WO2020026046A1

WO2020026046A1 - Seven forward and one reverse speed transmission unit

Info

Publication number: WO2020026046A1
Application number: PCT/IB2019/055081
Authority: WO
Inventors: Dheeraj Kumar SINGH; Basant Ballabh PATNI; Sthitadhi GHOSH; Sachin Agarwal
Original assignee: Ve Commercial Vehicles Ltd.
Priority date: 2018-08-03
Filing date: 2019-06-18
Publication date: 2020-02-06

Abstract

Described herein a transmission unit [100], comprising of an input shaft [106], an output shaft [108], and a lay shaft [110]. The input shaft [106] and the output shaft [110] supports a first, second, third, fourth, fifth, sixth, and seventh output gear [112a, 112b, 112c, 112d, 112e, 112f, 112g] and a reverse output gear [112h]. The lay shaft [110] supports a first, second, third, fourth, fifth, sixth, and seventh lay gear [114a, 114b, 114c, 114d, 114e, 114f, 114g] and a reverse lay gear [112h], meshing with the first, second, third, fourth, fifth, sixth, and seventh output gear [112a, 112b, 112c, 112d, 112e, 112f, 112g] and a reverse output gear [112h], respectively. Such arrangement provides for seven (7) forward speed ratios and one (1) reverse speed ratio, among which two (2) are overdrive speed ratios.

Description

SEVEN FORWARD AND ONE REVERSE SPEED TRANSMISSION UNIT

TECHNICAL FIELD

The present disclosure relates to a transmission unit capable of providing seven (7) forward speed ratios and one (1) reverse speed ratio. More specifically, the present disclosure relates to the transmission unit for providing better fuel economy.

BACKGROUND

Heavy vehicles are commonly known to employ a transmission unit to transmit engine power from engine to wheels of the vehicle. The transmission unit adjusts torque and rotational speed, while transferring engine power from the engine to the wheels of the vehicle. Particularly, the engine generates engine power at a defined rotational speed and a defined torque. The transmission unit adjusts the torque and the rotational speed, while transferring engine power from the engine to the wheels of the vehicle. Notably, the transmission unit adjust the torques and the rotational speed, based on user intervention. A manual transmission unit is commonly for enabling such transfer of the engine power.

The manual transmission unit may be structured and arranged to provide multiple rotational speeds (and correspondingly multiple torques), while transferring the engine power from the engine to the wheels of the vehicle. In an embodiment, the manual transmission unit may be employed to provide five (5) forward speed-ratios and one reverse speed-ratio. In such arrangements, the transmission unit is capable of providing five (5) different forward speeds (and correspondingly five (5) different forward torques), while transferring engine power from the engine to the wheels of the vehicle.

Conventionally, the manual transmission unit, providing five (5) forward speed-ratios and one reverse speed-ratio, includes an input shaft, an output shaft, and a lay shaft. The input shaft, the output shaft, and the lay shaft, in conjunction with each other, carries five (5) pairs of forward gears and one set of reverse gears. Each five (5) pairs of forward gears and one set of reverse gears has different gear-ratio and is therefore capable of providing different speed-ratio. Particularly, the input shaft and the output shaft rotatably carries five (5) output gears and one reverse output gear, while the lay shaft fixedly carries five (5) lay gears and one reverse lay gear. The input shaft, the output shaft, and the lay shaft are arranged, such that the five (5) lay gears meshes with the five (5) output gears, and one reverse lay gear meshes with the one reverse output gear via an intermediate gear. Further, the input shaft, the output shaft, and the lay shaft are arranged, such that the engine power received at the input shaft causes rotation of the five (5) output gears at different speeds defined. A rotational speed of each of the five (5) output gears corresponds to a gear ratio between each of the five (5) output gears and corresponding each of the five (5) lay gears. Further, the transmission unit employs an adjustment unit comprising of a number of synchronizer hub units, to connect one of the five (5) output gears and the one (1) reverse output gear to the output shaft, for enabling transfer of engine power therefrom. A speed-ratio attained by the output shaft is defined by the output gear among the five (5) output gears connected to the output shaft.

With the aforementioned arrangement, the conventional transmission unit is capable of providing five (5) forward speed-ratios and one reverse speed-ratio. However, the five (5) pairs of forward gears and one set of reverse gears employed by the conventional transmission units includes a gear-ratio greater than or equals one, and thus a speed-ratio so provided is always less than or equals one. Particularly, each of the five (5) pairs of forward gears and one set of reverse gears, are of speed-reducing nature. This speed-reducing feature is feasible and fuel efficient at low speed requirements. However, during high speed requirements, the transmission unit is capable of providing a speed-ratio only upto a limit of the input speed. Particularly, the such conventional transmission unit is capable of rotating he output shaft at a maximum rotational speed of a rotational speed of the input shaft. Therefore, for further increasing the rotational speed of the output shaft, more engine power is required to be generated. Therefore, such conventionally known transmission units are very less fuel efficient.

