Variable Valve Timing Systems from Original Equipment Manufacturers

22-02 Research the different electrical engine and valve timing control systems.

The basics of VVT systems and variable displacement systems (VDSs) are very simple; they require only the PCM for them to operate. This section will explore the way different original equipment manufacturers (OEMs) operate their VVT systems/VDSs and how they hope to increase the performance of the engine. The following unique systems are explained in depth to help familiarize technicians with how they operate. However, further study will be needed to become an expert in these systems.

BMW VANOS/Valvetronic

BMW VANOS (variable nockenwellen steuerung) is German for “variable valve timing” and has appeared on BMW vehicles since 1992. The premise behind the system is to use an oil-controlled screw phasers to advance or retard a camshaft. This system was first used in 1992 on the M50 engine, which had only a single-VANOS system that controlled the position of the intake camshaft (FIGURE 22-5). Dual VANOS was introduced in 1996 on the S50B32 engine, which then controlled both the intake and the exhaust CMPs (FIGURE 22-6). With the infinite variation of the camshafts, increased power and better fuel economy were realized. In later models, beginning in 2001, VANOS was coupled with BMW’s Valvetronic.

FIGURE 22-5 An early-model of VANOS controlled only the intake camshaft, which was effective in changing the intake valve operation to increase power and fuel economy.

FIGURE 22-6 The dual VANOS engine allows for unlimited control of the intake and exhaust camshafts so that picking the right combination for the situation will allow for the best driver experience.

Valvetronic is a separate system that works in tandem with VANOS to increase or decrease the lift of the valve to manage the operation of the engine. This is done by using intermediate arms that pivot to change the effect that the engine camshaft has on the valves (FIGURE 22-7). These pivot arms are controlled by an external motor that the PCM operates when the conditions warrant the need for this operation. These type of engines do not use the throttle valve like a conventional engine does. Instead, controlling the operation of the intake and exhaust valves controls engine rpm. By controlling the combustion event, the PCM can either speed it up or slow it down, thus controlling the speed of the engine.

FIGURE 22-7 The BMW Valvetronic engine management system allows the camshaft to control the amount of the valve opening by pivoting the rocker arm at a different angle, which affects the opening event.

Toyota VVT-iE

Toyota VVT-iE (variable valve timing with intelligence by electric motor) is a system that uses electric motors on the front of the camshaft to advance or retard up to 40 degrees in articulation. By limiting the use of oil-fed phasers, this system operates in conditions such as at low oil level, low temperatures, and low engine speeds (FIGURE 22-8). The ability to precisely control the advance or retard of the camshafts develops more power, lowers emissions, and increases fuel economy. This system has a phaser that is more mechanical than the oil-pressured vane phasers, which lends to needing more pieces, which increases the possibility of failures (FIGURE 22-9).

FIGURE 22-8 This system is electrically driven, so it is not as susceptible to oil system failures or loss of oil. Timing drive (UR series): 1. VVT-IE motor; 2. VVT-I control solenoid; 3. Crankshaft position sensor; 4. Camshaft position sensor (intake); 5. Camshaft position sensor (exhaust); 6. Water temperature sensor; 7. Camshaft position sensor.

FIGURE 22-9 VVT-iE actuator: 1. Motor; 2. Cover (stator gear); 3. Rotor; 4. Driven gear; 5. Spiral plate; 6. Levers; 7. Carrier; 8. Housing (sprocket); 9. Intake camshaft.

The PCM operates the VVT-iE motor at the speed of the camshaft: When advance is called for by the PCM, it speeds up the motor attached to the phaser to advance the camshaft. This happens when the engine is being accelerated or when increased power is needed. The reverse happens when the PCM is trying to retard the camshaft: It slows the VVT-iE motor to slow down the camshaft when economy is desired. This motor is a brushless direct current (DC) motor that has a control unit and a Hall-effect sensor in it to control position and operation.