applied sciences Article Adaptive Semi-Active Suspension and Cruise Control through LPV Technique Hakan Basargan 1 , András Mihály 2, Péter Gáspár 2,* and Olivier Sename 3 1 Department of Control for Transportation and Vehicle Systems, Budapest University of Technology and Economics, M˝uegyetemrkp. 3, H-1111 Budapest, Hungary; [email protected] 2 Systems and Control Laboratory, Institute for Computer Science and Control, Kende u. 13-17, H-1111 Budapest, Hungary; [email protected] 3 GIPSA-lab, INPG, Université Grenoble Alpes, 11 Rue des Mathématiques, 38000 Grenoble, France; [email protected] * Correspondence: [email protected]; Tel.: +36-1-279-6171 Abstract: Several studies exist on topics of semi-active suspension and vehicle cruise control systems in the literature, while many of them just consider actual road distortions and terrain characteristics, these systems are not adaptive and their subsystems designed separately. This study introduces a new method where the integration of look-ahead road data in the control of the adaptive semi-active suspension, where it is possible to the trade-off between comfort and stability orientation. This trade-off is designed by the decision layer, where the controller is modified based on prehistorical passive suspension simulations, vehicle velocity and road data, while the behavior of the controller can be modified by the use of a dedicated scheduling variable. The adaptive semi-active suspension control is designed by using Linear Parameter Varying (LPV) framework. In addition to this, it proposes designing the vehicle velocity for the cruise controller by considering energy efficiency and comfort together. TruckSim environment is used to validate the operation of the proposed integrated cruise and semi-active suspension control system. Keywords: adaptive semi-active suspension control; semi-active suspension control; cruise control; Citation: Basargan, H.; Mihály, A.; Linear Parameter Varying (LPV) Gáspár, P.; Sename, O. Adaptive Semi-Active Suspension and Cruise Control through LPV Technique. Appl. Sci. 2021, 11, 290. https://doi. 1. Introduction org/10.3390/app11010290 Vehicle suspension has been a trending research topic for a long time due to its important role in road damage, ride comfort, vehicle safety and stability and overall Received: 7 December 2020 Accepted: 23 December 2020 performances of the vehicle. Multiple types of suspension systems such as active, passive Published: 30 December 2020 and semi-active suspension systems are currently being studied and developed. Vehicle suspension systems can be classified in the three main categories, active, passive and Publisher’s Note: MDPI stays neu- semi-active according to their operation mode. The passive suspension is commonly used tral with regard to jurisdictional clai- but limited to improve tire deformation or driving comfort. Hence, developing new type ms in published maps and institutio- suspension be considered necessary. Active and semi-active suspension improves vehicle nal affiliations. safety, driving comfort through minimizing effect if the road distortions and disturbances. Active suspensions can store, dissipate or generate energy to the sprung and unsprung masses, although semi-active suspensions only dissipate the energy. Force-deflection speed space representation represents this difference, see Figure 1. A semi-active controller Copyright: © 2020 by the authors. Li- delivers forces within the two semi-active quadrants however, an active controller delivers censee MDPI, Basel, Switzerland. force within the four quadrants. This article is an open access article The classic semi-active suspension control strategy is the skyhook damping control, distributed under the terms and con- which was first introduced by Reference [1]. This skyhook strategy has been widely used ditions of the Creative Commons At- tribution (CC BY) license (https:// in the control for semi-active suspensions. This approaches aims to design an active sus- creativecommons.org/licenses/by/ pension control so that the chassis is linked to the sky to reducing the vertical acceleration 4.0/). of the chassis and the axle independently of each other [2]. There are many studies, which Appl. Sci. 2021, 11, 290. https://doi.org/10.3390/app11010290 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, 290 2 of 16 have been considered the skyhook control strategy due to its simplicity to achieve comfort requirement [3–6]. While it improves ride comfort, it is limited to improve road-holding performance. The hybrid model predictive control (Hybrid MPC) method is currently widely used but it still lacks robustness properties and application is not easy [7]. H¥ con- trol approach has been carried out in many publications. This control strategy guarantees good performance in the road holding, vehicle stability and ride comfort [8,9], however, due to the fixed weighting of the performances, a dynamic control