Design and Analysis of an Electric Over- Actuated Vehicle Suspension

Ankith Suresh Athrey

Master of Science Thesis TRITA-ITM-EX 2020:521 KTH Industrial Engineering and Management Machine Design SE-100 44 STOCKHOLM

Examensarbete TRITA-ITM-EX 2020:521

Utformning och analys av elektrisk överaktuerad fordonsupphängning

Ankith Suresh Athrey Godkänt Examinator Handledare 2020-09-16 Ulf Sellgren Mikael Nybacka Uppdragsgivare Kontaktperson ITRL, KTH Mikael Nybacka Sammanfattning

Huvudsyftet med detta examensarbete är att förbättra prestanda för Research Concept Vehicle (RCV). RCV är ett elektriskt överaktuerat fordon utvecklat vid Integrated Transport Research Lab (ITRL) vid KTH Royal Institute of Technology. Fordonet styr, reglerar cambervinkeln, kör och bromsar med varje hjul i fordonet. RCV har också olika driftlägen som 2WD, 4WD, 2WS och 4WS. RCV används som en forskningsplattform för att implementera, validera och demonstrera resultat från olika forskningsprojekt. RCV utvecklades år 2012. Nu är det nu ett krav att förbättra fordonets prestanda för att skapa en mer dynamiskt kapabel plattform att göra mer dynamiska tester med. Huvudsyftet med denna avhandling är att undersöka möjligheten att uppgradera upphängningssystemet med integrerad hjulnavmotor, elektrisk styrmanöverdon och elektrisk cambermanöverdon. Det handlar också om förpackning av det nya batteripaketet och förstärkning av chassit för att minska flex under drift. Stegen som följs innefattar analys av de nuvarande elektriska styrsystemen och de elektriska camber-ställdonssystemen med MBD-metoden för att testa prestandan. Med detta som bas bestäms krav på vad som måste göras för att förbättra prestandan genom att skapa en annan MBD-modell för att erhålla de nya prestandasiffrorna. Det nya batteripaketet ska också placeras på fordonets bottenplatta med hjälp av CAD-programvara. Chassit ska förstärkas med hjälp av tvärbalkar, även utformade på CAD-programvara. Spjällenheten måste placeras om för att rymma batteripaketet. Baserat på förändringarna i fordonet bestäms nya hårda punkter för det nya styrsystemet, camber- systemet och upphängningssystemet. Baserat på de nya prestandasiffrorna som erhållits från MBD presenteras kraven för de nya elektriska styr- och camber-ställdonssystemen. Styrkan i den nya ramen testas med FEM-metoden. Spjällenhetens nya position testas för prestanda med hjälp av en MBD-programvara. I slutet av denna avhandling erhölls kraven för att utveckla den nya och förbättrade RCV, vilket möjliggjorde en mer dynamisk testning med elfordonet. Nyckelord: RCV, ITRL, MBD, CAD, FEM.

Master of Science Thesis TRITA-ITM-EX 2020:521

Design and Analysis of Electric Over-actuated Vehicle Suspension

Ankith Suresh Athrey Approved Examiner Supervisor 2020-09-16 Ulf Sellgren Mikael Nybacka Commissioner Contact person ITRL, KTH Mikael Nybacka Abstract The main aim of this master thesis is to improve the performance of the Research Concept Vehicle (RCV). The RCV is an electric over-actuated vehicle developed at Integrated Transport Research Lab (ITRL) at KTH Royal Institute of Technology. The vehicle steer, camber, drive, and brake on each wheel of the vehicle. The RCV also has various operation modes such as 2WD, 4WD, 2WS and 4WS. The RCV is used as a research platform to implement, validate, and demonstrate results of various research projects.

The RCV was developed in the year 2012. There is now a requirement to improve the performance of the vehicle to create a more dynamically capable platform to do more dynamic tests with. The main aim of this thesis is to explore the possibility of upgrading the suspension system with integrated wheel hub motor, electric steering actuator and electric camber actuator. It also involves packaging of the new battery pack system and reinforcing the chassis to reduce the flex during operation.

Steps followed involves analysis of the current electric steering and electric camber actuator systems using MBD method to test the performance. With this as the base, requirements are decided as to what must be done to improve the performance by creating another MBD model to obtain the new performance figures. Also, the new battery pack is to be positioned on the base plate of the vehicle and this is achieved by placing the new battery pack onto the existing CAD model. The chassis is to be reinforced with the help of cross members, also designed on CAD software. The damper unit needs to be repositioned to accommodate the battery pack. Based on the changes in the vehicle, new hardpoints are decided for the new steering system, camber system and suspension system.

Based on the new performance figures obtained from MBD, the requirements of the new electric steering and camber actuator systems are presented. The strength in the new frame is tested using FEM method. The new position of the damper unit is tested for performance using an MBD software.

With the end of this thesis, the requirements to develop the new and improved RCV was obtained, thereby allowing for more dynamic testing to be done with the electric vehicle.

Keywords: RCV, ITRL, MBD, CAD, FEM.

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FOREWORD

First and foremost, I would like to take this opportunity to thank Mikael Nybacka, Project leader of the RCV platform at ITRL for believing in me, giving me this excellent opportunity of working on this thesis and mentor me along the way. My special thanks to Chirag Savant, Research Engineer at ITRL who provided me with invaluable guidance and help throughout the duration of the master thesis. Finally, I would like to thank my parents, family, and friends for providing me with the encouragement to pursue this master course.

Ankith Suresh Athrey

Stockholm, September 2020

NOMENCLATURE

Notations

Symbol Description

E Young´s modulus (Pa) r Radius (m) t Thickness (m) T Torque (Nm) v Velocity (km/h) vs Velocity (m/s) F Force (N) T Torque (Nm) N Speed of rotation (rpm) d Diameter of the tyre (m) a Acceleration due to gravity (m/s2)

Abbreviations

CAD Computer Aided Design CAE Computer Aided Engineering PLM Product Lifecycle Management MBD Multi Body Dynamics MBS Multi Body Simulation ITRL Integrated Transport Research laboratory RCV Research Concept Vehicle FEM Finite Element Method 2WD Two Wheel Drive 4WD Four Wheel Drive 2WS Two Wheel Steering 4WS Four Wheel Steering LIDAR Light Detection and Ranging RADAR Radio Detection and Ranging

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TABLE OF CONTENTS

FOREWORD IV

NOMENCLATURE VI

TABLE OF CONTENTS VIII

LIST OF FIGURES X

LIST OF TABLES XII

1. INTRODUCTION 1

1.1 Background 1 1.2 Purpose 2 1.3 Research Questions 3 1.4 Delimitations 3 1.5 Method 3

2. FRAME OF REFERENCE 5

2.1 Basic definitions 6 2.1.1 Track Width 6 2.1.2 Wheelbase 6 2.1.3 Suspension 7 2.1.4 Sprung and unsprung mass 8 2.1.5 Steering 8 2.1.6 Camber angle 8 2.1.7 Tyre forces 9 2.1.8 Linear actuators 9 2.2 The Current RCV 10 2.1.1 The motor 11 2.1.2 Body 12 2.1.3 Steering subsystem 13 2.1.4 Camber subsystem 15 2.1.5 Suspension system 17 2.1.6 Battery system 19

