Benefits Of the Technology

BENEFITS OF THE TECHNOLOGY

·                     ZF has developed a new automatic transmission for cars with eight speeds that can achieve more than 6% fuel savings. The priority aim in development, however, was not the maximum number of gears, but minimum consumption.

·                     ZF engineers had set the bar high to produce a new benchmark for automatic car transmissions. The second generation of the ZF 6HP 6-speed transmission, that entered production only in 2006, defines standards that are hard to top: reaction times faster than human perception, direct engine linkage by early-stage torque converter lock-up and intelligent, adaptive control software, that almost reads the driver's intentions from his foot. But the new transmission is capable of even more - it saves (even more) fuel. It also guarantees ultimate driving enjoyment, as well as the variability needed to be able to use future technologies.

·                     The best currently available technology for fuel saving by automatic transmissions defines the second generation of ZF 6-speed automatic transmissions (6HP). The new ZF 8-speed-automatic transmission (8HP) achieves an additional 6% fuel saving and thereby also reduces CO2 emissions.

Many improvements - one goal: less consumption!

Several innovations have been introduced in the new 8HP to reduce fuel consumption: the completely new transmission concept with four gear sets and only two shift elements open, a higher overall gear ratio, a variable oil pump, new torque converter, and optimized hydraulic and transmission control. A stop-start function is offered as an optional function. Idling at a standstill, the engine automatically switches off. When engaged again, the engine automatically starts up. Even at standstill times of just 10 seconds, switching off the engine cuts average consumption noticeably – and also CO2 emissions.

The start/stop function is enabled by the development of the hydraulic impulse oil storage (HIS). It supplies the hydraulic oil that the transmission's shift elements need for starting. When the engine is switched off, it allows for a quick start – as it is required with the start/stop function. Already 350 milliseconds after starting the engine, the vehicle is ready for setting off. With the start/stop function of the hydraulic impulse oil storage, it is possible to reduce fuel consumption by another 5%. Compared with the worldwide most efficient 6-speed automatic transmission by ZF, the newly developed 8-speed automatic transmission saves another 11%.

Benefit of HIS

With the HIS it is pssible to reduce fuel consumption by another 5%

The hydraulic impulse oil storage makes more complex solutions obsolete, such as a more powerful oil pump in the transmission or an electric hydraulic pump. As a larger dimensioned transmission oil pump would considerably neutralize the fuel savings in continuous operation, an electric pump is an additional burden on the main power supply, has disadvantages in terms of noise, and leads to a considerably higher integration effort. In contrast, with the hydraulic impulse oil storage, ZF engineers have already considered the lowest possible system costs and easy installation of the unit. Other expensive adaptations of the transmission are not required; after all, with the new development of the transmission, ZF engineers have already considered the integration of the hydraulic impulse oil storage by ensuring a favorable design of the components and the respective routing.

Farewell to conventional gear set concepts

 The ZF engineers went on the lookout for a completely new transmission system and discarded all previous established gear set concepts. Armed with a comprehensive list of criteria, the development engineers systematically appraised thousands of possible epicyclic gearing systems and their arrangement variants. The outcome was an 8-speed automatic transmission system leaving just four simple gear sets and five shift elements.

Lower drag losses and higher gear meshing efficiency

The clever thing, though is the shift plan. There are only 5 shift elements - multi-disc clutches and brakes in the heart of the transmission - and only 2 are open in each gear. The fewer open shift elements there are, the fewer transmission parts there are rotating relative to one another. On the bottom line, this results in a significant reduction of drag losses in the transmission. The development engineers were also able to increase the gear meshing efficiency with the new transmission concept. Energy is lost in some gears when power is transmitted through gear wheels. In the new automatic transmission, these losses are below 2% throughout - a further factor helping to reduce consumption.

Significantly lower CO2 emissions

The logical consequence of lower fuel consumption is a significant reduction in CO2 emissions - in real terms, this produces a further reduction of 200 g/km to 178 g/km CO2 emissions in a 3.0-liter 6-cylinder engine - with improved performance.

Faster acceleration

In addition to its positive effect on fuel consumption, the higher overall gear ratio improves the acceleration values of the ZF product. Shorter gear steps, particularly from first to second gear, give vehicles fitted with the 8HP faster acceleration and enable improved shift quality in the lower gears. Two additional gears also helped the ZF engineers achieve an increase in the overall gear ratio, without loading individual gears with excessive torque or speed. This harmonious torque and speed distribution is less harsh on parts and allows reliable operation with fewer "hefty" gear sets

Precise gear shifting

200 milliseconds is how long the 8HP 8-speed automatic transmission takes to carry out a gear shift - fast and smooth. Even a professional driver can't shift as fast as this. This gives gear shifting that impressively combines driving pleasure, efficiency, and maximum comfort. Direct gear jumps over two or more gears - including the extreme of shifting from eighth to second - are also possible. In conjunction with the intelligent adaptive shift strategies, this guarantees maximum agility and driving fun.

Extendable technologies

In addition to fuel savings and performance improvements, a further objective of the ZF development engineers was versatility. In a market environment likely to continue to be characterized by model pluralism, the new transmission series needs to be able to meet a wide range of different requirements. Right from the conception of the 8HP, attention was paid to ensuring its suitability as a modular kit for other starting and all-wheel concepts, without any changes to the basic transmission concept. In the clutch bell housing, the torque converter can be replaced by new starting elements (such as a hydrodynamic cooled clutch) or omitted completely with the assistance of an integrated starting clutch. On the power take-off end, the new product is compatible with all ZF all-wheel drive concepts and future developments of these.

Compatible with hybrid drive system

The new 8-speed automatic transmission is also ideally designed for hybridizing the driveline: ZF will be able to offer both a mild hybrid with crankshaft starter generator and a full hybrid as a parallel hybrid on the basis of the new 8-speed automatic transmission. This will allow all familiar hybrid functions to be implemented in conjunction with the new 8HP. Up to 25% fuel savings can be expected from the full hybrid version in urban-cycle traffic.

New gear set concept	Only 5 shift elements with 4 gear sets, of which only 2 are open in each gear. 3 multi-disc clutches and 2 brakes, enabling a compact, highly efficient design.
Higher overall gear ratio	Overall gear ratio of 7.0. The transmission consistently adapts to the optimum engine operating range for improved acceleration and lower fuel consumption.
Higher power-to-weight ratio	Lightweight components combined with a revolutionary gear set concept: 2 additional gears transfer more torque with fewer components and unchanged weight characteristics.
Lower drag loss and greater efficiency	Only 5 shift elements with 4 gear sets, of which only 2 are open in each gear, and a new axially parallel vane cell pump increase the efficiency of the transmission. Energy losses are reduced to a minimum.