Electric Car

Overview

An electric car is a passenger automobile that stores energy in a rechargeable battery and converts it to motion with one or more electric motors. It replaces the combustion engine, fuel tank, exhaust and multi-speed transmission of a conventional car with a Traction Battery Pack, one or two Electric Drive Unit modules and a power electronics chain. Because the motor delivers full torque from rest and runs efficiently across a wide speed range, a single-speed reduction gear is enough, and the drivetrain has far fewer moving parts than an engine-driven car.

The dominant structural concept is the skateboard platform: a flat Skateboard Platform that carries the battery in the floor between the axles and mounts the suspension, steering and drive units at each end. Placing the heaviest component low and central gives a low center of gravity and frees the space above for the cabin. The body and interior sit on top of this platform as a largely separate structure.

Energy storage

The Traction Battery Pack is the most expensive and heaviest subsystem, typically 400-700 kg and 50-100 kWh usable. It is built from Battery Module units, each a group of Prismatic NMC Cell cells joined by laser-welded busbars and monitored by a Module BMS Slave Board. The slave boards report every cell voltage and several temperatures to the Battery Management Master, which estimates state of charge, keeps cells balanced and decides when to open the HV Contactor contactors.

Cells sit on Battery Cooling Plate cold plates carrying glycol coolant, so the pack can be warmed before fast charging in winter and cooled during hard use. The whole assembly is sealed inside an Pack Tray and Lid that is also a structural member of the car. Safety devices include a HV Pyro Fuse pyrotechnic fuse that severs the circuit in a crash and a Manual Service Disconnect that lets a technician split the pack into two harmless halves.

Drive units

Each Electric Drive Unit integrates a motor, an inverter and a gearbox in one cast housing. The Traction Motor is usually a permanent-magnet synchronous machine: a wound Stator Assembly surrounds a Rotor Assembly carrying magnets, and an Rotor Position Resolver reports rotor angle so the controller can apply current at exactly the right moment. A dual-motor car places one unit on each axle for all-wheel drive and can shut one down at cruise to save energy.

The Traction Inverter turns the pack's direct current into three-phase alternating current for the motor. Modern designs use SiC Power Module silicon-carbide switches driven by the Gate Driver Board and commanded by the Inverter Control Board, which runs the field-oriented control loop thousands of times per second. The motor spins far faster than the wheels, so the Reduction Gearbox brings the speed down through a fixed helical ratio and splits torque across the Open Differential.

Chassis and brakes

The Skateboard Platform mounts a Suspension Corner at each wheel, combining a Coil Spring, a Shock Absorber and steering and locating links through the Ball Joint joints. The Steering Rack is electrically assisted by a Servo Motor, with no hydraulic pump to run.

Friction braking is handled by the Brake Corner at each wheel, where the Brake Caliper squeezes pads against a ventilated Brake Disc. In normal driving most deceleration comes from regeneration: the motor acts as a generator, slowing the car and returning energy to the pack, so the friction brakes and their Brake Pad Set last much longer than in a combustion car. The Wheel Assembly assemblies use low rolling resistance tyres and a TPMS Sensor sensor in each valve.

Body and interior

The Body Shell is a steel and aluminium unibody carrying the Door Assembly closures, the Windshield and the Floor Pan that seals over the battery. The front Front Hood often covers a storage compartment because there is no engine there. Inside, the Interior centers on a large Center Touchscreen that replaces most physical switches, a compact Driver Display for the driver, and powered Seat Assembly units with built-in heaters that warm occupants efficiently without heating the whole cabin.

Charging and thermal management

The Charging System supports two paths. For home and destination charging the Onboard Charger rectifies grid alternating current to direct current for the pack at 11-22 kW. For travel, a roadside DC charger bypasses the onboard unit and feeds the pack directly through the Charge Port at 100-250 kW, with the Charge Controller negotiating current and managing the locking inlet.

Charging speed depends heavily on temperature, which is why the Thermal Management is so important. Electric Coolant Pump pumps move coolant between the battery, drive units and an Heat Pump Module. The heat pump can move heat from the outside air, the motors or the cabin to wherever it is needed, which extends winter range compared with a simple resistive heater. A Coolant Routing Valve reroutes the loops so the same hardware can cool the battery during a fast charge and warm the cabin a few minutes later.

Electronics and assistance

A small number of powerful Domain Controller computers replace the dozens of separate control units in older cars, communicating over high-speed networks. The DC-DC Converter converter steps the high-voltage bus down to run the 12 V LV Wiring Harness, lights and controllers, backed by a Low-Voltage Battery. Driver assistance relies on the Driver Assistance Sensors suite of Camera Module modules, Radar Module units and Ultrasonic Sensor sensors fused by the controllers to enable adaptive cruise, lane keeping and automated parking. Ownership economics favour the electric car in running cost and maintenance, while purchase price and charging access remain the main trade-offs against combustion vehicles.