CA1272398A - Transmission for working vehicle having overtop drive - Google Patents

Abstract

Abstract of the Disclosure A transmission system for a vehicle comprising a main transmission, a bypass transmission line, an auxiliary transmission, and a rear wheel drive line.
The main transmission includes a multistep change speed mechanism, a first output gear for outputting a maximum speed provided by the multistep change speed mechanism, and a second output gear for outputting other speeds provided by the multistep change speed mechanism. The bypass transmission line is operatively connected to the first output gear, and the auxiliary transmission is operatively connected to the second output gear. The rear wheel drive line is operatively connected to the bypass transmission line and to the auxiliary transmission. The first output gear, bypass transmission line and front wheel drive line constitute an overtop drive transmission line.

Description

~7~398 The present invention relates to a transmission system for a working v~hicle, particularly an agricultural tractor, in which drive of an engine is transm~tted to a wheel drive mecha-nism after being sub~ected to change speed at a main transmission and an auxiliary transmissionO

In known transmission systems as noted above, the drive output by the main transmission, regardless of its speed, is transmitted to the wheel drive mechanism through the auxiliary 10 transmissiono Where, for example, an operation in one site i5 com-pleted and the vehicle should be moved to a nexk site of opera-tion, it is desirable to drive the vehicle at a maxlmum ~orward speed (hereinafter referred to as overtop speed) by shifting the main transmission to a high speed position. With the known transmission system, however, the shifting of the main transmis-sion to the high speed position does not produce the overtop speed if the auxiliary transmission is in a low speed position.
In order to obtain the overtop speed it is necessary to shift the auxiliary transmission to a high speed position also. Thus, it has been a troublesome operation to change the drive to the over-; top speed.

`~ 25 The present invention provides a transmission system capable of producing the overtop speed only by shifting the main transmission even when the auxiliary transmission remains in the low speed position, and to simplify transmission lines opera tlvely connecting the main transmission to drive wheels.
According to the present invent~on there is provided atransmission system for a vehicle having a pair of rear wheels, a pair of front wheels and an engine having an output shaft, said transmission system comprising a housing, a main transmission mounted in said housing including a first transmission shaft selectively en~ageable with said output shaft of said engine, a A ~ ~ b . .

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second transmisslon shaft mounted in said housing, said second transmission shaft spaced apart from and parallel wlth said first transmission shaft, a plurality of gear pairs including a plural-ity of input gears fixedly mounted to said first transmission shaft in meshing enyagement with a pluralit:y of output gears freely rotatably mounted on said second transmission shaft, one of said plurality of output gears being a maximum speed gear, means for selectively interconnecting one of said plurality of output gears with said second shaft; an auxiliary transmission having a plurality of gear pairs, said aux:Lllary transmission interconnected with said second transmission shaft, means for selectively engaging one said plurality of gear pairs of said auxiliary transmission to produce an output, a bypass transmis-sion including a bypass shaft rotatably mounted to said housing, said bypass shaft mounted parallel to and spaced apart ~rom said first and second transmission shafts, and overtop gear freely rotatably mounted to said bypass shaft for meshing engagement with said maximum speed gear of said main transmission, a clutch for interconnecting said overtop gear with said bypass shaft to produce a rotational output; means for driv1ny said rear wheels in response to said rotational output from said bypass transmis~
sion and said auxiliary transmission; and means for activating one of sald rneans for interconnecting one of output gears of said main transmission and said clutch of said bypass transmission, said means for activating operable to actlvate only one of said plurality of output gears and said overtop gear at a time, said means for activating operable to activate said bypass transmis-sion and said pair of rear wheels without engaging said auxiliary transmission to produce an svertop speed.

According to the above construction, when the main transmission is shifted to a position other than the overtop speed position, the resulting drlve is transmitted to the rear wheel drive means through the aux~liary transmission. When the main transmission is shifted to the overtop speed position, the drive is transmitted directly to the rear wheel drive means A

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bypassing the auxiliary transmission. There~ore, the vehicle is driven at the overtop speed only by shifting the mai~ transmis-sion to the overtop speed position regardless of the posltion of the auxillary -transmission. Thus, the present invention provides an improved operational efficiency.

