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After taking off, an airplane can fly for hours under almost the same environmental conditions, while a car will be continuously affected by various possible interference factors during the entire driving time. It is impossible to have a fixed working state. The design of all structural components must take this into account, so quality is the most important thing. Taking into account all the loads and influences that may occur in actual operation, more rigorous inspection is an indispensable prerequisite for producing high-quality products. 
Figure 1 Electric motor in aggressive environment
In modern, technically demanding vehicles, brushless electric motors, so-called BLDC drives, are increasingly being used for auxiliary and servo systems. Only steering servo drives that are tested under extreme conditions and can guarantee reliable operation can make our lives safer and more reliable.
Vehicles have to meet a wide range of requirements over their entire service life, and the car manufacturers take this into account when developing them. Off-road driving tests in the heat and dust of the Arizona desert or in the ice and snow of northern Rabland in Northern Europe are very common. Salt spray and tropical humid climate conditions also torture vehicle components. For ebm-papst, such preventive and production testing of electric motors installed in vehicles is the goal of being able to provide products that work effectively over the entire service life of the vehicle. Especially for safety-related steering servo motors that are exposed to the floor, even more stringent standards are imposed, and the test engineers have come up with a series of "torture" methods for them. After starting, the vehicle is directly exposed to complex influences such as engine vibrations, bumps caused by the road, braking forces and acceleration forces.
Figure 2 Continuous operation of the motor in the air conditioning box
Since even the most modern anti-collision and vibration damping systems cannot absorb all the impact forces, all vehicle components must withstand these impacts. In addition, there are gravel, moisture, dirt, etc., all of which can affect all structural components. Only by testing the structural components in advance can it be guaranteed that the finished vehicle can pass the off-road test later. Of course, the quality of the materials must be checked at the beginning and the manufacturing process must be monitored in a documented manner, because only high-quality materials and reliable manufacturing processes can produce high-quality products. All dimensions are then checked on the finished product. With these basic prerequisites, rigorous tests that simulate real-life conditions are then carried out. The test conditions are more stringent than those that occur in actual daily use, partly because the test time available is very short (real-life conditions must be simulated in a few weeks for many years to come), and partly because a certain safety factor must be taken into account so that users can withstand the special conditions in the future. During the test, the electric motor is bolted to a bracket that matches the flange of the steering mechanism. This ensures that the same conditions such as thermal deformation, heat conduction, condensation water formation, etc. will be created as in the actual use of the vehicle in the future. The test itself includes the familiar mechanical tests, such as vibration tests on a vibration table, fatigue load tests at fixed frequencies at different temperatures, etc. The "torture" is still going on. The heat test simulates the conditions of the Arizona desert. The thermal stability test is subjected to 16 hours at -40°C and 96 hours at 130°C. The motor must work properly even if it is on hot asphalt roads all day and spends the night in sub-zero temperatures in front of the hotel. In the temperature alternation test, the temperature changes in the temperature range of -40°C to +120°C in 5°C steps. Under these conditions, the electrical properties of the motor are tested. When the motor is still hot under the hood, cold water is suddenly sprayed for instant cooling. This is the spray water temperature shock simulation test. The drive unit is heated to a high temperature of 110°C and cooled by spraying with 0°C water for 3 seconds. In addition, the water contains 3% Arizona sand as an abrasive. This game is repeated about 100 times. After the test, the hood, seals and various properties must meet the specified specifications.
Basically, the electrical properties and integrity of the motor are checked after each test. However, good function alone is not enough. For example, water penetration must not affect the insulation resistance of the winding. Therefore, electrical measurements are always carried out during and after each test. Temperature changes can cause malfunctions. Summer and winter operating conditions are simulated quickly, like fast shots in a movie. For example, the motor is moved from -40°C to +120°C and then back again. It stays at each temperature for 1 hour and moves in this way for 4 days. After such a test, the so-called starting torque of the rotor must not deviate from the rated value when starting. Mechanical tests also include dust and gravel simulation tests. Because dust and dirt pollute the car, in practice, the car is steam-jet cleaned. This condition is simulated by a hot water spray test with a water pressure of 10 MPa and then immersion in 5% cold salt water at 0°C for 5 minutes at an operating temperature of 120°C.
Figure 3 Operation life and load test bench
The salt spray test under harsh conditions
has various chemical effects on the vehicle, especially in the vicinity of the vehicle chassis. No engine compartment is truly sealed, and fuel is often spilled in the engine compartment during maintenance and repair. All structural parts must be able to withstand such effects. The most serious are the salt and harmful gases in winter, which corrode the substances they come into contact with. In order to simulate the use of the vehicle in winter, six cycles of salt spray tests are required, each lasting 8 hours with a break of 4 hours. As a simulation of the natural gas pollution of the structural parts in actual use, the structural parts are corroded with diluted gases such as sulfur dioxide, nitrogen monoxide and chlorine at 75% air humidity over a period of 21 days. Most importantly, the contacts of the plug must not be corroded and the increase in contact resistance must not exceed 15%.
According to the Meuphy principle, everything that can happen will happen. There are many chemicals that can be spilled or spilled on the vehicle. Therefore, the test motors are exposed to liquids such as methanol, gasoline, diesel, biodiesel and windshield cleaner containing ethanol at a storage temperature of 80°C. At these temperatures, cold cleaning agents, alcohol, sand and wheel rim cleaners may also have an effect. Some substances with high boiling points, such as cooler antifreeze, battery acid (37% sulfuric acid) and brake fluid, begin to corrode at 100°C. At 125°C, the test pieces are exposed to engine oil, gear oil, hydraulic oil and automatic gear oil as well as the usual chassis preservatives. In this test, lemonade with sugar and caffeine is also used. The storage time at each temperature level is 24 hours. After the test, the operating function should not be affected in any way. All these tests are aimed at proving the resistance of the motor housing and mechanical components. Finally, the electrical function test is the most important task. Since the vehicle is subject to a large number of steering movements during its expected service life of 10 years, this test is the most important, time-consuming and expensive. In the test, the electric motor is accelerated to the rated speed in less than 200 ms, runs at this speed for a period of time, and then brakes to a complete stop in less than 200 ms.
After every 100,000 test cycles, the motor switches from right to left or vice versa. A total of about 1.6 million such reversing steering movements or 26 million motor rotations are simulated. During the test, the motor is tested under conditions of continuous loading or temperature alternation and constantly changing speed. Only by continuously feeding back "quality control" information to production can the quality requirements for exposed automotive parts such as steering servo motors be met. Therefore, tests in production are an important part of the manufacturing process. They simulate user requirements and therefore help to improve user satisfaction.
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