DOUBLE ROW BALL BEARING

Description

[0001] The invention relates to a double-row ball bearing which is suitable for transmitting radial forces as well as axial forces in both directions.

[0002] One possible design of a double-row ball bearing is described, for example, in DE 10 2008 061 832 A1. In this case, it is a bearing sealed on both sides, with a free space between the rows of rolling elements. In contrast, in a double-row ball bearing known from DE 10 2015 213 970 A1, the rows of balls are arranged such that the axial distance between the rows of balls is smaller than the ball diameter.

[0003] DE 25 18 129 A1 discloses a thin-walled, non-cutting race for a single-row ball bearing. The race can perform a slight adjustment movement relative to a seating surface to compensate for shaft deflections or shaft misalignment.

[0004] DE 10 2006 034 729 B3 discloses a double-row spherical roller or ball bearing. This bearing, intended particularly for steering spindles of motor vehicles, is intended to provide a low-backlash bearing arrangement, with both the inner and outer ring raceways formed by sheet metal.

[0005] Patent document 10 2006 028 200 A1 describes a self-aligning roller bearing designed as a roller bearing. The outer ring of the roller bearing is formed as a single piece and is arranged essentially free of play within a spherical inner surface of a housing. The inner surface of the housing is coated to provide a sliding contact surface with very low friction. Alternatively, the outer surface of the outer ring can be coated. Possible coatings include phosphating and an ELGO Glide coating.

[0006] DE 10 2014 221 949 B3 describes a self-aligning angular contact ball bearing designed as a tandem bearing and thus suitable for transmitting axial forces in exactly one direction. The contact angle axes of two rows of rolling elements are aligned parallel to each other.

[0007] Heavy-duty bearing arrangements capable of compensating for misalignment are often designed as double-row spherical roller bearings. Examples in this context are DE 10 2012 220 261 A1, DE 10 2012 224 148 A1, and DE 10 2011 078 840 A1. A possible cage for a spherical roller bearing is described in detail, for example, in DE 10 2017 129 773 A1.

[0008] Spherical roller bearings are capable of absorbing radial and axial forces and are used in a wide variety of stationary and mobile applications, including aircraft. A cage for a double-row spherical roller bearing intended for use in an aircraft is disclosed, for example, in EP 2 952 760 B1.

[0009] Helicopters with a single main rotor are known to be equipped with a tail rotor to compensate for torque. Examples in this context include documents DE 1 118 017 A and EP 3 023 328 B1.

[0010] DE 10 2010 053 671 A1 describes a multi-row rolling bearing whose outer ring has an at least partially spherical outer surface, which can interact or interacts with an at least partially spherical inner surface of a housing. One bearing row is formed by an angular contact ball bearing row.

[0011] The tail rotor generates a torque around the helicopter's vertical axis, or yaw axis. Adjusting the angle of attack of the tail rotor blades also changes the torque generated by the tail rotor. This adjustment can be achieved by the pilot, particularly using pedals. The pedal action is converted into an adjustment of the angle of attack of at least two of the tail rotor blades via a linear drive.

[0012] In principle, a helicopter's tail rotor can be driven in any way. An electric drive for a tail rotor is described, for example, in EP 2 412 630 B1.

[0013] US 1 262 208 A, FR 427 930 A and US 1 364 675 A each describe a double-row ball bearing with an outer ring which is tiltably mounted in a housing part and which has two annular, spaced-apart, convexly curved surface sections as sliding surfaces which describe one and the same spherical surface.

[0014] EP 3 753 850 A1 describes an anti-torque rotor for a helicopter, wherein a ball bearing is used in a tail rotor having a blade adjustment.

[0015] The invention is based on the object of specifying a rolling bearing which is further developed compared to the cited prior art and which is particularly suitable for use in a tail rotor of a helicopter having a blade adjustment.