In one preferred embodlment of the inventlon, the bypass transmission means acts also as front wheel drive llne where the vehicle employing the transmission system of this invention is a four wheel drive vehicle. Thus, the system fur-ther comprises mPans for driving said palr of front wheels, said means for driv~ng said front wheels selectivsly interconnected to said bypass shaft, and means for transferring said output of said auxiliary transmission to said bypass shaft when one of said plu-rality of output gears is in engagement wikh said second shaft.

According to this embodiment, when the maln transmis-sion is shifted to a posltion other than the overtop speed posi-tion, the drive is transmitted to the rear wheel drive line and the front wheel drive line through the auxiliary transmission.
Whsn the main transmission is shifted to the overtop speQd posi-tion, the drive is transmitted directly to the front wheel drive line bypassing the auxiliary transmission. Therefore, the vehi-cle is driven at the overtop speed only by shifting the main transmission to the overtop speed position regardless of the position of the auxiliary transmission. Thus, the present inven-tion provides an improved operational efficiency, and a simpli-fied transmission line by operatlvely connecting the front wheel drive line prov1ded as an intrinsic part of the working vehicle to the overtop speed output element of the main transmission.

In another embodiment of the present invention said clutch o~ said bypass transmission is mounted on sald bypass shaft for selectively engaging said overdrive gear to drive said bypass shaft. Suitably said means for selectively interconnect-ing one o~ said plurallty of drlve gears ~urther comprises at ~, '~,.

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least one clutch moun-ted on said second transmission shaft.
Desirably said maximum speed gear further comprises a boss for engagement with said overtop gear of said main transmission.
Suitably the system further comprises a power takesff intercon-nected with said first transmission sha~t. Desirably one saldplurality of gear pairs is intsrconnected to a reverse gear mounted on an independent shaft for reversing the directlon of said second shaft. Suitably said auxiliary transmission com-prises a third propelling drive shaftO

In a fu~ther embodiment of the present invention said means for driving said rear wheels comprises a drive shaft selectively interconnected to said auxiliary transmission and a drive gear fixedly mounted to said drive shaft. Suitably said bypass transmission comprises a bypass gear fixedly mounted to said bypass shaft and in meshing engagement with said drive gear of said means for driving.

The invention will now be descrlbed in more detail, by way of example only, with reference to the accompanying drawings, in which:-.
Fig. 1 is a schematic view of a transmission , ~

- ~7i~3~3 system embodying the present invention, Fig. 2 is a sectional view o a main transmission, Fig. 3 is a sectional view of a mechanism for controlling the main transmission, Fig. 4 is a section taken on line IV-IV of Fig.
3, Fig. 5 is a plan view of a shift position indicator, Fig. 6 is a schematic view showing operation of a changeover gear, and Fig. 7 is a sectional view of a modified overtop gear mounting portion.

Description of the Preferred Embodiments The present invention will be described further with re~erence to the accompanying drawings showing a transmission system for an agricultural tractor which is one example o working vehicle.
Referring to Fig. 1, the transmission system comprises a PTO drive line for driving an attached working implement and including a drive transmission shaft 1 for receiving power of an engine, not shown, a , :
driven transmission shaft 2l and a wet type friction clutch 3 between the shafts 1 and 2. The drive is transmitted from the driven transmission shaft 2 --5~

'7~3918 through a reduction gearing 4 to a power takeoff shaft 5. The driven transmission shaft 2 is provided with a changeover gear 6 to produce live, neutral and ground states oE PTO drive.
The transmission system further comprises a propelling drive line which will be described hereinafter. The propelling drive line includes a first propelling transmission shaft 7 relatively rotatably mounted on the drive transmission shaft 1 at an upstream position thereof. The first propelling transmission shaft 7 comprises an upstream shaft portion 7a and a downstream shaft portion 7b. The two shaft portions 7a and 7b are interposed by a planetary ~ gear type high and low speed switching mechanism 8 ; 15 including a frictional multidisk hydraulic clutch (which is known as dual change speed mechanism and is operable to reduce the high speed by about 25%). A
second propelling transmission shaft 9 is disposed ~' parallel to the downstream shaft portion 7b, and a main transmission 10 including a synchromesh change spee~ gearing 100 is provided between the downstream shaft portion 7b and the second propelling trans-mission shaft 9 to provide three forward speeds and one backward speed.
The second propelling transmission shaft 9 acts as means to output speeds of the main transmission 10 1~ 9~

