Abstract:
Disclosed herein is a fluid control system for varying the power available to a fluid powered tool, a hydraulically driven impact wrench. The system disclosed herein varies power available to the tool by use of a bypass mechanism that is downstream of a directional control valve spool. Among other things, the advantageous placement of the bypass valve limits the thermal burden in the hydraulic circuit.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to improved controls for varying the output power of a liquid driven tool such as a torque wrench. 
     BRIEF DESCRIPTION OF PRIOR DEVELOPMENTS 
     Certain construction and/or maintenance activities call for powered tools having great output. Hydraulic systems provide certain advantages for powering such tools and are commonly used in some industries. 
     Consider one task required of utility linemen, that of assembling utility poles, and the equipment thereon. This is typically completed with the pole in an erect position, and by a lineman elevated by a bucket truck. Due to limited space and production demands, versatile tooling that can quickly complete a few tasks is required. For example, the linemen must drill through a utility pole, and preferably without considerable exertion. Experience has shown that hydraulic impact wrenches are a preferred tool for this task. Once drilling has been completed, installation of hardware is typically undertaken. For the sake of convenience, linemen will frequently use the hydraulic impact wrench for hardware installation. However, the impact wrenches have enough power that damage to the installation hardware, and/or utility pole is a frequent result. 
     One example of a hydraulic impact wrench is the HIW-716 produced by FCI USA, Inc. of Etters, Pa. Another example is the H8508 Impact Wrench and Drill produced by Greelee of Fairmont, Minn. 
     Therefore, what is needed are method and apparatus for adjusting the output of a hydraulic tool, such as an impact wrench. 
     SUMMARY OF THE INVENTION 
     The foregoing and other problems are overcome by methods and apparatus in accordance with embodiments of this invention. 
     Disclosed herein is an adjustable torque wrench, which allows a user to select proper power and torque for different job applications. In preferred embodiments, torque is controlled by a knob for user adjustment. The knob provides for easy access, even with line-mans&#39; gloves on, and further minimizes the potential for breakage. The system disclosed herein provides for use in open or closed center type hydraulic systems, and further allows the user to quickly change from open to closed center circuits. 
     In the preferred embodiments disclosed herein, the outstanding torque of typical hydraulic wrenches is available to an operator, while torque reductions of up to about 50% may be realized. The preferred embodiments therefore provide a system that is both outstanding for drilling, as well as for hardware installation, providing for a drastically decreased risk of snapping off bolts and adaptors. 
     The variable torque impact wrench adjusts torque by dumping the flow of oil back to the supply without restricting flow, therefore avoiding heat build up and allowing the wrench to perform in multiple work settings. In preferred embodiments, the variable torque impact wrench is capable of providing more than 400 ft-lbs of torque, and enables the operator to quickly adjust the torque setting needed. Adjusting torque accommodates multiple functions, such as drilling robust materials or fastening hardware. In preferred embodiments, the knob is located so as to afford easy access, while remaining protected. One example is where the knob is located underneath the motor on the back of the handle. 
     In preferred embodiments, the variable torque impact wrench utilizes a gerotor drive motor, which provides very high and controlled horsepower with less vibration. The performance of the gerotor motor results in reduced wear to tool components, reduced damage to driven items, and smoother operation for the user. 
