GB2550934B

GB2550934B - Gear train for a vehicle

Info

Publication number: GB2550934B
Application number: GB1609563.0A
Authority: GB
Inventors: R Henderson Russell Jr
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2016-06-01
Filing date: 2016-06-01
Publication date: 2019-09-18
Anticipated expiration: 2036-06-01
Also published as: GB201609563D0; GB2550934A

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 geartrain 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 outputshaft 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 toextend the gear ratio beyond what can be provided by a single gear set andvariator. In order to seamlessly engage or disengage additional gear sets, anoutput speed of the variator must be changed in coordination with an engagementor disengagement of the additional gear sets present in the gear train. This mayincrease complexity in the control and operation of the variator and the additionalgear 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 gearsetsforming a compound planetary gearset assembly, a third planetary gearset, and aplurality of torque transmitting devices. The compound planetary gearsetassembly has a common ring gear, and a carrier gear for supporting a firstplurality of pinion gears and second plurality of pinion gears. The torquetransmitting devices include clutches and braking clutches. The transmission isconfigured to produce synchronous shifting between modes as the variator speedratio approaches the extreme ends of its range and the slip across the clutch dropsto 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 andengagement/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 setincludes a normally-held element such that the normally-held elements of thegear sets are connected together to rotate in unison. The gear train furtherincludes a variator that is configured to control the normally-held elements of thegear sets. The normally-held element comprises a sun gear, and a planet carrier ofone gear set is connected to a ring gear of an adjacent gear set.

[0007] In another aspect of the present disclosure, a method for operating a gear train includes providing a plurality of gear sets. The method furtherincludes connecting the plurality of gear sets in series. The method also includesconnecting together a normally-held element of each gear set so as to rotate inunison, wherein the normally-held element comprises a sun gear, and a planetcarrier of one gear set is connected to a ring gear of an adjacent gear set. Themethod then includes controlling the normally-held elements of the gear sets witha 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 arrangement, not claimed; 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 aschematic of a gear train 100 in accordance with an embodiment of thisdisclosure.

[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 102are disclosed herein, it may be noted that the three gear sets 102 are non-limitingof this disclosure. It will be appreciated by persons skilled in the art that thepresent disclosure can be similarly applied to gear trains having two or more gearsets 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 thisembodiment, is a sun gear 104 formed on a common shaft 106 such that the sungear 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 sectionalview of FIG. 1 in which each planet gear 110 is disposed in mesh with the sungear 104 and a ring gear 112 of the first gear set 102a. Likewise, the second gearset 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 ofthe planet gears 116 is disposed in mesh with the sun gear 104 and a ring gear118 of the second gear set 102b. Similarly, the third gear set 102c includes aplanet carrier 120 connected to one or more planet gears 122. Two planet gears122 are shown in the sectional view of FIG. 1 in which each of the planet gears122 is disposed in mesh with the sun gear 104 and a ring gear 124 of the thirdgear 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 gear112 of the first gear set 102a. Another end 130 of the input shaft 126 may becoupled 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 set102a 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 whilethe planet carrier 114 of the second gear set 102b is connected to the ring gear124 of the third gear set 102c. In addition, the planet carrier 120 of the third gearset 102c is rotatably coupled to an output shaft 134 of the gear train 100 via a pairof 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 gearset 102c while the output gear 138 is rigidly disposed on the output shaft 134 ofthe 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 isrotatably coupled to the input shaft 126 of the gear train 100 via a pair of inputgears 146,148 that are disposed in mesh with each other. The output shaft 144 ofthe variator 140 is rotatably coupled to the common shaft 106 on which the sungear 104 rests. As shown, the output shaft 144 of the variator 140 and thecommon shaft 106 are provided with a pair of intermediary gears 150, 152 thatare 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 itsoutput shaft 144 in relation to a rotational speed of its input shaft 142. Thevariator 140 may include, but is not limited to, a hydraulically operated variator,a mechanically operated variator, or a hydro-mechanically operated variator. Thepresent disclosure is not intended to be limited to a variator per se, and this termis intended to include other suitable devices which provide variable control of thenormally-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 mover132 rotates the input shaft 126 so as to rotate the ring gear 112 of the first gear set102a. 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 planetgears 110, the planet carrier 108 associated with the first gear set 102a is rotatedso as to rotate the ring gear 118 from the second gear set 102b. Rotation of thering gear 118 from the second gear set 102b in turn causes the planet gears 116from the second gear set 102b to rotate about the stationary sun gear 104. Withrotation of the individual planet gears 116, the planet carrier 114 associated withthe second gear set 102b is rotated so as to rotate the ring gear 124 from the thirdgear set 102c. Rotation of the ring gear 124 from the third gear set 102c in turncauses the planet gears 122 from the third gear set 102c and the associated planetcarrier 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 100in a basic torque multiplication mode. The low gear ratio of the basic torquemultiplication mode may be advantageously used to set a given load, forexample, a vehicle (not shown) from an initial state of rest into motion. Forexample, if the first gear set 102a has a gear ratio of 2.94, the second gear set102b 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 speedof the input shaft 126 to the rotational speed of the output shaft 134 is given bythe following equation:

Gear ratio -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 ratioassociated 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 thethird gear set 102c, the sun gear 104 is also rotated by the variator 140. As thesun gear 104 is rotated by the variator 140, the overall gear ratio of the gear train100 decreases. The overall gear ratio of the gear train 100 can be varied from, forexample, 12.8:1 to 1:1 (i.e., direct drive) seamlessly with increase in therotational 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 beadvantageously used to maintain the speed of the vehicle when the vehicle isalready 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 multiplicationmode and the direct drive mode by merely changing the rotational speed of thesun gear 104 by the output shaft 144 of the variator 140.

[0023] Referring to FIG. 2, a sectional view of a gear train 200 is shown in accordance with another possible arrangement, not claimed. For the sake ofsimplicity, recapitulation of the components present in this embodiment isomitted except where the components are configured differently from theforegoing embodiment of FIG. 1. In the illustrated arrangement of FIG. 2, theinput shaft 142 of the variator 140 is rotatably coupled to the input shaft 126 ofthe gear train 200 via the pair of input gears 146, 148. The output shaft 144 ofthe variator 140 is rotatably coupled to a common ring gear 202 of the gear train200 via an intermediary gear 150 disposed on the output shaft 144 of the variator140 and an idler gear 204 that is disposed between and meshed with theintermediary gear 150 and the common ring gear 202 of the gear train 200. Inanother arrangement, the idler gear 204 may be omitted and the intermediary gear150 may mesh with the common ring gear 202 of the gear train 200.

[0024] Moreover, in this arrangement, 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 thecommon 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. Theinput shaft 126 of the gear train 100 is rigidly coupled to the planet carrier 108 ofthe first gear set 102a. The sun gear 206 of the first gear set 102a is rigidlycoupled to the planet carrier 114 of the second gear set 102b. Likewise, the sungear 208 of the second gear set 102b is rigidly coupled to the planet carrier 120of 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 firstgear set 102a. This in turn causes the planet gears 110 from the first gear set102a to rotate about the sun gear 206. With rotation of the individual planetgears 110, the sun gear 206 associated with the first gear set 102a also rotates soas 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 theplanet 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 withthe second gear set 102b is also rotated so as to rotate the planet carrier 120 of thethird gear set 102c. As the planet carrier 120 of the third gear set 102c causes theplanet gears 122 from the third gear set 102c to rotate, the sun gear 210 from thethird gear set 102c also tends to rotate. In the illustrated arrangement of FIG. 2, aspline 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 lowoverall gear ratio is achieved by the gear train 200 which sets the gear train 200in a basic torque multiplication mode. The low gear ratio of the basic torquemultiplication mode may be advantageously used to set a given load, forexample, a vehicle (not shown) from an initial state of rest into motion. Forexample, if the first gear set 102a has a gear ratio of 2.94, the second gear set102b 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 geartrain 200 i.e., the ratio of the rotational speedof the input shaft 126 to the rotational speed of the output shaft 134 is given bythe 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 thirdgear set 102c, the ring gear 202 is also rotated by the variator 140. As the ringgear 202 is rotated by the variator 140, the overall gear ratio of the gear train 200decreases. The overall gear ratio of the gear train 200 can be varied from, forexample, 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 torquemultiplication mode to a direct drive mode. A direct drive may beadvantageously used to maintain the speed of the vehicle when the vehicle isalready 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 multiplicationmode and the direct drive mode by merely changing the rotational speed of thering gear 202 by the output shaft 140 of the variator 140.

