turbocharged In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pr ...

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

s, a boost controller is a device sometimes used to increase the boost pressure produced by the turbocharger. It achieves this by reducing the boost pressure seen by the wastegate.

Operation

The purpose of a boost controller is to reduce the boost pressure seen by the

wastegate A wastegate is a valve that controls the flow of exhaust gases to the turbine wheel in a turbocharged engine system.Robson, D. (2018). Aircraft General Knowledge. Aviation Theory Centre Pty Ltd. . Diversion of exhaust gases regulates the turbine ...

's reference port, in order to trick the wastegate into allowing higher boost pressures than it was designed for. Many boost controllers use a

needle valve A needle valve is a type of valve with a small port and a threaded, needle-shaped plunger. It allows precise regulation of flow, although it is generally only capable of relatively low flow rates. Construction and operation An instrument ne ...

that is opened and closed by an electric

solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...

. By varying the pulse width to the solenoid, the solenoid valve can be commanded to be open a certain percentage of the time. This effectively alters the flow rate of air pressure through the valve, changing the amount of air that is bled out instead of going to the wastegate's reference port. Solenoids may require small diameter restrictors be installed in the air control lines to limit airflow and even out the on/off nature of their operation. Two-port solenoid bleed systems with a

PID controller A proportional–integral–derivative controller (PID controller or three-term controller) is a control loop mechanism employing feedback that is widely used in industrial control systems and a variety of other applications requiring continuou ...

tend to be common on factory turbocharged cars. An alternative design is to use a

stepper motor A stepper motor, also known as step motor or stepping motor, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any posi ...

. These designs allow fine control of airflow based on position and speed of the motor, but may have low total airflow capability. Some systems use a solenoid in conjunction with a stepper motor, with the stepper motor allowing fine control and the solenoid coarse control.

Control system

Most modern designs are ''electronic boost controllers'' that use an

electronic control unit An electronic control unit (ECU), also known as an electronic control module (ECM), is an embedded system in automotive electronics that controls one or more of the electrical systems or subsystems in a car or other motor vehicle. Modern vehic ...

to control the boost via a

. The operating principle is the same as older ''manual boost controllers'', which is to control the air pressure presented to the wastegate actuator. Electronic controllers add greater flexibility in management of boost pressures, compared with the manual controllers. The actuation of an electronic boost controller can be managed by one of two control systems: * Open-loop is the simpler option, where control output is merely based on other inputs such as throttle angle and/or engine speed ( RPM). Since an open-loop system does not include any monitoring of boost pressure, the boost pressure may vary based on outside variables (such as weather conditions or engine coolant temperature). For this reason, open-loop systems are less common. * Closed-loop systems rely on

feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...

from a manifold pressure sensor to maintain a target boost pressure as closely as possible. These systems are more sophisticated and can more accurately control boost pressure under varying circumstances.

Advantages

By keeping the wastegate in a closed position more often, a boost controller causes more of the exhaust gas to be routed through the turbocharger, thus reducing

turbo lag In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

and lowering the boost threshold.

Disadvantages

Regardless of the effectiveness of the boost controller, wastegate actuator springs that are too soft can cause the wastegate to open before desired. This due to the exhaust gas

backpressure Back pressure (or backpressure) is a resistance or force opposing the desired flow of fluid through pipes, leading to friction loss and pressure drop. The term ''back pressure'' is a misnomer, as pressure is a scalar quantity, so it has a magnit ...

pushing against the wastegate valve itself, causing the valve to open of the actuator at all. Therefore, there is an upper limit to the effectiveness of a boost controller for a given spring stiffness in the wastegate actuator. To prevent excessive boost pressures in the event of a failure, the boost controller needs to be designed such that

failure mode Failure causes are defects in design, process, quality, or part application, which are the underlying cause of a failure or which initiate a process which leads to failure. Where failure depends on the user of the product or process, then human e ...

do not result in any pressure being bled off. For instance, a solenoid-type boost controller should direct all air to the wastegate when it is in the non-energized position (the common failure mode for a solenoid). Otherwise, the boost controller could get stuck in a position that lets no boost pressure reach the wastegate, causing boost to quickly rise out of control. Also, the electronic systems, extra hoses, solenoids and control systems add cost and complexity. Nonetheless, in recent times most automobile manufacturers use boost controllers on their turbocharged engines.

Alternatives

In the past, boost pressures have been controlled by restricting or bleeding off some intake air before it reaches the

intake manifold In automotive engineering, an inlet manifold or intake manifold (in American English) is the part of an engine that supplies the fuel/ air mixture to the cylinders. The word ''manifold'' comes from the Old English word ''manigfeald'' (from the ...

. Designs which restrict the intake air can use a

butterfly valve A butterfly valve is a valve that isolates or regulates the flow of a fluid. The closing mechanism is a disk that rotates. Principle of operation Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves ...

in the intake to restrict airflow as desired boost is approached. Designs which bleed off the intake air functioned similar to a blowoff valve, but on a constant basis to maintain the desired boost pressure. These methods are rarely used in modern system due to the large sacrifices in efficiency, heat, and reliability.

Variable geometry turbocharger Variable-geometry turbochargers (VGTs), occasionally known as variable-nozzle turbines (VNTs), are a type of turbochargers, usually designed to allow the effective aspect ratio of the turbocharger to be altered as conditions change. This is done ...

can be used to manage boost levels, negating the need for an external boost controller. Also, the

itself has a similar function to a boost controller, in that it is used to manage the turbocharger's boost pressure.

References

{{Automotive engine , expanded Automotive engine technologies Turbochargers