     Therefore, it is considered that the embodiments provided herein are illustrative only, and are not to be considered limiting of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read in conjunction with the attached Drawings, wherein: 
         FIG. 1  is an illustration of a torque wrench that incorporates the fluid control system disclosed herein; 
         FIG. 2  is a cross sectional view from the side of the torque wrench shown in  FIG. 1 ; 
         FIG. 3  is a cross sectional view as in  FIG. 2  with the trigger depressed; 
         FIG. 4  is a partial cross sectional view from the front of the motor reversing valve of the fluid control system; 
         FIG. 5  is a cross sectional view from the side depicting the oil bypass cavity; 
         FIG. 6  is a cross sectional view from the front depicting the flow of fluid into the motor; 
         FIG. 7  is a first illustration of the control spool knob; 
         FIG. 8  is a second illustration of the control spool knob; 
         FIG. 9  is a cross sectional view as in  FIG. 6  depicting the bypass spool configured for power limiting; and, 
         FIG. 10  is a cross sectional view as in  FIG. 4 , depicting the motor reversing valve of the fluid control system at a second position; 
         FIG. 11  provides an overview of the flow paths in the fluid control system; 
         FIG. 12  depicts closed center operation of the fluid control system; and, 
         FIG. 13  depicts the fluid control circuit disposed within a tool. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Disclosed herein are methods and apparatus for providing a fluid control system for a fluid operated tool, wherein the fluid control system provides for variable limitation of power output to the unit performing work. The fluid control system provides multiple flow paths to provide for, among other things, selectable diversion of a portion of flow to a work unit, and reversing the direction of the work unit. Although the work unit is disclosed herein as a gerotor motor (in the preferred embodiment, as a part of a hydraulically driven variable torque impact wrench), it is recognized that the fluid control system may be used with other types of work units contained within other fluid operated tools. These other tools may employ gerotor motors, or other apparatus adapted for fluid drive, such as a gear motor. Examples of other tools include, without limitation: wrenches, grinders, and drills. Therefore, the teachings herein are not limited to a hydraulically driven variable torque impact wrench comprising a gerotor motor. Rather, these teachings are considered to be only illustrative and non-limiting of the invention. 
     The teachings herein disclose a fluid control system that, in the preferred embodiments, limits the power available to the gerotor motor, thereby reducing output torque. The reduction in power is achieved by returning a portion of the total flow of powering fluid (i.e., hydraulic oil, or “oil” as used herein) to the fluid supply system. Returning a portion of the total flow is achieved by use of a bypass mechanism, or spool. In preferred embodiments, the bypass spool is located up stream of the motor intake. 
     The flow of oil passes through an orifice where the effective cross sectional area of the orifice can be varied by the operator. In preferred embodiments, the cross sectional area is varied by rotation of the bypass spool. The size of the exposed cross sectional area of the orifice can be altered from zero unit area (no bypass, providing full power) to a size that yields an appreciable loss of power available to the motor. In preferred embodiments, the appreciable loss is as high as fifty percent of full power. However, the orifice may be designed for power loss reaching up to as high as full power (100%). 
     One of the novel features of this invention is the location of the bypass valve. The valve is preferably located between a main directional control valve and the motor. One advantage of placing the bypass valve in this location is that heat is only created when high pressure oil travels to the motor; therefore heat is not generated while the tool is idle. Since the tool is operated in short time intervals relative to its idle state, the amount of heat generated in the hydraulic circuit is minimal in comparison with other systems. 
     Referring to  FIG. 1 , there is shown an illustration of a hydraulically driven variable torque impact wrench, or tool, as also referred to herein. The tool includes a handle  20  having an internal fluid control system  1 , a motor  2 , and an impact mechanism  3 . The fluid control system  1  may be disposed in other components of a tool. However, in the embodiment disclosed herein, the fluid control system  1  is disposed within the handle  20 . The tool preferably makes use of a gerotor motor  2  and an impact mechanism  3 , but the invention could be used with any type of fluid operated motor including a gear motor. 
     Referring to  FIG. 2 , aspects of the fluid control system  1  are shown. In operation, oil from a supply (not shown) enters the tool through the inlet port  4  disposed in the coupler  5 . The oil then flows through port  6  into the directional control valve cavity  7 . A directional control valve spool  8  traverses the directional control valve cavity  7 . In the idle state, the directional control valve spool  8  is pressed against the spool washer  9 . The idle position of the spool  8  is biased against the spool washer  9  by at least one spring, preferably included as springs  10  and  11 . Oil is prevented from leaking from the tool by seals  12 . In the idle state, the oil has a direct return path to the supply tank (not shown) through the cavity  13  surrounding the spool  8 . In the idle state, the oil passes from the cavity  13 , enters the return cavity  14  and then enters into the return port  15 . The oil passes preferably by a check ball  16 , into a slot  17  in the coupler  18  and returns to the supply tank. This embodiment of a flow path for the fluid control system  1  satisfies the requirements for open-center hydraulic circuits where oil continuously flows through the tool. 
     Although referred to as a “spool” in the preferred embodiment disclosed herein, the direction control valve bypass spool  8  may be any component, such as, in non-limiting embodiments, a valve, that otherwise provides for the functions described herein. Similarly, other “spools” disclosed herein may be suitably replaced by other components, such as other types of valves. 
