Abstract:
A tool for adjusting the tappet clearance in the valve actuation system of an internal combustion engine includes a screw adjustment portion that is driven by a pneumatic powered screw driver. The pneumatic power to the screw driver is regulated to cause the screw driver to position the screw so that the desired biasing force is present. The screw driver bit passes through the head portion of a torque limiting wrench which is used to loosen and tighten the jam nut that secures the tappet adjustment screw. The tool also has a pneumatic driven gripping mechanism to hold the screw driver bit in position and prevent inadvertent displacement of the tappet adjustment screw while the jam nut is tightened.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to the setting of tappet screws such as those used to adjust actuation of valves in internal combustion engines, and more particularly, to a tool for adjusting the tappet screw while engaging the jam nut that secures the tappet screw. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    The valve actuation system of internal combustion engines typically uses rocker arms to open the valves. One rocker arm is used in association with each valve. One end of each rocker arm engages a camshaft and the other end contacts the upper end of the valve stem to operate the valve. The rocker arm engages the valve stem to move it axially in opposition to a valve spring to open the valve. As the rocker arm moves away, the spring urges the valve to close again. Thus, as the cam shaft rotates the rocker arm moves back and forth opening the valve and allowing the valve to close. 
         [0003]    The end of the rocker arm that engages the valve stem has a tappet adjustment screw or tappet that engages the valve stem. The tappet adjustment screw has a very fine thread pitch, so that it is capable of being precisely positioned relative to the end of the valve stem. The position of the tappet screw is secured by a jam nut located on the top end of the screw adjacent to the upper surface of the rocker arm. Tappet clearance is the distance between the bottom end of the tappet screw and an upper end of the valve. It is important that the clearance between the tappet and the valve stem be set correctly so that the valves will operate properly. Once the tappet clearance is set, the tappet nut is tightened against the rocker arm so that further rotation of the tappet adjustment screw is prevented. Typically, setting of the tappet clearance is one of the final steps in engine assembly, and is performed with the cylinder head installed on the cylinder block. 
         [0004]    Various methods and devices for manually adjusting tappet screws are known in the art. When using such devices, it is a common practice for an assembler to walk along and manually adjust the tappet clearance as the engine travels on the assembly line. In accordance with one conventional method, the crankshaft or cam is put in the proper angular orientation, and feeler gauges are inserted between the camshaft and the rocker arm. The tappet screw then is rotated or adjusted toward the valve stem. This rotation of the tappet screw continues until the valve spring exhibits a biasing force of a predetermined value against the tappet screw. This method requires a device to turn the tappet screw, and this device is operated until the biasing force or load is such that no further rotation of the tappet screw should be made when the predetermined valve spring force is measured by the feeler gauge. Then a wrench is used to tighten the nut to hold the tappet screw in the precise desired position. A torque wrench is commonly used so that the nut is tightened to exactly the desired amount. This manual method requires positioning the feeler gauge, adjusting the tappet screw and then tightening the nut without disturbing the position of the tappet adjustment screw. It is often difficult to accomplish all of the actions precisely, and it is usually awkward to have all of the required tools in position simultaneously. 
         [0005]    Various devices have been developed to facilitate the setting of the tappet clearance. For example, the tool in U.S. Pat. No. 6,345,436 provides for a combination of a member for rotating the screw toward or away from the valve, and means for measuring the force on the screw so that it may be positioned precisely. U.S. Pat. No. 6,450,072 discloses a tool in which the tappet screw is adjusted by a hand-operated device that does not apply more than a predetermined torque limit, with a torque wrench which is used to loosen and tighten the jam nut. The proper amount of torque is achieved by the use of a clutch mechanism. This tool requires the operator to have the proper feel for the appropriate amount of torque. The operator can override the torque setting by exceeding the designated number of clicks produced by the clutch mechanism, or by turning the tool too fast, or by applying excessive force to the handle, or by spinning the tool insufficiently to engage the clutch. If the proper torque is not applied to the screw, the clearance will be set incorrectly. In addition, the tool requires a repetitive motion that has ergonomic deficiencies. 
