What affects premature undercarriage wear? Having installed the measuring equipment on the machine, the author tried to answer these questions - candidate of technical sciences, NAMI specialist in the field of loading, strength and durability of cars and their units.
A car is a very sensitive oscillatory system: even at low speeds, it reacts to barely noticeable irregularities with a height of 10 mm or more
A car is a very sensitive oscillatory system: even at low speeds, it reacts to barely noticeable irregularities with a height of 10 mm or more. A car is a very sensitive oscillatory system: even at low speeds, it reacts to barely noticeable irregularities with a height of 10 mm or more.
RIDING OR TESTING?
Our city roads are, firstly, an abundance of bumps that appear after the next repair (construction quality is unsatisfactory!). Secondly, there are many artificial obstacles: communication wells, storm water inlets, expansion joints on overpasses, bridges and tunnels.
To find out how natural and artificial obstacles on city streets affect the health of the car, I conducted road tests, recording vertical accelerations on the front shock struts. Having these data, as well as indicators of the fluctuating masses and weight characteristics of the machine, it is possible to evaluate the vertical loads that occur during movement. The higher the speed and the worse the road surface, the more impressive they are. The measurements made allowed us to estimate the frequency of occurrence of accelerations and their range (from minimum to maximum), which depends, inter alia, on the depth and height of irregularities. Of all these factors, the total dynamic loading is formed, which directly affects the durability of the car and the road.
GOING QUIET … DRIVE LONGER
A small section of a repaired road with new smooth asphalt. At a speed of 60 km / h, the maxima of the vertical accelerations of the suspension struts are in the range up to 2.2g. With these values, the load on the wheel increases by no more than 2% compared with the static state. More such roads! And now we’ll add the standard (i.e. ugly) built-in wells. Acceleration values increased to 12–13g, and the wheel load increased by almost 90% (see graph).
Thus, vertical accelerations (g) and dynamic loads (H) change depending on speed:
This changes the vertical acceleration (g) and dynamic loads (H) depending on the speed
All graphs and diagrams open in full size with a click of the mouse.
On the other road with wells and patches from patching, the picture is very bad: accelerations reach 23g, while the vertical load increases almost threefold. And if such accelerations and loads will occur constantly, then the resource of the chassis will be reduced at least twice. Even worse, on a site with broken, failed paving stones, hastily patched with asphalt blotches and, in addition, studded with well covers. At a vehicle speed of only about 10 km / h, accelerations on the suspension struts reach 15g. I do not advise rushing on such a road - suspension breakdowns fraught with serious consequences cannot be avoided.
Not only the car, but also the road surface suffers from carelessly equipped wells. Increasing vertical loads increase friction between the wheels and the road - cracks occur, gradually asphalt crumbles and sags, the neck of the well warps. And then - like a snowball from a mountain: the more cars drive through the well, the more severe the asphalt is broken and the higher the load on the chassis. At the same time, it is obvious that cars with stiffer suspensions and a larger mass exacerbate the situation.
The graphs of vertical accelerations when moving in tunnels and overpasses resemble a thick comb with broken teeth. Peaks that occur at a rhythmic frequency are crossings through expansion joints. On racks, their metal dividers are usually located above each support after 50–100 m. As long as the structures are fresh, accelerations are small (2.0–3.5 g), that is, the vertical load on the coating increases only by 2-3%. But at a high flux density, the coating in the rut quickly wears out, asphalt is knocked out next to the metal dividers. As a result, even on relatively new, but already broken overpasses, when moving a car through expansion joints at a speed of 60–70 km / h, wheel loads increase 2.3–2.6 times compared to the nominal.
With increasing speed, the load on the suspension and the body increases when the wheels get on bumps. At a speed of 20 km / h, the indicators increased one and a half times, and at 60 km / h - more than doubled
With increasing speed, the load on the suspension and the body increases when the wheels get on bumps. At a speed of 20 km / h, the indicators increased one and a half times, and at 60 km / h - more than doubled. With increasing speed, the load on the suspension and the body increases when the wheels get on bumps. At a speed of 20 km / h, the indicators increased one and a half times, and at 60 km / h - more than doubled.
LIGHT AT THE END OF THE TUNNEL
This is not to say that nothing is being done to improve roads. The volumes of repair and restoration work are growing, new technologies and materials are coming, and with them other designs and layouts of road structures. And at the same time, the current regulatory documents on road construction do not oblige to “smooth out” wells, expansion joints, storm sewer manholes. Many old structures require modernization, and the remake often does not stand a year of operation due to non-compliance with the very advanced technologies in construction and subsequent repair. We constantly feel the results under the wheels of our cars and on our budget: the costs of spare parts and extraordinary repairs are considerable.
Old hatch
Old hatch Old hatch
The rubberized collar around the neck of the well reduces dynamic loads, extending the life of the road and the car. Of the other improvements adopted from foreign colleagues, the combination of individual support beams of overpasses into continuous spans (the so-called temperature-continuous), which reduces the number of expansion joints
The rubberized collar around the neck of the well reduces dynamic loads, extending the life of the road and the car. Of the other improvements adopted from foreign colleagues, the combination of individual support beams of overpasses into continuous spans (the so-called temperature-continuous), which reduces the number of expansion joints. The rubberized collar around the neck of the well reduces dynamic loads, extending the life of the road and the car. Of the other improvements adopted from foreign colleagues, the combination of individual support beams of overpasses into continuous spans (the so-called temperature-continuous), which reduces the number of expansion joints.
Feel the difference: the distribution of vertical accelerations on a good road (top
schedule) and bad:
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The vertical axis represents the acceleration of the struts; the horizontal axis shows how many times they occurred. The wider the “beam”, the greater the dynamic load on the car.
