CREEPER SPEED MECHANISM FOR TRACTOR TRANSMISSION

Abstract: A dual power clutch arrangement for a tractor transmission includes first and second clutches (20,22) driveably connected to the engine shaft (l0) and adapted through selective engagement to driveably connect that shaft to the output of the clutch A creeper speed mechanism operates in combination with the torque delivery path of the dual power mechanism to produce high and low creeper speed ratios when a coupler (78) is moved into engagement with the speed reduction gearset, one of whose components is driveably connected to the gearset of the dual power mechanism. The coupler selectively connects the output component of one of the clutches (20,22) to the input shaft (72) of the transmission or connects the creeper gear (68) to the input shaft.

Description: This invention relates to a multiple speed ratio trasctor transmission. More particularly, the invention pertains to a dual power mechanism and to a creeper speed mechanism for producing an extraordinarily large gear ratio. Tractor transmissions are designed to produce a larger number of gear ratios within a mechanism located between the engine and the final drive or differential mechanism. In the conventional design, the gear arrangement of the transmission may produce a gear reduction or ratio of approximately 9:l between the speed of the transmission output and the engine speed. Typically, the torque delivery path of a tractor transmission includes a creeper speed mechanism located behind the transmission gear arrangement and before the differential mechanism. The creeper speed mechanism produces an additional speed reduction of about 5:l between the output of the transmission gear arrangement and the output of the creeper speed mechanism. This combination of speed ratios will produce an overall speed reduction of approximately 45:l between the output of the creeper speed mechanism and the engine. Because the creeper speed mechanism is an additional gear mechanism located in conventional tractor drivelines at the rear of the transmission, its presence increases the overall length of the transmission. It is preferable that the creeper speed mechanism be as short as possible so that the transmission can be fitted within the smallest space possible. Yet to produce a sufficiently large speed reduction between the engine and the transmission output required by tractor operators for certain conditions, the creeper speed mechanism must include several speed reductions which necessarily increase the space required by the mechanism. DE-A-2,410,164 discloses a change gear transmission which comprises a group transmission that precedes a main control group and in which the input shaft is driven by a driving engine through the intervention of an engageable and disengageable driving clutch and in which said change gear transmission includes two control stages, each of which is adapted to be engaged and disengaged by a friction clutch. According to the invention there is provided a a tractor transmission comprising a first shaft which is clutched to the engine, a transmission input shaft, creeper speed reduction means, first and second clutch means for selectively, driveably connecting the first shaft to the respective outputs of the first and second clutch means and speed reduction means driveably connected to the output of the first and second clutch means, characterised in that the creeper speed reduction means is driveably connected to the first speed reduction means, and the transmission further includes means for selectively, driveably connecting the creeper speed reduction means to the transmission input shaft. The clutches are engaged selectively by connecting a source of pressurized fluid to the respective clutch pistons. When the shift lever of the transmission is moved among the various speed ratios, for example, when the lowest speed ratio is selected by the tractor operator, a hydraulic valve opens communication between one of the clutches and the pressurized fluid source. If a higher speed ratio is required, movement of the shift selector to the higher gear ratio closes the connection to the first clutch and communicates the fluid pressure source to the second clutch. The first speed reduction means includes a countershaft rotatably mounted on the transmission casing parallel to the axis of the shaft that is connected to the engine. The counter shaft carries two pinions which turn with the countershaft and are engaged respectively with the output component of the first and second clutches. In addition to these pinions, a third pinion carried on the countershaft is continuously engaged with a creeper gear carried rotatably on the transmission input shaft. This pinion and the creeper gear produce a speed reduction between the countershaft and the input shaft. The connecting means includes a coupler, slideably mounted on the input shaft, and which moves between a position where the coupler is connected to the creeper gear and another position where the coupler is connected to the output component of one of the clutches. The coupler is continuously, driveably connected to the transmission input shaft. Therefore, movement of the coupler connects either the creeper speed gear or the output component of the clutch to the input shaft. The gears that are formed integrally with the clutch outputs and the