Stop smoothly, start dynamically: How important the oil volume accumulator is for automatic transmissions
Vehicles with automatic transmission and start-stop function require an oil volume accumulator (HIS) to maintain the oil pressure in the transmission
As a cost-effective repair solution, the oil volume accumulator is now available as a separate part
Damage is often caused by thermal stress and oil ageing – therefore, regular transmission oil changes are recommended
A large proportion of manufacturers of high-performance saloons and SUVs with rear-wheel or all-wheel drive, rely on the eight-speed automatic transmission 8 HP from ZF. Despite its high performance and exceptional reliability, oil ageing can still cause problems over the years. ZF Aftermarket therefore recommends regular oil changes and also offers spare parts for the 8 HP - now including the oil volume accumulator.
Luxury saloons, premium SUVs and sports cars also need the start-stop system to achieve lower emission values. However, as many of these vehicle types are equipped with hydraulically controlled torque converter automatic transmissions, a question arose: How can the necessary oil pressure be maintained during engine stop, in order to be able to start up dynamically immediately after the engine is restarted?
ZF has solved the problem for its 8 HP automatic transmission, which is used by many vehicle manufacturers, with the oil volume accumulator. It is the key component for the smooth functioning of the start-stop system. However, after many years of use and the inevitable ageing of the oil, in rare cases, the oil volume accumulator can be damaged. Defects become noticeable through the following symptoms:
· Failure of the start-stop function
· Error messages in the vehicle display
· Increased fuel consumption
· Reduced engine power
Thanks to the repair-friendly design of the ZF 8 HP, damage to the oil volume accumulator does not require a comprehensive transmission overhaul. This is because the component can be removed and replaced individually after dismantling the oil pan. For the first time ZF Aftermarket now supplies the necessary spare part to the independent aftermarket in proven OE quality.
Transmission oil change increases the service life and functional reliability of the transmission
Of course, it is not just the oil volume accumulator that suffers from oil ageing, but the entire transmission. This is because the additives contained in the transmission oil - i.e., the protective active ingredients - gradually degrade due to the pressure and shear forces as well as the thermal load. This additive degradation leads to lower lubricating performance, reduced protection against moisture and oxidation and increased stress on components such as the oil volume accumulator.
For this reason, ZF Aftermarket recommends regular oil changes for automatic transmissions, depending on the driving profile and operating conditions. A timely oil change
· reduces wear on clutches and valves
· ensures consistently smooth gear changes
· extends the service life of the transmission
· prevents expensive repairs.
Car workshops should recommend this service to their customers before signs of damage and wear appear on the transmission, because as important as the oil change is for a long transmission service life, defects that have already occurred cannot be "repairedׅ" with it.