N. D. Vaughan

Dynamic Behaviour of a High Speed Direct Injection Diesel Engine

Many Diesel engine development programs concentrate almost exclusively on steady state investigations to benchmark an engines performance. In reality, the inter-action of an engines sub-systems under transient evaluation is very different from that evident during steady state evaluation. The transient operation of a complete engine system is complex, and collecting test data is very demanding, requiring sophisticated facilities for both control and measurement. This paper highlights the essential characteristics of a Diesel engine when undertaking testbed transient manouevres. Results from simple transient sequences typical of on-road operation are presented. The tests demonstrate how transient behaviour of the engine deviates greatly from the steady state optimum settings used to control the engine. The operation of the EGR system and its interaction with other sub-systems, in particular VGT, has a significant effect on emissions, fuel consumption and driveability, highlighting the need for dynamic optimisation as an integrated system.

Integrated Cooling Systems for Passenger Vehicles

Electric coolant pumps for IC engines are under development by a number of suppliers. They offer packaging and flexibility benefits to vehicle manufacturers. Their full potential will not be realised, however, unless an integrated approach is taken to the entire cooling system. The paper describes such a system comprising an advanced electric pump with the necessary flow controls and a supervisory strategy running on an automotive microprocessor. The hardware and control strategy are described together with the simulation developed to allow its calibration and validation before fitting in a B/C class European passenger car. Simulation results are presented which show the system to be controllable and responsive to deliver optimum fuel consumption, emissions and driver comfort.

Modelling of loss mechanisms in a pushing metal V-belt continuously variable transmission. Part 1: Torque losses due to band friction

Abstract The power transmission efficiency of continuously variable transmissions (CVTs) based on the pushing metal belt is acknowledged to be lower than that of discrete ratio alternatives. This tends to negate the potential fuel economy benefits that are obtained by improved engine/load matching with a CVT. This series of three papers details an investigation into the loss mechanisms that occur within the belt drive as a first step to obtaining improvements in efficiency. Experimental work has been undertaken to investigate the no-load and low-load torque losses associated with a pushing metal V-belt CVT. This first paper describes a new analysis of the principal torque losses occurring in the metal belt CVT due to relative motion occurring between the belt segments and bands. The work takes into account new findings in other research and changes in the design of the metal V-belt. The torque loss model proposed in this paper is supported by experimental data from several different test procedures. A number of additional torque loss mechanisms, due to pulley deflections, are described in Part 2 of the series. The findings from this current paper support an analysis of belt-slip losses, which is described in detail in Part 3.

Modelling of loss mechanisms in a pushing metal V-belt continuously variable transmission: Part 2: Pulley deflection losses and total torque loss validation:

Abstract The power transmission efficiency of continuously variable transmissions (CVTs) based on the pushing metal belt is acknowledged to be lower than that of discrete ratio alternatives. This tends to negate the potential fuel economy benefits that are obtained by improved engine/load matching with a CVT. This series of three papers details an investigation into the loss mechanisms that occur within the belt drive as a first step to obtaining improvements in efficiency. This second part follows on from an initial paper in which an analysis was performed of the losses that occur due to relative motion between the bands and segments of the belt. Additional experimental work has been performed indicating that a significant deflection occurs in the pulleys of the variator. Further torque-loss models are proposed in addition to that discussed in Part 1, representing a smaller but still significant torque loss associated with the belt. The work takes into account new findings in other research and changes in the design of the metal V-belt. The third paper in this series develops a number of models to predict belt-slip losses in the variator system, based on force distribution models developed in Part 1.

Modelling of loss mechanisms in a pushing metal V-belt continuously variable transmission. Part 3: belt slip losses

Abstract The power transmission efficiency of continuously variable transmissions (CVTs) based on the pushing metal belt is acknowledged to be lower than that of discrete ratio alternatives. This tends to negate the potential fuel economy benefits that are obtained by improved engine/load matching with a CVT. This series of three papers details an investigation into the loss mechanisms that occur within the belt drive as a first step to obtaining improvements in efficiency. This third paper follows on from two previous papers in which an analysis was performed modelling the torque losses that occur due to relative motion between the bands and segments of the belt, and between the pulleys and the belt due to pulley deflection effects. It describes additional experimental work, measuring the belt-slip speed tangentially about both of the pulleys in the variator. Additional loss models are proposed beyond those discussed in Parts 1 and 2 to describe the belt-slip phenomena, based on existing theory proposed by others. The analysis produced in this paper is validated against a range of experimental data and additionally through its close interaction with the torque-loss and torque-force distribution models proposed in Parts 1 and 2. The work takes into account new findings in other research and changes in the design of the current metal V-belt.

