ECONOMIC AND FORWARD-LOOKING

FEV develops a compact and cost-effective automatic transmission for city cars

30. September 2015 | Engineering Service

An automatic transmission is particularly useful in A-segment city cars, especially with a view toward future functions. The automatic transmission adjusts to the city driving profile by enhancing comfort during the numerous gear changes and start-stop events. Worldwide, there was a volume of 5.2 million vehicles in 2014 with a predicted annual growth of two percent. This seemingly justifies the development of a dedicated dual clutch transmission (DCT) for this vehicle class as an alternative to the automated manual transmission (AMT). Given this background, FEV is developing a cost-effective and compact dual clutch transmission for a torque range up to 130 Nm – the 5DCT130 transmission.

Today, cost-intensive comfort functions and high-end technologies are oft en foregone in A-segment vehicles. The majority of these vehicles are therefore equipped with a conventional powertrain consisting of a naturally aspirated engine equipped with intake manifold fuel injection and a 5-speed manual transmission. In Japan the continuously variable transmission (CVT) is also predominant in this vehicle class while in India, customers are increasingly demanding automated manual transmissions.

Series components as the key to economy

From the perspective of product cost, the AMT has clear benefits compared to a DCT but, because of its design it presents the disadvantage of rough gear shifts caused by the traction interruption. To address this, it’s necessary to compare the cost benefit of the AMT with the potential advantages of the softer powershifts offered by the DCT. The cost disadvantage of the DCT can only be compensated by the re-use of high-volume production components. FEV has followed this approach in developing the 5DCT130 dual-clutch transmission, which relies on off-the-shelf parts for most of its components. It also fits within the spatial envelop of a narrow transmission for this vehicle segment, since it only has one output shaft. Dual clutch transmissions generally feature normally-open clutches for safety reasons. “To transmit the power, a clutch constantly has to be actively engaged  based on the torque requirement.  This causes a permanent energy demand,“ explains Dr. Ralf Marquard, COO of the FEV Group. “For a permanent energy demand it is more useful to minimize the number of energy conversions, since each individual conversion comes with an associated energy loss.“ For this reason, FEV’s experts selected a combustion engine-powered pump to realize clutch control and cooling, which also has the advantage of a compact arrangement. The solenoids of the compact hydraulic system have been carried-over from the BorgWarner product portfolio.

Future requirements for segment A vehicles

  • Additional comfort and safety functions such as hill start assist, braking assist, lane assist and parking assist systems
  • Further cross-linking such as Car2X communication (connected vehicles)
  • Further requirements in active and passive safety
  • Option of a battery-electric vehicle variant, using same vehicle platform
  • Sailing operation and autonomous driving in the final development stage
  • Extension of the warranty period to at least five years from vehicle registration

Effective combination of leading suppliers‘ technologies

The gear actuator in a dual clutch transmission is only operated sporadically. For this function, a power-on-demand gear actuator in the form of an electro-mechanic off-the-shelf system from LuK was well-suited. This system offered the added advantage of cost-effective introduction of a park-by-wire function. Three shift forks actuate the sliding sleeves to achieve the six speeds, accordingly. The park lock is actuated via a fourth shift  fork. This actuator is already being applied in series production. Apart from the gear actuator, series synchronization assemblies from Hoerbiger Antriebstechnik, a BorgWarner standard wet dual clutch, a standard differential from GKN as well as only off-the-shelf bearings have been used.  Thus, the concept which meets the individual demands of the A-segment in combination with a pool of competent partners establish a good basis for successful series development including short time-to-market.

Wesentliche Daten des Getriebes

  • Transmission characteristics: 5 forward speeds plus 1 reverse speed
    Shortest 1st speed: 16.1
  • Longest 5th speed: 2.8
  • Maximum ratio spread: 5.8
  • Center distance between crank-shaft  axis and diff erential axis: 183 mm or 170 mm
  • Dual clutch type:  Nested clutches arrangement, wet type
  • Dual clutch control and lubrication:  Hydraulic, lower pressure
  • Gear shift actuation : Electro-mechanic

 

Mechanische und elektromechanische Teilsysteme des  5DCT130-Getriebes mit Doppelkupplung: Nahezu alle Bauteile  sind Serienprodukte etablierter Zulieferer

5DCT130 mechanic, electro-mechanic sub-systems and dual clutch: Allmost all components consist of off-the-shelf parts from leading suppliers.

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