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, Bosch Rexroth was the only one pump manufacturer 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.
However, the Terex engineers found 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 pump based, as far as possible, on standard off-the-shelf components to avoid future delivery and availability problems.
"We have known Bosch Rexroth for many years, and we have always been very happy with the service offered by the company and by its products," says 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. 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 design developed by Bosch Rexroth comprises a pump from the company's standard range, used in conjunction with a rectifier block that ensures the pump itself receives a uni-directional drive, irrespective of the direction of motion of the vehicle.
Susan MacDonald says: "The TA35 and TA40 are completely new vehicles, 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."
Main hydraulic system
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 design based on two pumps mounted back-to-back and operating in tandem. Not only did this produce a very compact assembly, but the back-to-back arrangement also meant that only one PTO point was needed on the gearbox instead of the two employed 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 that had been adopted in earlier designs.
"Bosch Rexroth has given us excellent service," says Susan MacDonald. "And we have undoubtedly benefited both from the company's expertise, and from its huge range of well-proven products. We are continuing to work with the Bosch Rexroth team who are currently evaluating solutions that have the potential for delivering even more cost savings while maintaining the outstanding performance and reliability for which the company's products, like ours, are well known."