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3. IMPLEMENTATIONS 21

3.1 Requirement specifications 21 3.2 Concept Development 21 3.2.1 battery pack positioning 21 3.2.2 Steering actuation 23 3.2.3 Camber actuation 25 3.3 Concept Evaluation 27 3.3.1 battery pack positioning 27 3.3.2 Steering and camber subsystem 27 3.4 The new RCV 28 3.4.1 Motor requirements 28 3.4.2 Steering subsystem 29 3.4.3 Camber subsystem 35 3.4.4 Vehicle frame 39 3.4.5 Suspension system 42

4. RESULTS 44

4.1 Steering subsystem 45 4.2 Camber subsystem 46 4.3 Frame 47

5. DISCUSSION AND CONCLUSION 52

5.1 Discussion 53 5.2 Conclusion 53 5.2.1 Simulation on ADAMS/View 53 5.2.2 The different subsystems 54

6. FUTURE WORK 55

7. REFERENCES 57

APPENDIX A: GANTT CHART 60

APPENDIX B: RISK REGISTER 62

LIST OF FIGURES

Figure 1. 1: The RCV-E ...... 1 Figure 1. 2: The Research Concept Vehicle (RCV) ...... 2

Figure 2. 1: Wheelbase ...... 6 Figure 2. 2: Double Wishbone suspension [7] ...... 7 Figure 2. 3: MacPherson strut [7] ...... 7 Figure 2. 4: Sprung and unsprung mass [8] ...... 8 Figure 2. 5: Illustration of camber angle [11] ...... 9 Figure 2. 6: Tyre forces and moments [12] ...... 9 Figure 2. 7: Electric linear actuator [13]...... 10 Figure 2. 8: CAD of the current RCV ...... 10 Figure 2. 9: Hub motor on the RCV ...... 11 Figure 2. 10: Body of the RCV ...... 12 Figure 2. 11: Baseplate (Design and Implementation of an Experimental Research and Concept Demonstration Vehicle) ...... 13 Figure 2. 12: Current steering setup ...... 13 Figure 2. 13: Steering Adams/View model ...... 14 Figure 2. 14: Displacement versus time ...... 15 Figure 2. 15: Actuator Displacement versus time ...... 15 Figure 2. 16: Camber actuation on RCV ...... 15 Figure 2. 17: Camber actuation model on ADAMS/View ...... 16 Figure 2. 18: Linear displacement of tyre vs time ...... 17 Figure 2. 19: Linear actuation length ...... 17 Figure 2. 20: RCV suspension system ...... 17 Figure 2. 21: RCV spring stiffness ...... 18 Figure 2. 22: RCV damper characteristics ...... 18 Figure 2. 23: ADAMS/Car model of current RCV ...... 19 Figure 2. 24: Spring displacement ...... 19

Figure 3. 1: Concept 1 – battery placement ...... 22 Figure 3. 2: Concept 2 – battery placement ...... 22 Figure 3. 3: Concept 1: Rack and pinion with motor ...... 23 Figure 3. 4: Concept 2a – Linear Actuator ...... 24 Figure 3. 5: Concept 2b – Linear Actuator ...... 24 Figure 3. 6: Concept 3 – motor and gearbox direct to tie rod ...... 25 Figure 3. 7: Concept 1 – Push along inner upper A-arm ...... 25 Figure 3. 8: Concept 2: Motor-gearbox at the upper inner A-arm joint ...... 26 Figure 3. 9: Concept 3: Motor-gearbox to push upper inner A-arm ...... 26 Figure 3. 10: Steering model on Adams/View ...... 29 Figure 3. 11: Subframe setup in simulation ...... 29 Figure 3. 12: Contact force illustration ...... 30 Figure 3. 13: Contact force specifications ...... 31 Figure 3. 14: Rotational joint motion to rocker ...... 31 Figure 3. 15: Position of the tyre after actuation ...... 32 Figure 3. 16: Translational displacement of marker...... 32 Figure 3. 17: Tyre displacement - steering ...... 33 Figure 3. 18: Torque on rocker arm ...... 33 Figure 3. 19: Rocker dimensions ...... 34 Figure 3. 20: torque required – dynamic ...... 35 Figure 3. 21: Camber model on ADAMS/View ...... 35 x

Figure 3. 22: Rotational joint motion – camber subsystem ...... 36 Figure 3. 23: Camber model after actuation ...... 36 Figure 3. 24: translational displacement of tyre ...... 37 Figure 3. 25: Tyre displacement - camber ...... 37 Figure 3. 26: torque required for camber actuation ...... 37 Figure 3. 27: Upper inner A-arm ...... 38 Figure 3. 28: Camber actuation – dynamic ...... 39 Figure 3. 29: Cross members in the frame ...... 39 Figure 3. 30: Structure for battery mounting ...... 40 Figure 3. 31: Subframe structure ...... 40 Figure 3. 32: Subframe structure - b...... 40 Figure 3. 33: Battery pack positioning ...... 41 Figure 3. 34: Battery mounting ...... 41 Figure 3. 35: ADAMS/Car model of new suspension position ...... 42 Figure 3. 36: hard point locations ...... 43 Figure 3. 37: Spring displacement ...... 43

Figure 4. 1: New steering model ...... 45 Figure 4. 2: Required linear actuation ...... 46 Figure 4. 3: Stroke length of the actuator ...... 47 Figure 4. 4: Positive camber actuation ...... 47 Figure 4. 5: Model to test forces in joints ...... 48 Figure 4. 6: Longitudinal and lateral force on upright ...... 48 Figure 4. 7: Force in lower A-arm – x direction ...... 49 Figure 4. 8: Force in lower A-arm – y direction ...... 49 Figure 4. 9: Force in lower A-arm – z direction ...... 49 Figure 4. 10: Total deformation in frame ...... 50 Figure 4. 11: Directional deformation x-axis ...... 50 Figure 4. 12Directional deformation y-axis ...... 50 Figure 4. 13: Directional deformation z-axis ...... 51

LIST OF TABLES

Table 2. 1: RCV Specifications [14] ...... 11 Table 2. 2: Heinzmann PRA-230 specifications [15] ...... 12 Table 2. 3: Thomson MX24-B8M10E0-51 linear actuator [17] ...... 14 Table 2. 4: Camber actuator specifications [17] ...... 16

Table 3. 1: GBS-LFMP100AHX cell specifications [18] ...... 21 Table 3. 2: Steering subsystem decision matrix ...... 27 Table 3. 3: camber subsystem decision matrix...... 28

Table 4. 1: Steering actuator requirements ...... 46 Table 4. 2: Camber actuator requirements ...... 47

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1. INTRODUCTION

This chapter describes the background, the purpose of this thesis, the delimitations and the method used to complete the thesis.