Alternative to the above defined transmission unit, a transmission unit may employ a six speed transmission unit capable of providing five (5) forward speed-reducing speed ratios, one (1) speed- increasing speed ratio, and one (1) reverse speed-ratio. The additional speed-increasing speed ratio is termed an overdrive speed ratio. However, employment of a singular overdrive speed ratio may still be less fuel efficient at very high speed requirements of the vehicle. Also, such transmission units are relatively more complex and less compact. Further, such conventionally known transmission units are housed in a very complex and multi-part housing arrangement. This increases a total number of parts of the transmission unit and thus increases a complexity of the transmission unit. Particularly, assembly and disassembly of such transmission units is difficult and cumbersome, due to employment of a large number of parts in the transmission unit.

Accordingly, in light of the aforementioned drawbacks and several other inherent in the existing arts, there is a well felt need to overcome the above mentioned challenges of complying to stringent engine norms without causing any impact to the vehicle performance, fuel economy, and cost etc. There exist a need for the transmission system to meet the customer demands with more efficient transmission unit with compact size and a lower cost.

SUMMARY

The present disclosure relates to a transmission unit for providing seven (7) forward speed ratios and one (1) reverse speed ratio. The transmission unit includes a main shaft assembly and a layshaft. The main shaft assembly includes an input shaft and an output shaft. The input shaft and the output shaft support a first, second, third, fourth, fifth, sixth, and seventh output gear and a reverse output gear. The lay shaft supports a first, second, third, fourth, fifth, sixth, and seventh lay gear and a reverse lay gear, meshing with the first, second, third, fourth, fifth, sixth, and seventh output gear and a reverse output gear, respectively. Such arrangement provides for seven (7) forward speed ratios and one (1) reverse speed ratio, among which two (2) are overdrive speed ratios.

BRIEF DESCRIPTION OF DRAWINGS

The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings. These and other details of the present invention will be described in connection with the accompanying drawings, which are furnished only by way of illustration and not in limitation of the invention, and in which drawings:

Figure 1 illustrates a sectional view of a transmission unit, in accordance with the concepts of the present disclosure.

Figure 2 shows a schematic of the main shaft assembly, in accordance with the concepts of the present disclosure. Figure 3 is a sectional view of the lay shaft [110], in accordance with the concepts of the present disclosure.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, various specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, that embodiments of the present invention may be practiced without these specific details. Several features described hereafter can each be used independently of one another or with any combination of other features. An individual feature may not address any of the problems discussed above or might address only one of the problems discussed above. Some of the problems discussed above might not be fully addressed by any of the features described herein. Example embodiments of the present invention are described below, as illustrated in various drawings in which like reference numerals refer to the same parts throughout the different drawings.

The present invention encompasses systems and methods for providing a transmission unit [100] for vehicles, with improved fuel-efficiency and better performance. As used herein, a 'vehicle' refers any kind of commercial transport vehicle that transports people or cargo. Vehicle may include, but are not limited to, heavy-duty cars, trucks, buses, ambulances, and any other vehicles obvious to a person skilled in the art.

Figure 1 illustrates a sectional view of the transmission unit [100], in accordance with the concepts of the present disclosure. The transmission unit [100] as disclosed in the present disclosure is a combination of a transmission arrangement [102] and a housing arrangement [104] The transmission arrangement [102] provides for transmission of engine power, from an engine to wheels of the vehicle. The housing arrangement [104] is provided to house and support various components of the transmission arrangement, to be protected form external environment. A structure and arrangement of the housing arrangement [104] for housing and supporting various components of the transmission arrangement [102], will be explained later in details.

The transmission arrangement [102] of the transmission unit [100], in accordance with the concepts of the present disclosure, is a manual transmission arrangement capable of providing seven (7) forward speed ratios and one (1) reverse speed ratio. For enabling this, the transmission unit [102] includes a main shaft assembly including an input shaft [106] and an output shaft [108], a lay shaft [110], an input gear [112e], four (4) speed-reducing output gears [112a, 112b, 112c, 112d], two (2) speed-increasing output gears [112f, 112g], a reverse output gear [112h], a power gear [114e], four (4) speed-reducing lay gears [114a, 114b, 114c, 114d], two (2) speed-increasing lay gears [114f, 114g], one reverse lay gear [114h], an intermediate gear [116], a first non synchronizer hub unit [118], a second synchronizer hub unit [120], a third synchronizer hub unit [122], and a fourth synchronizer hub unit [124] The aforementioned components of the transmission arrangement [102], works in conjunction with each other, to enable the transmission arrangement [102] to provide for seven (7) forward speed ratios and one (1) reverse speed ratio. In particular, the input gear [112e], the four (4) speed-reducing output gears [112a, 112b, 112c, 112d], and the two (2) speed-increasing output gears [112f, 112g], respectively, meshes with power gear [114e], four (4) speed-reducing lay gears [114a, 114b, 114c, 114d], two (2) speed- increasing lay gears [114f, 114g], for enabling the seven (7) forward speed ratios. Further, the reverse output gear [112h] meshes with the reverse lay gear [114h] via the intermediate gear [116], for enabling one (1) reverse speed ratio. A structure and arrangement of various components of the transmission arrangement will be explained in details hereinafter.

