US20080081705A1

US20080081705A1 - Idler gear shaft support

Info

Publication number: US20080081705A1
Application number: US11/541,193
Authority: US
Inventors: Andrew Fanning
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 2006-09-29
Filing date: 2006-09-29
Publication date: 2008-04-03

Abstract

A component of a multi-gear, manual transmission, in particular, an idler gear shaft support which supports one end of a relatively short idler gear shaft within a transmission housing. The idler gear shaft has an idler gear mounted thereon, the idler gear being rotatable about a bearing, usually a needle bearing, relative to the idler gear shaft in order to provide a reverse output to the reverse gear on the output shaft of the transmission. More specifically, the idler gear shaft support of the present invention includes an offset bolt slot for securing the idler gear shaft to the transmission housing, and a non-symmetrical mass apportionment of the support on either side of the bolt slot with a larger portion thereof accommodating the maximum thrust load of the idler gear shaft.

Description

FIELD OF THE INVENTION

The present invention concerns a component of a multi-gear, manual transmission, in particular, an idler gear shaft support which supports one end of a relatively short idler gear shaft within a transmission housing. The idler gear shaft has an idler gear mounted thereon, the idler gear being rotatable about a bearing, usually a needle bearing, relative to the idler gear shaft in order to provide a reverse output to the reverse gear on the output shaft of the transmission. More specifically, the idler gear shaft support of the present invention includes an offset bolt slot for securing the idler gear shaft to the transmission housing, and a non-symmetrical mass apportionment of the support on either side of the bolt slot with a larger portion thereof accommodating the maximum thrust load of the idler gear shaft.

BACKGROUND OF THE INVENTION

A multi-gear transmission comprising a main transmission having a main drive train and a reversing gear train is well known in the art. Such manual transmissions transfer power from an input drive shaft to an output drive shaft often via a layshaft through one of a number of gear ratios defined by a plurality of gears and shiftable friction clutches supported on one of the input shaft, the output shaft or the layshaft.
In general, when the input shaft is driven by a prime mover, such as an engine, the power is transferred from the input shaft to a series of gears on the layshaft. These gears are generally in constant mesh with mating gears on the output shaft. Each of the meshed mating gear pairs consists of a rotatable gear and a rotatably fixed gear, i.e., a gear rotatably fixed to, and rotating with the respective layshaft or output shaft. A shift fork then acts to fix one of the rotatable gears to the respective shaft and impart the desired output torque of the transmission to the output shaft. As is well known, a reverse gear of the transmission may also be specifically provided in the manual transmission by interposing an idler gear between the reverse gear on the layshaft and the respective reverse speed gear on the output shaft. Because of the idler gear interposed therebetween and in constant mesh with both the reverse gears, the reverse gear on the output shaft is always driven in a direction opposite to that of the other forward output gears.
In most transmission designs, the reverse idler gear is often supported on its own short or stub idler gear shaft in a rear housing portion of the split transmission case. The idler gear shaft generally is not as long as the input shaft, the layshaft or the output shaft due to the fact that it only supports the reverse idler gear. A longer idler gear shaft would merely add weight and cost to the final transmission. Therefore, in many cases, the relatively short idler gear shaft must be independently supported within the rear housing portion of the split transmission case.
In general, a first end of the idler gear shaft is supported directly within a bore or receiving hole formed in the rear housing portion of the transmission case itself. However, when the opposing second end of the idler gear shaft is located significantly spaced from the transmission housing split, the idler shaft must often be supported by a spacer or support component, known hereinafter as the idler shaft support. An idler shaft support, known in the art, is a symmetrical, arcuate metal support, usually aluminum, having an outer support surface for supportively engaging the housing and an inner support surface for supportively engaging the idler shaft itself.
A central hole is formed through the idler shaft support so that a bolt may be inserted therethrough. The bolt is initially inserted through a co-linear respective bolt hole opening in the rear housing portion and then through the idler gear support hole and finally into a receiving bore in the idler gear shaft so as to secure the idler gear shaft and idler gear shaft support relative to the inside wall of the transmission housing. A gear pocket is thus formed between the idler gear shaft support and the transmission housing in which the idler gear is free to rotate as it is rotatably supported on the idler shaft.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an improved transmission component, particularly an improved idler gear shaft support, for supporting a free end of an idler gear shaft in a transmission.
It is another object of the present invention to reduce the amount of material and hence cost associated with the production of an idler gear shaft support.
It is a still further object of the invention to reduce the amount of material utilized to make such a gear shaft support by concentrating the necessary material in the appropriate position to accommodate a maximum load produced by the idler gear shaft on the idler shaft support.
A still further object of the invention is to provide an offset through a slot for receiving a bolt therein, to secure the idler gear shaft support to the inside of the transmission housing, and apply a greater mass of the idler gear shaft support on one side of the offset through slot.
The idler gear shaft usually has an idler gear mounted thereon, the reverse ratio gear being rotatable about a bearing sleeve relative to the idler gear shaft in order to provide a reverse output to the output shaft from the transmission. The idler gear shaft support of the present invention is provided with an offset bolt slot for securing the idler gear shaft to the transmission housing and the offset bolt slot further defines a non-symmetrical mass apportionment having a larger portion and a smaller portion on opposing sides of the bolt slot. The larger portion of the idler gear shaft support accommodates the maximum load of the idler gear shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a prior art manual transmission having a reverse gear idler shaft situated between the main and layshafts;

