## 4 Discussion and Conclusions  
This study conducts an in-depth investigation into the climbing characteristics of pure electric heavy-duty vehicles and their influencing factors and proposes longitudinal slope index limits applicable to the climbing characteristics of such vehicles. The research findings indicate that during uphill climbing, when the power of pure electric heavy-duty vehicles is insufficient to overcome the gradient resistance, the vehicle will decelerate, ultimately reaching an equilibrium state. Furthermore, a corresponding equilibrium speed exists for each longitudinal slope. Before reaching equilibrium speed, the steeper the slope, the faster the vehicle's speed decreases. This is because a steeper slope increases the gravitational resistance acting on the vehicle, causing it to decelerate more quickly. Consequently, a steeper slope results in a lower equilibrium speed, meaning the vehicle can maintain a lower stable speed when traveling uphill. Additionally, the rapid decrease in speed shortens the distance required to reach equilibrium speed. This phenomenon indicates that slope significantly impacts the vehicle's energy consumption and power requirements. Therefore, it must be thoroughly considered in vehicle design and energy management to optimize performance and efficiency. This discovery aligns with the results of [PERSON] et al. [12]. Under identical road conditions, compared to conventional fuel-powered heavy-duty vehicles, pure electric heavy-duty vehicles exhibit smoother acceleration and deceleration processes during uphill climbing, with minimal fluctuations in driving speed. Moreover, they achieve higher speeds for the same distance and have greater [PERSON] speed values. This is attributed to the rapid response and high torque output of electric motors, enabling them to promptly deliver the required torque. Furthermore, under different road conditions with \begin{table}
\begin{tabular}{c c} \hline \hline
**Evaluation Standard** & **Evaluation Indicator Value** \\ \hline Excellent & \(DV\leq 0.1\) \\ Good & \(0.1<DV\leq 0.2\) \\ Poor & \(DV>0.2\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Evaluation criteria for \(DV\) of vehicles. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Slope (\%)**} & \multicolumn{3}{c}{**Design Speed (km/h)**} \\ \cline{2-4}  & **120** & **100** & **80** \\ \hline
3 & 890 & 1000 & — \\
3.5 & 580 & 610 & 730 \\
4 & 420 & 430 & 460 \\
4.5 & — & 320 & 330 \\
5 & — & 250 & 250 \\
5.5 & — & — & 210 \\
6 & — & — & — \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Critical lengths of various grades. varying design speeds, pure electric heavy-duty vehicles exhibit a noticeable similarity in the speed variation trend at the same gradient. By introducing the climbing speed decay degree (\(DV\)), this study analyzes the characteristics of speed variation in pure electric heavy-duty vehicles under the joint influence of multiple factors. It is found that the power-to-weight ratio has a greater impact on the climbing speed of pure electric heavy-duty vehicles compared to initial vehicle speed, which only affects the vehicle's maximum travel speed. The dynamic performance of pure electric heavy-duty vehicles does not align with the maximum grade specified by \"Specification\". The equilibrium speed of these vehicles at the specified maximum grade is significantly lower than the minimum speed allowed by the road. The introduction of \(DV\) can reflect the perceptual differences of drivers when heavy-duty vehicles climb slopes at different design speeds. Therefore, using \(DV\) as a limit yields a more reasonable critical length. Different from other studies [3,8,14], the focus of this paper is on pure electric heavy-duty vehicles rather than traditional fuel-powered ones. With the widespread deployment of electric charging infrastructure, the number of pure electric heavy-duty vehicles is expected to increase further. In addition to electrification, intelligence is also a mainstream development direction for vehicles today.