Experimental tests, importance, purpose, classification, requirements
The importance of vehicle tests results from the fact that different types of tests, as an integrated part of the development process of a vehicle, make a decisive contribution to their permanent improvement in all phases of development. The tests verify that the main construction parameters, technical and economic indices, the quality of the execution, the performances, the safety and the resistance in operation correspond to the execution documentation.
In the case of manufacturing companies and repair units, the technological processes of manufacturing respectively of repair are validated by tests.
In the testing units, the optimum type of vehicle for certain working conditions is established, as well as the most advantageous operating modes. The tests performed on motor vehicles as a whole or on their subassemblies show:
- their functional features;
- sizes that characterize dynamism, stability or economics;
- determining the operating resistance; researching the processes that take place in different subassemblies and mechanisms, as well as in the vehicle as a whole; and so on
Among the main objectives of the tests, we can list the following:
- to check the technical-economic indicators provided in the design theme;
- to discover design, technology or material flaws;
- to verify the quality of the execution;
- to validate the constructive or technological improvements made to the initial project;
- to create complex databases that can be used when designing similar vehicles;
- provide data for the correct estimation of the service life of the vehicle; to verify the compatibility of the studied vehicle with different operating regimes;
- to verify that the design vehicle complies with the requirements imposed by the internal and international regulations, etc. by design and execution.
To ensure efficient and economical operation throughout the service period, the car must be carefully checked at the optimum time. Although it is not possible to make a very strict delimitation of the tests, we can classify them according to the following criteria:
- after the destination of the tests;
- after the subject undergoing experimental research;
- according to the purpose of the experimental research;
- according to the test conditions and methods.
Such a major classification is presented below:
- Scientific research tests
- Approval or type tests
- Periodic or batch control tests
- Reception attempts
According to the subject undergoing experimental research
- Testing of motor vehicle parts
- Tests of the vehicle as a whole
- Tests on scale models
According to the purpose of the experimental research
- Functional tests
- Resistance tests
- Durability tests
According to test conditions and methods
- Laboratory tests
- Road tests
- Operating tests
- Tests under special conditions
Classifying car tests
After the destination of the tests
Scientific research tests are the most varied in terms of objectives, scope, and means used to carry them out. These are carried out in order to solve complex problems of general interest such as the study of new vehicles or new subassemblies; the use of new types of fuels or lubricants; replacing some technologies with more modern ones; replacing some materials with more economical ones; researching in detail the processes that take place in the engine or other sub-assemblies of the vehicle; checking new mechanisms and parts; researching the interaction of the vehicle with the road and the environment; research regarding the establishment of new experimental research methods; and so on
This type of testing is usually carried out in powerful research institutes and research centers organized next to the traditional technical faculties. For the car industry, scientific research attempts are of particular importance, they being the main way of validating modern products and technologies, contributing to the continuous improvement of cars.
The approval tests have an official character and are usually carried out in accordance with the provisions of national or international normative acts with legal character. These are the prototypes to be introduced in the series production, the project is validated and the “zero series” is tested, validating the manufacturing technology of the new vehicle.
Therefore, there are two stages, the approval of the prototype, which constitutes the acceptance of the constructive solutions proposed to be introduced in the manufacture, and the approval of the zero series, having as objective the approval of the manufacturing technology of a vehicle approved as a prototype.
The process of developing a new car inevitably involves designing and making a prototype and testing and perfecting it. During the prototype tests, the deficiencies of the construction are highlighted and they appreciate the construction and exploitation materials used, the optimal settings are established.
The approval tests of the vehicle as a whole must be preceded by the approval tests of the main assemblies: engine; clutch; gearbox; longitudinal transmission; engine decks; suspension; steering system; and so on
After the validation of the prototype, the “zero series” test is started. Within it, at least a batch of 10-15 cars is executed, using the machine tools, devices, and testers designed and executed for mass production, to obtain satisfactory assessments. By testing the “zero series” the manufacturing technology is verified, they involve performing some tests under operating conditions, and repeating some tests performed when testing the prototype.