[0016] This object is achieved according to the invention by a double-row ball bearing having the features of claim 1. The ball bearing comprises an inner ring and an outer ring as bearing rings, as well as rolling elements, i.e. balls, rolling between the bearing rings and intended for transmitting axial forces between the bearing rings in both directions, wherein the outer ring is mounted in a housing part with limited tiltability.

[0017] The tiltable mounting of the outer ring in the housing part allows for compensation of misalignments between the inner ring and outer ring on the one hand, and the housing part on the other. In particular, the tilting bearing, which consists of the outer ring and the housing part as plain bearing components, is capable of accommodating tilting of ± 2° or more. A tilting moment can be transferred from the inner ring via the rolling elements to the outer ring without significantly tilting the inner ring relative to the outer ring. Tilting thus occurs exclusively, or almost exclusively, between the outer ring and the housing part.

[0018] According to one possible embodiment, the plain bearing comprises a first pair of sliding surfaces, formed by the outer ring and the housing part, respectively, and a second pair of sliding surfaces, formed in a corresponding manner. Each pair of sliding surfaces represents an overall annular plain bearing section, with the plain bearing sections spaced apart from one another and—provided there is no tilting—arranged mirror-symmetrically to a center plane of the ball bearing. Each plain bearing section can absorb radial forces as well as axial forces in exactly one direction.

[0019] Sliding linings of the tilting bearing can be located on the outer ring or in the housing part that contacts the outer ring. Ideal kinematics of the tilting bearing can be achieved in any case if the two sliding surfaces of the outer ring, which are designed as annular, spaced-apart, convexly curved surface sections, lie on one and the same imaginary spherical surface. The same applies to the inner surface of the housing part, insofar as this is designed as a sliding surface. If a tilting movement between the outer ring and the housing part is to be counteracted by a resistance that increases with increasing tilt angle, then according to an optional design, the areas of the otherwise spherical inner surface of the housing part that are furthest apart from one another in the axial direction and serve as a sliding surface can have a shape deviating from a spherical shape.

[0020] According to an advantageous development, a lubricant chamber is formed between the two convexly curved sliding surfaces of the outer ring, an outer peripheral surface of the outer ring located between these sliding surfaces in the axial direction of the ball bearing, and an inner peripheral surface of the housing part, which is filled in particular with grease as the lubricant. The outer peripheral surface of the outer ring, insofar as it lies between the sliding surfaces, can be cylindrical. Likewise, the inner peripheral surface of the housing part delimiting the lubricant chamber can be at least partially cylindrical.

[0021] According to the invention, the housing part designed as a plain bearing component is a housing ring which, during normal operation, i.e. when the inner ring can rotate freely relative to the outer ring, is coupled in a rotationally fixed manner to the outer ring.

[0022] According to the invention, a coupling between the outer ring and the housing ring which is fixed against rotation and at the same time allows limited tilting is produced by a predetermined breaking element, in particular in the form of a pin, wherein the predetermined breaking element is designed to release a relative rotation between the outer ring and the housing part when a maximum torque acting between the inner ring and the outer ring is exceeded.

[0023] This means that the tilting bearing functions as a rotary plain bearing as soon as the rolling bearing fails or becomes too stiff. Especially in such a case, i.e., during emergency operation, a lubricant reservoir located between a cylindrical outer peripheral surface of the outer ring and an inner peripheral surface of the housing part is advantageous.

[0024] The double-row ball bearing, for example, is designed as an O-arrangement. Alternatively, an X-arrangement is also possible. In any case, the double-row ball bearing can be sealed on both sides. The lubricant used in the interior of the rolling bearing is not necessarily the same as the lubricant used to lubricate the emergency plain bearing. In particular, oil can be used for rolling bearing lubrication.

[0025] The bearing rings can be constructed in one or more parts. In typical designs, the outer ring is the rotating bearing ring and the inner ring is the non-rotating bearing ring. Designs are also possible in which the inner ring represents the rotating bearing ring, or both bearing rings rotate.

[0026] An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. In the drawing: Fig. 1a double-row ball bearing in a sectional view.

