Machine element or mechanism – Elements – Gear casings
Reexamination Certificate
2000-02-22
2001-08-28
Wright, Dirk (Department: 3681)
Machine element or mechanism
Elements
Gear casings
Reexamination Certificate
active
06279423
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a countershaft transmission in which a plurality of speed change gear trains are disposed in parallel with one another on parallel shafts, and a gear change is carried out by selectively activating one of the clutches provided to the gear trains.
1. Field of the Invention
Many countershaft type transmissions are used in automobiles, and an example of a countershaft transmission is disclosed in Japanese Laid-open Patent Publication No. H6(1994)-221432(A). Typically, a countershaft transmission comprises a plurality of constant mesh type speed change gear trains, which are disposed in parallel with one another between two parallel shafts, and each gear train is provided with a clutch, for example, a synchromesh-type clutch. These clutches are activated selectively in correspondence to the manipulation of the shift lever by the driver to achieve a power transmission at a desired speed ratio.
2. Description of the Related Art
There is an attempt to increase the number of speed change ratios or gear ratios available for such countershaft transmissions, in order to improve the driving characteristics of the vehicles which incorporate countershaft transmissions. With this attempt, the number of speed change gear trains which are disposed in parallel with one another between the two parallel shafts is also increasing. This trend may lead to a problem that the size of the transmission will increase to include the shafts which are formed longer than ever to support these gear trains, which are increasing in number. Therefore, not to elongate the shafts too much for the purpose of keeping the transmission compact, there is a demand for improvements in the arrangement and construction of the speed change gear trains.
In the production of a countershaft transmission, the relation of the two parallel shafts must be maintained while a plurality of speed change gear trains each including drive and driven gears to mesh with each other are being mounted on these shafts, together with a plurality of clutches which select the gear trains for power transmission. Therefore, there is a need for a countershaft transmission which facilitates easy and simple assembly.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a countershaft transmission which facilitates the assembly of two parallel shafts disposed with a plurality of speed change gear trains therebetween and a plurality of clutches in a transmission case.
The present invention provides a countershaft transmission which rotatably incorporates first, second and third shafts in a transmission case. The first shaft (e.g., the input shaft
11
of the embodiment described in the following section) is connected to an engine, the second shaft (e.g., the countershaft
12
of the following embodiment) extends in parallel with the first shaft, and the third shaft (e.g., the output shaft
13
of the following embodiment) extends in a direction away from the engine against the first shaft. In addition, a plurality of speed change gear trains (e.g., the LOW, SECOND, THIRD, FOURTH, FIFTH, SIXTH and REVERSE gear trains of the embodiment described in the following section) are disposed in parallel with one another between the first shaft and the second shaft. In this transmission, the transmission case comprises separate first, second and third casings, which are connected in this order from the side where the engine is placed. In a first room which is defined by the first and second casings, disposed are the first shaft, the second shaft and the speed change gear trains, and the sides of the first and second shafts which are located toward the engine are supported rotatably by the first casing while the side of the first shaft which is located away from the engine is supported rotatably by the second casing. In a second room which is defined by the second and third casings, disposed are the side of the second shaft which is located away from the engine, the third shaft, and the transmission means (e.g., the gear train
28
a
and
28
b
of the following embodiment), which carries out power transmission between the second and third shafts, and the side of the third shaft which is located toward the engine is supported rotatably by the second casing while the sides of the second and third shafts which are located away from the engine are supported rotatably by the third casing.
The countershaft transmission which is designed in the above described way can be assembled by following the next assembly stages. At first, the first casing is set with the side end which is to meet the engine facing downward and the first room opening upward. Into the inside space of this first casing, the first and second shafts which are subassembled with speed change gears and clutches, respectively, are inserted vertically from above, with the sides of the first and second shafts which are located toward the engine facing downward, and then the ends of the first and second shafts are supported rotatably by the first casing. As a result, the two shafts stand vertically in the first casing, and the speed change gear trains are disposed between these shafts. Then, the second casing is mounted on the first casing such that the second casing encloses the first and second shafts, and the side of the first shaft which is located away from the engine and a middle portion of the second shaft are supported rotatably by the second casing. By this stage, the transmission has been assembled with the first and second shafts, which are disposed in parallel with each other and supported rotatably in the room surrounded by the first and second casings, and with a plurality of speed change gear trains, which are disposed in parallel with one another between these two shafts.
In this condition of the transmission, which is assembled with the second casing, the side of the second shaft which is located away from the engine protrudes upward from the second casing. Now, a gear which constitutes the above mentioned transmission means or transmission gear train is mounted on this protruding second shaft, and the third shaft subassembled with the other gear which constitutes the transmission gear train is mounted with the side of the third shaft which is located toward the engine facing downward. The third shaft in this condition is supported rotatably by the part of the second casing which faces the above mentioned second room. Then, the third casing is mounted on the second casing such that the third casing covers the second and third shafts. By this stage, the transmission have been assembled with basic parts, and the part of the second shaft protruding from the second casing, the transmission gear train and the third shaft are disposed in the room surrounded by the second and third casing. In this way, the transmission according to the present invention enables an orderly assembly in which the transmission is assembled in the order of the first, second and third casings while the engine side of the transmission is set downward, with the first, second and third shafts standing upward. Therefore, the assembly of the transmission is easy and simple.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5884525 (1999-03-01), Toyota et al.
patent: 5946971 (1999-09-01), Toyota et al.
patent: 6109393 (2000-08-01), Toyota et al.
patent: 57-33264 (1982-02-01), None
patent: 6-221432 (1994-08-01), None
Kitajima Kyoji
Mitani Masakazu
Udou Hideo
Armstrong Westerman Hattori McLeland & Naughton LLP
Honda Giken Kogyo Kabushiki Kaisha
Wright Dirk
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