     In another embodiment, shown in  FIG. 12 , the fluid control system  1  provides for a closed-center flow path. In this embodiment, the fluid control system  1  impedes flow when the tool is in the idle state. Referring to  FIG. 12 , the operator rotates the control valve spool  8  180 degrees on its&#39; axis using the screw driver slot  42 . Oil enters the tool through port  4  in the coupler  5 . The oil then passes through port  6  in the directional control valve cavity  7 . In the idle state, the directional control valve spool  8  sits pressed against the spool washer  9 , as shown also in FIG.  2 . The control valve spool  8  is biased in this position by at least one spring, preferably included as springs  10  and  11 . Oil is prevented from leaking from the tool by seals  12 . Note that in  FIG. 12 , the directional control valve spool  8  is shown as inverted from the configuration shown in FIG.  2 . In the inverted configuration shown in  FIG. 12 , a seal between the directional control spool  8  and the handle  20  prevents the oil from flowing into cavity  13 . As a result, the flow of oil is essentially “choked.” In this manner, the fluid control circuit  1  may be configured for closed-center operation. In the preferred embodiment, as otherwise presented herein, the fluid control system  1  is configured for open-center operation. 
     Referring to  FIG. 3 , when work is desired, the operator depresses the trigger  19 . The trigger  19  mounts pivotally on a mounting screw  21  and is secured with a pin  22 . The mounting screw  21  is preferably attached to the handle  20 . The trigger  19  is preferably attached to the directional control spool  8  with another pin  23 . The trigger  19  rotates around the pin  22  applying linear motion to the spool  8  until the spool  8  contacts the rear spool washer  24 . The rear spool washer  24  and the front spool washer  9  are held in place by retaining rings  25 . 
     Movement of the spool  8  closes the cavity  13 . The closing of cavity  13  forces the oil to travel into port  26 . Port  26  enters the main motor reversing directional control cavity  27 , shown in FIG.  4 . The main motor reversing directional control cavity  27  is used for controlling the direction of the flow to the motor  2 . The motor reverse spool  29  is sealed from the atmosphere by O-rings  47 . The motor reverse spool  29  is preferably restrained in place by knobs  45  on both sides of the spool  29 . The knobs  45  are fastened to the spool  29  by screws  46 . Once in the cavity  27 , the oil is forced into adjacent cavity  28  by the motor reverse spool  29 . The motor reverse spool  29  provides features that direct the oil to then enter port  30 . 
       FIG. 5  provides a lateral view of port  30 . In  FIG. 5 , oil enters the bypass cavity  31 . If the position of the bypass spool  33  is in the zero bypass position, as shown in FIG.  2  and  FIG. 6 , the oil will flow directly into the fluidic tube  32  and then into the motor  2  to perform work. The fluidic tube  32  is hydraulically sealed, preferably by O-rings  34 . As seen in  FIG. 6  the oil returns from the motor  2  through the fluidic tube  43  into the cavity  35 . In preferred embodiments, the oil is prevented from leaking from the tool by an NPT or SAE type plug  44 . The oil travels from the cavity  35  into port  36  (shown in FIG.  4 ). Also in  FIG. 4 , a case drain  48  in the motor dumps lubricating flow into port  37  for returning flow. The motor reversing spool  29  forces the oil into port  37 . The oil then travels through port  37 , and, switching back to  FIG. 2 , into the return cavity  14 , then back to the supply by traveling though port  15 , around the check ball  16 , and through the coupler  18 . 
     When full power is not required, the operator can rotate the control spool knob  38  up to ninety degrees, as shown in FIG.  7  and FIG.  8 . The knob  38  is preferably fastened to the bypass spool  33  with a screw  39 . The rotation of the knob  38  is preferably limited by two dowel pins  40 . The rotation of the bypass spool  33  by the rotation of the knob  38  changes the position of an orifice, or bypass hole  41  in the bypass spool  33 , as seen in FIG.  9 . The bypass  41  allows a portion of the oil to flow from the pressurized port  31  to the return port  35 . The maximum flow allowed to bypass is dependant on the cross sectional area of the bypass  41 , the shape of the bypass  41 , and the angular position of the bypass  41  relative to the vertical. In preferred embodiments, the bypass  41  is sized to permit enough flow to limit power output by roughly fifty percent when the bypass  41  is normal to the vertical, or in full communication with the return port  35 . When the bypass  41  is parallel to the vertical (shown in FIG.  6 ), or in position so as to be sealed from the return port  35 , zero percent of power is lost. Thus, in the preferred embodiment, the power output can be varied between about fifty percent and about one hundred percent with the rotation of the bypass spool  33 . However, the bypass  41  may be configured to provide for limiting power output between about zero percent and about one hundred percent of full power. 
