Emtron Drive By Wire control is more than just a DC position control system. Fundamentally, DBW as a system can be leveraged for many usages other than just opening and closing vs a pedal target. Because the Emtron strategy is embracing these concepts, it’s important to understand how it functions.
Screenshots 1: Pedal Demand
Often users are trying to quantify the relationship of Pedal Position to Servo Position. This is not a 1:1 relationship.
Observe the Driver Demand Torque tables in the Torque Management section.
“Pedal to Throttle Area Demand” translation tables are available to allow the user to dictate/curve/bend the demand of throttle area demanded into the torque model. This appears to be a traditional translation to servo position, but it’s a translation to Throttle Area which is a function of the Throttle Body Model.
Screenshots 2: Throttle Body Model
In the Engine Functions, Throttle Body Model, is the Throttle Body Area table. This is what the Pedal to Throttle Area Demand translates to. Only here can direct demand to raw servo position target be quantified.
In most cases, the calibrated Throttle Area will not be 1:1 with a calibrated position (0-100% or degrees even). Simply holding an actual throttle body in your hands and opening and closing it observing the visual area opened vs positions it’s obvious. In the past, mechanical throttles had mechanisms to help control/change the “ramp” input from the pedal/cable to throttle to actual throttle blades. This is especially true on engines with large throttles or carburettors with multiple barrels (primary/secondary ramps, etc).
Often the first instinct is to “target the DBW like a cable throttle 1:1”, but this is not the case on most cable throttle applications anyways. In a traditional “Pedal2Servo” PID controller system, often what happens is the calibrator ends up with a “bent” demand table (to make the car drivable). The table is inversely representing the actual throttle area of the given throttle body.
Screenshots 3: Throttle Body Area vs DBW Servo Position
The Emtron Throttle Body Model generates air flow through the model with the correct sensors equipped. It also calculates engine torque through a complex torque model (not a strict estimation system). These systems can be used to validate the throttle area to a true value. In the screenshots above you can observe the channels that show raw servo position (Throttle Position) vs the Throttle Effective Area channel on a calibrated throttle.
Circling back to the first instinct to “target DBW 1:1” is achieved furthermore through targeting the Throttle Area Demand 1:1 – NOT the Servo Position (see Section 1 – demand is mostly linear).
The added benefit to the calibrated systems is that at different engine loads, pressure ratios, etc – the throttle area demand for Torque Management can be reverse calculated as outflow to control engine torque. This is superior to a system set up to simply close raw servo position that would not be compensated by actual engine load/air flow/etc.