METHOD AND DEVICE FOR ESTABLISHING THE SPECIFIC FUEL CONSUMPTION BY AN INTERNAL COMBUSTION ENGINE

Abstract: The present invention relates to a method and a device for determining the specific fuel consumption of an internal combustion engine by measuring the change in weight of a pot containing fuel for consumption by the engine during a specific, selectable time. The device for execution of this method includes a data acquisition system (9) equipped with a number of measuring points. Sensors at the measuring points feed, through the data acquisition system, signals representing the change in weight of the fuel pot (1), the speed of the engine (2) and the torque of the engine into a computer (6). The computer is programmed for measuring at constant speed and constant torque, within selectable tolerance, and for measurement during a specific, selectable period of time. The method according to the invention permits the use of statistical methods to guarantee reliable and accurate measurement results with the shortest possible measurement period, while providing high flexibility in interfacing with the environment (operator, central computer system).

Description: The present invention relates to a method for determining the specific fuel consumption of an internal combustion engine by measuring the change in weight of a pot containing fuel and by using a data acquisition and computer system to monitor the speed and torque of the engine and the amount of fuel consumed by the engine during a preset, selectable period of time. The computer records the measurement values continuously during the measuring period, after which the information is processed and evaluated by the computer which is programmed for measurement at constant engine speed and torque. The invention also relates to a device for execution of the method by means of a fuel scale consisting of a pot containing fuel resting on a load cell with a built-in strain gauge, a pulse transducer attached to the engine shaft for measuring engine speed and a dynamometer for measuring engine torque and a data acquisition and computer system, connected to these sensor devices. Several known methods are based on determining the time it takes to consume a given amount of fuel, i.e. the time is recorded at start and stop of the consumption of the predetermined amount of fuel, without any monitoring of the process during the fuel consumption. The SE-A-394 744 Patent to Deere relates to a fuel weighing system for testing the brake specific fuel consumption of an engine. The US system will provide a direct reading of brake specific fuel consumption. It operates in continuous cycles and assures an adequate integrating period for each cycle by monitoring the time needed to consume a sample of fuel and automatically selecting a smaller or larger fuel sample for the next cycle if the time needed to consume the sample is above or below respectively, predetermined maximum and minimum time limits. In contrast to Deere, the device according to the present invention makes a measurement of the specific fuel consumption by means of measuring the change in weight of the fuel being consumed. It is important to make these measurements with great accuracy because the change in weight represents more directly the energy contents of the fuel consumption and therefore the specific fuel consumption of the engine can be determined without any converting factors. The SU-A-127 2119 Patent relates to a method for determining the hourly and specific fuel consumption. However, as the consumption is measured only under rated speed and torque conditions and the sensed speed and torque are multiplied for comparison with the power setting it would be difficult to get a mean value of the efficiency with sufficient accuracy, particularly as no limits of tolerance of the rated speed and torque values are mentioned. The invention described in AT Patent No. 298 821 relates to a measuring device for measuring the fuel consumption of an internal combustion engine on a test bench. It consists ot two measuring pots, each one supported by a weight measuring device based on the strain gauge principle. The pots are connected to a common fuel tank, and each one of the pots is connected to the internal combustion engine. The lines between the fuel tank and the measuring pots, as well as the lines between the measuring pots and the internal combustion engine, are equipped with electrically controlled valves. The measuring pots are drained and filled alternately by a switching device that opens and closes the valves in response to impulses from the weight measuring devices. As soon as preset maximum and minimum values of the weight of the pots are registered by the measuring devices, they transmit impulses to the switching device. The measuring period is divided into a number of time intervals, during which a fuel consumption corresponding to the change in weight of the measuring pots is determined. The total fuel consumption during the measuring period is determined by adding the consumption of the time intervals together. This method has the disadvantage that if disturbances occur during the measuring period, in the form of changes in engine speed or torque, and this is not detected, an erroneous result can be obtained. Also, even small measuring errors at start and stop will cause direct errors in the overall result. One object of the present invention is to provide a method for determining the fuel consumption, that meets high demands on reliability, accuracy and speed of measurement. The characteristics of the method are stated in the attached claims. Another object of the invention is to provide a measurement and fuel weighing system for execution of the method that contains few mechanical parts and that affords high reliability and easy maintenance. To achieve these objects, the invention comprises a method as defined in claim 1 and a device as defined in claim 2. According to the present invention, the fuel consumption of an internal combustion engine is determined by measuring the engine torque, the engine speed and the amount of fuel consumed by the engine during the preset, selectable period of time. According to the invention, the amount of fuel consumed by the engine is determined by a number of measurements of the change in weight of a pot containing fuel by means of a weight measuring device. The advantage of this method is that values are recorded continuously during the course of the measuring period and can be processed and evaluated afterwards. A prerequisite is that the change in weight of the pot can be measured with sufficient accuracy. This is accomplished by noise reduction through integration of the measuring signal during a preset, selectable period. It is also possible to increase the accuracy and statistical certainty of the fuel consumption measurement by increasing the length of the measuring period. The invention will be further described below, with reference to the attached drawing, which shows a block diagram of the equipment included in the measuring system. As shown in the block diagram, the system includes a number of measuring points for measuring the engine torque, the engine speed and the amount of fuel consumed. Sensors area provided at these measuring points whose output signals, representing the states of the different measuring points, are fed to a computer through a data acquisition and signal conditioning system. To simplify the evalation of the measurement, the computer is programmed for measuring at constant engine speed and engine torque, within preset, selectable limits of tolerance and for a preset, selectable measuring period. The computer can also be programmed for measuring at a preset, constant value of the engine speed as well as of the engine torque within preset selectable limits of tolerance of each value. The signals representing the amount of fuel consumed during the selected measuring period are also fed to the computer through-the data acquisition and signal conditioning system. This measurement is obtained by means of a pot containing fuel for engine consumption, supported by a load cell equipped with a strain gauge. Every change in weight of the pot will change the output signal from the strain gauge, which is read by the computer. In the embodiment of the device for executing the method shown in the block diagram, the fuel pot (1) is connected to an internal combustion engine (2) through a number of fuel pipes (4) equipped with valves (3). The fuel pot (1) is supported by a load cell (5) which contains a strain gauge. For every change in weight of the fuel pot (1) there is a change in the output signal from the strain gauge, which is sensed by a data acquisition system (9) that feeds the data into a computer (6). The total change in weight of the pot during a certain, arbitrarily selected time thereby constitutes a measure of the fuel consumption of the engine during that time. The engine speed is measured by means of a puls transducer (7) attached to the engine shaft and the engine torque by means of a dynamometer (8) connected to the engine shaft. The computer (6) is programmed for constant speed and constant torque within preset, selectable limits of tolerance. If the deviation from these values of speed and torque are too large, the computer will disqualify the cycle and start a new one. When the measuring cycle starts, the amount of fuel is measured by means of the strain gauge. The output signal from the strain gauge is recorded by the computer at times that are controlled by an accurate real-time clock in the computer system. Engine speed is measured as the mean rate of pulses from a pulse transducer attached to the engine shaft. Measurements of fuel amount, speed and torque are made several times per second, controlled by the computer real-time clock, and the results are stored in a table in the computer memory. During the entire masuring period, which can be varied in increments of 0.5 second in order to permit measurements with maximum accuracy, the total number of revolutions of the engine shaft is counted by continuous counting of the pulses from the pulse transducer update a counter in the computer. During the measurement period, the computer checks that the speed and the torque of the engine are within preset, selectable limits of tolerance from preset values. If the limits are exceeded, the measuring period will be interrupted and a new one started. At the end of the measuring period, the computer checks the sorted tabulated values to determine whether the speed has been constant within the preset limits of tolerance. If not, the measurement is disqualified and a new one is started. If the speed check approves the values, the computer calculates a linear fuel consumption curve as a function of time by means of the least-squares method, as well as a means torque. The deviation of the tabulated values from the consumption curve and from the mean torque is calculated. If the deviation is greater than a preset, selectable tolerance, the measurement is disqualified and a new one is started. If this check is also passed, the computer calculates the fuel consumption per piston stroke based on the fuel consumption curve, the number of engine shaft revolutions, the number of cylinders and the length of the measuring period. The computer program can, of course, be revised to suit other types of internal combustion engines or to deliver the result in other forms, e.g. consumption per unit time, while staying within the scope of the invention as claimed.

