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FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to attachments for work vehicles, and more particularly relates to fluid power systems for driving actuators on such attachments.  
         BACKGROUND OF THE INVENTION  
         [0002]    Commercial work vehicles such as skid steers, loader tractors and other similar heavy equipment vehicles are commonly used for many industrial, agricultural, and landscaping operations. Many of these work vehicles often have two laterally spaced loader arms that extend in front of the vehicle that are adapted to attach to a wide variety of attachments. Commercial work vehicles may also have a three point hitch at their back end. A number of attachments can be selectively attached and detached from the loader arms or the three point hitch to make these work vehicles applicable to a wide variety of applications. For example, a bucket is commonly provided to dig, dump and transport loose materials such as dirt, sand and gravel. The loader arms are hydraulically driven to raise and lower the attachment and pivot the attachment about a horizontal axis.  
           [0003]    Skid steer loaders and other work vehicles commonly have a single hydraulic hook-up which comprises a pair of hydraulic quick connect couplings (one for pressurized hydraulic flow and the other for return flow). The hydraulic hook-up can be utilized by the attachment for a desired powering purpose. A control lever is provided in the operator cab for controlling hydraulic flow to the attachment through the hydraulic couplings. One common use of the hydraulic output includes positioning the attachment tool (e.g. shifting the tool left or right about a vertical axis to effect a windrow and/or to direct dirt, gravel or debris, or raising and lowering or tilting the tool). The hydraulic output may also be used for hydraulically driving an engaging device such as the rotary rake of a rock raking attachment, a rotary blower of a snowblower or a rotary planner of a cold planner.  
           [0004]    More complex attachments include two or more hydraulic functions or actuators. For example rotary broom attachments, snow-blower attachments, back-hoes, cold planners are some of the attachments that have two or more hydraulic functions or actuators. U.S. Pat. No. 5,299,857 to Zanetis, U.S. Pat. No. 5,957,213 to Loraas et al. disclose some of the various types of attachments with multiple hydraulic functions for which the invention can be applicable, and as such these patents are hereby incorporated by reference in their entireties. These attachments may include one or more hydraulic cylinders for tilting or rotating the tool about one or more axes; and/or one or more hydraulically driven motors that rotate a tool (e.g. a broom, snow-blower or cold planner).  
           [0005]    When hydraulically positioning a hydraulically driven rotating tool, hydraulic power is typically diverted away from the main rotary motor of the tool. This can undesirably slow down the rotary speed of the tool. Currently, there is no ideal solution for maintaining a constant full or complete supply of hydraulic power to the main actuator or rotary motor of the tool.  
           [0006]    A further deficiency existing in the art as will be appreciated once the present invention is understood, is the lack of available options with respect to driving fluid actuators on attachments for skid steer loaders or other similar work vehicles.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    In light of the above, it is a general aim of the present invention to provide an alternative way to actuate fluid driven actuators on an attachment for a skid steer loader or other similar work vehicle.  
           [0008]    In accordance with these and other objectives, the present invention is directed toward a local fluid power system on a attachment for a skid steer loader or other commercial work vehicle. The local fluid power system can supplement the existing hydraulic power system provided by the commercial work vehicle or skid steer loader.  
           [0009]    The local fluid power system may comprise a hydraulic reservoir and a hydraulic pump fluidically connected to the hydraulic reservoir for providing a hydraulic power source. The local fluid power system may drive a first hydraulic actuator that acts upon the work attachment tool. The attachment may include a second actuator that is not driven by the local fluid power system, but instead by the existing hydraulic system provided by the commercial work vehicle.  
           [0010]    Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:  
         [0012]    [0012]FIG. 1 is a schematic of a power machine comprising in combination a skid steer loader and a skid steer attachment having a local fluid power system according to an embodiment of the present invention.  
         [0013]    [0013]FIG. 2 is a perspective illustration of a power machine comprising in combination a skid steer loader and a skid steer attachment according to the schematic arrangement shown in FIG. 1.  
         [0014]    [0014]FIG. 3 is an isometric drawing of a local fluid power system assembly for mounting to the skid steer attachment shown in FIG. 2. 
