Cold test technology of the hottest engine

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Engine cold test technology

1 Preface

with the continuous development of the automotive industry, the requirements of modern vehicles for reliability and safety are constantly improving, and the system is becoming increasingly complex. People pay more and more attention to the rapid and comprehensive diagnosis of engines in production; With the continuous progress of relevant testing technology and the rapid improvement of computer processing capacity, at present, more and more automobile manufacturers begin to use the engine cold test with faster beat, higher quality detection level and lower production cost to carry out the high-precision detection of the engine offline, so as to better ensure the product quality

because the engine cold test can not truly express the power and torque of the engine like the conventional hot test, but through the indirect way to investigate the assembly performance of the whole machine, the analysis of various parameters and curves are more involved in the test process. Therefore, in the process of engine cold test, the selection of test items and test schemes is relatively important, It needs to be finally determined through practical verification and continuous adjustment in actual production

2. Test principle of engine cold test

engine cold test is a method used to detect the assembly quality of internal combustion engine. When the cold test technology is used to test the engine, the engine does not need fuel to run, nor does it need coolant to cool. The tested engine enters the test bench, clamps the air inlet and exhaust ports of the engine through the air cylinder or hydraulic cylinder, and is connected to the equipment through the special oil pressure adapter. The flywheel or adapter of the engine is automatically clamped by the claw or other clamping mechanism. The servo motor of the test bench drives the engine to rotate at different speeds. At the same time, the test system simultaneously from the engine air inlet, air outlet The torque sensor of the clamping mechanism and the pressure sensor at the outlet of the main oil duct collect data. The collected test data are analyzed by the software of Dow's new vehicle amine free volatile polyurethane foam solution (zhuhongbo, market manager of Dow Automotive Systems Division Asia Pacific) for the test bench, and then the analysis results are compared with the limit values set by the test bench, so as to determine whether the engine is correctly assembled

in addition, in many application fields with safety and fire protection requirements, the equipment sends instructions to perform operations to the relevant sensors on the engine through the test program. At the same time, various sensors and actuators of the engine also feed back the feedback signals to the test bench through can line or K-line. The test bench software carries out a series of analysis and comparison of various information fed back by the engine, and finally determines whether all sensors and actuators of the engine work normally

3. Mechanical performance test in engine cold test

mechanical performance test in engine cold test mainly includes torque test (including disengagement torque, running torque, monitoring torque, etc.), intake vacuum test, exhaust pressure test, oil pressure test, engine timing test, etc

3.1 disengagement torque test

the torque generated by the engine from the static state to the moment it starts to move is called disengagement torque. The detection of breakaway torque is mainly to confirm whether there is any clamping stagnation between the moving parts inside the engine, such as missing bearing shells, wrong piston installation, etc. If the breakaway torque is too high, the equipment will automatically stop running and give an alarm, requiring the operator to detect the fault and solve it, so as to avoid irreversible damage to the engine caused by high-speed operation and reduce the production scrap cost

3.2 fuel rail inspection

the fuel injection system of the engine will undergo a series of strict tests before leaving the factory to ensure the quality of parts, but in the process of transportation and assembly, there will inevitably be a certain rate of bumps and other damage, so it is necessary for us to inspect it in the cold test

generally, the detection method of the fuel rail is to pass compressed air equivalent to the gasoline pressure of the engine working state into the fuel rail, and then control the fuel nozzles to open and close one by one by the test program, and determine the parts and assembly quality of the fuel rail by detecting the opening time of the fuel nozzle and the pressure drop of the compressed air

3.3 intake vacuum degree test

the change of intake vacuum degree can be measured by the pressure sensor installed on the intake side, which can detect the leakage of valve, the damage or leakage of intake manifold gasket, the connection of vacuum pipeline, etc

the figure is the schematic diagram of the intake vacuum detection device. One side of the sealing surface is connected with the engine intake manifold, and the solenoid valve on the other side controls the direction of the air circuit, and a pressure sensor is connected with the air circuit. When a rich energy-saving scheme is developed from various angles to detect the intake vacuum, the solenoid valve controls the valve to open, the air passage leads to the atmosphere, and the engine normally intake air (figure left); When detecting the intake vacuum, the solenoid valve controls the valve to close, and the gas enters the engine at a certain flow rate through the silencer, and the generated intake vacuum is detected by the pressure sensor connected to one side of the silencer (figure right)

schematic diagram of intake air vacuum degree detection

according to the plan of engine whole machine test, the intake air vacuum degree test can be divided into single cylinder test and whole machine test. The so-called whole machine test means that after the intake manifold is assembled, a pipeline is connected to the sensor at the throttle valve to measure the overall intake vacuum of the engine

intake air vacuum test waveform (multi cylinder test)

the so-called single cylinder test means that the intake manifold is not installed, and each sealing device seals the intake ports of each cylinder respectively; This test method has the advantages of high accuracy and can quickly determine the root cause of the intake failure. The disadvantage is that the overall performance and assembly of the intake manifold cannot be detected because the intake manifold is not installed

