What is a car camshaft timing system?

Shaft synchronization system

The valve timing system is a generally accepted international time variable. This system is designed to control the parameters of the gas distribution mechanism depending on the operating conditions of the engine. Using the system provides an increase in engine power and torque, fuel economy and reduction of harmful emissions. Adjustable timing options include. Valve opening or closing time and valve lift height. In general, these parameters make up the valve closing time. The duration of the intake and exhaust strokes, expressed by the angle of rotation of the crankshaft relative to the "dead" points. The timing phase is determined by the shape of the camshaft cam acting on the valve.

Cam cam

Different valve operating conditions require different valve adjustments. Thus, at low engine speeds, the time should be a minimum duration or a "narrow" phase. At high speeds, the valve timing should be as wide as possible. At the same time, the intake and exhaust channels are blocked, which means recirculation of natural exhaust gas. The camshaft cam has a certain shape and cannot simultaneously provide a narrow and wide valve torque. In practice, cam shape is a compromise between high torque at low speeds and high power at high speeds of the crankshaft. This discrepancy is precisely resolved by a variable valve system.

The principle of operation of the timing system and camshaft

Depending on the adjustable timing parameters, the following variable phase control methods differ. Rotating the camshaft, using different cam shapes and changing valve heights. It is most commonly used in racing cars. This increases some of the car's power from 30% to 70%. The most common valve control systems are camshaft rotation BMW VANOS, VVT-i. Variable valve timing with intelligence from Toyota; VVT. Variable valve duration with Volkswage VTC. Variable time control from Honda; Infinitely variable valve timing CVVT from Hyundai, Kia, Volvo, General Motors; VCP, variable cam phases from Renault. The principle of operation of these systems is based on the rotation of the camshaft in the direction of rotation, due to which an early opening of the valves is achieved compared to the initial position.

Elements of the synchronization system

The design of a gas distribution system of this type includes. Hydraulically controlled connection and control system for this connection. Diagram of a system for automatically controlling valve operating time A hydraulically controlled clutch, commonly called a phase switch, directly rotates the camshaft. The coupling consists of a rotor connected to a camshaft and housing. Which plays the role of a camshaft drive pulley. Between the rotor and the housing there are cavities into which motor oil is supplied through the channels. Filling the cavity with oil ensures the rotation of the rotor relative to the housing and the corresponding rotation of the camshaft at a certain angle. Most of the hydraulic clutch is mounted on the intake camshaft.

What does the synchronization system provide?

To expand the control parameters in individual designs, the couplings are installed on the camshafts of the intake and exhaust valves. The control system provides automatic adjustment of the clutch with hydraulic control. Structurally, it includes input sensors, an electronic control unit and actuators. The control system uses Hall sensors. Which evaluate the position of the camshafts, as well as other sensors of the engine management system. Crankshaft speed, coolant temperature and air mass meter. The engine control unit receives signals from the sensors and generates control actions on the drive mechanism. Also called electro-hydraulic distributor. The distributor is a solenoid valve and provides oil supply to the hydraulically controlled coupling and the outlet, depending on the operating conditions of the engine.

Adjustable valve control system operating mode

The variable valve timing system provides, as a rule, operation in the following modes: idling (minimum crankshaft rotation speed); maximum power; maximum torque Another type of variable valve control system is based on the use of cams of different shapes, which lead to a step change in the opening time and valve lift. Such systems are known: VTEC, variable valve control and electronic elevator control from Honda; VVTL-i, variable valve timing and intelligent lift from Toyota; MIVEC, Mitsubishi Innovative gas distribution system from Mitsubishi; Valvelift system from Audi. These systems are basically the same design and operating principle, with the exception of the Valvelift system. For example, one of the most famous VTEC systems includes a set of cameras of different profiles and a control system. System diagram VTEC.

Camshaft Cam Types

The camshaft has two small and one large cam. Small cams are connected through the respective rocker arms to a pair of suction valves. A large hump moves a free rocker. The control system provides switching from one operating mode to another. By actuating the locking mechanism. The locking mechanism has a hydraulic drive. At low engine speeds or also called low load, the inlet valves operate from small chambers. Moreover, the valve operating time is characterized by a short duration. When the engine speed reaches a certain value, the control system activates the locking mechanism. Rockers of small and large cams are connected using a locking pin and the force is transmitted to the intake valves from the large cam.

Synchronization system

Another modification of the VTEC system has three control modes. Which are determined by the work of a small hump or the opening of the intake valve at low engine speeds. Two small cams, which means two intake valves open at medium speed. And also a big hump at high speed. Honda's modern variable valve timing system is the I-VTEC system, which combines the VTEC and VTC systems. This combination significantly expands the engine control parameters. The most advanced variable valve control system in terms of design is based on valve height adjustment. This system eliminates gas under most engine operating conditions. The pioneer in this area is BMW and its Valvetronic system.

Timing Camshaft

A similar principle is used in other systems: Toyota Valvematic, VEL, variable valve and lift system from Nissan, Fiat MultiAir, VTI, variable valve and injection system from Peugeot. Valvetronic system diagram. In the Valvetronic system, the change in valve lift is provided by a complex kinematic scheme. In which the traditional rotor-valve clutch is complemented by an eccentric shaft and an intermediate lever. The eccentric shaft is rotated by the motor by means of a worm gear. Rotation of the eccentric shaft changes the position of the intermediate lever, which in turn determines a certain movement of the rocker arm and the corresponding movement of the valve. The valve lift is changed continuously, depending on the operating conditions of the engine. Valvetronic is only mounted on the intake valves.