Fall away transmission shift shaft switch profile

BACKGROUND OF THE INVENTION

This invention relates to a heavy duty manual transmission, and more particularly, the invention relates to a shift shaft switch for the transmission which senses the location of the shift shaft.

Heavy duty tractor trailer transmissions have become more complex in recent years. As class 8 transmissions have evolved from pneumatic to electric controls, electronic sensors have become necessary to provide information to the transmission controller. Some of these sensors affect the driver while in the act of engaging or disengaging gears.

Heavy duty manual transmissions typically have shift shafts supported by a transmission housing. Shift forks are typically connected to the shift shafts and move the clutch collars into and out of engagement with the gears as the shift shafts are rotated and translated in response to the operator manipulating the shift lever. The sensors coact with the shift shaft to sense the position of the shift shaft which corresponds to a particular gear position so this information may be sent to the controller for control of the transmission or other aspects of vehicle operation.

In the past, the shift shaft has included a single annular groove that corresponds to the neutral gear position of the transmission. A pin is biased into the groove by a sensor that has an integral spring. The sensor detects the location of the pin along the shift shaft. When the pin is seated in the annular groove, the sensor detects that the transmission is in a particular position or state, such as the neutral gear position. Undesirably, the vehicle operator must overcome the force of the spring as the pin travels up the annular groove when shifting out of the neutral position and into engagement with a gear. This may increase the shift effort or reduce the shift feel. Therefore, what is needed is an improved switch assembly and shift shaft arrangement that does not adversely affect shift effort or shift feel.

SUMMARY OF THE INVENTION AND ADVANTAGES

The present invention provides a transmission gear position sensing assembly. The assembly includes a transmission housing with a bore having a shift shaft, such as a shift shaft disposed therein. The shift shaft has an axis about which the shaft translates as the transmission is shifted between gear or synchronizer positions. The housing includes a hole with a switch assembly received in the hole transverse to the shift shaft axis. The shift shaft includes a profile aligned with the switch assembly. The profile has first, second, and third surfaces respectively spaced radially from the axis a first, second and third distance. The third surface is arranged between the first and second surfaces. The third distance is larger than the first and the second distances, and the third surface corresponds to a neutral gear position. The switch assembly includes a member biased into engagement with the profile by a spring. The switch assembly senses the gear position by the corresponding location along the profile. Since the third surface, which corresponds to the neutral position, is raised from the other surfaces, the shift effort is reduced as the vehicle operator shifts from the neutral position to one of the other gear positions. In this manner, the switch assembly and switch shaft configuration does not adversely effect the shift effort or shift feel.

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. 1

is a cross-sectional view of the present invention transmission switch shaft and switch assembly; and

FIG. 2

is a perspective view of the present invention shift shaft profile.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A torsion of a transmission

10

is shown somewhat schematically in cross-section in FIG.

1

. The transmission includes a housing

12

that may include a top cover and any number of other housing components that may be secured together in any suitable manner. The housing

12

includes a bore

14

with a portion of a shift shaft

16

disposed therein. The shaft

16

includes an axis A that translates along the axis as the vehicle operator manipulates the transmission with the shift lever (not shown). A shift fork

18

is typically supported by the shift shaft

16

to the transmission clutch collars between gears during shifting. Of course it is to be understood that the present invention may be used with any transmission shaft arrangement, as will be appreciated below.

A switch assembly

20

is received in a threaded hole

22

in the housing

12

. The switch assembly

20

is preferably transverse to the shaft

16

. The switch assembly

20

is of a type known in the prior art and is connected to a controller

24

via electrical contacts

23

. The switch assembly

20

includes a sensing device

25

such as a momentary switch, a proximity switch, or any other suitable sensing or switching device. The switch assembly

20

senses the position of the shift shaft

16

corresponding to the operator selected transmission gear position and sends a signal describing the gear position to the controller

24

. Although the switch assembly

20

is described as coacting with the shift shaft

16

, it is to be understood that the switch assembly

20

may coact with any suitable component within the transmission by which the transmission gear position may be determined.

The shaft

16

includes a profile

26

aligned with the switch assembly

20

. As the shaft

16

is translated when shifting between gear positions, the switch assembly

20

senses or coacts with the profile to determine the gear position. More specifically, the switch assembly

20

includes a pin

38

having a rounded end

39

received within a hole

40

in engagement with the profile

26

. A biasing member or spring

42

urges the pin

38

into engagement with the profile

26

as the shift shaft

16

is moved along axis A. The biasing member

42

introduces a force that may be felt by the vehicle operator during shifting. The biasing number

42

may be a spring integral with the switch assembly

20

.

The present invention shift shaft profile

26

includes first

28

, second

30

, and third

32

surfaces proximate to one another. The third surface

32

is arranged between the first

28

and second

30

surfaces. The first

28

, second

30

, and third

32

surfaces are radially spaced a first, second and third distance respectively from the axis A. For the shift shaft shown, the third surface

32

corresponds to the neutral gear position, and the first

28

and second

30

surfaces correspond to engaged gear positions. The surfaces may be indicative of other transmission positions or states depending upon the application. Although the surfaces

28

,

30

and

32

are shown flat they may also be curved. The distances are the apex of the surface. That is, for the first

28

and second

30

surfaces the distance would be the shortest radial distance to the axis A. Conversely, the distance for the third surface

32

would be the greatest radial distance from the axis A. Preferably, a first ramped surface

34

adjoins the first

28

and third

32

surfaces, and a second ramped surface

36

adjoins the second

30

and third

32

surfaces. The ramped surfaces

34

and

36

reduce the force needed to slide the pin

38

from the first

28

and second

30

surfaces to the third surface

32

.

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 dependent claims, the inventive may be practiced otherwise than as specifically described.