GB2150295A - Improvements relating to the measurement of fuel composition - Google Patents

Abstract

A device is provided to determine the rate of efficiency of fuel consumption in a vehicle. A computer 6 is fed with information concerning vehicle mass and fuel calorific value and has further inputs indicating rate of flow of the fuel 7 and vehicle speed based on wheel rotation 8 as controlled by a clock 9. An additional input to the computer is from a device 10 which gives an indication of apparent acceleration of the vehicle. This device may take many forms and in one arrangement comprises a mass whose extent of movement will be a function of vehicle acceleration and/or the angle of ascent or descent of the vehicle. The calculated rate of change of energy of the vehicle is converted into a fuel equivalent which is subtracted from the measured rate of use of the fuel to give a measure of the true rate of efficiency of fuel consumption. <IMAGE>

Description

SPECIFICATION Improvements relating to the measurement of fuel consumption Conventional equipment for measuring and indicating fuel consumption in motor cars is connected to sensors which determine the speed of the vehicle and the rate at which it is currently consuming fuel.

Dividing one quantity by the other gives the fuel consumption, typically measured in units of volume per unit of distance covered. This method of indicating fuel consumption is adequate for showing the rate of use of fuel over a substantial distance covered but the method of measurement is misleading if it is intended to give an instantaneous reading because during acceleration or retardation the kinetic energy stored in the moving vehicle is changing, and during ascents and descents its potential energy is changing. These changes are always reversible, that is the energy stored during acceleration or ascent is recovered during retardation or descent. The rate at which fuel is being "consumed", or wasted, is the rate of feed of fuel to the engine, less the fuel equivalent of the rate of change of stored energy.

The effect of this misleading method of measurement can be shown by simple example. During brisk acceleration, the conventional measurement of fuel consumption per unit of distance travelled gives a high figure, and during heavy braking when the throttle is closed it gives a low figure. The efficiency of the engine however is quite probably the reverse. Petrol engine losses are dependent mostly on engine speed, so that at large throttle openings the engine may produce a higher ratio of output power to losses and thus be more efficient than at small throttle openings. With the throttle closed the engine efficiency is close to zero.The most efficient way to burn the fuel (and therefore the one yielding the lowest fuel consumption per unit of distance travelled) may well be by alternately accelerating briskly for a time and then shutting off the engine and coasting for a time, although as a driving method on public highways this may not be acceptable.

It is an object of this invention to provide a method whereby a realistic measurement of instantaneous or short-term fuel consumption may be calculated.

Accordingly this invention provides, from one aspect, a method of determining the rate of efficiency of fuel consumption in a vehicle which comprises determining the rate of change of the potential and/or kinetic energy of a moving vehicle for a unit of time, converting the determined value to a fuel equivalent based on a known calorific value of the fuel being used to drive the vehicle, measuring the rate of the use of fuel by the vehicle over the same unit of time and subtracting the calculated fuel equivalent of the determined value from the measured rate of use of fuel to give a measure of the true rate of efficiency of fuel consumption.

Thus the invention relates to a method of determining the rate of change of energy stored in the moving vehicle, and from it deriving the rate of consumption of fuel which is recoverable. This is substracted from the rate at which fuel is fed to the engine, yielding the true rate of consumption or wastage of fuel. Dividing by measured speed will then give the true instantaneous rate of fuel consumption per unit of distance travelled.

If the true rate of efficiency of fuel consumption is displayed then the user of the vehicle can appreciate the driving conditions under which the most efficient use of fuel is achieved. Thus he can, for example, experiment to determine the optimum rate of acceleration to give the best fuel efficiency. Another possibility is to integrate the fuel consumption over a period or distance, so as to see for example how the amount of fuel wasted when climbing a particular hill is affected if the vehicle climbs it slowly at a light throttle opening, and then again quickly at a largerthrottle opening.

