Transmission mechanism for a working vehicle

Abstract: A transmission mechanism having a PTO transmission system and a traveling transmission system and used for a working vehicle, which is so constructed that a input shaft (8) is coaxially freely perforated through a hollow traveling clutch shaft (13), both ends of input shaft (8) projects from the traveling clutch shaft (13), and a selecting device (A) including a forward and rearward movement switching clutch (B), as an embodiment of an auxiliary speed change device, is disposed at the one projecting portion. At the front bearing plate (4) forms an oil relaying unit (4a) connected through a hydraulic control valve unit (35) attached to the outer wall of the front transmission casing (1) without need of piping. A PTO clutch (9) is coaxially disposed with the input shaft (8) sequentially to the projection thereof, between the input shaft (8) and the PTO clutch shaft (9) is disposed a PTO assembly of combination of a hydraulic PTO clutch (D) and hydraulic PTO brake (E). The idling of brake drum (53) is allowed in a predetermined angle with respect to the bearing wall (2a).

Description: Field of the Invention This invention relates to a transmission mechanism which comprises a traveling transmission system and a PTO transmission system and used for a working vehicle, such as a tractor, and more particularly to a transmission mechanism which is provided in the traveling transmission system with an auxiliary transmission having at least two transmission stages, such as a forward and rearward movement switching and a high-low speed switching. Description of Related Art Conventionally, the transmission mechanism for the working vehicle, such as the tractor, has been well-known which has a traveling transmission system having both a mechanism multi-stage transmission device and a PTO system transmission mechanism. In other words, a common input shaft transmitting the power from an engine output shaft is used to drive both of the traveling transmission system and the PTO transmission system by using gears and so on. Conventionally, however, the traveling system transmission shaft and PTO system transmission shaft are disposed in parallel to each other so that the separate spaces for transmission shafts of traveling and PTO systems are required to be axially disposed. In a case that the traveling system transmission device is the multistage transmission device, the disposing space thereof needs to be a considerably larger in part, whereby the transmission mechanism provided with both the traveling and PTO systems, the transmission shafts requires a further larger disposing space to that extent, and a housing for containing therein the mechanism must be of a large size. Also, such transmission mechanism for the working vehicle like the tractor which is provided with both the traveling system and PTO system having the multistage speed change device, is well-known to be provided between the engine and the multistage speed change device with an auxiliary speed change device provided with at least two speed-change stages. For example, a transmission mechanism disclosed in the Japanese Patent Publication No. Hei 5-26686 or the Japanese Patent Laid-Open No. Hei 7-117507 is provided between the engine and the main multistage speed change device for changing the speed of driving wheels with the speed change device for forward and rearward movement switching and for high-low speed changing. The traveling transmission mechanism of the prior art is complicated in construction of assembling the main multistage speed change device, forward and rearward movement switching device and auxiliary high-low speed change device, in the same chamber, on the same shaft or on each shaft to be engageable with each other. For example, even when only the multistage speed changing device is intended to be applied with the maintenance work, both the multistage speed change device and auxiliary speed change device must be detached so that it is difficult that the auxiliary speed change device is detachably mounted. In a case that such auxiliary speed change device comprises a hydraulic clutch, a supply structure for operating oil is complicated so that it is difficult to construct the hydraulic clutch to be easily detachably mountable. For example, the hydraulic clutch is disclosed in the Japanese Patent Laid-Open No. Hei 6-297971 (in which the clutch is for PTO power change over). A valve for supplying the operating oil is built in a housing and a hydraulic oil pipe is interposed between the valve and the hydraulic clutch, whereby the piping must be removed when the hydraulic clutch is detached or mounted. US-A-5 651 289 discloses a transmission mechanism for a working vehicle with the features of the preamble portion of claim 1. US-A-5 058 459 discloses a further transmission assembly for tractors which includes an input shaft and a hollow travelling system transmission shaft coaxially penetrated by the input shaft. The transmission assembly is disposed in a clutch housing which also incorporates the fly-wheel of the engine. The auxiliary speed change device is not inserted into the clutch housing from the opening at which the transmission housing is to be mounted to the engine housing but rather from the rear side at which a further transmission casing is mounted. The whole auxiliary speed change mechanism in this transmission assembly is disposed within the rear portion of the clutch housing. The transmission assembly furthermore contains a mechanical clutch between the input shaft and the hollow travelling system transmission shaft. Summary of the Invention An object of the invention is to provide a transmission mechanism which, in a case that the auxiliary speed change device in the traveling transmission system uses a hydraulic clutch in order to expect reliability or smooth operation of engagement or disengagement of the clutch, the piping for operating oil applied thereto is facilitated or deleted, thereby materializing the traveling transmission system to be compact, inexpensive to produce and easy to execute maintenance. The invention provides a transmission mechanism as defined in claim 1. Brief Description of the Drawings Fig. 1 is a skeleton diagram of an entire transmission adopting a PTO transmission device for a working vehicle according to the present invention, Fig. 2 is a partially sectional side view of a front transmission casing 1 showing the disposal of forward and rearward movement selecting device A, including a sectional interior view of a forward and rearward movement switching clutch B, Fig. 3 is an enlarged principal portion in Fig. 2, Fig. 4 is a