Schaeffler's New Switchable Finger Follower Offers Engine Gains

Tested on a prototype engine,Schaeffler's New switchable finger follower for controlling valve trains not only improves engine torque by 10 per cent, but also increases engine power by 15 per cent Note: A free brochure or catalogue is available from Schaeffler (UK) on the products in this news release. The switchable finger follower also cuts fuel consumption by 15 per cent. Valve train components designed as two-stage switches for cam profile switching and cylinder deactivation represent the simplest type of enhanced engine control. In Europe, this functionality is already in production in the form of switchable tappets. The design of the switchable finger follower is based on the concept of two meshed arms, joined to each other by a pivot axis. Lost motion springs on this pivot axis ensure contact with the cams when partial load conditions prevail. Designed for automotive engines with an overhead camshaft, the switchable finger follower transfers the cam stroke to the valve. One end of the finger follower is positioned above a supporting element in the cylinder head, the other end is located on the end of the valve stem. In order to guarantee the shortest possible oil supply paths, a latching mechanism is positioned directly over the hydraulic support element on the finger follower. In the event of cam profile switching, the part load cam stroke is transferred by a roller in the inner arm from the cam to the engine valve. This combines the benefits of the roller finger follower with the added reduction of the effective valve spring force. The latching mechanism means that both arms are coupled as a result of increased oil pressure in the engine, and the larger full load stroke is transferred to the engine valve by the bearing surfaces of the outer arm. The impressive fuel consumption figures and engine torque improvements were demonstrated in recent tests by Schaeffler on a prototype engine, based on a 2.2 litre, 4,000rpm, 220Nm Opel Vectra. Improved driveability is another added benefit from the new switchable finger follower and valve train. John Taylor, Director and General Manager at Schaeffler UK Automotive Division comments: 'There are two types of switchable system currently being mass produced for automotive passenger car engines - the bucket type switchable tappet and the switchable roller lifter'. However, already we are seeing much interest in the switchable finger follower, which includes a number of development projects with OE engine builders because of its dual benefit of reduced fuel consumption and reduced engine emissions'. However, for automotive OEMs, it is always a trade off between the cost and the benefits. At present, only the larger engine sizes, V6s and V8s for example, tend to justify using the switchable finger follower'. Volvo, Subaru and Porsche, for example, already use the bucket type switchable tappet on certain engine sizes and more will follow with this and other switching technology'. Taylor continues: 'For smaller engines, downsizing and turbocharging is the way most manufacturers are going, but when emissions regulations become even more stringent, these engine sizes may also start to see the benefits of switchable technology.