NZ195159A - Two speed transmission for tractor:hydraulic clutches select direct drive or drive via reduction gears - Google Patents

Description

195,159 Priority Datstc): Ccnv:;'j;o C/;ideation Filed i:,j:j[icct>cn C-:c: HS.JD Jcr-na!,No.

NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION "TRAVELLING DRIVE TRANSMISSION FOR A VEHICLE" HI We, KUBOTA LTD, a company organized and existing under the laws of Japan, of 22-banchi, 2-chome, Funade-cho, Naniva-ku, Osaka-shi, Osaka-fu, Japan hereby declare the invention for which H / we pray that a patent may be granted to ?fft?yus, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 195150 tf**- 'liv' ~ TRAVELLING DRIVE TRANSMISSION FOR A VEHICLE The present invention relates to a transmission for a vehicle such-as a tractor, and more particularly to a transmission adapted to transmit power from an 5 engine output shaft to a transmission shaft through two alternative lines.

Known transmissions for vehicles such as tractors used in agriculture, civil engineering and construction, have means to switch between a high speed 10 range and a low speed range on an input side of a first speed changing mechanism or main speed changing mechanism, and in some cases planetary gearing systems are employed to effect such switching. The prior art constructions as such are complicated and unsuitable 15 for incorporating into a tractor transmission having tightly packed gear trains.

Having regard to the above state of the art, the primary object of the present invention is to provide a transmission of simple construction allowing 20 speed changing between a high speed range and a low speed range to be carried out by a one touch operation. The transmission according to a specific embodiment of this invention is also adapted to perform an engine braking function and to enable the engine to be startejit . h by traction. jg b- A transmission for a vehicle according to thiJs®- I N invention comprises an engine output shaft; a transmission shaft for operative connection to a travel speed changing mechanism; TBS*"- 2- 195159 a first transmission line for direct coupling of said output shaft and said transmission shaft; a second transmission line including a reduction mechanism for operative connection of said output shaft to said transmission shaft to provide a slower speed of rotation of said transmission shaft than is provided by said first transmission line, said reduction mechanism including a first gear freely rotatably mounted on said engine output shaft, a . second gear fixed to said transmission shaft, and a reduction shaft carrying third and fourth gears in constant mesh with said first and second gears respectively; and clutch means for selecting between said first and second transmission lines, said clutch means comprising first and second hydraulically operated clutches mounted on said first and second transmission lines respectively and sharing a common driving disc, said clutches being disposed forwardly and rearwardly relative to each other across said disc., and being disposed between said first and second gears.

By operating the clutch means a high speed range or a low speed range iis selected forwardly of the travel speed changing mechanism to enable the tractor to travel at speeds suited to specific operations.

This selecting operation is carried out more simply than changing of the meshing relations of gears according to the prior art. In addition, this simple clutch operation is effective to prevent the engine from stopping at the time of an increased load falling on the transmission shaft. The speed range switching mechanism according to this invention has a simpler construction than prior art mechanisms utilizing planetary gearing. The transmission is capable of smooth acceleration and deceleration by the above noted speed range switching operation without involving a 1A5159 3- temporary drop in the travelling speed which is a disadvantage of the existing gear mesh changing systems.

The common driving disc is preferably fixed 5 to the engine output shaft. To enable the engine to be started by traction when an engine starting system is out of order and to enable the transmission to perform an engine braking function, a specific embodiment of the present invention provides that the 10 second clutch be resiliently biased toward its engaging position.

Other objects and advantages of the invention will be apparent from the following description with reference to the accompanying drawings in which: 15 Fig.'L.is a view in vertical section of a transmission according to an embodiment of the invention; Fig. 2 is a view taken on line A-A of Fig. i , and Fig. 3 is a view taken on line B-B of Fig. 2 .

Referring to Figs. 1 and 2, a tractor body 101 comprises a clutch housing 102 and a transmission case 103. Number 104 denotes a flywheel mounted on a crank . "-^patent office 31 AUG 1984 • •.veTD" •195159 4' shaft of an engine. A travelling system clutch 105 is providing on the flywheel 104 and includes a release lever 106. The clutch 105 is operatively connected to a clutch pedal not shown through a release hub 107, a release fork 108 and a fork rod 109. Number 110 denotes an attaching member whose main body portion 112 is peripherally removably fixed by bolts 113 to a support wall 111 formed on the clutch housing 102. The attaching member's main body portion 112 carries a forwardly projecting travelling drive shaft casing 114 at an upper portion thereof and a rearwardly projecting bearing retainer 115 at a lower portion thereof. The release hub 107 is fitted on the drive shaft casing 114 to be slidable backward and forward. The bearing retainer 115 is held rigid by a right and left pair of supports 116. Number 117 denotes a power takeoff drive shaft directly connected to the flywheel 104 .and operatively connected to a.power takeoff speed changing mechanism through a power takeoff clutch not shown.

