MOTOR VEHICLE TRANSMISSION MECHANISM

Abstract: A transmission mechanism wherein a reverse gear train (GR) and a plurality of forward gear trains (G1, G2) are provided between parallel input and output shafts (1 and 2) is characterised in that the reverse gear train (GR) and one of the forward gear trains (G1 or G2) is composed of a single planetary gear arrangement (4). This planetary gear arrange­ ment (4) may be changed over selectively to serve either as said one forward gear train, by engagement of a clutch element (9), or as the reverse gear train by operation of a brake element (10). By utilising a single planetary gear arrangement to serve as both the reverse gear train and one of the forward gear trains, the length of the mechanism in the axial direction is minimised and changeover operation between forward and reverse running is carried out without the use of a selection gear so that generation of impact noise is avoided. The planetary gear arrangement can be disposed on either of the input shaft or the output shaft giving freedom of design.

Description: MOTOR VEHICLE TRANSMISSION AECHANISAI This invention relates to motor vehicle transmission mechanism wherein a reverse driving train and a plurality of forward driving trains are provided between an input shaft and an output shaft, which shafts are disposed parallel with one another. In Figure 1 of the accompanying drawings there is shown, diagrammatically, a known transmission mechanism having parallel input and output shafts and in which an oil pressure operated clutch c for a forward driving train b provided on the input shaft a is used also as an oil pressure operated clutch for a reverse driving train d so that an oil pressure operated clutch exclusively for the reverse driving train is omitted, and thereby the axial longitudinal length of the transmission mechanism as a whole can be shortened to such a size that the mechanism can be mounted in a small-sized front-engine front-wheel-drive motorcar. It has been usual in such a transmission mechanism that the two driving trains b or d are selectively connected to the output shaft f through a selection gear e that is moved by operation of a shift lever, and consequently such mechanism involves various inconveniences as follows: i) The shift lever is usually given such a changeover operation that the lever has to be moved from a parking position to a forward driving position through a reverse driving position and a neutral position, so that in the course of changeover operation thereof from the parking position to the forward driving position, the selection gear e is moved unnecessarily first to the reverse driving position (on the right-hand side in Figure 1), and thereafter is moved to the forward driving position (on the left-hand side in Figure 1); As a result impact noise is liable to be generated owing to this gear movement. Furthermore, upon changeover to, or from, the reverse driving position, particularly upon changeover from the reverse driving position on the right-hand side to the forward driving position on the lefthand side, impact noise is liable to be generated. ii) It is necessary to move the selection gear e for changeover after rotation of this gear e has been stopped and the power transmission to the two driving trains cut off, and therefore it is inevitable that the oil pressure operated clutch c has to be provided on the input shaft a, and that the selection gear e has to be provided on the output shaft f, as illustrated. Thus, freedom of design to achieve a compact transmission mechanism is not available. There is also known a coaxial input/output shaft transmission mechanism wherein a plurality of planetary gears is used for effected change speed between a reverse driving stage and multiforward-driving stages. This type of mechanism is advantageous in that changeover of a gear as above becomes unnecessary and the generation of impact noise can be avoided, but the inconvenience arises that, because the number of gears is greater than in the parallel input/output shafts mechanism, the transmission efficiency is lowered. In addition, because an input section and an output section are disposed on mutually opposite sides of the plurality of planetary gears, the disposition of the input and output sections restricts freedom of design for achieving a compact mechanism. According to the present invention there is provided a transmission mechanism wherein a reverse gear train and a plurality of forward gear trains are provided between an input shaft and an output shaft which are disposed in parallel with one another, characterised in that the reverse gear train and one of the forward gear trains is composed of a single planetary gear arrangement comprising a sun gear that moves with the input shaft, a ring gear that moves with the output shaft, and a supporting arm supporting a planetary gear meshed with the sun and ring gears, the supporting arm being mounted on one of the shafts and that one of the two gears that moves with the shaft on which the supporting arm is mounted being fixed to this shaft whereas the other of the gears is connected to the shaft with which it moves through a gear train, the planetary gear arrangement being provided with a clutch element for causing the supporting arm to rotate fast with the sun gear in conjunction with the input shaft, and a brake element for restraining rotation of the supporting arm, so that the planetary gear arrangement may be changed over selectively to serve either as said one forward gear train by engagement of the clutch element or as the reverse gear train by operation of the brake element. In this transmission mechanism the length of the mechanism in the axial direction can be minimised, and changeover operation between forward running and reverse running is carried out without the use of a selection gear so that generation of impact noise is avoided. Additionally, the planetary gear arrangement can be disposed on either the input shaft or the output shaft giving freedom of design. When the planetary gear arrangement is selectively operated to function as the forward gear train, the sun gear and the ring gear are brought into a direct coupling condition and thus any lowering in the transmission efficiency is prevented. