## 1 Introduction  
With the increasing emphasis on environmental protection, automobile technology tends to develop in the direction of hybridization and electrification. Dual-motor electric drive tracked vehicles (DDTVs) have drawn much attention in the research of tracked vehicles due to their high transmission efficiency, low fuel consumption, silent driving performance, and easy maintenance [1; 2; 3; 4; 5; 6]. What is more, the introduction of two motors with fast dynamic response makes it feasible to control the rotational speed and torque of drive wheels accurately, rapidly, and independently. These characteristics of DDTVs set the stage for preventing the locking of drive wheels and tracks when emergency braking occurs, making full use of the road adhesion ability and improving the controllability of the vehicle under safety-critical driving situations. Most of the traditional antilock braking systems (ABS) simply rely on high-frequency switching of solenoid valves in hydraulic or pneumatic braking circuits and widely applied in various kinds of vehicles. However, this kind of control strategy may face decays of control effects when the adhesion coefficient of real roads is different from the one used to calibrate the ABS. Due to the working principle of the traditional ABS, the slip ratio may oscillate greatly in the process of braking, thus make it impossible to make full use of road adhesion. To overcome these disadvantages of traditional ABS, researchers started to seek direct ways to control the slip ratio of vehicles during emergency braking [7] and found that applying a sliding mode wheel-slip controller on a traditional ABS can improve the braking effect vastly whether the mechanical braking system is hydraulic [8; 9; 10] or pneumatic [11]. Electric vehicles (EVs) and hybrid electric vehicles (HEVs) have the ability of regenerative braking compared with diesel and petrol vehicles, which makes the emergency braking control strategies of EVs and HEVs different from traditional ways and results in some progress in different aspects. Currently, studies of emergency braking of electric drive vehicles are mostly concentrated on wheeled vehicles, and they can be divided into three main technical routes. The first route is to rely on the mechanical braking system as much as possible. In these control methods, regenerative braking works just in mild braking to regenerate energy and will be reduced when indicators like slip ratio or brake pedal travel exceed predefined criteria. Thus, the mechanical braking system and its antilock braking strategy take control of the vehicle. This control strategy can guarantee braking performance and braking reliability, as well as maintain the traditional mechanical braking structure, which helps to reduce the difficulties of theoretic analysis and application [12; 13]. The transient switching progress between mild and emergency braking of these methods is also studied to enhance the performance [14]. The second route aims to regenerate more energy while maintaining vehicle stability during emergency braking. Although different methods such as sliding mode [15; 16], phase plane theory [17], or improved linear quadratic Gaussian control [18] are used to derive the demanded braking force, the main strategy is making the motors provide as much braking force as possible, and the mechanical braking system follows the difference of demanded braking force and regenerative braking force [15; 16; 17; 18; 19]. However, the dynamic characteristics of these vehicles are not taken into consideration seriously in the above methods. Hence, we have the third route, which takes advantage of the motor's rapid torque response ability.