developed sectional side view showing a gear train of the selecting device A, Fig. 5 is a developed partially sectional plan view showing structure of an oil passage with respect to the forward and rearward movement switching clutch B of the selecting device A, Fig. 6 is a view looking in the direction of the arrows X-X in Fig. 2, Fig. 7 is a circuit diagram of oil passages for operating oil and lubricating oil with respect to the forward and rearward movement switching clutch B, and Fig. 8 is a sectional plan view of a PTO clutch and a PTO brake of the invention, which are mounted on a rear transmission casing 2. Description of the Preferred Embodiment of the Invention Fig. 1 is a structure of a whole transmission mechanism for a working vehicle, such as a tractor. Firstly, a housing is described in structure. The housing comprises a front transmission casing 1 and a rear transmission casing 2 which are longitudinally jointed. The rear transmission casing 2 is closed at the rear opening by a rear bearing cover 6. The front transmission casing 1 is open at the front end and rear end thereof, the front opening being integrally jointed with a flywheel housing 3 in a manner of longitudinally perforating. The rear transmission casing 2 also is open at the front end and rear end thereof, the front end opening communicating with the rear end opening of the front transmission casing 1. Within the front transmission casing 1, a boss 1a for fixing a front bearing plate projects inwardly of the casing and slightly rearwardly of the front opening, a front bearing plate 4 is fixed to the front of boss 1a so as to close the front opening of the front transmission casing 1 in an oil tight manner, and lubricating oil is filled only in a chamber behind the bearing plate 4. Furthermore, within the front transmission casing 1, a bearing wall 1b is formed which projects inwardly of the casing 1 and slightly rearwardly of the front bearing plate 4, and a partition 1c formed slightly rearwardly of the bearing wall 1b longitudinally divides the interior of front transmission casing 1 into a first chamber R1 and a second chamber R2, the first chamber R1 being formed between the front bearing plate 4 and the partition 1c. Also, an intermediate bearing plate 5 is connected to a boss provided rearwardly of the partition 1c and slightly frontward of the rear end opening so as to form the second chamber R2 between the partition 1c and the intermediate bearing plate 5 in the front transmission casing 1. Furthermore, within the rear transmission casing 2, a bearing wall 2a is formed slightly rearwardly of the front opening of casing 2, and in the front transmission casing 1 and rear transmission casing 2, a third chamber R3 is formed between the intermediate bearing plate 5 and the bearing wall 2a, and a fourth chamber R4 is formed from the bearing wall 2a to the rear end (a closed portion by a rear bearing cover 6) within the rear transmission casing 2. The transmission mechanism shown in Fig. 1 comprises a traveling transmission system and the PTO transmission system of the present invention, which are both disposed in the housing constructed as the above-mentioned. Firstly, explanation will be given on a schematic construction of the entire traveling transmission system. Between the bearing wall 1b and the intermediate bearing plate 5 is journalled a clutch shaft 13 (traveling transmission system shaft), and a middle portion thereof is journalled by the bearing wall 1c. The traveling clutch shaft 13 is hollow to freely insert therein an input shaft 8. In the first chamber R1 and between the front bearing plate 4 and the bearing wall 1b is disposed and on the input shaft 8 is disposed a forward and rearward movement switching clutch B of hydraulic clutch type, so that a cylinder casing 24 thereof rotates integrally with the input shaft 8, the forward and rearward switching clutch B being provided at the rear with a forward movement clutch unit Ba and at the front with a rearward movement clutch unit Bb. When the forward movement clutch Ba engages, the input shaft 8 is directly connected with the traveling clutch shaft 13 so that the transmission system, in which the power of input shaft 8 is directly transmitted to the traveling clutch shaft 13 through the forward movement clutch unit Ba 8 (in other words, it is transmitted to the forward rotation), is designated as a first transmission system (forward movement transmission system). An idle shaft 11 (refer to Figs. 4 and 6) is journalled onto the front bearing plate 4, and an intermediate shaft 12 for rearward movement is journalled between the front bearing plate 4 and the bearing wall 1b, in parallel to the idle shaft 11, and a gear train is disposed so as to form a second transmission system (transmission system for rearward movement) for transmitting the power from the input shaft 8 to the traveling clutch shaft 13 through the idle shaft 11 and intermediate shaft 12. When the rearward movement clutch unit Bb engages, the power is transmitted from the input shaft 8 to the idle shaft 11 so that the traveling clutch shaft 13 is rotated reversely to the first transmission system. As mentioned above, the first and second transmission systems are included between the first bearing plate 4 and the bearing wall 1b so as to form a selecting device A selectable of one of both the transmission systems by the forward and rearward movement switching clutch B, the selecting device A being an embodiment of the auxiliary speed change device having at least two speed change stages. Instead of the selecting device A, for example, a high and low speed selecting mechanism S to be discussed below may be assembled in this position as the auxiliary speed change device of the present invention. A concrete construction of the forward and rearward movement selecting device A and the built-in thereof into the front transmission casing 1 is to be described below. Next, a first traveling speed change shaft 14 is disposed in parallel to the traveling clutch shaft 13 in the second chamber R2 and journalled to the bearing wall 1c and intermediate bearing plate 5, and gear trains and clutches constructing a main speed change mechanism T1 of four speed traveling are disposed between the traveling clutch shaft 13 and the first traveling speed change shaft 14. In a flywheel housing 3 is disposed a flywheel 7 directly connected to the engine output shaft, the flywheel 7 connecting with the front end of input shaft 8, in other words, the input shaft 8 rotating integrally with the engine output shaft. As the above-mentioned, the selecting device A is constructed which has the forward movement transmission