Claims:We claim:
1. A shift fork (500) for transmission in a vehicle, the shift fork (500) comprising:
a hub portion (500a) connected with a shift shaft (508);
two fingers (501, 502) extending from the hub portion (500a) in circular path and adapted to engage with circular circumference of sleeve (901, 902); and
a double acting ball spring device (503) provided at lower end contact points of the two fingers (501, 502), wherein the double acting ball spring device (503) is adapted to engage with the sleeve (901, 902).

2. The shift fork (500) as claimed in claim 1, wherein the double acting ball spring device (503) of the finger (501) has different stiffness than the double acting ball spring device (503) of the finger (502).

3. The shift fork (500) as claimed in claim 1, wherein the shift fork (500) has equal stiffness at lower end touch points of both the fingers (501, 502).

4. The shift fork (500) as claimed in claim 1, wherein the shift fork (500) is an offset shift fork.

5. The shift fork (500) as claimed in claim 1, wherein the double acting ball spring device (503) comprises:
a cylindrical housing (503d);
a helical spring (503c); and
two balls (503a) are provided at end of the cylindrical housing (503d), wherein the helical spring (503c) is provided in between the two balls (503a), wherein the helical spring (503c) and the two balls (503a) are housed in the cylindrical housing (503d).

6. A shift fork (1000) for transmission in a vehicle, the shift fork (1000) comprising:
a hub portion (1000a) connected with a shift shaft (1100);
two fingers (1001, 1002) extending from the hub portion (1000a) in circular path and adapted to engage with circular circumference of sleeve (1101, 1102); and
a leaf spring (1003) provided at each surface (1001a, 1001b, 1002a, 1002b) of the two fingers (1001, 1002) at lower end contact points, wherein raised part of the leaf spring (1003) is adapted to engage with the sleeve (1101, 1102).

7. The shift fork (1000) as claimed in claim 6, wherein the leaf springs (1003) on both the surfaces (1001a, 1001b, 1002a, 1002b) of the fingers (1001, 1002) are mounted with a pin (1004) at the lower end contact points.

8. The shift fork (1000) as claimed in claim 6, wherein the lower end contact point of the fingers (1001, 1002) has step cut at each surface to accommodate the leaf spring (1003).

9. The shift fork (1000) as claimed in claim 6, wherein the leaf spring (1003) of the finger (1001) has different stiffness than the leaf spring (1003) of the finger (1002).

10. The shift fork (1000) as claimed in claim 6, wherein the leaf spring (1003) is made from strip of spring steel.

11. The shift fork (1000) as claimed in claim 6, wherein the lower end contact point of the fingers (1001, 1002) have equal stiffness.

12. A shift fork (700) for transmission in a vehicle, the shift fork (700) comprising:
a hub portion (700a);
two fingers (701, 702) extending from the hub portion (700a) in circular path and adapted to engage with circular circumference of sleeve; and
a double acting ball spring device (703) provided at lower end contact point of the finger (702) which has high stiffness, wherein the double acting ball spring device (703) lowers down the stiffness of the finger (702) to equivalent level of the finger (701).

