Hydraulic control system for vacuum sweeper trucks

A hydraulic control system for a vacuum sweeper truck including a hydraulic pump coupled to the truck's engine, a reservoir of hydraulic fluid, a hydraulic fan motor, a hopper actuator, and a valve assembly having three operative positions. In a first position the hopper actuator is deactivated and full power goes to the vacuum fan motor. In a second position the hydraulic fluid is diverted to the hopper actuator to raise the hopper and the vacuum fan motor is run at a reduced speed by hydraulic fluid returning to the reservoir. In a third position, the hydraulic fluid is again diverted to the hopper actuator to drive the hopper in a second direction, and again the fan motor is run at a reduced power level. A compensator is coupled to the hydraulic pump and is responsive to a cut-off setting and to the hydraulic pressure produced by the pump. A pressure adjustment means is provided in the cab of the truck which is coupled to the flow regulator to permit the truck operator to vary the cut-off setting of the flow regulator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to hydraulic control systems and more 
particularly to hydraulic control systems for utility vehicles. 
2. Description of the Prior Art 
To keep streets, parking lots, etc. free of debris and refuse motorized 
street sweepers are often used. Usually, the street sweeper apparatus is 
mounted on a truck's body, and includes a number of rotary sweeper brushes 
which engage the ground surface beneath the truck to propel the debris 
towards a conveyor system which deposits it into a hopper or other 
container. Some street sweepers include vacuum pickup heads as conveyors 
to draw the debris from the road surface and to deposit it in the hopper. 
Hydraulics have been commonly used to control the position of the brooms, 
hopper, etc. Hydraulic actuators require a pressurized source of hydraulic 
fluid which, in turn, implies a hydraulic pump coupled to a power source. 
The most logical power source is the truck's internal combustion engine, 
although it is not always used for reasons to be discussed subsequently. 
A major reason that a truck's internal combustion engine is often not used 
for powering a hydraulic pump is that the engine doesn't produce enough 
power at idling speeds to adequately pressurize the hydraulic fluid. One 
solution to this problem is to either manually or automatically increase 
the R.P.M. of the truck's engine until the hydraulic lines are 
sufficiently pressurized to power the actuators. This, however, tends to 
be wasteful and inefficient in that it results in high fuel consumption 
and in rapid wear of the engine's components. 
Another problem with powering a hydraulic pump from the truck's engine is 
that the output of the pump will vary with the engine R.P.M. as the truck 
accelerates and decelerates. A prior art solution to this problem has been 
to automatically regulate the pump's output in response to operating 
conditions. For example, in U.S. Pat. No. 4,343,060, of Hildebrand et. 
al., means are used for electronically sensing the rotational speed of the 
sweeping components, and then feeding the speed signal into an electronic 
computing and control unit which sends electric power to an electric 
displacement control valve on a variable and reversible flow piston pump. 
Such control system, however, are complex and tend to raise the cost of 
the street sweeper dramatically. 
Yet another problem with powering a hydraulic pump from a truck's engine is 
that the high starting load on the hydraulic pump will often kill the 
truck's engine. Prior art solutions to this problem include racing the 
truck's engine, which is very wasteful of fuel, or providing complex pump 
regulating devices such as that disclosed by Hildebrand et. al. 
An alternative method for powering the hydraulic pump is to provide an 
auxiliary internal combustion engine mounted at a convenient location on 
the truck's body. This auxiliary engine would run at a relatively high, 
constant R.P.M. to power the hydraulic pump. Auxiliary engines, however, 
are expensive, and again tend to be wasteful of fuel since they are in 
continuous operation. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a hydraulic control system for a 
vacuum sweeper truck which can be efficiently powered by the internal 
combustion engine of the truck. 
Another object to this invention is to provide a hydraulic control system 
which can be adjusted to sweep various terrains in an efficient manner. 
