Hybrid vehicles are one of the biggest challenges in today’s aftermarket.
Battery technology is an area that can be difficult to navigate because of the variety of different batteries utilised by today’s vehicles.
Many hybrids have a 12v battery along with a separate high-voltage battery, both performing different tasks.
The 12v batteries are used to power a vehicle’s ECUs rather than start up the vehicle itself – that is down to the high-voltage unit.
Instead, the 12v battery keeps the electrical system running while the car is parked and looks after items like the clock, key fob sensors and the security system.
The high-voltage batteries, usually of Nickel Cadmium (Ni-Cd), Nickel Metal Hydride (Ni-MH), Lithium Polymer (Li-Poly) or Lithium Iron (Li-Ion) type, then provide the power to the motor and drive the wheels when a vehicle is at low speed, before the engine starts up and drives the wheels through the power split device with assistance from the electric motor, powered from the generator.
When a vehicle is slowing down and braking, the engine and electric motor provide the braking effect and the battery is recharged from the generator via the power control unit.
There are some important safety tips to be aware of when using a high-voltage battery:
- If charged at over 4.2v there is the risk of explosion so only a dedicated lithium charger should be used
- If a lithium battery drops below its nominal voltage (3v), it cannot be recharged because it swells and becomes unfit for operation
- The battery cannot be safely charged when below 0 degrees centigrade
While the higher-voltage batteries are the main power supplies for a vehicle, the 12v batteries play an important role because of the elements they control – a fine example is Honda’s Integrated Motor Assist (IMA) system, in which the smaller batteries provide power to the 12v backup starter motor.
One other key player in the IMA system is the Battery Control Module, which works with the electrically assisted Internal Combustion Engine (ICE) and a three-phase AC motor-generator (MG) to give the IMA several distinct modes of operation:
- Assist – Provides assist to the ICE by adding horsepower and reducing fuel consumption
- Charging – Charging happens on deceleration, also known as regenerative braking
- Auto Idle stop – ICE turns off when it sees the brake pedal depressed and restarts when the pedal is released. If the pedal is depressed for longer than 90 seconds the ICE will restart to continue charging the 12v system
- Electric propulsion mode – Cylinders are deactivated via the V-TEC system. The ICE crankshaft continues to move with the IMA motor but all the valves are held closed as the pistons move in the cylinders
Hybrid technology vehicles feature heavily in the software updates available for the range of vehicle diagnostic tools from Snap-on.
Examples include IMA freeze frame data special functions for Honda’s Civic and Jazz hybrid models, pre-collision systems data and tests on the Toyota Rav4 Hybrid 2016-2018, and coverage for several Land Rover hybrid vehicles.
Component Test Meter coverage also includes a Hybrid Vehicle How To Class, covering specific topics such as safety, the different types of hybrid engines, and a glossary of important terminology.
Learn more about the current Snap-on diagnostic software release.
- Fill in your details in the box to the top of this page and get our Technical Focus articles sent directly to your inbox every month.
Date posted: 14 May 2019