Carbody hunting behaviour of high speed vehicles in low effective conicity of wheel-rail contact

In the past, bogie hunting instability garnered more attention due to its potential for causing serious safety issues. However, with the rise in high-speed vehicle speeds and operational mileage, the concerns arising from carbody hunting can no longer be overlooked. This article investigates the causes and solutions for low-frequency carbody swaying under low effective conicity in wheel-rail contact, employing a combination of experimental and numerical techniques. Initially, the study involves an in-depth analysis of time-domain signals from lateral and vertical accelerations of the carbody and bogie frame during a high-speed train field-test. The carbody vibration mode resulting from carbody hunting displays a swaying motion at a frequency of 1.5 Hz. Subsequently, a dynamic system model of the high-speed vehicle was established and the suspension mode of the model were verified. The frequency of the carbody upper sway motion is determined to be 1.39 Hz. Low effective conicity is induced when grinding wheel match with new rail or new wheel match with grinding rail. Under this low effective conicity, the hunting frequency of the vehicle is around 1.5 Hz, close to the frequency of the carbody upper sway motion. The coincidence of the hunting frequency and the upper sway motion frequency leads to the low-frequency swaying of the carbody. At last, the effects of wheel profiles, rail profiles and suspension parameters on the carbody hunting have been studied. The study demonstrates that addressing low-frequency carbody swaying can be achieved through targeted rail grinding. This process involves modifying the rail profile while ensuring careful grinding of the rail inner corner. Furthermore, it has been confirmed in the article that replacing suitable yaw dampers is also effective.