1.1 Background The world is moving towards a smarter and more sustainable transport system. One of the main problems to be addressed in today’s world is to reduce the impact of road transportation on the environment. There has been a massive research and development work reported in both academic and industrial areas [1]. This requirement of a more sustainable future has led to research in various areas of research and integration of the findings would help achieve the same. A major step towards smarter transport system would be autonomous driving. A drastic change has been observed in autonomous driving technology since the 1920s, when vehicles were controlled using radio waves, to 1960s when we first saw vision guided autonomous vehicles [2]. Companies like Protean and Elaphe have improved on the sustainable transport system by creating in-wheel motors for passenger and light commercial vehicles [3] Elaphe has been working on vehicle electrification and prototyping where they integrate the electric motor, introduce various technologies such as traction control, independent wheel control, energy regeneration, etc., onto existing electric or internal combustion vehicle [4]. Other companies such as Navia have developed an electric 10 passenger autonomous vehicle with a maximum speed of 20km/h using LIDAR and optical cameras [5]. Easymile is another company working towards autonomous vehicles with their technology capable of achieving level 4 of autonomous driving by employing of RADAR, cameras, and LIDAR sensors. They have also developed a passenger shuttle and an autonomous tow tractor [6]. This master thesis was conducted at Integrated Transport Research Lab (ITRL) at KTH Royal Institute of Technology (KTH). ITRL is a multi-disciplinary workplace with various research areas to solve challenges in the future of transport. Research fields at ITRL includes the development of electric vehicles, autonomous driving, and sustainable mobile solutions.

Figure 1. 1: The RCV-E

The Research Concept Vehicle (RCV) and RCV-E (Research Transport Vehicle – E) platform is a leap towards sustainable transport systems. The RCV and RCV-E are fully electric, over-actuated

1 vehicles developed with the collaborative efforts of both research engineers and students at ITRL. A system is over-actuated if there are more actuators than the number of degrees of freedom of the system that has to be controlled. The RCV-E platform is developed based on the RCV and is designed for autonomous driving.

Figure 1. 2: The Research Concept Vehicle (RCV) This thesis concentrates on the RCV. The first generation of the RCV is a two-seater, dynamic, and all-electric Four-Wheel Drive (4WD), Four-Wheel Steering (4WS) and active camber actuation vehicle developed in the year 2012 which utilizes a fully computerized drive by wire technology. The vehicle is driven by a hub motor in each wheel. All four wheels can steer independent of one another. The vehicle also houses active camber actuation system to alter the camber angle of each wheel, on the go. Each wheel houses a hub motor which supplies power to the wheel. The bottom plate of the vehicle is made of a carbon fiber sandwich to which the roll cage and suspension sub frames are bolted onto. The vehicle is powered by a 52V battery system which is mounted on the rear part of the vehicle, on top of the subframe. The design of the vehicle is modular and versatile to help test various functions such as 2WD, 4WD, 2WS, 4WS, etc. The RCV is utilized to validate and demonstrate the findings of various fields of research.

1.2 Purpose

The RCV series present at ITRL, KTH have been used to test, validate, and demonstrate various research projects at KTH. Although versatile, the first generation of RCV is due for an upgrade to improve the overall performance of the vehicle. The purpose of this degree project is to make the RCV more dynamically capable by upgrading the components of the vehicle to improve its performance to make more dynamic tests with it. Various subsystems of the vehicle can be upgraded to improve its overall performance. This is achieved by focussing on individual subsystems of the vehicle, mainly the electric steering system, electric active camber actuation system, hub motor, suspension, battery pack system and chassis performance. One of the main requirements for this thesis is to propose a solution to improve the speed of actuation of the steering and active camber subsystems. The other requirement is to propose the requirements of a hub motor to achieve better acceleration, deceleration, and braking results. To achieve the above requirements, the battery pack would have to be upgraded to a higher capacity system and to be positioned in an ideal way on the baseplate, rather than on the subframe in order to lower the center of gravity of the car. One of the other goals of this thesis is to redesign the frame of the vehicle by

2 introducing cross members to reduce the amount of existing flex in the bottom plate during operation of the vehicle.

1.3 Research Questions

The aim of this master thesis is to improve the overall performance of the vehicle is to answer the following research questions: 1. What are the requirements of the motor required to achieve better performance? 2. How to incorporate a bigger battery pack to improve the performance of the vehicle? 3. What are the requirements to improve the performance of the steering subsystem? 4. What are the requirements to improve the performance of the active camber actuation subsystem? 5. How to reduce the flex in the bottom plate during operation?

1.4 Delimitations

Following are the delimitations of this degree project: 1. The hardpoints of the steering subsystem is to be decided, detailed design of these subsystems is not involved. 2. The hardpoints of the camber actuation subsystem is to be decided, detailed design of these subsystems is not involved. 3. Performance of the linear actuators required for steering and camber actuation are defined, but the selection of linear actuators is not done. 4. All values of performance obtained are in an ideal case and real-life testing must be made to verify these values. 5. Detailed design of the frame of the vehicle and analysis of the frame is done during this thesis, but the optimization of the structure of the frame is not involved in the thesis. 6. The position of the battery management system has not been decided in this thesis. 7. Although changes are made to the frame of the RCV, analysis on how it results in the reduction of flex in the base plate is not conducted. 8. Specifications of the motor required would be defined, but the selection of the motor is not done during this thesis.

1.5 Method

As discussed earlier, the main aim of this thesis is to figure out ways to improve the performance of the RCV. This can be best addressed by dividing the RCV into various subsystems and work on each subsystem individually.

First, considering the hub motor, the performance figures required by the new motor such as torque, rotational speed, etc. are calculated and presented. A new hub motor is to be selected based on the obtained results.

For the steering and camber actuation systems, the approach will be to first analyze the performance of the current systems and devise a method to improve the performance to meet the requirements. Models of the current subsystems will be created on ADAMS/View. Once the current performance is obtained, various concepts will be generated for both the steering and camber actuation subsystems and the best concept for both is to be chosen. The requirements of the new actuators for both steering and camber subsystems are obtained with the help of ADAMS/View and based on the values obtained, requirements of the new actuators to achieve the requirements are defined.

With respect to the battery placement, the new battery pack is to be placed along the baseplate of the vehicle and not on the subframe as on the current RCV. This can be done by first analysing the dimensions, voltage, current and mass of each cell. Once this is done, the cells are to be positioned on the baseplate of the RCV, taking into consideration the space required for other components such as the seats, steering and camber actuation subsystems, the damper unit, etc. Once the position of the cells has been decided, a supporting structure is built around the cells using pipe structures using CAD software.

One of the other requirements is to reduce the flex in the baseplate during the operation of the RCV. The approach to solve this problem is to add cross members in the middle of the baseplate and to connect these cross members to the subframes. This would result in lowering the flex in the baseplate during operation. This is achieved by building cross members while considering the mounting holes already present in the baseplate, using CAD software. An ADAMS/View model is made to obtain the forces acting on mounting location of the A-arms by assuming a force equivalent to mass on each wheel multiplied by the acceleration due to gravity in the lateral and longitudinal directions on the tyre. The CAD model is then imported into an FEM software and these forces are input into it to obtain the deformation in the new frame.

2. FRAME OF REFERENCE This chapter presents a detailed description of the existing RCV. The focus is on the definition of each subsystem and explanation on how each subsystem is implemented on the RCV.

2.1 Basic definitions This subchapter includes the basic definitions required to understand the various terms being used in this thesis report.

