Rexroth Takes Aim at Electrification for Off-Highway Vehicles
Highlights of Bosch Rexroth’s 2022 EMPAC product showcase include electrified solutions for heavy machines, new drive systems and upgraded components for greater durability and ease of use.
Bosch Rexroth recently invited SAE Media to attend EMPAC, their Electrified Mobile Product & Application Conference in Schaumburg, Illinois. The show featured many of Rexroth’s latest electrification and software products for industrial and off-highway equipment as well as educational sessions on the direction of the brand moving forward.
Rexroth is endeavoring to work closely with customers to offer products that not only suit their needs, but also provide increased productivity, efficiency and durability. Some of those products highlighted at EMPAC are detailed here.
Electrification through eLION
Rexroth’s eLION is a product range aimed at the electrification of commercial machines. The product line includes electric motor-generators, inverters and accessories as well as gearboxes, hydraulics and software. These components are scalable in various sizes and applications of compact and heavy machines for power ranges from 20 to 200 kW with peak power output of 400 kW.
The eLION range can deliver a nominal torque of up to 1050 Nm (775 lb-ft) and maximum torque of up to 2400 Nm (1770 lb-ft). The motor-generators are available in four sizes with different lengths and winding configurations as well as in a fast or standard speeds. Rexroth states that over 80 configurations are available, and that all components meet ISO 13849. eLION also offers inverters with up to 300 A continuous current and high overload capacity and support DC bus voltages from 400 to 850 V.
Rexroth states that the eLION motor-generators and inverters are very robust and can be used in temperatures ranging from -40 to +100°C (-40 to +212°F). Shock and vibration resistance reportedly is up to 50 g and 10 g, respectively, and both components comply with IP6K9K ingress protection. Production of the eLION components is set to start this year.
“The aim is to use our technology to create a future with higher efficiency, lower noise emissions and less air pollution,” said Matthias Kielbassa, VP of Electrification of Mobile Machines. “We have the right products at the right time and we’re also helping our customers to strengthen their market position with future-viable mobile working machines.”
Also entering production in 2022 as part of Rexroth’s eLION platform is a line of spur gearboxes for use with electric motors. The one- and two-speed gearboxes are installed in the central section of the machine and can drive up to two axles with just one motor. The 1-speed spur gearbox (eGFZ 9100) and the 2-speed shift gearbox (eGFZ 9200) can connect or disconnect an axle for two- or all-wheel drive applications. A lockable center differential is also available for permanent all-wheel drive.
The gearboxes can be installed horizontally or vertically depending on the packaging requirements. Rexroth states that components such as the heat exchanger and oil pump enable both gearboxes to be seamlessly integrated into the existing cooling circuit of an electric driveline. Both gearboxes are equipped with DIN ISO-compliant flanges.
Hydraulics continue to be an important portion of Rexroth’s product portfolio. One of the latest offerings is its open circuit hydraulic architecture that controls hydromechanical functions via software instead of pressure, torque or the swivel angle. The central component behind this system is the eOC pump, which features a swivel angle sensor and pressure sensors to ensure the proper control of the necessary setpoint values for torque, pressure or flow.
The pump reportedly provides millisecond-level accuracy to modulate the pressure in combination with the eOC software. Characteristics such as dynamics and power control can be set, changed and combined via the software for machine optimization and makes it possible to set various control parameters flexibly during operation. Rexroth states that moving hydromechanical control functions to the software means control modes can be individually changed and combined during operation and the pump dynamics can be set variably.
Pressure, torque, flow and the swivel angle are all controlled independently of each other in this system, which means the pump behaves optimally regardless of function. Setpoint values and parameters can reportedly be adjusted via the CAN bus interface to allow additional functions and to adapt machines to meet specific customer requirements and specific tasks. The eOC software constantly adapts the hydraulic power to the available engine torque, which Rexroth claims will increase the overall productivity of the machine.
Rexroth also has upgraded its range of axial piston pumps and added new functions, such as dynamic control of pressure, swivel angle and torque gradients. Rexroth states that this allows the pump to not only reach a specific target value, but also determine the gradients that are needed to achieve this pressure. The net result is smoother and gentler motion, especially at the start of a movement.
