic
fluid is always available for compensating for fluid
loss by leakage or the like. When the trucking valve
100 is in its parallel passage forward position and the
inching throttle valve is at least partially closed,
the main pump 80 will direct high pressure fluid
through conduit 142 and a conduit 194 thereby holding
check valve 190 closed. Thus, the fluid from auxiliary
pump 82 flows through conduit 84 to the junction of the
check valves 190,192, but cannot open check valve 190.
However, check valve 192 is opened thereby direct
fluid through conduits 196,144 and 148 to provide a
supply of fluid to the motors 22,29 and the components
in the valve assembly 62.
When the stroking valve 100 is in its reverse
position, high pressure fluid from the main pump 80
will be conducted to check valve 192 through conduits
144,196 and holds it closed. Fluid from auxiliary pump
82 then flows through conduit 84, opens check valve 190
and flows through conduits 194,142 and 146 provide a
supply of fluid to the motor assemblies 54 and 56, and
to the pump assembly 62.
It will also be understood that the housings
of the pump assembly 50, the motor assemblies 54 and
56, and the valve assembly 62 each have conventional
"top drain" and "bottom drain" ports which drain
leaking fluid to the tank T through conduits (not
I ' t'
-12-
shown) in a convcntio~ l mallncr no thus will
described.
It will also be understood that thy specific
fluid l~rcssures rcC~rr~ o l~crcin art ~Jivcn as a-
proximate pressures to be used with the improved embodiment of the sweeper of the present invention, and
that these pressures are jot deemed critical.
In order to provide smooth operation of the
traction drive or propulsion system of the sweeper 12,
and to provide the operator with controls with which he
is familiar, operator controls have been provided which
are similar to those of the well known controls used on
certain modern automatic transmission motor vehicles.
Having reference to Figure 4, a control lever
210 is connected to the stroking valve 100 of the
traction pump 80 for controlling the position of the
wobble plate (not shown) of the pump between a reverse
position and a high speed forward position. A rod 214
is pivotal connected to the lever 210 and to a shift
lever 216 which is pivoted at 218. The ski t lever 216
cooperates with a quadrant 220 Wheaties detents 222
thereon which maintains the shifting lever 216 in one
of four positions until the operator moves it to
another position. As shown in Figure 4, the shift
lever 216 is placed in the low forward range L. The
lever may be shifted to the reverse position R; the
neutral position N which places the swish plate of the
pump perpendicular to its axis of rotation; to the low
position L at which time the forward speed range is
between 0-10 miles per hour; and to the high speed
range H of 0 20 miles per hour. When in the high speed
range H, the shift lever closes switch 176 in the two
speed shift control assembly 68 fig. 2).
It will be understood that movement of the
shift lever 216 between its several operative positions
will have no affect unless an accelerator pedal 224
(Fig. 5) is depressed since the inching throttle valve
31 to open when to depressed thus bet-
arcing the pressure on the forward and reverse swish
plate control units 106,10~.
The accelerator pedal 224 is pivoted inter-
mediate its ends to the floor of the cab 30 and isdiagrammati~ally illustrated as having a link 225
pivoted between a short arm of a bell crank 2~6 and the
pedal 224. The bell crank 226 is pivoted to the
floor and is pivotal connected to an inching throttle
lever ~28 by a rod 230. The inching throttle 31 is
diagrammatically illustrated as including a rotatable
core 232 with a passage 234 there through. When the
accelerator pedal 224 is not depressed, the passage 234
is fully opened thereby balancing fluid pressure in the
forward and rear pump control units 106,108 (Fig. I
respectively, by fluid flowing through conduits 236,238
(Figs. 2 and 5). When accelerator pedal 224 is grad-
Sally depressed and the mechanically operated stroking
valve 100 (Figs. 2,4 and I is placed in one of its
vehicle driving positions such as forward position L;
the passage 234 in valve 232 is gradually closed thus
increasing the pressure to the forward pup control
unit 106 (Fig. I When the passage 234 is fully
closed, the forward control unit 106 is at maximum
I displacement and pressure, and the reverse control unit
108 is opened to "bottom drain" which returns excess
fluid to tank T.
It has been determined that an optimum smooth
drive control is provided if the previously mentioned
orifice 32 in conduit 102 of Figure 2 is about 0.044
inches in diameter.