Briefly, the invention comprises a hydraulic pump coupled to the internal 
combustion engine of the truck, a reservoir of hydraulic fluid coupled to 
an input port of the hydraulic pump, a hydraulic fan motor having an 
output port coupled to the reservoir, a pair of bi-directional hopper 
actuators, and a valve assembly having three operative positions. A first 
position of the valve assembly couples the output port of the pump to the 
input port of the fan motor. A second position of the valve assembly 
couples the output port of the pump to first ports of the hopper actuators 
and couples second ports of the hopper actuators to the input port of the 
fan motor. A third position of the valve assembly couples the output port 
of the pump to the second ports of the hopper actuators and couples the 
first ports of the hopper actuators to the input port of the fan motor. 
Preferably, the hydraulic control system also includes a compensator 
responsive to a cut-off setting and to the hydraulic pressure at the 
output port of the hydraulic pump. The compensator is operative to 
maintain the hydraulic pressure on the pressurized lines at a level 
determined by the cut-off setting. The cut-off setting can be conveniently 
changed from the cab of the truck by means of a rotary coupling so as to 
vary the power delivered to the sweepers, pick-up head, hopper actuators, 
etc. in response to varying terrains and types of debris to be collected. 
An advantage of this invention is that expensive electronic control 
circuits, reversible hydraulic pumps, and auxiliary engines are not 
required. 
Another advantage of this invention is that the pump produces sufficient 
hydraulic pressure even when the truck's engine is idling. 
Yet another advantage of this invention is that the power output of the 
hydraulic devices can be manually controlled by the truck's operator from 
the cab of the truck. 
A still further advantage of this invention is that constant hydraulic 
pressure and flow can be maintained with varying engine speeds. 
These and other objects and advantages of the present invention will no 
doubt become apparent upon a reading of the following descriptions and a 
study of the several figures of the drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Referring to FIG. 1, a vacuum sweeper truck 10 (shown in phantom) includes 
a truck frame 12, an engine compartment 14, a cab 15, a dumping hopper 16, 
and wheels 18 in contact with the ground surface 20. Attached to truck 
frame 12 is a vacuum pickup head 22, a vacuum pump 24, and a flexible 
conduit 28 coupling the vacuum pump 24 to pickup head 22. Also attached to 
frame 12 are one or more sweeper brooms 30 which are rotated by broom 
motors 31. The brooms 30 and broom motors 31 are supported by pivoting 
links 32. 
The hydraulic control system of the present invention includes a hydraulic 
pump 34, a broom actuator 36, a vacuum pickup head actuator 38, and a 
hopper actuator 40. Actuator 36 causes broom 30 to move up and down as 
indicated at 42, actuator 38 causes vacuum pickup head 22 to move up and 
down as indicated by arrow 44, and actuator 40 causes hopper 16 to pivot 
between a loading and a dumping position as indicated by arrow 46. 
The hydraulic control system also includes a pair of valve assemblies 48 
and 50, and a hydraulic fan motor 52. An adjustment mechanism 54 is 
provided in the cab 15 of truck 10 to allow the truck's operator to 
conveniently reset the output pressure of pump 34. 
With reference to FIG. 2, the interconnection of the components of 
hydraulic control system will be discussed. The hydraulic pump 34 is 
coupled to the internal combustion engine 58 of truck 10. Pump 34 is 
preferably a variable, in-line piston unit such as the PVE21 manufactured 
by the Sperry Vickers Company of Troy, Mich. As will be discussed in 
greater detail subsequently, integrally formed with pump 34 is a pressure 
sensing flow regulator or (as it is often called) compensator 60 which 
maintains the pressure at an output port 62 of pump 34 at a level 
determined by the adjustment mechanism 54 of the present invention. 
A spring loaded check valve 64 is coupled to output port 62, and opens when 
the pressure at output port 62 exceeds 100 P.S.I. Thus, hydraulic pressure 
line 66 remains unpressurized until the output of pump 34 exceeds 100 
P.S.I., after which time the pressure on line 66 has a minimum pressure of 
100 P.S.I., and has a maximum pressure set by the adjustment mechanism 54. 
This pressure can be monitored at a test port 68 with a pressure meter or 
the like. 
An unpressurized reservoir 70 is provided to hold a supply of hydraulic 
fluid. An input filter 72 is coupled to the input line 74 of the reservoir 
and a filter 76 is coupled to an output line 78 of reservoir 70. A line 80 
couples filter 76 to the input port of hydraulic motor 34. 
