Cold test

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The cold test is a test procedure in the assembly process of an internal combustion engine that checks whether the previous assembly steps have been carried out correctly. The motor is driven passively by an electric motor and does not run on its own. It thus remains “cold” - in contrast to the hot test , in which the combustion engine is started for the first time with independent combustion of fuel .

The internal combustion engine is operated with engine oil in the cold test . In the case of diesel engines , additional fuel or an equivalent test oil must be added to prevent damage to the high-pressure pump . A cold test station is often located directly on the assembly line. One then speaks of an inline test station. The cold test is usually preceded by leak tests of the oil circuit and the cooling water circuit of the engine in a leak test station.

advantages

  • Test times shorter than 2 minutes.
  • No supply of fuel and cooling water necessary (media supply ).
  • No exhaust gases, therefore no fume cupboard or similar necessary.
  • In the event of a fault, the test item can easily be dismantled as there are no residues of fuel, cooling water or soot.
  • Significantly quieter than a hot test .
  • Better error detection than in the hot test

functionality

An electric motor is coupled to the internal combustion engine. The intake manifold and the exhaust openings are adapted to be pressure-tight. An oil pressure sensor is adapted via an opening in the cylinder block and / or head.

The test item is first turned for a few seconds at a low speed (approx. 75–150 / min). This checks whether the torque to be applied is too great or whether the motor is blocked. Sometimes gross leaks are looked for at this point. If necessary, the test is aborted and the engine is released for rework.

In the positive case, the test item is accelerated to a higher speed of 1500 to 3000 rpm so that the engine's own oil pump can build up pressure. This is necessary so that all bearing points in the engine are adequately supplied with lubricating oil. It is monitored whether sufficient oil pressure is reached after a certain time. Here, too, the test may be aborted and the engine released for rework.

If the necessary minimum oil pressure has been reached, the actual test begins. The speed is significantly reduced again (approx. 300 rpm) because the signals "intake negative pressure" and "exhaust gas back pressure" are more meaningful. The dynamic torque and the dynamic oil pressure are recorded and evaluated.

The injection nozzles can, for. B. can be tested in that a previously built up air pressure is reduced in a controlled manner. In petrol engines, the voltage curve on the spark plugs is compared with a target curve.

All in all, one can clearly decide from the measurements whether the test item has to be sent for dispatch or for rework.

Further exams

The test cycle described above describes the minimum tests, which can, however, be supplemented by further tests:

  • An ignition test determines the functionality of the ignition system (spark plug, ignition coil, ignition cable, possibly control unit).
  • A structure-borne noise test or vibration analysis determines the frequency spectrum of the vibration generated by the rotating motor. This test also allows conclusions to be drawn about errors in the assembly process.
  • Various electrical tests of other add-on parts such as throttle valve , exhaust gas recirculation valve (EGR), engine-own sensors / wiring harness, camshaft adjustment, etc.
  • Check the injection system with compressed air or test oil.
  • Camera system for checking the tightness of the fuel system (with fluorescent test oil, which glows under UV light)

Web links

Individual evidence

  1. ↑ cold test. ( Memento from January 23, 2010 in the Internet Archive ) at: jwf.com