STEPLESS ADJUSTABLE HYDRAULIC TRANSMISSION

Abstract: Continuously adjustable hydraulic transmission comprising a hydraulic pump and a hydraulic motor, the displacement volume of the motor being adjustable from the outside of the transmission, where the pump being an axial piston pump or a radial piston pump, the stator (1) of the pump being movable in relation to parts connected with the input shaft of the pump, the stator (1) of the pump being connected with and rotating with the output shaft (4) of the motor and hydraulic fluid being transferred between the pump and the motor through an oil distributor being stationary in relation to the motor.

Description: Stepless adjustable hydraulic transmission The present invention is related to a stepless adjust- s able hydraulic transmission, according to the preamble of the claims. Hydraulic transmissions having stepless adjustable transmission ratio have as such long been known. Often a hydraulic pump with a variable displacement volume has been used together with a hydraulic motor with fixed or adjustable displacement volume. Motor and pump partly have been produced as separate units having a common piping system, partly they have been assembled to one unit. In many cases an electrical asynchronous motor has been used as driven motor with a frequency converter, ensuring that the rotation of the motor is adjustable. Such combinations must be calculated according to maximum torque resulting oversize dimensions in relation to the normally used revolution ranges. Different principles and forms of hydraulic transmis¬ sions of the above mentioned types are described in publications such as FR 991 880, FR 1 020 522, GB 1 101 632, NO 171 030 and DE 2 332 621. The above described and other embodiments as well as separate units, however, are voluminous and rather heavy which in many connections limits the use strongly. Additionally the efficiency is relatively low, however depending on the transmis¬ sion ratio. The above mentioned disadvantages are avoided and further advantages achieved with the transmission according to the present invention as defined by the features stated in the claims. The transmission according the invention especially provides many advantages above known embodiments in cases where reduction in the rotation speed of the output shaft is connected with the need for corresponding increase in the torque. Examples of such applications are operation of winches, wood working equipment, machine tools and special vehicles. The transmission then will have less volume and lower weight in relation to commercial hydraulic transmission, as well as higher efficiency in an important part of the transmission ratio. This is achieved with a simple and compact design having a high energy density and especially being connected with the special way of assembling pump and motor to one unit. With the hydraulic transmission according to the 5 present invention, the output shaft torque is increased by increasing the transmission ratio in such a way that the output power is maintained substantially constant. The transmission ratio between input and output shafts may be adjusted manually, remotely controlled or controlled o automatically. The transmission according to the present invention provides a compact unit which may be inserted between a driving motor and the equipment to be driven. On the other side the transmission very easily may be built in as part of the driving motor or as part of the equipment. s Preferably the transmission may be provided with a valve for bypass in such a way that the output shaft stops and furthermore for the use at soft starting. Such a valve may be a reduction valve protecting the driving motor as well as the transmission and equipment to be o driven, against overloading which may occur in such situations, for example if the equipment is stuck. The transmission comprises an motor according to the principle of axial pistons or radial pistons, as well as a pump preferably according to the principle of axial pistons. 5 The hydraulic transmission according to the invention may be manufactured in a compact, closed unit which easily may be shaped in such a way that even the strong claims for hygiene set by the nutrient industry is satisfied. The drawing discloses in figure 1 a longitudinal section of a hydraulic transmission according to the present invention, in an embodiment as axial piston pump and axial piston motor and having axial oil distribution to the motor part, figure 2 discloses a corresponding section of another embodiment of the present invention, likewise having an axial piston pump and an axial piston motor, however with radial oil distribution, and figure 3 discloses schematically a block diagram of a third embodiment. A hydraulic motor 4 having adjustable displacement volume is manufactured according to known principles, such as having an motor according to the principle of axial pistons or the principle or radial pistons. An motor shaft 3 functions as the outgoing shaft, whereas the equipment to be driven may be connected to this free end. On the opposite end of the outgoing s shaft is arranged a cylinder block 2 of a hydraulic axial piston pump (swash plate pump) rotatably journalled. The cylinder block 2 of the pump is driven by an input shaft 11. The pump substan¬ tially is made according to known principles, whereby the swash plate 1 is secured to and following the motor shaft. Figure 2 o discloses another embodiment where the pump comprises double pistons and two swash plates 1 are secured to the motor shaft 3. The oil volume flow from the pump will, in such an embodiment, be proportional with the difference of the drive speed between input and output shafts. Additionally the torque s of the input shaft 11 is transferred directly to the output shaft 3. The swash plate or plates 1 of the pump may be fixedly secured or the inclination angle or angles may be adjustable, preferably from the outside of the transmission. The swash plate 9 of the motor is fixedly secured in o relation to the input shaft 11 and the motor shaft 3 and the angle may be adjusted from outside the transmission. The pump delivers pressurized oil to the motor and receives return oil from the motor through a rotating oil distributor 8 and in relation to shafts 3 and 11 stationary oil 5 distributor 7. The rotating oil distributor 8 may be shaped as a ring rotating together with the motor shaft 3 (figure 1), or the oil channels may be provided through the motor shaft 3 in such a way that it functions as a rotating oil distributor (figure 2) . To ensure good sealing of the rotating oil distribu- tor 8 against the motor shaft 3 in the embodiment according to figure 2, the area with the oil distributor may have a truncated shape. The rotating oil distributor 8 comprises sealing surfaces against the cylinder block of the pump as well as against the stationary oil distributor 7. The stationary oil distributor 7 additionally comprises sealing surfaces against the hydraulic motor 4 for supply of pressurized oil and receipt of return oil. A suitable feed pump having a valve assembly is prefer- ably adapted to deliver oil at a selected pressure to the return side of the oil circuit. The feed pump and valve assembly simultaneously enables the possibility of bypass (stop of the output shaft), soft starting and overload securement, as well as sufficient flow for cooling, filtering and venting. The pressure of the supply pump may be sufficient to press out the pistons 5, 6 of the pump as well as of the motor, or the pistons may be forced out by springs. Pistons 5, 6 are guided in cylinders 10, 12 respectively in the cylinder blocks 2, 4 of the pump and the motor. Figure 3 discloses a further embodiment of the inven¬ tion as axial piston pump and axial piston motor where the hydraulic pump 13 has adjustable or not adjustable displacement volume and a hydraulic motor 15 has a adjustable displacement volume as described above. The input shaft 11 is connected with the cylinder block of the pump 13 journalled in the housing of the pump, whereby the housing of the pump being supported rotating in the transmission housing 14. The swash plate of the pump 13 is connected with the pump housing which again is connected with an intermediate shaft 16. The intermediate shaft 16 and the cylinder block of the motor 15 are connected with the output shaft 3. Furthermore the swash plate of the motor 15 is fixed to the transmission housing and adjustable. A fixed oil distributor 7 is chematically discloses in the drawing.

