Patent Publication Number: US-6662556-B2

Title: Hydraulic systems for a small loader

Description:
This application refers to and priority is claimed from U.S. Provisional Patent Application Ser. No. 60/335,161 filed Nov. 15, 2001, the content of which is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a small self-propelled loader which has hydraulically powered drive and work elements, connected in a hydraulic system to provide desired operational functions utilizing the available horsepower efficiently. The engines on small loaders are also relatively low horsepower, and by using the hydraulic power available efficiently, various tasks can be carried out at the same time that the loader can be moved or driven at an appropriate speed. 
     Various small loaders have been advanced, and these usually do use an internal combustion engine with hydraulic drives for the propulsion system, as well as hydraulic cylinders for moving loader arms and driving attachments or accessories. These loaders generally do not have an operator&#39;s compartment, but the operator will stand on a platform, or on the ground, adjacent to controls at the rear of the loader. In order to efficiently use available power, it is desirable to have the full flow of hydraulic pumps available for propelling the vehicle at times, and at other times it is desirable to use a high pressure for accessories while permitting the vehicle to creep at a slow speed, for example when operating a trencher. The present hydraulic system is connected using standard components to achieve the desired results. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a hydraulic system for a small loader, as shown a track driven loader propelled by hydraulic motors. The internal combustion engine that is used is maintained at a small size and horsepower output based on the tasks involved. The loader is completely hydraulically driven and operated. 
     The loader of the present invention uses tandem gear pumps that can be controlled in various modes of operation. When maximum travel speed is desired, separate pump sections are connected to drive the hydraulic motors on the opposite sides of the loader or vehicle, so that each of the motors is receiving the full flow from one of the pump sections or separate pump. 
     A circuit is provided for carrying the flow of hydraulic fluid under pressure beyond the motors in one mode. The motor valves have a flow through center position where the flow enters a common drain line. The return side of the motors is also connected to the common line leading to a diverter valve and then to a work motor group valve, such as hydraulic lift cylinders for loader arms, a tilt cylinder for a loader bucket, and to auxiliary connections for driving hydraulic motors or actuators on attachments that are used with the loader. Excess flow then is returned to the reservoir or tank, after it has been passed through the necessary valves for controlling the work motor components. 
     Additionally, the hydraulic circuit is made so that when it is desired to direct the flow from the pumps primarily to work group motors, for example when the loader may be standing still or as will be explained when it is to move only at a very low or “creep” speed, the diverter valve can be operated to direct the primary flow from the pumps to the work group valve, so that substantially the full output of one pump, and, if desired, part of the output from the other pump can be used for operating work motors such as the loader lift cylinders or actuators, the tilt cylinder, or some rotary motors for auxiliary equipment connected through quick couplers that connect hydraulic components on attachments to lines on the loader. 
     The hydraulic system includes a flow control valve that is manually adjustable when the diverter valve is directing the major flow from the pump sections to the work group valve to permit a controlled amount of hydraulic fluid under pressure from one pump section to be divided and supplied to the valves for the drive or travel motors. The low, controlled flow to the respective drive motors permits a “creep” movement while the majority of the flow powers an attachment motor, such as a trencher or other component that requires some forward motion of the loader at the same time that the auxiliary attachment is working. 
     The hydraulic system provides efficiency of operation based on the available power. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a small loader having a hydraulic system made according to the present invention installed thereon; 
     FIG. 2 is a schematic block diagram of the hydraulic system of the present invention; 
     FIG. 3A is a first portion of a schematic drawing of the hydraulic system of the present invention; 
     FIG. 3B is a second portion of the schematic drawing of the hydraulic system and mating with FIG. 3A; and 
     FIG. 4 is a more detailed schematic showing a reverse speed limit valve in the motor circuits. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a small skid steer loader indicated generally at  10  is shown as a walk behind powered loader that has a body or frame  12 . The frame  12  supports a track assembly  14  on each side of the loader for propelling the loader in forward and reverse directions through the use of drive hydraulic motors  16 A and  16 B. Drive motors  16 A and  16 B are hydraulic motors operated from a pump assembly  18 , that includes two gear hydraulic pumps  18 A and  18 B, which are driven by an internal combustion engine  20  mounted on the body or frame  12  in a housing  17 . Other hydraulic motors and pumps can be used. 
     Each track assembly  14  includes a track frame  14 A, a drive sprocket  14 B, and a front idler wheel  14 C over which a track  14 D is mounted. Bogie wheels  14 E are also provided on the track frame  14 A for support of the track. 
