PTO gearbox

Abstract

Power take-off transmission with at least two switchable gear ratios, wherein the gear ratios are achieved by moving a shift fork (12, 15) from a first position to a second position and thereby a shaft (26, 3) is rotatably connected to a gearwheel (28, 29, 34, 35), wherein the shift fork (12, 15) is arranged with a push rod (11, 14) of a piston (8, 13) in a cylinder (6, 7), and the piston (8, 13) has a first piston surface (9) which can be acted upon by pressure medium and the piston (8, 13) has a second piston surface (10) which can be acted upon by pressure medium, wherein the second piston surface (10) is smaller than the first piston surface (9) due to the piston rod (11, 14), whereby when the first piston surface (9) is acted upon by pressure medium and the second piston surface (10) is acted upon by pressure medium at the same pressure level of the pistons (8,13) moves from a first position to a second position and, upon depressurization of the first piston surface (9) and pressurization of the second piston surface (10), the piston (8, 13) moves from the second position to the first position, wherein the power take-off transmission has four switchable gear ratios and two shift forks (12, 15) and two pistons (8, 13) with piston rods (11, 14), wherein a first shift sleeve (27) is arranged coaxially to a drive shaft (1) and interacts with the first shift fork (12), and a second shift sleeve (16) is arranged coaxially to an output shaft (3) and interacts with the second shift fork (15), and wherein the first shift sleeve (27) has a first idler gear (28) and a second idler gear (29) arranged coaxially to one another, and the second shift sleeve (16) has a third idler gear (34) and a fourth idler gear (35) are arranged coaxially to each other, characterized in thatthat two countershafts, each with two fixed gears (30, 31, 32, 33), are arranged between the input shaft (1) and the output shaft (3).

Description

[0001] The invention relates to a power take-off transmission according to the type defined in the preamble of claim 1.

[0002] Generic power take-off transmissions are used in particular in agricultural vehicles, such as tractors, in order to make the torque of a vehicle's drive engine available at a desired speed on a power take-off shaft that is usually exposed on the vehicle.

[0003] DE 10 2011 084 623 A1 discloses a power take-off transmission that provides four different speeds on the power take-off shaft, which are enabled by switching between different gear ratios. In tractors, switching between gear ratios is usually done by means of a cable.

[0004] DE 10 2011 084 623 A1 describes a power take-off transmission that meets practical requirements in an improved manner and is designed to be powershiftable. The power take-off transmission includes a drive shaft and two input shafts coaxial with the drive shaft, a power take-off shaft offset from the input shaft axis, and at least three spur gear stages for shifting gear ratios, each of which comprises a gear arranged on the input shaft axis and a gear arranged on the power take-off shaft axis. The power take-off transmission is a three- or four-stage transmission.

[0005] DE 16 30 726 A1 discloses a vehicle with a power take-off shaft that is driven via a frictional clutch. A positive clutch is arranged between the frictional clutch and the power take-off shaft.

[0006] From US 2008 / 0 264 188 A1, a hydraulically operated shift lever for a power take-off is known, which comprises a shift housing with an interior, a fluid connection, and an opening. Arranged inside the shift housing is a shift piston that is movable in a first and a second direction. The shift piston defines a first and a second chamber inside the shift housing. The fluid connection communicates with the first chamber, and the opening with the second chamber. The shift piston has a passage that establishes the connection between the first and second chambers inside the shift housing. A shift actuator is movably mounted on the shift piston and extends through the opening in the shift housing.

[0007] US 4,637,269 A discloses a drive device for a work vehicle, such as a tractor. It comprises an engine, an input shaft coupled to the engine, a gear change mechanism, a hydraulic clutch, an auxiliary gear change mechanism, and a reduction gear, all housed in a common transmission housing. Power from the reduction gear is transmitted to the rear wheels via a rear axle differential and to the front wheels via a drive shaft and a front axle differential.

