## 4 Analysis of Influence Factors
### Train Speed  
The simulated results under the conditions of a train speed at 5 km\(\cdot\)h\({}^{-1}\) (basic speed), 7.5 km\(\cdot\)h\({}^{-1}\), 10 km\(\cdot\)h\({}^{-1}\), 12.5 km\(\cdot\)h\({}^{-1}\) and 15 km\(\cdot\)h\({}^{-1}\) are shown in Figure 11.  
As seen in Figure 11, in general, since there are alignment irregularities on the tangent before the switch, the wheel-rail relationship just begins to deteriorate at this part, and the magnitudes of the wheel-rail contact forces on the tangent are higher than those of the switch zone. Alongside that, the variation of train speed has a significant influence on the dynamic performance of the train passing through the tangent and switch. The existence of alignment irregularities in the direction leads to a higher possibility of derailment under a respectively small train speed. In detail, the wheel-rail lateral forces of the outer leading wheels of the motor and the trailer increase with the increase in the vehicle speed in the tangent before the switch, but the increase rate is different, as the lateral force of the trailer wheel (independently rotating wheelset) grows faster under the respectively low train speed, and becomes gentle with higher train speeds, while the lateral force of the motor wheel (integrated wheelset) increases gently under low train speeds and faster under high train speeds. After entering the switch, the lateral forces of the motor and trailer wheel are smaller than those in the tangent, and the lateral force of the motor wheel slowly decreases before the speed of 12.5 km\(\cdot\)h\({}^{-1}\), while the lateral force of the trailer wheel decreases first and then increases. After the speed of 12.5 km\(\cdot\)h\({}^{-1}\), the lateral force of the motor wheel starts to increase while that of the trailer wheel decreases. The derailment coefficient sees the same trend as the wheel-rail lateral force. As for the wheel-rail vertical force, the vertical force of the trailer wheel is smaller than that of the motor wheel, whether in the tangent  
Figure 11: Dynamic characteristics of a train passing the tangent and switch under different train speeds. (**a**) Wheel–rail lateral force; (**b**) wheel–rail vertical force; (**c**) derailment coefficient; (**d**) wheel load reduction; (**—**) magnitudes in the tangent; (**–**) magnitudes in the switch.  
or in the switch zone, which is mainly because the axle load of the trailer is respectively light, at about one third of motor axle load. The variation trends of the vertical force of the motor and the trailer in the tangent and the switch zone are the same as the trends of the lateral force in the corresponding position, but the turning point of the vertical force variation of the motor is earlier at the speed of 10 km\(\cdot\)h\({}^{-1}\). The variation trend of the wheel load reduction is consistent with that of the vertical force. When there is bad alignment irregularity in the tangent before the turnout, the wheel-rail dynamic performance in the tangent is worse than that in the switch; the dynamic indexes of the integrated wheelset and the independently rotating wheelset increase with the train speed increasing, but at different increase rates. In the switch, the dynamic indexes of the integrated wheelset decrease first and then increase with the increase in speed, while those of the independently rotating wheelset first decrease, then increase and eventually decrease.