Abstract:
A push-pull coupling for coupling a valve spool to a coaxial cable includes a lost-motion connection which operatively disconnects the coaxial cable from the valve spool when in a first mode and positively connects the coaxial cable to the valve spool when in a second mode. Switching from the first mode to the second mode is accomplished by energizing an electromagnetic actuator within the coupling which locks components to one another to transmit push and pull motion. When the actuator is deenergized, the components move relative to one another, disconnecting the coaxial cable from the valve spool. The push-pull coupling is used in hydraulic machines to prevent operation of hydraulic cylinders when a driver is not seated on the machine so as to close a seat operated switch which energizes the electromagnetic actuator.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a push-pull coupling. More particularly, the present invention is directed to a push-pull coupling adapted to connect an operator to a device in both a push and a pull direction as well as to mechanically disconnect the operator from the device. 
     BACKGROUND OF THE INVENTION 
     It is frequently necessary or desirable to selectively couple and uncouple an operator from a device. A particular application of this coupling need is in hydraulic machines such as skid-steer loaders and other hydraulic devices which may have other functions, such as but not limited to, street sweepers, ground boring machines, bull dozers, graders and earth scoopers. It is necessary to enable hydraulic systems, such as hydraulic lifts, only when a person is seated on the machine. In the past, this has been done by a solenoid operated lock pin which prevents operation of a valve spool by engaging a groove in the spool to retain the spool in a neutral position. Due to tolerance stack-ups, if an operating lever is pushed hard enough, the device can receive a small amount of oil and creep instead of remaining in position. Moreover, this type of solenoid spool lock requires that the operating handle be returned to neutral before the lock pin re-engages the groove in the spool. This leads to dangerous conditions in which the hydraulic device moves or operates when the lock pin should be engaged. A primary drawback of the solenoid projected lock pin is that the operating handle is always positively connected to the spool and will apply a longitudinal force to the spool whenever the actuating lever is pushed or pulled. It is therefore necessary to rely on the interference of the lock pin in order to prevent operation of the hydraulic device. 
     Hydraulic machines are exemplary of devices having safety features which disabled the machines under certain circumstances. There are numerous other devices which employ safety devices that have drawbacks which may be similar, analogous or in addition to the afore-discussed drawbacks of solenoid operated locking pins. 
     The difficulties are especially acute when it is necessary to prevent the operation of a device which moves in both directions, i.e., a device which is both pushed and pulled during its operation. 
     In view of these and other considerations, there is a need for improving the reliability and safety of devices which utilize push-pull operators. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a push-pull coupling adapted to connect an operator to a device for moving the device in both push and pull directions. The invention comprises a body having first and second ends. A rod is disposed at the first end of the body and is mounted for slidable movement with respect to the body in both the push and pull directions, the rod being adapted to positively connect to the operator. A connector is located at the second end of the body and is adapted to positively connect the body to the device. A lost motion connection is disposed between the rod and the connector. The lost motion connection has a first mode in which there is a de-coupling of the rod to the connector resulting in lost mechanical motion in both the push and pull directions. The lost motion connection further has a second mode in which there is a positive coupling between the rod and the connector, wherein motion of the rod is transmitted to the connector. An electromagnetic actuator is associated with the lost motion connection for maintaining the lost motion connection in the first mode when deenergized and for maintaining the lost motion connection in the second mode when energized. 
     In a more specific aspect, the lost motion connection of the push-pull coupling includes first and second armatures. The first armature is positively connected to the push-pull rod only when the rod is pulled and is disconnected from the rod when the rod is pushed. The second armature is positively connected to the push-pull rod when the rod is pushed and disconnected from the rod when the rod is pulled. The electromagnetic actuator functions to disconnect both armatures from the body when in the first mode and for connecting both armatures to the body when in the second mode by applying electric current to electromagnets disposed within the body. 
     In a further aspect of the invention, first and second springs are provided for biasing armatures to the first positions in which the armatures are disconnectable from the coils of the electromagnets when the electromagnetic actuator is in the first mode and wherein the armatures positively couple with the coils when the electromagnetic actuator is in the second mode, whereby the armatures are disconnected from the body when the lost motion connection is in the first mode and are positively connected to the body when the lost motion connection is in the second mode. 
     In a still further aspect of the invention, the body is in the form of a housing having a connector at one end, and the push-pull rod at the other end with the armatures, electromagnets and springs disposed within the body. 