The approval tests are long-term complex tests, which aim to validate the design and manufacturing technology of a new vehicle. Periodic or batch control tests shall be carried out to verify that the manufacturer maintains the quality level of the vehicle established and certified by approval.
Within them are tested a small percentage of the vehicles manufactured in series, and their duration must be less than 6 months or 40,000 km run effectively. Usually, a car from a batch of 3000-6000 pieces or a vehicle per quarter is tested, depending on the size of the production series. It is reasonable for the period of repetition of these samples to be as large as possible, and their magnitude to be limited to the essential indicators to reduce the manufacturing costs.
Achieving this goal requires a high and stable quality of the vehicle’s manufacturer. During these tests, the durability of the vehicle bodies is also verified, this test is similar to one of the approval tests, with the difference that it is executed in a shorter time and on a shorter time.
There is also a minimum framework program under which the periodic control tests must be carried out, respectively a running of approximately 5,000 km, carried out in a minimum of 15 days. The acceptance tests can be considered as tests included in the technological manufacturing process.
These are done for the purpose of checking the quality of the vehicles in current manufacture or repairs. Apart from the final control, which is performed by the manufacturer on all cars, the reception control is performed by the beneficiary or his authorized person. In general, the reception tests are limited in character and they follow if the vehicle meets the general operating conditions.
According to the object prone to the experimental research
The tests are classified in: the test of the subassemblies and the aggregates, the test of the vehicle as a whole and tests performed on sacred models.
Subassembly testing is performed to determine the characteristics of each vehicle assembly and aggregate. This refers to the testing of the engine, transmission, steering, suspension, brakes, wheels and other parts and components of the vehicle.
Testing the assemblies under laboratory conditions must precede the testing of the vehicle as a whole, both under laboratory conditions and during the course.
The test of the vehicle as a whole is done to establish the main characteristics, parameters and performances regarding the dimensional and mass characteristics, dynamic qualities, economic qualities, passing ability, comfort, the ergonomics of the management post, reliability, traffic safety, establishing the coefficients that characterize the interaction between the car and the environment, transmission losses, and so on
Model scale tests are performed in order to eliminate some tests whose cost price is very high. Instead of the test object, scale models are used, following which the characteristics, parameters, and performances of the vehicle are determined, starting from the characteristics, parameters, and performances of the model based on the laws of geometric, kinematic and dynamic similarity.
According to the purpose of the experimental research, we distinguish the following main categories of tests: functional tests; resistance tests; durability tests.
Functional tests have the main purpose of highlighting some characteristics, parameters and functional and operating performance of the vehicle as a whole or of its different subassemblies, such as: passing capacity parameters; steering parameters, and so on
Resistance tests by which are set the requests that cause the destruction of the assemblies and subassemblies.
Durability tests, among which we distinguish the normal tests where the requests to which the parts are subjected are similar to those in operation and accelerated to which the requests are amplified in order to shorten the test time. Another method of shortening the test time for durability tests is to increase the frequency of application of periodic variable requests if it does not directly influence the service life.
Depending on the conditions and test methods, we distinguish the following main types of tests: laboratory tests; road tests; exploitation tests; tests under special conditions.
Laboratory tests of the car as a whole or of its subassemblies shall be carried out under stationary conditions, using facilities provided with appropriate equipment for loading, measuring and recording. Laboratory tests have the advantage that they allow the investigation of phenomena with high precision and make it possible to remove the influence of the factors that are not studied. The disadvantage of the method is that in the laboratory, the conditions under which the vehicle in operation can not be simulated cannot be precisely simulated.
Road tests are carried out on specially designed test tracks or on-road sections provided with unevennesses, with profiles and coverings so made that they correspond to the real operating conditions. If the test paths are correctly chosen, the test methods and the equipment used correspond to the purpose and conditions of the test, the accuracy of the test data will be fully satisfactory. The main advantage of the method is that the test is done in conditions very close to the ones in operation, which ensures that results similar to those in operation are obtained.
Exploitation tests are carried out periodically under the usual working conditions of the operating companies by qualified personnel in this regard, both from the producing and operating companies. The accuracy of the results is all the better as the number of vehicles tested is higher, the number of tests is higher and their duration is longer.