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to Figures 2 to 5 of the accompanying drawings, in which Figure 2 shows, diagrammatically, a motor vehicle transmission mechanism, Figure 3 shows, diagramatically, a modified form of mechanism, and Figures 4 and 5 are sectional side views of other forms of transmission mechanism. Referring first to Figures 2 and 3, in each of these Figures the transmission mechanism has two forward stages and one reverse stage. Numeral 1 denotes an input shaft connected to an internal combustion engine and numeral 2 denotes an output shaft connected through a differential gear 3 to driving road wheels of a vehicle, the input shaft 1 and the output shaft 2 being disposed in parallel with one another. There are provided between the two shafts 1, 2 a low speed first forward gear train G1 having a first speed clutch C1 of oil pressure operated type or electromagnetic type, a high speed second forward gear train G2, and a reverse gear train GR. The gear trains G2 and GR are composed of a single planetary gear arrangement 4. In the planetary gear arrangement 4 a sun gear 5 moves with the input shaft 1, a ring gear 6 moves with the output shaft 2, and a supporting arm 8 supporting a planetary gear 7 meshed with the two gears 5, 6 is mounted on the input shaft 1 as shown in Figure 2, or on the output shaft 2 as shown in Figure 3. The planetary gear arrangement 4 is provided with a clutch element 9 comprising a second speed clutch C2 for causing the supporting arm 8 to rotate fast with the sun gear 5, in conjunction with the input shaft 1, and a brake element 10 comprising an oil pressure operated or electromagnetic brake for restraining rotation of the supporting arm 8. In more detail, in the example shown in Figure 2, the input shaft 1 has fixed thereon the sun gear 5, whereas the ring gear 6 and the supporting arm 8 are rotatably supported on the shaft 1. The ring gear 6 is connected to the output shaft 2 through a gear train 11 connected to a supporting shaft 6a of the gear 6 and extending between the input and output shafts 1, 2. The supporting arm 8 is connected to the input shaft 1 through the clutch element 9. In the example shown in Figure 3, the output shaft 2 has fixed thereon the ring gear 6, whereas the sun gear 5 and the supporting arm 8 are rotatably supported on the shaft 2. The sun gear 5 is connected to the input shaft 1 through a gear train 11 connected to a supporting shaft 5a of the gear 5 and extending between the input and output shafts 1, 2. The supporting arm 8 is connected to the supporting shaft 5a through the clutch element 9. Numeral 12 denotes a one-way clutch interposed in the first speed forward gear train G1. Operation is as follows: If a shift lever (not shown) is changed-over to a reverse driving position, the brake element 10 is operated to restrain the supporting arm 8 from rotating and hence the planetary gear 7 is prevented from rotating round the shaft 1 or the shaft 2. By rotation of the sun gear 5 together with rotation of the input shaft 1, the ring gear 6 is given a reduced rotation in the direction reverse to the rotary direction of the sun gear 5 through the planetary gear 7. Thus, the planetary gear arrangement 4 has been selected to operate as the reverse gear train GR, and the vehicle will run in reverse, If the shift lever is changed-over from the reverse driving position to a neutral position, the restraining operation of the brake element 10 is released, and if the shift lever is then changed-over from the neutral position to a forward driving position for running with automatic speed changes, at first the first speed clutch C1 is engaged and thereby the first speed forward gear train G1 is established. Thereafter, as running speed increases, the clutch element 9 serving as the second speed clutch is engaged and thereby the planetary gear 7 is rotated round the shaft 1 or 2 fast with the sun gear 5 and therefore at the same rotational speed as the gear 5. As the ring gear 6 is meshed with the planetary gear 7 it also is rotated at the same speed as the sun gear 5. Consequently, there is brought about the condition that the sun gear 5 and the ring gear 6 are directly coupled together, and the planetary gear arrangement 4 has thus been selected to operate as the high speed second forward gear train G2, and thus the vehicle runs at the second speed state. In this running condition transmission loss between the sun gear 5 and the ring gear 6 decreased as much as possible because these two gears 5, 6 are in the direct coupling condition mentioned above, and thus the input shaft 1 and the output shaft 2 are in the condition that the two are directly connected through the gear train 11, and thus there is effected a high efficiency power transmission similar to that effected when running under the first speed forward gear train G1. Whilst explanation has been given with reference to the illustrated two forward stages/one reverse stage transmission mechanism, the mechanism could be a higher than two-stage multi-forward-stage transmission mechanism. In this connection, Figures 4 and 5 each show transmissions having four forward stages and one reverse stage. In these transmissions, a fourth speed forward gear train G4 and the reverse gear train GR are composed of a planetary gear arrangement 4 corresponding to that described with reference to Figure 2, but it could be that a third speed forward gear train G3 and the reverse gear train GR are composed of the planetary gear arrangement 4. Referring to Figures 4 and 5, numerals C3 