13. A shift fork (1200) for transmission in a vehicle, the shift fork (1200) comprising:
a hub portion (1200a) connected with a shift shaft;
two fingers (1201, 1202) extending from the hub portion (1200a) in circular path and adapted to engage with circular circumference of sleeve; and
a leaf spring (1203) provided at lower end contact point of the finger (1202) which has high stiffness, wherein the leaf spring (1203) lowers down the stiffness of the finger (1202) to equivalent level of the finger (1201).
, Description:SHIFT FORK WITH SPRING LOADED FINGERS FOR STIFFNESS BALANCE
FIELD OF INVENTION:
[001] The present subject matter described herein, relates to a shift fork structure of manual transmission or automated manual transmission in a vehicle, and, in particular, spring loaded fingers of the shift fork for stiffness balance and similar structure of shift fork of the vehicle.
BACKGROUND AND PRIOR ART:
[002] Generally, a shift fork is used to switch gears in a vehicle transmission in gear box. The shift forks are employed in vehicular transmissions to translate the means employed therein to select the desired gear ratio between the engine and the drive wheels of the vehicle. The shift forks receives input load from the shift shaft and moves the sleeve over gears for engagement. Generally, the shift fork is formed as a single piece structure. Further, the structure and use of the shift fork is well known in the art.
[003] Fig. 1, 2, and 3 illustrate structure and use of the shift fork in the vehicle transmission. The assembly 100 of gear box comprises a shift shaft 101, shift yoke 102, shift fork 103, a plurality of gears, such as first gear 104 and second gear 106, a sleeve 105. The shift fork 103 is mounted on the shift shat 101 which also refers are shift rails. The shift shaft 101 slides upon force on the shift yoke 102. The shift shaft 101 slides the shift fork 103 which moves the sleeve 105 for engagement and disengagement of gears. The shift fork 103 pushes the sleeve 105 which further pushes the corresponding gear for engagement. Generally, the vehicle transmission has 1-6th gear transmission mode, such as 1-2 gear, 3-4 gear, 5-reverse gear. Accordingly, there are three shift forks for the 1-2 gear, 3-4 gear and 5-reverse gear, the three shift forks are mounted on respective shift rails.
[004] Upon force on the shift yoke, the shift fork 103 slides the sleeve 105 over the hub to engage with gear dog for shifting of gears as shown in the figure 2. As shown in the figure 3, the shift fork 103 has two extended fingers 103a, 103b in circular path to push the circular sleeve 105. The fingers 103a, 103b of the shift fork touch the sleeve 105 at two points to push the sleeve 105 into desired gear engagement.
[005] Figure 4 illustrates structure of the shift fork 400 specifically 1-2 gear shift fork as known in the art. The shift fork 400 of the 1-2 gear is an offset shift fork which has different structure as compared to other shift forks of 3-4 gear and 5-reverse gear. The shift fork 400 has a hub section 403 which extend forwardly and bifurcate into two forked branches 401, 402 or two fingers 401, 402 which are provided with tips 401a and 402a or touch points 401a and 402a made of plastic material or suitable synthetic material, such as nylon and PVC.
[006] On the tips 401a and 402a, there are touch points which touches the sleeve on outer circumference. The touch points on the sleeve are on axis of the center. Distance ‘A’ between the touch point on the tip 401a and the shift shaft is more than the distance ‘B’ between the touch point on the tip 402a and the shift shaft. Due to the distance difference, there is difference between the stiffness of the fingers 401 and 402. The difference between the stiffness causes tilting of the sleeve during movement which is not acceptable in the vehicle transmission. Therefore, in order to avoid the tilting, the stiffness of the fingers 401, 402 at touch points is kept same by varying the cross section and thickness. The cross section ‘X’ of the finger 402 is more than the cross section ‘Y’ of the finger 401. Also sheet thickness of finger 402 is more than the finger 401.
[007] Technical problem associated with the offset shift fork, for example, shift fork for gear 1-2 arrangement, the offset shift fork can be provided for any gear arrangement in the vehicle transmission, for its layout constraint due to which stiffness varies at fingers or branches. The offset shift fork and corresponding gear arrangement is decided upon the layout of the gear box. Manufacturing of the offset shift fork is difficult and costly due to different cross section and thickness.