Fig. 2 shows a perspective of the main shaft assembly, in accordance with the concepts of the present disclosure. Referring to FIG. 1 and FIG. 2, the main shaft assembly is a combination of the input shaft [106] and the output shaft [108] An arrangement of the input shaft [106] and the output shaft [108], carries the input gear [112e], the four (4) speed-reducing output gears [112a, 112b, 112c, 112d], two (2) speed-increasing output gears [112f, 112g], the reverse output gear [112h], the first non-synchronizer hub unit [118], the second synchronizer hub unit [120], and the third synchronizer hub unit [122]

The input shaft [106] includes a first end [106a] and a second end [106b] The first end [106a] of the input shaft [106] is connected to a clutch mechanism to selectively receive engine power from the engine of the vehicle. The second end [106b] of the input shaft [106] fixedly supports the input gear [112e], for transferring the engine power to other components of the transmission arrangement [102] In an embodiment, the output shaft [108] may be directly coupled to the input gear [112e], for enabling a direct drive (direct transfer of power from the input shaft [106] to the output shaft [108]). Therefore, the input gear [112e] may be referred to as a fifth output gear [112e] interchangeably hereinafter.

The output shaft [108] is coaxially aligned with the input shaft [106] The output shaft is adapted to receive the engine power from the input gear [112a] of the input shaft [106], via a combination of one or more of other components of the transmission arrangement [102] Thereafter, the output shaft [108] transfers the engine power to the wheels of the vehicle. The output shaft [108] is an elongated shaft that includes a first end [108a] and a second end [108b] The first end [108a] of the output shaft [108] is proximal to the second end [106b] of the input shaft [106] The second end [108b] of the output shaft [108] is further connected to the wheels of the vehicle, for transfer of engine power to the wheels of the vehicle. The output shaft [108] supports the four (4) speed- reducing output gears [112a, 112b, 112c, 112d], the two (2) speed-increasing output gears [112f, 112g], and the reverse output gear [112h] The four (4) speed-reducing output gears [112a, 112b, 112c, 112d] are referred to as a first output gear [112a], a second output gear [112b], a third output gear [112c], and a fourth output gear [112d], interchangeably hereinafter. Further, the two (2) speed-increasing output gears [112f, 112g] are referred to as a sixth output gear [112f] and a seventh output gear [112g], interchangeably hereinafter. Notably, the first output gear [112a], the second output gear [112b], the third output gear [112c], the fourth output gear [112d], and the reverse output gear [112h] are rotatably supported on the output shaft [108] A rotatable support is facilitated by supporting each of the first output gear [112a], the second output gear [112b], the third output gear [112c], the fourth output gear [112d], and the reverse output gear [112h], on the output shaft [108] via a bearing component. Further, the sixth output gear [112f] and the seventh output gear [112f] are fixedly supported on the output shaft [108] The sixth output gear [112f] and the seventh output gear [112f] are fixedly attached to the output shaft [108] by a fixed attachment process, such as but not limited to, a welding process, a soldering process, a fit attachment process, and the like. Alternatively, the sixth output gear [112f] and the seventh output gear [112f] may be formed integrally with the output shaft [108] The gears are arranged on the output shaft [108] in a sequence of the reverse output gear [112h], the first output gear [112a], the second output gear [112b], the third output gear [112c], the sixth output gear [112f], the seventh output gear [112g], and the fourth output gear [112d], when seen from the second end [108b] to the first end [108a] of the output shaft [108] Furthermore, the output shaft [108] supports the first non-synchronous hub unit [118], the second synchronizer hub unit [120], and the third synchronizer hub unit [122], for connecting the output shaft [108] to either of the reverse output gear [112h], the first output gear [112a], the second output gear [112b], the third output gear [112c], the fourth output gear [112d], and the fifth output gear [112e] Particularly, the first non-synchronous hub unit [118] is provided between the reverse output gear [112h] and the first output gear [112a], for connecting either of the reverse output gear [112h] and the first output gear [112a] to the output shaft [108] The second synchronizer hub unit [120] is provided between the second output gear [112b] and the third output gear [112c], for connecting either of the second output gear [112b] and the third output gear [112c] to the output shaft [108] The third synchronizer hub unit [122] is provided between the fourth output gear [112d] and the fifth output gear [112e], for connecting either of the fourth output gear [112d] and the fifth output gear [112e] to the output shaft [108]

