Patent Application
20080011535
This invention relates generally to a transmission and more particularly to a motorcycle transmission utilizing a shift collar for engaging and disengaging one or more rotatable parts within the transmission.
Transmissions are known to include components for engaging and disengaging rotatable parts therein. Examples include the transmissions disclosed in JP 05-026065 (Transmission Control Device For Motorcycle); JP 2003-148614 (Transmission Device For Motorcycle); JP 2001-208196 (Motor-Driven Transmission For Motorcycle); JP 2003-301859 (Dog Clutch For Motorcycle Transmission), GB 2 081 822 A (Positive Clutch); WO 99/66229 A3 (Six Speed Overdrive Motorcycle Transmission); U.S. Pat. No. 4,019,586 (Shift Dog For Transmission); and U.S. Pat. No. 7,059,210 (Six Speed Motorcycle Transmission). These disclosures are incorporated by reference herein in their entirety.
As illustrated by the aforementioned disclosures, one area of concern in the transmission field involves the engagement and disengagement of gears during a shift from one gear to the next (or between neutral and a first gear). Some transmissions may utilize a shift collar with engagement dogs to engage and disengage a gear. Other transmissions may utilize a shift collar with splines to engage and disengage a gear. Both configurations have advantages and disadvantages related to durability, ease of shifting, likelihood of missing shifts, etc. that have caused developers to seek transmission improvements over the past century. Despite many advances in the transmission art, a need exists for further improvements to address limitations with existing designs.
As illustrated in the discussion below, various embodiments of the present invention are directed at a shift collar for use in a motorcycle transmission. It should be appreciated, however, that one or more of these embodiments may also be used in other applications, such as automotive transmissions, all terrain vehicle (ATV) transmissions, personal watercraft and boat transmissions, snowmobile transmissions, commercial equipment transmissions, lawn and garden equipment transmissions, etc. Thus, the disclosed embodiments should not be construed as being limited solely to motorcycle transmission applications.
Turning first to
According to one embodiment of the present invention, three identical shift collar assemblies 1000 are provided, wherein each shift collar assembly 1000 selectably engages and disengages one or two of three transmission gear sets. As shown in
Turning to
As shown best in
While it is contemplated to arrange the engagement dogs 1060 and engagement pockets 1070 in a variety of configurations, the engagement dogs 1060 are preferably arranged on the gear engagement surfaces 1020, 1040 in a substantially circular pattern concentric with a central axis of the shift collar 1000. More preferably, the engagement dogs 1060 are arranged substantially equiangularly about the central axis of the shift collar 1000. Other, configurations (e.g., those without equiangular spacing of the engagement dogs 1060) are also contemplated. Because the engagement dogs 1060 are to be smoothly and securely received in a corresponding engagement pocket 1070, the engagement pockets 1070 are arranged on the transmission gears 1030 in the same manner as the engagement dogs 1060 are arranged on the gear engagement surface 1020, 1040. This configuration—equiangularly spaced engagement dogs 1060 and a mirror arrangement of engagement pockets 1070—improves the manufacturability of the shift collar 1000 and the balance of the shift collar 1000 as it rotates in a transmission 120 (both in engaged and disengaged positions).
According to another embodiment of the present invention, the engagement dogs 1060 share a common profile as illustrated best in
Further, it should be appreciated that the side surfaces 1099 may be angled with respect to the planar engagement surface 1020, 1040 from which the engagement dogs 1060 project. In other words, the engagement dogs 1060 preferably have a “fatter” cross section on the top surface than at their intersection with the engagement surface 1020, 1040, with side surfaces 1099 that are angled outwardly. The acute angle between a plane perpendicular to the planar engagement surface 1020, 1040 and the plane in which an angled side surface 1099 lies is known in the art as “back angle.” Providing some degree of back angle promotes engagement between the engagement dogs 1060 and the engagement pockets 1070, particularly in configurations where the engagement pockets 1070 are angled outwardly to a degree that closely matches the back angle of the engagement dogs 1060. Specifically, when back angle is provided, the angled side surface 1099 of the engagement dogs 1060 “draws” or “pulls” the engagement dogs 1060 into engagement with the engagement pockets 1070.
According to one embodiment of the present invention, the engagement dogs 1060 (and/or engagement pockets 1070) include a back angle in a range of about 3° to about 5°. More preferably, the engagement dogs 1060 (and/or engagement pockets 1070) include a back angle of about 4°. Other configurations are also contemplated.
