Innovative valve lift adjustment optimizes hybrid drives
7 January. 2021 l Carola Borovnik
The innovative valve lift adjustment system – or how we call it: the Presta Sequential SlideCam System - makes combustion engines more economical and future-proof.
In conjunction with systematic hybridization and electrification, the career of this 150-year-old powertrain is far from over. Renowned car manufacturers are currently developing new generations of engines for use around the world. New units are being optimized specifically for combination with electric motors in plug-in hybrid vehicles, where they can operate in more efficient load ranges. So the prospects are good for a new advancement in valve train technology from thyssenkrupp Automotive: The Presta Sequential SlideCam System makes internal combustion engines more economical and fit for the future – while at the same time saving space and costs.
Eco-friendly in series
The innovative valve lift adjustment system combines robust sliding cam technology with a single actuator. Following extensive testing and validation the system is ready for production and can be implemented with no great expense. It is also ideal for making internal combustion engines in hybrid drives more efficient and thus eco-friendlier.
One of many points at which internal combustion engines can be optimized is the valve train. A variable valve lift adjustment system offers several advantages: One tried-and-tested method is cylinder deactivation. In the partial load range, the intake and exhaust valves are closed in line with power requirements via a valve lift adjustment system. As a result the remaining cylinders run at higher loads and are therefore more efficient.
Another solution used in several production powertrains is variable valve control, which allows two-stage adjustment of valve lift on the intake side of the valve train. In the partial load range, a shorter valve lift allows fresh air to be taken in efficiently in line with requirements, avoiding throttling losses. In higher load ranges the system switches to full valve lift to exploit the full power of the engine.
Alternative to conventional slide cams
All these systems are based on established sliding cam technology, which is highly robust and offers cycle-accurate operation.
But it is not possible to integrate conventional sliding cam technology into all engine architectures. One or two actuators are required for each sliding element and need to be mounted directly next to the camshaft. That means that enough space must be available to install the technology in the cylinder head. Modern engines already have numerous components in the direct vicinity of the camshaft, such as the crankcase ventilation system and adjacent fresh air infeed, that take up packaging space. Moreover, for price-sensitive vehicle classes the costs of the actuators and their controls are a further important factor in deciding whether the additional expense is worthwhile or whether efficiency gains can be realized at lower cost using a different technology.
The winning idea
“We looked at what could be left out to make valve lift adjustment functional and simple,” says Dr.-Ing. Heiko Neukirchner, head of Research and Development at thyssenkrupp in Chemnitz. “Our basic idea was to manage with just one actuator per camshaft. But then how could the other sliding elements be actuated?”
Marcel Weidauer and Jens Schirmer came up with an ingenious solution. The individual sliding elements are coupled mechanically by an actuator rod to allow them to be controlled by just one actuator. All components can be integrated in the cylinder head and need no additional packaging space outside the cylinder head cover.
In principle the system is suitable for all internal combustion engines with at least two cylinders in line. Its name: Presta Sequential SlideCam (PSSC) System. For 3-cylinder models and for R6, V6 and V12 engines in particular it offers high added value due to the phased firing sequence. Integration of the system requires just a few components for each camshaft: an actuator, a primary cam, two secondary cams, an actuator rod with coupling pins and a locking plate. But the system has also already been simulated for four-cylinder engines and is currently being tested.
How it works:
At a defined point during the rotation of the camshaft, the actuator pin is activated. It comes into contact with the guide groove and axially shifts the primary cam, which is guided by the toothed shaft. The pin is normally activated electromagnetically.
The axial movement of the primary cam resulting from the contact between pin and groove is transferred to the actuating rod via an additional groove and a coupling pin. In conjunction with the locking plate mounted axially in the cylinder head, the actuator rod is the key element in the system because it eliminates the need for further actuators. The actuator rod is mounted in a guide in the cylinder head. To ensure it stays in position even under no load, the actuator rod and sliding cams are fastened by detent mechanisms.
Sequential phase-shifted actuation of the secondary cams in line with the firing sequence is achieved through contact of the actuator rod coupling pins with the control grooves of the secondary cams. The coupling pins are only shifted in the direction of the camshaft axis, their radial position remains unchanged. The groove contours of the secondary cams are designed in such a way that during actuation of the primary cam and actuator rod no forces are transferred between actuator rod and secondary cams. A locking plate mounted on the camshaft prevents the shifting forces from the secondary cams from being transferred to the primary cam. This plate absorbs the secondary cam shifting forces transferred by the actuator rod. The locking plate is mounted axially in the cylinder head in such a way as to dissipate the forces directly. A corresponding recess in the locking plate guarantees the shifting of the rod during the movement of the primary cam.
All sliding cams are actuated within one rotation of the camshaft. As the conventional electric actuator of the primary cam can send a signal to the control unit, e.g. via the release of the actuating pin, and the entire actuating system is controlled mechanically, the actuating process of all valves can be recorded and processed electronically.
The actuator rod is free to move as long as the primary cam and the actuator rod itself is being shifted. As soon as this movement is completed, the actuator rod is locked in axial direction by the locking plate and the actuation processes for the secondary cams can take place. Around 120° cam angle is available for the actuation of a sliding element. Depending on the length of the cam profiles and targeted overlaps of the actuating ranges of the two secondary cams, it is possible to increase the available actuating angle for each cam element to up to 160° cam angle. This reduces the actuating forces and increases the maximum actuating speed of the system.
Conclusion: Economical and future-proof combustion engines thanks to PSSC
In developing the PSSC system, thyssenkrupp has succeeded in combining the robust sliding cam technology with a very simple actuating system that can be integrated easily into existing cylinder head architectures. Compared with a conventional sliding cam solution, this system saves on packaging space, weight, wiring and sealing. It also lowers the requirements on the engine control unit.
A further advantage makes the system even more future-proof: If required it can also deactivate all the valves and thus shut off the internal combustion engine completely. This is particularly significant for P0 or P1 hybrid drives as it allows the ineffective cycle change during freewheeling to be stopped. This reduces the braking torque of the internal combustion engine and increases the recuperation output of the electric motor. Another positive effect is that the exhaust gas treatment system does not need fresh air input during overrun phases, as these sensitive systems always require stoichiometric exhaust gas in order to operate effectively. Other configurations, such as valve lifting on just one camshaft or a three-stage system, are also possible.
The advantages at a glance:
Lower system weight
Only one actuator required per camshaft
Savings on wiring and sealing
Lower packaging space requirements
System can be installed below an existing crankcase ventilation system
Suitable for implementation in various cylinder head architectures
System available for use in a future production engine