JP2013047557A - Thrust bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thrust bearing, in which inner and outer rings are prevented from being damaged to achieve a long service life.SOLUTION: The thrust bearing includes: the inner ring having a track surface in the outer peripheral surface thereof and configured to be rotatable; the outer ring having a track surface in the inner peripheral surface thereof and fixed to a housing; a plurality of rolling elements disposed on both track surfaces of the inner ring and the outer ring so as to be rotatable; and a retainer for retaining the plurality of rolling elements in a circumferential direction at regular intervals. In the thrust bearing, at least the inner ring is formed of high cleanliness steel and subjected to special heat treatment.

Description

  The present invention relates to a thrust bearing used in a hydraulic continuously variable transmission, a hydraulic pump, a hydraulic motor, and the like.

  In a hydraulic continuously variable transmission, a hydraulic pump, a hydraulic motor, and the like, a thrust bearing is incorporated as a bearing. For example, in an agricultural machine such as a combine, a tractor, a rice planting machine, and a lawn mower, a shift from a gear mission system to a hydraulic continuously variable transmission is progressing. In such a hydraulic continuously variable transmission, a thrust bearing is employed in a portion that receives piston pressure when converting the rotational force of the shaft into hydraulic pressure or when converting the hydraulic pressure into rotational force of the shaft (for example, Patent Document 1).

JP 2003-194183 A

  In recent years, along with miniaturization of hydraulic continuously variable transmissions, thrust bearings incorporated therein have also been miniaturized and used under high load conditions. For this reason, in a thrust bearing, the raceway surfaces of the inner and outer rings, in particular, the raceway surface of the inner ring to which a load is applied, is likely to be peeled off, and the inner ring or the inner and outer rings may be damaged in some cases.

  Further, not only the hydraulic continuously variable transmission but also a hydraulic pump and a hydraulic motor have the same tendency.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a long-life thrust bearing that prevents damage to the inner and outer rings.

  In order to achieve the above object, the present invention has a raceway surface on the outer peripheral surface, a rotatable inner ring, an outer ring having a raceway surface on the inner peripheral surface and fixed to the housing, a raceway surface of the inner ring, and In a thrust bearing comprising a plurality of rolling elements that are rotatably arranged on a raceway surface of an outer ring and a cage that holds the plurality of rolling elements at equal intervals in the circumferential direction, at least the inner ring has a high cleanliness. Provided is a thrust bearing made of steel and subjected to special heat treatment.

  In the thrust bearing of the present invention, at least the inner ring, preferably the inner and outer rings, are made of high cleanliness steel and further subjected to special heat treatment, and have higher strength than the general material SUJ2, etc. The effect of suppressing is high, damage is suppressed, and long life is achieved.

It is sectional drawing which shows an example of a hydraulic continuously variable transmission. It is sectional drawing which shows an example of a thrust bearing. 6 is a graph showing the results of Test 1. 6 is a graph showing the results of Test 2.

  Hereinafter, the thrust bearing of the present invention will be described in detail by exemplifying a hydraulic continuously variable transmission.

  FIG. 1 is a cross-sectional view showing an example of a hydraulic continuously variable transmission. The hydraulic continuously variable transmission 30 is a variable capacity that converts a rotational driving force transmitted from an engine (not shown) to an input shaft 31 into an oil pressure. A pump 32 and a variable displacement motor 41 that returns the hydraulic pressure to the rotational driving force and transmits it to the output shaft 40 are provided, and the rotational driving force transmitted to the input shaft 31 is not used for the forward driving force and the backward driving force. It changes to a stage and outputs from the output shaft 40, or stops this output.

  The variable displacement pump 32 includes a cylinder block 33 that rotates integrally with the input shaft 31, a nose piston 35 that is reciprocated in the piston chamber 34, and a guide surface of the guide block 36. And a swash plate 37 rotating along the axis. The variable displacement pump 32 rotates the swash plate 37 to change the reciprocating stroke of the nose piston 35 and change the amount of oil discharged from the piston chamber 34. The thrust bearing 10 is disposed on the swash plate 37 at a position where the thrust bearing 10 contacts the tip of the nose piston 35, and the thrust bearing 10 rotates together with the swash plate 37.

