**4.4 No use of special systems**

Split torque gearboxes are used in order to reduce the weight of the gear system, so the simplest option is assembly without special systems for regulating torque split. Several authors support this option, for example, Kish (1993a, 1993b), who concluded from tests that acceptable values can be achieved without using any special torque split system, simply by

Fig. 14. Gear assembly using an elastomeric torsional isolator (Kish & Webb, 1992)

vibration and less noise during operation.

elements to achieve the same effect as the quill shaft.

arranged on each side of the gear teeth flange element (38)".

**4.3.3 Quill shafts based on spring elements** 

**4.4 No use of special systems** 

This assembly was tested in the Advanced Rotorcraft Transmission project (Kish, 1993a), by comparing it with conventional quill shafts. It was concluded that the torque split was excellent and also had other advantages such as lower transmission of force to supports, less

The main problem with using elastomers to achieve proper torque split is their degradation over time, especially when used in high-torque gear transmissions where temperatures are high and there is contact with oil. Some authors therefore propose the use of metallic

Some authors propose the use of metallic elements to achieve the same effect as the quill shaft. One such system (Gmirya & Vinayak, 2004) (Fig. 15) is based on achieving this effect by using *"at least one spring element (30) placed between and structurally connecting the gear shaft (32) and the outer ring of gear teeth (34). The gear shaft (32) has flange elements (36) that project radially outboard of the shaft. The ring of gear teeth (34), similarly, has a flange element (38) that projects radially inward towards the gear shaft".* In this case, a pair of spring elements (30) is

This assembly is designed in such a way that the spring elements absorb torsional deflection

Split torque gearboxes are used in order to reduce the weight of the gear system, so the simplest option is assembly without special systems for regulating torque split. Several authors support this option, for example, Kish (1993a, 1993b), who concluded from tests that acceptable values can be achieved without using any special torque split system, simply by

between the gears, thereby ensuring proportional torque split between paths.

Fig. 15. Load sharing gear in combination with a double helical pinion (Gmirya & Vinayak, 2004)

ensuring manufacturing according to strict tolerances and correct assembly. Krantz (1996) proposed the use of the clocking angle as a design parameter to achieve adequate torque split between paths. This author has studied the effects of gearshaft twisting and bending, and also tooth bending, Hertzian deformations within bearings and the impact of bearing support movement on load sharing.

Krantz (1996) defined the clocking angle as β and described the assembly prepared for measurement (Fig. 16): *"The output gear is fixed from rotating and a nominal counter-clockwise* 

Fig. 16. Assembly for measurement of the clocking angle

Split Torque Gearboxes: Requirements, Performance and Applications 71

The numerical relationships among the teeth number used in the text are listed below. C1, C1', C2, C2', C3 and C3' are functionS of n, a whole number which represents the pitch

<sup>2</sup> <sup>2</sup>

<sup>2</sup> <sup>2</sup>

2 2

2 2

1 4

*z z <sup>A</sup> z z*

3 4

2 4

3 4 *z z <sup>B</sup> z z*

4

1 3

4 3

2 3

4 3

4 3

1

1

2

1

1

1

' *z z <sup>B</sup> z z*

' *z z <sup>A</sup> z z*

1 13 14 *a zz zz* (14)

*b zz zz* 1 13 14 2 (15)

1 23 24 *c zz zz* (16)

*d zz zz* 1 23 24 2 (17)

1 13 23 *e zz zz* (18)

*f*1 13 23 2 *zz zz* (19)

1 14 24 *g zz zz* (20)

*h zz zz* 1 14 24 2 (21)

(22)

(23)

(25)

(26)

*z n <sup>C</sup> z z* (24)

α angle formed by the lines between centres, between wheels 3 4 1 β angle formed by the lines between centres, between wheels 3 2 4 γ angle formed by the lines between centres, between wheels 2 3 1 δ angle formed by the lines between centres, between wheels 1 4 2 n pitch difference between the two sides of the curvilinear quadrilateral

zi number of teeth in wheel i

difference in the curvilinear quadrilateral.

**7. Appendix** 

*torque is applied to the input pinion so that the gear teeth come into contact. When all the gear teeth for both power paths come into contact, then the clocking angle β is, by definition, equal to zero. If the teeth of one power path are not in contact, then the clocking angle β is equal to the angle that the firststage gear would have to be rotated relative to the second-stage pinion to bring all the teeth into contact"*.

The tests show that suitable (47 per cent/53 per cent) load sharing can be achieved merely by taking into account the clocking angle and ensuring proper machining and assembly.

This research into the clocking angle has been followed up by subsequent authors (Parker & Lin, 2004) who have studied how contact between different planetary gears is sequenced.