3.4 exhaust pressure test

exhaust pressure test in engine cold test, that is, remove the exhaust pipe, and install an independent pressure sensor at the exhaust port corresponding to each steam 6 and rear cylinder of the test machine every time to measure the pressure at the exhaust port. The principle of the detection device is the same as that of the detection device of the intake vacuum degree. Please refer to figure 1

according to different engine structures, the curve of exhaust pressure test has many forms. The combination of exhaust pressure test and intake vacuum degree test can be used to detect the defects of the intake and exhaust system, such as whether the valves are installed in place, whether the cylinder has leakage points, whether the piston rings are fully opened, whether the timing system and variable timing system are correctly assembled, as well as the assembly defects of camshaft and hydraulic tappet

3.5 torque test

there is a torque sensor between the servo motor and the engine clamping device. When the servo motor drives the engine to run, the torque acting on the drive shaft can be detected in real time through this sensor. After the torque sensor, there is an overspeed clutch, which can protect the torque sensor when the operating torque is seriously overloaded

3.6 oil pressure test

oil lubrication is an indispensable lubricant in the process of engine operation. If there is lack of sufficient lubrication, the engine will have scratches, shaft holding, bearing bush wear and other conditions. Therefore, during the test, it is necessary to ensure that the engine has sufficient oil pressure. In addition, the fluctuation value of oil pressure at a specific speed can also reflect the assembly of some parts of the engine, such as main shaft bearing shells, main oil gallery, etc

for oil pressure test, we mainly set monitoring oil pressure, low-speed oil pressure and high-speed oil pressure test

monitoring the oil pressure is mainly to ensure that each relative moving part has sufficient lubrication during the whole test cycle of the engine; Low speed oil pressure is to detect the assembly of main engine parts, such as crankshaft, main shaft bearing bush, etc; The high-speed oil pressure mainly tests whether the unloading valve (pressure limiting valve) of the oil pump can be opened correctly, so as to prevent the engine from being damaged due to high oil pressure during high-speed operation

3.7 engine timing system test

the detection of engine timing system is a comprehensive work. For engines with precise angle control, the installation angle of timing pulse plate can be accurately detected in the cold test, so it is very easy to determine whether the timing is installed correctly. For this type of engine, when setting parameters, we usually set the parameter range to the width of a flywheel tooth

at present, most of our engines with displacement less than 2.0 do not detect the crankshaft position and camshaft position accurately, so we need to indirectly detect whether the engine timing assembly is correct through mechanical performance tests such as exhaust pressure and running torque

for example, we can detect the angle value of the zero position of the torque of each cylinder to judge whether the timing installation is correct; In addition, the installation of timing can also be determined by the angle when the exhaust pressure turns

3.8 testing of other mechanical performance parameters

for some engines with variable timing technology, the working condition of the variable timing adjustment system needs to be further tested during the cold test

4. Electrical performance test in engine cold test

electrical performance test in engine cold test mainly includes the test of various sensors, actuators and ignition of the engine

4.1 various sensor tests

when the engine is running on the whole vehicle, the engine ECU module requires each actuator and sensor of the engine to carry out corresponding adjustment work according to the instructions sent by the ECU system of the whole vehicle. At the same time, there will be a feedback signal line on the sensor, which can detect the sensor and actuator during the cold test, That is, the detection is performed according to the feedback of the sensor signal and the change of the voltage or current signal when the actuator operates

for example, when the throttle is flipped to different positions, it will cause a change in the voltage value at both ends of the throttle position sensor. For a specific throttle position, the corresponding voltage value also has a certain range requirements. Therefore, by detecting the change of the voltage value, we can know whether the throttle actuator is flipped normally, whether the throttle position sensor is working normally, etc

4.2 test of ignition system

the test bench controls the operation of the engine ignition system, and indirectly judges the quality of the ignition system by sensing the changes of the surrounding magnetic field during the operation of the ignition coil through the sensor

the test of ignition system is a relatively complex test process. At present, there are many articles about the test of ignition system. The cold test is also one of the more mature test methods for the test of ignition system, which will not be described here

5. The production of cold test mapping

mapping is a foundation of engine cold test. Its meaning is that before the cold test bench is officially put into use, a certain number of engines need to be tested for various conditions, including qualified engines and various types of defects that may appear in simulated production. By collecting and analyzing these data, the cold test bench can be verified and adjusted accordingly, At the same time, it also accumulates the initial experience data for the engine test of specific models to form a set of initial cold test test system, which needs to be continuously improved in the subsequent mass production

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