Abstract:
A shift control linkage for a hydraulically controlled transmission includes a pivotally mounted input member coupled to a direction (forward, neutral and reverse) control valve spool and a speed (first, second, third, etc.) control valve spool by first and second output links and selectively operable to various positions to the opposite sides of a neutral position to respectively select various forward and reverse drive speeds.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to controls for effecting direction and speed changes in a hydraulic power shift transmission having multiple forward and reverse speeds and more particularly relates to shift control linkages for effecting direction and speed changes in such transmissions. 
     Various types of shift control linkages are known in the prior art which include a single lever for effecting direction and speed changes in hydraulic power shift transmissions. Examples of such linkages are disclosed in U.S. Pat. Nos. 3,242,758  granted to Harris et al on Mar. 29, 1966, 3,679,018 granted to Luft on July 25, 1972 and 3,853,019 granted to McAdams on Dec. 10, 1974. 
     The Harris et al and McAdams patents both show single shift levers which are mounted for pivoting sideways along a first path for selecting different drive directions (neutral, reverse or forward) and for being pivoted along separate paths oriented 90°  from the first path for selecting various drive speeds. The structure of these linkages which permit the use of a single shift lever are relatively complex and suffer from the disadvantage of being somewhat difficult to manufacture and assemble. 
     The Luft patent shows a single shift lever mounted for simply pivoting along a single fore-and-aft path to effect both direction and speed changes and accordingly much of the complexity of the aforementioned Harris et al and McAdams shift linkages is avoided. However, the Luft linkage includes a specially configured cam plate coupled to the shift lever for operating direction and speed selector valves for routing air pressure for operating the transmission shift control valves and consequently the Luft linkage and associated air pressure system still is a rather complex system for effecting shifting of the transmission thereof. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an improved linkage for effecting direction and speed changes in a hydraulic power shift transmission by manipulation of a single shift lever. 
     An object of the invention is to provide a simple shift control linkage, including a shift lever mounted for swinging along a single path of movement, for effecting both directions and speed changes in a hydraulic power shift transmission. 
     A more specific object is to provide a shift control linkage according to the previous object wherein the linkage components are simply constructed and mounted. 
     Yet another object of the invention is to provide a shift control linkage including an input link having first and second legs arranged to define an included angle of 90° and having first and second ends respectively coupled to direction and speed selector valves by first and second output links and being pivotally supported between its ends for movement about a fixed axis, and the first output link being yieldably extensible and retractable to permit various speeds to be selected without there being a change in the direction control valve, and the second output link being connected to the input link such that a line drawn through opposite ends of the second output link intersect the axis of rotation of the input link when the latter is in a centered, neutral position. 
     These and other objects will become apparent from a reading of the following description together with the appended drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic right side elevational view of the essential components of the transmission control linkage of the present invention with parts of the direction selector output link being shown in section. 
     FIG. 2 is rear side elevational view of the control linkage shown in FIG. 1 with part of the direction selector valve being shown in section. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, therein is shown a transmission shift control linkage, indicated in its entirety by the reference numeral 10, and a transmission 12. The linkage 10 includes an input link 14 having first and second legs 16 and 18, respectively, disposed at an angle of 90° relative to each other. The link 14 is pivotally mounted on a support bracket 20 for pivoting about a horizontal transverse axis defined by a pivot pin 22 extending through the link 14 at the juncture of the legs 16 and 18. When the link 14 is in a centered neutral position as illustrated, the first leg 16 extends horizontally and the second leg 18 extends vertically. 
     Pivotally connected to the link leg 16, by a pin 24, is the lower end of a first output link 26 having an upper end pivotally connected to the upper end of a spool 28 of a direction selector valve 30 by a pivot pin 32. The spool 28 is here shown in a neutral position N from which it may be shifted upwardly to a forward drive effecting position F or downwardly to a reverse drive effecting position R. 