Valve assembly 48 is preferably a three position, four way control valve 
having four ports 82, 84, 86, and 88. Port 82 is coupled to pressure line 
66 and port 84 is coupled to the input port of a fan motor by a line 90. 
The output port of fan motor 52 is coupled to filter 72 by a line 92. Port 
86 is coupled to a line 94, and port 88 is coupled to a line 96. 
Hopper actuators 40 preferably include a first set of ports 98 coupled 
together by a line 100, and a second pair of ports 102 coupled together by 
a line 104. Line 104 is coupled to line 94, and line 100 is coupled to 
line 96. When line 94 is pressurized output shafts 106 of actuators 40 
retract and when lie 96 is pressurized shafts 106 extend. 
Pickup head actuator 38 also includes ports 108 and 110, where port 108 is 
coupled to line 94 by a line 112, and where port 110 is coupled to line 96 
by a line 114. When line 94 is pressurized, the output shaft 116 is 
retracts, and when line 96 is pressurized shaft 116 extends. 
Valve assembly 48 includes a selector lever 118 having three operative 
positions as illustrated at 118, 118', and 118". When the selector switch 
is in the central position as illustrated at 118', ports 82 and 84 are 
coupled together such that the pressure lines 66 is coupled directly to 
the line 90 of fan motor 52. In this position, most of the power is 
provided to vacuum pump 24 (see FIG. 1) to provide maximum suction at 
pickup head(s) 22. 
When the lever is pivoted to the position shown at 118", ports 82 and 86 
are coupled together and ports 84 and 88 are coupled together. This causes 
pressure line 66 to be coupled to line 94 retracting shafts 106 of 
actuators 40 and retracting shaft 116 of actuator 38. The movement of the 
actuator shafts cause the dumper hopper to pivot into its resting position 
against truck frame 12, and raises the vacuum pickup head from the ground 
20. In this position, the sweeper truck is in its travel mode and may be 
driven normally on streets and highways. 
By pivoting the lever to the position shown at 118, ports 82 and 88 are 
coupled together, and ports and 84 and 86 are coupled together. This 
causes pressure line 66 to be coupled to line 96 which will extend shafts 
106 from the actuators 40, and will extend shaft 116 from actuator 38. In 
this position, the hopper is pivoted to its dumping position as 
illustrated in FIG. 1, and the vacuum pickup head is lowered to its 
operational position near ground level 20. As will be explained 
subsequently, actuator 38 can be be operated independently of actuators 40 
by lowering the pressure on line 66 to a point insufficient to activate 
actuators 40. 
When the lever is in either position 118 or 118", line 90 will be coupled 
to the low pressure or return line from actuators 38 and 40. This results 
in reduced power being provided to fan motor 52 during the dumping 
operation. 
Valve assembly 50 is also three position, four way control valve, although 
only two of the positions are operative, the third being a neutral 
position. The valve assembly 50 has four ports 120, 122, 124, and 126, 
where port 120 is coupled to line 92 by a line 128, and port 122 is 
coupled to pressure line 66 by a line 130. 
Broom actuator 36 has a first port 132 coupled to port 126 of valve 
assembly 50 by a line 134, and a second port 136 coupled to port 124 of 
valve assembly 50 by a line 138. When line 134 is pressurized, a shaft 139 
of actuator 36 is extended, and when line 138 is pressurized shaft 139 is 
retracted into actuator 36. An input port 140 of broom motor 31 is coupled 
to line 134 by a flow control valve 142. An output port 144 of broom motor 
31 is coupled to line 92. 
Flow control valve 142 has a variable orifice which is mechanically coupled 
by linkage 146 to shaft 139 of actuator 36. As shaft 39 extends from 
actuator 36, flow control valve 142 is opened to actuate broom motor 31. 
As shaft 139 retracts into actuator 36 the flow control valve 142 closes 
shutting off the broom motor. Thus, as broom 30 (see FIG. 1) is lowered 
into contact with ground 20 broom motor 31 is automatically activated, and 
as the broom is raised above ground level 20 the broom motor is 
de-activated. 