Claims: 1. A method for determining the specific fuel consumption of an internal combustion engine by: feeding from sensor through a signal conditioning system to a computer, signals representing the torque and the speed of the engine and the change in weight of a pot containing fuel for consumption by the engine, continuous recording and storing by the computer, during the measuring period, of values of the engine speed, the engine torque and the number of revolutions of the engine shaft, the computer being programmed for measurments at constant speed and torque within selectable, preset limits of tolerance from a preset, selectable value, for a selectable measuring period, which can be varied in small increments to achieve maximum accuracy, characterized by the following: continuous recording and storing by the computer, during the measuring period, of values of the change in weight of the fuel pot, whereby the signals representing the change in weight of the fuel pot are recorded with noise reduction through integration of the signals during the measuring period in order to accomplish a measurement with sufficient accuracy, if the engine speed torque exceeds the preset limits during the measuring period, the computer will terminate the measurement and start a new one, if the engine speed and torque are constant within the preset limits, the computer will, after the measurement period, calculate a linear fuel consumption curve by means of the least-squares method, and a mean torque and a mean speed, if the deviation of mean speed or mean torque from the preset values is greater than a preset selectable tolerance, or if deviation of any value of fuel consumption from the above-mentioned curve is greater than a preset, selectable tolerance, the measurement will be disqualified and a new one started, if the deviations are within the preset limits, the computer will calculate the fuel consumption per piston stroke based on the fuel consumption curve, the measuring period, the number of revolutions during the measuring period and the number of cylinders, whereby the statistical certainty of the result is also specified. 2. Device for execution of the method according to claim 1, characterized by the following combination: a fuel pot (1) which is connected to an internal combustion engine (2) through a number of fuel lines (4) equipped with valves (3), a load cell equipped with a strain gauge (5), on which the fuel pot is supported for measuring the change in weight of the pot during a preset, selectable time, resulting from the engine's consumption of fuel during said time, a pulse transducer (7) connected to the engine shaft, said transducer producing pulses indicative of the speed of the engine. a dynamometer connected to the engine shaft for measuring the engine torque, signal conversion units included in the data acquisition system (9) that convert analog input signals to frequency, a measuring unit included in the data acquisition system (9) that measures the mean pulse rate for a selectable number of pulses, programmable counters included in the data acquisition system (9) for integration of weight, torque and total number of revolution pulses, a computer system (6) for recording of the data fed to the computer through a data acquisition and signal conditioning system (9) from the sensors at each measuring point during the measuring period, for subsequent processing and evaluation of the measurements and check means included in the computer system (6) for disqualifying the measurements and starting a new measurement of the specific fuel consumption if deviations of speed, torque or stored tabulated value from a linear fuel consumption curve are greater than predetermined values.

Inventors: ANDERSSON, KJELL, ERIKSSON, LENNART
Applicants: ASE EUROPE AB
Application year: 1989
Main classification: G01F9
IPC codes: G01F9