54 November/December 2023 | E-Mobility Engineering The excavator also features a Fusion 800S that serves components such as the AC charger and traction inverter. One key requirement was that the excavator should be ready for operation in less than an hour after running its battery down. This can only be achieved with a DC fast-charging interface, so the Suncar team evaluated a solution that could be optionally integrated into a machine at a customer’s request with little effort, while not interfering with the operation of the separate AC charger. Known as Interflow, Suncar’s in-house DC fast-charging system interface module contains the comms unit that performs the handshake with the external charger, the current measurement unit and the relays that enable CCS standard charging of the HV battery pack. The 8.8 kg Interflow 500 used on the ZE150W is rated at up to 800 V and around 500 A. Its CCS 2.0 comms meets the DIN 70121 and ISO 15118 standards, while comms with the vehicle control system is via CAN. The module has galvanically isolated HV current and voltage measurement devices, along with temperature sensors on the AC and DC inlets to enable temperature-based reduction of the charging rate for safety. The main board also contains an interlock switch and a temperature sensor, and it is protected from electromagnetic interference by shielded cable glands. One decision that had to be made about the AC charging system was whether to site it in the upper carriage or undercarriage, with the latter winning out for several reasons. These included the fact that HV DC paths are already provided for the rotary feedthrough for the inverter that drives the traction motor, paths that can also be used to connect the AC charger to the HV battery. Furthermore, the undercarriage has unused space available. The final reason was that it would create better operational conditions for the cabling. Voltage and power The ZE150W’s HV electrical system operates at 650 V, in line with the trend towards higher voltages. Baettig says, “In this case it is evident that for the required power, 650 V components allow for much lower current, which helps keep cable diameters low. “Furthermore, suppliers are offering more and more components at this level, which makes life easier for manufacturers.” Motors and inverters, for example, are provided by several suppliers including Dana TM4, Bosch Rexroth, Bonfiglioli and ZF. The ZE150W has a working power rating of 100 kW, which is divided between the separate electric and hydraulic drives. Exactly which parts of the system are powered directly by electric motors or actuators, and which are powered by hydraulics, depends on the degree of electrification, Baettig notes. “In the maximally electrified version, only the bucket, the arm, shield and other small actuators are still powered hydraulically,” Baettig says. “For safety reasons, some of the drives require slight over-dimensioning to avoid any risk of over-torque.” Motor and actuator installations One electric motor replaces the diesel engine that drives the main hydraulic pumps, of which there are several as per the original vehicle’s architecture. The motor is attached in a similar manner to that of the displaced diesel engine, being mounted directly onto the pump distribution unit, which is in the vehicle’s hydraulics compartment. A traction drive motor powers the electric four-wheel-drive system, operating in ‘work’ and ‘road’ modes and mounting directly to the traction gearbox in the undercarriage. The challenge with traction drives in machinery such as 15 t excavators is that they are required to manoeuvre on steep slopes while also being capable of reaching speeds of up to 35 kph. “The right combination of torque and motor speeds has to be found while complying with tight dimensional constraints,” Baettig explains. The electric slew drive motor turns the upper carriage that supports the cab and bucket arm with respect to the undercarriage. This motor is coupled to a multi-stage planetary epicyclic gearbox mounted near the centre of the vehicle. This gearbox has a higher overall ratio than the system in the original diesel-powered machine, and the motor directly recuperates electrical energy when coming to a stop, in the manner of regenerative braking. Digest | Suncar ZE150W excavator General CAD view of the ZE150W’s upper carriage supporting the driver’s cab, battery packs and electrical interface boxes. Sourcing HV electrical rotary connections was a challenge
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