     
    
       [0015]    While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Referring to FIGS. 1 and 2, an embodiment of the present invention has been illustrated schematically as incorporated in a cold planner attachment  20  to illustrate one application of the present invention. The cold planer attachment  20  mounts to a commercial work vehicle shown as a skid steer loader  22 . The attachment  20  includes a tool  24  for performing a work operation, in this case grinding pavement. However, it will be understood that the invention is applicable to any one of a variety of attachments such as a back-hoe, a rotary broom, a snow-blower, a tree spade, grapples, or other such similar implements. One common element of each of the attachments to which the present invention pertains is that these attachments have one or more fluid powered actuators (typically either hydraulic cylinders or hydraulic rotary motors, although the invention may also be applicable to local pneumatic power systems).  
         [0017]    As shown schematically in FIG. 1, the skid steer loader  22  includes a conventional hydraulic power system  26  that is driven by the engine of the work vehicle. The hydraulic power system  26  supplies hydraulic power to various hydraulic actuators  28  on the skid steer loader  22 , such as those used to raise, lower and tilt the lift arms  30  (see FIG. 2). The lift arms  30  typically carry a conventional quick attach plate (not shown) to which the skid steer attachment  20  can quickly mount and dismount. The hydraulic power system  26  also includes a hydraulic power output at quick disconnect hydraulic couplings  32  that can attach with quick disconnect hydraulic couplings  34  of the skid steer attachment  20  to supply the skid steer attachment  20  with hydraulic power. A control valve  36  is often provided in the work vehicle to reverse or stop flow through the hydraulic lines  38 ,  40 . The control valve  36  may be a manually operated rocker lever valve or electrically controlled via an operator input device or other suitable valve device. The skid steer attachment  20  has a pair of hydraulic hoses  48 ,  50  for receiving and returning hydraulic oil to the skid steer loader  22 . The hoses  48 ,  50  terminate in the quick disconnect couplings  34  to provide for fast attachment and detachment from the hydraulic power system  26  of the skid steer loader  22 . The skid steer loader  22  also includes a conventional electrical power supply system  42  which is used to power various electrical functions on the skid steer loader  22 .  
         [0018]    In accordance with the present invention, the attachment  20  includes a local hydraulic power system  43  to provide a second source of fluid power separate from the hydraulic power system  26  of the skid steer loader  22 . In the disclosed embodiment, the local hydraulic power system  43  includes a hydraulic reservoir  44  and a hydraulic pump  45 . The hydraulic pump  45  is driven by an electrical motor  46 . The electrical motor  46  is in turn powered by the electrical power system  42  of the skid steer loader  22  through an electric supply wire  47  running therebetween.  
         [0019]    The attachment  20  includes multiple hydraulic functions. FIGS. 1 and 2 illustrate the attachment  20  as having five actuators including one hydraulic rotary motor  51  and four hydraulic cylinders  53 - 56 . In the disclosed embodiment, the hydraulic power system  26  of the skid steer loader  22  is dedicated to driving the rotary motor  51  and therefore rotating the tool  24 , while the local hydraulic power system  43  of the attachment  20  is dedicated to positioning the four hydraulic cylinders  53 - 56 .  
         [0020]    Because there are multiple hydraulic cylinders  53 - 56 , the hydraulic oil output of the local hydraulic power system  43  is typically routed to a hydraulic control block  52  where it can be distributed (equally or disproportionately) as desired. The control block  52  may include three corresponding control valves  57 - 59 , one for controlling the flow to each different hydraulic cylinder  53 - 56 , respectively (valve  59  controls flow to two cooperating hydraulic cylinders  55  and  56 ). The control block  52  centralizes flow, distribution and/or return of hydraulic fluid to the local hydraulic reservoir  44 .  
