Patent Publication Number: US-2015074938-A1

Title: Hydraulic Fluid Flow Management System and Method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Provisional U.S. Patent Application No. 61/211,098 filed Mar. 26, 2009 and is a continuation of U.S. patent application Ser. No. 12/732,028 filed Mar. 25, 2010. 
    
    
     STATEMENT REGARDING FEDERALLY FUNDED RESEARCH AND DEVELOPMENT 
     The invention described in this patent application was not the subject of federally sponsored research or development. 
     FIELD 
     The present invention pertains primarily to vehicles designed for transporting and then operating equipment using a hydraulic fluid flow system; more particularly, the present invention pertains to a hydraulic fluid flow management system which provides a variable flow of hydraulic fluid to operate equipment mounted on the vehicle. Those of ordinary skill in the art will understand that while the disclosed system and method is described in terms of its use on a self-propelled vehicle, the equipment used to implement the disclosed system and method may be mounted on a trailer, a railroad car or a stationary surface having sufficient space to accommodate hydraulic fluid flow operated equipment. 
     BACKGROUND 
     The use of a hydraulic fluid to operate hydraulic cylinders to produce linear mechanical forces and/or to cause hydraulic motors to produce rotational mechanical forces has become common particularly on commercial vehicles used in include dump trucks, tanker trucks, fire trucks, well service trucks, garbage trucks, snow removal trucks, construction equipment and pavement sweepers among others. 
     The current invention will be described in terms of its use and mounting on a pavement sweeper; however, those of ordinary skill in the art will understand that the disclosed system and method has utility on any type of vehicle or fixed installation whose operation depends on the flow of hydraulic fluid to hydraulic motors, hydraulic cylinders or other equipment operated by the flow of hydraulic fluid. 
     For many years working vehicles that carried equipment typically used a separate small auxiliary internal combustion engine or a mechanical connection to a power take-off from the transmission or drive train of the transporting vehicle to provide the needed mechanical power to operate the equipment carried by the vehicle. The next generation of working vehicles changed the power supply from a direct mechanical connection to a separate small auxiliary motor or a power take-off connection to either a combination of a mechanical connection with some combination of hydraulic fluid powered components or a system using all hydraulic fluid powered components. The prior art systems using all hydraulic fluid powered components were easily recognizable by the many tubes, fittings and connections used to manage hydraulic fluid flow. Such prior art hydraulic systems often used multiple pumps or required that one section of the hydraulically operated equipment be shut down while other sections of hydraulically operated equipment were put into use. Oftentimes it has been necessary to both carry large amounts of hydraulic fluid and to run the vehicle engine at a higher rotational flow of hydraulic fluid. 
     Emission requirements in many states have targeted limiting the use of small auxiliary internal combustion engines similar to those used to power the equipment on prior art working trucks. Accordingly, there is a need to find an alternative to the separate small auxiliary engines or motors used to partially or completely power the equipment carried by working trucks. 
     Many prior art working trucks that use hydraulic fluid flow to operate the equipment mounted on the truck use a hydraulic fluid pump that is mounted to the frame of the vehicle. One or more belts from either the engine or the transmission provide the needed rotational power to turn the pump. This frame-mounting arrangement of the pump causes two problems. First, the place on the frame for mounting the pump may include some sort of structural brace or may provide a mounting for parts to another system. Such a structural brace of mountings for other parts complicates the installation of a frame mounted pump. Secondly, the drive portion of each pump must be manually aligned with the engine or transmission. Any misalignment between the drive portion of the engine or transmission and the drive portion of the pump shortens drive belt life, creates vibrations felt in the drivers compartment, and accelerates the wear of the bearings in the pump. 
     Control over the volume of flow of hydraulic fluid from the hydraulic pump to the service equipment mounted on prior art trucks is typically done mechanically. A knob or rotating control connected to a throttle cable is made available to the driver. A gauge providing a reading indicative of the pressure of fluid flow is placed near the driver&#39;s compartment. In some prior art pavement sweepers, a hydraulic fluid flow pressure gauge is placed behind the driver&#39;s compartment. Thus, to attain the desired setting on the fluid flow pressure gauge, the driver may have to turn around to look at the pressure gauge, then turn a knob to obtain the desired setting on a pressure gauge. The throttle cable which is mechanically attached to the knob adjusts a valve which regulates the pressure of the hydraulic fluid to the hydraulically operated service equipment on the back of the truck. 