reconfiguration is not possible. Control reconfiguration is significant in terms of suspension control due to dif- ferent road conditions and irregularities. Therefore, the semi-active suspension control in this study is founded on the Linear Parameter Varying (LPV) framework, which is available for the configuration by changing the scheduling variable [10–12]. According to the detailed literature review [13–18], they do not consider the integration of velocity design, oncoming road conditions and the trade-off between vehicle safety and driving comfort simultaneously. Figure 1. Quadrant comparison between active and semi-active. This study introduces a new method where the integration of look-ahead road data in the control of the adaptive semi-active suspension. In addition to this, it proposes designing the vehicle velocity for the cruise controller by considering energy efficiency and comfort at the same time. TruckSim environment is used to validate the operation of the proposed integrated velocity and semi-active suspension control system. TruckSim environment has several sensors for the desired measurement signals and all results have been analyzed from data, which was provided by TruckSim simulation. The paper is organized as follows—Section2 involves energy-efficient cruise control. Section3 presents the LPV controller synthesis and the control-oriented quarter-car model. Section4 describes system integration and decision layer which is method of selection of scheduling variable r depends on GPS based road data and look-ahead cruise control. Section5 demonstrates the operation of the proposed method in high-fidelity TruckSim simulation environment with real road data. Finally, concluding remarks are presented in Section6. 2. Energy Efficient Cruise Control Reducing energy consumption by improving the driving style has drawn a lot of atten- tion nowadays. Many assistance systems have been developed to derive energy-efficient driving styles and provide suggestions by human-machine interfaces. However, it is really hard for the driver to follow such suggestions perfectly. Thus, efficient cruise- control should be used for further vehicle technologies. The cruise control system automatically modifies a steady speed of a vehicle as set by the driver by setting the longitudinal control forces. Generally, adaptive cruise control systems are considered only the instantaneous ef- fect of the road conditions, since they do not have information about onward road sections. But it is important to consider oncoming road sections The algorithm which performs look-ahead control has been already presented in a previous study [19]. As it is shown in Appl. Sci. 2021, 11, 290 3 of 16 Figure2, the look-ahead distance L is divided into n number of road sections with n + 1 number of points. 0 1 2 3 4 5 6 n s3 s1 s2 α4 Fl1 α1 original reference velocities: α1 vref 0 vref 1 vref 2 vref 3 vref 4 vref 5 vref 6 vrefn modified reference velocity: ξ˙0 Figure 2. Forward road segmentation. The rate of accelerations of the vehicle is considered between these points in order to make them constant. Thus, vehicle movement can be expressed as s1 = x˙0(x˙1 − x˙0)/x¨ + 2 (x˙1 − x˙0) /2x¨, where x˙0 and x˙1are the vehicle’s velocity at the initial point and at the first point respectively, s1 is the distance between points and x¨ + (Fl − Fd)/m is the acceleration of the vehicle, where m is the mass of the vehicle, Fl and Fd are traction and disturbance force, respectively. Thus, the velocity of the first section point is calculated as following: 2 x˙2 = x˙2 + 2x˙ + x˙2 + s (F − F ), (1) 1 0 s1 0 m 1 l1 d1 ˙2 2 where, x1 is velocity of the first section and defined as the reference velocity (v re f ,1). This ˙2 = ˙2 + ˙ velocity relationship also applies for the next section as x2 x1 2xs2 Equation (2) is used to calculate the velocity of the vehicle for nth section point by using similar expression to Equation (1). n ˙2 ˙2 2 2 xn = x0 + s1Fl1 − ∑ si Fdi = v re f ,n, (2) m i=1 where, Fdi is disturbance force and Fl1 is control force. Tracking the momentary value of the velocity also important and it can be considered in the following: ˙2 2 x0 ! v re f ,0. (3) Because of the collision risk, considering the preceding velocity on the lane is necessary: ˙2 2 x0 ! v lead. (4) In the next step, weights(g) are applied to both road slope and reference velocity in Equation (2), while additional weights Q and W are applied in Equations (3) and (4), respectively. The all weights are sum up to one. The weight gi expresses the rate of the road conditions, Q determines the tracking requirement of the reference velocity and W represents velocity tracking of the preceding vehicle, lead in order to avoid a collision. After consideration of the weights in the formulation, the following formula is written: 2 2 x˙2 + s (1 − Q − W)F − s (1 − Q − W)F = J, (5) 0 m 1 l1 m 1 d1,o where n n n 2 2 2 J = Qvre f ,0 + ∑ givre f ,i + ∑(si Fdi,r ∑ gj).