[0028] Although it is disclosed in the foregoing that the common sun gear 104 (FIG. 1) and, in the alternative arrangement, the common ring gear 202(FIG. 2) are the normally-held elements, in yet further alternative arrangements,not claimed, 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 ringgear 202 to form the normally-held components and such normally-heldcomponents can be selectively imparted with rotation from the output shaft 144of the variator 140 to achieve a variation in the overall gear ratio of the gear train100/200. It will be appreciated that a person having ordinary skill in the arthaving the benefit of teachings in this specification, may effect numerousmodifications to the gear train 100/200.

[0029] It is to be understood that individual features shown or described for one embodiment may be combined with individual features shown ordescribed for another arrangement. The above described implementation doesnot in any way limit the scope of the present disclosure. Therefore, it is to beunderstood although some features are shown or described to illustrate the use ofthe present disclosure in the context of functional segments, such features may beomitted from the scope of the present disclosure without departing from the scopeof the claims.

Industrial Applicability [0030] Embodiments of the present disclosure have applicability for use and implementation in producing compact and cost-effective gear trains havingwith 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 reducingcomplexity previously encountered in selectively and independently controllingeach 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 theillustrated embodiment of FIG. 1 and the arrangement of FIG. 2 respectively, itmay be noted that the present disclosure can be similarly applied to gear trainswith 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.As shown in the illustrated embodiment of FIG. 1, the normally-held element inthe gear train 100 is the common sun gear 104. In another possible arrangement,not claimed, as shown in FIG. 2, the normally-held element in the gear train 200is the common ring gear 202. At step 308, the method 300 then includescontrolling the normally-held elements of the gear sets 102a, 102b, and 102cwith the variator 140.

[0033] Use of embodiments disclosed herein may facilitate manufacturers of gear trains in manufacturing gear trains to compact configurations yet alsoeffectively vary gear ratios in a large range e.g., 12.8: 1 to 1:1 seamlessly. Theconfiguration of components disclosed herein can reduce an overall space claimby the gear train. Moreover, the variation in the gear ratios of the gear trains canbe made with ease as compared to conventionally known gear trains in whichshifting through individual gear sets and varying the gear ratio of one of the gearsets was carried out to compensate for the offset created by the shift and keep theprime mover e.g., an engine at a constant speed. Where an engine is used as theprime mover, with implementation of embodiments disclosed herein, the enginespeed 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 beunderstood by those skilled in the art that various additional embodiments may becontemplated by the modification of the disclosed machines, systems, methodsand processes without departing from the scope of the claims.

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 connectedtogether; and a variator configured to drive the normally-held elements of the gearsets; wherein the normally-held element of each gear set comprises a sun gear,and a planet carrier of one gear set is connected to a ring gear of anadjacent gear set.

2. The gear train of claim 1, wherein the sun gears of the gear sets are formedon a common shaft.

3. The gear train of claim 1, wherein an input shaft drives a ring gear of a firstgear set.

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

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

6. 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; wherein the normally-held element of each gear set comprises a sun gear,and a planet carrier of one gear set is connected to a ring gear of anadjacent gear set.

7. The method of claim 6 further comprising driving a ring gear of a first gear set.