other than a max.imum forward speed or overtop speed, and is operatively connected to an auxiliary trans-mission 12. A third propelling transmission shaft 11 is disposed in relatively rotatable abutment with the S second propelling transmission shaft 9.
The change speed gearing 100 will particularly be , described next with reference to Fig~ 2. As shown, `~ the downstream shaft portion 7b of the first propelling transmission shaft 11 carries a first input :l 10 gear 101a, a second input gear 102a, a third input gear 103a and a fourth input gear 104a, all fixed to . the shaft portion 7b. The second propelling transmission shaft 9 carries a first output gear 101b, a second outpuk gear 102b, a third input gear 103b and a fourth output gear 104b, all rotatable relative to the shaft 9. The~first input gear 101a is meshed with the first output gear 101a to constitute a ~irst gear pair 101. The second inpu-t gear 102a is meshed with .~
the second output gear 102b to constitute a second 20 gear pair 102. The third input gear 103a is meshed with the third output gear 103b to constitute a third gear pair 103. The fourth input gear 109a is in engagement with the fourth output gear 104b through a reversing gear 104c to constitute a reversing gear group 104.
A synchromesh type engaging device 106 is mounted _7_ .

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, between the first output gear 101b and the second output gear 102b for selectively placing the first output gear l01b and second output gear 102b in operatlve connection with the second transmission ~`. 5 shaft 9. Similarly, a synchromesh type engaging . device 107 is mounted between the third output gear 103b and the fourth output gear 104b for selectively placing the third output gear 103b and fourth output gear 104b in operative connection with the second 10 transmission shaft 9.
The first output gear 101b includes a boss portion carrying an intermediate gear 105 fixed thereto which is meshed with an overtop gear 34 to be described later. It is to be noted here that the 15 first gear pair 101 produces a higher speed-than the other gear pairs.
The auxiliary transmission 12 comprises a :
- reduction gearing 19 including a relay gear 16 meshed . with an output gear 13 -fixed to the second propelling transmission shaft 11 and a relay gear 17 meshed with an input gear 15 relatively rotatably mounted on the third propelling transmission shaft 11 by means of a - clutch sleeve 14. The relay gears 16, 17 are xelatively rotatably mounted on a front wheel drive transmission shaft 18 disposed parallel to the second and third propelling transmission shafts 16, 17. The ' , _~_ ' ' ~ ' .

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': ' ' ' ' ' 3!..~7X39~3 clutch sleeve 14 is switchable between a high speed position to directly connect the second transmission shaft 9 to the third transmission shaft 11 and a low speed position to transmit output of the second transmission shaft 9 to the tird transmission shaft 11 by way of the reduction gearing 19.
A propelling drive output shaft 22 is disposed rearwardly of the third propelling transmission shaft 11, which carries a bevel gear 21 at a rear end thereof for transmitting the drive to a rear differen-tial 20. The third propelling transmission shat 11 and the propelling drive output shaEt 22 are inter-posed by a super-reduction mechanism 23 for providing two, high and low, speeds. The super-reductlon mechanism 23 includes an outp,ut gear 24 mounted on the third transmission shaft 11, a clutch sleeve 26 acting as input gear 25 mounted on the output shaft 22, and relay gears 27, 28 meshed with the two gears 24 and 25, respectively and mounted on a shaft 30 supported by a transmission case 29.
:Thus, the drive output by the main transmission 10 in the speeds other than the overtop speed is transmitted through the auxiliary transmission 12 and the super reduction mechanism 23 to the rear wheel .25 drive line and then to the front wheel drive line.
:~The drive output by the main transmission 10 in the _g_ . .
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, 3~3 overtop speed is transmitted to the front wheel drive line, bypassing the auxiliary transmission 1~, and then to the rear wheel drive line. To describe ~ details of the front wheel drive line, output of the ; 5 propelling drive output shaft 22 constituting part of the rear wheel drive line is transmitted to the front wheel drive transmission shaft 18 through a gearing 31. The drive is then transmitted from the trans-mission shaft 18 through a reduction mechanism 33 to a front wheel output shaft 32 connected to a front differential not shown, whereby the front wheels are driven in synchronism with the rear wheels.
More particularly, as shown in Fig. 2, the front wheel drive transmission shaft 18 carries, relatively rotatably mounted thereon, the overtop gear 34 acting as an overtop speed ou-tput element of the main transmission 10. The overtop gear 34 is operativeIy connectable to the transmission shaft 18 by shifting a shift gear 44' of a synchromesh type engaging device 44 constructed by utilizing a boss portion of the overtop gear 34. Thus, by shifting a main change speed lever 35 to an overtop position, the drive is ~ : .
transmitted from the first propelling transmission ;~ shaft 7 to the front wheel drive transmission shaft 18 -~ 25 and then to the front wheel drive output shaft 32 and the propelllng drive output shaft 22, bypassing the : - 1 0 -~' ''' .