In order to reduce the frequency of missed shifts, the engagement dogs 1060 may further be designed to have a relatively small width relative to the width of the engagement pockets 1070. The ratio between engagement pocket width to engagement dog width is commonly referred to as an “aperture ratio” of a transmission. The aperture ratio should be greater than 1:1 because some backlash (defined below) is required for proper operation of the transmission 120. Similarly, problems exist if the aperture ratio is too high because the dogs become too narrow and the engagement pockets 1070 and corresponding webbing becomes too thin to support the torque of the transmission 120. Thus, the aperture ratio is preferably in a range of about 1.5:1 to about 7:1. More preferably, the aperture ratio is in a range of about 2.2:1 to about 3.2:1. Most preferably the aperture ratio is about 2.5:1. In other words, the engagement pockets 1070 are preferably 2.5 times wider than the engagement dogs 1060.
Backlash, referenced above, refers to a gap provided between engaging portions of rotating parts which prevents the parts from jamming and allows room for lubrication. To illustrate, an engagement dog 1060 may be designed to have a thickness smaller than an engagement pocket 1070 on a transmission gear 1030 such that a small gap exists when the engagement dog 1060 is received in the engagement pocket 1070—this gap is commonly known as “backlash.” Too much backlash is undesirable because it may degrade a user's “feel” for the transmission 120 and/or cause a lagging or jerking effect when transitioning from acceleration to deceleration and vice versa. Thus, it is preferable to maintain a relatively low backlash, but a balance must be struck between a low backlash and acceptable aperture ratio and back angle characteristics of the transmission 120.
Given the above, according to one embodiment of the present invention, the engagement dogs 1060 and engagement pockets 1070 are designed such that the transmission 120 has a backlash in a range of about 20° to about 30° and a back angle in a range of about 3° to about 5°. More preferably, the engagement dogs 1060 and engagement pockets 1070 are designed such that the transmission 120 has a backlash of about 24.4 and a back angle of about 4°. These design specifications may, of course, take into consideration the preferred aperture ratios previously discussed.
Turning next to
According to one embodiment of the present invention, at least one groove 2000 extends through a center of the inner surface of each engagement dog 1060. By providing grooves 2000 in the engagement dogs 1060, the engagement dogs 1060 help support the shift collar 1000 on the corresponding shaft. This allows the number of engagement dogs 1060 to be increased without sacrificing the degree of support for the shift collar 1000.
In addition to outer splines 2010, it should be appreciated that the shift sleeve 1090 may further include a plurality of inner splines 2020. Inner splines 2020 engage corresponding splines on the mainshaft 135 or countershaft 145 of the transmission 120 such that the shift sleeve 1090 and mainshaft are rotatably coupled (i.e., rotation of one of the shift sleeve 1090 and mainshaft/countershaft causes a corresponding rotation in the other of the shift sleeve 1090 and mainshaft/countershaft). In order to ensure a secure engagement between shift sleeve 1090 and mainshaft/countershaft, at least 23 splines 2020 are provided. Other configurations are also contemplated.
If the shift collar 1000 is rotatably coupled to the shift sleeve 1090, it follows that the shift collar 1000 is rotatably coupled to the mainshaft/countershaft via the shift sleeve 1090. The shift collar 1000 is not, however, rigidly attached to the shift sleeve 1090 or to the mainshaft/countershaft via the shift sleeve 1090. Rather, the shift collar 1000 is slidably positioned on the shift sleeve 1090 such that the shift collar 1000 can be laterally moved in a direction parallel to an axis about which the shift sleeve 1090 rotates. As described in greater detail below, lateral movement of the shift collar 1000 causes the shift collar 1000 to selectably engage and disengage the transmission gears 1030, thereby effecting a gear change.
Those of skill in the art will appreciate that many different techniques may be used to cause the shift collar 1000 to move laterally with respect to the axis about which the shift sleeve 1090 rotates, any of which may be used with various embodiments of the present invention. As is described in the U.S. Provisional Patent Application Ser. No. 60/698,108 (filed Jul. 11, 2005), for example, lateral movement of the shift collar 1000 may be provided using one or more shift forks (the '108 application is incorporated by reference herein in its entirety). Specifically, when a shifter weldment is moved, this causes lateral movement of one or more shift forks. The shift forks, in turn, each laterally move a corresponding shift collar 1000 into engagement and/or out of engagement with corresponding transmission gears 1030. This effects a gear change in the transmission 120. Other configurations are also contemplated.