system (the first transmission system ) and the rearward movement transmission system (the second transmission system) for directly transmitting the power from the input shaft 8 to the traveling clutch shaft 13 so as to be able to select one of both transmission systems by means of the forward and rearward movement switching clutch B and which can be formed as one assembly and built in the transmission casing. In addition, both the clutches Ba and Bb of the selecting device A are disengaged so as to enable the traveling transmission system to be put in a neutral state by use of a hydraulic control valve 35 shown in Fig. 5. Next, explanation will be given on a main traveling speed change mechanism T of 4-stages constructed between the traveling clutch shaft 13 and the first traveling speed change shaft 14 in the second chamber R2. In the same chamber, onto the traveling clutch shaft 13 are longitudinally fixed a 2-speed driving gear 67, a 1-speed driving gear 68, 4-speed driving gear 69, and a 3-speed driving gear 70, and a 2-speed driven gear 71, 1-speed driven gear 72, a 4-speed driven gear 73 and 3-speed driven gear 74, which are freely fitted onto the first traveling speed change shaft are permanently engaged with the driving gears 67, 68, 69 and 70 respectively. The driven gears 71 and 72 on the first traveling speed change shaft 14 are oppositely provided with clutch teeth 71a and 72a respectively, a clutch member 75 is disposed between both the clutch teeth 71a and 72a in relation of being non-relatively-rotatable and axially slidable with respect to the first traveling speed change shaft 14 and axially slidable, so as to be switchable to engage with the clutch teeth 71a and 72a and not to engage with either teeth. Similarly, the driven gears 73 and 74 are oppositely provided with clutch teeth 73a and 74a respectively, and a clutch member 76 is disposed onto the first traveling speed change shaft 14 between the clutch teeth 73a and 74a in relation of being non-relatively-rotatable and freely axially slidable, so as to be switchable into an engaging condition with the clutch teeth 73a or 74a and in a disengaging condition with either clutch teeth 73a or 74a. The main traveling speed change mechanism T1 allows the clutch member 75 or 76 to engage with any one of the clutch teeth 71a, 72a, 73a and 74a by use of one main speed change level (not shown), so that the driven gear, to which the clutch teeth are attached, is engaged with the first traveling speed change shaft 14, thereby driving the first traveling speed change shaft 14 in the speed reducing ratio on the basis of the gear trains. The first traveling speed change shaft 14 extends rearwardly of the intermediate bearing plate 5 and an intermediate shaft 16 for low speed is disposed within the third chamber R3 in parallel to the first traveling speed change shaft 14 and is journalled at the front end to the intermediate bearing plate 5. A second traveling speed change shaft 15 is disposed coaxially of the shaft 14 and rearwardly of the rear end thereof, freely fitted at the front end onto the rear end of the first traveling speed change shaft 14, and journalled at the middle portion onto the bearing wall 2a and at the rear end onto the bearing wall 2c. Within the third chamber R3, gear trains and clutches constituting the high and low speed switching mechanism S through the low speed intermediate shaft 16 are disposed between the first traveling speed change shaft 14 and the second traveling speed change shaft 15. Namely, a driving gear 77 for switching high and low speed is fixed onto the rear end of the first traveling speed change shaft 14 and clutch teeth 77a are fixed onto the side surface of the driving gear 77, which permanently engages with a first intermediate gear 78 fixed onto the intermediate shaft 16, and a second intermediate gear 79 is fixed thereto. A high and low speed switching, slide gear 80 is fitted onto the front end of the second traveling speed change shaft 15 in relation of being non-relatively-rotatable and freely longitudinally slidable. The slide gear 80 as shown in Fig. 1, disengages from the clutch teeth 77a and engages with the second intermediate gear 79 at the rear at the rear end of the longitudinally sliding area, and engages with the clutch teeth 77a so as to be to put in the disengaging condition from the second intermediate gear 79 at the front end of the same area. The former is the low speed condition of transmitting the power from the first traveling speed change shaft 14 to the second traveling speed change shaft 15 through the driving gear 77, first intermediate gear 78, second intermediate gear 79 and slide gear 80, and the latter is a high speed condition where the first traveling speed change shaft 14 is directly connected with the second traveling speed change shaft 15 so as to directly transmit a driving force of the first traveling speed change shaft 14 to the second traveling speed change shaft 15. A traveling output shaft 17 is journalled in parallel to the second traveling speed change shaft 15 between the bearing wall 2a in the fourth chamber R4, and gear trains and clutches constituting the substitute 3-stage traveling speed change mechanism T2 are disposed between the shafts 16 and 17. In other words, a substitute 3-speed driving gear 84, a substitute 2-speed driving gear 82 and a substitute 1-speed driving gear 83 are fixed onto the second traveling speed change shaft 15 sequentially form the front and always engage with a substitute 3-speed driven gear 84 a substitute 2-stage driven gear 85 and a substitute 1-stage driven gear 86 respectively. Clutch teeth 84a are attached to the side surface of the driven gear 84 and clutch teeth 85a and 86a are attached to the opposite surface of the driven gears 85 and 86 respectively. Furthermore, a clutch member 87 is longitudinally slidably fitted onto the traveling output shaft 17 between the clutch teeth 84a and the driven gear 85 respectively, and a clutch member 88 is similarly fitted onto the traveling output shaft 17 between the clutch teeth 85a and 86a. The substitute traveling speed change mechanism T2 allows the clutch member 87 and 88 to be longitudinally slidable by use of, for example, one substitute speed change lever, so as to switch the clutch member 87 and 88 to engage with one of the clutch teeth 84a, 85a and 86a, and to be put in the neutral state non-engaging with any one of them. In addition, the traveling output shaft 17, in the second chamber R2, extends at the front end thereof forwardly of the bearing wall 2a and is freely fitted onto the rear end of the low speed intermediate shaft 16 and extends at the rear end