Fig. 3 is a sectional view of the lay shaft [110], in accordance with the concepts of the present disclosure. Referring to FIG. 1 and FIG. 3, the layshaft [110] is positioned axially parallel to the main shaft assembly, for enabling transfer of the engine power from the input shaft [106] to the output shaft [108] The layshaft [110] includes a first end [110a] and a second end [110b] The layshaft [110] supports and mounts the power gear [114e], the four (4) speed-reducing lay gears [114a, 114b, 114c, 114d], the two (2) speed-increasing lay gears [114f, 114g], and the fourth synchronizer hub unit [124] The power gear [114e] is referred to as the fifth lay gear [114e], interchangeably hereinafter. Moreover, the four (4) speed-reducing lay gears [114a, 114b, 114c, 114d] are referred to as a first lay gear [114a], a second lay gear [114b], a third lay gear [114c], and a fourth lay gear [114d], interchangeably hereinafter. Further, the two (2) speed-increasing lay gears [114f, 114g] are referred to as a sixth lay gear [114f] and a seventh lay gear [114g], interchangeably hereinafter. The first lay gear [112a], the second lay gear [114b], the third lay gear [114c], the fourth lay gear [114d], the fifth lay gear [114e], and the reverse lay gear [114h] are fixedly attached to the lay shaft [110]. A fixed attachment means between one or more of the first lay gear [112a], the second lay gear [114b], the third lay gear [114c], the fourth lay gear [114d], and the fifth lay gear [114e], and the reverse lay gear [114h] are fixedly attached to the lay shaft [110] may include, such as but not limited to, a welding process, a soldering process, a fit attachment process, and the like. Alternatively, one or more of the first lay gear [112a], the second lay gear [114b], the third lay gear [114c], the fourth lay gear [114d], the fifth lay gear [114e], and the reverse lay gear [114h] may be formed integrally with the output shaft [108] Further, the sixth lay gear [114f] and the seventh lay gear [114g] are rotatably supported on the lay shaft [110]. A rotatable support is facilitated by supporting each of the sixth lay gear [114f] and the seventh lay gear [114g], on the lay shaft [110] via a bearing component. The gears are arranged on the lay shaft [110] in a sequence of the reverse lay gear [114h], the first lay gear [114a], the second lay gear [114b], the third lay gear [114c], the sixth lay gear [114f], the seventh lay gear [114g], the fourth lay gear [114d], and the fifth lay gear [114e], when seen from the second end [110b] to the first end [110a] of the lay shaft [110].

Furthermore, the lay shaft [110] supports the fourth synchronous hub unit [124], for connecting the lay shaft [110] to either of the sixth lay gear [114f] and the seventh lay gear [114g] Particularly, the fourth synchronous hub unit [124] is provided between the sixth lay gear [112f] and the seventh lay gear [112g], for connecting either of the sixth lay gear [112f] and the seventh lay gear [112g] to the lay shaft [110]. Notably, the lay shaft [110] is arranged axially parallel relative to the input shaft [106] and the output shaft [108] of the main shaft assembly. With such arrangement, the first lay gear [114a] meshes with the first output gear [112a], the second lay gear [114b] meshes with the second output gear [112b], the third lay gear [114c] meshes with the second output gear [112c], the fourth lay gear [114d] meshes with the second output gear [112d], the fifth lay gear [114e] meshes with the fifth output gear [112e], the sixth lay gear [114f] meshes with the sixth output gear [112f], the seventh lay gear [114g] meshes with the second output gear [112g], and the reverse lay gear [114h] meshes with the reverse output gear [112h] via the intermediate gear [116].

Furthermore, as is shown in FIG. 1, the housing arrangement [104] is provided to mount and support the transmission arrangement [102] The housing arrangement [104] is a three-part housing that houses and supports various components of the housing arrangement [104] The housing arrangement [104] includes a transmission housing [126], a clutch housing [128], and a rear cover [130] The transmission housing [126] includes a first end portion [126a] and a second end portion [126b], and is adapted to at least partially house the transmission arrangement [102] The clutch housing [128] is attached to and covers the first end portion [126a] of the transmission housing [126], while the rear cover [130] is attached to and covers the second end portion [126b] of the transmission housing [126] Further, the transmission arrangement [102] is housed within the transmission housing [126], such that the first end [106a] of the input shaft [106] extends beyond the first end portion [126a] of the transmission housing [126] within the clutch housing [128] The first end [106a] of the input shaft [106] may be connected to a clutch arrangement of the engine to receive engine power. Moreover, the transmission arrangement [102] is housed within the transmission housing [126], such that the second end [108b] of the output shaft [108] extends beyond the second end portion [126b] of the transmission housing [126] and the end cover [130] The arrangement of the input shaft [106], the output shaft [108], and the lay shaft [110] is supported on the housing arrangement [104] Particularly, the first end [106a] of the input shaft [106] and the first end [110a] of the lay shaft [110] are rotatably supported on bearing holes of the clutch housing [128] via roller bearing arrangements. Moreover, the second end [108b] of the output shaft [108] and the second end [110b] of the lay shaft [110] are rotatably supported on bearing holes of the transmission housing [128] via roller bearing arrangements. With such arrangement, the transmission arrangement [102] is supported within the housing arrangement [104]

