A PISTON ASSEMBLY OF A HYDRAULIC RADIAL PISTON-TYPE MACHINE

Abstract: The invention relates to a piston assembly of a hydraulic radial piston-type machine, an essential characteristic thereof being the arrangement of a rolling element (2) in a piston head. This means that the portion of contact surface of the rolling element (2) lying close to a crown (8) of the piston (1) is always arranged in the area between the piston crown (8) and a step (7) extending radially inwards and dividing the head (4) of the piston (1) from the guide portion (5).

Description: A piston assembly of a hydraulic radial piston-type machine The invention relates to a piston assembly of a hydraulic radial piston-type machine, comprising a cylindrical body to which is from the side lying opposite to the piston crown connected a laterally trimmed guide portion in which there is arranged and form-locked a rolling member. The above mentioned piston assembly is known (manufacturers, e.g. Poclain, France or Rexroth, Germany). With these known piston-type machines a rolling cylinder is incorporated into the piston in a way that the portion of a contact surface of the rolling cylinder, which lies close to the piston crown, is always arranged in the area of the laterally trimmed guide portion. The result thereof is a relatively great distance between the axis of the rolling cylinder and the piston crown causing relatively high lateral loads to the wall of the piston and the cylinder, respectively, when operating said hydraulic machine with piston assemblies of the above mentioned kind. The consequence thereof is relatively high wear and tear of the piston and the cylinder and relatively small hydraulic and mechanical efficiency. The aim of the invention is to create a piston assembly that will suppress the drawbacks of known solutions. According to the invention the aim as set above is solved in that a rolling element is arranged into the piston crown. This essentially means that the portion of a contact surface of the rolling element which lies close to the piston crown is always arranged as close to the piston crown as possible. According to a preferred embodiment of the invention said portion is always arranged in the piston crown with a circular cross- section. More precisely, said portion lies in the area between the piston crown and a step extending radially inward and dividing piston crown from a guide portion. The above-mentioned arrangement of the rolling element according to the invention is attained by a two-part piston design comprising a cylindrical body and a shell-like cover. The latter is mounted onto a cylindrical portion of the piston body and form- locked and force-locked therewith. With such an embodiment of the piston assembly that portion of the contact surface of the rolling element which lies close to the piston crown is arranged between the piston crown and an end piston surface abutting the step. According to the invention it is also provided that the piston has a one-part design. In that case the cylindrical body and the shell-like cover are joined into a single solid unit. However, also with such an embodiment that portion of the contact surface of the rolling element which lies close to the piston crown is arranged between the piston crown and the step which separates the piston crown from the guide portion. The piston assembly according to the invention may also comprise a bearing bush. The invention will further be described in connection with the preferred embodiment, reference being made to the accompanying drawings, in which Fig. 1 shows an exploded view of a piston assembly according to the invention; Fig. 2 shows a cross-section of the piston assembly of Fig. 1 across a rolling element, and Fig. 3 shows a cross-section of the piston assembly of Fig. 1 along a rolling element. A piston assembly according to the invention comprises a piston 1 and a rolling element 2 form-locked therein and rotating in a bearing bush 3 locked in the piston 1. The latter has a two-part form comprising a body 1' and a cover 1" mutually connected in form-locking and force-locking principle. The piston body V is essentially formed as a right cylinder having a cylinder portion 4 and a guide portion 5, both approximately of the same length. In order to mount the cover 1" onto the cylindrical portion 4 said portion is suitably formed with a smaller outside diameter than a piston itself while the guide portion 5 has the same diameter as the piston 1. The guide portion 5 has diametrically opposite sides laterally trimmed whereby guide faces 6, 6' are formed extending from the lower edge of the piston 1 to a step 7 running radially inwards, said step dividing portions 4 and 5. The cylindrical portion 4 is terminated with a face 8 used as a crown of the piston 1 when the latter operates. The piston body 1' is in the direction rectangular to the faces 6, 6' penetrated by a cylindrical through bore 9 reaching the cylindrical portion 4 and in which there is ex- changeably arranged a bearing bush 3. Said bush is protected against turning by means of two teeth 10, 10' integral with the piston body 1' and situated under the center line of the rolling element 2. The rolling element 2, the bearing bush 3 and the guide portion 5 are suitably formed with the same length. The piston cover 1" is essentially shaped as a conical shell the inner surface thereof being adapted to the outside surface of the cylindrical portion 4 of the piston body 1' so as to fit same as much as possible when both parts of the piston are assembled. The face 8 of the cylindrical portion 4 and the end surface of the piston cover 1" when assembled are aligned with each other while the other end surface of the piston cover 1" rests against the step 7. Furthermore, the piston cover 1" is formed with a radially extending annular groove 11 intended to carry a piston ring known per se and therefore not shown. The through bore 9 in the piston body 1' is formed in a manner that with the erected piston assembly the top portion of the rolling element 2, i.e. that plane area which lies close to the crown 8 of the piston 1, is always placed in the area of the piston 1 with the circular cross-section, i.e. outside and above the area of the guide portion 5, respectively. In essence this means that said top portion of the contact surface of the rolling element 2 always lies between the crown 8 and the step 7. The piston assembly according to the invention is erected in a manner that first the bearing bush 3 is inserted into the piston body 1' and into said bush is placed the rolling element 2. Thereafter, the piston cover 1" is mounted onto the piston body 1' from the side of the piston crown 8, said piston cover 1" locked against turning in a manner known per se, e.g. by welding, cementing, soldering, forging, or similar, onto the cylindrical portion 4. The piston 1 can also have a one-part form, which practically means that the piston body 1' and the piston cover 1" are joined into a single solid unit. The bearing bush 3, neither, is necessary since the rolling element 2 easily rests directly against the through bore 9 provided on the guide faces 6, 6'. Provided that the piston 1 is formed as a single solid unit and without the bearing bush 3, the rolling element 2 is placed into the bore 9 in a manner that the teeth 10, 10' in respect to the piston body V are forced apart in radial direction to the limit of elasticity, enabling the introduction of the rolling element 2. When the teeth 10, 10' return to their initial position they hold the rolling element 2 and prevent it from falling out of the seating. With the piston assembly according to the invention comprising either a one-part or a two-part form there is attained reducing of the dimensions of the piston assembly and of the volume abrasion of both the piston and the cylinder. The hydraulic and the mechanical efficiency are improved both in operation and at starting the hydraulic machine.