         [0006]    While these devices may operate generally satisfactorily, they require some expertise to operate correctly. Setting the precise tappet clearance still requires operator skill, and the possibility of error is unreasonably high. Fully automatic devices are available, but they are bulky and difficult to handle. They are also expensive to purchase and maintain. 
         [0007]    It is also difficult using existing machines to hold the tappet screw in precise position while the jam nut is being secured. If the tappet screw is moved from its set position while the nut is tightened, the tappet clearance will not be accurately set. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a unique tool for setting tappet clearance and a method for setting tappet clearance. In accordance with the present invention, the tappet screw can be accurately set to the desired clearance easily and accurately using a tool that is easy to handle and relatively easy to operate. 
         [0009]    The tappet adjustment tool of the present includes both a torque wrench to loosen and tighten the jam nut and a screw driver extending through the socket of the torque wrench for positioning the tappet screw at the desired setting when the jam nut is loosened, and both of the screw driver and the torque wrench are provided in a single tool, so that the tappet screw and the jam nut can be engaged simultaneously. 
         [0010]    The screw driver in the tappet adjustment tool of the present invention is pneumatically powered with an air motor that includes a spring clutch mechanism designed to shut the tool down at a predetermined desired torque. This allows the tappet screw to be rotated and adjusted into position until the desired opposing force of the valve spring is such that the screw is at exactly the desired setting. The setting of the tappet screw is performed automatically, without need for expertise of an operator who has the proper feel for the appropriate amount of torque. It also minimizes the possibilities that the operator can override the torque setting by turning the tappet screw too far or not far enough. 
         [0011]    To assure that the setting of the tappet screw is not disturbed while the jam nut is tightened, the tappet adjustment tool of the present invention includes a gripping mechanism that holds the screw driver bit in the exact position at which it stopped. The gripping mechanism is automatically actuated when the screw driver is disengaged, ensuring that the tappet screw will not move, and allowing the jam nut to be tightened by the torque wrench portion of the tool without disturbing the setting of the tappet screw. 
         [0012]    The tappet adjustment tool of the present invention has an ergonomic design which allows it to be easily handled by the operator with the screw driver portion in one hand the handle of the torque screw portion in the other hand, and permits both portions to be comfortably operated in a repetitive fashion. 
         [0013]    These and other advantages are provided by the present invention of a tool for adjusting the position of a threaded tappet screw relative to a spring biased valve, the tappet screw being selectively locked in position by engagement of a jam nut on the screw. The tool comprises a wrench portion having a socket adapted to engage the jam nut, a handle for turning the socket, and a clutch mechanism to prevent further turning of the socket by the handle when the socket encounters a predetermined torque level. The tool also comprises a bit extending through the socket. The bit is engageable with the tappet screw for rotating the tappet screw toward or away from the valve. The tool further comprises a powered rotational driver attached to the bit to turn the bit and move the tappet screw toward and away from the valve stem. The rotation of the screw driver stops when it encounters a predetermine torque has been encountered. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and further features of the invention will be apparent with reference to the following description and drawings, wherein: 
           [0015]      FIG. 1  is a side elevational view of the tappet adjustment tool of the present invention; 
           [0016]      FIG. 2  is a side elevational view taken along line  2 - 2  of  FIG. 1 , with the socket shown in a lower position. 
           [0017]      FIG. 3  is a side elevational view similar to  FIG. 2 , with the socket shown in an upper position. 
           [0018]      FIG. 4  is a cross sectional view taken along line  4 - 4  of  FIG. 1  showing a gripper mechanism in an activated or gripping position; 
           [0019]      FIG. 5  is a view similar to  FIG. 4 , but showing the gripper mechanism in a deactivated or non-gripping position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The invention will now be described in accordance with its preferred embodiments. The description with reference to the figures is intended to simplify the explanation of the invention and is not meant to limit the scope of the invention. 
