26 June 2020, 09:05
Tractor is ZETOR. The slogan, which everybody knows simply originated from the fact that machines of the ZETOR brand have become synonymous with tractors not only in the Czech Republic, but also in many markets abroad. Czech tractors gained the trust of customers all around the world for their high durability and reliability. Values that are so specific for ZETOR even today. After all, these values are reflected in all components of the tractor. Let's see how testing of some of these components look like in PTO boxes.
Tests in PTO boxes are performed in special test rooms via tractor's PTO, which is actually just an abbreviation of power take-off (PTO shaft). Tested tractor is connected via PTO shaft and cardan shaft to dynamometr. The dynamometr allows the engine to be loaded continuously at different speeds. "Measurements can be performed on speed control, when the required engine speed is set, or on torque control, when the engine is loaded to the required torque," adds Michal Novotný, Researcher of Field Tests. By loading the engine with a dynamometer, it is possible to measure individual technical parameters of the engine in the tractor, such as power, torque, fuel injection dose or fuel consumption.
Test boxes also contain powerful air conditioning, which allows to simulate an airflow when the machine is used in real operation. The ambient temperature can be regulated between 15 and 50 °C and technicians have the opportunity to test tractors at a temperature load that is set at 40 °C for most export markets. At this reference temperature, the cooling of the engine unit is tested, as well as the temperature limits of the individual components of the tractor. Examples of limit temperatures can be the maximum temperature of an alternator, which can reach up to 100 °C, or the temperature of engine control unit, which can rise up to 80 °C.
Measuring control panel is then able to simultaneously monitor and record up to 40 temperature and 10 pressure points. This makes it possible to achieve maximum repeatability of the measurement with each test cycle. In addition, control panel is used for complex and demanding tasks such as air flow through the bonnet grilles and through coolers, coolant flow through the cooling circuit or humidity measurement, as well as other requirements according to currently performed tests.
Powerful air conditioning of test boxes also enables testing of A/C units. At a constant ambient temperature of at least 38 °C, the average temperature drop is measured on several temperature sensors inside the cab. The drop is set at a minimum of 11 °C according to the applicable legislative standard. During tests of new air conditioning units used on all ZETOR models with a new roof, a temperature drop of more than 20 °C was achieved. Thanks to this, we offer a significant increase in comfort to our customers, especially when working in summer months.
In PTO boxes, life tests of individual components of the gearbox, transmission and hydrogenerators are also performed. Hundreds of hours of testing are designated to e.g. gearbox bearings, shafts, drive and driven wheels in a gearbox or transmission, and hydrogenerator drives. During these tests, technicians load the tractor body via the PTO shaft or via specially designed limit drive gear to achieve required load of the unit under test.
Transmission testing is then also possible on a passive cylindrical dynamometer. Employees mainly perform drive tests on it and tests of complete front driven axles of the tractor. „In this case, the transmission of torque to the rear axle is mechanically disconnected and all available machine power is transmitted via the gearbox and the descent to the PTO shaft for the front axle drive and then to the entire front axle," explains Michal Novotný.
The process of all tests takes place in automatic operation by the control computer, which records predetermined parameters, and in the case of any divergence from the limit values, an operator who analyzes the variance, is notified. Before and after test cycles, a thorough inspection of tested components takes place, followed by an evaluation that determines whether components can be released for serial production and used in our tractors.
Today we have learned what is being tested in PTO boxes and next time we will look under the hood of development and testing of perhaps the most important thing in tractors, engine units.
Source: ZETOR TRACTORS a.s.