2.1.1 Track Width

Figure 2. 1: Track width Track width of a vehicle is the distance between the center lines of two wheels on the same side of the vehicle.

2.1.2 Wheelbase

Figure 2. 1: Wheelbase Wheelbase is the distance between the centers of the rear and front wheels.

2.1.3 Suspension An automotive suspension consists of various components such as tyre, springs, shock absorbers and linkages that connects the vehicle to the wheels and allows relative motion between them. Car suspensions are used for various reasons including ride quality, to ensure road-wheel contact and to provide good handling, etc. Suspension systems are divided into three types:  Dependent suspension system  Semi-independent suspension system  Independent suspension system In this report, we focus mainly on the independent suspension systems. The two main types of independent suspension systems are:  Double wishbone (double A-arm) suspension

Figure 2. 2: Double Wishbone suspension [7] A double wishbone suspension is a type of independent suspension which consists of two A-arms used to support and locate the wheel. The spring and the damper unit are usually mounted onto the lower A-arm. A double wishbone suspension improves the stability and handling of the vehicle. This type of suspension is more versatile, modifying it to obtain the desired changes is comparatively easy. A short Long Arms (SLA) suspension is a type of double wishbone suspension in which, the upper A-arm is shorter than the lower A-arm.  MacPherson strut

Figure 2. 3: MacPherson strut [7]

A MacPherson strut suspension is a special type of SLA in which, the upper A-arm is replaced by a strut [19]. The upper end of the suspension is fixed to the body of the vehicle. Advantages of using the MacPherson strurt is that it allows for more space in the vehicle. It reduces the unsprung weight of the vehicle.

2.1.4 Sprung and unsprung mass

Figure 2. 4: Sprung and unsprung mass [8] Sprung mass is the portion of the total mass of the vehicle supported by the suspension. Components such as the body of the vehicle, the chassis, passengers, etc. are classified as sprung mass. Unsprung pass is the portion of the total mass of the vehicle that is not supported by the suspension. Components such as the tyre, wheel, brakes, hub motors, etc. are classified as unsprung mass.

2.1.5 Steering The steering system helps the driver in obtaining complete control on the maneuvering of the vehicle [9]. The main purpose of the steering system is to help the driver point the car towards a desired direction. This is possible by linking the wheels of the car with the steering wheel which is controlled by the driver. A conventional steering subsystem utilizes linkages, rack and pinion, etc. to translate the changes in the steering wheel onto the wheels of the vehicle. Nowadays, this has evolved to a more modern steer by wire system which helps eliminate the use of mechanical linkages with the use of electric motors and linear actuators to change the direction of the wheels and to provide feedback to the driver. Eliminating these mechanical linkages helps save space, it is easily modifiable and traction control can be implemented to improve the safety of the car [10].

2.1.6 Camber angle When viewed from the front, camber angle is the angle between the vertical axis of the wheel and the vertical axis of the vehicle.

Figure 2. 5: Illustration of camber angle [11] Altering the camber angle on the go can help improve the handling aspects of the vehicle. Having active camber control has various advantages such as having better cornering stability when the camber angle is negative and best straight-line performance when the camber angle is neutral. It also has advantages when testing and validating research.

2.1.7 Tyre forces

Figure 2. 6: Tyre forces and moments [12] Various forces act on the tyre during operation. Longitudinal force acts along the direction of wheel travel. Normal force acts along the vertical axis of the wheel. Lateral force acts perpendicular to the longitudinal force.

2.1.8 Linear actuators A linear actuator utilizes either electric, pneumatic, or hydraulic forces to create motion in a straight line.

Figure 2. 7: Electric linear actuator [13] An electric linear actuator converts the rotary motion of the motor to a linear motion with the help of a gearbox and a lead screw.

2.2 The Current RCV As explained in the earlier section of the report, the current RCV was built in the year 2012 and has been used to evaluate and demonstrate various forms of research within KTH. This chapter mainly concentrates the definition of each subsystem and how it has been implemented on the RCV.

Figure 2. 8: CAD of the current RCV

The RCV has the following specifications:

Vehicle parameters Value Vehicle Total mass (kg) 380 Track width (m) 1.5 Wheelbase (m) 2 Tyre radius (m) 0.317 Wheel unsprung mass (kg) 25 Steer angle interval -25° to 25° Camber angle interval -15° to 10° Table 2. 1: RCV Specifications [14] The RCV utilizes motorcycle tyres (Michelin Pilot Sport 3 170/60 R17). The corner modules (wheel, motor, suspension, steering and camber actuation) are identical on all four sides of the vehicle. The car can be divided into various subsystems such as steering, camber, suspension, body, and battery subsystems which are explained in detail in the following subchapters.

2.1.1 The motor The current RCV is a 4WD vehicle, meaning power is supplied to all four wheels of the vehicle. This is possible by hub motors. Hub motors are electric motors integrated within the wheel and powers the wheel. The RCV has individual hub motors to each wheel of the vehicle. The vehicle can be run in both 2WD mode and 4WD mode. A 4WD system improves the traction of the vehicle and helps in testing and validation of research.

The motor used on the RCV is a Heinzmann PRA-230.

Figure 2. 9: Hub motor on the RCV

The Heinzmann PRA-230 is a permanent magnet synchronous type motor. Specifications of the motor are as follows: Specifications Value Rated power (KW) 1.6 Rated speed (rpm) 420 Maximum torque (Nm) 160 Battery voltage (V) 48 Degree of protection IP54 Weight (kg) 16

Table 2. 2: Heinzmann PRA-230 specifications [15] This motor on all four wheels help the car achieve a top speed of 70km/h.

2.1.2 Body The body of the RCV consists of the baseplate, subframes and the roll cage. RCV is designed to hold two passengers. Various components such as the suspension, wheel, camber actuation, etc. are mounted onto the subframe. The rear subframe supports the battery pack as well. The roll cage as the term suggests is used to protect the passengers of the vehicle in the event of a crash resulting in the vehicle rolling over.

Figure 2. 10: Body of the RCV The roll cage and the subframes are mounted onto the baseplate of the vehicle.

Figure 2. 11: Baseplate (Design and Implementation of an Experimental Research and Concept Demonstration Vehicle)

The baseplate is made of a carbon fiber sandwich. It can be divided into two sections (as shown in the above figure), section 1 which has 11 layers of carbon fiber with a central core of PET ac115 [14] and section 2 with a core made of material H80 .

2.1.3 Steering subsystem

The RCV utilizes a steer by wire system with the help of linear actuators. This vehicle has 4WS, meaning all four wheels can be used to steer the vehicle. Advantages of 4WS include improvement of maneuvering of the vehicle at low speeds and stability at higher speeds [16].

Figure 2. 12: Current steering setup The input from the steering wheel is passed onto the linear actuators. This rotates the rocker and passes the motion onto the tie rod which helps in changing the direction of the wheels. This in turn

13 results in steering of the car. The linear actuator used is a Thomson MX24-B8M10E0-51. Specifications of the linear actuator are as follows:

Specifications Value Actuator voltage (V) 24 VDC Maximum stroke length (mm) 100 Maximum dynamic load (N) 800 No load speed (mm/s) 60 Maximum load speed (mm/s) 30

Table 2. 3: Thomson MX24-B8M10E0-51 linear actuator [17] The current performance of the steering actuation system can be obtained with the help of ADAMS/View.

