Pressure and Electrical Test System for Engine’s Cold Test

Abstract
The production process of vehicle engines requires a set of test and verification on engine itself. There are two ways to proceed. The first is to perform a hot test, with the engine fed with fuel. The second is to perform a cold test, that does not require the start of the engine. The latter has several advantages and is the most commonly used solution.
PETS.Ect system provides the necessary electronic resources for measuring, controlling and monitoring engine’s physical values during the cold test.
Introduction
PETS.Ect, acronym of “Pressure and Electrical Test System for Engine’s Cold Test” is an electronic apparatus to drive, measure and check fuel engines.
PETS.Ect can communicate with Siemens and Omron PLCs through Ethernet TCP/IP network.
Implementations of other protocols, or other PLC controllers can be developed as add-on.
The apparatus, thanks to this PLC interface, can work in a completely automatic way and it can be synchronized inside an automatic assembly line, without the need of an operator to attend the workstation. The human machine interface console is present with the main purpose of:

  • Allow diagnosis and maintenance service by qualified personnel
  • Give a visual indication about system status and about device under test status

If required, the PETS.Ect system is able to work off-line too. In this case the actions of test selection and run will be executed by the user, through the console.

Hardware description
The system is enclosed in a standard 19“ chassis, that allows an easy displacement of the unit.
PETS.Ect main internal parts are:

  • PC BOX, for control, data analysis, humanmachine interface, logging
  • National Instruments PCI-6221 DAQ Card, for data acquisition and I/O operations
  • Ttech T.Daq board, for signal conditioning and input/output interface
  • Ttech Security Board, to lock power supply if neighboring condition are unsafe.
  • 24 VDC Power Supply, for internal power.
  • External load box, custom defined

Operation
The MAIN page contains a list of values, for the measuring test phase. In addition, a set of graphs show the time evolution of measurements during the test in progress.

Figure 2 – PETS.Ect Software

The following actions list summarizes the step by step operating flow during a test.
1. The system waits for a start signal from PLC.
2. Once this signal is received, PETS.Ect check the product code sent by the PLC itself and, if required, make the product settings change.
3. After a set-up phase, the system starts with the check steps. The system traces the step progress and the status of step already done.
4. PETS.Ect measures the current consumption of the starter motor of the engine.
5. PETS.Ect performs voltage measurements of the three phases of the alternator.
6. Moreover, the system is able to acquire the pick-up output voltage and starting from this signal it calculates the speed (RPM) of the engine.
7. In addition to the electrical measurements, the system can read, with the same timing rate, the oil pressure inside the engine.
8. Finally, the system records the ambient temperature with a PT100 sensor with the same sampling frequency of the other signals.
9. The results collected are sent to PLC, with the global test status (pass or fail)
10. After a suitable synchronization cycle with PLC, the system comes back to the waiting phase
From what shown so far, it is clear that there is no need for the operator interaction, because all operations are internally executed on the system or performed by the PLC.

Advanced features
These functions are not usually visible to the user. To access them, it is necessary to log in the system with a user-id that has adequate permissions. Once the user is logged with privileges, some additional commands will appear on the main page. The main purpose of these additional commands is to modify test parameters.

Figure 3 – PETS.Ect Software

As previously seen, the system measures flywheel signal, battery voltage and current, alternator phases, temperatures, oil pressure.
These value are compared with reference limit during the test execution. The limits of voltages and current depend on the revolution speed of engine and, for oil pressure, on temperature.
PETS.Ect can define limits as parameterized function of one or two variables, suitable to define them properly.

 



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