Transient Investigation of Two Variable Geometry Turbochargers for Passenger Vehicle Diesel Engines

ABSTRACT The use of variable geometry turbocharging (VGT) as anaid to performance enhancement has been the subject ofmuch interest for use in high-speed, light-duty automotivediesel applications in recent times (4). One of the keybenefits anticipated is the improved transient responsepossible with such a device over the conventional fixedgeometry turbine with wastegate. The transient responses of two different types of variablegeometry turbocharger have been investigated on adynamic engine test bed. To demonstrate the effect of theturbocharger on the entire system a series of stepchanges in engine load at constant engine speed werecarried out with the turbocharger and exhaust gas recir-culation (EGR) systems under the control of the enginemanagement microprocessor.Results are presented which compare the different per-formance and emissions characteristics of the devices.Some control issues are discussed with a view to improv-ing the transient response of both types. Of particularimportance is the interaction between the turbochargersystem and the EGR system.

IMPACT OF ALTERNATIVE CONTROLLER STRATEGIES ON EXHAUST EMISSIONS FROM AN INTEGRATED DIESEL/CONTINUOUSLY VARIABLE TRANSMISSION POWERTRAIN

Abstract The use of an integrated powertrain including a continuously variable transmission (CVT) offers great scope for improvements in fuel consumption and emissions, although this must be achieved without adversely affecting vehicle drivability. These conflicting aims can best be resolved by the use of novel control strategies designed from the outset with these considerations in mind. Two alternative approaches to the task are presented here. These made use of artificial intelligence and more traditional and intuitive methods to allow the maximum flexibility in operation. Both strategies incorporated a novel optimization routine described in a companion paper to locate the best operating point for the engine. The two strategies were implemented for an integrated diesel CVT powertrain and compared with an existing controller and the equivalent manual transmission powertrain. Chassis dynamometer results show the newly designed controller strategies to have significant impact on vehicle exhaust emissions, while the structure of the software allows the controller action to be highly tuneable and fexible in order to balance the vehicle drivability requirements with economy and emissions targets.

Investigation of ‘Sweep’ Mapping Approach on Engine Testbed

Steady state mapping is fundamental to optimizing IC engine operation. Engine variables are set, a predefined settling time elapses, and then engine data are logged. This is an accurate but time consuming approach to engine testing. In contrast the sweep method seeks to speed up data capture by continuously moving the engine through its operating envelope without dwelling. This is facilitated by the enhanced capability of modern test rig control systems. The purpose of this work is to compare the accuracy and repeatability of the sweep approach under experimental conditions, with that of steady state testing. Limiting factors for the accuracy of the sweep approach fall into two categories. Firstly on the instrumentation side - transducers have a characteristic settling time. Secondly on the engine side - thermal and mechanical inertias will mean that instantaneous measurements of engine parameters differ from the steady state values. These errors can be reduced to satisfactory levels by modelling the engine and instrumentation responses. Some data i.e. air, fuel and emissions pose significant problems, with the response time of the equipment limiting the maximum sweep speed. Despite requiring intensive data processing and test bed sophistication, sweep mapping shows the potential to give accuracy comparable to steady state testing, but with much reduced mapping times.

Application of Alternative EGR and VGT Strategies to a Diesel Engine

This paper describes the results of an investigation into alternative control strategies for diesel engines equipped with Exhaust Gas Recirculation (EGR) and Variable Geometry Turbocharging (VGT). The objectives of the research were to improve the engine aircharge performance during transient maneuvers, thus bringing benefits for fuel economy, exhaust emissions and engine transient performance. Two of the investigated areas are detailed in this paper: The coordinated control of the EGR-VGT systems to improve transient airflow at low-speed, low-load operation; Transient VGT control using exhaust pressure feedback. A simple and effective method for coordinating the EGR-VGT system is demonstrated to improve airflow response to tip-ins and tip-outs. The exhaust pressure feedback method is shown to overcome difficulties in the transient control of VGT systems, offering improved engine torque response and reduced transient backpressure.

Performance Investigations of a Novel Rolling Traction CVT

The Milner CVT is a patented rolling traction transmission offering advantages of high power density and simplicity of construction and operation. A 90 mm diameter prototype variator is described which was sized for a maximum rated input power of 12 kW. Experimental data are presented demonstrating high efficiency and low shift forces. Resistance to overload torque is shown to be exceptional and preliminary durability trials indicate a highly viable concept for series production.