Date:  12/8/00    
  Contact:  Wolfgang Schmid
     (859) 282-4344
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ZF-Axle System Technology For The City Bus: News For The Market   
    If you want to know where we're going, have a look at the latest generation of city buses and their axle systems. ZF Passau GmbH - within the ZF Group responsible for the axle business worldwide - reports that the percentage of "genuine" low-floor buses is constantly rising. Another remarkable fact: Bus manufacturers are increasingly ordering complete systems including suspension, springs and damping elements.

ZF has become the full line supplier for bus axle systems. Not only with respect to the system approach but also with respect to the product range. Based on the standard bus with ZF RL 85A front axle and AV 132 portal axle 15m buses are equipped with ZF RL 85A tag axle (mostly actively steered with ZF RAS). For articulated buses ZF is offering the non-driven ZF portal axle, the AVN 132.

The genuine low-floor bus is gaining ground, with its vehicle floor lowered to a minimum height and its stepless interior platform. ZF made this technological transformation possible at an early time, with the development of the concept of a drop-center axle. Since 1983 more than 25,000 buses have been equipped with ZF drop-center axles - and every year thousands more are added. The new models of Mercedes-Benz (Citaro), Auwärter (Centroliner), Volvo (B10L), Scania (OmniCity), Dennis (Trident 2), IRIS.Bus (Renault Agoraline) and MAN contribute to the already comprehensive list of references. A number of further vehicle models with ZF drop-center axles are being processed through the prototype / pre-production stage and will be presented to the public soon.

Low entry level (405 mm)
Floor heights in the area of the rear axle of merely 16 inches are possible due to drop-center axle technology only. Pioneering in low-floor technology, ZF consistently transformed current and future market requirements into the third generation of drop-center axles, the AV 132. An essential objective of development work was to achieve a reduction in the variety of parts, apart from low noise level and high comfort.

The slim axle housing with laterally offset axle drive (drive angle: 80°, 87° or 90°) and differential is connected on its left and right side to a portal drive each. The portal drives are designed as power-split spur gears and represent the technical core piece of the axle. As a result of the splitting, the high torques required can be transmitted in spite of the limited portal distance.

Proper selection of ratios in the portal drives reduces the torque level in the bevel drive. Result: less noise is emitted. The portal gears are designed as ground helical multi-mesh gears - the only way to reduce the rolling noise of the gears to a minimum.

Years ago, ZF did pioneering work when it introduced the grinding technique for bevel gears, with the result that the passenger enjoys more comfort and the bus manufacturer is spared the trouble of additional expensive and voluminous noise-dampening measures. Casted suspension arms -which have been optimized for weight- connect the axle via a standardized interface to the pneumatic spring system and thus with vehicle body- another aspect contributing to the dampening of noise in the vehicle.

RL 85A axle system completes low-floor bus
For the low-floor technology to be consistently realized for the entire length of the bus, ZF is completing the low-floor bus concept by adding modern components and systems for the leading and trailing axle. Depending on the customer's wishes, independent suspensions or systems with rigid axle bridges will be used. The RL 85A complete system with axle loads up to 8.5 t is an interesting solution with regard to cost and efficiency, particularly for traditional beam design. On the other hand, it stands out for its robustness, maintenance friendliness and it meets modern requirements concerning kinematics and driving comfort. In combination with the ZF-RAS EC system an actively steered third axle can be realized.

Option: Disc brakes all around
While the disc brake had conquered its place on the front axle of city buses some time ago, now is it possible to equip the rear axle with a pneumatic disc brake as well with the introduction of the AV 132. Already today, about 70 percent of ZF portal axles are equipped with disc brakes. The modular design of the AV 132, however, permits the continued use of conventional drum brakes.

Apart from reduced maintenance work and more even response characteristics, the disc brake has even more advantages compared to the drum brake: better brake power dosing and a large degree of fading immunity.

Completely pre-assembled axle systems ready for the bus production line
Already in 1996, ZF presented a complete rear axle system with all suspension and spring system parts at the IAA. In the meantime almost every 2nd portal axle leaves ZF as a system with pre-assembled suspension elements. The rear axle system for the city bus can be delivered direct to the manufacturers' production line, in completely assembled condition. The complete system comprises suspension, spring and damping elements, brake activation elements, ABS sensors and elements indicating brake lining wear.

The global ZF Group, a leading automotive systems supplier of driveline technology, steering and suspension components, is headquartered in Friedrichshafen, Germany. It employs more than 33,000 people worldwide and operates over 50 facilities in 17 countries. In 1999 the ZF Group posted sales of $5.3 Euro. With sales of $1.4 billion in 1999, the ZF Group in NAFTA expects annual sales of over $2 billion by the year 2002. ZF Group North American Operations is headquartered in Cincinnati, OH and operates 17 production sites in the NAFTA region.

The AV 132 generation of drop-center axles sees ZF continuing along the road of systems supply. The system is delivered direct to the manufacturer assembly line complete with brakes, suspension, brake wear sensors and ABS.

ZF System of low floor front axle RL 85 A with axle beam, wheel heads, disc brakes, suspension and steering designed for axle loads up to 8.5 t.

Press Contact(s)
ZF Industries, Inc. ZF Group NAO
Martin Meissner Wolfgang Schmid
Marketing Services Manager Marketing & Communications Manager
Tel.: (847) 478-6785 Tel.: (859) 282-4344
Fax: (847) 478-6864 Fax: (859) 282-4311
E-Mail: martin.meissner@zf-group.com E-Mail: wolfgang.schmid@zf-group.com
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