Patent Application
20070151384
The subject invention relates to a transmission shift rail that has independent in-gear and in-neutral detents to control jumpout and allow adjustment of shift feel.
Heavy-duty vehicles, such as freight hauling Class 8 trucks, have a longer shift lever than shift levers found in passenger vehicles. Longer shift levers inherently have a high center of gravity. This high center of gravity makes certain shift levers more prone to un-requested shifts from an in-gear position to a neutral position. This phenomenon is often referred to as “jumpout.”
Different solutions have been used to reduce the occurrence of jumpout. One known solution provides a detent system. in combination with a control valve. The detent system includes a plunger with a tip that is received within the control valve. Pressure applied to the tip from the control valve is varied to selectively tailor detent forces. Another known solution provides a plunger actuator that is controlled to selectively extend and retract the plunger. These solutions are expensive and require complicated controls. Further, these methods can adversely affect shift feel when shifting from the neutral position to an in-gear position.
Thus, there is a need for a detent system that prevents the occurrence of jumpout, does not adversely affect shift feel, and which is also capable of adjusting shift feel.
A vehicle transmission includes a top cover and a shift rail that is supported by the top cover. A neutral detent mechanism cooperates with the shift rail to provide a first detent force when shifting from a neutral position to a gear engaged position. A gear detent mechanism cooperates with the shift rail to provide a second detent force when shifting out of the gear engaged position. In one example, the second detent force is greater than the first detent force to reduce the occurrence of jumpout.
The neutral and in-gear detent mechanisms operate independently from each other. The neutral detent mechanism includes a first resiliently biased member and the in-gear detent mechanism includes a second resiliently biased member. The first and second resiliently biased members are supported within bores formed within the top cover. The first resiliently biased member has a first spring defining a first spring force and the second resiliently biased member has a second spring defining a second spring force. The first and second spring forces can be varied to “tune” or adjust shift feel.
The shift rail includes a first detent profile that engages the first resiliently biased member and a second detent profile that engages the second resilient biased member. The first detent profile has a first contoured surface and the second detent profile has a second contoured surface. In one example, the second contoured surface has a sharper or steeper profile surface than the first contoured surface. This steeper groove surface requires a more aggressive shift force for shifting out of the gear engaged position. The first contoured surface has a more gradual or shallower groove surface that provides a good shift feel for an operator when shifting out of the neutral position and into the gear engaged position.
Thus, the subject invention provides a detent system that controls the occurrence of jumpout without adversely affecting shift feel, and which can be tuned to adjust shift feel. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A top cover 12 and a shift rail 14 as used in a vehicle transmission (not shown) are shown in
The top cover 12 also includes a central support member 30 that is positioned between the first 16 and second 18 support members. The central support member 30 includes a bore 32 that receives a center portion 34 of the shift rail 14.
The shift rail 14 defines an axis A that extends along a length of the shift rail 14. The shift rail 14 is axially moveable within the bores 24, 26, 32 in response to shift requests.
A stub lever (not shown) is coupled to the shift rail 14 to communicate shift requests from an operator to the shift rail 14. The stub lever cooperates with a shift sleeve 42, which is coupled to the shift rail 14, to perform shifting requests. Shift forks 44 are connected to the shift rail 14 to provide gear shifting. The shift forks 44 cooperate with clutch collars (not shown) to engage a desired gear as known. The stub lever is mounted within a shift lever housing 46 that is fastened or otherwise attached to the top cover 12.
A neutral detent mechanism 60 cooperates with the shift rail 14 to provide a first detent force when shifting from a neutral position to a gear engaged position. An in-gear detent mechanism 62 cooperates with the shift rail 14 to provide a second detent force when shifting out of the gear engaged position. The second detent force is greater than the first detent force to reduce the occurrence of jumpout. As previously explained, jumpout refers to a shifting phenomena in which the transmission inadvertently shifts from an in-gear position to a neutral position without a corresponding shift request from the operator.
Additionally, the use of separate detent mechanisms, i.e., the neutral detent mechanism 60 and the in-gear detent mechanism 62, allows for “tuning” or adjustment of shift feel. This will be discussed in greater detail below.
The neutral 60 and in-gear 62 detent mechanisms operate independently from each other. In one configuration, the neutral detent mechanism 60 operates at a lower detent force to provide a desired shift feel for the operator. The in-gear detent mechanism 62 operates at a higher detent force to reduce the occurrence of jumpout without affecting the desired shift feel for shifting out of the neutral position and into the gear engaged position. In another example configuration, the neutral detent mechanism 60 could operate at a higher detent force and the in-gear detent mechanism 62 could operate at a lower detent force.
The neutral detent mechanism 60 includes a first member 64 and the in-gear detent mechanism 62 includes a second member 66. The first 64 and second 66 members are supported within bores formed within the top cover 12. A first spring 90 resiliently biases the first member 64 and a second spring 92 resiliently biases the second member 66. This provides a dual spring configuration in which tuning of shift feel can be accomplished by using different spring forces and spring configurations.
The neutral detent mechanism 60 cooperates with a first detent profile formed on the shift rail 14. The first detent profile is defined by a first contoured surface 68. The gear detent mechanism 62 cooperates with a second detent profile formed on the shift rail 14. The second detent profile is defined by a second contoured surface 70 that is axially spaced apart from the first contoured surface 68 along the axis A.
The first contoured surface 68 preferably forms a groove 72 that extends inwardly from an outer peripheral surface 74 of the shift rail 14 toward the axis A. As shown in
The second contoured surface 70 preferably forms at least one groove 80 that extends inwardly from the outer peripheral surface 74 of the shift rail 14 toward the axis A. As shown in
The second contoured surface 70 has a sharper or steeper surface profile (
To further “tune” or adjust shift feel, spring configurations for the first 90 and second 92 springs can be varied. For example, the first 90 and second 92 springs can have different spring forces. Preferably, the in-gear detent mechanism 62 includes a stiffer or higher spring force than the neutral detent mechanism 60. This would provide a more aggressive or higher effort shift feel to shift out of an in-gear engaged position compared to shifting out of a neutral position.
In another example, shown in
It should be understood that varying spring force between the first 90 and second 92 springs and using nested springs are just a few examples of how varying spring configurations can be used to tune shift feel. Other spring configurations could also be used.
Also, it should be understood that
Finally, it should be understood that the top cover 12, shift rail 14, neutral detent mechanism 60, and gear detent mechanism 62 can be used with any type of transmission configuration including transmissions with countershafts and/or range gear shafts.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
