Overdrive (mechanics)
Overdrive is the name of economy cycle in automotive transmissions, the lowering of the required for a given speed the engine speed means (for thereby increased torque ). Overdrive is a registered trademark of Borg Warner Corporation.
Function
In a narrower sense are with Overdrive to the ordinary transmission downstream planetary gear in a separate housing, the electrically or manually - is switched on - mostly for the third and fourth gear. This reduces the overdrive with a constant output speed and ground speed input speed - and thus the engine speed - for example, by 22 percent in some Triumph and MG models or by 28 per cent in some Austin -Healey 3000 Jaguar types; this reduction in speed may be at 130 km / h in the order of 1000 rpm. Due to the reduced piston speed the loads of the engine can be reduced. Noise and fuel consumption can be reduced as well, but achievable in the plane speed decreases.
Another advantage is the easy insertion of a switch; However, the operation was considered too cumbersome especially by clients of brands Opel and Ford. Most importantly, it allows manufacturers to deliver a gentle cycle without major development effort. The switch was located on the steering column or gearshift.
In American GM vehicles had automatic between "N" and "D" shift position "O". This should be instead of " D " is used when the vehicle is towing heavy trailers and no permanent load change takes place. In this switch position the overdrive is activated automatically from a speed of 70 km / h or 40 mph when no high torque is transmitted. The overdrive can not transmit high torques. It provides an oil pressure loss reduced fifth gear of a gearbox inside the automatic transmission and will produce the speed on the speedometer when cruise control, and the vacuum are sampled from the intake manifold with a vacuum switch to the traction magnet to switch on the overdrive when needed. The switch position "D " disables this circuit so that the overdrive is disabled. Accelerator and cruise control are designed so that it can be dosed very precisely between idle and lower partial load. Here, the overdrive can only be switched off when it is no longer avoidable. With this function, the small block ( engine blocks with cylinder bore of 100 mm (4 ") ) could be maintained at speeds between 90 and 110 km / h under a consumption of 11.5 liters per 100 km.
History
Development
In the 1950s and 1960s, the overdrive was in English sedans and sports cars relatively common as ordering option in the performance category between 60 and 150 hp. The standard four-speed transmission, it could often fail to incorporate a fifth gear, but a reduction of speeds in cross-country trips in the growing motorway network and consequently higher travel speeds, more and more was wanted. An overdrive planetary stage could be quite easily grow to an existing transmission design: with a longer housing the propshaft for the planetary gear, with a slightly shorter drive shaft and an electrical switch to actuate the solenoid valve controlled and oil pressure actuated band brake of the planetary ring was the overdrive quite inexpensive to build. However, the maximum torque had to be considered: the lower, " more powerful " transitions an overdrive with the holding forces can not cope, so he can only be in the highest gear or only in the third and fourth gears operate.
Current
Today's vehicle transmissions usually have one or two longer passages translated, so that no downstream overdrive transmission is no longer required. In the 1950s and 1960s, however, the overdrive transmission was especially widely used by Volvo and British manufacturers. Opel offered it in the models Opel Kapitän, record E1 and Commodore C briefly to. Ford it offered a short time in the Taunus 17m (P2). However, this special equipment was discontinued after a short time again due to lack of demand, which was due to the somewhat awkward to use.
For the subsequent " Vollausstatten " of classic cars retrofitting a previously missing overdrive is still common when special equipment was available for the vehicle type in question.
An overdrive transmission was standard in the motor vehicle models Lincoln Town Car, Mercury Grand Marquis, Ford Crown Victoria ( sold until 2007, from then only as a fleet vehicle) offered, as well as the Cadillac DTS. Here, the overdrive added each have a four-speed automatic, all these models have a V -8 engine and ran in the year 2011.
Currently, GM still offers a six-speed manual transmission with overdrive in the Buick LaCrosse. It is offered as a free alternative to the normal " six-speed gearbox and can be ordered only with e- Assist, four-cylinder engine.
Manufacturers and licensees
As a major manufacturer Laycock de Normanville is mentioned. Previously presented the Adlerwerke appropriate gears forth under license.
Similar concepts
Similar to a classic overdrive transmission does the APA developed in the 1990s by the company Cetoni (Additional Powertrain Adjustment) transmission. It involves a two-step synchronized additional gear that works depending on the installation direction as step-down or step-up gear. The circuit operates electro-hydraulically and is operated by a small switch on the gear lever. When using the APA gear twice as many switching levels are as in the standard manual transmission. It can be used in almost any rear-wheel drive and four-wheel drive in many vehicles to enhance either the speed or the pulling force.
Terms
In the DIN standard 70023 " Designation of cars items " from April 1954 following gear types include listed under the auxiliary transmissions: "Mountain -speed transmission ", " Overdrive Transmission " and " overdrive gear " (not " overdrive gear "). In the accompanying supplement dated April 1958, contains the following English translations: " overdrive " for saving gear and overdrive gear, and "hill gear" for the Mountain -speed transmission. Today, the term overdrive is commonly used in vehicle tests as well as product for very long passages translated. Likewise, the use of transitions is common that are not translated into Slow, but the Fast.