         [0021]    With reference to  FIGS. 1-3 , a tappet adjustment tool  10  is shown. The tool includes a screw adjustment portion  11  for positioning the tappet adjustment screw and jam nut engaging portion  12  for tightening and loosening the jam nut to prevent or allow positioning of the tappet adjustment screw. 
         [0022]    The screw adjusting portion includes a pneumatically powered screw driver  13  mounted on the top of a base  14 . The screw driver  13  has an air motor with a spring clutch mechanism designed to shut the tool down at a predetermined desired torque. Extending from the bottom of the base is a hollow elongated sleeve  15 . An elongated bit  16  is attached to the drive of the screw driver  13 . The bit  16  extends through the sleeve  15 . The bottom of the bit  16  is provided with a flat screw engaging end  17  for engaging a slot formed in the top of the tappet adjustment screw  18  ( FIG. 3 ). 
         [0023]    A jam nut engaging portion  12  generally resembles a torque wrench, and comprises a head  19  which fits over the sleeve  15 , a socket  20  that is attached to the bottom end of the head, and a handle  21  attached to the top of the socket. The socket  20  is attached to the bottom of the head by a set screw  22 . The bottom of the socket  20  has a hex wrench opening  23  designed to engage the jam nut  24 . The head  19  is longitudinally slidable along the sleeve  15 , so that the head may be moved upwardly as shown in  FIG. 3  to facilitate the placement of the drive bit  16  on the screw  18 , and then moved downwardly to the position shown in  FIG. 2  so that the socket  20  engages the jam nut  24 . A cylindrical PTFE bushing  25  is preferably positioned between the outside of the sleeve  15  and the inside of the head  19  to facilitate movement of the head along the sleeve. 
         [0024]    The head  19  of the jam nut engaging portion is located coaxially with the bit  16  on the screw driver such that the bit extends through the wrench socket  20  without interference, and thereby allows for forward and reverse rotation of the bit to adjust the position of the tappet screw  18  upwards or downwards to precisely the exact desired position. 
         [0025]    A control box  26  is mounted on the upper end of the screw driver  13 . The control box  26  includes a fitting  27  for connection to a line  28  supplying pneumatic pressure to the tool. It also includes a fitting  29  for connection to a line  30  supplying pneumatic pressure to drive the screw driver  13  in the forward direction, and a fitting  31  for connection to a line  32  supplying pneumatic pressure to drive the screw driver  13  in the reverse direction. Inside the control box  26  is a three-way stem valve  33  to control the pneumatic pressure supplied to the screw driver  13 . 
         [0026]    As shown in  FIG. 2 , two control pushbuttons  34  and  35  extend from control box  26 . The first control pushbutton  34  is connected to the valve  33  in the control box  26  to actuate the valve to supply pneumatic pressure to drive the screw driver  13  in the forward direction. When the control pushbutton  34  is actuated, it moves the valve  33  to connect the line  30  to the pneumatic supply line  28 , causing the screw driver  13  to turn in the forward direction or clockwise when viewed from above, so that the tappet adjustment screw  18  is driven downwardly. The second control pushbutton  35  is connected to actuate the valve  33  in the control box  26  to cause the valve supply pneumatic pressure to drive the screw driver  13  in the reverse direction. When the control pushbutton  35  is actuated, it moves the valve  33  to connect the line  32  to the pneumatic supply line  28 , causing the screw driver  13  to turn in the reverse direction or counter clockwise when viewed from above, so that the tappet adjustment screw  18  is moved upwardly. Preferably, the control pushbuttons  34  and  35  are differently colored; for example, the forward pushbutton  34  is colored green, and the reverse pushbutton  35  is colored red. 