     The loader body or frame  12  has upright supports  22  at the rear of the frame and these supports  22  extend upwardly a little higher than waist level of an operator standing on the ground. The upright supports in turn pivotally support base or rear ends of a lift arm assembly  24  on pivots  21 . Lift arm assembly  24  includes individual lift arms  24 A and  24 B on opposite sides of the body or frame  12 . Lift arm assembly  24  is raised and lowered with extendible and retractable double acting hydraulic motors, in the form of cylinders or actuators  26 , operating with hydraulic pressure from the pumps  18 A and  18 B, as will be explained, and controlled by suitable valves, as will be explained. The valves are part of a work valve assembly that forms part of the overall controls for the loader or other machine. 
     The hydraulic lift cylinders  26  (there is one cylinder on each side of the frame, and only one is shown in FIG. 1) have base ends pivotally mounted as at  28  to the body or frame  12 , and the cylinders have extendible and retractable rods  29  that have rod ends that are pivotally mounted as at  30  to each respective lift arm of the lift arm assembly  24 . Lift arm assembly  24  has a bucket  34  at the front end, mounted on the lift arms, and controlled by a bucket control hydraulic motor, in the form of a tilt cylinder or actuator  36 . Tilt cylinder  36  has its base end connected to an upright strut  38  on the lift arm assembly. The bucket tilt cylinder also is operated through suitable work valves, as will be shown in the hydraulic schematic portion of the description. 
     An operator&#39;s station shown at  52  is at about waist level with an operator, and various hydraulic control valve handles are provided at the station. The operator stands at the rear of the loader, and can operate the drive motors, the lift arms, the bucket, and any powered attachment or accessories. It should be noted that motors on attachments or accessories can be connected to hydraulic lines that are controlled by a valve as will be explained, and which are connected to lines from the valve through quick couplers shown at  43 A and  43 B, respectively. 
     Referring to FIG. 2, a block diagram representation of the hydraulic system for the loader is provided. In FIG. 2, the engine  20  is driving the pump assembly  18 , which includes individual gear pumps or pump sections  18 A and  18 B. A first diverter valve  40  is a spool type valve, which has ports for receiving the flow from the pumps  18 A and  18 B, individually along lines  42 A and  42 B. In one position of the diverter valve  40  flow is provided through output ports and lines  44 A and  44 B to a valve block having first and second drive or traction motor control valves shown in block diagram form at  46 A and  46 B. 
     The valves  46 A and  46 B are used for controlling flow to the drive motors  16 A and  16 B, respectively, that in turn drive sprockets  14 B and the tracks  14 D. The valves  46 A and  46 B have a center through flow position where the drive motors are not powered, and in this position the flow passes to a line  48 . The return flow from each of the motors, that is the low pressure side, is also provided to line  48  that is termed a “power beyond line” or common drain line. Line  48  carries the flow from the drive motors and/or valves  46 A and  46 B and will provide this flow to various other work motors or components on the loader. 
     The line  48  is connected to a second diverter valve  50  the spool of which is mechanically coupled to the diverter valve  40  so that the two diverter valves  40  and  50  are simultaneously operated by an operator moving a control handle. When the valve  40  is set to direct flow into the individual lines  44 A and  44 B and thus to the diverter valve  50  will provide the flow from line  48  to an output line  54  and to a work group valve block  56 . 
     The work group valve block  56  has individual manually controllable 4-way valves connected to motors including the lift cylinders  26 , tilt cylinder  36  and when needed to motors  58  for auxiliary equipment or attachments. The work group valve block  56  is arranged so that separate relief valves are provided for controlling maximum pressure of the lift and tilt cylinders, which is separately relieved from a relief valve for the overall work group valve which when it is separately used and not in series with the line  48 , as will be explained, will provide a much higher pressure to the motor for auxiliary equipment  58 . A line  60  leads from the work group valve to a hydraulic tank  62 . 
     As will be more fully shown, when movement of the loader is stopped or is to be very slow, arrangement is made so that the flow from the one of the hydraulic pumps  18 A and  18 B and partial flow from the other is diverted to the work group valve  56 , in particular for running auxiliary equipment represented at  58 . 
     A shift position of the diverter valve  40 , and the simultaneously operated diverter valve  50  (these are tied together so they operate at the same time) will cause the flow from one pump to be diverted to the work group valve  56  along with at least some flow from the other pump. 
     In the alternate position of diverter valves  40  and  50 , pump  18 A provides flow to flow control valve assembly  70  and pump  18 B provides flow along line  63 B. Flow control valve assembly  70  has a manually adjustable flow control valve internally that can be closed to divert all of the flow from pump  18 A out a line  65  which connects to line  64  or opened to provide for a portion or most of the flow from the line  63 A to go through a flow splitter  71 A,  71 B and into lines  72 A and  72 B which connect to the lines  44 A and  44 B leading to the valves  46 A and  46 B. The flow from lines  72 A and  72 B is then available for use for driving the drive motors  16 A and  16 B. 
