GB2563210A

GB2563210A - A gear box

Info

Publication number: GB2563210A
Application number: GB1708898.0A
Authority: GB
Inventors: Ramshaw Andrew
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2017-06-05
Filing date: 2017-06-05
Publication date: 2018-12-12
Also published as: GB201708898D0

Abstract

A gear box comprises a pinion gear 21 having a core 25 arranged centrally of a wheel portion 26 which meshes with a crown gear 24. The core has a first axis (C-C) about which the wheel portion rotates. A drive shaft 22 has a second axis aligned with the first axis and is mounted to the core to drive the pinion gear. A solitary bearing 27 in which the core is arranged to rotate, is fixedly mounted to a supporting structure and the solitary bearing has a double outer race 28. The solitary bearing may be position at the drive shaft side of the pinion gear with the opposite end of the drive gear being free from constraint. The inner race of the solitary bearing may be integrally formed with the core or it may be formed from a different material from the core.

Description

A GEAR BOX

The present disclosure concerns a gear box. For example, but without limitation, the assembly may comprise part of an accessory gear box in a gas turbine engine.

Crown and pinion gear arrangements are well known. The crown gear may be a linear gear that the pinion gear, which is circular, is meshed with. Alternatively the crown gear may be a second circular gear arranged to rotate on an axis which is at an angle to the pinion gear’s axis of rotation. The pinion gear is driven in rotation so as to move the crown gear. One known application of such arrangements is in the aerospace industry, for example in the accessory gear box of an aircraft.

Figure 1 shows a prior known pinion and crown gear box assembly. As shown, the assembly comprises a pinion gear 1 mounted to an end of a shaft 2. The shaft 2 and pinion gear 1 are arranged to rotate about shaft centre line C. The pinion gear 1 meshes with a crown gear 4. Pinion gear 1 comprises a centrally located core 5 from which the wheel 6 of the pinion gear 1 extends. At a shaft end, the core 5 is mounted for rotation on the shaft 2 by a primary bearing 7 which in turn is mounted in a casing 8. At an opposite end, the core 5 is mounted for rotation in a secondary bearing 9 mounted in a dedicated support structure 3. The secondary bearing 9 and support structure 3 serve to resist deflection in the alignment between the core mounting portion 5 and shaft 2 (i.e. away from the centre line C) due to high mesh loads occurring at the interface between the pinion gear 1 and the crown 4. It will be appreciated that due to the radial distance between the core mounting portion 5 and the interface where the wheel 6 meshes with the crown 4 that at high loads, there is a tendency for the core 5 to be pushed out of alignment with the axis C-C. In the shown arrangement, such loads are resisted by the inclusion of the dedicated support structure 3 in which the pinion is mounted by means of the secondary bearing 9.

In the context of bearings, the term “setting” indicates the amount of end play (axial clearance) or preload in a bearing. “Preloading” involves a measure of axial interference between rolling elements and races of the bearing so as to resist axial movement. A moderate preload is commonly used in pinion and crown applications to increase rigidity of highly stressed pinion components that might otherwise be adversely affected by excessive deflection and misalignment of the pinion. A tradeoff is that an excessive preload can drastically reduce bearing fatigue life or cause high temperatures that may result in bearing wear and damage.

The burden of setting bearings is often left to assembly workers in the absence of any special tooling, monitoring or test equipment. Consequently, setting accuracy and consistency is heavily dependent on the assembler’s skill and experience.

In aircraft applications, consistent and accurate product assembly may be critical to reliable and safe performance.

In accordance with the present invention there is provided a gear box comprising; a pinion gear having a core arranged centrally of a wheel portion, the core having a first axis about which the wheel portion is intended to rotate, a crown gear in meshing engagement with the pinion gear, a drive shaft for driving the pinion gear, the drive shaft having a second axis about which, in use, the drive shaft is driven to rotate, the core mounted to the drive shaft with the first axis in alignment with the second axis, a solitary bearing in which the core is arranged to rotate, the solitary bearing, in use, being fixedly mounted to a supporting structure, wherein the solitary bearing has a double outer race.

