Sweep and Lightoff Package

 

This software package is also geared toward engine emission controls and testing. It is design to allow the user to generate various Air to Fuel Ratio patterns which then generates exhaust emission patterns. These patterns can be used to test many different things including

  • Catalytic converter
  • Exhaust sensors
  • Exhaust manifolds
  • Injector/fuel delivery systems
  • Ignition systems
  • Tailpipes
  • Muffler

The software can also be helpful in testing code written for On Board Diagnostics and other programmed functions within the engine control module.

Sweep and Lightoff Basic Principles:

The program is divided into sections. Each section provides the user with a different function. The sections include:

  • User Interface
  • Engine Mapping
  • Waveform execution

User Interface:

The User Interface Allows the user to define up to 32 segments. Each segment can be 9999 sec long and can have various parameters associated with it. The picture shows the various parameters which are associated with a segment, in this cased segment #2. The starting time of the segment is based on the ending time of the previous segment. The remaining buttons allow for the following to be set:

Frequency: The frequency of a function such a a sine or square wave. (Hz)

Curve: Type of function, Sine, Square, Triangle etc..

+Amp: The Positive amplitude, in the case of a sine wave, this is the amplitude of the positive portion of the wave. The amplitude is in units of Air Fuel Ratio. Therefore, a value of 1 means 1 AFR above the zero portion of the sine wave.

-Amp: The Negative Amplitude control functions similarly to positive amplitude but works on the negative portion of the wave.

Slope: This control adds an additional function onto the wave. The function can be a line or a function such as parabolic or logarithmic.

Slope Constant: The multiplication factor that the slope is multiplied by. This allows adjustment of the slope in the case of a line or the shape of a parabola.

Slope start/end: An addition control of the slope of a line.

Step No: This adds a step function to the wave. The value indicates the number of steps requested.

Step Start/End defines the height of the overall step. For example, if a value of Step Start is 0 and the End is 2, then all the steps defined in Step No. would span 2 AFR's.

Random AFR: This control adds random AFR spikes to the wave, up to the size specified using this button. A value of .5 for example, inserts random spikes up to .5 AFR in maximum size onto the waveform.

Offset: This is a simple linear offset of the entire wave. A value of -1  for example shifts the wave down 1 AFR (rich).

This pictures shows two segments, one sine wave, one square wave.

Once the segment is defined, the DONE button allows the user to add additional segments if needed up to 32.

 

Engine Mapping:

 Once all the segments (waveforms of AFR) have been defined, then the engine injectors must be commanded to produce the waveforms. There are a few different methods which can be used to command the injectors, including a feedback method where an AFR signal is feed back to the controller and adjustments are made until the desired AFR is achieved. This method is not very accurate and does not work well with higher frequency AFR waveforms. Therefore, the Sweep/Lightoff program utilizes a feed forward method to command the injectors. This method utilizes a mapping of the injector pulse widths to convert AFR waveforms into injector pulse width waveforms.

 As a result, for this software to function, the engine must be mapped before a run or sweep can occur. To prevent this mapping from being a headache for technicians, we automated the process by including automatic mapping routines in the software which will a create steady-state mapping  of your engine. This map is used to generate the injector pulse widths needed to run the test.

 

 Waveform Execution:

This routine is used to control the injector pulse width once they  are generated by the engine mapping routines. The pre-calculated pulse widths are sent to the EMAS II and are injected into the engine. The pulse widths are updated on each engine cycle which provides good resolution of the waveform.  This  is important when higher frequency waveforms are used.