  As shown in FIG. 2, the thrust bearing 10 includes an inner ring 12 having an inner ring raceway surface 11 and an outer ring 14 having an outer ring raceway surface 13 facing each other, and between the inner ring raceway surface 11 and the outer ring raceway surface 13, A plurality of balls 15 which are rolling elements are arranged so as to be freely rollable. Furthermore, the thrust bearing 10 includes a cage 16 that holds a plurality of balls 15 at equal intervals in the circumferential direction.

  The inner ring 12 is rotatable, and the tip of the nose piston 35 contacts the end surface 21 opposite to the surface on which the inner ring raceway surface 11 is formed. On the other hand, the outer ring 14 is fixed to the swash plate 37. Therefore, the thrust bearing 10 receives a high load received from the nose piston 35 by the inner ring 12 and escapes to the outer ring 14 side fixed to the swash plate 37 via the ball 15.

  In the present invention, at least the inner ring 12, preferably the inner ring 12 and the outer ring 14, are made of high cleanliness steel and further subjected to special heat treatment. High cleanliness steel has a low oxygen content, and the inclusions in the steel also have a small particle size, so that it is possible to suppress the occurrence of internal origin separation on the raceway surface. The smaller the oxygen content, the better, and more preferably 6 ppm or less. Moreover, the particle size of inclusions is preferably as small as possible, and more preferably 30 μm or less.

  Further, in the special heat treatment, carburizing treatment, nitriding treatment or carbonitriding treatment is performed to increase the hardness of the high cleanliness steel. Surface-origin peeling can be suppressed by curing by special heat treatment.

  In addition, although the ball | bowl 15 can use general SUJ2 steel etc. as it is, it is preferable to give a special heat processing and harden. Further, it may be made of high cleanliness steel.

  Moreover, it can also be set as the thrust roller bearing which replaced the rolling element with the ball | bowl 15 and used the roller.

  Furthermore, since the inner ring 12 receives a high load from the nose piston 35 as described above, it can be made thicker than the outer ring 14.

  The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

(Test 1)
An inner ring and an outer ring of a bearing “6206” manufactured by Nippon Seiko Co., Ltd. were produced using high cleanliness steel, and designated as test bearing A. Further, the same bearing composed of the inner and outer rings made of SUJ2 was designated as test bearing B. The test bearings A and B were made of SUJ2 and subjected to special heat treatment, and the same type of lubricant was enclosed. Then, the test bearings A and B were rotated at a ratio (P / C) of the equivalent load P to the basic dynamic load rating C: 0.71, and at a speed of 3900 rpm, and the lifetimes were compared. The result is shown in FIG. 3, and by using high cleanliness steel, peeling of the raceway surface is suppressed and the life is extended five times or more.

(Test 2)
An inner ring and an outer ring of a bearing “6206” manufactured by NSK Ltd. were made of SUJ2, and further subjected to special heat treatment (carbonitriding treatment) to obtain a Vickers hardness of 540 Hv, and a test bearing C was obtained. Further, the bearing comprising the inner and outer rings made of SUJ2 was designated as test bearing D. The test bearings C and D were made of SUJ2 and subjected to special heat treatment, and sealed with the same type of lubricant. Then, the test bearings C and D were rotated at a contamination condition (particle diameter 74 to 147 μm), the ratio of the equivalent load P to the basic dynamic load rating C (P / C): 0.32, and the speed: 3000 rpm. Lifespan was compared. The result is shown in FIG. 4, and by performing special heat treatment, peeling of the raceway surface is suppressed, and the life is extended more than twice.

  From Test 1 and Test 2 described above, it can be seen that the inner ring and the outer ring are made of high cleanliness steel and subjected to special heat treatment to suppress the occurrence of peeling and to have a long life.

DESCRIPTION OF SYMBOLS 10 Thrust bearing 12 Inner ring 14 Outer ring 15 Ball 16 Cage 30 Hydraulic continuously variable transmission

Claims (1)

A raceway surface is provided on the outer circumferential surface, a rotatable inner ring, a raceway surface on the inner circumference surface, an outer ring fixed to the housing, a raceway surface of the inner ring, and a raceway surface of the outer ring are arranged to be rotatable. In a thrust bearing comprising a plurality of rolling elements and a cage that holds the plurality of rolling elements at equal intervals over the circumferential direction,
A thrust bearing, wherein at least the inner ring is made of high cleanliness steel and is subjected to special heat treatment.

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