Optionally the solitary bearing is positioned at a drive shaft facing end of the core, and an opposite end to the drive shaft facing end of the core is free of constraint.

Embodiments of the invention are particularly advantageous where the pinion wheel and crown gear mesh along a plane which intersects the first axis at a non-zero angle a. For example a may be in the range from 15° to 75°, optionally the range from 25° to 65°. Optionally a is less than 55°. Optionally a is greater than 30°.

Multiple benefits derive from the introduction of a solitary double outer-race bearing in place of the axially spaced pair of single race bearings of the prior art. The gear box can be made more compact and lightweight by removal of a second bearing and the associated removal of part of the core of the pinion and the bearing mount and support structure for the second bearing. In aircraft applications this reduced weight can contribute to improved engine efficiency. Since the pinion gear is mounted on just one bearing, it is possible for the double outer-race bearing to be preloaded in advance of assembly as there is no second bearing against which the preload needs to be balanced.

The bearing may, for example, comprise a ball bearing, a roller bearing or a tapered bearing. The bearing race may comprise a different material than the core.

Optionally an inner race of the double outer-race bearing is integrally formed with the core of the pinion gear. In another aspect therefore, the invention comprises a pinion gear assembly for a gear box in accordance with the first aspect, a pinion gear having a core arranged centrally of a wheel portion, the core having a first axis about which the wheel portion is intended to rotate and a solitary bearing having a second axis the core coaxially located in the solitary bearing wherein a wall of the core forms an inner race of the solitary bearing and the solitary bearing has a double outer-race.

The pinion gear assembly may form part of an accessory gear box for a gas turbine engine.

Embodiments of the invention will now be further described with reference to the accompanying drawings in which:

Figure 1 shows a crown and pinion gear arrangement as is known from prior art gear boxes;

Figure 2 shows a crown and pinion gear arrangement of a gear box in accordance with a first embodiment of the invention;

Figure 3 shows a crown and pinion gear arrangement of a gear box in accordance with a second embodiment of the invention;

Figure 4 shows a crown and pinion gear arrangement of a gear box in accordance with a third embodiment of the invention;

Figure 5 shows a crown and pinion gear arrangement of a gear box in accordance with a fourth embodiment of the invention;

Figure 6 shows a crown and pinion gear arrangement of a gear box in accordance with a fifth embodiment of the invention;

Figure 7 shows a gas turbine engine into which a gear box in accordance with the invention may be usefully applied.

As can in Figure 2 a pinion gear 21 is mounted to an end of a shaft 22. The shaft 22 and pinion gear 21 are arranged to rotate about shaft centre line C. The pinion gear 21 meshes with a crown gear 24 along a plane M which is inclined to the shaft centre line C at an angle a. The pinion gear 21 comprises a centrally located core 25 from which the wheel 26 of the pinion gear 21 extends. The core 25 is mounted for rotation on the shaft 22 by means of solitary bearing 27 which in turn is mounted in a casing (not shown) by means of bearing mounts 23. The bearing mounts 23 extend from an outer-race 28 of the bearing 27. As can be seen the outer race 38 is a double outer-race which includes tracks for two sets of balls 29a, 29b. An inner race 30 of the bearing 27 is fixedly mounted to the core 25 which in turn is fixedly mounted to the drive shaft 22.

In further contrast to the arrangement of Figure 1, the core 25 does not extend beyond the rim of the pinion gear wheel 26, since there is no requirement for the secondary bearing and support structure.

