MAIN BEARING DEVICE FOR MOTOR OF BENT AXIS TYPE AXIAL PISTON PUMP

Abstract: This invention relates to a main bearing device for the motor of a bent axis type axial piston pump constructed in such a fashion that the sum of a thrust load and a radial load acting on first and second bearings disposed in a tandem arrangement in the axial direction of the main bearing device, or in other words, a total load, becomes uniform. The main bearing device has a first bearing (8) and a second bearing (9) that are disposed in the tandem arrangement through inner and outer wheel seats (10, 11) and a gap of from 10 to 30 mu is defined between the inner end surface (12) of the outer wheel (8b) of the first bearing (8) and the inner end surface (13) of the outer wheel seat.

Description: The present invention relates to a main bearing device for a bent axis type axis piston pump/motor according to the preamble of claim 1. In general, for example, as shown in Fig. 1, a bent axis type axial piston pump/motor has been heretofore constructed such that a shaft 2 is rotatingly borne through a main bearing device 3 to a housing 1, that a central support pintle 5 supported by a cylinder block 4 and tilted at a predetermined tilt angle ϑ with respect to the shaft 2 is tiltably connected to the shaft 2, and that pistons 7 slidingly inserted into cylinder holes 6, respectively, of the cylinder block 4 is tiltably connected to the shaft 2. In such a bent axis type axial piston pump/motor as described above, since the pistons 7 are connected to the shaft 2 at a position where the pistons 7 are offset in the outer peripheral side of the axis of the shaft 2, and further the pistons 7 are tilted with respect to the axis of the shaft 2, the pistons 7 are thrusted against the shaft 2 by a force F₁ in the direction shown by an arrow due to a hydraulic pressure within the cylinder holes 6. As a result, a thrust load and a radial load are acting on the shaft 2. Therefore, the main bearing device 3 is constructed such that first and second bearings 8 and 9 of a conical roller type are disposed in a tandem arrangement, and that both the thrust load and the radial load can be received continuously by connecting inner races 8a, 9a of the first and the second bearings 8, 9 and outer races 8b, 9b of the first and the second bearings 8, 9 through an inner wheel seat 10 and an outer wheel seat 11, respectively. In such a main bearing device 3 as described above, the thrust load Fa is equally acting to the first and the second bearings 8, 9 as indicated by an arrow of dotted line in Fig. 2, but the radial load Fr₁ acting on the first bearing 8 becomes larger than the radial load Fr₂ acting on the second bearing 9, because the radial loads are acting tiltingly on positions, respectively, which are offset from the axis of each roller. Therefore, the total load acting on the first bearing 8 becomes larger than that acting on the second bearings 9. As a result, the life time of the first bearing becomes short, and hence the life time of the main bearing devices becomes short. The US-A 2,404,615 discloses a bent axis type axial piston pump/motor according to the present kind having a main bearing device comprising two ball bearings. The ball bearings are mounted such that they only transfer a radial load from the main shaft to a housing. The present invention has been made in view of the above-mentioned circumstances, and has for its aim to provide a main bearing device for a bent axis type axial piston pump/motor in which the sum of thrust loads and radial loads acting on a first bearing and a second bearing, respectively, disposed in a tandem arrangement in the axial direction of the main bearing device, that is, respective total loads are equally acting on the first and the second bearings. To comply with this object, the main bearing device according to the present invention is characterized by the characterizing features of claim 1. In order to achieve the above-described aim, according to another aspect of the present invention, there is provided a main bearing device for a bent axis type axial piston pump/motor characterized in that the gap set forth in the above-mentioned main aspect is defined within the range of 10 to 30 µ. As is clearly understood from the foregoing description, it is an advantage of the present invention having the above-mentioned aspect that the life of the main bearing device as a whole can last for a longer time, because respective sums, that is, respective total loads of the thrust load and the radial load acting on the first bearing and of those acting on the second bearing are kept in equal to each other. It can be possible for anyone skilled in the art to understand the above and other object, features and advantages of the present invention under the fact that those are manifested with reference to the following detailed description and accompanying drawings in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic, entirely sectional view of the prior art bent axis type axial piston pump/motor; Fig. 2 is a partial sectional view of the prior art main bearing device; Fig. 3 is a partial sectional view of an embodiment of the present invention; Fig. 4 is a graph showing the relationship between respective lives of a first bearing and a second bearing and an interval of gap formed at an outer wheel seat; and Fig. 5 is a partial sectional view of another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, some of preferred embodiments of the present invention are explained in detail with reference to Figs. 3 to 5. But, since the structure of a general bent axis type axial piston pump/motor is as described hereinabove and moreover generally well known, the description thereof is omitted here. As shown in Fig. 3, a gap α is defined between the inner side end surface 12 of an outer race 8b of a first bearing 8 and the inner side end surface 13 of an outer wheel seat 11. An interval of the gap α is set within the range of 10 to 30 µ, but it is varied according to a hydraulic pressure applied to a piston 7. By defining thus, since in the initial stages a thrust load Fa is transmitted from an inner race 8a of the first bearing 8 to an outer race 9b of a second bearing 9 via, in turn, an inner wheel seat 10, an inner race 9a of the second bearing 9 and a conical roller 9c as indicated by an arrow of perforated line in Fig. 3, the thrust load does not act on a conical roller 8c of the first bearing 8. In the meantime, when the thrust load Fa is increased to a certain degree, the inner race 9a and the outer race 9b are moved in the axial direction thereof so that the inner side end surface 12 of the outer race 8b of the first bearing 8 is allowed to pressurizedly abut against the inner side end surface 13 of the outer wheel seat 11. As a result, the thrust load acts on the conical roller 8c also. Stating in brief, since the thrust load acts on the first bearing 8 after a certain degree of the thrust load acts on the second bearing 9 as a previous load, the thrust load acting on the first bearing 8 is decreased less than that acting on the second bearing 9 by an amount of the previous load. Therefore, even if respective magnitudes of radial loads Fr₁ and Fr₂ acting on the first bearing and the second bearing, respectively, are different from each other, it can be possible to equalize respective total loads acting on the first bearing 8 and the second bearing 9, respectively, to each other. Fig. 4 is a graph showing the relationship betweeen an interval α of gap formed at the outer wheel seat of the main bearing device shown in Fig. 3 and the load acting on the bearings (lives of the bearings) which is obtained by a simulation calculation with using a computer while taking the main shaft bearing structure of a bent axis type axial piston pump/motor and the axial rigidity into consideration. It is clearly understood from the graph that respective total loads acting on the first and the second bearings 8, 9, respectively can be equal to each other, thereby extending the total life time of the main bearing device to the maximum extent. Further, as shown in Fig. 5, it has been clear that the same results as described above are also obtained in angular-contact type bearings in which balls 8d, 9d are used in the first and the second bearings 8, 9.