In some cases, it is recommended to perform the combined laboratory and exploitation tests to complete and validate the results obtained by each method separately. If the number of vehicles chosen for the test is large enough, the research may be carried out concurrently.
The tests under special conditions shall be carried out in the case of vehicles to be operated under special conditions. Special test conditions may include: prolonged column run on dusty roads; prolonged rolling at high temperatures (35-45 C); low speed rolling on sandy and marshy terrain; rolling under very low temperature (below -25 C); rolling in tropical conditions; high altitude rolling, and so on
It is noteworthy that these types of test classifications are indicative, the precise delimitation of the tests being very difficult to achieve. Obtaining conclusive results most often involves performing combined tests that complement each other.
The main requirements imposed on the tests are objectivity; repeatability; correctness; the speed of execution; the economy.
The requirement for the tests to be objective arises by itself if one considers the importance of defining an optimal constructive solution or of the real knowledge of the technical state of a motor vehicle in operation without preconceived ideas and/or subjective considerations.
The objectivity of the tests is achieved by the impartial and impartial attitude of the tester; ensuring certain conditions of non-singling and non-privileged testing from the point of view of the efforts imposed on the vehicles; eliminating the possibility of subjective interpretations of the test results, by rigorously adhering to the test program, the large-scale use of the test equipment with data recording possibilities, observing the data processing methodology; establishing the causes that led to the failure to register some constructive and functional parameters within the limits provided by the technical documentation.
For vehicles, the repeatability of the tests involves the test under the same conditions such that for a given vehicle with a well-specified technical condition, the results of repeated and / or similar tests do not differ significantly, and the resulting ratings remain invariant.
The repeatability of the tests is achieved by using some test methods that are not affected by the random environmental factors; eliminating or mitigating the influence of the human factor by using the same test driver or drivers with psycho-physiological structure and similar professional training; limitation to the range of variation of the test conditions, these being very precisely established by the standards governing the tests
The ideas of repeatability are also subscribed to the efforts of international organizations (I.S.O., D.I.N., S.A.E.) to elaborate some normative tests with a high degree of generality accepted in different countries.
Obtaining the correctness of the tests is closely correlated with ensuring their objectivity and repeatability, but it also implies: detailed knowledge of the phenomena investigated by testing; judiciously establishing the limits of variation of the measured parameters, the use of measuring schemes and a judiciously chosen apparatus; the correct and complete preparation of the test program, compliance with the standards related to it; ensuring the measurement accuracy required by standards; fair interpretation of the results obtained from the tests; repeating the tests whenever the results obtained are contradictory or do not correspond to those available from previous tests and/or determined by calculation.
It is not hard to imagine the serious consequences that some decisions can have on accepting the launch in the manufacture and/or operation of vehicles whose project and technology have been validated by incorrect tests.
The importance of quickly obtaining the results of a test is sometimes urgent, as it risks becoming a goal in itself and essentially compromising the tests.
The objective of the rapidity of the tests must be achieved without diminishing other qualities imposed on them, by judicious programming of the succession of the test phases (elimination of dead times); use of accelerated test methods as much as possible; the rapid processing and interpretation of the data by using the modern systems of acquisition and storage of data obtained from the tests; minimizing the volume of tests with a reasonable level of confidence.
The tests are non-productive operations directly, consuming time, fuel, materials, labor, and their cost is directly reflected in the price of the vehicle.
Ensuring the economics of the tests involves: drawing up the test program so that the volume and duration of the works are minimal without affecting their quality; performing tests as much as possible on stands and in polygons; in the case of road tests, the combination of tests of aggregates and assemblies on the same vehicle; testing a large number of aggregates or assemblies on automobiles in operation; use of the data provided by the service system of the manufacturing enterprise; the use of highly qualified personnel when tested.
Preparing the cars for tests
In most cases the testing of a vehicle or its assembly is done on the basis of a research program theme, annexed to the contract or order issued by the beneficiary of the test. The team of specialists who will perform the test must formulate the objectives of the test very clearly, make the necessary corrections where this is required so that the tests will be optimal and its results will fully satisfy the needs of the beneficiary.