[008] Therefore, there is a need in the art to manufacture the offset fork with optimized cross section and equal stiffness at the touch points. The present invention has been conceived in view of the aforementioned circumstances.
OBJECTS OF THE INVENTION:
[009] The principal objective of the present invention is to provide shift fork with optimized cross section, same thickness and equal stiffness at touch points on fingers.
[0010] Another object of the present invention is to provide a shift fork with spring loaded fingers.
[0011] Another object of the present invention is to provide a shift fork with double acting ball spring arrangement to provide equal stiffness.
[0012] Another object of the present invention is to provide a shift fork with leaf spring arrangement to provide equal stiffness.
[0013] Another object of the present invention is to provide a shift fork with spring arrangement only on one fork finger with higher stiffness to provide equal stiffness.
[0014] Yet another object of the present invention is to provide a simple, effective, and cost efficient shift fork with spring loaded arrangement for equal stiffness.
SUMMARY OF THE INVENTION:
[0015] The subject matter disclosed herein relates to a shift fork, specifically, offset shift fork, with spring loaded finger for equal stiffness. The shift fork has a hub section which extended and bifurcated into two branches or fingers. The two fingers of the shift fork adapted to engage with sleeve and to slide the sleeve for gear engagement. Further a double acting ball spring device is provided at lower end contact points of the two fingers. The double acting ball spring device at both the fingers touch the sleeve and slides the sleeve upon force. Both the fingers have optmized cross section due to which stiffness of both the fingers varies from each other. In order to achieve the same stiffness, the fingers are provided with the double acting ball spring device with different stiffness. The finger which has longer distance from shift shaft joint has stiffer double acting ball spring device than the other.
[0016] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0018] Fig. 1 illustrates gear box arrangement with shift fork in general;
[0019] Fig. 2 illustrates another view of the fig. 1;
[0020] Fig. 3 illustrates arrangement of shift fork and sleeve in gear box as known in the art;
[0021] Fig. 4 illustrates structure of the shift fork as known in the art;
[0022] Fig. 5 and 6 illustrate structure of shift fork with spring loaded fingers, in accordance with an embodiment of the present subject matter;
[0023] Fig. 7a illustrates detailed view of the lower end face as shown in the fig. 6, in accordance with an embodiment of the present subject matter;
[0024] Fig. 7b illustrates another arrangement of the shift fork with single spring loaded finger, in accordance with an embodiment of the present subject matter;
[0025] Fig. 8a and 8b illustrate double acting ball spring arrangement for lower end face of the shift fork, in accordance with an embodiment of the present subject matter;
[0026] Fig. 9 illustrates the arrangement of the shift fork with sleeve, in accordance with an embodiment of the present subject matter;
[0027] Fig. 10 illustrates shift fork with leaf type spring loaded fingers, in accordance with an embodiment of the present subject matter;
[0028] Fig. 11 illustrates arrangement of the shift fork with leaf type spring loaded fingers with sleeve, in accordance with an embodiment of the present subject matter; and
[0029] Fig. 12 illustrates another arrangement of the shift fork with single spring loaded finger, in accordance with an embodiment of the present subject matter.
[0030] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0031] The subject matter disclosed herein relates to a shift fork, specifically, offset shift fork, with spring loaded finger for equal stiffness. The shift fork has a hub section which extended and bifurcated into two branches or fingers. The two fingers of the shift fork adapted to engage with sleeve and to slide the sleeve for gear engagement. Further a double acting ball spring device is provided at lower end contact points of the two fingers. The double acting ball spring device at both the fingers touch the sleeve and slides the sleeve upon force. Both the fingers have optimized cross section due to which stiffness of both the fingers varies from each other. In order to achieve the same stiffness, the fingers are provided with variable the double acting ball spring device with different stiffness. The finger which has longer distance from shift shaft joint has stiffer double acting ball spring device than the other. Further, there is no requirement of the plastic part at lower end contact points in the fingers.