Figure 2. 13: Steering Adams/View model The geometry of the tyre and suspension geometry was imported from Solid Edge. A marker is placed on the tip of the tyre to check the linear displacement of the tyre.

Figure 2. 14: Displacement versus time The actuator was given a linear speed of 30mm/s. The length of linear actuation is as follows:

Figure 2. 15: Actuator Displacement versus time It takes a total of 1.02s to obtain the steering angle of 25° and results in 31mm of linear actuation. This gives it a steering speed of 24.5°/s, which is different from the measured value of 37°/s.

2.1.4 Camber subsystem The RCV uses an active camber control system with the help of linear actuators.

Figure 2. 16: Camber actuation on RCV

The linear actuator is connected to the upper inner A-arm. For camber control, the linear actuator pushes against the upper inner A-arm which helps in camber actuation. The linear actuator used is Thomson PR2405-4A65D15DCS. The specifications of the linear actuator are as follows: Actuator Voltage (V) 24 VDC Maximum stroke length (mm) 100 Maximum dynamic load (N) 2250 Maximum static load (N) 4500 No load speed (mm/s) 28 Maximum load speed (mm/s) 23

Table 2. 4: Camber actuator specifications [17]

The performance of the camber actuation system can be obtained with the help of ADAMS/View.

Figure 2. 17: Camber actuation model on ADAMS/View The linear actuator was given a speed of 23mm/s. This resulted in the translational displacement of the tyre in the y axis to be 82.5mm. This resulted in the negative camber of 15°.

Figure 2. 18: Linear displacement of tyre vs time This resulted in the total linear actuation of 36mm.

Figure 2. 19: Linear actuation length This gives the current camber actuation system a speed of 9.3°/s, which is higher than the measured value of 6°/s.

2.1.5 Suspension system

Figure 2. 20: RCV suspension system The RCV uses a double wishbone type independent suspension system. The damper unit is not directly connected to the lower A-arm, but the pushrod pushes against the rocker arm which compresses and expands the damper unit. Advantages of having this setup is that the damper unit is closer to the center of gravity of the vehicle and changes can be made to the rocker arm ratio, position of the damper unit, etc.

Figure 2. 21: RCV spring stiffness

Figure 2. 22: RCV damper characteristics The RCV uses Öhlins TTR dampers and the springs made by Lesjöfors with a stiffness of 50N/mm (Tomner thesis). It has the following stiffness and damping characteristics.

An ADAMS/Car model was developed to analyse the current suspension setup.

Figure 2. 23: ADAMS/Car model of current RCV The compression and damping value characteristics were input into the system and the above model was developed on ADAMS/Car. To test the suspension, a simple parallel wheel travel simulation was performed with 50mm of bump and rebound travel.

Figure 2. 24: Spring displacement This results in 56mm of spring displacement.

2.1.6 Battery system The current RCV has two batteries, the main battery being a lithium polymer type, 14 cells, made by Elite Power Solution LLC, in series to produce a nominal voltage of 52V and a peak current of 400A. This main battery is used to power the motors. The auxiliary battery is of 24V, 10Ah system used to operate other systems. It is charged by the main battery.

3. IMPLEMENTATIONS

In this chapter, first the requirement specifications are defined, followed by concept development, concept evaluation and defining the requirements for the new RCV. 3.1 Requirement specifications

As discussed in the previous chapter, it is evident that the even though the car has good performance, it has areas such as steering and camber actuation systems, suspension system, motor, battery system and body. The main aim of this thesis was to meet the following requirements to improve the performance of the vehicle.

 Requirements to increase the speed of steering and camber actuation to 50°/s.  Requirements of the motor to have an acceleration equivalent to the acceleration due to gravity multiplied by the mass of the vehicle and a top speed of 90km/h.  Provide hard points for steering, camber, and suspension.  Position a 100V battery pack system onto the vehicle, which would lower the center of gravity of the vehicle.  Reposition the suspension to accommodate the battery pack.  Reduce the flex in the bottom plate of the RCV by introducing cross members in the middle of the vehicle.

3.2 Concept Development

In this subchapter, the requirement specifications are met by generating concepts and choosing the best concept of the lot with the help of a decision matrix.

3.2.1 battery pack positioning

One of the main requirements of this thesis is to accommodate a 100V battery system onto the vehicle. This would be a huge upgrade over the previous 52V battery system. Upgrading the battery system would help with the use of better performing motors which would improve the performance of the vehicle. It was decided to use the same cells as what is used on the RCV-E. The cells are GBS-LFMP100AHX, manufactured by Elite Power Solutions LLC. These are lithium ion cells and the specifications of each cell is as follows:

Specifications Value Cell capacity (Ah) 100 Nominal voltage (V) 3.2 Maximum cell voltage (V) 4 Minimum cell voltage (V) 2.5 Dimensions(mm) 140x62x241 Weight(kg) 3.2

Table 3. 1: GBS-LFMP100AHX cell specifications [18]

Based on the above specifications, we would need 32 cells in parallel to obtain the total nominal voltage of 100V.

3.2.1.1 Concept 1

Initially, the plan was to utilize the same battery pack which is used on the more recent RCV-E.

Figure 3. 1: Concept 1 – battery placement

This would mean that there would be not additional manufacturing required as the battery boxes were already available. But the disadvantages would be that the weight of the battery pack would be concentrated towards the end of the vehicle and this would help increase the twisting moment on the baseplate and the whole idea of reducing the flex on the base plate would be counterproductive. Also, using a battery box at the ends would mean that there would be less space for the suspension, steering and camber actuation subsystems.

3.2.1.2 Concept 2

Figure 3. 2: Concept 2 – battery placement 22

To address the issues faced in the previous subsection, it would be a better idea to distribute the cells along the length of the car. This would mean to ensure there is enough space to mount the seats of the vehicle. Also, it would provide enough space to mount the suspension, camber and steering actuator and reduce the flex in the baseplate due to better weight distribution. Modifications would have to be made to the subframe and the roll cage to accommodate the battery pack.

3.2.2 Steering actuation

As described earlier, steering actuation of 50°/s is a requirement. Various types of steering actuation and the positions of each of these types of steering were explored, and the following concepts were generated.

3.2.2.1 Concept 1: Use of rack and pinion

Figure 3. 3: Concept 1: Rack and pinion with motor

In this concept, a motor connected to a gearbox would run the pinion. There would be a rocker between the rack and tie rod. The pinion would be in meshed with a rack and that would push or pull the tie rod. This would result in faster actuation as the motor and gearbox can be chosen based on the requirements. Although the design complexity would increase as it is hard to find the required product and would also lead to assembly of different components.

3.2.2.2 Concept 2: Use of linear actuators

Figure 3. 4: Concept 2a – Linear Actuator

Figure 3. 5: Concept 2b – Linear Actuator

Concept 2 involves the use of faster and stronger liner actuators. Concept 2a is the same as the existing setup whereas, concept 2b utilizes linear actuators in opposite direction. Space being the biggest constraint, Concept 2a would be ideal as the battery pack would be placed in the center of the subframe.