     There is, therefore, a need in the art for a hydraulic fluid flow management system and method which is simple to use, easy to install and easy to service. 
     SUMMARY 
     The disclosed hydraulic fluid flow management system and method of the present invention is simple to use, easy to install, and easy to service. 
     The disclosed hydraulic fluid flow management system and method has three subsystems. 
     The first subsystem is the engine mounted hydraulic fluid pump and electrically operated flow control proportioning valve combination. 
     The second subsystem is the modular hydraulic flow distribution manifold assembly which receives the hydraulic fluid from the engine mounted hydraulic fluid pump and electrically operated flow control proportioning valve combination. This modular manifold assembly guides the hydraulic fluid to the various locations where it is needed to operate hydraulic equipment such as hydraulic motors and hydraulic cylinders. For example, in a pavement sweeper, the modular hydraulic fluid flow distribution manifold assembly guides the flow of hydraulic fluid to a fan motor. The fan motor turns the fan responsible for creating a negative pressure at the debris pick-up head and within the debris retention hopper. This negative pressure enables debris to be sucked up by the pick-up head and conveyed to the debris retention hopper. 
     The hydraulic fluid from the modular manifold assembly is also directed to the hydraulic cylinders which are used to position the debris pick-up head in relation to the surface of the pavement being swept and to position the hydraulic cylinders which cause the debris retention hopper to move to a dump position when it becomes necessary to empty the collected debris from the debris retention hopper. 
     Yet additional hydraulic fluid from the modular flow distribution manifold assembly is directed to a hydraulic motor which turns one or more rotating curb broom(s) and activates the hydraulic cylinder(s) which position the small rotating curb broom(s) with respect to the ground surface being swept. 
     The third subsystem is the computer operated controller and display. The computer operated controller and display sends an electrical signal to the electrically operated flow control proportioning valve to regulate the flow of hydraulic fluid from the engine mounted and engine driven variable displacement hydraulic piston pump. 
     The computer operated controller and display is mounted in the driver&#39;s compartment, typically in or under the dashboard. The flow control portion on the face of the computer controlled display is segmented into substantially ten percent flow increments up to 100% which are sent to the electrically operated flow control proportioning valve. In most situations, it is expected that the driver will set the computer controlled display somewhere between 60% to 100% flow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       A still better understanding of the hydraulic fluid flow management system and method may be had by reference to the drawing figures, wherein: 
         FIG. 1  is a side elevational view of a pavement sweeper as being an example of a vehicle on which the hydraulic fluid flow management system and method would have utility; 
         FIG. 2  is an exemplary schematic of a prior art hydraulic fluid flow system heretofore used on a vehicle such as shown in  FIG. 1 ; system and method; 
         FIG. 3  is a general schematic of the hydraulic fluid flow system and method of the present invention; 
         FIG. 4  is a schematic flow chart illustrating the interconnection of the componentry of the disclosed system and method; 
         FIG. 5  is a schematic diagram illustrating the mounting of the hydraulic fluid pump on the engine of the vehicle; and 
         FIG. 6  is an elevational view of the computer operated display available to the operator of the disclosed system and method. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     As explained above, the hydraulic fluid flow management system and method  100  of the present invention may be used on a variety of different types of vehicles or in different settings. The pavement sweeper  1000  shown in  FIG. 1  and on which the following description is based is typically used by government agencies or by sanitation contractors for street sweeping and private companies for cleaning parking lots. Sweeper  1000  is but one example of the many types of vehicles on which the disclosed invention may be used. 
