GB2550934A

GB2550934A - Gear train for a vehicle

Info

Publication number: GB2550934A
Application number: GB1609563.0A
Authority: GB
Inventors: Henderson Russell Jr
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2016-06-01
Filing date: 2016-06-01
Publication date: 2017-12-06
Anticipated expiration: 2036-06-01
Also published as: GB201609563D0; GB2550934B

Abstract

A gear train 100 for a vehicle includes a plurality of gear sets 102 that are connected in series. Each gear set includes a normally-held element such that the normally-held elements of the gear sets are connected together to rotate in unison. The gear train further includes a variator 140 that is configured to control the normally-held elements of the gear sets. The gear sets may be planetary gear sets and the normally-held elements may comprise a sun gear formed on a common shaft 104. The planet carrier 108, 114 of one gear set may be connected to the ring gear 118, 124 of the adjacent gear set and there may be 3 gear sets in the transmission. The normally-held element may instead be a ring gear (202 fig. 2) formed as a single gear.

Description

GEAR TRAIN FOR A VEHICLE

Technical Field [0001] The present disclosure relates to a gear train having a plurality of gear sets, and more particularly to a gear train in which a gear ratio of the gear train can be seamlessly varied using a variator.

Background [0002] Compound gear trains may typically include two or more gear sets for achieving a range of discrete gear ratios between an input shaft and an output shaft associated with the gear train.

[0003] Some gear trains couple a variator to one of the gear sets to vary the gear ratio of this gear set. Additional gear sets are then selectively engaged to extend the gear ratio beyond what can be provided by a single gear set and variator. In order to seamlessly engage or disengage additional gear sets, an output speed of the variator must be changed in coordination with an engagement or disengagement of the additional gear sets present in the gear train. This may increase complexity in the control and operation of the variator and the additional gear sets present in the gear train.

[0004] PCT Publication WO 2014/179719 discloses a transmission having an input member, an output member, a variator, two planetary gearsets forming a compound planetary gearset assembly, a third planetary gearset, and a plurality of torque transmitting devices. The compound planetary gearset assembly has a common ring gear, and a carrier gear for supporting a first plurality of pinion gears and second plurality of pinion gears. The torque transmitting devices include clutches and braking clutches. The transmission is configured to produce synchronous shifting between modes as the variator speed ratio approaches the extreme ends of its range and the slip across the clutch drops to zero.

[0005] Hence, there is a need for a gear train that provides a range of gear ratios without the complexity of coordinating variator speed and engagement/disengagement of additional gear sets.

Summary of the Disclosure [0006] In an aspect of the present disclosure, a gear train for a vehicle includes a plurality of gear sets that are connected in series. Each gear set includes a normally-held element such that the normally-held elements of the gear sets are connected together to rotate in unison. The gear train further includes a variator that is configured to control the normally-held elements of the gear sets.

[0007] In another aspect of the present disclosure, a method for operating a gear train includes providing a plurality of gear sets. The method further includes connecting the plurality of gear sets in series. The method also includes connecting together a normally-held element of each gear set so as to rotate in unison. The method then includes controlling the normally-held elements of the gear sets with a variator.

[0008] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of the Drawings [0009] FIG. 1 is a sectional view of a gear train for a vehicle, in accordance with an embodiment of the present disclosure; [0010] FIG. 2 is a sectional view of a gear train, in accordance with another embodiment of the present disclosure; and [0011] FIG. 3 shows a method for operating a gear train, in accordance with an embodiment of this disclosure.

Detailed Description [0012] The present disclosure relates to a gear train in which gear ratios of individual gear sets can be seamlessly varied using a variator. FIG. 1 shows a schematic of a gear train 100 in accordance with an embodiment of this disclosure.

[0013] As shown in the illustrated embodiment of FIG. 1, the gear train 100 includes multiple gear sets 102. In the illustrated embodiment of FIG. 1, three gear sets 102 are shown provided in series. Although three gear sets 102 are disclosed herein, it may be noted that the three gear sets 102 are non-limiting of this disclosure. It will be appreciated by persons skilled in the art that the present disclosure can be similarly applied to gear trains having two or more gear sets therein.