[0032] In another embodiment of the present subject matter, the double acting ball spring device comprises a cylindrical housing, a helical spring and two balls. In the cylindrical housing, two balls are provided at the end and the helical spring is provided in between the two balls. Further, stiffness of the double acting ball spring device is varied by varying stiffness of the helical spring.
[0033] In yet another embodiment of the present subject matter, the shift fork is provided with leaf spring at lower end contact points to achieve equal stiffness in optimized cross sectioned fingers. The lower end of the fingers has a step cut at both the surface which is in contact with the sleeve to accommodate the leaf spring at both surfaces. On both the surfaces, the leaf springs are fixed on the lower end contact points by a pin. Further, one end of the leaf spring is free and other end is mounted on the fingers at upper side. The leaf spring on one finger has different stiffness as compared to other finger. The leaf springs at lower end contact points are adapted to engage with the sleeve for gear engagement. Further, due to leaf springs with variable stiffness, it becomes possible to achieve same stiffness on both the fingers having optimized cross section in the offset shift fork.
[0034] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various assembly that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0035] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0036] The present shift fork is an offset shift fork, for example, shift fork for gear 1-2 arrangement, the offset shift fork can be provided for any gear arrangement in the vehicle transmission. It depends on the layout of the gear box. Generally, the offset shift fork is the shift fork which does not have touch points at equal distance from shift shaft center due to layout and assembly constraints. As shown in the figure 5, the shift shaft 508 joining with the shift fork 500 is away from the center line. Due to which stiffness of both the fingers of the shift fork varies. In the known arts, the stiffness is maintained by increasing the cross section of one finger. In the present subject matter, same stiffness at both the fingers having approximately equal cross section or optimized cross section is achieved by springs with variable stiffness. The details of the structure is explained in the below figures.
[0037] Fig. 5 illustrates structure of shift fork with spring loaded fingers, in accordance with an embodiment of the present subject matter. The shift fork 500 has a hub portion 500a which is connected with the shift shaft 508 at offset location away from the center line. The hub portion 500a extends and bifurcates into two fingers 501, 502 or branches which extending radially or in circular path having common center as of sleeve. The two fingers 501, 502 are adapted to engage with circular circumference of the sleeve (as shown in the figure 9) for slide movement of the sleeve. Further, distance ‘X’ between lower end contact point 502a of the finger 502 and the shift shaft and hub joint 509 is smaller than the distance ‘Y’ between lower end contact point 501a of the finger 501 and the shift shaft and hub joint 509. Due to the difference, the farther lower end contact point 501a has less stiffness as compared to the other lower end contact point 502.
[0038] A double acting ball spring device 503 is provided at the lower end contact point 501a, and 502b of both the fingers. Accordingly, two double acting ball spring devices 503 are used to provide equal stiffness at both the lower end contact points of the shift fork 500. The double acting ball spring device 503 at the finger 501 has more stiffness as compared to the double acting ball spring device 503 of the finger 502. By varying the stiffness of the double acting ball spring device 503, the equal stiffness can be achieved at both the fingers.
[0039] For example, if 20N/mm stiffness is required at both the fingers end. Originally, there is 40N/mm stiffness at closer lower end contact point and 30N/mm at the farther lower end contact point. In order to achieve same stiffness at both the ends, a double acting ball spring device with 40N/mm stiffness is provided at the closer end and a double acting ball spring device with 60N/mm stiffness is provided at farther end. By this arrangement, equal stiffness is achieved at both end keeping the cross section approximately same. This example is given for only pedagogical purpose. This example uses the vague numbers to explain the concept and working of the present subject matter for better understanding and illustration.
[0040] In present subject matter, equivalent stiffness of the system will be similar to that of spring in series system as shown below, where we can assume k1 is the finger stiffness and k2 is the spring stiffness:-

