1. Field of the Invention
The invention relates to an axial piston displacement machine for converting hydraulic work into mechanical work or vice-versa having a plurality of hydraulic cylinders which are positioned about a joint longitudinal rotation axis and which define parallel axes, pistons being movably arranged in the cylinders and connected with a swivellable plate, an adjusting device for setting the swiveling angle of the plate, a sleeve which is non-turnable with respect to the cylinders arranged outside of the plate, and engagement means for transmitting a torque between the plate and the sleeve arranged on the plate and on the sleeve.
2. The Prior Art
Axial piston displacement machines of the aforementioned kind are capable of converting the energy of a pressurized hydraulic medium into mechanical work in the form of a rotational movement. Motors of this kind are used for various machines such as forklifts or backhoes. In the opposite case, such a machine will also allow pumping operation by pressurizing a hydraulic medium through the drive of the machine.
Machines of the aforementioned kind are referred to in practice as swash plate machines. A relevant feature of swash plate design is that the pistons rotate about a common longitudinal axis with the driven speed. The reciprocating movement of the cylinders which are arranged in this piston is achieved in such a way that the p-stons rest on a swivellable plate. The stroke of the piston depends on the angle about which the plate is swiveled. In this way it is possible to provide a very simple control of the output and speed of such a machine.
From WO 86/00376, an axial piston displacement motor is known which is arranged in the above-described manner. Slide blocks are attached in an articulated manner on the faces of the individual pistons which are hydrostatically held on a swivellable, but non-rotating plate. During the working stroke a lateral force is exerted on each piston by inclining the plate, which force exercises a torque on the common cylinder body in which all pistons are arranged. In this way the cylinder body is made to rotate. The respective torque can be tapped through a shaft on which the cylinder body is wedged up, with the shaft extending through the swash plate.
Such a known apparatus has a number of disadvantages. Firstly, the swiveling angle of the swash plate is limited to a maximum value of approx. 18.degree. for constructional reasons. On the one hand, this is due to the fact that the space must be kept free for the penetrating driven shaft. On the other hand, lateral forces, which during the working strokes of the pistons are exerted on the same, cause moments of tilt which strongly stress the piston guides. It is obvious that these moments of tilt will rise strongly with increasing angle of inclination of the swash plate. This also limits the angle of inclination. On the other hand, the efficiency of such a machine strongly depends on the angle of inclination of the swash plate. One can observe a strong decrease in the efficiency at smaller angles. At an angle of 4.degree. or less, self-Locking can occur, i.e. the efficiency is zero in motor operation.
U.S. Pat. No. 765,434 discloses an axial piston displacement machine which is provided with rotatable hydraulic cylinders whose pistons are in connection with a swivellable plate. The swiveling angle of the plate can be set through an adjusting device. The transmission of the torque from the swivellable plate to the piston unit occurs through a toothing which is arranged on the circumference of the piston unit and in the form of conical rods projecting forwardly in the axial direction. The cylinder unit is held on a shaft and is rigidly connected with this shaft which extends through the plate. The torque is introduced through this shaft during pumping operation and is tapped through this shaft during motor operation. For this reason the permitted swiveling range of the plate is Limited. Moreover, the diameter of the cylinder unit must not be below a certain minimum value.
WO 96/02735 shows a similar solution in which the drive and driven shaft penetrates the plate. In this case too the swiveling angle of the plate is limited for space reasons. In the solution as described in GB 1 106 486 A, the swiveling angle of the plate cannot be operatively changed. Merely a minor adjusting possibility has been provided for. In this solution the central shaft also penetrates the plate.
The above-described known solutions have in common that the torque which is to be introduced into the plate during pumping operation or which is to be tapped from the plate during motor operation is conducted outwardly through a central shaft. The central shaft is either connected with the plate per se through a kind of cardanic mounting or the torque is guided through the cylinder unit which is in non-positive connection by way of an outer sleeve or the like. Both solutions have in common that the centrally arranged shaft limits the swiveling angle of the plate.