A M C Odhams

Predictive and linear quadratic methods for potential application to modelling driver steering control

A brief review of the literature reveals that both predictive control theory and linear quadratic (LQ) control theory have been used to design path-following controllers with preview, but it is not clear how the controllers compare. This article derives optimal linear preview controllers using the two approaches starting from a common state-space description of the vehicle dynamics. The transformation of the controllers from ground-fixed axes to vehicle-fixed axes is discussed. The influences of preview horizon, control horizon and cost function are investigated. For the case of long preview and long control horizons, it is found that the predictive and LQ approaches give identical controllers. The results in this article provide a basis for identifying human steering behaviour from measured data.

Active Steering of a Tractor-semi-Trailer

This paper develops a path-following steering control strategy for an articulated heavy goods vehicle. The controller steers the axles of the semi-trailer so that its rear end follows the path of the fifth wheel coupling: for all paths and all speeds. This substantially improves low-speed manoeuvrability, off-tracking, and tyre scrubbing (wear). It also increases high-speed stability, reduces ‘rearward amplification’, and reduces the propensity to roll over in high-speed transient manoeuvres. The design of a novel experimental heavy goods vehicle with three independent hydraulically actuated steering axles is presented. The path-following controller is tested on the experimental vehicle, at low and high speeds. The field test results are compared with vehicle simulations and found to agree well. The benefits of this steering control approach are quantified. In a low-speed ‘roundabout’ manoeuvre, low-speed off-tracking was reduced by 73 per cent, from 4.25 m for a conventional vehicle to 1.15 m for the experimental vehicle; swept-path width was reduced by 2 m (28 per cent); peak scrubbing tyre forces were reduced by 83 per cent; and entry tail-swing was eliminated. In an 80 km/h lane-change manoeuvre, peak path error for the experimental vehicle was 33 per cent less than for the conventional vehicle, and rearward amplification of the trailer was 35 per cent less. Increasing the bandwidth of the steering actuators improved the high-speed dynamic performance of the vehicle, but at the expense of increased oil flow.

Factors influencing the energy consumption of road freight transport

Abstract Key factors that influence the energy consumption of heavy goods vehicles are investigated. These factors include engine efficiency, aerodynamic drag and rolling resistance, vehicle configuration (number of vehicle units), traffic congestion, speed, payload factors, and the use of regenerative braking. An accurate, validated model of the fuel consumption of a 38 tonne tractor-semitrailer vehicle is used as a basis to derive fuel consumption models of a number of other vehicle configurations. These models included a rigid four-axle truck with maximum gross vehicle mass (GVM) of 26 tonnes; a six-axle tractor semitrailer with GVM of 44 tonnes, with and without regenerative braking; a ‘B-double’ with GVM of 60 tonnes; and an ‘A-double’ with GVM of 82 tonnes. These vehicle models were driven over a simple hypothetical drive cycle with a fixed maximum speed and varying numbers of stops in a 10 km stretch of road. It is concluded that: (a) improving engine efficiency, unladen mass, rolling resistance, and aerodynamic drag can yield relatively small improvements in fuel consumption, compared with other factors; (b) larger vehicles are always significantly more energy-efficient than smaller ones when fully loaded; (c) transferring freight from articulated vehicles to smaller rigid vehicles for urban deliveries typically increases fuel consumption by approximately 35 per cent; (d) running vehicles partially loaded can increase the energy per unit freight task by up to 65 per cent; and (e) under urban start—stop conditions, the use of regenerative braking systems can reduce heavy vehicle fuel consumption by 25–35 per cent.

Application of linear preview control to modelling human steering control

Abstract A well-known linear optimal preview controller has been investigated for potential application to modelling human steering control. The controller was modified to account for some characteristics of human control: limited understanding of the system being controlled, time delay in the control action, and a neuromuscular system with a finite bandwidth. The standard and modified controllers were compared in terms of their state and preview gains, and also in terms of their response during a lane-change manoeuvre. A technique for dealing with target paths that turn through more than 90° within the preview distance is introduced that overcomes a limitation of previous time domain implementations of linear optimal preview steering control. The results suggest some conditions necessary to identify models of human steering control. Identification of human time delay is likely to require non-previewed disturbances to the system. Identification of a drivers limited understanding of vehicle dynamics is likely to require the controlled vehicle to have non-simple dynamics. Work to identify the steering control models described in this paper from driving simulator experiments has been completed and will be reported in a later paper.

High-speed optimal steering of a tractor-semitrailer

A high-speed optimal trailer steering controller for a tractor–semitrailer is discussed. A linear model of a tractor–semitrailer with steered trailer axles is described, and an optimal trailer steering controller is introduced. A path-following controller is derived to minimise the path-tracking error in steady-state manoeuvres using active trailer steering. A roll stability controller is introduced by adding the lateral acceleration of trailer centre of gravity as another objective in the steering controller, so as to improve roll stability in transient manoeuvres. A strategy to switch between these two control modes is demonstrated. Simulation results show that the steering controller can ensure good path tracking of articulated vehicles in steady-state manoeuvres and improve roll stability significantly in transient manoeuvres, while maintaining the path-tracking deviation within an acceptable range. Tests with an experimental tractor–semitrailer equipped with a high-bandwidth active steering system validate the controller design and simulation results. The roll stability controller reduces the measured rearward amplification by 27%.