FIG. 2 is an exploded view of the alignment of a reverse idler gear, idler gear shaft and a prior art shaft support in a rear portion of the split transmission case;

FIG. 3A is a side elevational view of a idler gear shaft;

FIG. 3B is a cross-sectional end view of the idler gear shaft and bolt receiving hole;

FIG. 3C is an alternative cross-sectional view of a idler gear shaft which is solid in nature as opposed to hollow;

FIG. 4A is a front side elevational view of the known prior art idler gear shaft support;

FIG. 4B is a cross-sectional view of the known idler gear shaft support;

FIG. 5 is a partial cut away cross-sectional view of a rear housing portion transmission case, including the idler gear, the idler gear shaft and the idler gear shaft support situated therein;

FIG. 6 is a perspective rear face view of the idler gear shaft support of the present invention;

FIG. 7 is a perspective front face view of the idler gear shaft support of the present invention;

FIG. 8 is a planar view of the rear face of the idler gear shaft support;

FIG. 9 is a top view of the outer support surface of the idler gear shaft support;

FIG. 10 is a planar view of the planar front face idler gear shaft support of the present invention; and

FIG. 11 is a partial cut away cross-sectional view of a rear housing portion transmission case, including the idler gear, the idler gear shaft and the improved idler gear shaft support situated therein.

