Friedrichshafen, Germany/Kortrijk, Belgium. Improved ride comfort and constantly high stability of the vehicle body do not have to be mutually exclusive. ZF Friedrichshafen AG has proven this with its Premium Comfort Valve (PCV) hydraulic damping system. The performance of the new ZF valve system has been impressive, above all, in modern buses. Gradual fine-tuning and settled oil flows increase the way drivers and passengers perceive comfort. That is why an increasing number of vehicle manufacturers are opting to use the new dampers in volume bus production.
ZF’s PCV technology shows how the chassis design can combine drive comfort and driving stability to create a noise-optimized and cost-effective solution. In fact, PCV is a purely hydraulic vibration damper that does not require any electronic or pneumatic add-on systems. After proving itself successful as standard volume production equipment in buses from MAN, Solaris, SOR and Wrightbus, Chinese manufacturer Yutong will outfit its vehicles with PCV starting July 2017.
The heart of PCV technology is the newly developed oil feed system on the piston end. “Thanks to the different spring washers, valves and bores, PCV provides us with considerably more parameters for the characteristic curve design than standard dampers,” explains Georg Memmel, head of Development. “As a result, the damper characteristics can be defined much more specifically to match customer requirements and the vehicle’s field of application.”
A significant increase in the damping force in the low speed range reduces rolling and pitching motions to a minimum. Above all, this increases bus driver and passenger safety during braking and starting maneuvers. At medium speeds, the PCV with its modified oil feed system ensures a slower rise in the damping force. The progression of the characteristic curve is flatter, which is expressed in a softer, more comfortable suspension response. The PCV also adjusts the oil flow at high speeds to keep the vehicle uniformly stable and to prevent the vehicle body from pitching and subsequently rocking. Higher flow resistance leads to a further increase in the damping force. The vehicle body remains stable. This ensures safe vehicle handling.
PCV offers yet another plus in terms of drive comfort: Thanks to the new valve geometry, the oil flow in the bypasses is much calmer compared to traditional twin-tube dampers. “This approach enabled us to considerably reduce the functional hydraulic flow noise in the dampers with PCV – a factor that has become increasingly important in the appeal of buses and coaches with alternative and already more silent drives,” Mr. Memmel explains. “PCV therefore also promotes the new, comfortable feel when traveling in electric and hybrid buses, for example.”