Search Results

Previous investigations using a single-pin-disc system have suggested that the mechanism of disc brake squeal is explainable in terms of a geometrically induced or kinematic constraint instability. The experimental results and theoretical analysis to be presented further endorse this idea while demonstrating that interactive coupling effects using a two-pin system can produce both enlarged and reduced regions of noise generation. Two steel pins independently supported on flexible cantilevers are pressed into contact with a steel disc which rotates at a constant speed. Assuming the system to be undamped and having linear characteristics, the pin sub-systems are each modelled to have three degrees-of-freedom and the disc to have a single degree-of-freedom. The unstable regions are shown to depend primarily on the orientations of the pins to the disc surface.

Analyses of squealing disk brakes generally show main frequencies from 1 to 10 kHz. On a test stand holograms exposed by time average and double-pulse techniques are recorded from various types of disk brakes. Photographs of reconstructions from those holograms display a vibration pattern in a simple topographical map of fringes, which represents contours of equal vibration amplitudes on the brake components: That would be i.e. yoke-type or fist-type callipers, brake pads and brake disk. Holographic Vibration Analysis is a useful method for looking at these small vibration amplitudes to understand different mechanisms of coupling. Also it is possible to localize vibration sources in squealing disk brakes.

Better methods of analyzing combustion dynamics in internal combustion (IC) engines are needed as a consequence of increasing demands for greater thermal efficiency, lower pollutant output, and improved fuel flexibility. In response to these needs, both improved diagnostic devices and computational techniques are being developed. Together, these developments may lead to a more detailed understanding of the combustion process. In particular, advanced numerical simulation techniques, may ultimately produce the capability of calculating both the spatial and temporal evolution of the fuel/air mixture for the IC engine cycle as well as the combustion process itself. During the last several years, a number of publications have appeared, describing both one-dimensional and two-dimensional, transient computer codes which indicate steady progress toward the goal of a computational tool which is capable of making performance predictions at a reasonable cost.

A theoretical model has been developed for calculations of the evolution of fuel injected into internal combustion engine chambers. Fuel injection in the form of a gaseous jet and in the form of a liquid droplet spray are considered. The model uses the basic equations of conservation of mass, momentum, and energy in both the gaseous and liquid phases. Applications in two dimensional symmetry of the gaseous jet form of the numerical model are described in stagnant and swirling air flows. The liquid droplet spray model, including coupling between the droplets and the gas phase medium, is described. Applications of the two phase model are described for the case of axially symmetric injection. Finally, the liquid spray model and the gas jet model are applied to the same conditions, leading to a general assessment of the ranges of validity of the gas jet model.

The trade-off between engine operating efficiency and NOx emissions in the prechamber three-valve stratified-charge engine is examined in a series of parametric studies using an improved model developed at M.I.T. (1). Engine geometric, operating, and combustion parameters are varied independently and the effects on brake-specific-fuel-consumption, exhaust temperature and brake-specific-NO observed. Parameters chosen for study are: timing of the start of combustion, overall air-fuel ratio, prechamber air-fuel ratio at the start of combustion, main-chamber combustion duration, prechamber size (prechamber volume and orifice diameter), EGR (in main and prechamber intakes), and load. The results quantify trade-off opportunities amongst these design and operating variables which are available to the engine designer.

This paper describes the development of a mathematical model for the compression, combustion, expansion, exhaust and intake processes of a three-valve stratified charge engine. After calculating the mixture formation at the end of compression process, a simple combustion model was developed to compute the gas temperature, gas pressure and the rate of formation of NO and CO at each crankangle, using basic energy and reaction kinetic equations for both the auxiliary and main chambers. The evaluation of the model was carried out by comparing the computed and experimental data. A satisfactory correlation was observed between them.

This paper reviews 20 years of data dealing with customer reaction to gasoline octane quality. Four technical studies and one marketing survey are covered. An analysis of the data shows that customer reaction to engine knock has not changed during this period. Agreement among three of the technical studies was good. ΔRON, the difference in Research Octane Number requirements between trained observers and customers, varied from 3.0 RON at the 50th percentile satisfaction level to 1.7 RON at the 90th percentile satisfaction level. The marketing survey shows that these values of ΔRON are a good measure of the number of customers in the marketplace who consider knock to be a problem. The fourth technical study measured ΔRON to be at least twice as large as the values in the other studies. This discrepancy is traced to the design of the questionnaire used to evaluate customer reaction to knock.

Octane requirements of late model vehicles were determined by trained knock raters and compared with those determined by customers. Average differences of independent distributions of customer and rater requirements were about 3 Research Octane Numbers/2 Motor Octane Numbers at part-throttle and 6 RON/4 MON at full-throttle and maximum octane requirement conditions. Five percent of the customers objected to knock when their cars were operated on fuel matching rater requirements, while 50 percent objected when using fuel 6 RON/4 MON lower. Another program is planned because differences between rater and customer octane requirements were greater than expected.

The influence of driving procedures and extraneous car noise on perception of engine knock has been studied with late model cars. Year to year changes in reports of knock by both customers and raters and changes in octane requirements were also reviewed. Customers generally accelerated cars less vigorously and tended to perceive knock less often than raters. However, in cars that had maximum octane requirements at part-throttle, customers perceived knock about as frequently as raters. Octane requirements, as determined by raters, were reduced by about 2 Research Octane numbers when the car radio was turned on and the windows closed. Both customers and raters reported more knock with 1975-1977 model cars than with earlier models. Since 1975, octane requirements of certain car models tended to be adjusted to the octane quality of available gasoline.