DETAILED DESCRIPTION OF THE INVENTION

An idler shaft support component of a manual transmission 1 is the support for one end of a idler gear shaft 3 for an idler gear 5 within a manual transmission gearbox. A reverse idler gear, also referred to in the specification as an “idler gear”, is an integral part of almost any parallel shaft or layshaft transmission. As is well known in the art, and shown for example in FIG. 1, an idler gear 5 is a freely rotating gear supported passively on an associated idler gear shaft 3 and performs several functions one of which is to effect a reverse gear 13 of the transmission.
As previously discussed, a reverse ratio idler gear is generally constantly meshed between the driving gears on a layshaft 7 and the reverse gear 13 on the main or output shaft 9 to impart a reverse gear ratio to the transmission output shaft 9. It is only when the appropriate reverse gear 13 is engaged to the output shaft 9 by activating the clutch C to rotatably affix the reverse gear 13 to the output shaft 9 that the reverse ratio is imparted to the output shaft 9. It is to be appreciated that the transmission 1 may have other forward and reverse gear arrangements than those shown in FIG. 1, as such transmission gearing is well known in the art, no further discussion is provided.
Turning to FIG. 2, conventionally, the idler shaft 3 is a short shaft or stub shaft, which can be hollow or solid, supporting solely the reverse ratio idler gear 5. The idler gear shaft 3 has a first end 4 which is supported by a housing bore 8 (see FIG. 5) formed directly in a rear housing 23 of the transmission case 21. In certain types of split transmission cases 21, a problem occurs with respect to support of a second end 6 of the idler gear shaft 3. In some transmission arrangements, a corresponding bore can be formed directly in the front housing (not shown). When the front housing and the rear housing 23 of the transmission case 21 are fixed together, the shaft is then supported directly by the front and the rear housings 23 between the relative bores. However, this is only feasible in split transmission housings where the idler gear 5 and the idler gear shaft 3, or at least the second end 6 thereof, is located immediately adjacent the transmission case split.
In transmissions where the idler gear 5 and the idler gear shaft 3 cannot be positioned adjacent the transmission case split, it is also known to support the first end 4 of the idler gear shaft 3 in the housing bore 8 formed in the rear housing 23. However, because the idler gear shaft 3 is located deep within the rear housing 23, usually at a significant distance from the transmission split, a corresponding bore cannot be readily formed in the front housing. In this case, the idler gear 5 and the idler gear shaft 3 must be supported solely in the rear housing 23 and an idler shaft support 27 must be affixed within the rear housing 23 to support the second end 6 of the idler gear shaft 3. As also shown in FIG. 2, the idler gear 5 is supported on the idler gear shaft 3 by a bearing, usually a needle bearing 29, and a bolt 30 is provided which extends through a passage in the rear housing 23, then through a center hole 28 in the idler shaft support 27 to secure the idler gear shaft 3 and the idler shaft support 27 to the rear housing 23.
Turning to FIGS. 3A, 3B and 3C, the idler gear shaft 3 is provided with a bolt receiving bore 15, usually threaded, which receives a correspondingly threaded end of the bolt extending through the housing and the idler shaft support 27. FIG. 3B is a cross-sectional view showing the axially hollow passage 17 formed through the idler gear shaft 3 and FIG. 3C is an alternative cross-section indicating an alternative solid embodiment of the idler gear shaft 3.
An idler shaft support, known in the art, is a symmetrical arcuate metal support, as seen in FIGS. 4A and 4B, usually manufactured of die-cast aluminum, having an outer surface 31 for engaging the transmission housing and an inner surface 33 for supportively engaging the idler gear shaft 3 itself. A center hole 28 is formed, e.g., drilled, directly through the center of the idler shaft support 27 so that the bolt 30 may be inserted therethrough and pass through the idler shaft support 27 and into the bolt receiving bore 15 in the idler gear shaft 3.
The known idler shaft support 27 is a symmetrical arcuate support wherein the outer support surface 31 and the inner support surface 33 extend between radially spaced apart ends about a central axis point A, as shown in FIG. 4A. The known idler shaft support 27 is symmetrical about a central axis P which extends through the center hole 28 of the idler shaft support 27. The outer surface 31 has a radius of curvature to matingly engage with a corresponding support surface formed on the inside surface of the transmission housing. The inner diameter may have a parallel radius of curvature to the outer surface 31 of the idler gear shaft 3 about axis point A so as to receive and secure the idler gear shaft 3 therein. Both the inner and outer surfaces 33, 31 extend approximately 180 degrees about the central axis point A so as to encompass approximately half the circumference of the idler gear shaft 3 within the inner surface 33. In the manufacture of the known support 27, the idler shaft support 27 is usually die-cast as a complete circle, i.e., a 360 degree support blank which is then divided in half to form two (2) separate idler gear shaft supports 27 as described above.
Observing FIGS. 4A-B, the inner and outer axial support surfaces 33, 31 of the known idler shaft support 27 are spaced apart by a web 34 or a series of webs symmetrically spaced about the central axis P. Intermediate spaces 36 between the webs 34 may be open so as to lighten the support or define passages through the support which essentially eliminate material to make the idler shaft support 27 lighter.
Defining the position of the known support about a vertical axis V and a horizontal axis, i.e., the central axis P as in FIG. 4A, experiments have shown, and where a finite element analysis of the maximum loads applied to the known idler shaft support is procured, it is seen that the applied maximum thrust load F through the idler shaft support 27 occurs at between approximately 50-80 degrees, and more specifically about 60-70 degrees from the vertical axis V.
FIG. 5 is a cross-sectional view of the above discussed components as positioned within the rear housing 23 of the transmission case 21. The first end 4 of the idler gear shaft 3 is fixed within the housing bore 8 formed in the rear housing 23 and the second end 6 is supported by the known idler shaft support 27. The bolt 30 extends through the rear housing 23, through the central hole 28 of the idler shaft support 27, and into the bolt receiving bore 15 in the idler gear shaft 3. With the idler gear shaft 3 thus secured within the rear housing 23, it can be seen that the bearing sleeve and the idler gear 5 mounted on the shaft fit compactly between the idler shaft support 27 and the inner wall of the rear housing 23.
Turning to FIG. 6 is seen the embodiment of the present invention which improves the idler shaft support component as described above. The present embodiment of the improved idler shaft support 40 is non-symmetrically aligned about a bolt slot 45 formed on a front face 41 of the improved idler shaft support 40. It is to be appreciated that the non-symmetrical alignment of the improved idler shaft support 40, as shown about the V-P-Z axis of FIGS. 8-10, concentrates the mass of the idler support in the region of the support which receives the maximum thrust load F from the idler gear shaft 3. In other words, the non-symmetrical idler shaft support 40 is designed around the load path from the idler gear shaft 3, rather than symmetrically around the center hole 28 or the idler gear shaft 3 itself as in the known idler support components.
