The new 8- speed automatic transmission from ZF makes vehicles more economical. Honsel assisted ZF by developing the optimal casting process for the gearbox housing. The light metal expert supplies light compact housings as well as high-precision control parts for the gear shifting mechanism. Honsel manufactures the components on a new fully automated production line.
With its new 8-speed transmission known as 8 HP 45, ZF has succeeded in increasing the power-to-weight ratio while at the same time substantially reducing fuel consumption. Compared with ZF's already-perfected 6-speed automatic transmission, fuel consumption is reduced by a further six percent. This is due to a higher overall spread of gear ratios in the new gearbox which keeps the engine in the most economical r.p.m. range as well as to improved torque converters. In addition, a start-stop function for the engine is possible, thereby saving an additional five percent. Thanks to the hydraulic storage and boost unit (HIS), ZF was able to build the first automatic transmission without an auxiliary pump. This pump was previously needed to maintain the oil pressure when the engine was switched off. The high shifting speeds achieved by the 8 HP 45 increase the comfort and vehicle dynamics. Modular design enables a high flexibility of the transmission regarding various power-train configurations extending from rearwheel to four-wheel and even to hybrid drives.
13 kg only is the weight of the gearbox housing, which Honsel produces for ZF on a new, fully automated production line. It contains the new 8-speed transmission ZF 8HP45, characterized by a high shifting speed and a further reduction of fuel consumption.
The high functional density of the transmission system, whose size is virtually equal to that of the 6-speed automatic, means that the individual components have to fulfil more functions. This causes high demands on the development of the housing, a field in which the extensive experience of Honsel's light-metal specialists played an important part. For example, they tested and improved the castability of the housing, the valve body and the ditch plate, which together form the control unit. The result is a compact lightweight gearbox housing weighing only 13 kg, which is virtually the same weight as its predecessor. The ditch plate and the valve body too weigh almost the same as those in the 6-speed version because all the functions for shifting the eight speeds are accommodated in the same space.
The gearbox housing and housings for the control unit of the ZF automatic transmission system are produced at Honsel's die casting facility in Nuremberg. All production steps – from casting to mechanical machining, from deburring to inspection of the finished part – take place in a fully automated production line specially installed for the new transmission parts. Compared to the previous production of gearbox housings, cycle time is shortened substantially.
The complexity of the components causes high demands on the entire production process. The oil ducts in the ditch plate and valve body must meet very high tolerance requirements in order to achieve the short shifting times and high shifting precision of the transmission. The gearbox-housing has to be provided with casted oil ducts through which hydraulic oil flows when it is in operation. To avoid expensive drilling on the unfinished component, concealed steel tubes are cast into the housing as oil pipes. Depending on the transmission version, robots locate one or two tubes automatically in the die before the melt flows in.
For quality-control purposes, every component has an individual code to allow the systematic monitoring of the production process. Honsel also uses three-dimensional laser scanning. During the production cycle, robots check the surface quality and dimensional accuracy of all components. After successful completion of the final inspection, Honsel delivers the gearbox housings and control parts from its die casting plant in Nuremberg to ZF for final machining. The interior aluminium components for the gearboxes are delivered to ZF ready for assembly from the Honsel plant Fonderie Lorraine in France.
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