If the results of the test bulletin are unfavorable, the causes that led to the invalidation of the product and the corrections to be eliminated must result. In order to allow certain flexibility of the test program and a correct dosage of the material and human efforts, in order to make the test process more efficient, a delimitation of the main and secondary objectives is required.
Achieving viable results from testing vehicles or sub-assemblies must be ensured from the test preparation stage. In this phase, the team that will carry out the tests must form a clear and correct vision on: the objectives of the test; the means to be used during the test; the steps to be taken during the test; the likely area in which the test results will fall. It often takes weeks or even months of preparation for a day, hour, minute, or fraction of a second in which the test is performed.
Preparation of the test program
The general testing program is usually imposed by internal standards or norms to the institution that performs the work, the organizers of their development have the obligation to elaborate a detailed program that will ensure maximum efficiency of the tests.
The test program must include:
- The objectives of the test;
- The test phases presented in chronological order, specifying the partial objectives specific to each phase and the deadlines;
- Details of each test phase, detailed enumeration of the specific works, places, routes, polygons or test stands and the deadlines;
- The environmental requirements needed for testing;
- The test regimes envisaged during the tests, the payload of the vehicles to which the test is being run, the speed regime, etc .;
- The number of parameters investigated, the complexity of the tests and the number of repetitions of the experiments;
- Accuracy of measuring the parameters determined by tests, which must be in accordance with the values recommended by the technical documentation and by the national and international standards;
- The equipment for measuring, acquiring and processing data, which must allow a rapid assessment, if possible in real-time of the results to assess the success of the test and, if necessary, the need for partial or total resumption of the test with the maintenance or change of the method to try;
- Responsibilities of contracting parties and/or collaborators for material assurance of testing;
- Responsibilities that fall individually to the test personnel;
- Specific conditions for stand tests, if applicable;
- Number of products tested;
The program of tests depends on: the purpose of the experimental research (determination of dynamic qualities, exploitation, etc.); of the type of the vehicle (car, truck, field car, field truck, train, transport tractors, agricultural tractors, industrial tractors, etc.); by the destination of the test (scientific research, type approval or type, periodic or batch control, reception).
Considering the above, it turns out that the test programs will differ, but they will also have many common elements.
The elaboration of the test program represents one of the most important phases of the car tests, in which the personnel involved must have a clear and unitary vision that will lead to carrying out objective, correct, repeatable tests, performed in a timely manner and with maximum economic efficiency.
Selection and reception for vehicle testing
The number of vehicles being tested is chosen according to the type of tests scheduled. In the approval tests, for example, the whole batch of prototypes and the whole “zero series” is tested, if the number of vehicles does not exceed 10-15 pcs. In the case of periodic control tests, the vehicles are selected from the current manufacture, depending on the volume of production.
Acceptance tests are performed on all manufactured vehicles. In the case of other types of tests, such as those of scientific research or exploitation, the number of vehicles being tested shall be determined on a case-by-case basis, depending on the purpose pursued and the test program established. In all cases, it is intended that the vehicles are properly assembled, fully equipped with accessories and tools and fully comply with the technical state imposed by the specification.
Therefore, the choice of the cars to be tested should be made so that it or they are respectively representatives of a well-defined category for which it is sought to obtain viable information through different types of tests. If these rules are not respected, there are large dispersions of the results, and their usefulness decreases until it becomes insignificant.
Depending on the character and volume of the tests the vehicle is subjected to, it is prepared for the test, which includes the following stages: checking the technical state of the vehicle tested, respectively receiving the vehicle for the test; drawing up the technical specification of the vehicle; calibration and installation of data measuring, storage, and processing apparatus; establishing the test methodology according to the norms and standards in force.
The vehicle is received according to the type of tests to be performed. For example, in the case of periodic tests, the vehicle must be chosen in such a way that it is not possible to remove the manufacturing defects by additional adjustments, which can create a false image on the quality of the current production.
