FABV and Controllability impact of Autonomous Systems Introduction and future application Jim Crawley Haldex Brake Products Ltd. 1
Presentation Content Contents Introduction to the Fast Acting brake valve Conventional system theory FABV Principle System performance and results FABV and integration into future vehicle systems FABV and Autonomous Systems 2
Current Situation Current Conventional Pneumatic ABS Theory Provide short stopping distances Maintain Vehicle stability and steer ability Cycling pressure to avoid wheel lock Free wheeling Conventional ABS Speed [m/s] Brake Pressure Reduced Here Free-wheeling Wheel speed (solid) Vehicle speed (dashed) Time [s] (Henderson et al, 2016) 3
Conventional ABS slip Curve Theory Definition Slip ratio = [Vehicle speed Wheel speed]/vehicle speed x 100% When slip ratio is 0%, the vehicle speed corresponds exactly to the wheel speed. When it is 100%, the wheels are completely locked [rotating at a zero speed] while the vehicle is moving. Coefficient of friction between tire and road surface Normalised force (unitless) min F x max F x ABS Longitudinal tyre force, F x Range of F x (Henderson et al, 2016) Longitudinal slip, λ (unitless) Slip Ratio Provide short stopping distances Maintain Vehicle stability and steer ability Optimum braking occurs at between 10-20% If the wheel speed and vehicle speed are the same wheel slip -0% A locked wheel will have a wheel slippage of 100% 4
Conventional ABS slip Curve Theory Definition Slip ratio = [Vehicle speed Wheel speed]/vehicle speed x 100% When slip ratio is 0%, the vehicle speed corresponds exactly to the wheel speed. When it is 100%, the wheels are completely locked [rotating at a zero speed] while the vehicle is moving. Coefficient of friction between tire and road surface Normalised force (unitless) max F y ABS Longitudinal tyre force, F x Lateral tyre force, F y min F y Longitudinal slip, λ (unitless) Slip Ratio Range of F y Range of F x (Henderson et al, 2016) Provide short stopping distances Maintain Vehicle stability and steer ability Optimum braking occurs at between 10-20% If the wheel speed and vehicle speed are the same wheel slip -0% A locked wheel will have a wheel slippage of 100% 5
Conventional ABS slip Curve Theory Definition Slip ratio = [Vehicle speed Wheel speed]/vehicle speed x 100% When slip ratio is 0%, the vehicle speed corresponds exactly to the wheel speed. When it is 100%, the wheels are completely locked [rotating at a zero speed] while the vehicle is moving. Coefficient of friction between tire and road surface Normalised force (unitless) λ dem Slip control Longitudinal tyre force, F x Lateral tyre force, F y Range of F x Range of F y (Henderson et al, 2016) Longitudinal slip, λ (unitless) Slip Ratio Providing Slip control provides optimum use of friction coefficients Minimising stopping distances whilst maintaining stability 6
Slip control Comparison Comparison Theory Slip control allows optimum use of the slip corridor Maximum utilisation of adhesion Shorter stopping distances Speed [m/s] Conventional ABS Slip Control Wheel speed (solid) Vehicle speed (dashed) Main requirements for slip control implementation High-bandwidth control of brake chamber pressure required Known parameters 1. Vehicle speed 2. Adhesion force at the wheel 3. Approximate slip curve peak Time [s] (Henderson et al, 2016) 7
Fast Acting Brake Valve Principle Joint development between Haldex, Cambridge and Chalmers Direct acting reduces the pneumatic delays in conventional valves High speed valve can change state very quickly High flow sufficient for a single brake chamber A conventional ABS valve operates much slower 8
Fast Acting Brake Valve Technology System Performance Eliminates system time delays Fast Response than conventional Systems Shorter stopping distances Lower air consumption Conventional Trailer ABS/EBS Valves Prototype Valves Gen 2 (Henderson, 2013) 9
