Thomas A. Keim

Design and experimental implementation of an electromagnetic engine valve drive

In conventional internal combustion engines, engine valve displacements are fixed relative to crankshaft position. If these valves were actuated as a variable function of crankshaft angle, significant improvements in fuel economy could be achieved. To this end, a new type of electromagnetic valve drive system (EMVD) for internal combustion engines was more recently proposed. This EMVD incorporates a disk cam with a very desirable nonlinear profile which that functions as a nonlinear mechanical transformer. Modeling and simulation results showed significant advantages of this EMVD over previously designed electromagnetic engine valve drives. In this articles, we describe an experimental implementation of the proposed EMVD, which was developed to confirm these benefits. The EMVD apparatus was designed, constructed, and integrated into a computer-controlled experimental test stand. The experimental results confirm the benefits of using a nonlinear mechanical transformer in a motordriven engine-valve spring system, as seen in the small average power consumption and low valve seating velocity. In addition, a valve transition time sufficient for 6000-rpm engine operation was achieved. The results also suggest ways to improve the EMVD apparatus in the future.

Electromechanical valve drive incorporating a nonlinear mechanical transformer

a Nonlinear Mechanical Transformer by Woo Sok Chang S.M., Mechanical Engineering, Massachusetts Institute of Technology (1999) M.S., Electrical Engineering, Seoul National University (1990) B.S., Electrical Engineering, Seoul National University (1988) Submitted to the Department of Electrical Engineering and Computer Science in Partial Fulfillment of the Requirements for the Degree of Doctor ofPhilosophy in Electrical Engineering and Computer Science at the Massachusetts Institute of Technology

Thermal modeling of Lundell alternators

Thermal analysis of Lundell alternators used in automobiles is presented. An analytical thermal model for Lundell alternators is proposed, and procedures for acquiring the model parameters are elucidated. Based on the thermal model, the temperature profile of an operating Lundell alternator can be predicted analytically. The predicted alternator temperatures are found to be consistent with the experimental measurement. The presented models and measurement methods are useful for embedding switched-mode power electronics into the alternator with low manufacturing cost.

A new electromagnetic valve actuator

In conventional internal combustion engines, engine valve displacements are fixed relative to crankshaft position. If these valves are actuated as a variable function of crankshaft angle, significant improvements in fuel economy can be achieved. Existing electromagnetically actuated variable-valve-timing (WT) systems characteristically use springs to provide the large inertial power to move the engine valves. However, the large spring forces generated when the valve is being closed or opened make it difficult to hold the valve without using a normal-force electromagnetic actuator. With normal-force electromagnetic actuators, it is difficult for the valve to engage its seat at a low velocity. Furthermore, from a control systems perspective, these unidirectional normal-force actuators pose difficult design challenges when compared to bi-directional shear-force actuators, as the former have nonuniform force constants. In this paper, we propose a novel electromagnetic valve drive (EMVD) system, and discuss the design and construction of the experimental apparatus, power electronics and controllers for the EMVD. This EMVD comprises an electric motor that is coupled to an engine valve-spring system with a nonlinear mechanical transformer. Simulation results show significant advantages of this EMVD over previously designed actuation systems.

Topologies for future automotive generators. Part I. Modeling and analytics

This paper compares the relative suitability of four different alternator topologies for use in an advanced automobile electrical system. The four candidate topologies are: the salient-and non-salient-pole wound-field synchronous alternators, the Lundell alternator, and the homopolar inductor alternator. The analysis is made with the alternator utilizing a switched-mode rectifier that enables load matching for optimal power transmission. This paper models and compares the alternators using hand calculations. Lumped parameter models of each of the four alternators are derived. The output power and efficiency of each machine is evaluated when utilized with a switched-mode boost rectifier and operating at the load matched condition. A direct mathematical comparison of the sizing equations for the four classes of machines is offered. Based on the analysis, the Lundell alternator has the highest power output and efficiency when compared at the same dimensions and field ampere turns excitation. Part II will cover a more detailed and accurate cost optimization of the four alternators while subject to the constraints and requirements of future automobiles.