According to another embodiment of the present invention, a method of shifting gears in a motorcycle transmission may be performed using a shift collar assembly such as the shift collar assembly 1000 disclosed in the previously described embodiments. As shown in
Once step 710 has been completed, the transmission is ready for operation. Thereafter, during use of the transmission, when a user seeks to shift gears (e.g., from neutral to first, first to second, second to third, third to fourth, fourth to fifth, fifth to sixth, sixth to fifth, fifth to fourth, fourth to third, third to second, second to first, first to neutral), the user causes the shift collar to be moved to a first gear engagement position in step 720. As an example, a user may operate a shifter weldment which causes lateral movement of one or more shift forks. Lateral movement of the shift forks, in turn, cause lateral movement of one or more shift collar assemblies, thereby causing the shift collar to be moved to the first gear engagement position. According to some embodiments, multiple shift collars may be moved into engagement with corresponding transmission gears as part of step 720 (preferably simultaneously).
As the shift collar is moved into the first gear engagement position in step 720, at least seven engagement dogs (e.g., engagement dogs 1060) projecting from the shift collar engage in step 730 a corresponding number of engagement pockets (e.g., engagement pockets 1070) on a first transmission gear (e.g., gear 1030). The engagement dogs (and/or engagement pockets) may include an angled side surface (e.g., side surface 1099) such that the engagement dogs “pull” or “draw” themselves into proper alignment with the engagement pockets as part of step 730, thereby helping to attain a positive engagement during a partial shift under load and to maintain a positive engagement under load. Once step 730 has been completed, the user has effected a shift into the desired gear and power is transmitted through the transmission using the selected and engaged gear.
When a user desires a shift into a different gear, the user again causes the shift collar to be moved—this time away from the first gear engagement position. As an example, the user may operate the noted shift weldment as previously described. As the shift collar is moved away from the first gear engagement position, the engagement dogs are disengaged from the engagement pockets in the previously selected gear in step 740. Thereafter, a shift collar is moved to a second gear engagement position in step 750—i.e., to engage the gear desired by the user. The shift collar moved in step 750 may be the same shift collar moved in step 720 or may be a different shift collar in the transmission, or the same shift collar may be moved in combination with other shift collars. Step 750 may be performed, for example, using the shift forks previously described.
As the shift collar is moved to the second gear engagement position in step 750, at least seven engagement dogs projecting from the shift collar engage in step 760 a corresponding number of engagement pockets on a second transmission gear. One of skill in the art will appreciate that step 760 is analogous to step 740, albeit with a different transmission gear. If the shift collar moved in step 750 is the same as the shift collar moved in step 720, the engagement dogs referenced in step 760 are preferably on an opposite side of the shift collar as the engagement dogs referenced in step 730. Further, if the shift collars moved in steps 750 and 720 are the same, the movement referenced in step 750 occurs in an opposite direction as the movement referenced in step 720.
Once step 760 has been completed, the user has effected a shift into the desired gear. Thereafter, similar gear shifts may be performed using steps analogous to those previously described. In a six speed transmission, for example, a user may shift between six gear sets and a neutral position—i.e., seven “shifting” operations may be performed. Other configurations are also contemplated.
The above described embodiments may provide numerous advantages over known configurations. To illustrate, deficiencies in previously known transmissions could not be sufficiently addressed by simple design changes because compromises had to be made between the strength of the components therein and the overall performance of the transmission, tight limits on acceptable backlash and back angle had to be maintained, and known manufacturing limitations had to be taken into account. Embodiments of the present invention, by contrast, can be used to fabricate a helical transmission with minimal missed shifts, a relatively high 2.5:1 aperture ratio, an acceptable 24° of backlash, and an acceptable 4° back angle. Such a configuration is relatively easy to manufacture, and offers improved performance over known designs. Other advantages may also be realized by those of skill in the art.
The foregoing description of various embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.
This invention claims the benefit of and priority to U.S. Provisional Patent Application No. 60/819,629, the entire contents of which are incorporated by reference herein in its entirety. This application is related to Published U.S. Patent Application No. 2007/0006673, which is similarly incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60819629 | Jul 2006 | US |