3.2.2.3 Concept 3: Motor and gearbox direct to tie rod

Figure 3. 6: Concept 3 – motor and gearbox direct to tie rod

In this concept, a motor would be coupled to a gearbox and the torque from the motor would in turn drive the gearbox housing to which the tie rod is connected to. This would push or pull the tie rod and would result in the steering motion.

3.2.3 Camber actuation

As explained in the previous chapters, an angular speed of 50°/s is required in camber actuation. As in the case of steering, various options were considered, and the concepts were generated.

3.2.3.1 Concept 1: Push along inner upper A-arm

Figure 3. 7: Concept 1 – Push along inner upper A-arm

This concept is like the existing design, except the linear actuator is moved to the top to reduce the forces acting the actuator and to also reduce the length of actuation. This would also increase space in the subframe to accommodate the batteries.

3.2.3.2 Concept 2 – Motor-gearbox at the upper inner A-arm joint

Figure 3. 8: Concept 2: Motor-gearbox at the upper inner A-arm joint

In this concept, a motor connected to a gearbox would run a lead screw which would in turn change the angle of the upper inner A-arm. This idea requires a custom design of the gearbox based on the motors available in the market and is a complex design.

3.2.3.3 Concept 3 – Motor-gearbox to push upper inner A-arm

Figure 3. 9: Concept 3: Motor-gearbox to push upper inner A-arm

This concept is like concept 3 of steering actuation. The motor would make the gearbox housing rotate which would in turn push the linage against the upper inner A-arm and result in camber actuation.

3.3 Concept Evaluation

Based on the concepts generated, the concepts are evaluated and the best concept for each subsystem is chosen.

3.3.1 battery pack positioning

In concept 2, it is possible to accommodate 32 cells along the length of the car. It has a row of 2 cells at the subframe region and 3 cells at the body of the RCV. This would mean that there would be more space to accommodate the suspension, steering and camber actuation subsystems. Structural members can be added around the cells using the mounting holes already present in the baseplate to locate the cells in place. Thus, concept 2 is chosen.

3.3.2 Steering and camber subsystem

Unlike the previous case, a decision matrix will be used to decide the best concept for steering subsystem. The concepts will be graded based on various criteria such as ease of manufacture (off the shelf components), size, precision, mass, cost, etc. A 3-stage scaling (+1, 0, -1) is used rate the concepts in each criterion. The ratings are given based on the current design which is a zero in each criterion.

3.3.3.1 Steering subsystem

REQUIREMENTS CONCEPT 1 CONCEPT 2a Concept 2b CONCEPT 3 Responsiveness +1 0 0 +1 Ease of manufacture (off -1 +1 +1 - the shelf components Size 0 0 0 +1 Precision -1 0 0 0 Mass -1 0 0 -1 Cost -1 0 0 -1 Feasibility with battery -1 0 -1 -1 pack Durability 0 0 0 0 Total -4 +1 0 -1

Table 3. 2: Steering subsystem decision matrix

According to the above matrix, concept 2a is the best option. The main issue with the other two concepts was the introduction of the battery pack in the middle due to which there would not be enough space. Therefore, it will be the same layout as that of the current RCV, but with a more capable linear actuator.

3.3.3.2 Camber subsystem

REQUIREMENTS CONCEPT CONCEPT 2 CONCEPT 3 1 Responsiveness 0 0 0 Ease of manufacture (off the shelf 0 -1 -1 components) Size (space within subframe) +1 +1 0 Precision 0 0 0 Mass 0 0 0 Cost 0 -1 -1 Feasibility with battery pack +1 -1 -1 Durability 0 -1 -1 Total +2 -3 -4

Table 3. 3: camber subsystem decision matrix

According to the above matrix, concept 1 is the best option. This would mean that the linear actuator would be placed at the top of the subframe, parallel to the baseplate.

3.4 The new RCV

In this subchapter, the current performance of the RCV is analyzed and the changes that need to be made according to the decided concepts is presented.

3.4.1 Motor requirements

The requirement if for the car is to have a top speed of 90km/h and an acceleration equivalent to the force of gravity.

The calculation for the torque required and speed of the motor is calculated:

We have,

푉 = 90 푘푚/ℎ 푎 = 9.81 푚/푠2 푑 = 0.635 푚

푉 ∗ 1000 푉푠 = = 25 푚/푠 3600

퐹 = 푚 ∗ 푎 = 1962푁 푑 푇 = 퐹 ∗ ( ) = 623푁푚 2 푉푠 ∗ 60 푁 = = 752 푟푝푚 푑 2 ∗ 휋 ∗ (2)

Based on the calculations performed, the motor needs to have a torque of 623Nm and a rotational speed of 752rpm.

3.4.2 Steering subsystem

From the previous chapter, it was evaluated that the steering has an actuation speed of 24.5°/s. But, according to the requirements, an angular speed of 50°/s is required.

In the case of the new steering actuator, due to space constraints, concept 2a was chosen. To evaluate the forces in the steering subsystem and the torque required to actuate the steering, a new ADAMS/View model was built to replicate the quarter of the RCV.

Figure 3. 10: Steering model on Adams/View

The steering model consists of the tyre, control arms, road, tie rod, rocker and the subframe.

Figure 3. 11: Subframe setup in simulation

The mass acting on each wheel of 200kg is simulated as a singular force of dimension 1962N acting downward, at the center of the subframe. The subframe has all degrees of freedom restricted except vertical movement with the help of the combination of the orientation and inline primitive joints. The damper unit is attached to the subframe.

Figure 3. 12: Contact force illustration

The tyre has a point mass to represent the hub motor. A contact force is created between the tyre and the road and the tyre is made to fall on the road for a short distance to establish the contact. The contact force has the following specifications:

Figure 3. 13: Contact force specifications

After the tyre is in contact with the road, the rocker arm is given a rotational joint motion with the help of a step function feature while defining the motion.

Figure 3. 14: Rotational joint motion to rocker

A marker is placed at the tip of the tyre to obtain translational displacement of the marker before and after actuation.

Figure 3. 15: Position of the tyre after actuation

Figure 3. 16: Translational displacement of marker

The total translational displacement is 134mm. This results in a total angular displacement of the tyre to be 25°, shown in the below figure.

Figure 3. 17: Tyre displacement - steering

The green line represents the tyre axis from the center before actuation and the red line represents the tyre axis from the center after actuation.

The torque acting on the rocker arm is as follows:

Figure 3. 18: Torque on rocker arm

It has a peak torque of 59,500Nmm. Irregularities in the graph are due to the tread pattern on the tyre changing the contact force. Considering the dimensions of the rocker:

Figure 3. 19: Rocker dimensions

Based on the dimensions, force required by the actuator is:

푇 = 퐹 ∗ 푟

푇 퐹 = 푟

59500 퐹 = 61

퐹 = 975 푁

The required force is 975N from the actuator when the speed of actuation is 50°/s, when the vehicle is stationery.

However, if a lateral force equivalent to the gravitational force multiplied by mass on each wheel (200 (mass on each wheel) * 9.81 = 1942N) is considered, we get the following torque required.