Valve assembly 50 includes a three position control lever 148. When the 
control lever 148 is in the position shown in solid lines, ports 120 and 
126 are coupled together, and ports 122 and 124 are coupled together. In 
this position, line 138 is pressurized causing shaft 139 to retract within 
actuator 36. When the lever is in the position shown at 148', none of the 
ports 120-126 are coupled together such that there is no connection 
between lines 128 and 130. When the lever is pivoted to the location shown 
at 148", ports 120 and 124 are coupled together, and ports 122 and 126 are 
coupled together. This causes line 134 to become pressurized which, in 
turn, causes shaft 139 to extend from actuator 36. 
As an option, and only for the very smallest of engines, a throttle 
adjustment actuator 150 can be provided having an input port 152 coupled 
to pressure lines 66 by a line 154. An adjustable biasing spring 156 is 
provided within actuator 150 to adjust the pressure at which shaft 158 
extends from actuator 150. Shaft 158 pushes against the throttle of engine 
58 to maintain the R.P.M. of the engine at a constant level as the load on 
the engine increases. 
As mentioned previously, one type of hydraulic pump 34 that can be utilized 
in the present invention is the model piston pump PVE21 produced by Sperry 
Vickers. In operation of the PVE21, rotation of a pump drive shaft causes 
a cylinder block, shoe plate, and piston to rotate. A number of piston 
shoes are held against the yoke face by the shoe plate. The angle of the 
yoke face imparts a reciprocating motion to each piston within the 
cylinder block. Inlet and outlet ports connect to a kidney slotted wafer 
plate. As the pistons move out of the cylinder block, a vacuum is created 
and fluid is forced into the void by atmospheric pressure. The fluid moves 
with the cylinder block past the intake kidney slot to the outlet 
(pressure) kidney slot. The motion of the piston reverses and the fluid is 
pushed out of the cylinder block into the outlet port. 
Referring now to FIG. 3, a prior art, flat cut-off flow compensator 60 
which controls the output of the PVE21 is illustrated. The compensator 60 
causes the pump to maintain a constant load pressure for all values of 
flow within the capacity of the pump providing the load is sufficient to 
build up pressure. 
The operation of the compensator 60 is as follows. When a no-load condition 
exists, the pump will deliver maximum flow at zero pressure. As the 
actuator load increases, pressure will rise although the flow will remain 
at maximum until pressure reaches the compensator 60 spring setting 
(cracking pressure). As a further increase in load occurs, system pressure 
will cause the compensator spool to move against the compensator spring, 
metering flow to the yoke stroking piston. The yoke stroking piston then 
moves the yoke to reduce flow. 
As flow is reduced, system pressure reduces slightly causing the 
compensator spool to return to the null position. At null, flow to the 
yoke stroking piston stops, as will the movement of the yoke, causing the 
flow to stabilize at a reduced value. If the load were to continue to 
increase, the pump flow will reduce to zero, and a deadhead pressure 
condition would exist. The pressure differential needed to cause the 
compensator spool to change from maximum flow (cracking pressure) to zero 
flow (deadhead pressure) is approximately 50 to 150 P.S.I. 
Pump outlet flow is proportional to the control range from cracking 
pressure to deadhead pressure. For example, if cracking pressure is 2900 
P.S.I. (maximum flow) and if deadhead pressure is 3000 P.S.I. (minimum 
flow), a pressure of 2950 P.S.I. would be equal to 50% of maximum flow. 
If the load decreases, pressure will decrease proportionally and the 
compensator spring will move the spool down, opening the yoke stroking 
piston to the case drain. As fluid is metered from the yoke stroking 
piston, the yoke spring will stroke the yoke to increase flow. The 
increase in flow causes a proportional increase in system pressure. The 
increase in system pressure returns the compensator 60 spool to a null 
position and flow from the yoke stroking piston will stop, as will the 
movement of the yoke. The flow will stay constant until another change of 
load occurs. 
If the load continues to decrease, pump flow will continue to increase, 
holding the outlet at compensator cracking pressure. When maximum flow is 
reached (at maximum stroke) a maximum flow and a maximum pressure 
condition exists. A further decrease in load will lower the outlet 
pressure until a final theoretical condition of maximum flow and zero 
pressure is obtained. 