     A glossary of the terms used in this Description of the Embodiments follows:
           100  hydraulic fluid flow management system and method;     200  engine driven pump and electrically operated flow control proportioning   valve combination;     210  engine mounted variable displacement hydraulic piston pump;     211  filter;     220  electrically operated flow control proportioning valve;     221  filter;     230  modular fluid flow distribution manifold assembly;     231  flow control (on/off) valve;     232  pressure relief valve;     233  check valve;     234  flow limiter;     235  flow control (on/off) valve;     236  pressure relief valve;     237  check valve;     242  fixed displacement axial hydraulic motor;     252  debris collection hopper positioning hydraulic cylinders;     254  pick-up head positioning hydraulic cylinders;     258  check valve;     260  computer operated controller;     262  auxiliary power port;     263  auxiliary power port;     264  sweep mode icon;     266  curb broom icon;     268  spot light icon;     270  warning light icon;     272  spot light movement buttons;     280  display;     282  vertical bar graph;     298  electrical signal;     299  electrical signal;     910  pump;     915  mechanical cable and linkage assembly;     920  one-way valve;     925  fixed displacement hydraulic motor;     926  radial turbine fan;     930  pick-up head positioning hydraulic cylinders;     935  debris retention hopper positioning hydraulic cylinders;     940  small separate fixed displacement gear pump;     945  curb broom positioning hydraulic cylinder;     950  curb broom motor;     955  valving;     960  valving;     965  hydraulic fluid reservoir;     970  filter;     1000  pavement sweeper;     1020  wheels;     1030  pick-up head;     1040  chassis frame;     1050  fan assembly;     1060  driver&#39;s compartment;     1070  rotating broom assembly;     1080  debris retention hopper.       

     As explained above, prior art systems used on a sweeper  1000  such as the exemplary sweeper shown in  FIG. 1 , have used a mechanical cable  915  ( FIG. 2 ) to increase or decrease the hydraulic fluid pressure from the engine driven hydraulic fluid pump  910 . This change in hydraulic fluid pressure increases or decreases the flow of hydraulic fluid. In the prior art system shown in  FIG. 2  the speed of the fan assembly which creates the negative pressure at the debris pick-up head is determined by the hydraulic fluid pressure output from pump  910  to a fixed displacement axial piston hydraulic motor  925 . The axial piston motor  925  provides rotational force to turn the radial turbine fan  926  using a small separate fixed displacement gear pump  940 . A small fixed displacement gear pump  940  causes hydraulic fluid to flow through a valve  955  to control a second fixed displacement gear pump  950  attached to the rotating curb broom assembly. The rotational speed of the curb broom itself is adjusted by the use of a mechanically controlled adjustable relief valve. The adjustable relief valve limits the amount of hydraulic fluid that can be returned to the hydraulic fluid reservoir  965 . 
     The pavement sweeper  1000  shown in  FIG. 1 , like most road vehicles has four or more wheels  1020  which are mounted to a chassis frame  1040 . Mechanical power which causes the drive wheels  1020  to turn, typically the rear wheels, is provided by an engine/transmission combination (not shown) located at the front of the vehicle  1000 . In the vehicle  1000  shown in  FIG. 1 , the engine/transmission combination is located underneath the driver&#39;s compartment  1060 . Such design is often referred to as a “cab over” design as the entire driver&#39;s compartment  1060  can be tilted forward to provide access to the engine/transmission combination. The remaining part of the vehicle  1000  is the space behind the driver&#39;s compartment  1060  wherein the equipment to be transported by the vehicle, to include the fan assembly  1050 , is placed. Those of ordinary skill in the art will understand that the system and method of the present invention may also be used in conventional vehicles where the engine is located in front of the driver&#39;s compartment  1060 . 
     At the very back of the equipment space is a debris retention hopper  1080  for holding the debris picked up from the pavement surface by the negative pressure at the pick-up head  1030 . The debris retention hopper  1080  is made to tilt so that when the debris retention hopper becomes full of debris, the debris retention hopper  1080  may be positioned to enable the debris collected from the pavement surface to fall out. Such tilting of the debris retention hopper  1080  is caused by the extension of the hydraulic cylinders  935  (not shown in  FIG. 1 ) located underneath the debris retention hopper  1080 . 
     As previously indicated, debris from the area of pavement being swept is lifted into the hopper  1080  by a negative pressure at the pick-up head  1030 . This negative pressure is caused by a fan assembly  1050  located at the entrance to the hopper  1030 . The position of the pick-up head  1030  is set to ride close to the ground surface to the enable the greatest removal of debris from the ground surface by the negative pressure at the pick-up head  1030 . 