     The flown control valve  70 A can be adjusted so that the loader will only “creep” along a very slow rate. In this alternate position of the diverter valves, flow through from the motors then connects to line  48 , and diverter valve  50 , when shifted, directs this low flow from the motors  16 A and  16 B or through the flow from the motor valve through a line  76  to the reservoir or tank  62 . 
     Both lines  63 B and  65  connect to a line  64  that tees into the line  54  to the work group valve so all or most of the pump flow is available for auxiliary equipment. A check valve  66  (FIG. 3) prevents back flow through diverter valve  50 . 
     In FIGS. 3A and 3B, similar numbering is used as in FIG. 2, but more detail is provided in relation to the use of different relief valves for the different functions. The engine  20  is illustrated along with the pump assembly  18 , and individual pumps or pump sections  18 A and  18 B. These pumps provide for flow along the lines  42 A and  42 B to the first diverter valve assembly  40 . The diverter valve  40  is a spool type valve that is essentially a 6-way diverter valve, and in the diverter valve position shown in FIG. 3A, it can be seen that the line  42 A is connected to the line  44 A and line  42 EB is connected to the line  44 B. These lines lead directly to the valve block  46  that contains drive motor control valves  46 A and  46 B, respectively. The valves  46 A and  46 B are spool valves that are controlled through the use of handles  80 A and  80 B, which are shown schematically in FIG.  1 . These spool valves are made so that they can provide a proportional flow to the travel motors based on displacement of the valve spools. The spools are reversible so that the motors  16 A and  16 B can be reversed in rotation. Again, the speed is controlled by displacing the spools from a central position, and the amount of movement will determine the speed of travel. 
     Each of the valves  46 A and  46 B has a separate relief valve for the motors as shown at  46 C and  46 D, respectively. These valves are set at a high pressure, for example 2800 psi or 193 bar. These are the highest pressure relief valves in the system. In part this is because the power beyond line  48 , which is connected to the valves  46 A and  46 B at a common terminal as shown at  48 A, carries pressure to the work group valve and to actuators and auxiliary equipment in series so that pressure in the work group with diverter valves  40  and  50  in their first positions will add to the pressure at the travel motors  16 A and  16 B. The higher pressure is thus necessary because of the series fluid pressure connection. When the relief valves  46 A and  46 B open, they will dump flow into a return line  86  that leads to tank  62 . The flow from both of the pumps or pump sections  18 A and  18 B is about 14 gallons per minute. In this first position of valve  50 , the flow goes to the line  54  and through check valve  66  to work group valve  56 . The line  54  is connected to the pressure side of work group valve  56 . 
     Work group valve  56  includes a work spool valve  88  that is used for controlling the tilt cylinder  36 . A tilt lockout solenoid valve  90  is illustrated in the circuit and can be provided, if desired. The pressure and return lines from the tilt cylinder have relief valves  92 A and  92 B respectively that are set at about 1400 psi or 96.5 bar, which is a lower pressure than that of valves  46 A and  46 B, but adequate for operating this cylinder. 
     A work spool valve  94  is used for controlling the lift cylinders  26 , and again a solenoid lockout valve  96  is used in the line to the base of the lift cylinders. Suitable relief valves  92 C and  92 D, which are set at the same pressure as valves  92 A and  92 B are connected into the lines for the lift cylinders  26  as well. As can be seen, the lift cylinders  26  are connected in parallel, and the lockout solenoid valves  90  and  96  are on the pressure sides of the respective cylinders when the cylinder is being used to lift the bucket. 
     A main relief valve  98  in the work group valve block  56  is set at a higher pressure, for example 2500 psi or 175 bar and is the relief pressure setting for the auxiliary equipment represented at  58 . 
     The auxiliary equipment is operated through a spool valve  100 , that is controlled by a valve control handle such as those shown at  102  generally in FIG.  1 . 
     The relief pressure for the valve  100 , and thus for the auxiliary equipment, is from relief valve  98 , which is set high enough for operation of motors on trenchers or diggers when those machines are the auxiliary equipment or attachment. 
     The 6-way diverter valve  40 , as shown, will provide flow along line  63 A and along the lines  63 B and  64  when the diverter valve  40  is shifted to connect the input ports A and B shown in FIG. 3A to ports E and F on the 6-way diverter valve  40 . The adjustable orifice or flow control valve shown at  70 A in valve  70  can be manually closed with a handle  70 H and all flow along line  63 A will be diverted to line  65 . 
