Minimum Race-Time Planning-Strategy for an Autonomous Electric Racecar

Increasing attention to autonomous passenger vehicles has also attracted interest in an autonomous racing series. Because of this, platforms such as Roborace and the Indy Autonomous Challenge are currently evolving. Electric racecars face the challenge of a limited amount of stored energy within their batteries. Furthermore, the thermodynamical influence of an all-electric powertrain on the race performance is crucial. Severe damage can occur to the powertrain components when thermally overstressed. In this work we present a race-time minimal control strategy deduced from an Optimal Control Problem (OCP) that is transcribed into a Nonlinear Problem (NLP). Its optimization variables stem from the driving dynamics as well as from a thermodynamical description of the electric powertrain. We deduce the necessary first-order Ordinary Differential Equations (ODE)s and form simplified loss models for the implementation within the numerical optimization. The significant influence of the powertrain behavior on the race strategy is shown.Comment: Accepted at The 23rd IEEE International Conference on Intelligent Transportation Systems, September 20 - 23, 202

MRacing: Improve Low Speed Cornering

ME450 Capstone Design and Manufacturing Experience: Fall 2020The MRacing team competes in the FSAE competition annually. In past years, MRacing vehicles have struggled in low speed cornering, specifically the Skid pad event. The aim of this project is to improve the low cornering performance of the 2021 MRacing vehicle to increase points achieved at FSAE competitions.MRacing Formula SAE, Wilson Student Team Project Centerhttp://deepblue.lib.umich.edu/bitstream/2027.42/164445/1/MRacing_Improve_Low_Speed_Cornering.pd

Aerodynamic Effects of the Salient Flow Features in Grand Prix Car Wakes

Grand Prix cars are the fastest circuit racing cars in production, a large part of this is due to the high downforce generated by the car's aerodynamic surfaces, in excess of the car's own weight above 150kph. It is well known that a race-car operating in the wake of an upstream vehicle experiences a reduction of aerodynamic drag, and a corresponding increase of ultimate straight line speed. There is also a loss of aerodynamic downforce, predominately from surfaces acting on the front axle. The effect of the reduced downforce is an increase of lap-time and degraded handling characteristics, thereby reducing tyre life and the ability to follow the lead car or affect an overtake. The wake of a generic Formula 1 car is shown to be characterized by a counter-rotating vortex pair, with centreline up-wash and a region of total pressure deficit, which is predominately a dynamic pressure deficit, with Cpo < 0. The streamwise vorticity is dominated by the tip vortex pair emanating from the rear wing, which merges with other vortices, forming a coherent structure by just half a car length behind the rear of the car. The vortices have an influence on the location and strength of the total pressure deficit, sweeping the loss to the centreline, and upwards to surround the vortex cores, forming a 'mushroom' shaped wake. The effect of an upstream vehicle wake has been measured in the wind tunnel and computationally, with downforce and drag losses of up to 67% and 29% respectively. The use of a short axial length bluff-bodied wake generator allows for a longer axial separation to be achieved with a complete downstream vehicle, in a conventional length wind tunnel working section, without further compromising the downstream model scale. The sensitivity of the downstream car to the various salient flow features in the upstream wake have been investigated using the method of imposing the wake on the inlet of a CFD simulation. Imposing the wake has meant that the wake can be altered without the need to modify the upstream vehicle surfaces. The key wake feature has been shown to be the axial velocity deficit, which accounts for up to 90% of the downforce loss experienced by the following vehicle. While secondary flows in the wake do result in downforce loss for the following vehicle, they are also beneficial in diverting the dynamic pressure deficit over the following vehicle, thereby introducing higher energy flow onto the following vehicle

Comparison of direct and indirect methods for minimum lap time optimal control problems

Minimum lap time simulations are especially important in the design, optimisation and setup of race vehicles. Such problems usually come in different flavours, e.g. quasi-steady state models vs full dynamic models and pre-defined (fixed) trajectory problems vs free trajectory problems. This work is focused on full dynamic models with free trajectory. Practical solution techniques include direct methods (i.e. solution of an NLP problem, widespread approach) and indirect method (i.e. based on Pontryagins principle, less common, yet quite efficient in some cases). In this contribution the performance of the direct and indirect methods are compared in a number of vehicle related problems

