Elliott Manufacturing - The Science of Flexible Transmission

The Science of Flexible Transmission

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e-novation™: Flex Shaft Steering

The Elliott steering shaft features a high-strength, bidirectional, flexible design approach using a flexible shaft instead of a universal joint (U-joint) (Figure 5). This system is unique compared to a conventional U-joint design in that it achieves constant velocity operation at operational loads. A flexible shaft is considered to have true constant velocity because the input is rotating at the same speed and direction as the output along a common axis of rotation. Conversely, U-joints cannot provide constant velocity application due to their construction technique and rotational geometry. Our flexible shaft design is used in many vehicle applications, notably for John Deere in current vehicles, example pictured in Figure 6. The steering shaft design offers exceptional torsional strength, in excess of 270Nm in either direction. It sustains continuous torque loads of at least 135 Nm and temporary loads up to 225 N. As such, this design ensure reliable, smooth and easy operation.The steering shaft will tilt, as required, without any effect on steering resolution. Flexible shaft steering design is cost effective to maintain over the long-term, as there is no U-joint to lubricate and/or repair. Steering Column Housing Structure Upper and Lower Tube Housings made from AISI 1020 Carbon Steel. Both tubes utilize noticeably smaller diameters than other designs by simply using a Flexible Steering Shaft, which requires far less clearance to operate successfully. Pivot Cradle made from ASTM A36 stamped Carbon Steel. This Cradle is made much more compact by utilizing the Flexible Steering Shaft design and eliminating the inefficient and costly U-joint. Tilt Bracket made from ASTM A36 Stamped Carbon Steel. A rugged and proven design, with a simplified tilt mechanism interface. Heavy-duty tilt mechanism designed to use only four parts (from seven): Handle - adjustable, made from zinc die cast. Lock Shaft - made from “Stress proof” carbon steel. Lock - Bolt ASTM A29 Steel. Spacer Washer - ASTM A29 Steel. Finish: (all parts unless noted) Yellow Iridescent Coversion Chromate Zinc Plating for superior corrosion protection. Using the smaller tube housings in conjunction with the more compact pivot cradle enables Elliott to reduce the size, and hence weight of the metal steering column structure, thus reducing the overall footprint of the assembly. Moreover, this also enables us to minimize the size of the console panels, providing maximum leg space and visibility for the operator.
		Figure 5. Flexible steering shaft.


		Figure 6. John Deere 4000 series tractor using flexible steering shaft.


		Figure 7. Steering shaft assembly..

The Elliott flexible steering system achieves:

True constant velocity operation for superior steering “resolution” resulting in smoother, easier steering.
Exceptional torsional strength.
Economical to maintain over long-term (no U-joint to lubricate).
Protected from corrosion.
Smaller overall footprint, reduced weight, improved driver sight lines.
Proven design, as verified by many OEM customers.

Steering Shaft Design Verification

The Elliott flexible steering shaft complies with the following standards when installed as part of a complete steering system:

EN1726-1 Safety of Industrial Trucks
EN1459:1999 Safety of Industrial Trucks
ISO 5010:2007 Earth moving machinery – rubber tyred machinery – steering requirement.

Current test data and performance experience:

Environmental Performance

Test
Steering shaft assemblies shall withstand 96-hours of salt spray testing, 75-90% white corrosion and 0% red corrosion.

Experience
Flexible steering shafts have been used by OEM’s for a number of years in harsh conditions without problem or failure.

Dynamic Cycling Performance & Fatigue performance

Test
Dynamic cycling performance is as follows (Table A):

Table A

LOAD	TEST CYCLES
15 Nm (132.89 in.lbs.)	70,000
35 Nm (309.98 in.lbs.)	40,000
80 Nm (708.53 in.lbs.)	20,000
160 Nm (1,417.06 in.lbs.)	250

Experience
Flexible steering shafts have been used by OEM’s for a number of years in harsh operating conditions without fatigue failure.