     In one application of the invention, the push-pull coupling is disposed between the spool of a hydraulic valve and an operator for that valve and enables reciprocation of the spool within the valve only when the electromagnetic actuator is energized, thus providing a safety device which in a specific aspect enables reciprocation of the spool only when the person operating the valve is correctly positioned to manipulate the operator, such as being seated on a seat which closes a switch that energizes the electromagnetic operator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a machine such as a skid-steer loader which employs a push-pull coupling configured in accordance with the present invention; 
     FIG. 2 is a side elevation of a valve utilizing a solenoid operated lock pin in accordance with the prior art; 
     FIG. 3 is a side elevation of a valve having a valve spool coupled to a push-pull cable utilizing a push-pull coupling configured in accordance with the principles of the present invention; 
     FIG. 4 is a side elevation of the coupling in accordance with the prevent invention showing electromagnets utilized in the present invention in a deenergized state with a push-pull operating cable not being operated; 
     FIG. 5 is a view similar to FIG. 4 with the electromagnetics in a deenergized state and showing the push-pull cable pushing toward the coupling; 
     FIG. 6 is a view similar to FIG. 5 showing the electromagnetics in a deenergized state and showing a push-pull cable being pulled away from the coupling; and 
     FIG. 7 is a view similar to FIGS. 4-6 showing the electromagnets within the push-pull coupling in an energized state so that the push-pull coupling has no lost motion and moves concurrently with the operating cable in order to reciprocate the spool of the valve with which it is connected. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, there is shown a device such as a skid steer loader  10  which includes a seat  12 , a seat operated switch  14 , a control valve  16  which is enabled for operation by the seat switch  14 , and a device such as a hydraulic cylinder  18  which is driven by fluid dispensed by the valve  16 . When the hydraulic cylinder  18  is activated, it raises and lowers a boom  20  in order to perform functions such as raising and lowering a forklift, such as a forklift  22 , or operating a loader bucket, street broom, boring tool, or dozer blader (none of which are shown). Flow of fluid to the hydraulic cylinder  18  is controlled by an operating lever  24  mounted on the skid-steer loader  10  adjacent the seat  12 . 
     Referring now to the prior art arrangement of FIG. 2, it is seen that the operating valve  16  has a spool  26  that is biased to a neutral position by a coil spring  27 . The spool  26  is engaged by a locking pin  30  that is reciprocated in a radial direction by a solenoid  32 . Normally, the locking pin  30  is spring projected into the groove  28 , however, when a person operating the machine  10  sits on the seat  12 , a switch  14  closes which energizes the solenoid  32 . The solenoid  32  then overcomes the bias of the spring projecting the locking pin  30  and the locking pin is withdrawn from the groove  28 . This permits the spool  26  to be moved in a longitudinal direction by an operator in the form of a coaxial cable  36  that is attached to the handle  24 . In accordance with the present invention, solenoid operated lock  32  is replaced with a push-pull coupling  40  which is shown in FIGS. 3-7. 
     Referring now to FIG. 3, the push-pull coupling  40  has a first end  42  which is coupled directly to an end  44  of the valve spool  26  and a second end  46  which is connected to a push-pull rod  48  which is in turn directly connected to the coaxial cable  36 . In accordance with the present invention, when the push-pull coupling  40  is in a first mode, there is lost motion between the push-pull rod  48  and the end  44  of the spool  26 , disabling operation of the valve spool by the coaxial cable  36 . When the push-pull coupling  40  is in a second mode, there is a positive connection between the push-pull rod  48  and the end  44  of the valve spool  26  wherein when the coaxial cable  36  is either pushed or pulled, the valve  26  moves longitudinally with the cable because there is no lost motion. 
     Referring now to FIG. 4, where the push-pull coupling  40  is shown in detail, it is seen that the first end  42  of the push-pull coupling includes a connector in the form of a lug  50  which has a hole  52  therethrough which receives a pin or bolt  54  for positively connecting the lug to the end  44  of the spool  26 . The lug  50  is retained within a first end  56  of a housing and is rigidly retained therein by screws  58  to form an integral body  57 . The housing  56  has a second end  60  having an opening therethrough  62  which receives a small diameter portion  64  of the rod  48  and allows the rod  48  to reciprocate within and with respect to the housing  56 . The push-pull rod  48  has a second portion  66  which has a relatively large diameter and is positioned within a chamber  68  defined by the housing  56 . 