As seen in FIGS. 6 and 7, the non-symmetrical idler shaft support 40 includes an axial outer surface 44 and an axial inner surface 46. The axial outer surface 44 is for supportively engaging a respective mating surface portion of the transmission housing. The axial inner surface 46 supportively engages an outer circumference of the idler gear shaft 3. The improved idler shaft support 40 also includes a first end 48 and a second end 50, which define the relative arcuate length of the improved idler shaft support 40.
Importantly, and different from the known embodiments, the non-symmetrical improved idler shaft support 40 of the present invention is significantly shorter in arcuate length than the known idler supports. In other words, the first and second ends 48, 50 are closer together and define a significantly shorter arcuate length about the Z axis than the known idler shaft support. In particular, noting FIGS. 8-10, the non-symmetrical improved idler shaft support, as shown positioned with the central axis P extending through the bolt slot 45, the improved idler shaft support 40 has an overall arcuate length of about 80-100 degrees, and preferably about 90-100 degrees. This is significantly shorter from the almost 180 degree arcuate length of the known idler shaft support. Thus, the non-symmetrical idler shaft support 40 of the present invention has a shorter arcuate length, which allows a significant reduction in material used to make the non-symmetrical improved idler shaft support 40.
The improved idler shaft support 40 also has the front face 41 and a rear face 43 which are spaced apart by an intermediate width w. An overall width W of the improved idler shaft support 40 includes the bolt slot 45, as seen in FIG. 10. When the idler shaft support 40 is inserted in the transmission, the front face 41 which is planar, generally, is adjacent the rotating idler gear so as to define the gear pocket in which the gear rotates. The rear face 43 of the idler support is substantially planar and faces away from the idler gear, but includes the bolt slot 45 formed therein. As seen in FIG. 10, the overall width W, as well as the intermediate width w of the improved idler shaft support 40 is also narrower than the known supports. It is important to realize that the improved idler shaft support 40 is non-symmetrical about the bolt slot 45 and the central axis P in the Z-axis direction or, in other words, it is also non-symmetrical or offset width-wise relative to the central axis P. Also, because the bolt does not have to be fully enclosed by a center hole 28, the narrower overall width W and the further narrower intermediate width w of the improved idler shaft support 40 also eliminates a substantial amount of unnecessary material and weight of the component.
The bolt slot 45 is defined between a first ridge 47 and a second ridge 49 extending above the planar rear face 43 of the improved idler shaft support 40. Each ridge 47, 49 extends radially along the rear face 43 from the axial inner surface 46 to the axial outer surface 44. The bolt slot 45 formed therebetween includes a bottom U-shaped portion 53 which is formed below the plane of the rear face 43, and an upper U-shaped portion 55 formed between the respective inner side walls 51 as defined by the first and second ridges 47, 49 which extend above the plane of the rear face 43.
Observing FIG. 9, the bolt slot 45 is positioned in an offset manner, i.e., a non-symmetrical manner between the radially spaced apart first end 37 and the second end 39 of the idler shaft support 27. This non-symmetrical positioning or offset defines a larger portion 57 of the idler shaft support 27 on one side of the bolt slot 45, and a smaller portion 59 and less massive portion of the idler shaft support 27 on the other side of the bolt slot 45. The larger portion 57 of the support having a longer arcuate length than the smaller portion 59, and having a greater mass than the smaller portion 59 so as to accommodate the maximum thrust load F from the idler gear shaft 3. On the smaller portion 59 on the opposing side of the bolt slot 45, which does not incur the maximum thrust load F, the smaller portion 59 has significantly less mass and is thus formed shorter in arcuate length compared to the larger portion 57.
As seen in FIGS. 8 and 9, the maximum thrust load F is exerted on the improved idler shaft support 40 at an angle between approximately 50-80 degrees, and more specifically about 60-70 degrees from the vertical axis V. The improved idler shaft support 40 is thus positioned relative to the bolt slot 45 in such a manner that the maximum thrust load F goes approximately through the middle, in a radial direction, of the larger and more massive portion 57 of the improved idler shaft support 40. This particular alignment and structure ensures that the necessary mass and material strength of the improved idler shaft support 40 is positioned where it is needed to accommodate the maximum thrust load F while minimizing the material and mass where the thrust load F is less so as to reduce the size and weight of the component and thus the associated cost of producing such a component.
Returning to FIGS. 6 and 7, at each of the first and second ends 48, 50 of the improved idler support 40, a slightly hooked shaped buttress section 61 is formed. An end wall 60 of each of the first and second ends 48, 50 extends from the axially inner surface 46 in a relatively linear manner and then curves outward away from the bolt slot 45 so as to form the buttress section 61 having a planar end face 63. Such a buttress section 61 provides for an extension of slightly more surface area for the axial outer surface 44 than if the end walls 60 were merely linear. This provides for secure seating of the axial outer surface 44 against the inner wall of the rear housing 23.
The improved idler shaft support 40 of the present invention is preferably formed in a powder metal process which is an improvement over certain prior art methods which often use cast or wrought materials. Powder metallurgy is useful in fabricating parts that have irregular curves or recesses which are hard to machine and is suitable for high volume production with very little waste of material. Secondary machining is virtually eliminated and, therefore, powder metal is an extremely efficient and economical fabrication process.
In order to achieve the benefits of powder metal process, the part must be designed in a particular manner. The part should be designed to allow for easy ejection from the die, sidewalls should be perpendicular, hole axes should be parallel to the direction of opening and closing of the die, and undercuts are not permissible. This is generally not possible with the known designs since the known supports included both a bolt hole for permitting the passage of a bolt, as well as undercuts and other passages through the support to remove material. Thus, even though powder metal manufacture of certain idler supports may be known, these known supports had to be made by less economical processes and even several processes, such as forming the support and then subsequently drilling the bolt hole through the part. Additionally, none of the other known designs have an optimized load path through the strongest portion of the idler support.
Importantly, the above described support of the present invention can be easily manufactured by the powder metal process with little to no further machining required. Critically, there are no throughbores or completely enclosed passages formed in the support. The support is a solid piece having only the bolt slot and corresponding ridges defining the bolt slot. Neither the shape, nor the structural relationships of any of the elements of the support, for example, the sidewalls, ends or edges of the support need further machining or present any issue with respect to powder metal fabrication. Thus, the manufacture of the described support is optimized both economically and weight wise by the above described design by powder metal fabrication.
Since certain changes may be made in the above described improved idler gear shaft support without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.