Another new function offered by the eOC is auto-calibration. This feature removes the calibration step from the OEM’s end of production line and the system is calibrated cyclically while the machine is operating. The eOC software records specific calibration data when the machine starts, as well as other data whenever the operating conditions allow. The data will account for factors such as aging effects or temperature differences, and automatically adjust the operating parameters.
The system also features a secondary logic system to control the hydraulic motor’s displacement and output torque to achieve the desired rotational speed. Rexroth claims that by moving the control of the hydraulic system into the software, fewer components are needed in the machine and the overall architecture is simpler. For example, travel direction valves and brake valves are no longer needed in this system. Additionally, Rexroth states that the combination of working and travel functions in one hydraulic circuit allows the recovery of hydraulic energy during braking or lowering. This ensures that the optimum use is made of available drive power.
Rexroth also offers an electronic variant of its hydrostatic travel drives. The BODAS-drive eDA is aimed at industrial machines such as wheeled loaders, telescopic handlers and forklifts, but can reportedly be utilized for any application that previously used conventional DA controls. The system consists of a an electrified A4VG drive pump and A6VM hydraulic motor. The nominal pressure of the system is 400 bar (5800 psi) and a maximum pressure of 530 bar (7690 psi). The eDA package also supports the digital conversion of hydrostatic drives with features such as ECO drive, inching, a variable creeping mode, different driving modes and adjustable reversing behavior. It is available either completely pre-programmed or as an open system.
Rexroth states that customers can integrate specific desired features, such as operating functions of the travel drive, working hydraulics or the vehicle’s electrical system. Alternatively, they can also jointly develop them in cooperation with Rexroth. The SRC-eDA electronic control unit serves as the central interface of the software and all components in the BODAS-drive system. The unit can reportedly be freely positioned in the machine and is EN ISO 13849 compliant.
Radial piston motors
Rexroth has expanded its range of direct drives for compact tracked loaders and other tracked vehicles. One of its latest products in this sector, MCR-T, offers up to a 55% increase in maximum torque and a 20% increase in flow capability compared with the existing and dimensionally similar motors. The new design is offered in frame sizes 5, 6 and 10. It features larger bearings that are flushed with case oil as well as new seals to ensure high levels of durability in harsh environments. An integrated flushing valve contributes to increased service life by supporting the cooling of the oil when used in closed hydraulic circuits. The control valve is integrated into the motor, enabling the operator to shift smoothly between travel speeds via the soft-shift mode in both directions of travel.
In high-speed mode the motor runs with a standard reduced displacement of 66%, which is also configurable on request, reducing oil flow in the circuit and improving system efficiency. Additionally, the direct drive design of the MCR-T is said to result in greater efficiency, longer service life and lower noise than typical gearbox-based solutions. The differential pressure of the motor is rated at a maximum of 450 bar (6530 psi) with the MCR8T version achieving an output torque of up to 9,000 Nm (6640 lb-ft). The displacement of the MCR-T product currently ranges from 380 cc to 1,340 cc.
Rexroth has also released the MCR-S motor suited for chain drive applications. The MCR-S features a repositioned parking brake to the body of the motor, integrated two-speed shifting spool, and optimized main port locations. The motor is up to 33% shorter, 41% lighter and reportedly delivers enhanced efficiency without compromising durability. The MCR-S also utilizes low friction properties within the flow passages and rotating elements of the motor to deliver higher levels of efficiency. Its MCR4 frame was specifically developed for motor displacements between 325 cc and 470 cc. Its 9-piston rotary group configuration reportedly helps limit the maximum vehicle travel speed.
“As mobile construction machines continue to become increasingly complex and sophisticated, we’ve seen far greater demands for space within the engine compartment, making the motor length a critical design factor,” said Gary Whitelaw, MCR director of sales at Bosch Rexroth. “Our new MCR-S has been specifically engineered to answer these demands and do so in a way, which doesn’t simply answer the need for more space, but also drives greater levels of efficiency throughout its lifetime.”
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