     Within the chamber  68  of the housing  56 , there is a first armature  70  and a second armature  72 . The first armature  70  has a central opening  74  extending completely therethrough which slidably receives the narrow diameter portion  68  of the push-pull rod  48 . The second armature  72  has a flat rear face  76 , which abutted by a flat end face  78  of the relatively wide portion  66  of the push-pull rod  48 . The relatively wide portion  66  of the push-pull rod  48  also defines a rear shoulder  80  which abuts a front face  82  of the armature  70 . Consequently, the push-pull rod  48  is not positively connected to the rear face  76  of the second armature  72  because it can be pulled away from the rear face  76 . Moreover, the rod  48  is not positively connected to the front face  82  of the first armature  70  because it can be pushed away from the front face. 
     Disposed within the cavity  68  of the housing  40  is a first annular coil  86  and a second annular coil  88 . These coils are separated by a spacer  90 . Both the coils  86  and  88  and the spacer  90  have hollow bores  92 ,  94  and  96  extending therethrough through which the large diameter portion  66  of the push-pull rod  48  is slidably received. The coil  86  is held in abutment with a shoulder  100  within the chamber  68  of the housing  56  by the spacer  90  while the coil  88  is held in abutment with the spacer  90  by a shoulder  102  at the end of the lug member  50 . Consequently, the coils  86  and  88  are locked within the housing  56  so as not to move longitudinally or radially with respect to the body  57  which is comprised of the housing  56  and the lug member  50 . 
     A first coil spring  110  is seated within a cavity  112  at the first end  60  of the housing  56  and biases the first armature  70  against the first coil  86 . The coil spring  110  also biases the end face  78  of the enlarged portion  66  of the push-pull rod  48  towards the end face  76  of the second armature  72 . A second coil spring  116  engages the front end face  117  of the second armature  72  and urges the second armature against the second coil  88  as well as against the end face  78  of the enlarged portion  66  of the push-push rod  48 . When the first coil  86  and the second coil  88  are not energized, the first armature  70  and second armature  72  are free to displace axially through gaps  118  and  119  from the first and second coils upon overcoming the bias of the first and second springs  110  and  116 . This is shown in FIGS. 5 and 6. 
     Referring now to FIG. 5, when the push-pull rod  48  is pushed and the coils  86  and  88  are deenergized, the large portion  66  of the push-pull rod moves to the left and pushes the second armature  72  against the bias of the spring  116  and away from the second coil  88  as is seen by the gap  120 . Thus, the push motion on the push-pull rod  48  is lost and the spool  26  (see FIG. 3) is not moved. The first armature  70  remains stationary because the spring  110  biases it against the first coil  86 . 
     Referring now to FIG. 6, when the push-pull rod  48  is pulled, the first armature  70  moves against the bias of spring  110  and compresses spring  110  because the rear surface  80  of the enlarged portion  66  of push-pull rod  48  bears against the front surface  82  of the first armature pulling the first armature away from the first coil  86 . Thus there is a lost motion indicated by the gap  122  between the coil  86  and the front face  82  of the first armature  70 . Consequently, the spool  26  of the valve  16  is not pulled back upon pulling on the coaxial cable  36  with the handle  14 . 
     The phenomenon of FIGS. 5 and 6 illustrates that there is a lost motion connection in both the push and pull directions within the body  57  of the push-pull coupling  40  when the coupling is in a first mode due to the coils  86  and  88  being deenergized. In the embodiment of the invention exemplifying a use in a hydraulic machine, the lost motion connection occurs when a person is not sitting on the seat  12  to close the switch  14  in order to energize the coils  86  and  88 . 
     Referring now to FIG. 7, when in the exemplary embodiment, a person sits on the seat  12 , the switch  14  is closed thereby energizing the electromagnets  86  and  88 . The first and second armatures  70  and  72  are then magnetically held against the coils  86  and  88  creating a rigid assembly of the body  57  with no lost motion. A pushing motion on the coaxial cable  36  from the lever  14  moves the push-pull rod  48  and the lug  52  to push the valve spool  26  within the valve housing toward the left against the bias of coil spring  27  (see FIG.  3 ). This causes the valve to operate the hydraulic device associated therewith, by allowing hydraulic fluid to flow thereto so as to operate for example the hydraulic cylinder  18  of FIG.  1 . When the coaxial cable  36  is pulled, the valve spool  26  moves to the right against the bias of coil spring  27 , again because the body  57  becomes a rigid assembly when both coils  86  and  88  are energized (see FIG.  3 ). When the seat  12  becomes unoccupied, the switch  14  interrupts current to the coils  86  and  88  and lost motion within the body  57  allows the spring  27  to return the spool  26  to its neutral position. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modification of the invention to adapt it to various usages and conditions. 
     Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.