Number 118 denotes a hollow engine output shaft loosely fitted on the power takeoff drive shaft 117 and rotatably mounted in the drive shaft casing 114 by means of bearings 119 and 120. The output shaft 118 is in operative connection with the travelling system clutch 105. Number 121 denotes a hollow transmission shaft loosely fitted on the power takeoff drive shaft 117 rearwardly of the output shaft 118 and supported by a partition wall 123 through a bearing 122. A travel speed changing mechanism is mounted in the transmission case 195159 <. L o CO (?}S 1-3 P t ir" 7\ r. 103. Number 125 denotes a reduction shaft mounted below and parallel to the output shaft 118 and rotatably supported at both ends by bearings 1^6 and 127 fitted in the main body portion 112 of the attaching 5 member 110 and the bearing retainer 115 respectively. The reduction shaft 125 carries adjacent to the forward end thereof a gear 128 rotatable in unison therewith and at the rearward end thereof a gear 129 integral therewith. The gear 128 is in constant mesh with a gear 130 freely 10 rotatably mounted on the output shaft 118, and the gear 129 is in constant mesh with a gear 131 mounted on the forward end of the transmission shaft 121. The reduction shaft 125 and the gears 130, 128, 129 and 131 constitute a reduction mechanism 133 whose reduction rate is in the 15 order of 30 per cent. Number 134 denotes a high speed range hydraulic clutch adapted to directly couple the output shaft 118 to the transmission shaft 121 via a first transmission line. Number 135 denotes a low speed range clutch adapted to connect the output shaft 118 and 20 the- transmission shaft 121 by way of the reduction mechanism 133 in a second transmission line. The two clutches 134 and 135 are arranged one behind the other axially of the output shaft 118 and the transmission shaft 121 and are assembled into a common driving disc 2I5 136. More particularly, the hydraulic clutches 134 and 135 comprise the driving disc 136 keyed to the rear end of the output shaft 118, annular ^cylinder chambers 137 and ' 138 provided forwardly and rearwardly of the driving disc 136, -1 195158 6- pistons 139 and 140 slidably mounted in the cylinder chambers 137 and 138, support plates 141 and 142 fitted in forward and rearward ends of the driving disc 136, driven members 143 and 144, and a plurality of clutch discs 145 and 146 disposed between the pistons 139 and 140 and the support plates 141 and 142 and connected to the driving disc 136 and to the driven members 143 and 144, respectively. The pistons 139 and 140 are held rigid together in the axial direction at plural peripheral positions by spacer collars 147 and bolts 148, Each of the spacer collars 147 is axially slidably fitted in a receiving bore defined on the driving disc 136 between the cylinder chambers 137 and 138. Of the two cylinder chambers 137 and 138, the chamber 138 associated with the low speed range clutch 135 includes resilient means 149 to bias the piston 140 in a direction to compress the clutch plates 146, namely in a direction to engage the clutch 135. The resilient means 149 comprises an annular disc spring. The driven member 143 is splined to the forward end of the transmission shaft 121 while the driven member 144 is integril with the gea-.* 130 and is freely rotatably fitted on the output shaft 118. Each of the cylinder chambers 137 and 138 is in communication with a control valve (not shown) via' oil passages 150 and 151 defined in the output shaft 118 and the attaching member 110 respectively, whereby pressure oil is supplied in a controlled manner from a hydraulic pump (not shown) directly connected to the engine.

The described construction operates as follows. yhe hydraulic pump operates while the engine is running. \ 195159 7' When the control valve is set for a high speed range, the pressure oil from the hydraulic pump is fed to the cylinder chamber 137. This causes the piston 139 to compress the clutch discs 145 disposed between the piston 139 and the support plate 141 and to connect the driving disc 136 to the driven member 143 through the clutch discs 145, which places the high speed range hydraulic clutch 134 in operation. Therefore, with the travelling clutch 105 connected, engine power is transmitted through the travelling clutch 105, the output shaft 118, the high speed range hydraulic clutch 134, and the transmission shaft 121, to the travel speed changing mechanism, thereby enabling the tractor to travel at a desired speed.