     Shown in  FIG. 1 , on the driver&#39;s side of the vehicle, is a rotating curb broom assembly  1070  turned by motor  950 . The rotating curb broom assembly  1070  loosens debris from the ground surface and moves it toward the debris pick-up head  1030 . Such rotation of the curb broom assembly  1070  is caused by the rotation of a small hydraulic motor. The rotating curb broom assembly  1070  is moved into a position wherein the ends of the bristles of the rotating broom will contact the ground surface being cleaned near a curb. Such location of the rotating curb broom assembly  1070  is controlled by a hydraulic cylinder  945 . If desired, a second rotating curb broom assembly  1070  may be placed on the opposite side of the pavement sweeper  1000 . 
     A still better understanding of an exemplary prior art fluid flow system  900  used on the vehicle  1000  such as that depicted in  FIG. 1  may be had by reference to the exemplary prior art hydraulic fluid flow system  900  as shown in  FIG. 2 . 
     In  FIG. 2 , it may be seen that fluid flow in a prior art system begins at a hydraulic pump  910  whose output is controlled by throttle cable  915  or mechanical cable and linkage assembly as discussed above. Fluid from the hydraulic pump  910  passes through a one-way valve  920  to a fan motor  925  which drives the fan  926  mounted on the front of the debris retention hopper  1080  as shown in  FIG. 1 . Recall that it is the fan  926  which produces a negative pressure at the pick-up head  1030  which negative pressure draws debris into the debris retention hopper  1080 . 
     In the exemplary prior art fluid flow system shown in  FIG. 2 , the hydraulic fluid pressure and flow volume from the hydraulic fluid pump  910  driven by the engine is typically not sufficient to supply the needed power to drive the pick-up head locating cylinders  930  or the debris retention hopper cylinders  935  particularly when the vehicle&#39;s engine is at idle speed. Thus, an additional hydraulic pump  940  is needed to assure that the needed hydraulic fluid flow, at the desired pressure, is supplied. This additional flow of hydraulic fluid is also used to provide the hydraulic fluid needed to move the rotating curb broom assembly positioning cylinder  945  and to cause the curb broom motor  950  to turn. Appropriate valving  955 ,  960  is used to assure the flow of hydraulic fluid for controlling the operation of the hydraulically operated equipment. A hydraulic fluid reservoir  965  and filter  970  is used to assure that the proper amount of clean hydraulic fluid is supplied. 
     In many prior art systems, the nest of hoses and connections created from the implementation of the system shown in  FIG. 2  is complicated, time consuming to install and difficult to service. 
     As shown in  FIG. 3 , the system and method of the present invention  100  is implement by the use of three subsystems. The first subsystem is the engine mounted, variable displacement hydraulic piston pump  210  and electrically operated flow control proportioning valve  220  combination  200 . Rotational power for the variable displacement hydraulic piston pump  210  is provided directly from the front of the crank shaft of the vehicle&#39;s engine using a pulley  304  which engages a dedicated belt  302  as shown in more detail in  FIG. 5 . To assure proper tensioning of the dedicated pump drive at all times, a belt tensioner  324  made by the Gates Corporation of Denver, Colo. is used. 
     The engine driven and engine mounted variable displacement hydraulic piston pump  210  used in the preferred embodiment is made by Casappa of Parma, Italy. The electrically operated flow control proportioning valve  220  is made by Hydraforce, Inc. of Lincolnshire, Ill. Unlike prior art systems, the variable displacement hydraulic piston pump  210  of the disclosed system and method is mounted directly to the engine block and cylinder head. Such mounting to the engine block and cylinder head reduces the vibration felt by the driver when a prior art hydraulic fluid pump is mounted to the frame of the vehicle. Such mounting of the variable displacement hydraulic piston pump  210  to the engine also provides extended life for the variable displacement hydraulic piston pump drive belt  302 . 
     The flow of hydraulic fluid exiting the variable displacement hydraulic piston pump  210  passes through the electrically operated flow control proportioning valve  220  before entering the hoses which lead to the second subsystem, the modular flow distribution manifold assembly  230  located in the equipment space behind the driver&#39;s compartment  1060 . 
