Hybrid Electric Vehicles (HEVs) can be divided into three categories according to how the two propulsion systems (the thermal and the electric ones) supply the driving torque to the vehicle. When the torque is supplied only by an electric propulsion system, while the heat engine takes care of generating the electricity needed to operate the system, it is called a hybrid-series. Conversely, when both propulsion systems provide torque, the vehicle is identified with parallel hybrid wording. Among the parallel hybrids there is a particular configuration called Through-the-Road (TTR). In this configuration, the two propulsion systems are not mechanically connected to each other, but it is precisely the road that allows hybrid propulsion. This architecture, dating back to the early twentieth century, is still used by several manufacturers and carries with it peculiar configurations and control methods. It is also a configuration that fits well with the transformation of conventional vehicles into a hybrid. The paper presents a survey of the TTR HEV solution, evidencing applications, potentialities and limits.

中文翻译：

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公路混合动力汽车研究

混合动力电动汽车（HEV）可以根据两个推进系统（热动力系统和电动动力系统）如何向车辆提供驱动扭矩而分为三类。当扭矩仅由电力推进系统提供时，而热机负责发电以运行该系统所需的电力，则称为混合动力系列。相反，当两个推进系统都提供扭矩时，将使用并行混合文字来识别车辆。在并联混合动力车中，有一种特殊的配置，称为通过公路（TTR）。在这种构造中，两个推进系统没有机械地彼此连接，但是恰恰是允许混合推进的道路。这种建筑的历史可以追溯到20世纪初，许多制造商仍在使用它，并带有特殊的配置和控制方法。这也是非常适合将传统车辆转变为混合动力车的配置。本文对TTR HEV解决方案进行了调查，以证明其应用，潜力和局限性。