Claims: A main bearing device for a bent axis type axial piston pump/motor having a main shaft (2) rotatably arranged within a housing (1) thereof, a cylinder block (4) connected through a tiltable central support pintle (5) to a proximal end of the main shaft (2) at a predetermined tilt angle with respect to the main shaft, and a plurality of tiltable pistons (7) slidingly inserted into a plurality of cylinder holes (6) formed in the cylinder block (4) so as to extend in the axial direction thereof, respectively, their respective leading ends being connected to the proximal end of the main shaft (2); said main bearing device comprising a first bearing (8) and a second bearing (9) both adapted to rotatably support said main shaft (2) against both of thrusting load and radial load, wherein in order to bear the main shaft (2) rotatably within the housing (1), these first and second bearings (8,9) are disposed in a tandem arrangement in the axial direction of the main bearing device between the housing (1) and the main shaft (2) through inner and outer wheel seats (10,11) provided between the first and second bearings (8,9), said main bearing device being characterized in that a gap is defined between the inner side end surface (12) of the outer race (8b) of the first bearing (8) and the inner side end surface (13) of the outer wheel seat (11) the width of said gap being such that the outer race (8b) of the first bearing (8) and the outer wheel seat (11) contact each other at a certain degree of thrusting load, whereby a thrusting load is exerted to both the first bearing (8) and the second bearing (9). A main bearing device for a bent axis type axial piston pump/motor as claimed in claim 1, characterized in that said gap is defined within the range of 10 to 30 µ.

Inventors: ARIMOTO TAKEO, NAGAHARA KAZUYOSHI, OGATA TAKASHI, ARIMOTO, TAKEO, NAGAHARA, KAZUYOSHI, OGATA, TAKASHI
Applicants: KOMATSU MFG CO LTD, NTN TOYO BEARING CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO, NTN CORPORATION
Application year: 1989
Main classification: F03C1
IPC codes: F03C1, F04B53, F04B1, F16C19