Parameter measurement for heavy-vehicle fuel consumption modelling

A mathematical model is developed to predict the energy consumption of a heavy vehicle. It includes the important factors of heavy-vehicle energy consumption, namely engine and drivetrain performances, losses due to accessories, aerodynamic drag, rolling resistance, road gradients, and driver behaviour. Novel low-cost testing methods were developed to determine engine and drivetrain characteristics. A simple drive cycle was used to validate the model. The model is able to predict the fuel use for a 37 t tractor–semitrailer vehicle over a 4 km drive cycle within 1 per cent. This paper demonstrates that accurate and reliable vehicle benchmarking and model parameter measurement can be achieved without expensive equipment overheads, e.g. engine and chassis dynamometers.

Dynamic safety of active trailer steering systems

The dynamic safety of an active steering system for an articulated heavy goods vehicle is investigated. The vehicle is a tractor semi-trailer with two independently steerable axles on the trailer. Several different vehicle dynamics modelling approaches are used to investigate the aspects of the safety of the steering system. These include ‘back of envelope’ calculations, a single degree-of-freedom yaw model, a simplified yaw-plane model using Matlab SimMechanics, with realistic controller frequency response assumptions, and a complex multi-body model of the whole vehicle using TruckSim. Specific safety issues of concern associated with the primary active steering function are: (a) the necessary actuation bandwidth for stable response at high speeds, and (b) the performance implications of disturbance rejection requirements, e.g. side winds and split friction braking. It is found that vehicle tracking improves with increased bandwidth up to 8.3 Hz, but beyond this, performance is limited by other factors. Also, the steering system is able to reject off-tracking disturbances from side winds and split-friction braking, although the latter has a small effect. Additional ‘failsafe’ issues of concern are: (a) whether an independent centring system is necessary on each steerable axle or whether failure of an axle can be safely managed by steering the remaining axles in opposition, (b) the force levels needed in the automatic safety centring system, and (c) the maximum slew rate for centring the axles in an emergency. It is found that individual centring systems for each axle are necessary because axle ‘opposition’ is not a safe strategy for a trailer with two steered axles. The steering actuator is required to generate 32 kN during all modes of operation in order to maintain safety during the specified manoeuvre. A maximum steering slew rate of 11°/s is found to limit additional lateral acceleration to less than 0.2 g.

An Analysis of Ride Coupling in Automobile Suspensions

Abstract The tuning of a pitch-plane model of a passenger car with a ‘coupled’ suspension system was investigated and compared to that of a conventional suspension system. Direct comparison of stiffness matrices for the two models was used as well as modal analysis and frequency domain analysis, to gain insight into the optimal pitch-bounce tuning. Performance was measured in terms of body acceleration, dynamic tyre force, and suspension working space. Optimum tuning of the coupled system was found to be at lower pitch stiffness, but greater pitch damping than that of a popular saloon car. Uncorrelated inputs to the model were found to give tuning suitable for a realistic range of road speeds from 5 to 25 m/s. The Olley suspension tuning criterion was found to represent an optimal conventional suspension stiffness tuning for dynamic tyre force minimization, but not for driver chest acceleration minimization.

Implementation of active steering on longer combination vehicles for enhanced lateral performance

A steering-based controller for improving lateral performance of longer combination vehicles (LCVs) is proposed. The controller steers the axles of the towed units to regulate the time span between the driver steering and generation of tyre lateral forces at the towed units and consequently reduces the yaw rate rearward amplification (RWA) and offtracking. The open-loop effectiveness of the controller is evaluated with simulations and its closed loop or driver in the loop effectiveness is verified on a test track with a truck–dolly–semitrailer test vehicle in a series of single- and double-lane change manoeuvres. The developed controller reduces the yaw rate RWA and offtracking considerably without diminishing the manoeuvrability. Furthermore, as a byproduct, it decreases the lateral acceleration RWA moderately. The obtained safety improvements by the proposed controller can promote the use of LCVs in traffic which will result in the reduction of congestion problem as well as environmental and economic benefits.

Implementation of Trailer Steering Control on a Multi-Unit Vehicle at High Speeds

A high-speed path-following controller for long combination vehicles (LCVs) was designed and implemented on a test vehicle consisting of a rigid truck towing a dolly and a semitrailer. The vehicle was driven through a 3.5 m wide lane change maneuver at 80 km/h. The axles of the dolly and trailer were steered actively by electrically-controlled hydraulic actuators. Substantial performance benefits were recorded compared with the unsteered vehicle. For the best controller weightings, performance improvements relative to unsteered case were: lateral tracking error 75% reduction, rearward amplification (RA) of lateral acceleration 18% reduction, and RA of yaw rate 37% reduction. This represents a substantial improvement in stability margins. The system was found to work well in conjunction with the braking-based stability control system of the towing vehicle with no negative interaction effects being observed. In all cases, the stability control system and the steering system improved the yaw stability of the combination.