In the case of receiving the experimental models, it is acceptable to eliminate the manufacturing defects before the execution of the tests, in order to match the vehicle tested with the technical conditions imposed by the designer.
The first activity of receiving the test vehicle, regardless of the type of tests to be performed, is the confrontation with the provisions of the execution or accompanying documentation. Of these, the following can be listed: type; the producing enterprise; engine serial number; VIN; the technical characteristics of the vehicle as a whole and its components.
The assembly of the vehicle is characterized by the mass parameters, the dimensional parameters, the functional parameters, and the energy parameters, and its components are characterized by the specific parameters, such as: the transmission ratio; return; the depreciation coefficient; coefficient of friction; and so on
The technical documentation on the basis of which these checks can be performed must include: the overall drawings of the vehicle; the assembly and assembly drawings of the main subassemblies; the list of accessories and tools included in the delivery set; maintenance and operating instructions; repair book; the spare parts catalog; and so on
Starting from the requirements of the test program, initial measurements of parts subject to wear (tires, spring bolts, friction linings, shafts, gears, etc.), stand checks of some sub-assemblies (braking system, control system) can be performed. direction, lighting system), seals of components to which no interventions are allowed during the test.
Before any type of test, the technical condition of the vehicle will be checked, and before dynamic and consumption tests, the engine and transmission will be heated to the nominal temperature by running a sufficient length and the total losses will be checked by the free-running method.
Making the adaptations for the installation of the measuring equipment, acquisition, and processing of the experimental data, verification of their operation and calibration are stages that are part of the preparation of the vehicle for testing.
It should be specified that the tests can be performed only after the vehicle is run according to the specifications of the manufacturing plant and after it reaches the nominal operating regime.
Choosing and preparing the measuring equipment
In order to obtain the desired information regarding the qualities of the vehicles tested and to record as accurately as possible the results of the tests, in digital, analog or graphic form, outside the standard equipment, additional measuring, acquisition, and data processing devices will be fitted.
The number and complexity of the equipment required for the tests depend mainly on:
- the type of test
- test conditions
- the degree of equipment of the laboratory to carry out the experimental research.
Ensuring a high quality of experimental research, under conditions of maximum economic efficiency, involves the use of installation for measuring, acquiring and processing the appropriate data. The correct choice of the measurement method, the use of the most suitable devices for measuring, acquiring and storing data, the use of the most efficient data processing software and the correct conception of the measurement chain are the main prerequisites for obtaining viable results from the tests.
Also, optimal conditions of operation of the entire measuring chain must be ensured by vibration isolation, protection from excessive actions of the environment, ensuring the proper supply voltage, etc.
The quality of measurement also depends on:
- metrological characteristics (accuracy class, sensitivity, sensitivity threshold, resolution power)
- dynamic characteristics (dynamic range, transfer function, frequency range) of the equipment used.
Given that in order to streamline the development process of a vehicle it is necessary to shorten the test time, the accelerated tests of the components and / or vehicles as a whole are increasingly used. This requires increasing the volume and speed of obtaining the data following the tests, which has led to the use of very efficient data measurement, acquisition, processing, and storage chains, which allow the online processing of the data, at the end of the test being obtained. and the first final form of the results.
An important step in the preparation of the equipment for measuring, acquiring, processing and storing data is the verification of the operation and the calibration of the entire chain. This will be done at the beginning of the experiment and then periodically at certain time intervals or before important tests to see if in the meantime there have been no disturbances that may affect the test results.
Choosing and preparing the measurement routes
Depending on the character of the experiment or the performance that is determined, the test of the vehicles is done on different road categories. Regardless of the type of road tests, the road conditions in which the tests are carried out are specified exactly.
In case of carrying out the tests for establishing the dynamic and economic parameters of the vehicles, the road must meet the following requirements:
- to have strong clothing, without unevenness (with concrete or asphalt coating);
- be horizontal, within a maximum inclination of ± 5%; to be rectilinear; have a length of 4-5 km (so as to ensure both the launch and the braking portion);
- 7.5 m wide; to be protected from the wind (especially from the side);
- to be set with mileage and hectometric stones.