In assembly, the transmission unit [102] provides for seven (7) forward speed-ratios and one (1) reverse speed-ratio. Particularly, a first forward speed-ratio is enabled by meshing of the first lay gear [114a] with the first output gear [112a] Notably, a gear-ratio between the first lay gear [114a] and the first output gear [112a] is greater than one and therefore the speed-ratio so provided is less than one. A second forward speed-ratio is enabled by meshing of the second lay gear [114b] with the second output gear [112b] Notably, a gear-ratio between the second lay gear [114b] and the second output gear [112b] is greater than one and therefore the speed-ratio so provided is less than one. A third forward speed-ratio is enabled by meshing of the third lay gear [114c] with the third output gear [112c] Notably, a gear-ratio between the third lay gear [114c] and the third output gear [112c] is greater than one and therefore the speed-ratio so provided is less than one. A second forward speed-ratio is enabled by meshing of the fourth lay gear [114d] with the fourth output gear [112d] Notably, a gear-ratio between the fourth lay gear [114d] and the fourth output gear [112d] is greater than one and therefore the speed-ratio so provided is less than one. As the gear ratios between each of the first output and lay gear [112a and 114a], the second output and lay gear [112b and 114b], the third output and lay gear [112c and 114d], and the first output and lay gear [112d and 114d], is greater than one and thus provides for a speed-ratio less than one, these are considered as speed-reducing forward output gears. Further, a fifth forward speed-ratio is enabled by direct meshing of the output shaft with the fifth output gear [112e] As the fifth output gear [112e] provides for gear-ratio and speed-ratio of one, the fifth output gear [112e] is termed as direct gear. Furthermore, a sixth forward speed-ratio is enabled by meshing of the sixth lay gear [114f] with the sixth output gear [112f] Notably, a gear-ratio between the sixth lay gear [114f] and the sixth output gear [112f] is less than one and therefore the speed-ratio so provided is greater than one. A seventh forward speed-ratio is enabled by meshing of the seventh lay gear [114g] with the seventh output gear [112g] Notably, a gear-ratio between the seventh lay gear [114g] and the seventh output gear [112g] is less than one and therefore the speed-ratio so provided is greater than one. As the gear ratios between each of the sixth output and lay gear [112g and 114g] and the seventh output and lay gear [112h and 114h], is greater than one and thus provides for a speed-ratio less than one, these are considered as speed-increasing forward output gears. Particularly, the sixth output and lay gear [112g and 114g] and the seventh output and lay gear [112h and 114h] are termed as the overdrive gears. Such employment of the two pairs of overdrive gears, provides for better fuel economy. Particularly, in situations of less-torque and high-speed requirements, two levels of such adjustment is enabled. This provides for better fuel economy of the vehicle. Furthermore, a reverse speed ratio is enabled by meshing of the reverse lay gear [114h] with the reverse output gear [112h] via the intermediate gear [116].

In operation, the transmission arrangement [102] provides for seven forward speed-ratios and one reverse speed-ratio. The first non-synchronous hub unit [118], the second synchronous hub unit [120], the third synchronous hub unit [122], and the fourth synchronous hub unit [124] are manipulated by an adjustment mechanism, to manipulate provide one of the seven (7) forward speed-ratios and one reverse speed-ratio. A flow of engine power for attaining each of the (7) forward speed-ratios and one (1) reverse speed-ratio, will be explained and discussed hereinafter. The input shaft [106] receives the engine power at the first end [106a], which is required to be delivered to the output shaft at the second end [108b] As the fifth output gear [112e] on the input shaft [106] is always meshed with the fifth lay gear [114e] of the lay shaft [110], the engine power causes rotation of each of the input shaft [106] and the lay shaft [110]. However, the engine power requires to be manipulated for attaining different speed-ratios and different torque at each of the (7) forward speed-ratios and one (1) reverse speed-ratio. An arrangement for each of the (7) forward speed-ratios and one (1) reverse speed-ratio, will be discussed hereinafter.

For attaining the reverse speed-ratio, the first non-synchronizer hub unit [118] is slidably engaged to the reverse output gear [112h], to connect the reverse output gear [112h] to the output shaft [108] Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows from input shaft [106] to the output shaft [108], via the pair of fifth output gear [112e] (the input gear [112e]) and the fifth lay gear [114e] (the power gear [114e]) and the set of the reverse lay gear [114h], the intermediate gear [116], and the reverse output gear [112h] Particularly, as the reverse output gear [112h] is connected to the output shaft [108] by the first non-synchronizer hub unit [118], an engine power is transferred to the output shaft [108] through the set of the reverse lay gear [114h], the intermediate gear [116], and the reverse output gear [112h] A speed ratio so obtained is defined by the gear ratio between the set of the reverse lay gear [114h], the intermediate gear [116], and the reverse output gear [112h]