     Within the modular flow distribution manifold assembly  230  is a fluid flow divider configuration. The fluid flow divider configuration assures that the needed amount of hydraulic fluid at the required pressure is provided to the hydraulic motor  242  which drives the radial turbine fan assembly  240 . The hydraulic cylinders  254  which cause the debris retention hopper to tilt, the hydraulic cylinders  252  which position the debris pick-up head, the hydraulic cylinder(s)  256  which position the rotating curb broom(s) also are placed downstream from the modular flow distribution manifold assembly  230 . All required valving is contained within the modular flow distribution manifold assembly  230 . Thus, if there is an operational problem, a service technician does not need to troubleshoot the entire hydraulic system; rather, the modular flow distribution manifold assembly  230  is simply replaced. 
     Within the driver&#39;s compartment  1060  is the third subsystem, the computer operated controller  260  and display  280  which governs the operation of the electrically operated flow control proportioning valve  220 . When the vehicle is not being used for cleaning an area of pavement, there is a switch available to the driver which places the hydraulic fluid flow management system  100  is a shut-down or “road mode”. The road mode save fuel. When the vehicle arrives at a new job site, the road mode of operation is turned off and a “sweep mode” operation is initiated by the driver. Initiation of the sweep mode sends an electrical signal  298  to the flow control valve  231  and an electrical signal  299  to the flow control valve  235  as is shown in  FIG. 4 . 
     Control over the speed of the rotating curb broom assembly  1070  and the amount of negative pressure at the debris pick-up head is directly related to the volume of hydraulic fluid flow. To set the amount of hydraulic fluid flow needed to properly sweep the surface to be traversed by the sweeper vehicle, the driver is presented with a computer operated visual monitor  280  connected to a controller  260 . The visual monitor  280  has display resembling a bar graph as described below. The low flows of hydraulic fluid are represented by a short vertical bar as a percentage of the left side of the display and higher flows of hydraulic fluid represented as a longer vertical bar on the right side of the display. While normal operation is at full flow or at a substantially 100% on the bar graph display, certain dusty conditions are better cleaned with a lower flow of hydraulic fluid such as substantially 70%. 
     Operation 
     The electrically operated flow control proportioning valve  220  is used to either increase or decrease the flow of hydraulic fluid emitted by the engine driven variable displacement hydraulic piston pump  210 . As the level of flow of hydraulic fluid to the fixed displacement axial hydraulic motor  242  which turns the radial turbine fan assembly  240  increases, the pressure of the hydraulic fluid also increases. This increase in hydraulic fluid pressure increases the horsepower output of the fixed displacement axial hydraulic motor  242  which is related to the quantity of hydraulic fluid flow, and the torque output, related to the flow pressure of the hydraulic fluid. Thus, the speed of the radial turbine fan assembly  240  spools up as the horsepower and torque output of the fixed displacement axial hydraulic motor  242  increase. 
     Changes in the flow of hydraulic fluid are regulated and controlled by driver inputs to the computer operated controller  260  by using the display  280  mounted in the driver&#39;s compartment  1060 . As previously indicated, the computer operated controller  260  and display  280  enables two modes, a road mode and a sweep mode. The road mode is used when the vehicle is traveling between jobs and there is no need for a flow of hydraulic fluid to the equipment located on the back of the vehicle. In the sweep mode the hydraulic fluid provided to the equipment located on the back of the vehicle. In the road mode the electrically operated flow control proportioning valve  220  is automatically set to 0% flow. In the sweep mode, the electrically operated flow control proportioning valve  220  is energized according to a setting established by the driver after evaluating the debris to be picked up and the condition of the surface to be swept. 
     The logic in the computer operated controller  260  and display  280  ( FIG. 6 ) is programmed with a short ramp up function to prevent a sudden impact on the drive belts and engine components. The ramp up function also provides a soft start to the hydraulic fluid power management system  100  and the variable displacement hydraulic piston pump  210  mounted on the engine. 
     The computer operated controller  260  and display  280  also retains a memory between the road mode and the sweep mode. This memory eliminates the need for the driver to reset the hydraulic fluid power management system  100  each time that there is a switch from road mode to sweep mode. 