2015 Test Vehicle System trial Prototype System 1 Test Installation with prototype system Prototype System Performance Slip controller electronics Test carried on wet basalt tile at MIRA, UK Laden bobtail FABV 10 Valve block Tractor-semitrailer (BBC) (Henderson et al, 2016)
Results from 2015 System Trial System Results System testing performed by CVDC at MIRA Combination system tested on Wet Basalt Improvements in Air usage and stopping distances Total combination weight: 31 tonne Surface: Wet basalt tile, MIRA, UK Tractor Steer Axle Tractor Drive Axle Trailer axles Axle load (static) 6.1 tonne 9.8 tonne 5.1 tonne Coefficient of adhesion 0.106 0.106 0.117* 11
2015 Test Vehicle System trial Prototype System 1 12 Tractor-semitrailer (BBC) (Henderson et al, 2016)
Future System Integration Integration into Vehicle Motion Management (VMM) systems The FABV with its improved controllability of individual brake torques is an enabling technology for advanced full vehicle control systems Motion devices controlled (using Control Allocation theory) by a single Vehicle Motion Management controller. As described in Laine, 2007 VMM communicates directly with all devices All devices broadcast capability to the VMM, VMM uses live information in optimised control allocation calculations The VMM transmits individual requests to each actuator Conventional EBS have a central global braking controller. Allowing the VMM to communicate and directly control brake torque reduces communication delays. 13 (Henderson et al, 2016)
Future heavy vehicle braking Levels of automation for on-road vehicles defined by SAE J3016 (SAE, 2014) 14
Future heavy vehicle braking Levels of automation for on-road vehicles defined by SAE J3016 Level 4 to 5 High to Full Automation (SAE, 2014) SAE levels 4 and 5 the vehicle control system can no longer rely on a human driver to intervene in the event of a system fault. Conventional EBS with pneumatic back up unsuitable for fully autonomous driving due to human intervention A vehicle control system with dual, independent electrical power sources (batteries) and communication networks required for level 4/5. 15
Future heavy vehicle braking Levels of automation for on-road vehicles defined by SAE J3016 Level 5 Full Automation (SAE, 2014) Level 5 - full-time performance by an automated driving system of all aspects of the dynamic driving task under all roadway and environmental conditions that can be managed by a human driver This cannot be realized without live, accurate knowledge of the tyre-road characteristics, in all driving modes. FABV can enable this 16
Conclusions Summary FABV provides improved controllability of wheel torques and longitudinal slip Stopping distance reduction achieved on prototype system FABV constant Monitoring of tyre and road conditions is an enabler for future full vehicle motion management systems Reduction in communication delays Improved controllability FABV System enables compliance to SAE standard for Fully automated Vehicle control systems by supporting:- The automated driving system must perform a dynamic driving task under all road and environmental conditions. The automated driving system must perform all-aspects of a dynamic driving task even if a human driver does not respond appropriately 17
References Henderson, L., Cebon, D., & Laine, L. (2016). Brake system design for future heavy goods vehicles. The 14th International Symposium on Heavy Vehicle Transport Technology. Rotorua, New Zealand. Henderson, L. (2013). Improving emergency braking performance of heavy goods vehicles (PhD thesis), Cambridge University Engineering Department. Laine, L. (2007). Reconfigurable Motion Control Systems for Over- Actuated Road Vehicles (Ph.D. Thesis). Chalmers University of Technology. Society of Automotive Engineers (SAE). (2014). J1306: Taxonomy and Definitions for Terms Related to On-Road Motor Vehicle Automated Driving Systems. 18
Contact Details Jim Crawley MSOE, MIRTE Homologation Engineer Mobile: +44 7780958452 Direct: +44 2476 400334 E-mail: jim.crawley@haldex.com http://www.haldex.com Haldex Brake Products Ltd MIRA Technology Park Lindley Warwickshire CV13 6DE United Kingdom 19