and C4 denote a third speed clutch and a fourth speed clutch which are, respectively, operated by respective shift operations to third speed and fourth speed running, and in the illustrated forms the clutch element 9 of the planetary gear arrangement 4 is the fourth speed clutch C4 itself. Transmission torque is comparatively large when driving in reverse and when running at the first forward speed, so that the input and output shafts 1, 2 are liable to be deformed. For preventing this, it is preferable that the first speed forward gear train G1 and the planetary gear arrangement 4 are disposed one on one side and the other on the other side, that is, to the front and to the rear, of a shaft supporting wall 14 of a transmission casing 13. Namely, the arrangement 4 is in front of this wall and the gear train G1 is to the rear thereof as shown in Figure 4, or vice versa as shown in Figure 5. If, as mentioned above, the forward gear train which is constructed in common with the reverse. gear train GR is a high speed stage (for example, third or fourth speed stage), that is a speed stage that is used comparatively more frequently, there is minimised the possibility that the direct coupling between the sun gear 5 and the ring gear 6 lowers transmission efficiency. Thus there is achieved an impovement in minimising fuel consumption. As, in all the forms described, one of the plurality of forward gear trains and the reverse gear train, provided in a parallel input/output shaft transmission, are composed of the planetary gear arrangement, the length of the mechanism in the axial direction can be minimised, and changeover operation between forward running and reverse running is carried out without the use of a selection gear so that generation of impact noise is avoided. Additionally, the planetary gear arrangement can be disposed on either the input shaft or the output shaft giving freedom of design. When the planetary gear arrangement is selectively operated to function as the forward gear train, the sun gear and the ring gear are brought into a direct coupling condition and thus any lowering in the transmission efficiency is prevented. This feature, in conjunction with the fact that the other forward gear train(s) is/are of a non-planetary interengaging gear construction, results in a transmission efficiency that is extremely excellent in comparison with that in a coaxial input/output shaft transmission.

Claims: CLAIMS 1. A transmission mechanism wherein a reverse gear train (GR) and a plurality of forward gear trains (G1, G2) are provided between an input shaft (1) and 'an output shaft (2) which are disposed in parallel with one another, characterised in that the reverse gear train (GR) and one of the forward gear trains (G1 or G2) is composed of a single planetary gear arrangement (4) comprising a sun gear (5) that moves with the input shaft (1), a ring gear (6) that moves with the output shaft (2) and a supporting arm (8) supporting a planetary gear (7) meshed with the sun and ring gears (5 and 6), the supporting arm (8) being mounted on one of the shafts (1 or 2) and that one of the two gears (5 or 6) that moves with the shaft (1 or 2) on which the supporting arm (8) is mounted being fixed to this shaft whereas the other of the gears (6 or 5) is connected to the shaft (2 or 1) with which it moves through a gear train (11), the planetary gear arrangement (4) being provided with a clutch element (9) for causing the supporting arm (8) to rotate fast with the sun gear (5) in conjunction with the input shaft (1), and a brake element (10) for restraining rotation of the supporting arm (8), so that the planetary gear arrangement (4) may be changed over selectively to serve either as said one forward gear train (G1 or G2) by engagement of the clutch element (9) or as the reverse gear train (GR) by operation of the brake element (10). 2. A transmission mechanism as claimed in claim 1, wherein the forward gear trains comprise a first speed train (G1) and a second speed train (G2), and wherein it is the second speed train (G2) that is said one forward gear train. 3. A transmission mechanism as c ] aimed in claim 1, wherein the forward gear trains comprise a first speed train (G1), a second speed train (G2), a third speed train (G3) and a fourth speed train (G4), and wherein it is the third speed train (G3) that is said one forward gear train. 4. A transmission mechanism as claimed in claim 1, wherein the forward gear trains comprise a first speed train (G1), a second speed train (G2), a third speed train (G3) and a fourth speed train (G4), and wherein it is the fourth speed train (G4) that is said one forward gear train. 5. A transmission mechanism as claimed in any one of claims 1 to 4, wherein the sun gear (5), the ring gear (6) and the supporting arm (8) are provided on the input shaft (1), the ring gear (6) is connected at its supporting shaft (6a) to the output shaft (2) through the gear train (11), and the supporting arm (8) is connected to the input shaft (11) through the clutch element (9). 6. A transmission mechanism as claimed in any one of claims 1 to 4, wherein the sun gear (5), the ring gear (6) and the supporting arm (8) are provided on the output shaft (2), the sun gear (5) is connected at its supporting shaft (5a) to the input shaft (1) through the gear train (11), and the supporting arm (8) is connected through the clutch element (9) to the output shaft (2). 7. A transmission mechanism as claimed in any one of the preceding claims, wherein the planetary gear arrangement (4) is disposed to one side, and the (or each) forward gear train (G1 or G2) other than said one forward gear train is disposed on the other side of a shaft supporting wall (14) of a casing (13) of the transmission mechanism.

Inventors: NISHIMURA, SADANORI
Applicants: HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1982
Main classification: F16H37
IPC codes: F16H3, F16H37