Shift biased detent profile

Information

  • Patent Grant
  • 6769325
  • Patent Number
    6,769,325
  • Date Filed
    Tuesday, February 19, 2002
    22 years ago
  • Date Issued
    Tuesday, August 3, 2004
    20 years ago
Abstract
A detent assembly for a transmission is provided including a transmission component, such as a shift rail, movable between a plurality of shift positions including first, second, and neutral shift positions. A contoured surface on the shift rail includes first and second recesses, respectively, corresponding to the first and second shift positions. A neutral recess is arranged between the first and second shift recesses corresponding to the neutral shift position. The first and second recesses, respectively, include first and second transition surfaces sloping towards the neutral recess with the second transition surface being steeper than the first transition surface. A detent assembly includes a biasing member and a detent member with the biasing member urging the detent member into engagement with the contoured surface. The biasing member generates a first work along the first transition surface and a second force along the second transition surface greater than the first work.
Description




BACKGROUND OF THE INVENTION




This invention relates to a shift detent assembly for a transmission, and more particularly, the invention relates to a shift detent to be used on manual transmission shift rails.




Manual transmissions are widely used in commercial trucks. Many transmission, engine, and driveline combinations, each of which may have several different lengths, are available to commercial truck consumers to meet their particular needs. As a result, the overall length of the driveline varies depending upon the particular combination.




A shift lever extends from the manual transmission into the vehicle cab and terminates with a knob in a location proximate the vehicle operator. The shift lever may be up to two to three feet in length. The driver moves a shift lever through a shift pattern. For balanced shift feel, the shift lever is configured so that it extends vertically from the shift lever pivot such that the center of gravity of the shift lever is over the shift lever's pivot.




A detent assembly, which is in engagement with a transmission component, such as a shift rail, provides a shift feel to the vehicle operator during gear shifts and maintains the desired gears in engagement with one another. However, to accommodate the various powertrain combinations, the shift lever must be bent in such a manner to place the knob proximate to the vehicle operator. Vehicle vibrations acting at the center of gravity of the bent shift lever may cause an undesirable condition commonly known as “jump out”. Jump out occurs when the detent mechanism is unable to retain the shift rail in the selected position because of vibratory forces exerted by the shift lever on the shift rail. As a result, the selected gear becomes disengaged. A particular shift lever geometry may typically make the transmission susceptible to jump out in a particular direction. Therefore, what is needed is a detent assembly that prevents jump out in applications using a particular shift lever.




SUMMARY OF THE INVENTION AND ADVANTAGES




The present invention provides a detent assembly for a transmission including a transmission component, such as a shift rail, movable between a plurality of shift positions including first, second, and neutral shift positions. A contoured surface on the shift rail includes first and second recesses, respectively, corresponding to the first and second shift positions. A neutral recess is arranged between the first and second shift recesses corresponding to the neutral shift position. The first and second recesses, respectively, include first and second transition surfaces sloping towards the neutral recess with the second transition surface being steeper than the first transition surface. A detent assembly includes a biasing member and a detent member with the biasing member urging the detent member into engagement with the contoured surface. The biasing member generates a first force along the first transition surface and a second force along the second transition surface that increases at a greater rate than that of the first force. Said another way more work is required to move detent assembly out of the second recess than the first recess.




In this manner, a certain force versus rail displacement profile set may be generated to prevent jump out of first. Likewise, an opposite profile set may be generated to prevent jump out of second.




In addition to the symmetrical profile used for levers not prone to jump out, the above invention provides two shift rails with opposite, non-symmetrical profiles that can be used to prevent jump out with problematic shift levers.











BRIEF DESCRIPTION OF THE DRAWINGS




Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:





FIG. 1A

is a cross-sectional view of a portion of a manual transmission;





FIG. 1B

is a schematic view of a shift pattern for the manual transmission shown in

FIG. 1A

;





FIG. 2

is an enlarged cross-sectional view taken of the area indicated at


2


in

FIG. 1A

; and





FIG. 3

is a view similar to

FIG. 2

depicting an alternative embodiment.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




A manual transmission


10


is shown in FIG.