     The computer operated controller  260  and display  280  also controls the rate of hydraulic fluid flow increase and then converts the input signal into the vertical bar graph  282  on the driver&#39;s display  280  where each bar represents a substantially 10% increase in the flow of hydraulic fluid as shown in  FIG. 6 . The driver simply pushes a button to desired amount of flow and the proper electrical signals are sent to the electrically controlled flow proportioning valve  220 . To centralize control, the computer operated controller  260  and display  280  also includes an icon  264  verifying that the vehicle is in the sweep mode. Operation of optional equipment such as the curb broom, a spot light (to include spot light movement buttons  272 ), flashing warning lights, dust suppression water flow (not shown) may all be represented by icons  266 ,  268 , and  270  respectively on the computer operated display  280 . 
     The hydraulic fluid exiting the variable displacement hydraulic piston pump  210  whose flow is regulated by the electrically controlled flow proportioning valve setting placed on the visual display  280  by the driver, is directed to a modular flow distribution manifold assembly  230  which may be mounted in close proximity to equipment powered by the flow of hydraulic fluid. As shown in  FIG. 4 , the modular flow distribution manifold assembly  230  contains all of the necessary componentry to direct the flow of hydraulic fluid as well as the pressure relief valve  236  in the rotating curb broom assemblies and the pressure relief valve  232  before both the hopper positioning hydraulic cylinders  252  and pick-up head positioning hydraulic cylinders  254 . The modular design of the flow distribution manifold assembly  230  allows for easy adjustment and maintenance. The need for a complicated nets of fittings and hoses to connect the various pilot operated check valves, relief valves, and solenoid valves is eliminated by the used of the disclosed system and method 
     Those of ordinary skill in the art will understand that the hydraulic fluid flow circuit shown in  FIG. 4  is divided into three parts. On the left side of the hydraulic fluid flow circuit shown in  FIG. 4  is the first part which conducts fluid to the fixed displacement axial hydraulic motor  242  which turns the radial fan assembly  240 . Because there are no flow control valves, relief valves, or flow limiters in this part of the circuit, the hydraulic motor  242  receives a flow of hydraulic fluid whenever there is output from the electrically controlled flow proportioning valve  220 . Because the radial fan assembly  240  is always turning in sweep mode, there is always a negative pressure enabling the pick-up of debris by the pick-up head. 
     In the middle of the hydraulic fluid flow circuit shown in  FIG. 4  is the second part which conducts hydraulic fluid to the hydraulic cylinders  252  which control the position of the debris collection hopper  1080  and the hydraulic cylinders  254  which control the position of the pick-up head  1030  with respect to the ground. On/off flow control valve  231 , when actuated by electrical signal  298  opens up the second part of the hydraulic fluid flow circuit to the flow of hydraulic fluid. As indicated above, there are no limitations to the flow of hydraulic fluid in the first part of the hydraulic fluid flow circuit including the fan motor  242 . However, in the second part of the hydraulic fluid flow circuit shown in  FIG. 4 , pressure relief valve  232  limits the flow of hydraulic fluid to the debris collection hopper positioning hydraulic cylinders  252  and the pick-up head positioning hydraulic cylinders  254 . 
     On the right side of the hydraulic fluid flow circuit shown in  FIG. 4  is the third part of the hydraulic fluid flow circuit which conducts hydraulic fluid to the hydraulic cylinder(s)  256  which control the position of the rotating curb broom(s) and the motor  257  which turns the rotating curb broom(s). On/off flow control valve  235 , when activated by electrical signal  299 , opens up the third part of the hydraulic fluid flow circuit to the flow of hydraulic fluid. As indicated above, there are no limitations to the hydraulic fluid in the first part of the hydraulic fluid flow circuit including hydraulic motor  242 . And, as indicated above, there is a hydraulic relief valve  232  in the second part of the hydraulic fluid flow circuit which restricts the flow of hydraulic fluid to the two sets of positioning hydraulic cylinders  252  and  254 . In the third part of the hydraulic circuit which conducts hydraulic fluid to the curb broom positioning cylinder(s)  256  and the curb broom motor(s)  257  there is not only a relief valve  236 , but there is also a flow limiter  234  which is set to a hydraulic fluid flow rate of about 4.0 gpm in the preferred embodiment. 