[0014] For sake of simplicity in this disclosure, the three gear sets 102 will hereinafter be referred to as “the first gear set”, “the second gear set”, and “the third gear set” and denoted using alpha-numerals “102a”, “102b”, and “102c” respectively. Each of the first gear set 102a, the second gear set 102b, and the third gear set 102c includes a normally-held element which, in this embodiment, is a sun gear 104 formed on a common shaft 106 such that the sun gear 104 is mutually shared by each of the first, second, and third gear sets 102a, 102b, and 102c.

[0015] The first gear set 102a includes a planet carrier 108 connected to one or more planet gears 110. Two planet gears 110 are shown in the sectional view of FIG. 1 in which each planet gear 110 is disposed in mesh with the sun gear 104 and a ring gear 112 of the first gear set 102a. Likewise, the second gear set 102b includes a planet carrier 114 connected to one or more planet gears 116. Two planet gears 116 are shown in the sectional view of FIG. 1 in which each of the planet gears 116 is disposed in mesh with the sun gear 104 and a ring gear 118 of the second gear set 102b. Similarly, the third gear set 102c includes a planet carrier 120 connected to one or more planet gears 122. Two planet gears 122 are shown in the sectional view of FIG. 1 in which each of the planet gears 122 is disposed in mesh with the sun gear 104 and a ring gear 124 of the third gear set 102c.

[0016] With continued reference to the illustrated embodiment of FIG. 1, one end 128 of an input shaft 126 of the gear train 100 is coupled to the ring gear 112 of the first gear set 102a. Another end 130 of the input shaft 126 may be coupled to a prime mover 132, for example, an engine or an electric motor so that the prime mover 132 can operatively rotate the ring gear 112 of the first gear set 102a by rotating the input shaft 126.

[0017] Moreover, in this embodiment, the planet carrier 108 of the first gear set 102a is connected to the ring gear 118 of the second gear set 102b while the planet carrier 114 of the second gear set 102b is connected to the ring gear 124 of the third gear set 102c. In addition, the planet carrier 120 of the third gear set 102c is rotatably coupled to an output shaft 134 of the gear train 100 via a pair of output gears 136, 138 that are disposed in mesh with one another. As shown, the output gear 136 is rigidly coupled to the planet carrier 120 of the third gear set 102c while the output gear 138 is rigidly disposed on the output shaft 134 of the gear train 100.

[0018] The gear train 100 also includes a variator 140 having an input shaft 142 and an output shaft 144. The input shaft 142 of the variator 140 is rotatably coupled to the input shaft 126 of the gear train 100 via a pair of input gears 146, 148 that are disposed in mesh with each other. The output shaft 144 of the variator 140 is rotatably coupled to the common shaft 106 on which the sun gear 104 rests. As shown, the output shaft 144 of the variator 140 and the common shaft 106 are provided with a pair of intermediary gears 150, 152 that are disposed in mesh with one another.

[0019] The variator 140 disclosed herein may embody any type of device known in the art that is capable of operatively varying a rotational speed of its output shaft 144 in relation to a rotational speed of its input shaft 142. The variator 140 may include, but is not limited to, a hydraulically operated variator, a mechanically operated variator, or a hydro-mechanically operated variator. The present disclosure is not intended to be limited to a variator per se, and this term is intended to include other suitable devices which provide variable control of the normally-held elements, such as a variable braking device.

[0020] In a first mode of operation, the sun gear 104 of the gear train 100 is held stationary by the variator 140. In this mode of operation, the prime mover 132 rotates the input shaft 126 so as to rotate the ring gear 112 of the first gear set 102a. This in turn causes the planet gears 110 from the first gear set 102a to rotate about the stationary sun gear 104. With rotation of the individual planet gears 110, the planet carrier 108 associated with the first gear set 102a is rotated so as to rotate the ring gear 118 from the second gear set 102b. Rotation of the ring gear 118 from the second gear set 102b in turn causes the planet gears 116 from the second gear set 102b to rotate about the stationary sun gear 104. With rotation of the individual planet gears 116, the planet carrier 114 associated with the second gear set 102b is rotated so as to rotate the ring gear 124 from the third gear set 102c. Rotation of the ring gear 124 from the third gear set 102c in turn causes the planet gears 122 from the third gear set 102c and the associated planet carrier 120 to rotate about the stationary sun gear 104.