         [0021]    As shown, each valve  57 - 59  has an electrical solenoid control mechanism  61 - 63  (which actually comprises two solenoids for each valve and often return springs to center the valve), respectively, for valve position control. Each valve  57 - 59  is also shown as being of the four way, three position type with blocked center. It will be appreciated that the types of valves  57 - 59  and their control may be different depending upon the particular needs of the attachment  20 . The valves  57 - 59  may also be of the variable position type with a variable position electrical control device that takes variable positions corresponding to the magnitude of the electrical signal on respective electrical control lines  65 - 67 , respectively.  
         [0022]    The positions of each of the valves  57 - 59  are controlled via electrical signals conveyed along electrical wires or control lines  65 - 67 . In FIG. 1, the lines  65 - 67  receive control signals from an operator input device  70  mounted in the cab  72  of the skid steer loader  22  for access by the work vehicle operator. The operator input device  70  typically will receive power from the electrical power system  42  of the skid steer loader  22 . The electrical wires  65 - 67  are contained within a wire harness  74  that includes a wire coupling  76  interposed thereon to provide for easy coupling and de-coupling when the attachment  20  is attached and detached from the skid steer loader  22 . Similarly the electric supply wire  47  includes a wire coupling  78  interposed thereon for a similar purpose. Although hard wiring is shown, it will be appreciated that wiring can be removed if desired and replaced with wireless communication and a local battery or power supply system on the attachment.  
         [0023]    As shown in FIG. 1, the local hydraulic power system  43  may preferably includes a check valve  80  to ensure one way flow from the hyraulic pump  45  to the hydraulic control block  52  and a pressure relief valve  82  to relieve excess pressure and/or bypass hydraulic oil to the reservoir  44  when desired.  
         [0024]    As shown in FIG. 3, the reservoir  44 , the pump  45 , the electrical motor  46  and the hydraulic control block  52  are provided in a compact unit and supported by a common support flange or mount  84 . This centralizes the hydraulic system on the attachment and allows all of these elements to be easily mounted or dismounted from the attachment  20 . As shown in FIG. 2, the support flange or mount  84  can be fastened or secured directly to the support frame  86  of the skid steer attachment  22 , the back side of which provides the quick attach plate mechanism for mounting and dismounting to the quick attach plate of the lift arms  30  of the skid steer loader  22 .  
         [0025]    Although a local hydraulic power system  43  is shown herein, it will be appreciated that in other embodiments, the local fluid power system may be pneumatic and include a compressor that pressurizes a compressed air reservoir. In such embodiments, compressed air may be used for driving actuators.  
         [0026]    Another possible use of a local hydraulic power system  43  is for hydraulic power boosting. Currently, most commercial work vehicles are able to supply up to about 3300 psi to work attachments. However, many hydraulic cylinders can be driven at about 5000 psi or more. It certain applications such as rock crushing or other applications requiring large hydraulic power requirements, the relatively moderate hydraulic power supply afforded to the attachment by the work vehicle may not be sufficient. The local hydraulic system  43  may thus be used to provide a greater and higher hydraulic power supply to drive hydraulic cylinders for hydraulic functions that need a higher hydraulic power source. In such an application, the local hydraulic power system  43  may be independent of the work vehicle hydraulic system or the local hydraulic system  43  may be provided in series with the hydraulic system of the work vehicle and thereby no local hydraulic reservoir may be needed. With this type of a system, when the local hydraulic system is boosting the power, it may be temporary disconnected either automatically, manually or when determined by appropriate sensors from the hydraulic power system of the vehicle when excess hydraulic power is required to drive a hydraulic actuator.  
         [0027]    All of the references cited herein, including patents, patent applications, and publications, are hereby incorporated in their entireties by reference.  
         [0028]    The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Summary:
A local fluid power system is provided on a attachment for a skid steer loader or other commercial work vehicle. The local fluid power system can supplement the existing hydraulic power system provided by the commercial work vehicle or skid steer loader. The local fluid power system may comprise a hydraulic reservoir and a hydraulic pump fluidically connected to the hydraulic reservoir for providing a hydraulic power source. The local fluid power system may drive a first hydraulic actuator that acts upon the work attachment tool. The attachment may include a second actuator that is not driven by the local fluid power system, but instead by the existing hydraulic system provided by the commercial work vehicle.