For attaining the first speed-ratio, the first non-synchronizer hub unit [118] is slidably engaged to the first output gear [112a], to connect the first output gear [112a] to the output shaft [108] Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows from the input shaft [106] to the output shaft [108], via the pair of fifth output gear [112e] (the input gear [112e]) and the fifth lay gear [114e] (the power gear [114e]) and the pair of the first lay gear [114a] and the first output gear [112a] Particularly, as the first output gear [112a] is connected to the output shaft [108] by the first non-synchronizer hub unit [118], the engine power is transferred to the output shaft [108] through the pair of the first lay gear [114a] and the first output gear [112a] A speed ratio so obtained is defined by the gear ratio between the pair of the first lay gear [114a] and the first output gear [112a] As the gear- ratio between the pair of the first lay gear [114a] and the first output gear [112a] is greater than one (1), the speed-ratio so obtained is less than one. Therefore, the rotational speed of the output shaft [108] is less than the rotational speed of the input shaft [106] while a torque of the output shaft [108] is greater than the torque of the input shaft [106]

For attaining the second speed-ratio, the second synchronizer hub unit [120] is slidably engaged to the second output gear [112b], to connect the second output gear [112b] to the output shaft [108] Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows from the input shaft [106] to the output shaft [108], via the pair of fifth output gear [112e] (the input gear [112e]) and the fifth lay gear [114e] (the power gear [114e]) and the pair of the second lay gear [114b] and the second output gear [112b] Particularly, as the second output gear [112b] is connected to the output shaft [108] by the second synchronizer hub unit [120], the engine power is transferred to the output shaft [108] through the pair of the second lay gear [114b] and the second output gear [112b] A speed ratio so obtained is defined by the gear ratio between the pair of the second lay gear [114b] and the second output gear [112b] As the gear-ratio between the pair of the second lay gear [114b] and the second output gear [112b] is greater than one (1), the speed-ratio so obtained is less than one. Therefore, the rotational speed of the output shaft [108] is less than the rotational speed of the input shaft [106] while the torque of the output shaft [108] is greater than the torque of the input shaft [106] For attaining the third speed-ratio, the second synchronizer hub unit [120] is slidably engaged to the third output gear [112c], to connect the third output gear [112c] to the output shaft [108] Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows from the input shaft [106] to the output shaft [108], via the pair of fifth output gear [112e] (the input gear [112e]) and the fifth lay gear [114e] (the power gear [114e]) and the pair of the third lay gear [114c] and the third output gear [112c] Particularly, as the third output gear [112c] is connected to the output shaft [108] by the second synchronizer hub unit [120], the engine power is transferred to the output shaft [108] through the pair of the third lay gear [114c] and the third output gear [112c] The speed ratio so obtained is defined by the gear ratio between the pair of the third lay gear [114c] and the third output gear [112c] As the gear-ratio between the pair of the third lay gear [114c] and the third output gear [112c] is greater than one (1), the speed-ratio so obtained is less than one. Therefore, the rotational speed of the output shaft [108] is less than the rotational speed of the input shaft [106] while a torque of the output shaft [108] is greater than the torque of the input shaft [106]

For attaining the fourth speed-ratio, the third synchronizer hub unit [122] is slidably engaged to the fourth output gear [112d], to connect the fourth output gear [112d] to the output shaft [108] Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows from the input shaft [106] to the output shaft [108], via the pair of fifth output gear [112e] (the input gear [112e]) and the fifth lay gear [114e] (the power gear [114e]) and the pair of the fourth lay gear [114d] and the fourth output gear [112d] Particularly, as the fourth output gear [112d] is connected to the output shaft [108] by the third synchronizer hub unit [122], the engine power is transferred to the output shaft [108] through the pair of the fourth lay gear [114d] and the fourth output gear [112d] The speed ratio so obtained is defined by the gear ratio between the pair of the fourth lay gear [114d] and the fourth output gear [112d] As the gear-ratio between the pair of the fourth lay gear [114d] and the fourth output gear [112d] is greater than one (1), the speed-ratio so obtained is less than one. Therefore, the rotational speed of the output shaft [108] is less than the rotational speed of the input shaft [106] while a torque of the output shaft [108] is greater than the torque of the input shaft [106]

For attaining the fourth speed-ratio, the third synchronizer hub unit [122] is slidably engaged to the fifth output gear [112e], to connect the fifth output gear [112e] to the output shaft [108] Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows directly from the input shaft [106] to the output shaft [108], via the fifth output gear [112e] As such engagement of the fifth output gear [112e] on the input shaft [106] to the output shaft [108] is a direct drive, the speed ratio so obtained equals one (1). Therefore, the rotational speed and torque of the output shaft [108] equals the rotational speed and torque of the input shaft [106]

