Virtual Bleed Off increases the efficiency of excavators

Flexible drive and control system for the construction machinery market of tomorrow

  • Electrohydraulic system solution as a basis for automation
  • Quick adaptation to new requirements
  • Modular hardware and software for flexible use

Increasingly restrictive statutory regulations for exhaust and noise emissions, the growing variety of attachments, and increasing energy efficiency requirements put manufacturers and suppliers of tracked and wheeled excavators under greater pressure. In order to support manufacturers in these challenges, Bosch Rexroth has further advanced its Virtual Bleed Off (VBO) flexible drive and control system. It opens up new possibilities for increasing efficiency and paves the way for the electronification –and consequently automation – of tracked and wheeled excavators.

On the market, there is a growing demand for customized and flexible solutions. Machine manufacturers try to meet these requirements with a high degree of variance and technical compromises, and sometimes reach the limits of optimization. It is therefore all the more important to rely on a flexible and expandable technological basis.

For this purpose, Bosch Rexroth has continued to develop its VBO system, first introduced in 2009. “Virtual Bleed Off” is a closed-center excavator system in which the losses, previously incurred in the neutral line, are entirely prevented. At the same time, the excavator operator still has the same agreeable load sensitivity as with an open-center system. In addition, the VBO 2nd Gen system offers three key components: the A28VO variable double pump, the RCS main control valve, and the RC electrical control unit with VBO 2nd Gen software.

Variable pump in a compact design

The limit values for permissible exhaust gas emissions are being made more stringent around the world, and can only be complied by excavator manufacturers with elaborate exhaust gas after-treatment and additional components. Installation space is becoming a scarce commodity. That is why Rexroth developed the A28VO variable double pump, the most compact tandem pump in its class. It is a variable double pump in swashplate design, with significantly increased dynamics and accuracy, thanks to optimized actuating forces on the pump controller and on the adjustment system.

Flexibly configurable for each function

The new RCS main control valve is a closed-center design that can be installed both vertically and horizontally. The RCS concept is based on two parallel, independent pump channels with low pressure losses. The functional axes can be flexibly configured in terms of their quantity, sequence, and size in order to exactly fulfill the required function. The RCS valve platform is available in three nominal sizes and can be used for excavators with a weight of approx. 20 up to 400 tons.

In order to be able to offer OEMs utmost flexibility for differentiating their machines in the market, the VBO 2nd generation uses a modular valve kit that can be adjusted individually to the task in the field. Moreover, it is possible to configure relief valves, anti-drift valves, Rexroth eValves or load-holding valves, plugs, and hydraulic or electrohydraulic control covers for each functional axis.

Modular software concept

VBO 2nd Gen software is running on Series 40, the latest generation of Rexroth control units. The open software architecture approach offers freedom in the use of the software modules and flexibility regarding the selection of the control units. This basis offers the option to freely program the flow distribution to the various consumers in order to meet the requirements of the end-user with utmost precision. Therefore modular and individually customizable software packages are made available. The OEM has the choice to use the complete VBO software solution or the modular software kit.

Simplified commissioning, diagnosis and maintenance

Thanks to the simplified system architecture, numerous hoses and pipes can be omitted. This reduces installation effort and expense. In combination with the new pump generation, the electrohydraulic version of the RCS reduces the cost-intensive optimization process for series introduction and simplifies diagnosis and maintenance in the field. Test series show that the new VBO attains the best results in its class in terms of energy efficiency, controllability, and productivity.

In comparison with Electrical Positive Control (EPC), the energy-efficiency (filled excavator buckets per liter of fuel consumed) is improved by a factor in the double-digit percentage range. VBO also optimally utilizes the power of modern diesel engines under dynamic load conditions, which is discernible, for example, based on smaller and shorter speed reductions. Thanks to its modular hardware and software structure, VBO 2nd Gen is already fit for future market requirements, starting with the electrification and hybridization of assistance systems, automated movement control, on to the autonomous work execution.


Second generation Virtual Bleed Off can be seen live at the bauma trade fair in Munich, from April 8 – 14, 2019, and is now immediately available.

Source: Bosch Press News


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