The influence of the deviation from the road’s horizontality can be reduced by an acceptable measure by repeating the sample from the opposite direction and adopting as a final result the test of the arithmetic mean of the two or more samples.
In the case of the tests carried out on public roads, sections with reduced traffic will be chosen, which can be temporarily closed, with the agreement of the relevant authorities. At the ends and on the side entrances of the road sections used for tests, preventive inscriptions are placed.
In order to prevent the accidental occurrence of some vehicles during the tests carried out with the closing of the traffic (usually the tests for determining the dynamic parameters) the main and side entrances are blocked or provided with guard posts.
Of the endurance or durability test methods of motor vehicles as a whole or their subassemblies, one of the most accurate is the test under real traffic conditions, which are carried out on normal public roads, loaded at nominal or partial capacity, with drivers who manifests different driving temperaments and in specific meteorological conditions of the operating regimes.
During these tests, it is recommended that the necessary data be collected for the correct determination of the calculation regimes and the test regimes on the stand or in the polygon.
In order to choose as accurately as possible the routes on which endurance tests are carried out, statistical studies are required to highlight the factors that determine the operating regimes and decisively influence the requests from the different components of the vehicles. The main characteristics of the route on which the tests are carried out are given by the road surface characteristics.
The tread pattern is characterized mainly by the longitudinal inclination as a function of space or time, which can be statistically characterized by the frequency of occurrence of the different classes of longitudinal tilt.
Another important component of the road surface is the road configuration which is given by the number of turns per km traveled; the radius of turns; transverse tilt; visibility; and so on From the point of view of the road surface, the following four road categories can be considered as representative:
- urban or city road;
- hill and mountain road.
From the point of view of the road surface, there are the modernized and the non-modernized roads. Statistical data show that most drivers do not use the vehicle on the same type of road, at about 95% observing a “mixture” of types of road used.
In the case of the tests to be performed on public roads, areas with reduced traffic will be chosen, which fulfill the conditions imposed by the test standards in force. For the tests carried out in order to determine the dynamic and braking parameters, the road section for the test is temporarily closed in order to ensure the test conditions.
If the test program does not require the road sections that are tested, they are chosen in areas where there are no deep drainage ditches, steep slopes or other natural or artificial obstacles.
The electrical measurement of non-electric sizes
Generalities regarding the measurement chain
The electrical measurement of a non-electric size consists of its conversion into an electrical signal – usually in electrical voltage – whose value is proportional to the measured size.
The main components of a measuring chain are:
- the electrical connection circuit of the transducer;
- the display or recording system;
- data acquisition, storage, and processing board.
The transducer transforms the measured non-electric size (displacement, speed, acceleration, force, temperature, etc.) into an electrical size proportional to it. For this purpose, the translator is attached to the measuring object.
The power supply system provides the electricity needed for the transducer. It can be an electric battery or an audio frequency oscillator. In the case of transducers that generate electricity by conversion, no separate power system is required.
The electrical connection circuit ensures that the output circuit from the transducer is adapted to the input to the amplifier. It must ensure the sensitivity and precision of measurement required by the tests to be performed.
The amplifier has the role of amplifying the signal to ensure the desired sensitivity of the measurement system, as well as to adapt the signal level to the value required by the display and recording equipment and / or the data acquisition and storage system.
The display and recording system provides the possibility to read, view and / or record the output signal value from the measurement chain. For this purpose, analog, numerical, oscilloscope, paper or magnetic tape recorders are used. In the case of modern measurement chains, the role of the file and registration system is fully taken over by the data acquisition and processing systems.
The data acquisition and processing system have the role of retrieving the analog data from the amplifier or the magnetic tape recorder, making their digital-analog conversion, recording them on harddisk. With the data processing software in addition to processing and resuming processing according to the desired algorithms, it is also possible to display data in real-time in the form of oscillograms, time variation of sizes, etc.
These systems have the following advantages: they allow the storage of a large number of research data; data collection can be done with high sampling frequencies; they allow the resumption of data processing without the resumption of evidence.