For attaining the sixth speed-ratio, the fourth synchronizer hub unit [124] is slidably engaged to the sixth lay gear [112f], to connect the sixth lay gear [112f] to the lay shaft [110]. Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows from the input shaft [106] to the output shaft [108], via the pair of the fifth output gear [112e] (the input gear [112e]) and the fifth lay gear [114e] (the power gear [114e]) and the pair of the sixth lay gear [114f] and the sixth output gear [112f] Particularly, as the sixth lay gear [114f] is connected to the lay shaft [110] by the fourth synchronizer hub unit [124], the engine power is transferred to the output shaft [108] through the pair of the sixth lay gear [114f] and the sixth output gear [112f] . The speed ratio so obtained is defined by the gear ratio between the pair of the sixth lay gear [114f] and the sixth output gear [112f] As the gear-ratio between the pair of the sixth lay gear [114f] and the sixth output gear [112f] is less than one (1), the speed-ratio so obtained is greater than one. Therefore, the rotational speed of the output shaft [108] is greater than the rotational speed of the input shaft [106] while a torque of the output shaft [108] is lesser than the torque of the input shaft [106]

For attaining the seventh speed-ratio, the fourth synchronizer hub unit [124] is slidably engaged to the seventh lay gear [112g], to connect the seventh lay gear [112g] to the lay shaft [110]. Notably, with such arrangement, one of all other pair of gears are disengaged from the respective shafts. Therefore, the engine power flows from the input shaft [106] to the output shaft [108], via the pair of the fifth output gear [112e] (the input gear [112e]) and the fifth lay gear [114e] (the power gear [114e]) and the pair of the seventh lay gear [114g] and the seventh output gear [112g] Particularly, as the seventh lay gear [114g] is connected to the lay shaft [110] by the fourth synchronizer hub unit [124], the engine power is transferred to the output shaft [108] through the pair of the seventh lay gear [114g] and the seventh output gear [112g] The speed ratio so obtained is defined by the gear ratio between the pair of the seventh lay gear [114g] and the seventh output gear [112g] As the gear-ratio between the pair of the seventh lay gear [114g] and the seventh output gear [112g] is less than one (1), the speed-ratio so obtained is greater than one. Therefore, the rotational speed of the output shaft [108] is greater than the rotational speed of the input shaft [106] while the torque of the output shaft [108] is lesser than the torque of the input shaft [106]

The transmission unit [100], as disclosed in the present disclosure, provides multi-fold advantages. One such advantage relates to improved fuel economy. Particularly, the transmission unit [100], as disclosed in the present disclosure, provides two overdrive speed-ratios (sixth speed-ratio and the seventh speed-ratio). As the transmission unit provides multiple level of speed adjustment for overdrive, a better fuel economy of the vehicle is achieved.

Another advantage of the transmission unit [100], as disclosed in the present disclosure, includes a compact structure. Particularly, as the transmission unit [100] discloses usage of four hub units [118, 120, 122, and 124] for attaining eight gear-ratios (7 forward speed ratio and one reverse speed ratio), an optimized number of hub units are employed for such hub units [118, 120, 122, and 124] is used. Thereby, an optimized number of parts are employed. Thus, the compact structure of the transmission unit [100] is achieved. Additionally, the fourth synchronizer hub unit [124] is installed on the lay shaft [110] instead of the output shaft [108], a compact structure of the output shaft [108] is enabled. Thereby, a compact structure of the transmission unit [100] is enabled.

Yet another advantage of the transmission unit [100], as disclosed in the present disclosure, includes a compact, easy assembly, and easy serviceability of the transmission unit [100] Particularly, the transmission unit [100], as disclosed in the present disclosure, discloses a three- part housing arrangement [104], a relatively lesser number of parts are used by the housing arrangement [104] for housing the transmission arrangement [102] Therefore, relatively lesser number of parts are required to be disassembled for accessing the transmission arrangement [102] for servicing, thereby improving serviceability of the transmission unit [100]

While the preferred embodiments of the present invention have been described hereinabove, it should be understood that various changes, adaptations, and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims. It will be obvious to a person skilled in the art that the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive.

List of Components:

100 - Transmission Unit

102 - Transmission Arrangement

104 - Housing Arrangement

106 - Input Shaft

106a - First End of 106

106b - Second End of 106

108 - Output Shaft

108a - First End of 108

108b - Second End of 108

110 - Output Shaft

110a - First End of 110

110b - Second End of 110

112a - First Output Gear/ First Speed-reducing Output Gear

112b - Second Output Gear/ Second Speed-reducing Output Gear 112c - Third Output Gear/ Third Speed-reducing Output Gear 112d - Fourth Output Gear/ Fourth Speed-reducing Output Gear 112e - Fifth Output Gear/ Input Gear

112f— Sixth Output Gear/ First Speed-increasing Output Gear 112g - Seventh Output Gear/ Second Speed-increasing Output Gear