     In sum, the hydraulic fluid flow circuit shown in  FIG. 4  shows a first part which has no flow restricting relief valves or flow limiters to enable continuous operation of a hydraulically powered motor whenever there is hydraulic fluid flow from the electrically controlled flow control proportioning valve. In the second part of the hydraulic fluid flow circuit shown in  FIG. 4 , there is an on/off hydraulic fluid flow control valve and a relief valve which enables the operation of positioning cylinders whenever the on/off hydraulic fluid flow control valve allows hydraulic fluid to flow into the second part of the hydraulic fluid flow circuit. Then in the third part of the hydraulic fluid flow circuit shown in  FIG. 4 , there an on/off hydraulic fluid flow control valve, a relief valve and flow limiter which enables the operation of hydraulically operated devices at a flow rate determined by the flow limiter whenever said on/off hydraulic flow control valve permits the flow of hydraulic fluid and the hydraulic fluid pressure in the third part of the hydraulic fluid flow circuit is sufficient to enable the flow of hydraulic fluid through the relief valve. 
     As may be further seen in  FIG. 4 , the variable displacement  210  output flow is limited by the electrically operated flow control proportioning valve  220 . Hydraulic fluid entering the modular hydraulic fluid flow distribution manifold assembly  230  passes through a filter  211  on its way to the control valve  231 , relief valve  232  and a check valve  233  combination. The position of the control valve  231  is determined by electrical signal  298 . The hydraulic fluid which does not pass through the pressure/flow control  234  operates the cylinders  252  which tilt the debris collection hopper and the hydraulic cylinders  254  which vertically position the pick-up head as well as operate the fan motor  242 . The hydraulic fluid which flows through the flow limiter  234 , the second flow control valve  235 , which is positioned by electrical signal  299 , relief valve  236  and check valve  237  combination goes on to operate the curb broom(s) positioning cylinder  256  which position the rotating curb broom broom(s) and the motor(s)  257  which cause the rotating curb broom(s) to turn. As may be seen in  FIG. 4  a flow control check valve  258  is placed between motor  257  and cylinder  256 . Both the variable displacement hydraulic piston pump  210  and the electrically operated flow control proportioning valve  220  are protected by filters  211 ,  221 . 
     Another key feature of the disclosed system and method are the two auxiliary hydraulic fluid power ports  262  and  263  located in the first part of the hydraulic fluid flow circuit including the motor  242 , as shown in  FIG. 4 . Such fluid power ports  262  and  263  enable a variety of equipment to be mounted to and powered by the disclosed hydraulic fluid flow circuit. For example, a hydraulically operated positionable snow plow could be mounted to the front of a sweeper and a hydraulically operated sand spreader could be attached to the rear of a sweeper. If a sweeper is used to clean up an area following a storm, one auxiliary power port could be used to power an arm for picking up small trees or branches and loading them into another vehicle. The other power port could be used to power a trailer mounted chipper for chopping up small tress and sending the wood chips to another vehicle. 
     As shown in  FIG. 5 , the variable displacement hydraulic fluid piston pump  210  receives power from a dedicated drive belt  302  connected to a pulley  304  mounted on the end of the crankshaft of the engine. Brackets  306 ,  308  may be used to mount the variable displacement hydraulic fluid piston pump  210  to the top of the engine for easy assembly and maintenance. Existing serpentine belts  312 ,  314  shown in dashed lines may still be use to power the various items typically driven by the engine such as a water pump  316 , an air conditioner compressor  318 , an alternator and/or power steering pump  322 . In the preferred embodiment the variable displacement hydraulic fluid piston pump  210  is driven with an eight groove, shallow V-belt which is tensioned by a spring loaded tensioner  324  as described above. 
     The disclosed system and method provides the following advantages:
         a single hydraulic fluid pump can be used to operate multiple items of hydraulically powered equipment whether the equipment is vehicle mounted, trailer mounted, or in a fixed location;   auxiliary hydraulic fluid power ports are provided;   the flow controls, relief valves, etc. are contained in a modular distribution manifold assembly;   all items of service equipment may be operated while the engine remains at idle speed;   the system may be installed on a vehicle without having to move parts of the truck installed by the truck manufacturer;   the system is emission free and is eco-friendly as it may be used with biodegradable hydraulic fluid.       

     While the disclosed system and method has been explained according to the illustrated embodiment, those of ordinary skill in the art will understand that numerous other embodiments and modifications thereof may be made without departing from the disclosed system and method. Such other embodiments and modifications shall be included within the scope and meaning of the appended claims.