In the first of a two-part series, Sealey Tools looks at hybrid vehicle servicing and how it works.
During recent years the strive for greater fuel economy and lower emissions has seen a rapid increase in electric and hybrid drive vehicles being available. This of course means more of these vehicles are being presented to vehicle workshops for servicing and repair. The systems used on these vehicles vary in operation and complexity, but one thing they all share is the use of a high voltage DC system to power the electric traction motor(s).
There are three main types of hybrid systems currently in use on road cars in the UK.
Full Hybrid System
A normal internal combustion engine paired with an electric motor. This system uses a battery powered electric motor and an internal combustion engine. The vehicle uses a control system so each drive system can be used at the same time, or in isolation, to drive the vehicle. The vehicle’s hybrid control system can seamlessly and automatically switch between electric power and conventional engine power, and is capable of adapting to different driving conditions. The system intelligently controls the power coming from both power sources and combines them for the best efficiency and performance. This is currently the most popular hybrid system in the world and was first seen in the Toyota Prius when it was launched in Japan in 1997.
A recent advancement has seen the introduction of the PHEV vehicle, this stands for Plug-in Hybrid Electric Vehicle. This system works in the same way as a full hybrid system, but also uses household mains power to supplement the on-board charging system. This system has an increased battery capacity which allows the vehicle to be driven purely as an electric vehicle when required, but still has its conventional internal combustion engine to use when required, or when the battery power has been depleted.
Parallel Hybrid System
Uses an internal combustion engine as the main source of power; an electric motor is fitted between the engine and the gearbox to provide additional power when required. This type of system can be more restricted in its operation than that of a full hybrid system, this is due to the space available having a limiting factor on the size of the electric motor which can be fitted – the power output of the motor is limited to the space available. This type of system does not normally have a starter motor or alternator fitted – the function of these two units is combined within the traction motor/generator unit.
Series Hybrid System
Where the electric motor provides all the drive for the vehicle. The vehicle’s internal combustion engine is used to power a generator to charge the on board batteries to power the electric motor. This system allows the engine to be run at its optimum speed for fuel efficiency. This means a relatively small engine can be used to power a comparatively large vehicle. One problem for the system is maintaining battery charge during periods of heavy and prolonged current draw. For this reason series hybrids are currently quite rare.
How are the batteries charged?
The traction batteries are charged in a variety of ways depending what system the vehicle is using.
Regenerative charging
This system uses electrical energy recovered during braking to charge the battery pack. Every time the brakes are applied or the accelerator is released, the system diverts the electric charge produced during overrun back to the battery.
Instead of the energy being lost as heat, for example through the braking system, it is captured in the form of electricity, and then reused for propulsion when required. This is particularly beneficial in urban traffic where the system can recover, store, and reuse a great deal of this energy.
Generative charging
The vehicles on board generator charges the battery pack. This type of system has some advantages, as the range that can be achieved is greater than can be achieved with a full electric vehicle.
External charging
The battery is charged via a charging socket. This type of charging has until recently only been seen on full electric vehicles. The introduction of PHEV’s has seen the introduction of this type of charging on full hybrid vehicles.
Hybrid vehicles often have a conventional 12V battery to run the vehicles electrical systems, the conventional battery is charged via a take-off point from the main traction battery pack. If the vehicle requires jump starting, specific procedures as supplied by the individual manufacturer will need to be followed.
How long do hybrid batteries last?
The batteries in hybrid vehicles are efficient and corrosion-resistant units, they are designed to last many years if used and operated correctly. The batteries are recyclable and broadly speaking it is possible to recycle well over 90% of the batteries from hybrid cars. The recycled parts are remanufactured to make new batteries or other forms of stationary energy. Battery packs will develop a memory effect if used incorrectly which can shorten their life cycle. Prolonged periods of inactivity is the most frequent cause of this. As the battery pack becomes less efficient, more frequent charging will be required which will have a detrimental effect on the vehicles fuel consumption.
As part of the charging/discharging process the battery pack will become very warm. Cooling fans are built into the system to prevent the batteries from overheating. It is worth noting that the vehicle may have air ducts for cooling the battery pack; these ducts must be kept free from obstructions to maintain airflow.
Can the hybrid battery pack be repaired?
Diagnostic fault codes will be recorded to assist the technician in detecting and tracing faults. The battery pack is a non-service item and dismantling of the unit should not be attempted under any circumstances.
There are high amperage fuses built into some systems which are accessible. The fuses have glass particles encased in them which will melt in the event of fuse failure to extinguish the arc caused at the point of failure.