Figure 3 shows an alternative embodiment to that of Figure 2. As can be seen in Figure 3 a pinion gear 31 is mounted to an end of a shaft 32. The shaft 32 and pinion gear 31 are arranged to rotate about shaft centre line C. The pinion gear 31 meshes with a crown gear 34 along a plane M which is inclined to the shaft centre line C at an angle a. The pinion gear 31 comprises a centrally located core 35 from which the wheel 36 of the pinion gear 31 extends. The core 35 is mounted for rotation on the shaft 32 by means of solitary bearing 37 which in turn is mounted in a casing (not shown) by means of bearing mounts 33. The bearing mounts 33 extend from an outer-race 38 of the bearing 37. As can be seen the outer race 38 includes tracks for two sets of balls 39a, 39b. An inner race 40 of the bearing 37 is integrally formed with the core 35 which in turn is fixedly mounted to the drive shaft 32.

The arrangement shown in Figure 4 is very similar to that of Figure 2. The same reference numerals have been used for similar components. The arrangement of Figure 4 is distinguished from Figure 2 by the introduction of one or more shims 201 between mounts 23 and a casing 202 in which the bearing, pinion gear and driveshaft are located. The introduction of shims 201 allows for the pinion gear 21 to be optimally aligned and meshed with the crown gear 24. This can accommodate tolerance ranges of components in the assembly. The introduction of shims is made possible by the absence of a secondary bearing 9.

The arrangement shown in Figure 5 is very similar to that of Figure 3. The same reference numerals have been used for similar components. The arrangement of Figure 4 is distinguished from Figure 3 by the addition of a sensor 300 located in a socket provided in the inner race 40. The sensor 300 may, for example, sense rotation speed of the pinion gear 31. In other options, without limitation, the sensor might be a pressure sensor or a temperature sensor. A pick-up 301 for the sensor 300 is received in an aperture of the double outer race 38 and can be electrically connected to a monitoring or control system (not shown). Whilst the pick-up 301 is shown to have a wire for connecting to a monitoring or control system, it is to be understood that the pick-up 301 may alternatively be wirelessly connected to a monitoring or control system.

Whilst the sensor 300 is shown arranged in a radial outer surface of the inner bearing race 40, it should be appreciated that the sensor 300 may alternatively be located in an end surface of the inner bearing race 40.

The arrangement shown in Figure 6 is very similar to that of Figure 2. The same reference numerals have been used for similar components. The arrangement of Figure 6 is distinguished from Figure 2 by the introduction of a cold rolled end 401 of the core 25. In prior known arrangements, it is common to use a nut and threaded washer to secure the bearing inner race 30 to the core 25, such arrangements allow adjustments to accommodate a secondary bearing 9, however the thread torque variances can result in inconsistent product. In the absence of a secondary bearing in the assembly, cold rolling can be applied to an end 401 of the core 25 to clamp the solitary bearing to the core 25 with the bearing precisely pre-set. The pinion gear 21 and bearing 28, 29a, 29b, 30 can then be provided for assembly as a module, reducing variance in performance. The arrangement of Figure 6 may optionally be used in combination with the shims (201) described in relation to Figure 5.

With reference to Figure 7, a gas turbine engine is generally indicated at 100, having a principal and rotational axis 41. The engine 100 comprises, in axial flow series, an air intake 42, a propulsive fan 43, a high-pressure compressor 44, combustion equipment 45, a high-pressure turbine 46, a low-pressure turbine 47 and an exhaust nozzle 48. A nacelle 50 generally surrounds the engine 100 and defines the intake 42.

The gas turbine engine 100 works in the conventional manner so that air entering the intake 42 is accelerated by the fan 43 to produce two air flows: a first air flow into the high-pressure compressor 44 and a second air flow which passes through a bypass duct 51 to provide propulsive thrust. The high-pressure compressor 44 compresses the air flow directed into it before delivering that air to the combustion equipment 45.

In the combustion equipment 45 the air flow is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high and low-pressure turbines 46, 47 before being exhausted through the nozzle 48 to provide additional propulsive thrust. The high 46 and low 47 pressure turbines drive respectively the high pressure compressor 44 and the fan 43, each by suitable interconnecting shaft. A gear box in accordance with the invention may, for example, be mounted to casing 53 between turbine stages.

Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. three) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the invention as defined by the accompanying claims. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

1. A gear box comprising; a pinion gear (21) having a core (25) arranged centrally of a wheel portion (26), the core having a first axis (C-C) about which the wheel portion (26) is intended to rotate, a crown gear (24) in meshing engagement with the pinion gear (21), a drive shaft (22) for driving the pinion gear (21), the drive shaft (22) having a second axis (C-C) about which, in use, the drive shaft (22) is driven to rotate, the core (25) mounted to the drive shaft (22) with the first axis in alignment with the second axis, a solitary bearing (27) in which the core (25) is arranged to rotate, the solitary bearing (27), in use, being fixedly mountable to a supporting structure, wherein the solitary bearing (27) has a double outer race (28).

2. A gear box as claimed in claim 1 wherein the solitary bearing (27) is positioned at a drive shaft facing end of the core (25), and an opposite end to the drive shaft facing end of the core is free of constraint.

3. A gear box as claimed in claim 1 or claim 2 wherein the pinion wheel and crown gear mesh along a plane (M-M) which intersects the first axis (C-C) at a nonzero angle a.

4. A gear box as claimed in any preceding claim wherein a is in the range from 15° to 75°

5. A gear box as claimed in claim 4 wherein a is in the range from 25° to 65°.

6. A gear box as claimed in claim 4 or claim 5 wherein a is less than 55°.

7. A gear box as claimed in claim 4, 5 or 6 wherein a is greater than 30°.

8. A gear box as claimed in any preceding claim wherein the solitary bearing (27; 37) comprises a type selected from; a ball bearing, a roller bearing or a tapered bearing.

9. A gear box as claimed in any preceding claim wherein the bearing race comprises a different material than the core (25;35).

10. A gear box as claimed in any preceding claim wherein an end of the core (25) is cold rolled against the bearing (27) whereby to clamp the bearing (27) in position with respect to the core (25).

11. A gear box as claimed in any of claims 1 to 8 wherein an inner race (40) of the double outer-race bearing (37) is integrally formed with the core (35) of the pinion gear (31).

12. A gear box as claimed in any preceding claim further comprising a socket for receiving a sensor, the socket provided in a radially outer surface of the inner race (30; 40).

13. A gear box as claimed in claim 11 further comprising an aperture for receiving a sensor pick-up (301), the aperture provide in a radial surface of the double outer race.

14. A bear box as claimed in any preceding claim further comprising one or more shims (201) arranged between a mount (23) of the bearing (27) and a casing (202) in which the gear (21), bearing (27) are located.

15. A pinion gear assembly for a gear box in accordance with any preceding claim, the pinion gear (31) having a core (35) arranged centrally of a wheel portion (36), the core (35) having a first axis about which the wheel portion (26) is intended to rotate and a solitary bearing (37) having a second axis the core coaxially located in the solitary bearing (37) wherein a wall of the core (35) forms an inner race (40) of the solitary bearing (37) and the solitary bearing (37) has a double outerrace (38).

16. A pinion gear assembly as claimed in claim 15 further comprising a sensor (300) arranged in a socket provided on a surface of the inner race and a sensor pickup (301) received in an aperture provided in the double outer race.

17. A gas turbine engine comprising an accessory gear box, the accessory gear box comprising a pinion gear (21) having a core (25) arranged centrally of a wheel portion (26), the core having a first axis (C-C) about which the wheel portion (26) is intended to rotate, a crown gear (24) in meshing engagement with the pinion gear (21), a drive shaft (22) for driving the pinion gear (21), the drive shaft (22) having a second axis (C-C) about which, in use, the drive shaft (22) is driven to rotate, the core (25) mounted to the drive shaft (22) with the first axis in alignment with the second axis, a solitary bearing (27) in which the core (25) is arranged to rotate, the solitary bearing (27), in use, being fixedly mounted to a supporting structure, wherein the solitary bearing (27) has a double outer race (28).