Claims: Claims: 1. A piston assembly of a hydraulic radial piston-type machine, comprising a cylindrical body to which is from the side lying opposite to the piston crown connected a laterally trimmed guide portion in which there is arranged and form-locked a rolling member, characterized in that a body (T) of the piston (1) comprises a cylindrical portion (4) and a guide portion (5) provided with a through bore (9) in which there is arranged and form-locked a rolling element (2), and in that the portion of contact surface of the rolling element (2) lying close to a crown (8) of the piston (1) is arranged in the area between the piston crown (8) and a step (7) extending radially inwards and dividing the cylindrical portion (4) of the piston (1) from the guide portion (5). 2. A piston assembly according to claim 1, characterized in that the piston (1) has a one-part form comprising a cylindrical body (1') and a shell-like cover (1") mounted onto the cylindrical portion (4) of the body (1'), said body (1') and said cover (1") being mutually interconnected in form-locking and force-locking manner. 3. A piston assembly according to claim 1 or 2, characterized in that in the cylindrical body (!') there is arranged a bearing bush (3).

Inventors: MANFREDA JURIJ, MANFREDA, JURIJ
Applicants: MANFREDA JURIJ, MANFREDA, JURIJ
Application year: 1997
Main classification: F16J1
IPC codes: F01B1, F04B1, F04B53, F16J1