ACCELERATION MODULATION

The linearity of acceleration relative to pressing the accelerator pedal (hereinafter referred to as AP) is the dependence of acceleration on AP. It is characterized by:

• straightness
• absence of dips and jerks – the car does not react unexpectedly abruptly or with a delay to pressing the AP – the driver easily dispenses traction.

Linearity is extremely important for confident and smooth driving and ensures its intuitiveness – the driver feels a direct "connection" with the car. It depends on the calibrations of the engine control system.

The nonlinear characteristic is often referred to as "damped". This feature is used to control the car more smoothly (less jerks and sudden accelerations in urban driving modes) and to increase transmission life.

Dependence with dips and jerks is an indicator of crude calibrations and is rarely found on production vehicles.

The engine control system includes:

• input sensors
• an electronic control unit (ECU), a miniature computer with "hardwired" software - calibrations
• actuators of the engine systems

Input sensors measure specific engine operating parameters and convert them into electrical signals. The information received from the sensors is the basis for engine control.

In modern cars with internal combustion engines, the following sensors are used:

• fuel pressure / intake manifold pressure sensor – strain gauge, which detects pressure changes due to membrane deformation, converting the shape change into an electrical signal
• the rotational speed of the crankshaft sensor - measures the change in the magnetic field from the teeth of the disk on the crankshaft, generating electrical impulses
• the position of the accelerator pedal / throttle sensor - fixes the angle of pressure of the AP by changing the contact position
• the mass air flow potentiometer – fixes the change in heating of the sensor element, which is cooled by air
• the detonation resistance sensor - fixes engine vibrations during detonation, converting them by the piezoelectric element into electrical signals
• coolant temperature, oil, intake air, oxygen sensors and others

The electronic engine control unit receives information from sensors and generates control signals to the actuators of the engine systems in accordance with the calibrations. In its work, the electronic control unit interacts with the control unit of the automatic transmission, the ESC (or ABS) system, electric power steering, airbags, etc.

The main actuators are part of specific engine systems:

• the fuel system– an electric fuel pump – creates pressure by feeding fuel from the tank to the engine
• the injection system – injectors – supply fuel, spraying it in the form of small droplets for better mixing with air
• the intake system – the throttle actuator – controls the position of the circular plate by adjusting the air flow into the engine at the command of the control unit
• the ignition system – the ignition coil – converts 12 V of low voltage into a high–voltage pulse (up to 30 kV) for a spark on the spark plug
• the exhaust gas recirculation system – an electromagnetic valve – opens and closes by regulating the gas flow at the signal of the control unit
• the gasoline vapor capture system – the adsorber purge solenoid valve – opens at the signal of the control unit, passing gasoline vapor from the adsorber into the intake manifold for combustion.

During calibrations of the engine control system, the following main groups of parameters are studied (presented in the form of maps (tables), curves, or individual constants):

• fuel cards: fuel injection parameters for different operating modes (RPM, load, t°, etc.).
• ignition timing angle maps: the ignition moment depends on the engine speed, load, t°, and fuel type.
• parameters for controlling the composition of the mixture: air/fuel ratio values.
• throttle control parameters: pedal sensitivity, filtering, damping.
• idle speed parameters: target RPM, XX correction in different modes (start-up, warm-up, load).
• temperature correction cards: injection and ignition adjustments on a cold/hot engine.
• limitations for engine protection: maximum revolutions, torque limitation, cutoff revolutions, and emergency temperatures.
• valve timing adjustments: operation maps of timing shifters.
• exhaust gas cleaning parameters: EGR valve operating zones, reactions to O2 sensor signals.
• parameters for different environmental modes (Euro 5/6 and higher)
• conditions for interaction with other systems: air conditioning, power steering, start-stop system. For example, in kick-down mode, the air conditioner turns off to increase the use of engine power for acceleration.