In the preferred embodiment the rate of change of energy is calculated from the change in position of a mass held within the vehicle due to vehicle acceleration or ascent/descent. One method of measuring accelerative force would incorporate a mass able to move in the direction of travel of the vehicle but restrained by a spring (or springs), and whose displacement was measured by a transducer. The spring might be replaced by a solid billet whose deformation was measured by, for example, a strain gauge bonded to it; or by a semiconductor device whose electrical properties would be changed by the application of force.

However most of these methods might be unsuitable for use in passenger cars because of their high cost and (in some cases) their poor performance at low levels of acceleration. A preferred method of measuring accelerative force is by determining the extent of displacement of a pendulum weight. Thus the pendulum could be attached to the spindle of an electrical potentiometer, the angular displacement of the pendulum being determined by the electrical signal obtained from the moving contact of the potentiometer.

Ideally there will be a damping mechanism for damping movement of the mass so that extraneous vibrations will not unduly affect the measurements being made. The damping mechanism could be in the form of a dashpot attached to the mass or a viscous fluid through which the mass will move. Alternatively damping could be achieved by means of a calculator which would average various readings of the position of the mass during the short predetermined time period.

The invention also extends towards apparatus constructed to carry out the method of this invention as hereinbefore defined. This could comprise a calculator having inputs from devices which measure the rate of use of fuel by the vehicle over a short unit of time, a device for determining the rate of change of the potential and/or kinetic energy of the moving vehicle during the same unit of time, means for introducing a value for a fuel equivalent based on a calorific value of the fuel being used to drive the vehicle and ideally also a device for recording the instantaneous speed of the vehicle.

The invention may be performed in various ways and a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which Figure 1 is a diagrammatic illustration of a vehicle incorporating a device for determining the rate of change of energy of the vehicle, in accordance with this invention; and Figure 2 is a block circuit diagram of parts enabling a calculation of rate of efficiency of fuel consumption of the vehicle to be carried out.

Figure 1 illustrates a vehicle 1 which is being driven up a hill 2 at a steady speed. A pendulum 3 suspended from a pivot 4 will therefore hang vertically, due to gravitational influence, and thus form an angle 6 with the normal vertical line 5 through the vehicle when the vehicle is at rest on a level surface.

In this instance the rate of change of stored potential energy is mgv sin 6 where mis the mass of the vehicle, g is the gravitational constant, and v is the instantaneous speed of the vehicle.

It will be appreciated that if the vehicle is accelerating over a level surface the pendulum will again swing away from the vertical and in this instance the rate of change of stored kinetic energy is the value mgv tan 8.

For the range of conditions likely to be encountered 6 will be small and so tan 6 may be regarded as equal to sine. Thus the angle of the pendulum 3 will provide a variable which can be used to calculate the rate of change of stored energy. Other variabies which will be required to enable a calculation of rate of efficiency of fuel consumption to be made are the rate of consumption of fuel (C) ) for a unit of time (t) the distance (d) travelled during that unit of time, and the velocity (v) which will be equal to d/t. Also required will be a calorific value (c) which will be used to determine a fuel equivalent for the type of fuel being used to drive the vehicle. The apparatus shown in Figure 2 provides a means for carrying out calculations using the values referred to above.Thus a computer 6 will be supplied with inputs from a device 7 indicating rate of flow of fuel and a device 8 giving a measurement of the rate of rotation of a wheel which can be converted to a distance travelled from a known value of the wheel circumference. Both units 7 and 8 are fed by a clock 9. A further device 10 gives a value for apparent acceleration. This could be just the angle 6, with the computer 6 making the necessary calculations of rate of change of energy from this value. There would also be variable devices 11 for providing a predetermined inputforthevehicle mass and 12forproviding the fuel calorific value for the fuel being used.

