CrankSmart® :
Top Quality Combustion Analysis Results and Reduced Costs
 Is the underlying architecture of today's combustion analysis instruments still cutting edge? A team of experts made up of engineers from the Research Institute of Automotive Engineering and Vehicle Engines Stuttgart (FKFS) and Kistler now has the answer to this question with an innovative solution derived from intensive team research.
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Clear competitive edge in engine development
With over-the-road testing in particular the application engineer is predominantly concerned with measurements involving transient (including start/stop) engine operation. The low application costs and high quality of different combustion analysis results at the end of the measuring and evaluation chain are crucial to this work. These are achieved with an optimized combustion analysis system architecture:
• Time-based signal acquisition for – by comparison with conventional systems –
significant improvement in the quality of the measurement data with analog and
digital signal processing methods.
• Relation to TDC and crank angle without optical crank angle encoder, using instead
a standard in-vehicle sensor such as the 60-2, whose special characteristics
are allowed and compensated for in conditioning to ensure data of comparable
quality.
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 CrankSmart® – High resolution time-based sampling rate for optimal data quality
With the CrankSmart solution from Kistler cylinder pressure signals, low-pressure indication, ignition or injection pulses and crank angle marks are measured synchronously on a time basis. The angle marks used can be generated from a relatively low resolution signal, for example by the "60-2" wheel sensor. With conventional combustion analysis systems, to control data acquisition high-resolution crank angle pulses have to be generated by extrapolation in real time. With CrankSmart, relation of the measurement signals to crank angle is correctly interpolated with a very high resolution of 0,1° of CA, as the complete timing of the crank marks is already known at the time of signal processing. The changes in speed within the cycle are taken into account. To avoid aliasing effects analog signals pass through a low-pass filter before digitization. After digitization the data streams (pressure curves, angle marks, etc) of digitally optimized quality are accurately merged using the common time basis. |
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Effects of CrankSmart® on cylinder pressure signals
• The individual measuring channel provides data for evaluations related to time and
crank angle.
• Time-based data allows highly reliable and sensitive evaluations in the
frequency domain (combustion noise and knocking).
• Signal noise such as pipe oscillation is filtered out of the cylinder pressure curves.
Simple sensor mounting solutions (measuring spark plugs, glow plug adapters,
measuring glow plugs, etc.) and even standard vehicle sensors can be used even
where stringent data quality requirements are imposed.
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 Time versus crank angle basis
There are a very wide range of data resolution requirements depending on the evaluation necessary. Whereas time-based data is ideal for knock analysis and combustion noise, evaluations related to TDC, such as IMEP calculations, etc., have to be related to crank angle. For some functions the ideal basis for the data (such as injection duration in "degrees of crank angle" or comparison of actual value with set point in "microseconds") depends on the precise application. However, rather than being primarily dependent on the angle marks, data acquisition should generally be coupled to the "senior instance of time" with a high sampling rate. This is the only approach yielding an extremely accurate relation of the measurement data for IMEP calculations to TDC – even with crank angle encoders with low pulse rates.
Optimized method of relating to crank angle and TDC
• High-quality values and combustion position data is also possible with
the "60-2" wheel/speed sensor. Interpolation allows extremely accurate
generation of additional data points here.
• Speed-dependent phase errors are compensated for.
• Even with transient and start/stop engine operation, combustion analysis can
dispense with an optical crank angle encoder.
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Kistler involved in winter testing: expert support during test runs under extreme conditions
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