A problem with using the compensator of Sperry Vickers for vacuum sweeper 
trucks in its unmodified form is that the cracking pressure of the 
compensator 60 is set and sealed at the factory at the highest allowable 
working pressure, which is approximately 2000 P.S.I. Since the compensator 
60 senses load pressure to adjust the flow of the pump and since the 
start-up pressure for the hydraulic loads of this invention are high, the 
unmodified compensator 60 will cause the pump to operate under a maximum 
load during pump start-ups, which will often kill the truck's engine. If 
the truck's engine were raced to avoid being killed, the hydraulic 
components would operate in an uncontrollable manner under the maximum 
(cracking) pressure. 
Another problem with using an unmodified compensator 60 is that during 
highway travel the flow to the hydraulic loads should be shut off, 
requiring a valve of some sort on the pressure line 66. The back pressure 
caused by the shut off valve would be sensed by the compensator 60 which 
would cause the pump to operate at maximum pressure. This would cause a 
considerable drag on the truck's engine, causing high fuel bills and 
considerable engine wear, and would result in massive heat losses in the 
system. 
Referring now to FIG. 4, adjustment mechanism 54 modifies the Sperry 
Vickers compensator 60 to permit the cracking pressure of the compensator 
60 to be reset from the cab 15 of the vacuum sweeper truck 10. Adjustment 
mechanism 54 includes a cap member 160 having threads 162 engaging threads 
provided in the housing 164 of compensator 60. A lower end 166 of cap 
member 160 forms a shoulder for engagement with compensator spring 168. 
An upper end of cap member 160 is provided with threads 170 which engages a 
threaded bore 172 of a lower end 174 of a flexible cable 176. An upper end 
178 of cable 176 is provided with a threaded bore 180. Cable 176 rotates 
such that a torsion force applied to upper end 178 is transmitted by cable 
176 to lower end 174 with very little loss. 
Adjustment mechanism 54 further includes a mounting plate 182 which 
attaches to a portion of the dashboard assembly 184 of the truck 10 within 
cab 15, and a support 186 attached at substantially right angles to the 
mounting plate 182. Support 186 is provided with a threaded bore 188. 
A screw 190 has a first end engaged with threaded bore 180 of cable 176, a 
central portion engaged with threaded bore 188 of support 186, and a 
second end attached to knob 192. A pair of stop nuts 194 and 196 are 
threaded onto screw 190. 
As knob 192 is rotated, cable 176 is caused to rotate, adjusting the 
position of cap member 160 within housing 164. The movement of the 
shoulder formed by the lower end 166 of cap member 160 adjusts the 
compression of spring 168 to set the cracking pressure of compensator 60. 
The end surface of upper end 178 of the cable 176 and the nuts 194/196 
determine the minimum and maximum cracking pressure by limiting the 
rotation of screw 190. 
Before starting the truck's engine, the cracking pressure of compensator 60 
is set to a low level by rotating knob 192 in a counter-clockwise 
direction. After the truck's engine is idling smoothly, the cracking 
pressure is increased by rotating the knob 192 in a clockwise direction 
until the pressure on line 66 is sufficient for the job at hand. For 
freeway and road travel, the cracking pressure of compensator 60 is again 
set to a low level to avoid energy (heat) losses in the pump 34. 
To raise and lower pickup head(s) 22 without moving the hopper 16, knob 192 
is rotated until the pressure on line 66 is sufficient to activate 
actuator 38 but is less than sufficient to activate actuators 40. This is 
possible because the energy required to move hopper 16 is much greater 
than the energy required to move the relatively lightweight pickup head(s) 
22. Thus, the combination of adjustment mechanism 54 and valve assembly 48 
permits the pickup head(s) 22 to be controlled independently of the 
dumping hopper 16. 
While this invention has been described in terms of a few preferred 
embodiments, it is contemplated that persons reading the preceding 
descriptions and studying the drawing will realize various alterations, 
permutations and modifications thereof. It is therefore intended that the 
following appended claims be interpreted as including all such 
alterations, permutations and modifications as fall within the true spirit 
and scope of the present invention.