     The adjustable orifice or valve  70  can be manually controlled for providing a limited or partial flow from line  63 A to a pair of flow splitter valves  71 A and  71 B, respectively, that will divide the flow from adjustable orifice or valve  70 A so that it will be provided along lines  72 A and  72 B to lever  44 A and  44 B and then to the respective valves  46 A and  46 B. This, again, provides for a major portion of the flow to go to the work group valves along line  64 , and in particular to the attachment  58 . 
     If the attachment  58  is a trencher or a digger where there should be movement of the loader, the creep speed control for permitting the vehicle or loader to creep slowly is obtained by adjusting the variable orifice of the flow control valve  70 A. In effect, the present hydraulic system provides for two circuits in one. In one mode, one pump will supply a valve for one of the drive motors, and the other pump will provide flow to the valve for the other drive motor. Speed, again, is controlled by moving the spools in valves  46 A and  46 B, so that the flow can be from zero to full flow, and all of the excess flow will go out through the power beyond or common drain line  48 , along with the return flow from the motors. 
     In the second mode, the diverter valves  40  and  50  are shifted so that the work group, including the attachment motor lines and connection or couplers  43 A and  43 B or work cylinders will be provided with high flow, and the pressure available for work motors, such as cylinders or attachments will be controlled by relief valve  98 . The arrangement permits the use of gear pumps in tandem, for providing a hydraulic fluid under pressure. 
     When the work cylinders are provided with flow from common drain line  48  the pressures from the work cylinders and the drive motors are in series or additive. Thus pressure at relief valve  46 C is additive with pressures from the work cylinders and drive motors. There are times when the work cylinders are loaded and the drive motors are used, that the setting of relief valve  46 C will be exceeded. 
     In the second position of the diverter valves  40  and  50  the relief valves  46 C and  98  no longer are in series and the pressures are no longer additive. The relief valves  46 C and  98  will operate independently, so the pressures at the drive motors and work cylinders are capable of providing independent operating pressures to the respective work members or motors. 
     As shown in FIGS. 3B and 4, each of the motors has a counterbalance valve indicated at  120 A and  120 B. These valves are used in the motor circuit, so that the respective motor will be locked unless the valve spool is being operated, and there is pressure being supplied to one side of the motor or the other. 
     It also should be noted that in FIG. 4, the drive motors  16 A and  16 B are connected into a reverse speed limit valve  125 , which will limit the speed of the loader in reverse by passing the flow through a selected orifice  126 A and  126 B, respectively that can be adjusted. Bypass check valves are provided for flow when the motors are being driven in the forward direction, as can be seen. The reverse flow control then does limit only the reverse speed of the loader. 
     The valves  46 A and  46 B are shown in greater detail in FIG. 4 as well, and the valve  46 A, which is the left-hand travel or drive motor control spool, has a spool assembly shown at  130 A that provides for a center flow through passageway  132  when the valve is in its neutral position, and there is no flow to the left motor. This central flow passageway  132 A is connected to the junction  48 A, previously shown, which in turn is connected to the power beyond or common drain line  48  that leads back to the diverter valve  50  or to drain. 
     In the valve position where the motor would be driven in a forward direction, it can be seen at  134 A that the valve spool will block flow through the inflow line shown at  136 A, to the junction  48 A, and when the spool is moved in an opposite direction, which is the reverse side as shown at  138 A, the flow from the line  136  to junction  48 A is closed as well, but in those positions and condition of drive the flow is to the respective motor and the return flow through the valve is connected to the lines shown at  140 A that is connected to the junction  48 A to provide for the common flow into the line  48 . 
     In the right-hand travel spool  46 B, the same connections are shown, but are numbered with the “B” designation. In the neutral position, there is a flow through to the junction  48 A with connection passageway  132 B, and the bypass line  140 B is connected again to provide for the return flow from the motor back to the junction  48 A and line  48 . The high pressure relief valves, both designated  46 C, are also shown in FIG.  4 . 
     The line to tank  86  is shown in FIG. 4 as well, as are the motors  16 A and  16 B. 
     Thus, the full functions of the walk behind small loader are achieved with a hydraulic system that utilizes the power available efficiently, and in particular provides for differential flows to the drive motors to accommodate different operating conditions and desires. The relief valve settings are made so that they will be operated in series when the work group motors or work group valves are not requiring high pressures and flows, but that travel across the ground is to be maximized. The system will permit diverting flow from one pump or pump section to the work group valves, at which time the work group valves are provided with a high pressure output so that attachment motors connected to the quick couplers that are provided can be operated at high pressures for tasks such as trenching or digging. 
     It should also be noted that an operator platform can be provided at the rear of the loader, if desired, and folded out of the way for making a walk behind unit. This way the operational features are enhanced, and in particular, if the loader is to be moved for some distance, the operator can stand rather than walk. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.