     For a purpose described more fully hereinbelow, the first output link 26 is constructed to yieldably extend or collapse, from a normal condition shown in response to encountering a predetermined resistance to lengthwise movement thereof. Specifically, the link 26 includes an upper first section including an upper tubular portion 34 and a lower second section including a straight portion 36 formed of a rod reciprocably received in the portion 34 and normally held in place relative to the latter by a spring loaded detent ball 38 carried by the upper portion 34 and received in an annular groove 40 in the lower portion 36. It is here noted that the direction selector valve 30 includes a spring biased detent ball 42 located for yieldable reception in upper, intermediate and lower grooves 44, 46 and 48 respectively formed annularly in the spool 28 for respectively holding the spool 28 in its reverse, neutral and forward drive effecting positions. Located above the upper groove 44 is an annular flange or shoulder forming an upper stop 50 and located below the lower groove 48 is an annular flange or shoulder forming a lower stop 52. The spring biased detent ball 42 is designed to yieldably release the valve spool 28 when a predetermined force is exerted on the spool 28 by the first output link 26, such predetermined force being less than the predetermined resistance for effecting yieldable extension or collapse of the link 26 so that the link 26 will always be effective to shift the spool 28 among its neutral, forward and reverse drive effecting positions and will only extend or collapse upon the detent ball 42 coming into engagement with one or the other of the stops 50 and 52. For example, it has been found that the link 26 will operate properly if the detent ball 38 is designed to become released from the groove 40 under a load of 35 lbs. (15.88 kg.) to permit extension or collapse of the link 26 while the detent ball 42 is designed to become released from any one of the grooves 44, 46 and 48 of the spool 28 under a load of 25 lbs. (11.34 kg.). 
     Pivotally connected to a lower end of the link leg 18, by a ball and socket connector 54, is the lower end of a second output link 56 having an out-turned upper end 58 pivotally received in the upper end of a valve spool of a speed selector valve 60, here shown in a first speed effecting position from which it is shiftable upwardly to second and third speed effecting positions. It is noted that with the input link 14 in its illustrated neutral position, a line drawn through the opposite ends of the link 56 will intersect the rotational axis of the input link. Thus, it will be appreciated that movement of the input link 14 in opposite directions from its neutral position will effect movement of the second output link 56 and hence the the speed selector valve 60 in exactly the same way. 
     A push-pull cable 64 is reciprocably supported on the bracket 20, as at 66, for fore-and-aft movement and a pin 68 extends through a clevis fixed to the rear end of the cable and connects the clevis to the link leg 18 at a location below the pivot pin 22. The forward end of the cable 64 is connected in a similar manner to a lower end of a shift control lever 70 mounted, as at a pin 72 received in a middle location of the lever 70, for fore-and-aft pivotal movement, to opposite sides of a neutral position N, in which the lever is illustrated, to a series of three forward spaced positions F 1 , F 2 , and F 3  and a series of three rearward speed positions R 1 , R 2  and R 3 . 
     The operation of the invention is as follows. Assuming the linkage 10 to be in the condition illustrated, the shift control lever 70 will be in its neutral position and the input link 14 will be in a corresponding neutral position wherein it holds the direction control valve spool 28 in its neutral position and, consequently, the transmission 12 will be in neutral. 
     If it is then desired to place the transmission in its first speed forward driving condition, the operator needs only to push the shift control lever 70 forwardly to its F 1  position. The cable 64 will transmit this movement to the input link 14 to move the latter to its corresponding F 1  position. During this movement of the input link 14, the first output link 26 will move the direction selector valve spool 28 upwardly to its forward drive effecting position F. However, the movement of the input link 14 will only cause minimal displacement of the second output link 56 and due to tolerances at the connection joints of the link 56, no displacement of the spools of the speed selector valve 60 will occur. 
     Shifting of the transmission 12 to its second speed forward is accomplished by moving the shift control lever 70 further forwardly to its F 2  position. The cable 64 will transmit the movement to the input link 14 to move the latter to its corresponding F 2  position. Initial movement of the link 14 will be resisted due to the detent ball 42 being against the lower stop 50, however, once the resistance to movement results in a force sufficient for overcoming the force tending to hold the detent ball 38 in place, the link 26 will collapse. Upon collapse of the link 26, the input link 14 will continue to move and cause the second output link 56 to shift the speed selector valve spool to its second speed position F 2 . 
     The shifting of the transmission 12 to its third speed position is accomplished in a manner similar to that for shifting it to its second speed position however the first output link 26 is now already collapsed so the detent ball does not initially resist movement of the input link 14. 
     Shifting of the transmission 12 to its first, second and third speed reverse conditions is accomplished in a manner similar to that described above for shifting the transmission to its corresponding forward drive speed conditions with the differences being that the shift control lever 70 is pulled rearwardly and the input link 14 rotates to exert a downward force tending to extend the first output link 26.