rearwardly of the bearing wall 2c so as to connect with a rear wheel differential mechanism 92 disposed between the bearing walls 2c and 2d within the fourth chamber R4. In the above-mentioned construction, the engine output shaft (flywheel 7) rotates to drive the traveling clutch shaft 13 in the forward to rearward movement transmitting state from the input shaft 8 through the forward movement transmission system (the first transmission system) or the rearward movement system (the second transmission system) and the power is transmitted from the traveling clutch shaft 13 to the first traveling speed change shaft 14 through the main traveling speed change mechanism T1, the first traveling speed change shaft 14 drives the second speed change shaft 15 through the high and low speed selecting mechanism S in the high speed transmission or the low speed transmission, and further drives the traveling output shaft 17 through the substitute traveling speed change mechanism T2 so as to drive the rear wheel differential mechanism 92. In this embodiment, forward movement of 24 stages and rearward movement of 24 stages are made possible. Furthermore, an expanded (swollen) portion 2e is formed at the forward lower end of the rear transmission casing 2, and a mid PTO shaft 18 is journalized into the expanded portion 2e in parallel to the traveling output shaft 17, so that the gear trains and clutches of the front wheel driving system are disposed between the output shaft 17 and the mid PTO shaft 18. In other words, the driving gear 89 is fixed to the traveling output shaft 17 so as to permanently engage with a driven gear 90a freely fitted onto the front wheel driving shaft 18, and clutch teeth 90a is attached to the front end of driven gear 90. In front thereof, a clutch member 91 is fitted onto the front wheel driving shaft 18 in relation of being non-relatively-rotatable and freely longitudinally slidable, so as to be switched into the state of engaging with the clutch teeth 90a and that of disengaging therefrom. The front wheel driving shaft 18 is journalled at the rear end thereof onto the bearing wall 2b formed in the rear transmission casing 2 and at the front end to the expanded portion 2e and further projects forwardly, so as to connect with, for example, a transmission system with respect to the front wheel differential mechanism. When the clutch sleeve 91 engages with the clutch teeth 90a, the traveling vehicle loading thereon the transmission is four-wheel-driven, and, when disengaged, only the rear wheels are driven. The respective shafts of PTO system and traveling system are journalled within the front and rear transmission casings 1 and 2 as the above-mentioned. For example, the input shaft 8 directly serves as the input shaft of PTO system and also as the input shaft of traveling system, the traveling clutch shaft 13, regarding the respective traveling system transmission shaft, is freely fitted onto the input shaft 8 coaxially of the input shaft 8, the first traveling output shaft 14 and second traveling speed change shaft 15 being coaxially disposed, and the low speed intermediate shaft 16 and traveling output shaft 17 being coaxially disposed. In the PTO system transmission shafts, the PTO clutch shaft 9; the PTO system transmission shaft at the downstream side of transmission of input shaft 8, is sequentially coaxially disposed at the rear of the input shaft 8 as discussed below. Such arrangement of the respective shafts of traveling system and PTO deletes disposal spaces of shafts in the entire transmission casing so as to contribute to construction of the compact transmission. Next, explanation will be given on schematic construction of the entire PTO transmission system in accordance with Fig. 1. The input shaft 8 perforates the front bearing plate 4 and is journalled therethrough, perforates the bearing wall 1b, partition 1c and intermediate bearing plate 5, and can transmit at the rear end the power through the hydraulic multi-disc type PTO clutch D disposed in the third chamber R3 to the clutch shaft 9 extending coaxially and rearwardly of the input shaft 8. The PTO clutch shaft 9 is braked in synchronism with disengagement of PTO clutch D by means of a hydraulic multi-disc type PTO brake E disposed just behind the PTO clutch D in order to prevent the PTO clutch shaft 9 from co-rotation when the PTO clutch D disengages. In other words, the input shaft 8 rotates integrally with the engage output shaft as the above-mentioned, but when the PTO clutch D engages, the PTO brake E is put in the not-braking state, so that the PTO clutch shaft 9 rotates integrally with the input shaft 8. On the other hand, when the PTO clutch D is disengaged the PTO clutch shaft 9, so that the PTO clutch shaft 9 is braked in the power cut-off state. In Fig. 8, the PTO clutch D and PTO brake E form an integrated PTO assembly C and can integrally be built-in, the PTO brake E being mounted onto the front surface of the bearing wall 2a of the rear transmission casing 2. The PTO clutch shaft 9 perforates the bearing wall 2a and is journalled thereto, further extends rearwardly, is journalled at the half way onto a bearing wall 2d, and journalled at the half way onto a bearing wall 2d, and journalled at the rear end to the rear bearing cover 6. A rear PTO shaft 10 is journalled to the bearing wall 2d and rear bearing cover 6 in parallel to the PTO clutch 9, driving gears 93 and driven gears 94 of reduction gears fixed to the shafts 9 and 10 respectively permanently engage with each other between both the shafts 9 and 10 so as to form a PTO reduction gear train. The rear PTO shaft 10 projects rearwardly from the rear bearing cover 6 to enable the power to be transmitted to a working machine (for example, rotary cultivator) mounted onto the rear of tractor. The schematic construction of the entire transmission is as the above-mentioned. Next, explanation in detail will be given on the construction of forward and rearward movement selecting device A of the invention including the forward and rearward movement switching clutch B disposed in the first chamber 1 in accordance with Figs. 1 through 7. Firstly, the second transmission system of gear train for rearward transmission, as shown in Fig. 6, is so constructed that a cylindrical portion for covering the outer periphery of the input shaft 8 is formed on the front surface and at an about laterally center of the bearing plate 4, the cylindrical portion extending slightly downwardly and one-sidedly so as to form an oil relaying unit 4a. Also, an idle shaft 11 is journalled to the lower portion of cylindrical portion as shown in Fig. 4. A driving gear 19 for rearward