[0027] A rolling bearing 1 designed as a double-row ball bearing is part of a blade adjustment system, designated overall by 10, of a helicopter's tail rotor. The rolling bearing 1 has an inner ring 2 and an outer ring 3 as bearing rings, wherein the inner ring 2 in this case is formed in two parts, namely from a first inner ring part 4 and an identically shaped inner ring part 5 arranged as a mirror image of the first inner ring part. Each inner ring part 4, 5 provides an inner ring raceway 9 on which balls roll as rolling elements 6. The balls 6, which also contact outer ring raceways 14, are thus arranged in the form of two rows of rolling elements 7, 8. A center plane ME, which is placed between the inner ring parts 4, 5, is located centrally between the rows of rolling elements 7, 8. Pressure lines through the centers of the rolling elements 6 are designated DL. Overall, the rolling bearing 1 is a double-row bearing in an O arrangement.The outer ring 3, which, unlike the inner ring 2, is a single-piece design, has an annular center web 15, to which the outer ring raceways 14 are connected. The rolling elements 6 are guided in a cage 11. Seals located on both end faces of the rolling bearing 1 are designated 12 and 13.

[0028] The outer ring 3 is accommodated in a housing part 16, which is designed as a housing ring. Between the housing ring 16 and the outer ring 3, a tilting bearing in the form of a plain bearing 17 is formed. Figure 1 In the non-tilted position of the rolling bearing 1 shown, the annular components 2, 3, 16 have a uniform center axis MA. If the inner ring 2 and with it the outer ring 3 are tilted relative to the housing part 16, which results in an alignment error, a Figure 1Exaggerated angle α between an axis FL and the central axis MA. The tilting by the angle α is completely absorbed by the tilting bearing 17 and can be up to 2°.

[0029] During proper operation of the blade adjustment system 10, the outer ring 3 rotates together with the housing ring 16, while the inner ring 2 represents a stationary bearing ring. The adjustment of a tail rotor blade is achieved by moving the inner ring 2 in the adjustment direction VR, i.e., along the center axis MA. This inevitably also moves the outer ring 3 and the housing ring 16 rotating with it. Any slight tilting between the outer ring 3 and the housing ring 16 is irrelevant during this adjustment process thanks to the tilting bearing 17.

[0030] The tilting bearing 17 comprises two annular sliding surfaces 18, 19, which are provided by the outer ring 3 and define a spherical shape SP. The two spaced-apart sliding surfaces 18, 19 border the end faces of the outer ring 3 and are arranged mirror-symmetrically to the center plane ME. Between the two sliding surfaces 18, 19 is a substantially cylindrical outer peripheral surface 20 of the outer ring 3. The outer peripheral surface 20 is concentrically surrounded by an inner peripheral surface 21 of the housing ring 16. The sliding bearing sections designated 22, 23 border the inner peripheral surface 21 and are each formed on the one hand by one of the sliding surfaces 18, 19 and on the other hand by a sliding lining 24 on the housing ring 16. A lubricant chamber 25 filled with grease is formed between the outer peripheral surface 20 of the outer ring 3 and the inner peripheral surface 21 of the housing part 16.

[0031] As long as the outer ring 3 is freely rotatable relative to the inner ring 2, the plain bearing 17 functions exclusively as a tilting bearing. Each rotation of the outer ring 3 about the central axis MA is accompanied by a corresponding rotation of the housing ring 16 about the central axis MA. For this purpose, a pin 26 is firmly inserted into a bore 27 in the outer ring 3. The pin 26 simultaneously engages an opening 28 located in the housing part 16.

