Internal combustion engines must be individually tested at the end of the manufacturing process. In recent years classical hot test stands, where the engine is run for several minutes, are being replaced by cold test alternatives. The latter allow fast testing cycles using an external motoring device without using any fuel. The absence of fuel and combustion lowers the health and safety requirements for the plant itself and subsequent engine transport, but this comes at the cost of additional difficulties for the verification of the correct assembly and operation of the combustion system hardware.
This paper presents a cold test concept, which includes dedicated measurements and algorithms for the detection of common failures in the manufacturing process, including those of the combustion hardware. Between other parameters, the test stand evaluates the existence of compression leaks, the correct variable valve timing (VVT) phasing, the operation of the ignition coils and injectors, and verifies the spark plugs gap to be within specifications.
In all cases, non-intrusive sensors are used and the installation is done taking advantage of the standard wiring of the engine. Compression leaks are detected using the motoring torque and engine speed, and performing a frequency domain analysis of the signal; VVT phasing is verified by camshaft and crankshaft encoders, and with the recognition of the pulsation of the pressure in the manifolds; for the case of ignition coils and injectors, the system is electrically actuated and pattern recognition is applied to the intensity profile; finally, spark plug gap is inferred from the spark success rate at different energizing times.