Figure 3. 20: torque required – dynamic

The maximum torque required is 106670Nmm. Thus, the force needed for actuation is 1748N. The contact force established between the tyre and the road, all the joints and other forces are ideal cases and experimental validation of these values would be necessary to validate these values.

3.4.3 Camber subsystem

As discussed in the previous chapter, the speed of camber actuation is around 9.3°/s which is very less when compared to the 50°/s requirement.

To obtain the force required by the linear actuator used for the camber subsystem, an ADAMS/View model is made. Negative camber value of 15° is considered to generate this model.

Figure 3. 21: Camber model on ADAMS/View

The camber actuation model is very similar to the steering model with respect to the subframe, forces acting on the subframe, tyre-road contact and the damper unit. Please refer to the procedure from the previous subchapter of steering subsystem to see how the model is setup.

To evaluate the force required by the actuator, rotational joint motion is given to the upper inner A-arm at the connection between the subframe and the A-arm.

Figure 3. 22: Rotational joint motion – camber subsystem

A marker is placed on the end of the tyre to check translational displacement of the tyre.

Figure 3. 23: Camber model after actuation

Figure 3. 24: translational displacement of tyre

The tyre moves by 82mm in the y direction. This results in a total angular displacement of 15° as shown in the figure.

Figure 3. 25: Tyre displacement - camber

Figure 3. 26: torque required for camber actuation

The torque required at the upper inner control arm for 15° of camber actuation at 50°/s is 112950Nmm.

Considering the geometry of the upper inner A-arm,

Figure 3. 27: Upper inner A-arm

푇 = 퐹 ∗ 푟

푇 퐹 = 푟

112950 퐹 = 150

퐹 = 753 푁

The actuator requires to supply a force of 753N to obtain a camber angle of -15° at 50°/s speed, when the vehicle is stationery.

However, as this actuator must be used when the vehicle is moving, a lateral force equivalent to acceleration due to gravity multiplied by mass on each wheel (1942N) is added to evaluate the force required by the actuator.

Figure 3. 28: Camber actuation – dynamic

The maximum torque required increases to 327820Nmm. In this case, the force required from the actuator is 2185N. The contact force established between the tyre and the road, all the joints and other forces are ideal cases and experimental validation of these values would be necessary to validate these values.

3.4.4 Vehicle frame

One of the other requirements is to make the chassis more rigid to reduce the flex occurring during vehicle operation in the baseplate. The idea is to add cross members in between the subframes and connect these cross members to the subframe to increase the rigidity of the vehicle.

Figure 3. 29: Cross members in the frame

The above cross members were sketched keeping into consideration, the mounting holes already present in the baseplate, and the structural member command was used in SolidWorks to generate the pipes of dimension 33.7x4.0 mm. Rounded members were avoided as much as possible in order to ease the manufacturing process. Subframe was connected to the cross members to increase the strength of the frame.

Figure 3. 30: Structure for battery mounting

Additional structures were created to help mount the battery pack onto the frame. Based on this initial design, the subframes were also constructed on top of the cross members.

Figure 3. 31: Subframe structure

Figure 3. 32: Subframe structure - b

The mounting points for the upper and lower A-arms are identical to that on the previous design. Additional cross members were added on the subframe structure to further strengthen it.

Mounting holes to mount the structure onto the bedplate was added. The cells were placed in a 3mm thick sheet metal box (represented in red and yellow boxes) and fixed onto the structure. But, the position for the battery management system such as heating, cooling and regulation of the battery has not been decided.

Figure 3. 33: Battery pack positioning

Figure 3. 34: Battery mounting

Additional structures were created to help keep the battery pack in place. The tubes shown in the above figure is for representation purpose and the detailed design of the battery support structure is to be made.

3.4.5 Suspension system

The position of the damper unit had had to be moved to accommodate the battery pack within the subframe. This would mean changing the position of mounting of the damper unit, redesign of the hardpoints for the rocker and redesign of the pushrod. ADAMS/Car was used to relocate the hard points and to test the new position of the damper unit. The model was designed by first using the template builder mode and then analyzed on the standard interface by creating a suspension assembly.

Figure 3. 35: ADAMS/Car model of new suspension position

The damper unit is placed such that a cross member can be created to mount it onto the subframe. The rocker arm hard point position was decided based on keeping the spring displacement the same as the previous design. The spring and damper characteristics were input into the model. The hardpoint positions are as follows:

Figure 3. 36: hard point locations

The hard point locations are in respect to the origin, which is the center of the vehicle, on the surface of the ground. A simple parallel wheel travel simulation was conducted to verify the model and to check the spring displacement.

Figure 3. 37: Spring displacement

With this parallel wheel travel simulation, the total spring displacement was found to be 58mm. The value is similar to the existing suspension subsystem present in the RCV.

4. RESULTS

In the results chapter the results that are obtained with the process/methods described in the previous chapter are compiled and analyzed and compared with the existing knowledge and/or theory presented in the frame of reference chapter. 4.1 Steering subsystem In the previous chapter, calculations were made to determine the force required by the actuator of the steering subsystem to achieve 50°/s of angular speed and 25° of rotation of the wheel. In this chapter, the requirements of the actuator are determined. To test the stroke of the actuator required, the geometry is added onto the ADAMS/View model. Since the concept is the same as the existing design, the required stroke length would be the same.

Figure 4. 1: New steering model

Figure 4. 2: Required linear actuation It requires 31mm of linear actuation for 25° of steering rotation in 0.5s, so if we consider the steering to be actuated both outward and inward, we will need a total stroke of 62mm and linear actuation speed of around 62mm/s. The requirements of the new linear actuator for the steering subsystem would be as follows:

Specifications Value Required stroke length (mm) 62 Maximum static load (N) 975 Maximum dynamic load (N) 1748 Maximum load speed(mm/s) 62 Table 4. 1: Steering actuator requirements

4.2 Camber subsystem In the previous chapter, calculations were made to determine the maximum static and dynamic force required by the new camber actuator to achieve -15° of camber angle with a speed of 50°/s. In this chapter, the requirements of the new actuator are determined.

To check the stroke of actuation required, a simple piston cylinder geometry is created in ADAMS/View.

Figure 4. 3: Stroke length of the actuator The new linear actuator would need around 52mm of stroke to achieve -15° of camber and the speed of actuation would be 130mm/s.

Figure 4. 4: Positive camber actuation

Now, considering +10° of camber actuation, the required stroke decreases to 34mm. So, the total stroke of linear actuation required is 86mm. The requirements of the new camber actuator are as follows:

Specifications Value Required stroke length (mm) 86 Maximum static load (N) 753 Maximum dynamic load (N) 2185 Maximum load speed(mm/s) 130 Table 4. 2: Camber actuator requirements

4.3 Frame After constructing the frame in SolidWorks, it had to be tested against the force that would act on it. Considering the worst-case scenario, the maximum force acting on each wheel would be a force equivalent to the gravitational force in the longitudinal direction while braking and lateral lateral direction while cornering. Both these forces were added to the upright on ADAMS/View and the translated forces on the A-arm joints were noted.

Figure 4. 5: Model to test forces in joints

Bushings were created where the A-arms would connect to the subframe and very high stiffness and damping values were given.

