Automatic Performance Control (APC) was the first engine knock and boost control system. The APC was invented by

Per Gillbrand Per Sune Evaldsson Gillbrand (23 March 1934 – 30 November 2016) was a Swedish automobile engineer. Born in Tidaholm, Gillbrand is best known for his contribution to the development of several engines for Saab, and in particular their turbocharg ...

at the Swedish car maker SAAB. SAAB introduced it on the turbo charged

Saab H engine The Saab H engine is a redesign of the Saab B engine, which in turn was based on the Triumph Slant-4 engine. Despite the name it is not an H engine or horizontally opposed engine, but a slanted inline-4. The H engine was introduced in 1981 in ...

s in 1982, and the APC was fitted to all subsequent 900 Turbos through 1993 (and 1994 convertibles), as well as 9000 Turbos through 1989. The APC was sold to Maserati to equip the carbureted

Maserati Biturbo The Maserati Biturbo is a family of executive grand tourers produced by Italian automobile manufacturer Maserati between 1981 and 1994. The original Biturbo was a two-door, four-seater notchback coupé (of somewhat smaller dimensions than the BM ...

, with different settings for the Biturbo, and was known as the Maserati Automatic Boost Controller (MABC). The APC allowed a higher

compression ratio The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...

(initially, 8.5:1 as opposed to 7.2:1, and, on 16-valve variants introduced in 1985, 9.0:1). This improved fuel economy and allowed the use of low-octane petrol without causing engine damage caused by knock. The APC controls boost pressure and the overall performance, specifically the rate of rise and maximum boost level - and it detects and manages harmful knock events. To control the turbocharger, the APC monitors the engine's

RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

and inlet manifold

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

via a pressure

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contr ...

, and uses these inputs to control a solenoid valve that trims the rate of rise of pressure as well as the maximum pressure by directing boost pressure to the turbocharger's pneumatic

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 ...

actuator An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) a ...

. To detect knock, a

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical s ...

knock

sensor A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

(basically a

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...

) bolted to the engine block responds to unique frequencies caused by engine knock. The sensor generates a small voltage that is sent to the

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 ...

, which processes the signal to determine if, in fact, knock is occurring. If it is, then the control unit activates a solenoid valve that directs boost pressure to the turbocharger's pneumatically controlled wastegate, that opens to bypass exhaust gases from the turbocharger directly to the exhaust pipe, lowering turbo boost pressure until the knock subsides. Knock events that are managed by the APC can be discerned when the in-dash boost needle "twitches" slightly. The APC unit has a 'knock' output where an

LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...

may be connected. This LED will then light up if knock is detected. Because the knock sensor becomes less accurate at high revolutions, the APC tapers maximum boost pressure after approximately 4,500 RPM.

APC boost gauge

Saab Full Pressure Turbo (FPT) models with this unit include the APC name displayed on a non-numeric boost

pressure gauge Pressure measurement is the measurement of an applied force by a fluid ( liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pres ...

in the instrument panel. Although knock sensors are common even on non-turbocharged and turbocharged engines today, Saab has continued to use the APC name prominently as a differentiating feature. The white area on the left side of the scale shows

manifold vacuum Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the ...

under normal driving conditions, the short white dash is atmospheric pressure (engine off), the orange scale is where there is safe turbo boost, the red scale is boost above 0.5 - 0.7

bar Bar or BAR may refer to: Food and drink * Bar (establishment), selling alcoholic beverages * Candy bar * Chocolate bar Science and technology * Bar (river morphology), a deposit of sediment * Bar (tropical cyclone), a layer of cloud * Bar (u ...

where the wastegate may be opened or a

fuel cut A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...

due to overboost may occur. Saab integrated the APC's boost control functionality with ignition control in 1990 with the introduction of the DI/APC system, available in 9000 models only. The DI/APC system managed knock not only by decreasing boost via a solenoid but by retarding

ignition timing In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need for ...

as well; DI/APC also managed the engine's basic ignition timing.

References

{{Automotive engine , collapsed Engine technology Saab

APC boost gauge

See also

References