movement is freely fitted onto the input shaft 8 in proximity to the inside surface of the front bearing plate 4, an idle gear 20 is fixed onto the idle shaft 11 as shown in Fig. 4, both the gears 19 and 20 being permanently engaged with each other. Furthermore, an intermediate shaft 12 for rearward movement, as shown in Figs. 2 through 6, is journalled at the front end thereof to the front bearing plate 4, and a first intermediate gear 21 is fixed to the intermediate shaft 12 for rearward movement in proximity to the inside surface of the front bearing plate 4 and permanently engages with the idle gear 20. As shown in Figs. 2 through 5, the traveling clutch shaft 13 coaxially disposed with the input shaft 8 and the rear end of the intermediate shaft 12 for rearward movement are journalled onto the bearing wall 1b, the driven gear 23 for switching the forward and rearward movements is freely fitted onto the input shaft 8 in proximity to the front end surface of bearing wall 1b, and a second intermediate gear 22 is fixed to the intermediate shaft 12 for rearward movement, both the gears 22 and 23 permanently engaging with each other. In addition, the driven gear 23 is journalled onto the bearing wall 1b and fixed to the front end of traveling clutch shaft 13 in spline connection. Explanation will be given on the construction of forward and rearward movement switching clutch B in accordance with Fig. 3. The forward and rearward movement switching clutch B of hydraulic clutch system is covered by a cylinder casing 24, which has therein a partition 24a for longitudinally dividing the forward movement clutch unit Ba from the rearward movement clutch Bb, the input shaft 8 engaging through a key with a boss 24b provided at the center of partition 24a. Namely, the cylinder casing 24 integrally rotates with the input shaft 8. A rear half portion of the cylinder casing 24 from the partition 24a is a clutch chamber forming the forward movement clutch unit Ba, and a boss of the driven gear 23 freely fitted onto the input shaft 8 extends into the clutch chamber. Splines 23a are formed on the outer periphery of the boss, the splines 23a longitudinally slidably engage with friction plates 25, a piston 26 is longitudinally slidably disposed between the friction plate 25 nearest to the partition 24a (at the foremost end) and the partition 24a, and a check plate 28 is fixed to the cylinder casing 24 in the vicinity of the rear end opening of the forward movement clutch unit Ba behind (outside) the outermost friction plate 25a. Between the friction plates 25 and between the rearmost friction plate 25 and the piston 26 are disposed spacers 27 respectively so as to longitudinally slidably engage with respect to the cylinder casing 24, the piston 26 being biased by a biasing spring 26 toward the partition 24a. Meanwhile, a front half portion within the cylinder casing 24 before the partition 24a becomes a clutch chamber forming the rearward movement clutch unit Bb, into which chamber the boss of driving gear 19 extends, splines 19a are formed on the outer periphery thereof, and friction plates 30 longitudinally slidably engage with splines 19a. A piston 31 is longitudinally slidably disposed between the friction plate 30 closest to the partition 24a (at the rearmost end ) and the partition 24a, and a check plate 33 is fixed to the cylinder casing 24 in the vicinity of the front end opening of the outermost ( the foremost end ) friction plate 30. Spacers 32 are disposed between the respective friction plates 30 and between the respective friction plates 30 and between the foremost end friction plate 30 and the piston 31 so as to longitudinally slidably engage with respect to the cylinder casing 24, the piston 31 being biased by a biasing spring 34 toward the partition 24a. In the input shaft 8 are bored an operating oil passage 8a for forward movement, an operating oil passage 8b for rearward movement, and a lubricating oil passage 8c, which extend axially and in parallel to each other. The operating oil passage 8a communicates through an oil passage 24c bored in the boss 24b with the pressurized chamber between the partition 24a and the piston 31, the operating oil passage 8b communicates through an oil passage 24d bored at the boss 24b with the pressurized chamber between the partition 24a and the piston 31, and the lubricating oil passage 8c communicates through oil passages 24e and 24f bored at the boss 24b and orifices 26a and 31a bored at the pistons 26 and 31 with the friction plates 25 and 30 spacers 27 and 32 respective clutch units Ba and Bb. When the operating oil is supplied through the operating oil passage 24c into the pressurized chamber of the piston 26, the piston 26 is pushed by the operating oil against the biasing spring 29 so as to leave the partition 24a to slide outwardly (rearwardly) and put the friction plates 25 and spacers 27 between the piston 26 and clutch plate 28 so as to be brought in press contact and so as to put the forward movement clutch into the engaging state, at which time the power by the input shaft 8 is directly transmitted to the traveling clutch shaft 13 through the first transmission system: the cylinder casing 24 and driven gear 23, the traveling clutch shaft 13 rotating in the same direction as the input shaft 8, that is, the forward movement direction of the vehicle body. In addition, in this state, the rearward movement clutch is in the disengaging state so as to cut-off transmission between the cylinder casing 24 integral with the input shaft 8 and the driving gear 19 always interlocking with the traveling clutch shaft 13 through the gear train, thereby cutting off power transmission of the second transmission system. Meanwhile, when the operating oil is supplied into the pressurized chamber of the piston 31 through the operation oil passage 24d, the piston 31 is pushed by the operating oil against the biasing spring 34 so as to leave the partition 24a and slide outwardly (forwardly) to put the friction plates 30 and spacers 32 between the piston 31 and the check plate 33 and bring them in press contact with each other to put the rearward clutch in the engaging state, at which time the power from the input shaft 8 is transmitted through the cylinder casing 24, driving gear 19, idle gear 20 and first intermediate gears 21 and 22 to the forward and rearward movement switching driven gear 23, whereby the traveling clutch shaft 13 rotates reversely to the rotation of the input shaft 8, that is, in the rearward movement direction of the vehicle body, at which time the forward movement clutch disengages so as to cut-off the first transmission system from the cylinder casing 