Figure 4. 6: Longitudinal and lateral force on upright A longitudinal and lateral force was added to the center of the upright. The forces obtained in the lower A-arm joint is as follows.

Figure 4. 7: Force in lower A-arm – x direction

Figure 4. 8: Force in lower A-arm – y direction

Figure 4. 9: Force in lower A-arm – z direction Similarly, there were forces obtained on each A-arm joint from the simulation. These forces were input into ANSYS to test the deformation in the frame. Baseplate is not included in this analysis. Adding the forces to the point of mounting of the A-arms onto the frame:

Figure 4. 10: Total deformation in frame

Figure 4. 11: Directional deformation x-axis

Figure 4. 12Directional deformation y-axis

Figure 4. 13: Directional deformation z-axis

The maximum total deformation is in the order of 0.19053mm. The maximum directional deformation in the x-axis is 0.00475mm, in the y-axis is 0.17191mm and in the z-axis is 0.0045mm.

5. DISCUSSION AND CONCLUSION

A discussion of the results and the conclusions that the authors have drawn during the Master of Science thesis are presented in this chapter. The conclusions are based on the analysis with the intention to answer the formulation of questions that is presented in Chapter 1. 5.1 Discussion The main aim of this thesis was to improve the overall performance of the RCV. A thesis is complete when the answers to the research questions are presented. The following are the answers to the research questions: 1. What are the requirements of the motor required to achieve better performance? As per the requirement specifications, the new RCV would have to achieve an acceleration figure of 9.8m/s2 and a top speed of 90km/h. Based on these requirement figures, simple calculations were made to obtain the requirements of the new hub motor. 2. How to incorporate a battery pack of higher voltage to improve the performance of the vehicle? If the motor is to be upgraded, the power source for the motor must be upgraded as well. The current battery pack being a 52V system would not have been sufficient to power the new set of hub motors. Thus, the battery system would have to be upgraded as well. Another issue is the current battery pack is located on top of the subframe. To accommodate a higher capacity 100V system and, to lower the center of gravity, concept 2 was chosen to achieve more uniform weight distribution and, to lower the center of gravity of the RCV. 3. What are the requirements to improve the performance of the steering subsystem? According to the ADAMS/View model built based on the current steering, the current speed of steering actuation is 24.5°/s. To achieve of 50°/s of speed of actuation, the requirements of the new linear actuator to be used is proposed in this thesis. 4. What are the requirements to improve the performance of the active camber actuation subsystem? According to the ADAMS/View model built based on the current steering, the current speed of camber actuation is 9°/s. To achieve of 50°/s of speed of actuation, the requirements of the new linear actuator to be used is proposed in this thesis. 5. What are the methods to reduce the flex in the bottom plate during the operation of the RCV? To reduce the flex in the base plate, the frame of the RCV was modified by introducing cross members to stiffen the structure. The subframe is connected to the frame to further improve the stiffness. Due to lack of time, the analysis of the reduction in flex in the base plate was not achievable.

5.2 Conclusion

5.2.1 Simulation on ADAMS/View Majority of this thesis was performed on ADAMS, ADAMS/View, in particular. This was achieved by importing the required geometry for simulation from CAD software in parasolid format onto the ADAMS software. There are certain in-built material properties present within the software. However, new materials can be defined manually. Material of the road and tyre were

53 defined manually in the models present the previous chapters. Although, the software takes some time to figure out, it is quite a useful tool once it if familiarized.

5.2.2 The different subsystems As discussed in the previous chapters, the car was divided into various subsystems and the performance of each subsystem was analyzed, concepts were generated to improve the performance and solutions were suggested as to how the performance of the vehicle would be improved by improving each subsystem. Although, it would have been complete if detailed design of each subsystem were performed, alas it was not possible as time was the biggest issue.

5.2.2.1 Steering subsystem The current steering subsystem supplies enough force for static operation, but not for dynamic actuation. The new steering concept generated is the same concept as the current steering mechanism, but with a more powerful linear actuator. The next steps would be to choose the actuator available in the market based on the forces obtained in chapter 4. This would help reach the steering actuation speed of 50°/s.

5.2.2.2 Camber subsystem The current camber actuation is quite slow in actuation when compared to the requirement of 50°/s. Also, to accommodate the battery pack, the linear actuator would have to be relocated. Based on the concepts generated, a solution was proposed with the requirements of linear actuator based on the concept and requirement.

5.2.2.3 Battery pack One of the biggest changes on the RCV was to change the current 52V battery pack to a 100V battery pack. In the current design, there was no specific position assigned to the battery pack. This led to the battery pack being mounted on the subframe. This would lead to higher center of gravity, lack of space to increase the capacity and would not be aesthetically pleasing. The proposed changes would locate the battery pack on the baseplate, along the length of the car. This would help lower the center of gravity of the RCV and 100V system could be accommodated as well.

5.2.2.4 Frame One of the requirements was to reduce the flex in the bottom plate. The concept generated was to add cross members in the middle of the baseplate and to connect these members to the subframe of the vehicle. This would help reduce the flex in the baseplate but would also increase the weight of the vehicle. The structure can be further optimized by adding and reducing the number of cross members to further improve the stiffness and lower the weight of the frame as well.

6. FUTURE WORK In this chapter, recommendations on more detailed solutions and/or future work in this field are presented.

Based on the work done during this master thesis, various things can be done towards the goal of achieving a better performance of RCV.

1. The requirements for a new actuator for both steering and camber actuation is defined in this thesis. The first step would be to choose the best suitable linear actuator for both these subsystems to best match the requirements. 2. Based on the hard points generated, a detailed design of various components such as the mounting points for the linear actuators on the subframe, rocker for steering, rocker for suspension, mounting for the suspension, etc. 3. Analysis of each component based on the detailed design performed. 4. Further optimizing the position of the hardpoints to obtain the best performance in the vehicle. 5. Changing the suspension geometry to account for the change in mass of the car to find the most ideal position of roll center. 6. Full vehicle simulation on ADAMS/Car to validate the changes in design and compare as to how it is better with the existing design.

7. REFERENCES

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[11] Come and drive it, “Camber angle”, URL: https://www.comeanddriveit.com/suspension/camber-caster-toe

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[13] Progressive Automations, Inside an electric linear actuator, URL: https://www.progressiveautomations.com/blogs/products/inside-an-electric-linear-actuator

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[15] Heinzmann PRA-230, heinzmann motors, URL: https://www.heinzmann-electric-motors.com/en/component/jdownloads/send/33-allgemein/137- product-catalogue-electric-drives?Itemid=303

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APPENDIX A: GANTT CHART

APPENDIX B: RISK REGISTER

Risk Impact Planned Probability Consequence Action Requirements Objectives of Invest more time Medium High are not met the thesis not and analyse if the met deliverables are feasible Insufficient Incomplete Extend time or Medium Medium time to thesis reiterate the complete deliverables objectives Chosen concept Solution not Generate multiple Low Low not feasible possible concepts Solution Delay in thesis Choose an Low Medium developed fails completion alternative concept in analysis stage Thesis not Delay in thesis Rectify the issue Low High approved completion present