Topologies for Future Automotive Generators – Part II: Optimization

For pt.I see ibid., p.819-30, (2005). This paper compares the relative suitability of four different alternator topologies for use in an advanced automobile electrical system. The four candidate topologies are: the salient-and non-salient-pole wound-field synchronous alternators, the Lundell alternator, and the homopolar inductor alternator. In part I, each of the four alternators was modeled. Relative power and efficiency were evaluated based on hand calculations. Part II involves a more accurate optimization of each of these alternators for cost, subject to constraints on output and efficiency. The performance of each machine is determined both with a conventional diode rectifier bridge and also with a switched-mode boost rectifier. Mechanical finite element analyses are performed to evaluate stresses. The most cost effective machines are compared based on size, weight, and inertia. The results reveal that the Lundell and salient-pole wound-field synchronous alternators are the most cost effective. Most surprising is the finding that the Lundell is capable of meeting the challenging next-generation requirements of power and efficiency while meeting the mechanical constraints set on the machines. Also noteworthy is the fact that the switched-mode boost rectifier gives a decrease in cost of more than 10% for each of the least expensive machines

Performance improvement of alternators with switched-mode rectifiers

The use of a switched-mode rectifier (SMR) allows automotive alternators to operate at a load-matched condition at all operating speeds, overcoming the limitation of optimum performance at just one speed [D.J.Perreault and V.Caliskan, (2000)]. While use of an SMR and load matching control enables large improvements in output power at cruising speed, no extra power is obtained at idle. This document introduces a new SMR modulation strategy capable of improving alternator output power at idle speed without violating thermal or current limits of the alternator. The new modulation scheme may be implemented with simple control hardware, and without the use of expensive current or position sensors. After introducing the new modulation method, we develop approximate analytical models that establish the underlying basis for the approach. Implementation considerations are addressed, and both simulation and experimental results are provided that demonstrate the advantages of the proposed control method.

Design and experimental evaluation of an electromechanical engine valve drive

In conventional internal combustion (IC) engines, engine valve timing is fixed with respect to crankshaft angle. Flexibly controlled valve timing offers significant improvements in fuel efficiency, engine performance and emissions. One way to achieve variable valve timing (VVT) is by using an electromechanical valve drive (EMVD). In this paper, we describe the design and experimental evaluation of a new EMVD comprising an electric motor coupled by a nonlinear mechanical transformer to a resonant valve-spring system. Experimental results demonstrate that a 3.3 ms transition time adequate for 6 krpm engine speed, reasonable power consumption, and low valve seating velocity are obtained with the design.

Design of dual-output alternators with switched-mode rectification

The push to introduce dual-voltage (42 V/14 V) automotive electrical systems necessitates power generation solutions capable of supplying power to multiple outputs. A number of approaches for implementing dual-voltage electrical systems have been proposed, but most suffer from severe cost or performance limitations. This paper explores the design of alternators incorporating dual-output switched-mode rectifiers (SMRs). The proposed approach enables the full load-matched power capability of the alternator machine to be achieved, with power delivered to the two outputs in any desired combination. SMR topologies for this application are introduced. Alternator/SMR design guidelines are established, and appropriate control laws are derived. Simulation and experimental results are presented that demonstrate the feasibility and high performance of the approach.

Design and Evaluation of a 42 V Automotive Alternator with Integrated Switched-Mode Rectifier

This paper presents techniques for the design of high-power Lundell alternators with integrated switched-mode rectifiers. A multi-section stator winding and interleaved rectifier arrangement is introduced that enables high power levels to be achieved using small semiconductor devices, and which greatly reduces the output filter capacitor requirements. We also demonstrate control methods suited to this interleaved system. In addition to accurate closed-loop output voltage control, we introduce methods to provide (partial) synchronous rectification for reduced loss, and to provide tight load dump transient control. The proposed technology is validated in the design and experimental evaluation of a 42 V, 3.4 kW alternator with fully integrated power electronics and controls. The prototype alternator achieves approximately a factor of 2.1 increase in power and 1.6 increase in power density as compared to a conventional diode-rectified alternator.