Claims: Patent claims s 1. Continuously adjustable hydraulic transmission comprising a hydraulic pump and a hydraulic motor, the displace¬ ment volume of the motor being adjustable from the outside of the transmission, CHARACTERIZED IN the pump being an axial piston pump or a radial piston pump, the stator (1) of the pump being o movable in relation to parts connected with the input shaft of the pump, the stator (1) of the pump being connected with and rotating with the output shaft (4) of the motor and hydraulic fluid being transferred between the pump and the motor through an oil distributor being stationary in relation to the motor. 2. Transmission according to previous claim, CHARAC¬ TERIZED IN the swash plate (1) of the pump being connected with the output shaft (3), the cylinder block (2) of the pump being connected with the input shaft (11), the cylinder block (2) of the pump being rotatably supported on the output shaft (3 ) , the rotor of the motor being connected with the output shaft (3) and the hydraulic fluid being transferred between the cylinders of the pump and the motor through channels in the cylinder blocks (2, 4), through an oil distributor (8) connected with the output shaft and through an oil distributor (7) being stationary in relation to the pump and the motor. 3. Transmission according to previous claims, CHARAC¬ TERIZED IN the displacement volume of the pump being adjustable from outside the transmission, manually, automatically or remotely. 4. Transmission according to previous claims, CHARAC¬ TERIZED IN the displacement volume of the motor being adjustable from outside the transmission manually, automatically or remotely. 5. Transmission according to previous claims, CHARAC- TERIZED IN the return side of the fluid circuit being supplied with pressurized fluid from a feed pump and the pistons (5, 6) of the pump and the motor being returned in the corresponding cylinders by the pressure on the return side of the circuit. 6. Transmission according to claim 5, CHARACTERIZED IN the feed pump supplying pressurized fluid through the stationary oil distributor (7). 7. Transmission according to previous claims, CHARAC¬ TERIZED IN the output shaft (3) being supported in the input s shaft (11).

Inventors: TENFJORD JOHAN, TENFJORD, JOHAN
Applicants: TENFJORD JOHAN, TENKRAFT A S, TENFJORD, JOHAN, TENKRAFT A/S
Application year: 1996
Main classification: F16H39
IPC codes: F16H39