pinions with which they are engaged on the countershaft are sized to produce a torque amplification and speed reduction between the shaft that is connected to the engine and the countershaft. The creeper gear and the pinion with which it is engaged on the countershaft are sized to produce an additional speed reduction and torque application between the countershaft and the transmission input shaft. The output of one of the hydraulically actuated clutches is connected by the coupler directly to the transmission input shaft. When the other hydraulic clutch is actuated and the coupler is positioned other than for creeper operation, the transmission input shaft is overdriven with respect to the engine shaft. However, when the coupler is moved into engagement with the creeper gear, the output of the first clutch drives a pinion on the countershaft, which produce a speed reduction. The connection that the coupler makes with the creeper gear produces a second speed reduction between the speed of the countershaft and the transmission input shaft. When the coupler is located at the normal drive position, the transmission input shaft is either over-driven with respect to the engine speed or it is directly connected to the engine. Otherwise, when the coupler is positioned for creeper speed operation, the two speed ratios that result from selective engagement of the first and second clutches and the speed reduction associated with the creeper speed mechanism product two larger speed reductions between the engine and the transmission input shaft. The invention will now be described further by way of example with reference to the accompanying drawings in which: Figure l is a cross section through a plane that contains the axes of the engine shaft and transmission input shaft at the fron portion of a tractor transmission according to this invention. The output shaft of an engine is driveably connected to the power take off shaft l0 of a tractor transmission through a neutral clutch l2. The transmission is housed in a casing l4 comprising several segments which are joined at bolted connections l6. A bulkhead or web l8, connected to the casing, supports various shafts, gears, clutches and synchronizers. A first hydraulically actuated disc clutch assembly driveably connects shaft l0 to first and second output components of the clutches. For example, when a first clutch 20 or a second clutch 22 is engaged, shaft l0 is connected to clutch output components 28 or 30, respectively. The input element 24 of the clutches is joined at a spline 26 to shaft l0; their output components 28, 30 are rotatably supported on the shaft and are formed integrally with gears 32, 34, which are in continuous meshing engagement with pinions 36, 38. These pinions are rotatably supported on countershaft 40, which is substantially parallel to the axis of shaft l0. Clutch 20 includes a hydraulic cylinder 42 driveably connected to the input component 24, a piston 44, a first set of clutch discs 46 splined to the cylinder 42, a second set of clutch discs 48 splined to output component 28, a spring retainer 52, a coiled compression spring 50 fitted between the spring retainer and the piston, seals 53, 54 for hydraulically sealing the pressurized portion of the cylinder from the unpressurized portion, and a bearing 56 for rotatably supporting the output component on shaft l0. The hydraulic system of the transmission connects a source of high pressure hydraulic fluid through a hydraulic passage 58 to the interior of the cylinder. The low pressure portion of the cylinder is connected by passage 60 to a reservoir or sump at atmospheric pressure. Clutch 22 includes corresponding components to those described with respect to clutch 20 and functions in the same way as clutch 20 when its cylinder is pressurized through passage 62 from the source of hydraulic pressure. Clutches 20 and 22 are operated alternately; they are not fully engaged concurrent during any of the forward drive, reverse drive or creeper speed ratio conditions. When clutch 20 is energized, its cylinder is pressurized and the clutch discs 46, splined to the cylinder, are forced into frictional contact with discs 48, splined on the output component 28. When the pressure in the cylinder rises sufficiently, the input component 24 is driveably connected to the output component 28 and driveably connects shaft l0 and gear 32. Similarly, when clutch 22 is pressurized, a driveable connection is made through engagement of the corresponding disc sets between shaft l0 and gear 34. Pinion 36 is formed integrally with countershaft 40, and pinions 38, 66 are connected by spline 64 to the countershaft. Pinion 66 is in continuous engagement with creeper gear 68, which is rotatably mounted by bearing 70 on the outer surface of the transmission input shaft 72. Shaft l0, the power takeoff shaft, extends from the front of the transmission to the rear through a bore in shaft 72. The gear wheel on which creeper gear 68 is formed includes a set of dog teeth 74 engageable by a corresponding set of dog teeth 76 located on the circumference of a coupler 78. Located at the forward end of the input shaft is a set of splines 80, with which the splines 82 on the inside diameter of coupler 78 are continuously engaged. Located at the rearward end of the output component 30 of clutch 22 is a set of dog teeth 84, which is engageable