## 1 Introduction  
As a transport tool, the forklift plays a very important role in cargo moving in ports, workshops, logistics warehouses, airports, and other fields. The electric power steering system has become a common steering power system because of its energy saving features, environmental protection, compact structure, and many other advantages. The electric power steering system of electric forklift is mainly composed of a mechanical steering device, a power motor, sensors, controllers, and other main components [1, 2]. Losing power steering of electric forklifts may lead to difficult steering and even collision, resulting in vehicle damage and injuries. Faults in the EPS systems of electric forklifts are mainly related to sensors and actuators. Due to the complexity of the work, the probability of actuator failure is higher than that of other parts. Actuator failure in the EPS system will reduce the mobility and handling performance of the vehicle, and even cause serious safety risks. Therefore, actuator faults in the EPS system of electric forklifts need to be accurately diagnosed, and the realization of the corresponding FTC is the key to improve the reliability of electric forklift EPS system [3]. In the last few years, various types of observers and controllers have been used for actuator fault estimation and fault tolerant control, such as an integrated FE and FTC design for Lipschitz nonlinear systems subject to uncertainty, disturbance, and actuator/sensor fault. A NUIO without rank requirement is proposed to estimate the system states and faults simultaneously. On this basis, the author constructed an adaptive sliding mode fault tolerant control (FTC) system [4, 5]. FE is an advanced and important fault diagnosis technology, which is developed to determine the location, occurrence and sizes of the fault. As a result, the estimated fault signals can be directly used for FTC system design. Great achievements have been made in FE design [6], such as a fault detection and diagnosis (FDD) method of an EPS system based on the physical model of EPS system which is data driven. This method requires large-scale statistical analysis of experimental data, which increases the difficulty of the work. In addition, fault estimation cannot be carried out with low fault degrees [7]. An active FTC method is designed for the satellite attitude system with external disturbances and multiple actuator failures. Firstly, the model of a rigid satellite with multiple actuator faults is established. Secondly, the actuator fault diagnosis scheme is given, and its estimated value is obtained. Then, a fault-tolerant attitude controller based on the terminal sliding mode was designed by using backstepping control technology, which ensured the asymptotic stability of the rigid satellite attitude closed-loop system in the case of multiple actuator failures [8]. [PERSON] et al. proposed an FTC scheme based on SMC for actuator faults of a variable cycle engine (VCE). The basic idea of the design is to explore and utilize the functional redundancy brought by the multiple variable geometry in VCE. The FTC design of the actuator is divided into a fault reconstruction part and an FTC part [9]. An integrated robust active FTC design based on linear matrix inequality (LMI) is proposed for a class of nonlinear systems with actuator failures [10]. [PERSON] et al. proposed a new method to design a fault-tolerant controller with FE capability by using a generalized Takagi-Sugeno fuzzy model for nonlinear systems [11]. [PERSON] et al. put forward the unknown input observer gain calculation method when applied to fault estimation [12]. [PERSON] et al. proposed a robust predictive control method with high computational efficiency for continuous time underactuated SISO systems with actuator saturation and state-dependent uncertainties. Based on model prediction and adaptive fuzzy sliding mode control, the parameters of the sliding mode surface are adjusted by predicting the expected effect of uncertainty [13].