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Pump provides simple answer for complex hydraulics

When Terex Equipment, one of the UK's leading developers and manufacturers of off-highway earth-moving equipment, needed a hydraulic pump to supply emergency power for the steering in its new TA35 and TA40 ranges of articulated dump trucks, the requirement seemed deceptively simple. But, as it turned out, only one pump manufacturer - Bosch Rexroth - was able to supply the right product for the job. Large off-highway vehicles are very dependent on hydraulic power in particular, without it they are impossible to steer.

To ensure that steering control can be maintained even if the main hydraulic power pack fails while the vehicle is in motion, an auxiliary pump, driven from the wheels, is fitted to provide a source of emergency hydraulic power for the steering systems.

The Terex engineers found, however, that sourcing a suitable pump for its new dump truck ranges presented a considerable challenge.

A major complication was that the pump had to operate correctly irrespective of whether the vehicle was moving forward or backward.

There was also very limited space on the vehicle to accommodate the pump.

Finally, Terex wanted a solution based, as far as possible, on standard off-the-shelf components to avoid future delivery and availability problems.

'We've known Bosch Rexroth for many years, and we've always been very happy with service offered by the company and by its products', said Susan MacDonald, Terex Product Manager for Articulated Vehicles: 'so we naturally asked the company to quote for the pumps'.

'We also approached several other suppliers, with the objective of having a number of alternative solutions from which to choose'.

'However, Bosch Rexroth was the only company to offer a suitable solution', she continued.

'Not only would its pump fit within our very tight space envelope, it would also couple easily and directly with the spline of the power take off (PTO) point on our gearbox'.

The solution developed by Bosch Rexroth comprises a pump from the company's standard range, used in conjunction with a rectifier block, which ensures that the pump itself receives a unidirectional drive, irrespective of the direction of motion of the vehicle.

'The TA35 and TA40 are completely new vehicles', said Susan MacDonald: 'so there were many unknowns in the early stages of the project'.

'However, we received exceptional support from Bosch Rexroth throughout our design work'.

'The company even flew in engineers from Germany to assist with commissioning and with the validation of our prototype vehicle'.

Because of the flexibility, expertise and enthusiasm it demonstrated in addressing the challenges which Terex faced with its auxiliary steering pumps, Bosch Rexroth was subsequently asked to work with Terex engineers in developing a design for the main hydraulic system of the new vehicles.

Once again, lack of space was a major concern.

This lead the Bosch Rexroth team to propose an innovative solution based on the use of two pumps mounted back-to-back and operating in tandem.

Not only did this produce a very compact assembly, the back-to-back arrangement also meant that only one PTO point was needed on the gearbox instead of two for the arrangement used by Terex on earlier concepts.

A further benefit of the new arrangement is that the pumps incorporate load sensing, which makes their operation much more efficient than the open-loop pumps which had been adopted in earlier designs.

'Bosch Rexroth has given us excellent service', said Susan MacDonald: 'and we have undoubtedly benefited both from the company's expertise, and from its huge range of well proven products'.

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