[0032] As from Figure 1As can be seen, the pin 26 in the opening 28 has considerable play in the longitudinal direction of the central axis MA. This play enables the described tilting of up to 2° between the outer ring 3 and the housing ring 16. In the orthogonal direction, i.e. in the circumferential direction of the outer ring 3 and the housing ring 16, there is no or only minimal play of the pin 26. Relative rotation between the outer ring 3 and the housing ring 16 is thus excluded. However, if excessive forces occur between the outer ring 3 and the housing part 16, which in extreme cases can be attributable to a blockage between the inner ring 2 and the outer ring 3, the pin 26 breaks, thus constituting a predetermined breaking element. At this moment, rotation between the outer ring 3 and the housing ring 16 is released, which means that the plain bearing 17 is converted into a rotary bearing.In this state, the lubricant reservoir in the lubricant chamber 25 contributes significantly to heat dissipation. The kinematics of the blade adjustment mechanism 10 remain intact even during this emergency function of the plain bearing 17, which otherwise serves only as a tilting bearing. List of reference symbols

[0033] 1Rolling bearing, double-row ball bearing 2Inner ring 3Outer ring 4Inner ring part 5Inner ring part 6Rolling element, ball 7Rolling element row 8Rolling element row 9Inner ring raceway 10Blade adjustment 11Cage 12Seal 13Seal 14Outer ring raceway 15Center web 16Housing part, housing ring 17Plain bearing, tilting bearing 18Sliding surface of the outer ring 19Sliding surface of the outer ring 20Outer peripheral surface 21Concave inner peripheral surface 22Plain bearing section 23Plain bearing section 24Sliding lining 25Lubricant chamber 26Pin, predetermined breaking element 27Bore in the outer ring 28Opening in the housing part αAngle DLPressure line FLAxis of the inner ring with misalignment MACenter axis MECenter plane SPspherical shape VRAdjustment direction

Claims

1. A double-row ball bearing, having an inner ring (2) and an outer ring (3) as bearing rings (2, 3), and having balls (6) that roll between the bearing rings (2, 3) for transmitting axial forces between the bearing rings (2, 3) in both directions, wherein the outer ring (3) is tiltably mounted in a housing part (16), wherein the outer ring (3) has two annular, convexly curved surface sections spaced apart from one another as sliding surfaces (18, 19), which describe one and the same spherical surface (SP), characterised in that the housing part (16) is designed as a housing ring coupled in a rotationally fixed manner to the outer ring (3) during normal operation, i.e. when the inner ring (2) can be freely rotated relative to the outer ring (3), wherein, in order to produce the rotationally fixed coupling between the outer ring (3) and the housing ring (2), which at the same time allows for limited tilting, a predetermined breaking element (26), in particular in the form of a pin, is provided, which is designed to release a relative rotation between the outer ring (3) and the housing part (16) when a maximum torque acting between the inner ring (2) and the outer ring (3) is exceeded.

2. The ball bearing according to claim 1, characterised in that a tilting bearing designed as a sliding bearing (17) is formed by the outer ring (3) and the housing part (16).

3. The ball bearing according to claim 2, characterised in that a lubricant chamber (25) is formed between the two convexly curved sliding surfaces (18, 19) of the outer ring (3), an outer circumferential surface (20) of the outer ring (3) lying in the axial direction between said sliding surfaces (18, 19) and an inner circumferential surface (21) of the housing part (16).

4. The ball bearing according to claim 3, characterised in that the inner circumferential surface (21) of the housing part (16) delimiting the lubricant chamber (25) is at least partially cylindrical.

5. The ball bearing according to any one of claims 1 to 4, characterised in that the mounting of the outer ring (3) in the housing part (16) allows a tilting of at least ± 2° between the outer ring (3) and the housing part (16).

6. The ball bearing according to any one of claims 1 to 5, characterised in that said ball bearing is designed as a double-row bearing in an O-arrangement.

7. A use of a double-row ball bearing comprising an inner ring (2) and an outer ring (3) and balls (6) which roll between the bearing rings (2, 3) for transmitting axial forces between the bearing rings (2, 3) in both directions, wherein the outer ring (3) is tiltably mounted in a housing part (16), wherein the outer ring (3) has two annular, convexly curved surface sections spaced apart from one another as sliding surfaces (18, 19), which describe one and the same spherical surface (SP), in a helicopter tail rotor having a blade feathering system (10).