The following calculations can then be made: rate of change of energy = mgv sin 6 fuel equivalent = mgv sin 6 c fuel equivalent per unit time = mgvsin 6 tc true rate of efficiency of fuel consumption = e ~ mGv sin 0 tc true rate of fuel consumption per unit distance travelled = elv mgv sin 8 eiv ~ mg sin6 tcv tc This last value (or its inverse indicating the potential distance of travel per unit of fuel) as calculated by the computer 6 can then be displayed on a display device 13 to give the user of the vehicle an instantaneous indication of the true rate of efficiency of fuel consumption for the particular manner in which the vehicle is being driven at that particular time.

There are several possible ways of measuring the rate of change of potential and/or kinetic energy of which the simple pendulum method described above is one. It is appreciated that the pendulum will be subjected to vibration due to inadequate suspension and as the vehicle rides over bumps in the road. Thus some form of mechanical damping may be necessary to reduce the effects of vibration. This could be a dashpot connected to the pendulum. Alternatively the pendulum could be mounted in a sealed container enclosing a viscous liquid. Another possibility is to arrange for the computer to produce the average of a number of closely spaced readings taken over a short period of time and this will have the same effect as mechanical damping. It will be appreciated also that the use of a pendulum is given only as an example and it could be replaced, for instance, by a mass attached to a spring which will be subjected to linear displacement as the vehicle accelerates or climbs.

Additional damping mechanisms or adjustments may be needed to correct for the fact that the vehicle may tend to tilt during cornering and that the attitude of the vehicle itself may be disturbed during acceleration and deceleration.

Claims (15)

1. A method of determining the rate of efficiency of fuel consumption in a vehicle which comprises determining the rate of change of the potential and/or kinetic energy of a moving vehicle for a unit of time, converting the determined value to a fuel equivalent based on a known calorific value of the fuel being used to drive the vehicle, measuring the rate of use of fuel by the vehicle over the same unit of time and subtracting the calculated fuel equivalent of the determined value from the measured rate of use of fuel to give a measure of the true rate of efficiency of fuel consumption.

2. A method according to claim 1, wherein the rate of change of energy is calculated from the change in position of a mass held within the vehicle due to vehicle acceleration or ascent/decent.

3. A method according to claim 2, wherein the mass is positioned to be able to move along the direction of travel of the vehicle but is restrained by a resiliently deformable member.

4. A method according to claim 3, wherein the resiliently deformable member is one or more springs.

5. A method according to claim 2, wherein the resiliently deformable member is a solid billet having a strain gauge or other displacement measuring device attached to it.

6. A method according to claim 2, wherein the resiliently deformable member is a semiconductor device connected in a circuit which measures changes in electrical properties thereof upon deformation.

7. A method according to claim 2, wherein the mass is carried by a pendulum suspended from a fixed part of the vehicle.

8. A method according to claim 7, wherein the pendulum is attached to the spindle of a potentiometer connected in a circuit to measure changes in the electrical signal through the potentiometer as the spindle rotates.

9. A method according to any one of claims 2 to 8, wherein a damping mechanism is provided for damping movements of the mass.

10. A method according to claim 9, wherein the damping mechanism is a dashpot attached to the mass or a viscous fluid through which the mass will move.

11. A method according to claim 9, wherein the damping mechanism is a calculator for averging various readings of the position of the mass during a short predetermined time period.

12. A method according to claim 1 and substantially as herein described.

13. Apparatus constructed to carry out the method according to any one of claims 1 to 12 and as defined therein.

14. Apparatus for determining the rate of efficiency of fuel consumption in a vehicle and comprising a calculator having inputs from devices which measure the rate of use of fuel by the vehicle over a short unit of time, a device for determining the rate of change of the potential and/or kinetic energy of the moving vehicle during the same unit of time, means for introducing a value for a fuel equivalent based on a calorific value of the fuel being used to drive the vehicle and ideally also a device for recording the instantaneous speed of the vehicle.

15. Apparatus for determining the rate of efficiency of fuel consumption in a vehicle and substantially as herein described with reference to the accompanying drawings.