[0021] As the sun gear 104 is held stationary by the variator 140, a low overall gear ratio is achieved by the gear train 100 which sets the gear train 100 in a basic torque multiplication mode. The low gear ratio of the basic torque multiplication mode may be advantageously used to set a given load, for example, a vehicle (not shown) from an initial state of rest into motion. For example, if the first gear set 102a has a gear ratio of 2.94, the second gear set 102b has a gear ratio of 2.94, and the third gear set 102c has a gear ratio of 1.48, then an overall gear ratio of the gear train 100 i.e., the ratio of the rotational speed of the input shaft 126 to the rotational speed of the output shaft 134 is given by the following equation:

Gearratio = 2.94 * 2.94 * 1.48 = 12.8:1 eq. 1.

It may be noted that equation 1 has been derived taking into account a gear ratio associated with the pair of output gears 136,138 respectively.

[0022] In a second mode of operation, as the input shaft 126 drives the ring gear 112 from the first gear set 102a to rotate the planet carrier 120 from the third gear set 102c, the sun gear 104 is also rotated by the variator 140. As the sun gear 104 is rotated by the variator 140, the overall gear ratio of the gear train 100 decreases. The overall gear ratio of the gear train 100 can be varied from, for example, 12.8:1 to 1:1 (i.e., direct drive) seamlessly with increase in the rotational speed of the sun gear 104 by the output shaft 144 of the variator 140. The gear train 100 can thus transition seamlessly from the basic torque multiplication mode to a direct drive mode. A direct drive may be advantageously used to maintain the speed of the vehicle when the vehicle is already in motion. It may be noted that a range of gear ratios can be achieved, using the gear train 100 disclosed herein, between the basic torque multiplication mode and the direct drive mode by merely changing the rotational speed of the sun gear 104 by the output shaft 144 of the variator 140.

[00231 Referring to FIG. 2, a sectional view of a gear train 200 is shown in accordance with another embodiment of this disclosure. For the sake of simplicity, recapitulation of the components present in this embodiment is omitted except where the components are configured differently from the foregoing embodiment of FIG. 1. In the illustrated embodiment of FIG. 2, the input shaft 142 of the variator 140 is rotatably coupled to the input shaft 126 of the gear train 200 via the pair of input gears 146, 148. The output shaft 144 of the variator 140 is rotatably coupled to a common ring gear 202 of the gear train 200 via an intermediary gear 150 disposed on the output shaft 144 of the variator 140 and an idler gear 204 that is disposed between and meshed with the intermediary gear 150 and the common ring gear 202 of the gear train 200. In another embodiment, the idler gear 204 may be omitted and the intermediary gear 150 may mesh with the common ring gear 202 of the gear train 200.

[0024] Moreover, in this embodiment, the gear train 200 comprises three gear sets 102a, 102b, and 102c (hereinafter collectively denoted with numeral “102”). The normally-held element from each of these gear sets 102 is the common ring gear 202 that is disposed in mesh with the planet gears 110, 116, 118 from each of the three gear sets 102a, 102b, and 102c respectively. The input shaft 126 of the gear train 100 is rigidly coupled to the planet carrier 108 of the first gear set 102a. The sun gear 206 of the first gear set 102a is rigidly coupled to the planet carrier 114 of the second gear set 102b. Likewise, the sun gear 208 of the second gear set 102b is rigidly coupled to the planet carrier 120 of the third gear set 102c.

[0025] In a first mode of operation, the ring gear 202 of the gear train 200 is held stationary by the variator 140. In this mode of operation, the prime mover 132 rotates the input shaft 126 so as to rotate the planet carrier 108 of the first gear set 102a. This in turn causes the planet gears 110 from the first gear set 102a to rotate about the sun gear 206. With rotation of the individual planet gears 110, the sun gear 206 associated with the first gear set 102a also rotates so as to impart rotation to the planet carrier 114 of the second gear set 102b. Rotation of the planet carrier 114 of the second gear set 102b in turn causes the planet gears 116 from the second gear set 102b to rotate about the sun gear 208. With rotation of the individual planet gears 116, the sun gear 208 associated with the second gear set 102b is also rotated so as to rotate the planet carrier 120 of the third gear set 102c. As the planet carrier 120 of the third gear set 102c causes the planet gears 122 from the third gear set 102c to rotate, the sun gear 210 from the third gear set 102c also tends to rotate. In the illustrated embodiment of FIG. 2, a spline 212 couples the sun gear 210 to the output shaft 134.