1


A and includes a forward end


12


and a rearward end


14


. A transmission housing


16


supports a gear shaft


18


having main gears


20


. Clutch collars


22


are supported on the shaft


18


adjacent to the main gears


20


for selectively engaging the main gears


20


for rotation with the shaft


18


. A shift rail


24


supports a plurality of shift forks


26


that cooperate with the clutch collars


22


to move the collars


22


in and out of engagement with the gears


20


to shift the transmission


10


. A shift sleeve


28


is connected to the shift rail


24


and receives an end of a stub lever


30


. A shift lever


32


is connected to the stub lever


30


, which is manipulated by the vehicle operator through a shift pattern P, shown in FIG.


1


B. These manipulations translate and rotate the shift rail


24


.




The shift pattern P includes first shift positions F, a neutral shift position N, and second shift positions S. Different gear positions within each shift position correspond to a different rotational position of the shift rail


24


. The shift positions F, P, and N are defined by a contoured surface


34


on the shift rail


24


, as shown in FIG.


2


. The contoured surface


34


provides a shift feel and feedback to the operator when shifting the shift lever through the shift pattern P.




A detent assembly


36


includes a pin


38


biased toward the contoured surface


34


by a spring


40


having a constant spring rate. The detent assembly


36


may be received within a bore in the housing


16


. Together the detent assembly


36


and contoured surface


34


retain the shift rail


24


, and in turn a clutch collar


22


and main gear


20


, in engagement with one another once the operator has selected a desired gear within a particular shift position. As discussed above, when the shift lever


32


is subjected to vibrations during vehicle operation, the detent assembly


36


and contoured surface


34


may not be able to maintain the shift rail


24


in the desired shift position, and the transmission


10


may jump out of gear. To prevent jump out, the present invention includes an improved contoured surface


34


shaped in a manner to counteract the vibrations on the shift level


32


.




The contoured surface


34


includes first


42


, second


44


, and neutral


46


recesses that respectively correspond to first F, second S, and neutral N positions. The first recess may include a first seat


48


that receives the pin


38


when the transmission is in one of the first shift positions F. The first recess


42


includes a first transition surface


52


adjoining the first seat


48


and sloping upwardly toward the neutral recess


46


. The second recess


44


includes a second seat


50


receiving the pin


38


when the transmission


10


is in one of the second shift positions S. The second recess


44


includes a second transition surface


54


adjoining the second seat


50


and sloping upward toward the neutral recess


46


. The neutral recess


46


includes a neutral seat


56


, which may be arranged in an elevated manner relative to the first


48


and second


50


seats. The seats


48


,


50


, and


56


may be flat, as shown in the Figure.




For the shift lever


32


shown in

FIG. 1A

, vibrational force acting at the center of gravity of the shift lever


32


creates a tendency for the shift rail


24


to translate toward the rearward end


14


. The first


52


and second


54


transition surfaces may be sloped differently than one another to counteract the effects of the vibrational force on the shift lever


32


and prevent jump out and to modify the shift feel for shift levers with different bends and centers of gravity. For example, the second transition surface


54


may be steeper than the first transition surface


52


to provide a similar shift feel to the operator when shifting from the second shift position S to the neutral position N as from the first shift position F to the neutral position N. In this way, the work done by the contoured surface or profile


34


on the spring


40


will be greater when shifting towards the forward end


12


than the rearward end


14


.




The neutral recess may also be designed to provide different detent forces and to modify the shift feel through the neutral position. The neutral recess


46


may include a first neutral transition surface


58


sloping upward toward the first recess


42


and a second neutral transition surface


60


sloping upward toward the second recess


44


. The first


58


and second


60


neutral transition surfaces adjoin the neutral seat


56


on opposing sides. The first neutral transition surface


58


may be steeper than the second neutral transition surface


60


such that the work done by the profile


34


on the spring


40


will be greater when shifting towards the forward end


12


than the rearward end


14


. The steeper first neutral transition surface


58


may act as a stop for the pin


38


as it comes out of the second recess


44


, which includes the steep second transition surface


54


.