[0041] In order to have equivalent stiffness at both the fingers, spring ball device can be added to the fingers. As shown in the figures 5, 6, and 7, to have equal stiffness, spring can be added to both fingers to bring their stiffness down to equal level.
[0042] In another embodiment of the present subject matter as shown in the figure 7b, a single ball spring device is added to a finger with higher stiffness to make its stiffness equal to finger with lower stiffness. As shown in the figure 7b, the shift fork 700 has two fingers 701 and 702. The finger 701 has lower stiffness Keq as compared to the finger 702. The finger 702 has higher stiffness as K1. In order to make stiffness of the fingers 701, 702 equal is to just provide spring arrangement 703 on the one finger 702 with higher stiffness. Adding spring will lower down the stiffness of finger to equivalent level by using following formula:-
Keq = k1*k2
k1+k2
Where Keq is the equivalent stiffness required at finger = stiffness of other finger (lower stiffness)
K1 is the finger stiffness (higher stiffness)
K2 is the spring stiffness (stiffness of spring ball arrangement)
[0043] Figure 6 and 7a illustrates the shift fork 500 with the double acting ball spring device 503 at lower end contact points.
[0044] Figure 8a and 8b illustrates structure of the double acting ball spring device 503, in accordance with the present subject matter. The double acting ball spring device 503 comprises a cylindrical housing 503d, a helical spring 503c, and two balls 503a at both ends. In the cylindrical housing 503d, the two balls 503a are provided at the end and the helical spring 503c is provided in between the two balls 503a. Further, stiffness ‘K’ of the double acting ball spring device is varied by varying stiffness of the helical spring 503c. The cylindrical housing 503d is bend inner side 503d at both ends to avoid popping out of the two balls 503a due to spring action. The double acting ball spring device 503 is fitted inside the through cavity at lower end of the fingers 501, 502.
[0045] As shown in the figure 9, the shift fork 500 sandwich in between the two sleeves 901, 902 of the gears. The double acting ball spring device 503 at lower end contact points are engaged with the sleeves 901, 902 for sliding movement for engagement of gears.
[0046] After installation of the shift fork in the gear box, when driver moves shift lever to change gear, shift fork slides sleeve by applying push force at two contact points. Since spring loaded contact points have same stiffness, so load required for sliding sleeve (Gear shift load) is equally distributed at each point. Due to equal load application at both points there will not be any tendency of sleeve tilt.
[0047] Figure 10 illustrates structure of the shift fork with leaf spring loaded fingers with equal stiffness, in accordance with an embodiment of the present subject matter. The shift fork 1000 has a hub portion 1000a which is connected with the shift shaft 1100 at offset location away from the center line XY. The hub portion 1000a extends and bifurcates into two fingers 1001, 1002 or branches which extending radially or in circular path having common center as of sleeve 1101, 1102. The two fingers 1001, 1002 are adapted to engage with circular circumference of the sleeve (as shown in the figure 11) for slide movement of the sleeve. Both the fingers 1001, 1002 have ’. Further, distance ‘Xx’ between lower end contact point 1002a of the finger 1002 and the shift shaft and hub joint 1103 is larger than the distance ‘Yy’ between lower end contact point 1001a of the finger 1001 and the shift shaft and hub joint 1103. Due to the difference, the farther lower end contact point 1002a has less stiffness as compared to the other lower end contact point 1001a.
[0048] Each finger 1001, 1002 has two faces towards the sleeves 1101, 1102. The finger 1001 has two faces 1001a and 1001b where one faces the one sleeve face, such as 1101 and other faces the other sleeve face, such as 1102. The lower end portions of both the fingers have a step cut at both the faces to accommodate a leaf spring 1003 at both faces. The step cut is provided to level the surface of the leaf spring equal with the surface of the finger. The leaf springs 1003 are mounted on each faces (1001a, 1001b, 1002a, 1002b) of the fingers 1001, 1002 at the lower end contact points. The leaf springs 1003 are mounted with a pin 1004 at lower end contact points. The leaf springs 1003 are mounted at one end whereas the other end is free to move or compress upon application of force for sliding the sleeve 1101. The leaf spring is made from strip of spring steel. The stiffness value K of the leaf springs 1003 of each finger is different from each other. Both the fingers 1001, 1002 have equal stiffness at lower end contact points.
[0049] In another embodiment of the present subject matter as shown in the figure 12, a single leaf spring device is added to a finger with higher stiffness to make its stiffness equal to finger with lower stiffness. As shown in the figure 12, the shift fork 1200 has two fingers 1201 and 1202. The finger 1201 has lower stiffness Keq as compared to the finger 1202. The finger 1202 has higher stiffness as K1. In order to make stiffness of the fingers 1201, 1202 equal is to just provide spring arrangement 1203 on the one finger 1202 with higher stiffness. Adding spring will lower down the stiffness of finger to equivalent level by using following formula:-
Keq = k1*k2
k1+k2
Where Keq is the equivalent stiffness required at finger = stiffness of other finger (lower stiffness)
K1 is the finger stiffness (higher stiffness)
K2 is the spring stiffness (stiffness of leaf spring)
[0050]
[0051] The present shift fork is easy to manufacture with optimized cross section at both the fingers.
[0052] The term “vehicle” as used throughout this detailed description and in the claims refers to any moving vehicle that is capable of carrying one or more human occupants and is powered by any form of energy. The term “vehicle” is a motor vehicle which includes, but is not limited to: cars, trucks, vans, minivans, hatchback, sedan, MUVs, and SUVs.
[0053] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0054] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.