Camshaft Adjusters for Production Engines

After the start of mass production of the Alfa Romeo camshaft adjuster, other designs were used by other companies such as Mercedes-Benz, Nissan, and others. Most of these systems used straight/helical teeth similar to Alfa Romeo as the functional principle.

A system that adjusts the control times by changing the chain side length is the camshaft chain timing device by the company Hydraulik-Ring. The adjusting element is between the dual camshaft drive wheels, and the intake camshaft is driven by the exhaust camshaft. The timing device system combines a chain tensioner that is commonly used for such a short drive with a hydraulic cylinder to change the chain side length. The hydraulic cylinder under oil pressure on both sides is moved, depending on the desired control time position. In this manner, one chain side is lengthened, and the other is simultaneously shortened. This timing device provides two control time positions for the intake camshaft (Fig. 10-70).

Fig. 10-70. Functional principle of the camshaft chain timing device

During adjustment, the chain drive remains taut between the two drive wheels of the camshaft because of the chain tensioner integrated into the system. The adjustment cylinder of the timing device is controlled by an electronically controlled hydraulic 4/2-way valve. The timing device solution shown here uses hydraulically variable valve actuation since the end positions are held only by oil pressure. The design is such that the adjustment is made with the available engine oil pressure even under difficult conditions. A costly additional oil pump can be dispensed with. This timing principle is used in various series engines by Audi, Porsche (Fig. 10-71), and Volkswagen.

Fig. 10-71. Camshaft adjusters as a chain timing device for the Porsche Boxster

Developments of the continuously variable adjustment of intake camshafts have enabled more than two camshaft positions to be held.

BMW was the first to use continuously variable adjustment of the camshaft in mass production (Fig. 10-72). First, this was used only for the intake camshaft, but it was followed later by continuously variable adjustment of the intake and the exhaust cams.

Fig. 10-72. Continuously adjustable camshaft adjustment for a BMW six-cylinder engine

A new generation of camshaft adjusters is represented by systems designed around the principle of swing motors.

In this system, both the intake and the exhaust camshafts can be easily adapted to existing cylinder heads. Inside the timing device is a pivotable rotor that is firmly fixed to the camshaft. The outer part is driven either by a chain or a cogged belt. The connection between the outer and inner parts is formed by the oil space that is filled with engine oil pressure and that contains the pivotable rotor. Both sides of the blades of the rotor are supplied with oil pressure via an electronically controlled 4/2-way proportional valve.

The relative angular position of the camshaft is changed depending on the change in oil pressure on both sides of the rotor. The angular position of the camshaft measured with a sensor is compared to the position set by the Motronic system. The desired position of the camshaft is permanently readjusted by controlling the proportional valve to hold stable intermediate positions of the rotor and, hence, of the camshaft. The oil is supplied only by engine oil without an additional pump.

The system is controlled by the speed, load, and engine temperature. In comparison to conventional, toothed, continuously variable camshaft adjusters, these systems represent a much more economical solution so that one can expect their increasing use in series spark-ignition engines. The time and money spent on manufacturing the components can also be reduced when parts of the components are sintered and the seal of the oil chamber has a simple design. Timing devices of this type can be even more economical than toothed two-step timing devices.

The design of the dual camshaft adjusters with swing motors by Hydraulik-Ring for a six-cylinder engine is shown in Fig. 10-73.

Fig. 10-73. Functional principle and control loop of a continuously variable camshaft adjuster designed with a swing motor

Figures 10-74 and 10-75 show the arrangement of dual camshaft adjusters with swing motors for the left cylinder bank of the 3.0 1 Audi V6 engine. In this engine, a two-step timing device is used on the exhaust valve side, and a continuously variable timing device is used on the intake valve side. With this design of a cogged belt camshaft drive, the timing device housing needs to be encapsulated oil-tight.

Fig. 10-74. Camshaft adjuster arrangement in a six-cylinder engine based on a swing motor principle

Fig. 10-75. Dual cam adjustment system in a 3.0 1 V6 spark-ignition engine by Audi

In addition to Hydraulik-Ring series systems used by Audi and VW, similar systems with swing motors are used by Renault, Toyota, and Volvo.

A wide variety of hydraulic valves are used for the hydraulic control of the camshaft adjuster. Usually, directional controlled valves are used to control the oil flow. These can be subdivided into proportional and switching valves. Camshaft adjusters that hold only two end positions and, hence, can have only two different control times are equipped with 4/2-way valves.

Fig. 10-76. A cross section, Q-I characteristic curve, technical data, and the hydraulic symbol of 4/3-way proportional valves

Today, primarily 4/3-way proportional valves are used for continuously variable systems (Fig. 10-76). The bulk of hydraulic valve engineering has less to do with manufacturing individual valves for small series than with implementing the technical requirements for economical large series production. The difficult problems of series production need to be dealt with such as dirty oil, engine vibration, high temperature fluctuations, or fluctuations in the vehicle power supply. Usually a special valve is used to adapt the valves to the individual engine. A well- thought-out modular system is useful to meet the primary requirement of economical mass production. Close collaboration between the developers of the variable valve actuation system and the developers of the engine is essential for successful mass production.