Development of a Fuzzy Slip Control System for Electric Vehicles with In-wheel Motors

Abstract

A two-passenger all-wheel drive urban electric vehicle (AUTO21EV) with four direct-drive in-wheel motors and an active steering system has been designed and developed at the University of Waterloo. A novel fuzzy slip control system is developed for this vehicle using the advantage of four in-wheel motors. A conventional slip control system uses the hydraulic brake system in order to control the tire slip ratio, which is the difference between the wheel center velocity and the velocity of the tire contact patch along the wheel plane, thereby influencing the longitudinal dynamics of a vehicle.The advantage of the proposed fuzzy slip controller is that it acts as an ABS system by preventing the tires from locking up when braking, as a TCS by preventing the tires from spinning out when accelerating. More importantly, the proposed slip controller is also capable of replacing the entire hydraulic brake system of the vehicle by automatically distributing the braking force between the wheels using the available braking torque of the in-wheel motors. In this regard, the proposed fuzzy slip controller guarantees the highest traction or braking force on each wheel on every road condition by individually controlling the slip ratio of each tire with a much faster response time. The performance of the proposed fuzzy slip controller is confirmed by driving the AUTO21EV through several test maneuvers using a driver model in the simulation environment. As the final step, the fuzzy slip controller is implemented in a hardware-and operator-in-the-loop driving simulator and its performance and effectiveness is confirmed.

Development of an Advanced Fuzzy Active Steering Controller and a Novel Method to Tune the Fuzzy Controller

“…The fuzzy active steering controller applied an equivalent maximum steering wheel angle of about 50 degrees (Figure 18-b). In short, this maneuver confirms that the cooperation between the fuzzy slip controller that was developed previously [20] and the fuzzy active steering controller developed here has allowed the driver to accelerate the AUTO21EV on a μ-split road with the maximum possible traction forces on all four wheels, no spin-out effects on the wheels, and no side-pushing effect on the vehicle. Finally, we conduct a braking test on a μ-split road, where the driver holds the steering wheel fixed and intends to stop the vehicle in an emergency braking situation from 80 km/h on a road that has an ice patch on its left side between 15 m and 25 m from the initial position of the vehicle.…”

“…Due to the amount of computation involved, a vehicle model with a torque driver applied to each wheel has been implemented on one Central Processing Unit (CPU) core of the quad-core PXI system, and the four in-wheel motor models are executed on a separate core. The advanced slip controllers [20] are run on the third CPU core, receiving sensor signals from the vehicle model and broadcasting control signals at regular intervals. A Windows-based laptop running LabVIEW communicates with the PXI system over Ethernet throughout the simulation.…”

Development of a Path-following and a Speed Control Driver Model for an Electric Vehicle

“…Note that, at the beginning and end of the test maneuver, where the vehicle is travelling at lower speeds, the maximum motor torque is available at each wheel; as the vehicle speed increases, the maximum possible motor torque decreases. It is important to notice that the slip controllers on the front axle have limited the motor torques at the beginning of the maneuver in order to avoid tire spin-out, and the slip controllers at the rear wheels have limited the motor torques at the end of the maneuver in order to avoid tire lock-up [3]. …”

“…Figure 9-a illustrates the vehicle trajectory when driving through the double-lane-change maneuver at 40 km/h. In this simulation, the AUTO21EV vehicle model developed in the ADAMS/View environment is used [3], which is equipped with tires using the Pacejka 2002 [15] tire model. The simulation time is 8 seconds with a sample time of 1 millisecond.…”

“…This vehicle has a similar configuration to the commercially available Smart fortwo, but it is equipped with four direct-drive in-wheel motors and an active steering system on the front axle. Further details about AUTO21EV can be found in [3]. In order to evaluate the handling and performance of the AUTO21EV and analyze the effectiveness of different chassis control systems before implementing them in the real vehicle, the simulation of a large number of different test maneuvers is necessary.…”