Energy Management Strategy for an Autonomous Electric Racecar using Optimal Control

The automation of passenger vehicles is becoming more and more widespread, leading to full autonomy of cars within the next years. Furthermore, sustainable electric mobility is gaining in importance. As racecars have been a development platform for technology that has later also been transferred to passenger vehicles, a race format for autonomous electric racecars called Roborace has been created. As electric racecars only store a limited amount of energy, an Energy Management Strategy (EMS) is needed to work out the time as well as the minimum energy trajectories for the track. At the same time, the technical limitations and component behavior in the electric powertrain must be taken into account when calculating the race trajectories. In this paper, we present a concept for a special type of EMS. This is based on the Optimal Control Problem (OCP) of generating a time-minimal global trajectory which is solved by the transcription via direct orthogonal collocation to a Nonlinear Programming Problem (NLPP). We extend this minimum lap time problem by adding our ideas for a holistic EMS. This approach proves the fundamental feasibility of the stated ideas, e.g. varying racepaths and velocities due to energy limitations, covered by the EMS. Also, the presented concept forms the basis for future work on meta-models of the powertrain's components that can be fed into the OCP to increase the validity of the control output of the EMS.Comment: Accepted at the IEEE Intelligent Transportation Systems Conference - ITSC 2019, Auckland, New Zealand 27 - 30 Octobe

The effect of Ackermann steering on the performance of race cars

open2While several papers dealing with the kinematic of mechanisms that approximate the well-known Ackermann steering are available, apparently there are no contributions related to the effect of Ack- ermann steering on vehicle performance. This work focuses on the effect of Ackermann steering and parallel steering on the performance of a racing car, after a discussion on the different definitions of Ackermann steering ratio available in the literature. Three scenarios are considered: steady turning, slalom and a circuit lap. Nonlinear optimal control techniques are employed to assess the maximum performance. A Formula SAE car model is used and validated against experimental data in acceleration, steady turning and slalom. Then the same model is employed to investigate the effect of different steering layouts.openVeneri, M.; Massaro, M.Veneri, M.; Massaro, M

Optimal energy management for formula-E cars with regulatory limits and thermal constraints

In this paper, novel solutions are proposed for energy and thermal management in Formula-E cars using optimal control theory. Optimal control techniques are used to optimize net energy consumption (accounting for loss-reductions from energy recovery from regenerative braking) to achieve minimal lap time which is a crucial element in developing a competitive race strategy in Formula E races. A thermal battery model is used to impose thermal constraints on the optimal energy management strategy in order to realistically capture working constraints during a race. The effects of energy and thermal constraints on the proposed strategy are then demonstrated and two different pedal lifting techniques were introduced. Both the current second generation and a concept third generation type of formula-E cars are studied and compared. While third generation is significantly more efficient with 10% to 30% less energy consumption, it potentially faces more critical thermal issues with more than 60% more heat generation

A free-trajectory quasi-steady-state optimal-control method for minimum lap-time of race vehicles

Minimum lap time problems are usually solved employing quasi-steady-state models on a pre- determined (fixed) trajectory or employing dynamic models on a free (i.e. not predetermined) trajectory. This work describes a third approach, where the minimum-lap-time problem is solved using quasi-steady-state models and free trajectory. The method builds upon g-g maps that can either be derived numerically or experimentally. Such g-g-speed surfaces can either represent the performance of a car or a motorcycle. Both a double-track car model and a motorcycle model are employed as examples of applications. The effect of the free-trajectory vs. fixed-trajectory assumption is also discussed

Minimum-lap-time optimisation and simulation

The paper begins with a survey of advances in state-of-the-art minimum-time simulation for road vehicles. The techniques covered include both quasi-steady-state and transient vehicle models, which are combined with trajectories that are either pre-assigned or free to be optimised. The fundamentals of nonlinear optimal control are summarised. These fundamentals are the basis of most of the vehicular optimal control methodologies and solution procedures reported in the literature. The key features of three-dimensional road modelling, vehicle positioning and vehicle modelling are also summarised with a focus on recent developments. Both cars and motorcycles are considered