24 integral with the input shaft 8 to the driven gear 23. A hydraulic control valve unit 35 for controlling the operating and lubricating oil with respect to the forward and rearward movement switching clutch B, as shown in Figs. 5 and 6, is attached onto one side wall of the front transmission casing 1 so as to connect through pipings (not shown) with an external hydraulic pump; further at the one side wall of the front transmission casing 1, an expanded portion 1d is formed on the boss 1a for fixing thereto the bearing plate 4; and in the expanded portion 1d, a forward movement operating oil passage 1e, a rearward movement operating oil passage 1f and a lubricating oil passage 1g are bored in the L-like shape so as to open at the mounting surface of bearing plate 4 while communicating with a forward movement operating oil passage 35a, a rearward movement operating oil passage 35b and a lubricating oil passage 35c respectively of the hydraulic control valve unit 35. The front end surface of boss 1a connects with the rear surface of the front bearing plate 4 as the above-mentioned, and the front end surface of the expanded portion 1d abuts at a portion including the openings of forward movement operating oil passage 1e, rearward movement operating oil passage 1f and lubricating oil passage 1g, against the rear end surface of front bearing plate 4. The abutting portion of the front bearing plate 4 is the rear end surface of the oil relaying unit 4a, on which are bored the respective openings of a forward movement operating oil passage 4c and a lubricating oil passage 4d bored in the L-like space in the oil relaying unit 4a, the openings communicating with the forward movement operating oil passage 1e, rearward movement operating oil passage 1f and lubricating oil passage 1g respectively. The respective other ends of forward movement oil passage 4b, rearward movement operating oil passage 4c and lubricating oil passage 4d at the oil relaying unit 4a, are axially disposed and open on the peripheral surface that covers a cylindrical portion of the input shaft 8 at the front bearing plate 4 and communicate with a forward movement operating oil port 8d, a rearward movement operating oil port 8e and a lubricating oil port 8f respectively. The hydraulic control valve unit 35 and the forward and rearward movement switching clutch B. communicate therebetween through a forward movement operating oil passage L1 (35a-1e-4b-8d-8a-24c), a rearward movement operating oil passage L2 (35b-1f-4c-8e-8b-24d) and a lubricating oil passage ( 35c-1g-4d-8f-8c-24e-24f ) in a manner of perforating the expanded portion 1d of front transmission casing 1, oil relaying unit 4a, input shaft 8, and boss 24b of cylinder casing 24, thereby executing control for supplying operating oil and lubricating oil with respect to the forward movement switching clutch B by controlling the hydraulic control valve unit 35. Explanation will be given on the construction of hydraulic circuit in accordance with Fig. 7. Pressurized oil is supplied from an external hydraulic pump P to the hydraulic control valve unit 35 and at first, supplied to a F-N-R switching valve V2 within the hydraulic control valve unit 35 through an inching valve V1 switched by treading clutch pedal of the working vehicle, the forward and rearward movement operating oil passage 35a and 35b communicating through the F-N-R switching valve V2 with the respective forward and rearward movement oil passage L1 and L2 extend from the F-N-R switching valve V2. The inching valve V1, when the clutch pedal not trod, sends discharged oil from the hydraulic pump P to the F-N-R switching valve V2, and drains operating oil in part through a throttle valve as the clutches trod to thereby reduce feed oil pressure, so that, when completely trod, the discharged oil from the hydraulic pump P is unloaded to discharge the operating oil from the forward and rearward movement switching clutch B. The F-N-R switching valve is operated by, for example, a control lever attached in the vicinity of a handle of the working vehicle and switched into three positions of a forward movement position F, a rearward movement positions of R, and a neutral position N. In a case that the F-N-R switching valve V2 is in the forward position F, the operating oil is supplied to the forward movement clutch unit Ba through the forward movement operating oil passage 35a and L1 and the operating oil in the rearward movement clutch unit B is drained through the rearward movement operating oil passage L2 and 35b. On the other hand, in a case of rearward position R, the operating oil is supplied to the rearward movement clutch unit Bb through the rearward movement operating oil passages 35b and 12 and the operating oil in the forward movement clutch unit Bb is drained through the forward movement operating oil passages L1 and 35a. Furthermore, in the hydraulic control valve unit 35, an oil passage is branched from the upstream side of inching valve V1 and a delay relief valve V3 is interposed therein, the valve V3 gradually becomes a valve closing state from a valve opening state when the operating oil rises up with respect to the forward and rearward movement switching clutch units B so as to rise pressure of the operating oil passage L1 or 12 up to the specified value, thereby autmatically smoothly engaging the clutch units Ba and Bb with each other. Furtheremore, a lubricating oil passage 35c is branched to a relief drain oil circuit of delay relief valve V3 and a lubricating valve V4 is connected to the relief drain oil circuit. An open-close valve V5 of pilot pressure operation type is interposed in the lubricating oil passage 35c. The open-close valve V5 is introduced therein with the operating oil guided from between the inching valve V1 and the F-N-R switching valve V2, so that, when the operating oil is pressurized to start the engagement of forward movement clutch Ba or the rearward movement clutch Bb, the open-close valve V5 is set to be put in a "opening position". The lubricating oil discharged from the open-close valve 5 communicates through the lubricating oil passages 35c and L3 with the orifices 26a and 31a. When the forward movement clutch unit Ba disengages, the orifice 26a communicates with the lubricating oil passage 24 bored in the boss 24b so that the lubricating oil is supplied to the clutch unit Ba. When the operating oil is supplied to the forward movement clutch unit Ba and the piston 26 slides in the direction of engaging the clutch, a sectional area of a communicating portion of the orifice 26a with the lubricating oil passage 24e gradually becomes larger so as to flow a large amount of