by the splines 82 of the coupler. The coupler is mounted for axial sliding movement on the input shaft and remains continuously engaged with the input shaft. When coupler 78 is moved rearward from the neutral position shown in the figure, it is brought into driveable engagement with creeper gear 68. When the coupler is moved forward from the neutral position, it is brought into driveable engagement with the output component of clutch 22. The device embodying to this invention will produce, through selective operation of clutches 20 and 22, a dual power input between the engine shaft and the input shaft 72 of the transmission. When clutch 20 is engaged, clutch 22 is disengaged, coupler 78 is moved forward to its normal position, and output shaft 72 is overdriven with respect to the engine, i.e., the speed of shaft 72 is greater than the engine speed. When the clutches and coupler are so disposed, power is transmitted from power takeoff shaft l0 through clutch 20, gear 32, pinion 36, spline 64, pinion 38, gear 34 and coupler 78 to the input shaft 72. The relative sizes of the meshing gears and pinions 32, 40 and 38, 34 cause input shaft 72 to be overdriven approximately l.6 times the speed of shaft l0. When clutch 22 is engaged, clutch 20 is disengaged and coupler 78 is moved forward to its normal position, shaft l0 is connected to the input shaft 72 through the torque delivery path that includes spline 26, the discs of clutch 22, output component 30 and coupler 78. This torque delivery path causes the input shaft 72 to be driven at the speed of shaft l0. The dual power input mechanism connects the engine through clutches 20 and 22 either directly to the transmission input or through the speed reduction gearset to the transmission input. However, in addition to the dual power input, the creeper mechanism according to this invention has the capacity to produce a speed reduction between the engine and the transmission input by moving the coupler rearward from the position of engagement with the output of clutch 22 and into engagement with creeper gear 68. When this is done, selective engagement of clutches 20 and 22 produces two ratios of the speed of the input shaft with respect to the engine shaft. The creeper speed mechanism produces the higher creeper speed ratio or the lower torque ratio when clutch 20 is engaged, clutch 22 is disengaged and coupler 78 is moved rearward to the creeper speed position. With these components so disposed, the torque delivery path between shaft l0 and input shaft 72 includes clutch 20, gear 32, pinion 36, creeper pinion 66, creeper gear 68, dog teeth 74, 76 and coupler 78. The creeper speed mechanism produces the lower creeper speed ratio or the higher torque ratio when clutch 20 is disengaged, clutch 22 is engaged and coupler 78 is moved rearward to bring its dog teeth 76 into engagement with the the dog teeth 74 on the creeper gear wheel 68. With these components so disposed, the torque delivery path that connects shaft l0 to shaft 72 includes clutch 22, gear 34, pinion 38, creeper pinion 66, creeper gear 68, dog teeth 74, 76, and coupler 78. From the relative sizes of the engaged gears and pinions of this torque path, it can readily be seen that the speed of input shaft 72 is substantially slower than the engine speed. From the relative sizes of the engaged gears and pinions of the other torque path, the input shaft speed is seen to be higher than its speed when clutch 22 is engaged and clutch 20 is disengaged, for a constant engine speed.

Claims: A tractor transmission comprising a first shaft (10) which is clutched to the engine, a transmission input shaft (72), creeper speed reduction means (68), first and second clutch means (20,22) for selectively, driveably connecting the first shaft (10) to the respective outputs of the first and second clutch means (20,22), and first speed reduction means (36,38,40,66) driveably connected to the output of the first and second clutch means (20,22), characterised in that the creeper speed reduction means (68) is driveably connected to the first speed reduction means (36,38,40,66), and the transmission further includes means (78) for selectively, driveably connecting the creeper speed reduction means (68) to the transmission input shaft (72). A tractor transmission according to Claim 1, wherein the connecting means (78) selectively, driveably connects the output of the second clutch means (22) to the transmission input shaft (72). A tractor transmission according to Claim 1 or 2, wherein the first speed reduction means (36,38,40,66) includes a countershaft (40) mounted for rotation parallel to the first shaft (10), carrying a first pinion (36) in meshing engagement with the output of the first clutch means (20) and a second pinion (66) driveably connected to the creeper speed reduction means (68), said first and second pinions (36,66) being rotatably fixed to the countershaft (40). A tractor transmission according to Claim 3, wherein the first speed reduction means (36,38,40,66) further includes a third pinion (38) carried on the countershaft (40) in meshing engagement with the output of the second clutch means (22) and driveably connected to the second pinion (66).

Inventors: BEIM, RUDOLF
Applicants: FORD FRANCE SOCIETE ANONYME, FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1987
Main classification: F16H3
IPC codes: F16H3, F16H37