[0026] However, as movement of the ring gear 202 is restricted by the variator 140 i.e., by the stationary held output shaft 144 of the variator 140, a low overall gear ratio is achieved by the gear train 200 which sets the gear train 200 in a basic torque multiplication mode. The low gear ratio of the basic torque multiplication mode may be advantageously used to set a given load, for example, a vehicle (not shown) from an initial state of rest into motion. For example, if the first gear set 102a has a gear ratio of 2.94, the second gear set 102b has a gear ratio of 2.94, and the third gear set 102c has a gear ratio of 1.48, then an overall gear ratio of the gear train 200 i.e., the ratio of the rotational speed of the input shaft 126 to the rotational speed of the output shaft 134 is given by the following equation:

Gear ratio = 2.94 * 2.94 * 1.48 = 12.8:1 eq. 2.

[0027] In a second mode of operation, as the input shaft drives the planet carrier 108 from the first gear set 102a to rotate the sun gear 210 from the third gear set 102c, the ring gear 202 is also rotated by the variator 140. As the ring gear 202 is rotated by the variator 140, the overall gear ratio of the gear train 200 decreases. The overall gear ratio of the gear train 200 can be varied from, for example, 12.8:1 to 1:1 (i.e., direct drive) seamlessly with increase in the rotational speed of the ring gear 202 by the output shaft 144 of the variator 140. The gear train 200 can thus transition seamlessly from the basic torque multiplication mode to a direct drive mode. A direct drive may be advantageously used to maintain the speed of the vehicle when the vehicle is already in motion. It may be noted that an range of gear ratios can be achieved, using the gear train 200 disclosed herein, between the basic torque multiplication mode and the direct drive mode by merely changing the rotational speed of the ring gear 202 by the output shaft 140 of the variator 140.

[0028] Although it is disclosed in the foregoing embodiments that the common sun gear 104 (FIG. 1) and the common ring gear 202 (FIG. 2) are the normally-held elements, other components from respective ones of the gear sets 102a, 102b, and 102c can be used in lieu of the common sun gear 104 and the common ring gear 202 to form the normally-held components and such normally-held components can be selectively imparted with rotation from the output shaft 144 of the variator 140 to achieve a variation in the overall gear ratio of the gear train 100/200. Thus, a scope of the normally-held components disclosed in conjunction with the gear train 100/200 is not limited to the specific embodiments disclosed herein. It will be appreciated that a person having ordinary skill in the art having the benefit of teachings in this specification, may effect numerous modifications to the gear train 100/200 without departing from the spirit of the present disclosure.

[0029] It is to be understood that individual features shown or described for one embodiment may be combined with individual features shown or described for another embodiment. The above described implementation does not in any way limit the scope of the present disclosure. Therefore, it is to be understood although some features are shown or described to illustrate the use of the present disclosure in the context of functional segments, such features may be omitted from the scope of the present disclosure without departing from the spirit of the present disclosure as defined in the appended claims.

Industrial Applicability [0030] Embodiments of the present disclosure have applicability for use and implementation in producing compact and cost-effective gear trains having with the capability to vary gear ratios in a large range as compared to individual gear sets of gear trains being conventionally controlled by a variator. Moreover, embodiments of the present disclosure also have applicability in reducing complexity previously encountered in selectively and independently controlling each of the gear sets for varying gear ratios in a given gear train.

[0031] FIG. 3 shows a method 300 for operating a gear train (e.g., gear train 100/200) includes providing a plurality of gear sets (e.g., gear sets 102a, 102b, and 102c). Although three gear sets 102a, 102b, 102c are disclosed in each of the illustrated embodiments of FIGS. 1 and 2 respectively, it may be noted that the present disclosure can be similarly applied to gear trains with two or more planetary gear sets to seamlessly vary gear ratios. At step 304, the method 300 further includes connecting the plurality of gear sets 102a, 102b, 102c in series.

[0032] At step 306, the method 300 also includes connecting together a normally-held element of each gear set 102a, 102b, 102c so as to rotate in unison. For example, as shown in the illustrated embodiment of FIG. 1, the normally-held element in the gear train 100 is the common sun gear 104. In another example as shown in the illustrated embodiment of FIG. 2, the normally-held element in the gear train 200 is the common ring gear 202. At step 308, the method 300 then includes controlling the normally-held elements of the gear sets 102a, 102b, and 102c with the variator 140.