lubricating oil into the forward clutch unit Ba. In the rearward movement clutch unit Bb, the orifice 31a bored in the hydraulic piston 31 and the lubricating oil passage 24f have the same relation as the above. The construction of selecting device A is as the above-mentioned. Next, explanation will be given on an assembly process of the forward and rearward selecting device A into the transmission casing 1, the device A being assembled with the front bearing plate 4 prior to the assembly into the front transmission casing 1. In detail, the input shaft 8 and idle shaft 11 are journalled to the front bearing plate 4, and the forward and rearward movement switching clutch B inclusive of the rearward movement driving gear 19 and disposed onto the input shaft 8, the driving gear 19 being put in the state of engaging with the idle gear 20. Furthermore, the rearward movement intermediate shaft 12 attached with the first and second intermediate gears 21 and 22 is journalled at the front end thereof to the front bearing plate 4, so as to allow the first intermediate gear 21 to engage with the idle gear 20 and the second intermediate gear 22 to engage with the driven gear 23. Thus, the selecting device A, which temporarily build the forward and rearward movement clutch B in the front bearing plate 4, is inserted into the front transmission casing 1 through the front end opening (opening portion), the driven gear 23 freely fitted onto the input shaft 8 is build-in the bearings 36 mounted into the bearing wall 1b and journalled thereto, and the rearward movement intermediate shaft 12 is journalled at the rear end thereof to the bearing wall 1b through a bearing 37 built therein. In addition, at the rear end of the boss of driven gear 23 are formed internal tooth splines, so that the traveling clutch shaft 13 is inserted from the rear of bearing wall 1b into the driven gear 23 in a manner of trapping the input shaft 8, and the splines formed on the outer periphery of the front end of the traveling clutch shaft 13 engage with internal tooth splines of driven gear 23, thereby connecting the driven gear 23 to the traveling clutch shaft 13. The front bearing plate 4 temporarily mounted onto the boss 1a through a positioning pin 39 and thereafter tightened by bolts 38 so as to complete the build-in of the selecting device A. In addition, the front bearing plate 4 is only mounted onto the boss 1a, the respective oil passages bored in the oil relaying unit 4a of front bearing plate 4 naturally communicate with the respective oil passages bored at the expanded portion 1d and boss 1a of the front transmission casing 1. The selecting device A is constructed as mentioned above. Next, explanation will be given on structure and mounting construction of a PTO assembly C of PTO clutch D and PTO brake E of hydraulic type in the PTO transmission system in accordance with Figs. 1 through 8. The transmission mechanism of the invention for the working vehicle is constructed as the above-mentioned. Next, explanation will be given on the effect of the present invention. The transmission construction provided with the traveling system and PTO system in which the bearing wall in the housing is formed, the hollow traveling system transmission shaft is journalled at one end thereof into the one side of bearing wall in the housing, the input shaft perforating the traveling system transmission shaft perforates the bearing wall to project toward the anti-traveling system transmission side. Also, the other end side of traveling system transmission shaft, the PTO system transmission shaft is coaxially drivingly connected to the input shaft perforating the traveling system transmission shaft. Therefore, the three shafts: the input shaft, traveling system transmission shaft and PTO system transmission shaft, are coaxially disposed to thereby be reduced in a disposal space in the radial direction in comprarison with the case of disposing them in parallel to each other. Accordingly, the compact transmission mechanism can be formed. In a case that the mechanical speed change device is included in the traveling system, the disposal space in the radial direction is apt to be larger in position of multistage speed change device, whereby the compact structure is effective in restricting the space in the radial direction of transmission shaft at the entire transmission mechanism. The housing containing therein these members also can be compact and contribute to a low manufacturing cost. Next, in the traveling transmission system, when an auxiliary speed change device provided with at least two speed change stages is interposed between the engine and the traveling system speed change mechanism such as the main traveling speed change mechanism and substitute traveling speed change mechanism, one end thereof is rotatably supported together with coaxial traveling system transmission shaft onto the bearing wall formed in the housing, and journalled at the other end to the bearing plate, thereby completing with ease the assembly of auxiliary speed change device. The bearing plate is detachably mounted, so that the one end in the state where the bearing plate is removed, the one end of auxiliary speed change device can easily built in the bearing wall through the opening at the housing. Thereafter, the bearing plate is disposed at the opening, whereby the other end of auxiliary speed change device is easily journalled to the bearing plate, thus facilitating detachable mounting of the bearing plate, and also maintenance. The auxiliary speed change device is not so complicatedly built-in with other speed change mechanism as the conventional, but is independent of other speed change mechanism so as to be disposed between the bearing wall and the bearing plate. Therefore, the auxiliary speed change device can be detachably mounted independently of other speed change mechanism, in which the assembling and maintenance are very easy to exert. The auxiliary speed change device has the first transmission system directly transmitting the power from the input shaft to the output shaft and the second transmission system for transmitting the power from the input shaft to the output shaft through the intermediate shaft, whereby, for example, in the case that the auxiliary speed change device is used as the selecting device, the first transmission system is used as the forward movement transmission system and the second transmission system can be used as the rearward movement transmission system by interposing the idle shaft between the intermediate shaft and the input shaft or the output shaft. In a case that the auxiliary speed change device is used as the high and low