Claims

1. An idler gear shaft support for a transmission comprising:

an outer surface for engaging an inner wall of a transmission housing;

an inner surface radially spaced from the outer surface for engaging and supporting an idler shaft;

a substantially planar front face; and

a rear face defining a bolt slot extending radially between the inner surface and the outer surface.

2. The idler gear shaft support for the transmission as set forth in claim 1 wherein the bolt slot extends non-symmetrically across the rear face of the idler gear shaft support.

3. The idler gear shaft support for the transmission as set forth in claim 2 wherein the non-symmetrical bolt slot defines a larger portion of the idler gear shaft support on one side of the bolt slot and a smaller portion on the opposing side of the bolt slot.

4. The idler gear shaft support for the transmission as set forth in claim 3 further comprising a first and a second parallel ridge running along the front face of the idler gear support and defining the bolt slot therebetween.

5. The idler gear shaft support for the transmission as set forth in claim 4 wherein the bolt slot has an upper portion defined between the first and second parallel ridges and a lower portion formed below a planar surface of the front face.

6. The idler gear shaft support for the transmission as set forth in claim 5 further comprising a first end wall and a second end wall defining an arcuate length of the idler gear shaft therebetween and wherein the first end and the second end walls each have a radially extending linear portion contiguously attached to a curved portion defining an extended buttress section circumferentially extending the arcuate length of the axial outer surface.

7. A transmission having a reverse idler gear shaft support for a reverse idler gear shaft, the reverse idler gear shaft support comprising:

a radial aligned passage for receiving a bolt extending through the gear shaft support to engage the non-rotating gear shaft;

a larger portion having a greater mass of material on a first side of the radial aligned passage and a smaller portion having less mass of material on a second side of the radial aligned passage.

8. The transmission having a reverse idler gear shaft support for a reverse idler gear shaft as set forth in claim 7, the reverse idler gear shaft support further comprising a thicker portion having a greater mass of material on a third side of the radial aligned passage than on a fourth side of the radial aligned passage.

9. The transmission having a reverse idler gear shaft support for a reverse idler gear shaft as set forth in claim 7, wherein the radial aligned passage of the gear shaft support comprises an open slot in which a bolt can be inserted into the open slot in at least one of a radial direction and an axial direction.

10. A method of manufacturing a gear shaft support according to the steps of:

forming the gear shaft support having an attachment point offset from a center of mass of the gear shaft support;

determining the maximum thrust load vector of the non-rotating gear shaft acting on the gear shaft support; and

aligning a portion of greater mass on a first side of the attachment point with the maximum thrust load vector of the non-rotating gear shaft; and

fabricating the gear shaft support by a powder metal process.

11. The method of manufacturing a gear shaft support as set forth in claim 10 further comprising the step of eliminating any drilling of the gear shaft support whereby the gear shaft support is fabricated solely by the powder metal fabrication process.