Another profile


34


for a shift rail


24


is shown in FIG.


3


. The neutral recess


46


is designed such that it is more difficult for the shift rail to be moved from the neutral recess


46


to the first recess


42


. The peak formed by the first transition surface


52


and the first neutral transition surface


58


is higher than the peak formed by the second transition surface


54


and the second neutral transition surface


60


. As a result, the work done by the profile


34


in the spring


40


will be greater when shifting toward the forward end


12


than the rearward end


14


.




The slope of the transition surfaces may be changed in a manner other than shown to counteract the vibrational forces for the particular shift lever


32


. The relative steepness could be reversed for a shift lever


32


whose center of gravity is rearward


14


of the stub lever


30


pivot. Furthermore, it should be understood that a detent assembly other than the assembly shown in the drawings may be used. Moreover, the contoured surface


34


may utilize a different shape than shown, that is, the surfaces and seats may be curved.




The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.



Claims
  • 1. A detent assembly for a transmission comprising:a transmission component movable between a plurality of shift positions including first, second, and neutral shift positions; a contoured surface on said transmission component including first and second recesses respectively corresponding to said first and second shift positions, and a neutral recess arranged between said first and second recesses corresponding to said neutral shift position, said first and second recesses respectively including first and second transition surfaces sloping toward said neutral recess with said second transition surface being steeper than said first transition surface; and a detent assembly including a biasing member and a detent member with said biasing member urging said detent member into engagement with said contoured surface, said biasing member generating a first work along said first transition surface and a second work, along said second transition surface, greater than said first work.
  • 2. The assembly according to claim 1, wherein said first and second transition surfaces are generally flat.
  • 3. The assembly according to claim 1, wherein said first and second recesses respectively include first and second seats adjoining said first and second transition surfaces respectively coacting with said detent member while in said first and second shift positions respectively.
  • 4. The assembly according to claim 3, wherein said first and second seats are generally flat.
  • 5. The assembly according to claim 1, wherein said transmission component is a shift rail.
  • 6. The assembly according to claim 1, wherein said biasing member is a spring having a constant spring rate.
  • 7. The assembly according to claim 1, wherein said neutral recess includes first and second neutral transition surfaces, respectively, sloping toward said first and second recesses with said first neutral transition slope steeper than said second neutral transition slope, said biasing member generating a third work along said second neutral transition surface and a fourth work, along said first neutral transition surface, greater than said third work.
  • 8. The assembly according to claim 7, wherein said neutral recess includes a neutral seat between said first and second neutral transition surfaces coacting with said detent member while in said neutral position.
  • 9. The assembly according to claim 8, wherein said neutral seat is generally flat.
  • 10. The assembly according to claim 1, wherein said neutral recess includes first and second neutral transition surfaces respectively sloping toward said first and second recesses, respectively, and forming first and second neutral peaks with said first neutral peak higher than said second neutral peak, said biasing member generating a third work along said second neutral transition surface and a fourth work, along said first neutral transition surface, greater than said third work.
  • 11. A method of preventing jump out in a manual transmission comprising the steps of:a) producing a first detent work when moving from a first shift position to a third shift position; and b) producing a second detent work when moving from a second shift position to the third shift position with the second detent work greater than the first detent work wherein the third shift position is arranged between the first and second shift positions.
  • 12. The method according to claim 11, wherein the third shift position corresponds to a neutral shift position.
  • 13. The method according to claim 12, further including the steps of:c) producing a third detent work when moving from the neutral shift position to the second shift position; and d) producing a fourth detent work when moving from the neutral shift position to the first shift position with the fourth detent work greater than the third detent work.
US Referenced Citations (6)
Number Name Date Kind
2131263 Barnes Sep 1938 A
4338828 Ruhlman Jul 1982 A
4704916 Wilhelmy Nov 1987 A
5085303 Frost Feb 1992 A
5309783 Doolittle et al. May 1994 A
20010017063 Wildeshaus et al. Aug 2001 A1