9~3 auxiliary transmission 12. The main transmission 10 is controllable by shifting the main change speed lever 35 back and forth and right and leftO
An interlocking structure between the change speed lever 35 and the main transmission 10 will be described with reference to Figs. 3 through 5O The change speed lever 35 is connected at a lower end thereof to one end of a rod 36 supported by the transmission case 29 to be movable back and forth.
`10 The rod 36 carries an engaging pin 37 at the other end thereof, which is engageable with engagement members 42, 43 and 46. The engagement members 42 and 43 are secured to bosses of shlft forks 40 and 41 for operating shift gears 38 and 39 of the engaging 15 devices 106 and 107, respectively, to produce the three forward speeds and one backward speed. The engagement member 46, which has a U-shaped configura-tion, connected through a link mechanism A to a shift fork 47 for operatlng the shift gear 44' of engaging ~20 device 44 to produce the overtop speed. The three i~ ~forward speeds, the overtop speed and the backward speed are selectively produced by shifting the change speed lever 35 backward or forward to select one of the shift forks 40, 41 and 45 first and then by shifting the lever 35 rightward or leftward.
The link mechanism A comprises a pin 47 extending -- .

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~7~3~3l3 into the engagement member 46 and supported by the transmission case 29, and a rod 50 connecting an outer end of the pin 47 to a control rod 49 of a control arm 48 connected to the shift fork 45.
Number 51 in Fig. 3 denotes a ball spring for retaining the change speed lever 35 in an overtop speed position. Reference B in Fig. 1 denotes a clutch for switching the drive mode between a two wheel (rear wheel~ drive mode and a four wheel drive 1 0 mode .
The changeover gear 6 mounted on the driven transmission shaft 2 will be described further with reference to Fig. 6. The changeover gear 6 is operable by a control lever 60 having a limit switch 62 at a position therebelow,. The limit switch 62 controls an electromagnetlc valve 61 ~or engaging and disengaging the friction clutch 3 only when the changeover gear 6 is switched from a Iive PTO position to a neutral PTO position and vice versa. More particularly, the cont~rol lever 60 defines a projec-tion 60a at a lower end thereof which contacts and turns on the llmit switch 62 with an initial shift of the control lever 60 for switching the changeover gear 6 from the neutral PTO position to the live PTO
~; 25 position. This switches the electromagnetic valve 61 to disengage the friction clutch 3. As the control ~;~7~3~3 lever 60 is shifted Eurther to place the changeover gear 6 in the live PTO position, the limi-t swi-tch 62 is turned off whereupon the valve 61 is switched to a drain position by the biasing force of a spring 63 thereby engaging the friction clutch 3. This construction assures gear engagement free of damage to meshing portions of the gears. When switching the changeover gear 6 from the live PTO position to the neutral PTO position, similarly the friction clutch 3 is disengaged first and then the gears are brought out of mesh. This reduces a force of the control lever 60 for operating the changeover gear 6.
~ In the foregoing embodiment, the overtop gear 34 ;~ is combined with the synchromesh type engaging device 44 mounted on the front wheel drive transmission shaft 18, and the combination is contained wholly in the ; transmission case 29. Alternatively, as shown in Fig.
7, the overtop gear and engaging device may be ~ disposed outside a transmission case defining an ; Z0 opening. In this modified example, the front wheel drive transmission shaft 18 carries, relatively rotatably mounted thereon, an overtop input gear 52 -~, meshed with the intermediate gear 1~5. ~he overtop input gear 52 1s also meshed with an overtop gear 34' relatively rotatably mounted on an overtop shat 55 supp-rted by an overtop gear case 57 attached to the . ~ . . .

