Methods to improve fuel economy, even if incrementally, is a pervasive topic at the booths of global truck and bus OEMs and their suppliers at the IAA Commercial Vehicles tradeshow in Hanover, Germany. Engine downspeeding—operating an engine at lower rpm during highway cruising by employing faster axle ratios—is one of the levers companies can pull to achieve this goal.
Downspeeding, however, creates some challenges, namely higher torque stresses that must be managed. Higher levels of vibration in the gearbox and engine need to be mitigated to prevent noise and possible failure. Valeo has developed a High Torque Low Stiffness (HTLS) clutch disc that helps solve this problem, according to Norberto Termenon, Marketing Director, Valeo Transmission Group.
The HTLS technology serves as a “downspeeding enabler,” he said, increasing damping performance by 40% compared to a standard damper while transmitting a torque up to 4200 N·m (3100 lb·ft). This allows a reduction in the engine speed by up to 200 rpm, which translates into fuel savings between 1% and 2%, depending on vehicle application and usage.
“It allows the engine maker to say, ‘Ok, the truck now is running on the highway at 1100 rpm; thanks to this damper, I can run it at 1000 rpm, keeping the torque at the same level without impacting the durability of my gearbox,’” Termenon said.
The HTLS damper consists of five spring sets, 4-faces hysteresis and pivoting seats. “We have increased the inner diameter of the facing and give more space to the damper, which means we can put in longer springs to reduce the stiffness of the damper. We keep the same outer diameter,” he explained. “But then we have to deal with more pressure, more thermal strain on the facing. So we have been obliged to realign the facing grooves to improve the airflow inside to cool down the clutch in a better way.”
No changes were made to the materials used.
Compatible with manual and automated manual transmissions, the HTLS technology is now in series production. One current application is 5- and 6-cylinder hybrid and non-hybrid Scania buses, Termenon said.
Taking this damping concept a step further, Valeo is developing another solution that, when combined with HTLS, allows additional downspeeding—up to another 200-rpm reduction. The technology, called Pendulum, uses specifically dimensioned floating masses to dynamically absorb the engine vibrations. The damping performance increases by 30%, thus offering 1% to 2% of additional fuel savings.