speed selecting device, the first transmission system is used as the high speed transmission system and the second transmission system forms the reduction gear train through the input shaft, intermediate shaft and output shaft, so as to be used as the low speed transmission system. Such the auxiliary speed change device provided with the first and second transmission system can easily be detachably mounted to the housing as the integral assembly. The second transmission system of the auxiliary speed change device is provided with the idle gear to serving as the transmission system for reversely transmitting the rotation of input shaft to the output shaft through the idle gear so as to travel the auxiliary speed change device to be used as the selecting device which uses the first transmission system as the normal rotation transmission system and the second transmission system as the reverse rotation transmission system. Also, the idle gear can be journalled by using the bearing plate so that the gear train of second transmission system can be formed compact and easily. The auxiliary speed change device is provided with the hydraulic clutch alternatively switchable of the first or second transmission system into the transmission state by operating the hydraulic control valve, and forms, in the bearing plate, the oil relaying unit for fluid-communicating between the hydraulic clutch and the hydraulic control valve disposed outside the housing for switching the hydraulic clutch, so that the first and second transmission systems of the auxiliary speed change device can be selected by the hydraulic clutch, whereby the clutch engagement when the transmission system is selected, can be smooth and easy. Also, the oil relaying unit is formed by use of the bearing plate so as to lead to saving of the number of parts and simplification of structure. Both the hydraulic clutches for the first and second transmission systems are provided onto the input shaft, whereby the hydraulic clutch can be reduced in capacity and auxiliary speed change device can be compact as a whole. Regarding the structure of oil passage with respect to the hydraulic clutch, the hydraulic control valve is mounted onto the outer wall of housing, the oil passage communicating with the hydraulic control valve is formed in a thick portion of the outer wall, and the thick portion of the outer wall of housing joints with the bearing plate, so that the oil passage communicates with the oil relaying unit, and the oil passage communicates with the oil relaying unit, whereby the hydraulic control valve and hydraulic clutch are automatically connected following assembly of bearing plate during the assembly of auxiliary speed change device, thereby saving labor of piping.

Claims: A transmission mechanism for a working vehicle, comprising: a transmission housing (1), an input shaft (8), a hollow traveling system transmission shaft (13) coaxially penetrated by said input shaft (8), a speed change device (A), including a hydraulic clutch (B), interposed in a transmission path between said input shaft (8) and said traveling system transmission shaft (13), and a PTO system transmission shaft (9) coaxially connected in a driving manner to said input shaft (8) projecting from said traveling system transmission shaft (13), characterized in that said transmission mechanism is disposed in said transmission housing (1) adapted to be connected to an engine housing (3) and having an opening in the vicinity of the connection portion, said hydraulic clutch (B) is inserted into said transmission housing (1) through said opening of said transmission housing (1), a bearing plate (4) is provided so as to cover said opening of said transmission housing (1) and to rotatably support said input shaft (8) so as to allow connection thereof to an output shaft of said engine in said engine housing (3), and said bearing plate (4) is provided with a hydraulic relaying portion (4a) formed therein with at least one hydraulic passage (4b,4c,4d) for fluidly connecting said hydraulic clutch (B) to a hydraulic control valve unit (35). The transmission mechanism for a working vehicle as set forth in claim 1, wherein said hydraulic control valve unit (35) is mounted on an outer wall of said transmission housing (1), and said outer wall of said transmission housing (1) is formed therein with at least one hydraulic passage (1e,1f,1g) joined to said at least one hydraulic passage (4b,4c,4d) in said hydraulic relaying portion (4a) of said bearing plate (4). The transmission mechanism for a working vehicle as set forth in claim 1 or 2, wherein said hydraulic clutch (B) is mounted on said input shaft (8), and said input shaft (8) is formed therein with at least one hydraulic passage (8a,8b,8c,8d,8e,8f) for connecting said at least one hydraulic passage (4b,4c,4d) in said hydraulic relaying portion (4a) of said bearing plate (4) to said hydraulic clutch (B). The transmission mechanism for a working vehicle as set forth in any one of claims 1, 2 and 3, wherein said hydraulic clutch (B) comprises two clutch units (Ba,Bb) which are selectively engageable for either changing the traveling direction of an output of said transmission or for changing the traveling speed level of said transmission. The transmission mechanism for a working vehicle as set forth in claim 4, wherein said speed change device (A) is provided with a drive train (19,20,21,12,22,23) including an intermediate shaft (12) extending in parallel to said input shaft (8) and said traveling system transmission shaft (13), one (Ba) of said hydraulic clutch units is engageable to directly connect said input shaft (8) to said traveling system transmission shaft (13), and the other (Bb) is alternatively engageable to transmit power from said input shaft (8) to said traveling system transmission shaft (13) through said drive train (19,20,21,12,22,23) including said intermediate shaft (12), and said intermediate shaft (12) is supported at one end to said bearing plate (4) and at the other end to a wall portion (1b) formed in said transmission housing (1). The transmission mechanism for a working vehicle as set forth in claim 5, wherein said two hydraulic clutch units (Ba,Bb) are provided for changing the traveling direction of an output of said transmission, and wherein said drive train (19,20,21,12,22,23) includes an idle gear (20) supported to said bearing plate (4).

Inventors: INANAGA MASASHI, KOJIMA MASAAKI, RYUGO AKINOBU, INANAGA, MASASHI, KOJIMA, MASAAKI, RYUGO, AKINOBU
Applicants: KANZAKI KOKYUKOKI MFG CO LTD, KANZAKI KOKYUKOKI MFG. CO., LTD.
Application year: 1998
Main classification: B60K17
IPC codes: B60K17, F16H61, F16H37