[0033] Use of embodiments disclosed herein may facilitate manufacturers of gear trains in manufacturing gear trains to compact configurations yet also effectively vary gear ratios in a large range e.g., 12.8: 1 to 1:1 seamlessly. The configuration of components disclosed herein can reduce an overall space claim by the gear train. Moreover, the variation in the gear ratios of the gear trains can be made with ease as compared to conventionally known gear trains in which shifting through individual gear sets and varying the gear ratio of one of the gear sets was carried out to compensate for the offset created by the shift and keep the prime mover e.g., an engine at a constant speed. Where an engine is used as the prime mover, with implementation of embodiments disclosed herein, the engine speed can be maintained fairly constant, preferably, at its optimum rotational speed to deliver maximum efficiency in terms of fuel consumption, performance, and power output.

[0034] While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems, methods and processes without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

LIST OF ELEMENTS TITLE: GEAR TRAIN FOR A VEHICLE FILE: 16-0080 100 gear train 102 gear sets 102a first gear set 102b second gear set 102c third gear set 104 sun gear 106 common shaft 108 planet carrier of first gear set 110 planet gears of first gear set 112 ring gear of the first gear set 114 planet carrier of second gear set 116 planet gears of second gear set 118 ring gear of the second gear set 120 planet carrier of third gear set 122 planet gears of third gear set 124 ring gear of the third gear set 126 input shaft of gear train 128 one end of input shaft of gear train 130 another end of input shaft of gear train 132 prime mover 134 output shaft of gear train 136 output gear associated with planet carrier of third gear set 138 output gear associated with output shaft of gear train 140 variator 142 input shaft of variator 144 output shaft of variator 146 input gear associated with input shaft of variator 148 input gear associated with input shaft of gear train 150,152 pair of intermediary gears 200 gear train 202 common ring gear 204 idler gear 206 sun gear of first gear set 208 sun gear of second gear set 210 sun gear of third gear set 212 spline 300 method 302 step 304 step 306 step 308 step

Claims

Claims What is claimed is:

1. A gear train for a vehicle, comprising: a plurality of gear sets connected in series, each gear set including a normally-held element; wherein the normally-held elements of the gear sets are connected together; and a variator configured to drive the normally-held elements of the gear sets.

2. The gear train of claim 1, wherein the normally-held element of each gear set comprises a sun gear.

3. The gear train of claim 2, wherein the sun gears of the gear sets are formed on a common shaft.

4. The gear train of claim 2, wherein a planet carrier of one gear set is connected to a ring gear of an adjacent gear set.

5. The gear train of claim 2, wherein an input shaft drives a ring gear of a first gear set.

6. The gear train of claim 1, wherein the normally-held element of each gear set comprises a ring gear.

7. The gear train of claim 6, wherein the ring gears of the gear sets are formed as a single gear.

8. The gear train of claim 6, wherein a sun gear of one gear set is connected to a planet carrier of an adjacent gear set.

9. The gear train of claim 6, wherein an input shaft drives a carrier of a first gear set.

10. The gear train of claim 1, wherein three gear sets are provided in series.

11. The gear train of claim 1, wherein the gear train has a variable gear ratio of in the range of 0.5-2 : 1 and 6-24 : 1.

12. The gear train of claim 7, wherein the gear train has a variable gear ratio of in the range of 1: 1 and 12-15: 1.

13. A method for operating a gear train, the method comprising: providing a plurality of gear sets; connecting the plurality of gear sets in series; connecting together a normally-held element of each gear set; driving the normally-held elements of the gear sets with a variator.

14. The method of claim 13, wherein the normally-held element of each gear set comprises a sun gear.

15. The method of claim 14, wherein a carrier of one gear set is connected to a ring gear of an adjacent gear set.

16. The method of claim 14 further comprising driving a ring gear of a first gear set.

17. The method of claim 13, wherein the normally-held element of each gear set comprises a ring gear.

18. The method of claim 17, wherein a sun gear of one gear set is connected to a carrier of an adjacent gear set.

19. The method of claim 18 further comprising driving a carrier of a first gear set.