112h - Reverse Output Gear

114a - First Lay Gear/ First Speed-reducing Lay Gear

114b - Second Lay Gear/ Second Speed-reducing Lay Gear

114c - Third Lay Gear/ Third Speed-reducing Lay Gear

114d - Fourth Lay Gear/ Fourth Speed-reducing Lay Gear

114e - Fifth Lay Gear/ Power Gear

114f - Sixth Lay Gear/ First Speed-increasing Lay Gear

114g - Seventh Lay Gear/ Second Speed-increasing Lay Gear 114h - Reverse Lay Gear

116 - Intermediate Gear

118 - First Non-synchronizer Hub Unit

120 - Second Synchronizer Hub Unit

122 - Third Synchronizer Hub Unit

124 - Fourth Synchronizer Hub Unit

126 - Transmission Housing of 104

128 - Clutch Housing

130 - End Cover

Claims

We Claim

1. A transmission unit of a vehicle for providing seven (7) forward speed ratios and one (1) reverse speed ratios, the transmission unit comprising:

- a main shaft assembly, including:

an output shaft rotatably supporting four (4) speed-reducing forward output gears and one (1) reverse output gear, the output shaft fixedly supporting two (2) speed-increasing forward output gears; and

an input shaft axially aligned with the output shaft, and fixedly supporting one (1) input gear; and

a lay shaft fixedly supporting a power gear meshing with the input gear of the input shaft, four (4) speed-reducing forward lay gears meshing with the four (4) speed-reducing forward output gears of the output shaft, and one (1) reverse lay gear meshing with the reverse output gear via an intermediate gear, the layshaft further rotatably supporting two (2) speed-increasing forward lay gears meshing with the two (2) speed-increasing forward output gears of the output shaft, wherein

a gear ratio between each of the four (4) speed-reducing forward lay gears and the four (4) speed-reducing forward output gears is greater than one (1), and

a gear ratio between each of the two (2) speed-increasing forward lay gears and the two (2) speed-increasing forward output gears is less than one (1).

2. The transmission unit as claimed in claim 1, wherein the four (4) speed-reducing forward output gears include a first output gear, a second output gear, a third output gear, and a fourth output gear.

3. The transmission unit as claimed in claim 1, wherein the input gear is the fifth output gear.

4. The transmission unit as claimed in claim 1, wherein the two (2) speed-increasing forward output gears include a sixth output gear and a seventh output gear.

5. The transmission unit as claimed in claim 1, wherein the four (4) speed-reducing forward lay gears include a first lay gear, a second lay gear, a third lay gear, and a fourth lay gear.

6. The transmission unit as claimed in claim 1, wherein the power gear is a fifth lay gear.

7. The transmission unit as claimed in claim 1, wherein the two (2) speed-increasing forward lay gears includes a sixth lay gear and a seventh lay gear.

8. The transmission unit as claimed in claim 1 and claim 2, further includes a first non synchronizer hub unit positioned on the output shaft between the reverse output gear and the first output gear, such that the first non-synchronizer hub unit connects either of the reverse output gear and the first output gear to the output shaft for enabling transfer of power of either of the reverse output gear and the first output gear to the output shaft therefrom.

9. The transmission unit as claimed in claim 2, further includes a second synchronizer hub unit positioned on the output shaft between the second output gear and the third output gear, such that the second synchronizer hub unit connects either of the second output gear and the third output gear to the output shaft for enabling transfer of power of either of the second output gear and the third output gear to the output shaft.

10. The transmission unit as claimed in claim 2 and claim 3, further includes a third synchronizer hub unit positioned between the fourth output gear on the output shaft and the fifth output gear on the input shaft, such that the third synchronizer hub unit connects either of the fourth output gear and the fifth output gear to the output shaft for enabling transfer of power of either of the fourth output gear and the fifth output gear to the output shaft.

11. The transmission unit as claimed in claim 7, further includes a fourth synchronizer hub unit positioned on the lay shaft between the sixth lay gear and the seventh lay gear, such that the fourth synchronizer hub unit connects either of the sixth lay gear and the seventh lay gear to the lay shaft for enabling transfer of power of the layshaft to either of the sixth lay gear and the seventh lay gear.

12. The transmission unit as claimed in claim 1 to claim 11, further includes a three-part housing arrangement for housing and supporting the transmission unit.

13. The transmission unit as claimed in claim 12, wherein the three-part housing arrangement includes a clutch housing, a transmission housing, and a rear housing.

14. The transmission unit as claimed in claim 13, wherein the transmission housing houses and covers at least partially the transmission unit, such that one end of the input shaft extends beyond the transmission housing from a first end portion, while an opposite end of the output shaft extends beyond a second end portion of the transmission housing.

15. The transmission unit as claimed in claim 13, wherein the clutch housing at least partially covers the first end portion of the transmission unit.

16. The transmission unit as claimed in claim 13, wherein the rear housing at least partially covers the second end portion of the transmission unit.

17. The transmission unit as claimed in claim 13, wherein one end of each of the input shaft and the lay shaft is rotatably supported on the clutch housing, while on opposite end of each of the output shaft and the lay shaft is rotatably supported on the transmission housing.