[0008] EP 1 225 343 A1 discloses a drive device comprising a fluid-actuated working cylinder having a drive unit with a piston arranged in the cylinder housing and a piston rod connected to the piston and protruding from the cylinder housing at one end face. The piston separates two cylinder chambers provided for the application of an actuating fluid, wherein the piston rod (at least on its longitudinal section located within the associated cylinder chamber) has a cross-sectional area that amounts to between 35% and 80% of the application area of ​​the drive unit on the rodless side of the piston.

[0009] The present invention is based on the object of creating a power take-off transmission which can be switched in a simple manner and which has at least two switchable gear ratios.

[0010] The problem is solved by a generic power take-off transmission which also has the characterising features of the main claim.

[0011] According to the invention, the power take-off transmission has at least two selectable gear ratios, which can be switched by moving a shift fork. The shift fork interacts with a push rod of a piston, whereby the piston has a first piston surface that can be subjected to pressure medium and a second piston surface that can be subjected to pressure medium. Due to the push rod, the second piston surface that can be subjected to pressure medium is smaller than the first piston surface that can be subjected to pressure medium.

[0012] According to the invention, the PTO transmission is designed with four switchable gear ratios, wherein the PTO transmission has two shift sleeves, each interacting with a shift fork. Each shift fork interacts with a piston of a piston-cylinder unit. According to the invention, the first shift sleeve is arranged coaxially to the input shaft of the PTO transmission, and the second shift sleeve is arranged coaxially to the output shaft of the PTO transmission. This makes it possible to arrange the two cylinders at a distance from one another on one side of the transmission housing of the PTO transmission. The cylinders are preferably arranged on the transmission side on which the PTO output is arranged. This makes it possible to switch four switchable gear ratios using two piston-cylinder units, each of which can be controlled by a 3 / 2-way valve.By permanently connecting both cylinders to the pressure source, a constant return force is exerted on each cylinder. This force remains constant even over the travel of the piston. Thus, a simple hydraulic circuit provides a reliable PTO shifting system.

[0013] Further features can be found in the figure description.

[0014] They show: Fig. 1 a section through the PTO gearbox; Fig. 2 the hydraulic diagram of a cylinder of the power take-off shaft; and Fig. 3 the transmission diagram of the PTO gearbox. Figure 1:

[0015] A drive motor of the vehicle (not shown) drives the drive shaft 1 of the power take-off transmission. The output shaft 3 of the power take-off transmission is driven depending on the selected gear ratio and whether the clutch 2 is engaged. A first cylinder 6 and a second cylinder 7 are arranged on one side 4 of the transmission housing 5. In the first cylinder 6, a first piston 8 with a first piston surface 9 and a second piston surface 10 is arranged. A first piston rod 11 is connected to the first piston 8, which interacts with a first shift fork 12. In the second cylinder 7, the second piston 13 with a first piston surface 9 and a second piston surface 10 is arranged. The second piston 13 interacts with the second piston rod 14, which interacts with the second shift fork 15. The second shift fork 15 engages the second shift sleeve 16, whereby the latter is displaced depending on the movement of the second piston 13.By arranging the first cylinder 6 and the second cylinder 7 on one side 4 of the transmission housing 5, the cylinders can be easily connected to the hydraulic control system. If side 4 of the transmission housing 5 is arranged on the side of the output shaft 3, the first cylinder 6 and the second cylinder 7 are easily accessible for servicing. If the second shift fork 15 is to be moved into its first shift position, the first piston surface 9 and the second piston surface 10 are pressurized from a pressure medium source. If the second shift fork 15 is to be moved into its other shift position, the second piston surface 10 remains pressurized, while the first piston surface 9 is depressurized. The first shift fork 12 is switched in the same way. Figure 2:

[0016] The hydraulic control is explained using a single cylinder as an example. In a PTO transmission with two cylinders, this control is present twice. Pressure fluid from a pressure source 17, for example a pump, flows via line 18 into chamber 19 and pressurizes the second piston surface 10. Via line 20, pressure fluid flows from the pressure source 17 to the 3 / 2-way valve 21, which, when de-energized, is held in its one switching position by the spring 22. This connects chamber 24, and thus the second piston surface 9, to a pressure fluid reservoir 25 via line 23.

