Powertrain Overview: Electric Vehicles

Since the creation of the first modern automobile nearly a century and a half ago, there has been one dominant engine option on the market, the gasoline internal combustion engine. Now the gasoline internal combustion engine has some challengers trying to steal the crown. There have been many different types of engines in the past but many of them relied solely on fossil fuels to operate.

Recently though, because of increasing fuel economy standards and emission awareness, a new breed of engines is emerging. Many of these rely on electricity to aid in powering the vehicle. With these new power plants comes a new set of rules and warnings on how to repair them. A lot of collision technicians have an idea about how some of the new powertrains work, but not a full understanding of what is going on under the hood. It is important to understand the inner workings of the engine in order to safely and properly diagnose and repair them after a collision. In this series, we’ll walk you through many of the current engine options and how they convert the fuel they’re consuming into usable power. Let’s explore the electric vehicle (EV) powertrain.

EVs, sometimes referred to as Battery Electric Vehicles (BEVs) use a large high-voltage (HV) lithium ion battery to store electricity. Some EVs use a battery that nearly covers the whole floor of the passenger compartment. The primary charging of the HV battery is done by plugging in the vehicle to an electrical outlet of charging station. The power that comes from houses or the power grid is alternating current (AC). However, AC cannot be stored in a battery. In order to store energy in a battery the AC must be converted to direct current (DC). This is done with an inverter.

The vehicle is driven with an electric motor. The motor requires AC to operate so the DC from the HV battery must again pass through an inverter to change back to AC. The inverter acts as the brains of the vehicle by regulating how much power is sent to the motor. The electricity powers the motor which powers the wheels. A simple single speed transmission is used to reduce wheel speed and multiply torque.

EVs also utilize regenerative braking to recharge the HV battery, which extends its range. When the accelerator pedal is not being depressed the current forward momentum continues to spin the electric motor which turns it into a generator producing AC. This then must be changed to DC to be stored.

The battery, motor, and inverter all produce heat, so a cooling system is used to dissipate heat. This system is similar to what would be used on a traditional internal combustion engine, but a special coolant is required. Another concern is when the lithium ion battery needs to be removed. Due to its large size and heavy weight, it will normally take special tools and procedures to safely remove it.

These vehicles have a 12 V battery to run accessories and an HV battery to run the electric motor. Due to the high-voltage it is extremely important to properly disable the battery before service is performed. The HV battery can cause serious injury or death if not handled properly. Make sure to consult the service information for proper disable procedure. Also, the 12 V battery will need to be disconnected and isolated when welding is performed so that damage does not occur.

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