         [0027]    The adjuster drive bit  16  is held in position during the tightening of the jam nut  24  by means of a gripper mechanism  36 . With reference to  FIG. 4 , the gripper mechanism  36  comprises a pneumatically operated parallel gripper actuator  37  mounted within the base  14 . The actuator  37  is connected to a pneumatic line  38 , and is spring biased to the open position. The actuator  37  is operative to close when it receives pneumatic pressure, and to open when there is no pressure. A pair of gripper fingers  39  and  40  extends from the actuator  37  on each side of the bit  16 . A finger extension  41  and  42  is mounted on each of the gripper fingers  39  and  40 , and each of the finger extensions is configured to provide maximum contact with the exterior periphery of the bit  16 . 
         [0028]    The pneumatic line  38  from the gripper mechanism  36  is connected though a fitting  43  on the control box  26  to the control valve  33 . The valve  33  is arranged so that when neither of the control pushbuttons  34  or  35  is actuated and the valve is in its resting position, pneumatic pressure is supplied through the line  38  to the gripper mechanism  36  to close the gripper fingers  39  and  40  and hold the screw driver bit  16  securely in its present position. When either of the control pushbuttons  34  or  35  is actuated to move the position of the valve  33  and supply pneumatic pressure to the screw driver  13  to turn the screw driver bit  16  in either direction, pneumatic pressure to the gripper mechanism  36  is cut off, and the gripper fingers  39  and  40  open to allow the screw driver bit to rotate. 
         [0029]    Thus, when the tappet adjustment screw  18  is set in the precise desired position, pneumatic pressure is supplied by the line  38  to the actuator  37  to close the fingers  39  and  40  together and hold the bit  16  in the exact position where the bit is holding the tappet adjustment screw at the desired setting. While the gripper mechanism  36  holds the bit  16 , the jam nut engaging portion  12  can be used to tighten the jam nut  24  to secure the screw  18  in this position. 
         [0030]    The pneumatic line  38  from the gripper mechanism  36  extends alongside the screw driver  13  from the gripper mechanism to the control box  26 . The line  38  is protected by a sleeve  44  which extends parallel to the screw driver  13 . The exterior of the screw driver  13  and the sleeve  44  together provide a means by which the tool may be easily gripped by the operator. 
         [0031]    In the operation of the tappet adjustment tool  10  of the present invention, the operator locates the tappet jam nut  24 , and positions to tool on the nut such that the socket  20  engages the nut. The operator then places shim stock, the size of the shim stock dependent on the desired gap, between the valve stem and the distal end of the tappet adjustment screw. Holding the screw driver portion of the tool in the left hand, the operator uses the right hand on the handle  21  to turn the socket  20  and loosen the jam nut. This allows the tappet adjustment screw  18  to turn freely. The operator then triggers forward movement of the pneumatic powered screw driver  13  by actuating the control pushbutton  34 . The screw driver  13  runs until it encounters the torque shutoff point, indicating that the tappet adjustment screw  18  is at precisely the right setting for the desired tappet clearance. When this occurs the regulated pneumatic pressure supplied to the screw driver  13  will be insufficient to driver the screw driver further, and the screw driver will stop in the desired position. The operator then releases the control pushbutton  34  which actuates the gripper mechanism  36  to clamp down on the driver bit  16 , and the screw driver  13  is turned off. The operator then uses the handle  21  to turn the socket  20  and manually lock the jam nut  24  in place while holding the tool by griping the screw driver portion. The clutch mechanism in the wrench  12  will limit the amount of torque that is applied to the jam nut, so that the jam nut is tightened to the proper tightness. The tool is removed from the jam nut, and the tappet clearance is set. 
         [0032]    If it is necessary to back up the tappet screw to re-set it, the tool  10  can be re-positioned as before, and, with the jam nut loosened, the operator actuates the other control pushbutton  35  to reversely drive the screw driver  13  and cause the tappet screw  18  to move into position where it can be re-set using the above procedure. 
         [0033]    While the present invention has been described with particularity herein, it is considered apparent that the present invention is capable of numerous modifications, substitutions, and rearrangements of parts without departing from the scope and spirit of the present invention. Therefore, the invention is not to be limited to the particular preferred embodiments described hereinbefore, but rather only defined by the claims appended hereto.