[0017] Thus, in this switching position of valve 21, the force on the second piston surface 10 predominates. If valve 21 is energized and thus switched against the spring force of spring 22, pressure medium from pressure source 17 flows via line 20 and line 23 into chamber 24, whereby the force on the first piston surface 9 predominates due to the larger area of ​​the first piston surface 9 compared to the second piston surface 10. The first piston 8 moves accordingly into its other position. Figure 3:

[0018] The drive shaft 1 is driven by a drive motor (not shown). If the clutch 2 is actuated in the closing direction, the shaft 26 and with it the first shift sleeve 27 are driven. Depending on the pressure applied, the first shift sleeve 27 engages either with the first idler gear 28 or with the second idler gear 29. The first idler gear 28 is operatively connected to the first fixed gear 30 and the second idler gear 29 is operatively connected to the second fixed gear 31. The first fixed gear 30 and the second fixed gear 31 are connected to one another in a rotationally fixed manner. The second fixed gear 31 is operatively connected to a third fixed gear 32. The third fixed gear 32 is connected to a fourth fixed gear 33. The third fixed gear 32 is operatively connected to a third idler gear 34 and the fourth fixed gear 33 is connected to a fourth idler gear 35. Depending on the switching position of the second shift sleeve 16, the output shaft 3 is connected in a rotationally fixed manner either to the fourth idler gear 35 or to the third idler gear 34.This means that four different gear ratios can be switched with the PTO gearbox, whereby the PTO gearbox can be powershifted via clutch 2. Reference symbol 1 drive shaft 2 clutch 3 Output shaft 4 Page 5 Gearbox housing 6 first cylinder 7 second cylinder 8 first piston 9 first piston surface 10 second piston area 11 first piston rod 12 first shift fork 13 second piston 14 second piston rod 15 second shift fork 16 second shift sleeve 17 Pressure medium source 18 Line 19 Room 20 Line 21 Valve 22 spring 23 Line 24 rooms 25 Pressure medium reservoir 26 Wave 27 first shift sleeve 28 first loose wheel 29 second idler gear 30 first fixed gear 31 second fixed gear 32 third fixed gear 33 fourth fixed gear 34 third idler gear 35 fourth idler gear

Claims

[1] Power take-off transmission with at least two switchable gear ratios, wherein the gear ratios are achieved by moving a shift fork (12, 15) from a first position to a second position and thereby a shaft (26, 3) is rotatably connected to a gearwheel (28, 29, 34, 35), wherein the shift fork (12, 15) is arranged with a push rod (11, 14) of a piston (8, 13) in a cylinder (6, 7), and the piston (8, 13) has a first piston surface (9) which can be acted upon by pressure medium and the piston (8, 13) has a second piston surface (10) which can be acted upon by pressure medium, wherein the second piston surface (10) is smaller than the first piston surface (9) due to the piston rod (11, 14), whereby when the first piston surface (9) is acted upon by pressure medium and the second piston surface (10) with pressure medium at the same pressure level of the pistons (8,13) moves from a first position to a second position and, upon depressurization of the first piston surface (9) and pressurization of the second piston surface (10), the piston (8, 13) moves from the second position to the first position, wherein the power take-off transmission has four switchable gear ratios and two shift forks (12, 15) and two pistons (8, 13) with piston rods (11, 14), wherein a first shift sleeve (27) is arranged coaxially to a drive shaft (1) and interacts with the first shift fork (12), and a second shift sleeve (16) is arranged coaxially to an output shaft (3) and interacts with the second shift fork (15), and wherein the first shift sleeve (27) has a first idler gear (28) and a second idler gear (29) arranged coaxially to one another, and the second shift sleeve (16) has a third idler gear (34) and a fourth idler gear (35) are arranged coaxially to each other, characterized bythat two countershafts, each with two fixed gears (30, 31, 32, 33), are arranged between the input shaft (1) and the output shaft (3).

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