The Acceleration Performance Instrument was developed to reduce the manpower and equipment required for vehicle performance testing. Using only a single person and test vehicle, data may be obtained in five operating modes. The instrument prints time-to-speed and time-to-distance information on paper tape during vehicle acceleration and coastdown. Acceleration testing may utilize a standing or moving start at any speed up to 99 mph. Vehicle coastdown data may be obtained between any two speeds and is useful for determining aerodynamic drag and rolling resistance. Special modes provide Federal consumer passing information without the use of additional personnel or vehicles. The instrument requires the addition of a 5th wheel and an AC power inverter for operation. THE ACCELERATION PERFORMANCE INSTRUMENT was developed to meet the demands of increased performance measuring capability using reduced manpower and vehicle time.

The preparation and testing of polyurethane foam for seating applications is described. Designed experimentation utilizing low vapor pressure isocyanates was used to optimize conditions. Components and conditions which produced the most satisfactory product are noted.

Problem areas of general applicability in the field of detection of knock in commercial engines are discussed. These include (a) the expedients adopted to reduce the effect of noise on the sensibility of the measuring instrument, (b) the characteristics of the pass-band electronic filter employed in this type of instrumentation and possible distortion effects, (c) the type and mounting of the transducer employed, with emphasis on devices outside the combustion chamber, and (d) the interpretation of the phenomena as detected with the devices used and its relation to the energy released from knock and the danger of mechanical damage.

Spark plug pressure transducers were used in an experimental study to determine the suitability of such devices for measuring indicated work in internal combustion engines. Three piezoelectric transducers were studied to compare response of the spark plug unit with a reference device; the comparative data were obtained from a single-cylinder engine fitted with both a flush mounted pressure transducer and a spark plug pressure transducer. Signals from both transducers were recorded simultaneously, combined with a volume function, and analyzed for output differences. The volume function used in the calculations of indicated work was generated about an angular reference point recorded with the pressure data. Typically, indicated work calculated from the spark plug pressure transducer was found to be from -3.2 to +7.6% of that calculated from the flush mounted pressure transducer. The sources of inaccuracy associated with the spark plug pressure transducer are discussed.

A new method which automates collection and processing of brake test data has been developed to replace the more traditional methods of using an observer or Ultra Violet recorder. This method improves accuracy and also substantially reduces cost and can be applied to vehicle or dynamometer testing. Improved versions of the instrument would allow investigation of transient conditions.

A new knock intensity meter, based on a criterion which correlates knock intensity and kinetic energy associated to knock-typical pressure oscillations, is described. Operating principles, electronic chain, as well as the method that led to an instrument able of accurate measurements (both on laboratory engines and on automotive engines at high speed) are analysed.

A Microcomputer Based Eight Channel Data Acquisition System has been developed for customer correlation and routine vehicle field testing applications. The eight channel system includes a self-contained signal conditioning system designed for a variety of transducer types and data frequency requirements. Calibration, signal gain, and channel zero offset adjustments can be performed under software control. The microcomputer system is based on a Motorola M6800 microprocessor and a non-volatile core memory module. The paper describes the design, development, field performance, and data processing characteristics of the system and presents specific automotive applications and field test results.

The national goals of more fuel efficient automobiles are being achieved in part by smaller and lighter vehicles resulting in demands for smaller and compatible instrumentation. Previously designed towing dynamometers for regular-sized vehicles were unable to provide adequately low drawbar levels for small cars like the Chevette. The dynamometer trailer provides a controllable retarding force on the passenger car to simulate hill climbing. This paper describes electrical and mechanical characteristics and operation of a dynamometer specifically designed for contemporary vehicles. An improved method is outlined for supplying controlled electrical power to eddy-current retarders used on the dynamometer. The improved system uses a 24 volt production alternator to supply controlled direct current to the eddy-current retarder. The current delivered to the eddy-current retarder is controlled by adjusting the alternator's field current.

A study was conducted by the National Highway Traffic Safety Administration to determine the applicability of Federal motor vehicle safety standards to electric and hybrid vehicles. Addressed in the study were vehicles to be included in the demonstration fleets called for in Public Law 94-413 and vehicles anticipated for future consumer use. Descriptions are given of existing and future electric and hybrid vehicles,and results of safety tests are reported. It was concluded that Federal safety standards, with few exceptions, should be applicable to electric and hybrid vehicles, with the possible exception of special purpose, limited performance and use vehicles.

A 1975 California model automobile with an 8:1 C.R. 350 CID engine was modified by increasing the compression ratio to 9:1 which resulted in improved fuel economy. The higher NOx emissions were reduced to the base level by substituting a back pressure-controlled EGR unit for the original valve and increasing the EGR flow. Octane requirement was controlled by a knock sensor-actuated spark timing retard system. The knock sensor (accelerometer) is attached to one of the cylinder heads of the engine. When knock occurs, the vibration is picked up by the sensor, the signal is filtered to remove some of the engine background noise, and the knock pulse is detected. When the amplitude of the detected knock signal exceeds a threshold, the spark timing is retarded. When no knocking is detected over a waiting period, the timing is advanced back to its normal schedule.

This paper was prepared in connection with a broader study of the opportunities and risks associated with a demonstration program defined by the Congress of the United States in the Electric and Hybrid Research, Development and Demonstration Act of 1976. The paper develops estimates of the number of accidents, injuries, and fatalities which might result from introduction of electric and hybrid vehicles into the general passenger vehicle fleet. In order to derive such an estimate, we have referred to existing accident data banks for small internal combustion engine cars operating primarily in urban areas, and have extrapolated from that data to some assumed electric vehicle populations. In addition, we have considered some particular problems of electric vehicles which might produce new dangers, such as electric shock, battery acid, and low acceleration capability. The desirability of imposing existing or new safety standards on these vehicles is considered.