It is apparent that when the shift lever 216
(Fig. 4) is in reverse R, that stroking valve 100 (Fig.
2) will be shifted to the cross passage position and
the sweeper 12 will be driven in reverse in response to
depressing the accelerator pedal 224.
p
-14-
As shown in Figures 2 and 6, the solcrloid
operated hydrostatic brake valve 33 is shown in an
inoperative position with the fluid in conduit 23b,238
being okayed from flow through thy gore of the
valve 33. A conventional rake pedal 240 is pivotal
mounted in the cab 30 and when depressed moves a cam
241 into position to close a switch 242 connected to
the solenoid 244 of valve 33 for shifting the valve 33
to its open parallel passage position thereby allowing
fluid to flow between conduits 236 and 238~ through
conduits 102 and 10~ to the forward and reverse stroke
in valve 106 and 108, respectively. While the fluid
pressure is equalizing in the forward and reverse
stroking valves, and the pump wobble plate (not shown)
is returning to its neutral position, a hydrostatic
braking action acts on the rear wheel motors 22 and 24
thereby slowing and then stopping the sweeper 12.
The operator primarily relies on the ho-
drostatic braking system for stopping the sweeper
whether moving forward or in reverse. However, further
depression of the brake pedal 240 actuates a convent-
tonal hydraulic rear wheel braking system illustrated
only by a master cylinder 246, which conventional
system is used primarily for panic stops. The brake
valve 33 may also be operated by a manual fail safe
push button 248 which overrides the solenoid 244 and
prevents movement of the sweeper 12 even though the
operator has the shift lever 216 in the reverse or one
of the forward positions and has depressed the act
celebrator pedal 224. A brake light switch 250 is
closed upon depressing the brake pedal 2400
In operation of the hydrostatic propulsion
system 10 of the present invention, the engine 29 (Fig.
1) is first started thereby providing hydraulic fluid
to the system 10. The operator r while seated in the
cab 30, then places the shift lever 216 (Fig. I in
reverse R, low L, or high H, depending on which direct-
I
ion and at what speed rye he desires. ~ssumincJ 1ha~the operator places the shift lever 216 in the high
speed range, the high speed switch 176 (Figs. 2 and 4)
is closed and the oilier r Clue Conner vcl~icle Jo
travel between 0-20 miles per hour by depressing the
accelerator pedal 224 (jig. 5) different amounts.
Shuffling the lever 21G into the high speed position has
no affect until the operator depresses the accelerator
pedal 224 fig. 5) thereby shifting thy core 232 of lo
inching throttle valve I from its fully open position
to a partially or fully closed position depending upon
whether he wishes to drive slowly or fast.
If the operator removes his foot from the act
celebrator pedal 224, while driving, the valve core 232
will ye spring urged into its open position thereby
providing the hydrostatic braking action. If the
operator wants additional braking action, he depresses
the brake pedal 240 (Fig. 6) a sufficient amount to
close switch 242 and open solenoid brake valve 33 which
provides hydrostatic braking action which is normally
used to stop the vehicle. If a panic.bxaking situation
occurs, the operator depresses the brake further
thereby actuating the master cylinder 246 of a con-
ventional hydraulic braking system which applies the
braking force to stop the rear wheels 18 only one being
shown (Fig, 1).
From the foregoing description it is apparent
that a hydrostatic propulsion system is disclosed which
makes available to the operator standard automobile
type controls for operating a hydrostatic propulsion
driving system smoothly without abrupt jerking as
experienced with known hydrostatic drives, The con-
trots are also safe to operate since the shift lever
has no affect when in any of its selected positions
until the inching throttle valve is closed in response
to the operator depressing the accelerator pedal. When
the operator permits the accelerator pedal to raise
I
-16-
when he is driving the wiper, a hydrostatic breakneck
action occurs, and the vehicle is normally stopped by
lightly depressing a brake pedal which closes a switch
and applies a hydrostatic braking force sufficient to
S stop the vehicle under normal conditions
Although the best mode contemplated for
carrying out the present invention has boon herein
shown and described, it will be apparent that mod-
ligation and variation may be made without doper J
lo from what is regarded to be the subject matter of the
invention.
AJM:lw
