E-Mobility Engineering 017 l ECE Doosan electric excavators dossier l In Conversation: Matt Faulks l Battery testing focus l Battery Show North America 2022 report l Ariel Hipercar digest l Cathode materials insight l Thermal management focus

controller, and now we do the same, only we request the rpm from the ECU [also from Danfoss] on the inverter instead,” Van Hal explains. “Feedback from the ECU then goes to the hydraulics controller, which sends signals as to whether the e-motor should speed up or slow down to get the right flow and pressure of hydraulic fluid going through the arm, bucket or travel systems. So essentially, the Bosch Rexroth hydraulic controller is the master and the Danfoss ECU is the slave; the latter listens to the former and adjusts its speed according to the command signals it receives. “And remember that the hydraulic pumps are limited to speeds of 1800 and 2200 rpm, which is why we don’t run the e-machines at their peak power outputs just yet. It’s a limitation in terms of speed, but the power at which hydraulic fluid is pumped doesn’t affect the downstream power with which the arm and bucket lift, or the power used for movement. “The outward flow from the pumps is controlled by valves that split the fluids going to the arm, boom, bucket and drivetrain. Each valve has an integrated pressure sensor to tell the controller whether it should be requesting higher or lower speeds from the e-motor. “They can also be configured to open simultaneously or for one to shut when a conflicting system is in use. For instance, the bucket’s valve typically shuts off fluid flow to that system, restricting its movement, when the traction system is in use. “And in addition to the high-pressure hydraulics for all those systems, a low-pressure hydraulic network runs from the operator’s levers, pedals and steering wheel for sending manual control signals to the different systems’ valves via the hydraulics controller,” Van Hal says. With hydraulic force governed via these valves, the DX165W’s pumps allow for up to 34.3 MPa of liquid pressure, which translates to 350 kgf/cm 2 , during lifting work and 36.3 MPa during traction. The DX300LC’s pumps are configured for the same pressure and force despite their design difference, so it follows that the smaller excavator is less likely to require the maximum possible hydraulic force while working or being driven. As mentioned, both EVs’ motors drive a pair of hydraulic pumps: while the first covers the lifting actions, as discussed above, the second is for travel and bucket actuation. The second pump driven by the DX300LC’s T800 motor directly propels three hydraulic axial piston motors. The first of these is used for rotating the cabin, and hence also the lifting arm. It also drives an oil-immersed two-stage planetary reduction gear, in order to rotate the cabin at up to 9.88 rpm, with up to 12,137 kgf/m applied. The other two axial piston motors each work one of the drive tracks for the DX300LC’s traction through a planetary reduction gearbox. Each is an independent, high-torque motor, whose controllers respond to CAN signals coming from a pair of foot pedals in the cabin. They and the gearboxes are protected by the track frames, as are multi-disc track brakes, which are applied via springs and released via the hydraulics. On the DX165W, the second of its two hydraulic pumps drives a hydraulic motor that connects to a pair and counterweights to accommodate the PowerBoxes. However, there is an area of interplay between the powertrain’s electrical systems and the mechanical systems for use on the roads and at construction sites. There are also reasons why an e-motor can provide the same capabilities as a diesel engine without the need for a lot of new and thus expensive and heavy gearboxes to account for differences in speed, torque and acceleration. It is important as well to understand where hydraulic systems still have an advantage over existing electric and electro-mechanical technologies. ECE retained much of the hydraulics because its r&d found the hydraulics to be superior over electro-mechanics for applying force responsively at low cyclic frequencies. The flange on the Danfoss motors means their shafts can be directly connected to and drive the hydraulic pumps, just as the diesel engines would. These load-sensing pumps were developed by Bosch Rexroth, and in the DX300LC they are tandem variable displacement axial piston types with a maximum flow rate of 248 litres/ minute each at 1800 rpm. The DX165W uses a pair of bent-axis axial piston pumps with a maximum flow rate of 176 litres/minute each at 2200 rpm. In addition to being the same models as on the original Doosan architectures, the means by which they transmit power to the digging and traction system is also the same. As the operator pulls the control levers in their cabin, the hydraulic pump controller (also from Bosch Rexroth) sends requests for power to the EPOS (electronic power optimising system), which is the central computer that processes all the control inputs and functional outputs of each excavator. “The EPOS would calculate and request the necessary rpm from the diesel engine’s ECU to satisfy the power request from the hydraulics Webasto’s Vehicle Interface Box serves as the BMS in addition to delivering key battery performance and health information to vehicle control and fleet management systems (Courtesy of Webasto) January/February 2023 | E-Mobility Engineering 29 Dossier | ECE electric Doosan DX165W and DX300LC