While the tractor runs on the road or engages in normal ground working, the high speed range clutch 134 is connected to transmit power as described above. If an excessive load occurs for some reason or other reducing the rotational rate of the engine, then the control valve is set for the low speed range to switch from the high speed range hydraulic clutch 134 to the low speed range hydraulic clutch 135, whereupon the travelling speed is reduced by about 30 percent by the reduction mechanism 133 in order to avoid stopping of the engine. In other words, when the control valve is set for the low speed range, the pressure oil enters the cylinder chamber 138 and the piston 140 presses the clutch discs 146 against the support plate 142 to connect the driving disc 136 to the driven 195159 8' member 144 via the clutch discs 146 thereby establishing the operation of the low range hydraulic clutch 135.

Accordingly the output of the output shaft 118 is transmitted by way of the driving disc 136, the clutch disc 146, the driven member 144, the gear 130, the gear 128, the reduction shaft 125, the gear 129, and the gear 131 to the transmission shaft 121. Since the speed is reduced between the gears 130 and 128 and between the gears 129 and 131 by about 30 per cent, the tractor will slow down thereby preventing the engine from stopping.

The control valve is returned to the high speed range when the overload on the engine is eliminated and its rotational rate is recovered. The travelling speed of the tractor is very easily changed in both ways, namely for acceleration and for deceleration, by switching the control valve.

In case the engine stops running thereby to cut oil supply from the hydraulic pump, the resilient means 149 mounted in the cylinder chamber 138 of the low speed range hydraulic clutch, 135 presses against the piston 1^0 to compress the clutch discs 146 between the piston 140 and the support plate 142 thereby placing the low speed range hydraulic clutch in operation. Therefore, when the engine stops during uphill traveling or the like, the low speed range clutch 135 will immediately operate to effect a braking action by means of the engine thereby to avoid accident. Since the resilient means 1U9 is mounted in the PATZhlT OrrFZl' J ! $umm4 I 195159 low speed range hydraulic clutch 135, the resilient means 149 may have a small resilient force compared with the case of being mounted in the high speed range hydraulic clutch 134. Moreover, since the two 5 pistons 139 and 140 are rigidly interconnected in the axial direction by the spacer collars 147 and the bolts 148, the resilient means 149 also functions as return means for the high speed range hydraulic clutch 134.

As described above, the low speed range hydraulic clutch 135 is in operative condition whenever the engine stops. Therefore, it is possible to start the engine by towing the tractor.

This invention as embodied above provides the 15 high speed range hydraulic clutch adapted to directly connect the output shaft to the transmission shaft, and the low speed range hydraulic clutch adapted to connect tbe two shafts through the reduction mechanism, whereby switching.between the high speed range and the 20 low speed range is effected by operating the control valve to select the high speed range hydraulic clutch or the low speed range hydraulic clutch, and such a switching operation is a very easy, one touch operation. Thus, even when the engine is subjected 25 to a frequent occurrence of excessively heavy load, its inadvertent stopping can be avoided by slowing down the tractor or switching from the high speed range to the low speed range.

|" N.Z. PATENT OFFICE 7 3 1 AUG 1984

Claims (4)

■« -195159 10- MHAT WE CLAIM IS:

1. A transmission for a vehicle comprising an engine output shaft; a transmission shaft for operative connection to a travel speed changing mechanism; 5 a first transmission line for direct coupling of said output shaft and said transmission shaft; a second transmission line including a reduction mechanism for operative connection of said output shaft to said transmission shaft-to provide a 10 slower speed of rotation of said transmission shaft than is provided by said first transmission line, said reduction mechanism including a first gear freely rotatably mounted on said engine output shaft, a second gear fixed to said transmission shaft, and a 15 reduction shaft carrying third and fourth gears in constant mesh with said first and second gears respectively; and clutch means for selecting between said first and second transmission lines, said clutch.means 20 comprising first and second hydraulically operated clutches mounted on said first, and second transmission lines respectively and sharing a common driving disc, said clutches being disposed forwardly and rearwardly relative to each other across said disc, and being 25 disposed between said first and second gears.

2. A transmission according to Claim 1, wherein said common driving disc is fixed to said engine output shaft.

3. A transmission according to Claim 1 or 2, wherein said second clutch is resiliently biased toward its engaging position.

4. A transmission for a vehicle, substantially as hereinbefore described with reference to the accompanying drawings. By^hS/their authorised Agents, A. J. PARK & SON« PEft