033-13 Lohr am Main, 2013-04-10

Start-Stop for construction machines

start-stop function

During idle periods of construction machines the hydraulic start-stop function by Bosch Rexroth reduces fuel consumption to zero.

Bosch Rexroth applies automotive approach to hydraulics

- Energy storage provides power reserve

- Reductions in fuel consumption for applications with high idle time

- Atlas Weyhausen presents wheel loader with optional start-stop at bauma 2013 in Munich

Bosch Rexroth is presenting a hydraulic start-stop solution for construction machinery at bauma 2013 in Munich. Together with new hydrostatic drives and hybrid solutions, the system makes it possible to meet TIER 4 emissions standards. At the same time, the ease of operation and work efficiency of wheel loaders and tippers, for instance, is increased. This will enable manufacturers to meet customer demand for fuel-efficient, yet high-performing machinery while at the same time fulfilling ever stricter emissions standards.

Bosch has developed a number of technologies to improve the efficiency of the internal combustion engine. One of these is start-stop technology, which significantly reduces fuel consumption and has become a standard feature in many new vehicles. While the starter systems that have become so wide-spread in automotive technology are not available for mobile work machines, Bosch Rexroth has taken up the idea of start-stop technology and applied it to hydraulics. In so doing, Rexroth development engineers had to consider that off-highway machines not only drive, they mainly work very hard. Hence, they must have enough power to effectively dig, lift, or carry. Only if no energy is required for the machine’s driving and work functions can the internal combustion engine be turned off – providing there is a sufficient power reserve for a hydraulic start.

The hydraulic fly wheel system (HFW), which always operates in the open circuit, builds up the required power reserve. HFW comprises Rexroth components (axial piston pump, control block, hydraulic accumulator, and control unit). Ii is connected to the travel drive or working hydraulics only via basic machinery components such as a tank, filter, and cooling system. The HFW system briefly gathers energy and makes it available to the machine later on as needed, for instance to provide a boost, support the diesel engine in the event of a power peak, or to power a start-stop function.

As a result, energy is applied in a much more efficient manner. First, the axial piston unit picks up torque at the combustion engine shaft. The hydraulic oil flow generated is fed to an accumulator, where pressure and thus the amount of stored energy increase accordingly. If the accumulator is unloaded, the axial piston unit serves as a hydraulic motor – a special characteristic of several mooring-capable Rexroth components – and converts the oil flow back into energy for the combustion engine shaft.

This concept is the force behind the new start-stop solution. Here, the electronics assess whether enough pressure is available to restart the diesel aggregate once it has been switched off. If the internal combustion engine is off, the electronics evaluate the consumer’s potential energy needs. If the travel drive or work hydraulics require energy, the start-stop system immediately restarts the diesel engine with energy stored earlier on. The engine speed needed for travel and working functions is reached practically instantaneously with no time lag.

The start-stop function is also possible without the additional pump/motor unit required for the HFW approach. Here, the only prerequisite is a mooring version of the working hydraulics pump already available. This mooring pump can also serve as a hydraulic motor that can restart the diesel engine if needed.

This is exactly the solution that Atlas Weyhausen has implemented together with Bosch Rexroth in the 4.4 t wheel loader AR 60. Technical background information about the Hydraulic Fly Wheel, including the start-stop system can be seen on the Bosch Rexroth booth, number 319/414 in Hall A4.

Economical, precise, safe, and energy efficient: drive and control technology from Bosch Rexroth moves machines and systems of any size. The company bundles global application experience in the market segments of Mobile Applications, Machinery Applications and Engineering, Factory Automation, and Renewable Energies to develop innovative components as well as tailored system solutions and services. Bosch Rexroth offers its customers hydraulics, electric drives and controls, pneumatics, gear technology, and linear motion and assembly technology all from one source. With locations in over 80 countries, more than 37,500 associates generated sales revenue of approximately 6.5 billion euros in 2012.

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The Bosch Group is a leading global supplier of technology and services, active in the fields of automotive technology, energy and building technology, industrial technology, and consumer goods. According to preliminary figures, more than 306,000 associates generated sales of 52.3 billion euros in 2012. The Bosch Group comprises Robert Bosch GmbH and its more than 350 subsidiaries and regional companies in some 60 countries. If its sales and service partners are included, then Bosch is represented in roughly 150 countries. This worldwide development, manufacturing, and sales network is the foundation for further growth. Bosch spent some 4.5 billion euros for research and development in 2012, and applied for over 4,700 patents worldwide. The Bosch Group’s products and services are designed to fascinate, and to improve the quality of life by providing solutions which are both innovative and beneficial. In this way, the company offers technology worldwide that is “Invented for life.”

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Susanne Herzlieb
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Phone: +49 9352 18-1573