57 so that’s the saving grace in terms of weight and volume,” says Drummond. The company takes a system-level approach to battery and electrical safety, including an industry-standard, high-voltage interlock loop (HVIL), insulation monitoring, and crash switches that open the battery contactors in the event of a severe impact. The BMS has a ‘master-slave’ distributed architecture. Instead of wires running from every battery cell to a central point, the system has a series of distributed microprocessors balancing the charges among the cells in each module, and reporting states of charge and temperature to the BMS computer over a CAN bus. This enables sophisticated management of the battery while requiring far less wiring. “We manage the power demands on the battery in accordance with temperature limits and we manage the cooling system, both through VCU processes based on information supplied by the BMS,” says Drummond. As with the other conversion kits, the E-type has a 12 V electrical system with its own battery, whose main job is to operate the contactors that activate the HV system, of which the DC-DC converter is a part. In normal operation, the DC-DC converter supplies all the 12 V electrics and trickle-charges the 12 V battery, which retains enough energy to keep the car lights on, even if the driver ignores the warnings and allows the traction battery to run down, and it also preserves the radio presets when the car is switched off. The other major design element is the electronics and control software. “Because that’s our software, we control the whole environment, so we can make it do what we want. You can have different drive modes, although in an E-type the standard EV options are normally fine. We have a sports mode, a traffic mode that gives more re-gen on lift-off so you can drive on one pedal, and an economy mode,” Drummond says. “The system allows you to select modes, but also manages the way the vehicle drives.” The firm also builds the electronics that control the original dials on the dashboard, repurposing some of them. While the speedometer still shows speed, the rev counter shows the driver how much power is being used and how much is flowing back to the battery via re-gen at any given moment, along with the battery’s state of charge. “The same device can drive display screens, but most of our customers don’t want screens,” Drummond says. Running on a CAN bus, the instrument control system converts the digital signal’s output by the electric powertrain’s electronics to the analogue electrical/mechanical inputs that the old dials need. For example, the box of tricks simulates the square waves that the rev counter looks for when counting sparks from the ICE’s spark plugs, so it can drive it, even though the square waves now represent different parameters. Drummond says the system takes vehicle speed from the motor rpm and the fixed transmission ratio, and interpolates them into an rpm for the speedometer. Vehicle control philosophy In overall control of the entire powertrain is the VCU. “There are different philosophies, but the approach we take to the VCU is to implement it as a central command module,” Drummond says. “When you put your foot on the accelerator pedal, that moves a potentiometer, which provides a signal that tells the VCU how hard the driver wants to accelerate. Then, the VCU asks the BMS if it can take the required amount of power, and if the BMS says yes, the VCU tells the inverter to supply that much power to the motor. But, if the BMS says no, there is a whole decision tree of what happens. There’s a whole bunch of interlock safety systems that make sure the way the car responds to the controls is commensurate with the health of the batteries,” he explains. That control philosophy also extends to usability features that can be provided as custom options, such as offroad hill-descent modes for the Land Rovers that Electrogenic is working on for the British Army, or traction control and cruise control for the E-type. What’s next? Although there are many physical differences among the classic cars for which Electrogenic builds conversion kits, the basic electrical and electronic architecture is common to all of them. This approach enables them to create kits for other cars more easily, and there are several currently in the works, including one for the DeLorean and the Jaguar XJS. E-Mobility Engineering | May/June 2024 Electrogenic E-type conversion | EVD Most customers opt to retain the Jag’s original instruments, which are driven by an electronic module that provides the square wave signals they need, sometimes repurposed
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