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transmission case 29. The overtop shaft 55 further carries an engaging device 56 to establish and break opera-tive connection between the overtop gear 34' and the overtop shaft 55.
Furthermore, the overtop shaft 55 carries a first overtop output gear 54 fixed thereto, and the front wheel drive transmission shaft 18 carries a second overtop output gear 53 fixed thereto. By a shift of the engaging device 56, the drive from the first gear pair 101 is transmitted to ~he front wheel drive transmission shaft 18 through the overtop gear 34'.
In this example, the overtop gear 34' is relatively rotatably mounted on a boss portion of the overtop output gear S4 to render the overtop gear case :` ~
compact.
According to this modification, the entire over-top mechanism is outwardly fitted to the transmission case in the manner known as the cassette type attach-ment. Therefore, the overtop mechanism is achieved without effecting an extensive modification to existing transmission structures. Where the tractor does not require the overtop mechanism, the overtop gear case 57 may~be replaced by a planar cover.

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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A transmission system for a vehicle having a pair of rear wheels, a pair of front wheels and an engine having an output shaft, said transmission system comprising a housing; a main transmission mounted in said housing including a first transmission shaft selectively engageable with said output shaft of said engine, a second transmission shaft mounted in said housing, said second transmission shaft spaced apart from and parallel with said first transmission shaft, a plurality of gear pairs including a plurality of input gears fixedly mounted to said first transmission shaft in meshing engagement with a plurality of output gears freely rotatably mounted on said second transmission shaft, one of said plurality of output gears being a maximum speed gear, means for selectively interconnecting one of said plurality of output gears with said second shaft; an auxiliary transmission having a plurality of gear pairs, said auxiliary transmission interconnected with said second transmission shaft, means for selectively engaging one said plurality of gear pairs of said auxiliary transmission to produce an output; a bypass transmission including a bypass shaft rotatably mounted to said housing, said bypass shaft mounted parallel to and spaced apart from said first and second transmission shafts/ and overtop gear freely rotatably mounted to said bypass shaft for meshing engagement with said maximum speed gear of said main transmission, a clutch for interconnecting said overtop gear with said bypass shaft to produce a rotational output; means for driving said rear wheels in response to said rotational output from said bypass transmission and said auxiliary transmission, and means for activating one of said means for interconnecting one of output gears of said main transmission and said clutch of said bypass transmission, said means for activating operable to activate only one of said plurality of output gears and said overtop gear at a time, said means for activating operable to activate said bypass transmission and said pair of rear wheels without engaging said auxiliary transmission to produce an overtop speed.

2. The transmission system as claimed in claim 1, wherein said clutch of said bypass transmission is mounted on said bypass shaft for selectively engaging said overdrive gear to drive said bypass shaft.

3. The transmission system of claim 1 wherein said means for selectively interconnecting one of said plurality of drive gears further comprises at least one clutch mounted on said second transmission shaft.

4. The transmission system as claimed in claim 1 wherein said maximum speed gear further comprises a boss for engagement with said overtop gear of said main transmission.

5. The transmission system as claimed in claim 1 further comprising a power takeoff interconnected with said first transmission shaft.

6. The transmission system as claimed in claim 1 further comprising: means for driving said pair of front wheels, said means for driving said front wheels selectively interconnected to said bypass shaft, and means for transferring said output of said auxiliary transmission to said bypass shaft when one of said plurality of output gears is in engagement with said second shaft.

7. The transmission system of claim 1 wherein said means for driving said rear wheels comprises a drive shaft selectively interconnected to said auxiliary transmission and a drive gear fixedly mounted to said drive shaft.

8. The transmission system of claim 7 wherein said bypass transmission comprises a bypass gear fixedly mounted to said bypass shaft and in meshing engagement with said drive gear of said means for driving.

9. The transmission system of claim 1 where one said plurality of gear pairs is interconnected to a reverse gear mounted on an independent shaft for reversing the direction of said second shaft.

10. The transmission system of claim 1 wherein said auxiliary transmission comprises a third propelling drive shaft.