     To reverse the direction of the motor  2 , the motor reversing spool  29  may be pushed or pulled as appropriate to provide lateral movement thereof, thus redirecting the flow. Referring to  FIG. 10 , once redirected, the oil reverses the direction of travel through the flow control circuit  1  described in the foregoing. Therefore, in reverse operation, once in the cavity  27 , the oil is forced into adjacent cavity  36  by the motor reverse spool  29 , as shown in FIG.  4 . Regardless of the direction of oil flow, the bypass spool works in the same way. Note that in  FIG. 10  many of the features described in  FIG. 4  are also shown. These features are not described again for the sake of brevity. Also note that a case drain  50  provides for the return of lubricating flow in reverse operation. Also note that the knobs  45  preferably appear on both sides of the handle  20 , although not shown as such in FIG.  4 . 
     In addition to the foregoing aspects of the fluid control system  1  described, it is within the teachings herein to include diversion from the flow of oil at selected locations for other purposes. That is, in addition to the features above, the fluid control system  1  may contain bleeder valves or other features that provide oil supply for such purposes as tool lubrication. 
       FIG. 11  provides an overview of the flow of fluid in the fluid control circuit disclosed herein. As shown in  FIG. 11 , operation of the fluid control circuit  1  begins at step  60 , wherein a fluid supply provides fluid to the fluid control circuit  1 . Next, in step  61 , the direction control valve spool  8  is either set for work, or set for idle. In the case  62  where the tool is idle, the directional control valve is set for one of either: routing the fluid back to the supply (in the open circuit mode); or provides a seal wherein flow is stopped (in the closed circuit mode). In the case  63  where the tool is set for work, the trigger  19  is depressed for operation of the tool. The hydraulic fluid flows through various features to the motor reverse spool  29 . A shown in step  64 , the motor reverse spool  29  directs flow in one of two directions  65 ,  66  through the fluid control circuit  1 . Flow from either direction  65 ,  66  then reaches the bypass spool  33 ,  66 , which is rotated so the bypass  41  is either: in position so as to permit a portion of flow to go directly into the return port  35 ; or, closed off from incoming flow, thereby causing all flow to go directly to the work unit  2 . In the case  68  where limited power is needed, a portion of the flow enters the bypass  41  and does not reach the work unit  2 . Where full power is needed  67 , all of the flow is directed to the work unit  2 . As shown in step  70 , once the fluid exits from the work unit, the fluid is returned to the supply for recycling. 
     A hydraulically driven tool comprising the fluid control circuit  1  disclosed herein provides for selectably varying the flow of hydraulic fluid to a work unit  2 , and therefore the output of the tool. In the embodiment wherein the fluid control circuit  1  is used as a part of a variable torque impact wrench, the wrench can be used effectively for robust drilling jobs, as well as the installation of hardware. 
       FIG. 13  provides an exemplary embodiment of other tools where teachings herein may be practiced. In  FIG. 13 , a tool  100  contains a work unit  102  and a fluid control circuit  101 . In operation, the fluid control circuit  101  is coupled to a fluid supply (not shown) by connector  104 . In the embodiment shown in  FIG. 13 , the fluid control circuit  101  is used to control flow through at least one fluidic tube  132  to the work unit  102 , thus providing for control over the output of the tool  100 . Examples of tools  100  that may be constructed according to this embodiment, or variations thereof, include, without limitation: wrenches, grinders and drills. 
     One skilled in the art will recognize that the invention disclosed herein is not limited to use in a variable torque impact wrench. For example, the fluid control system  1  disclosed herein may be used in wrenches, grinders, drills, chain saws, pole saws, circular saws, pruners, tampers, and other tools having similar power requirements. As another example, features of the present invention could be used in a pneumatic tool rather than a hydraulic tool. Therefore, it is within the teachings contained herein to use this invention, and variations thereof, in other applications.