GB2127545A - Fuel consumption indicator and travel cost display system - Google Patents

Abstract

A vehicle fuel consumption indicator system comprises a memory arranged to hold one or more reference values of fuel consumption determined theoretically or empirically. Reference data or updating data can be entered and fed to a computing means and/or the memory from a keyboard, and the computing means is arranged to compute the instantaneous fuel consumption using at least said reference value or values and the instantaneous speed. A continuously updated indication of the instantaneous fuel consumption is displayed. In a preferred form, a display of travel costs, actual or predicted, is also available. <IMAGE>

Description

SPECIFICATION Fuel consumption indicator and travel cost display system This invention relates broadly to the determination and display of fuel consumption in a vehicle, and also to a travel cost display system which incorporates a data entry keyboard and a driver performance indicator, i.e. an indicator of fuel consumption.

Purchasers of new cars in the EEC are already familiar with the display of fuel consumption figures in a standard manner required by law so as to permit the comparison of fuel efficiency between different vehicles and under a range of conditions. In the United Kingdom these conditions are fuel consumption during a standardised urban driving cycle involving driving at generally low speeds but with various changes in speed, fuel consumption at a constant 56 mph, and fuel consumption at a constant 75 mph.

It is upon this principle that fuel consumption varies with speed and changes in speed that the instantaneous fuel consumption indicator of the present invention is based.

Systems are known which emit an audible signal when a certain speed is exceeded by the driver.

Another system emits an audible signal when certain levels of acceleration or deceleration are exceeded and a record is made of the number of times these levels are exceeded.

Meters and displays are known where the driver of a vehicle may receive continuously updated information from a meter or display showing fuel consumption information in units of fuel per unit distance or distance per unit fuel. In these systems, distance travelled by the vehicle is derived from a distance transducer and measurement of fuel consumption is made by a fuel flow meter placed in the fuel line. Many alternative methods of detecting fuel flow have been achieved by placing transducers appropriately to detect changes in the fuel supply system which are causally related to the supply of fuel to the engine; these have included, either singly or in combination, measurement of engine manifold vacuum, carburettor settings including air intake choke setting angle, fuel pump activity and fuel injection rate.

There are disadvantages with the existing fuel flow metering or measurement systems, namely, that the flow of fuel measured between the fuel tank and the carburettor is generally characterised by short periods of high flow rates and longer periods of low flow rates. Such pulsating flows require to be averaged out before the flow rate information may be presented usefully to the driver. Such smoothing necessarily incurs a delay in time before the driver can be presented with the information. Secondly, because fuel consumption rather than energy dissipation is measured, energy dissipated as heat of friction whilst braking is not displayed to the driver at the time of braking but is displayed only when accelerating back to the original speed. This again introduces delay in the feedback of information.

Thirdly, each of these methods of fuel consumption requires the introduction and calibration of transducers which incur expense to the user or purchaser of these devices.

A further known system for monitoring vehicular travelling costs is described in our U.K. Patent Application 8,132,622. U.K. Patent Application 8,132,622 describes meters and metering and display systems appropriate for monitoring and providing a record and/or display of vehicular travelling costs.

The metering and metering and display system of that application are particularly applicable to a payas-you drive scheme where a number of users share one or more vehicles, or where passengers share the cost of travel with the driver. It is the main object of that invention to provide an improved system which offers a display of the actual cost of travel, taking due account of actual fuel consumption, i.e.

with the fuel consumption being reflected in the "cost" figure which is displayed.

It is a further object of the aforesaid invention to provide means whereby a travel cost figure may be apportioned to specific individuals in a shared system, for example by operating on a "key" basis. The system which is the subject of the aforesaid patent application is one in which, when the meter is used to allocate travel costs to specific users, the cumulative travel costs of any of the users may be displayed on demand. The provision of a travel cost display as compared with the other, known types of display enables car drivers to achieve greater efficiency in the use of resources, to have an increased awareness of journey costs, and also possibly to give information as to the state of tuning of the vehicle engine.

In the system as described in the aforesaid patent application the petrol cost and distance cost information is fed into the computing device by way of switches.

In the aforesaid patent application switches were located internally to the device and were intentionally not calibrated in easily understood units, such as pence per mile, in order to improve the security of these variables from fraudulent change. According to a feature of one aspect of the present invention, an external keyboard is used to replace and extend the functions performed by the switches.

This is of particular value to voluntary users of the travel cost display where the security of the price settings is not of interest. Where security of the price setting is required, the entry of a correct code number is necessary before price settings may be altered.

Again, in the system described in the aforesaid Patent Application, the display of travel cost information is produced from the combination of calibrated pulse trains from distance and fuel flow transducers.

There are a number of objects, and advantages, of the present invention.

The primary object of the invention is to provide a vehicle fuel consumption indicator which will operate on the output from just a single transducer which measures distance travelled by the vehicle or which has an output directly representative of vehicle speed. By examining the distance travelled with respect to time, vehicle road speed can be computed, and, using an appropriate reference fuel consumption value or values, a current fuel consumption value can be computed based upon the current vehicle road speed.

In accordance with one aspect of the invention there is provided a vehicle fuel consumption indicator system comprising a transducer which provides a measure of distance travelled by the vehicle, computing means receiving the output of said transducer and arranged to compute road speed therefrom, storage means arranged to hold one or more reference values of fuel consumption, in-vehicle keying means by means of which reference data or updating data can be entered and fed to said computing means and/or said storage means, said computing means being arranged to compute, using at least said reference value or values, the instantaneous fuel consumption, and display means providing a continuously updated indication of said instantaneous fuel consumption.

In accordance with another aspect of the invention there is provided a vehicle fuel consumption indicator system comprising a transducer which provides an output signal representative of road speed, computing means receiving the output of said transducer, storage means arranged to hold one or more reference values of fuel consumption, in-vehicle keying means by means of which reference data or updating data can be entered and fed to said computing means and/or said storage means, said computing means being arranged to compute, using at least said reference value or values, the instantaneous fuel consumption, and display means providing a continuously updated indication of said instantaneous fuel consumption.

Several methods of determining the reference fuel consumption value or values are possible, including the keyboard entry of fuel purchases.

It is a further object to improve the accuracy of this basic minimum information input system by arranging for the current fuel consumption value to be dependent also on any recent change in vehicle speed, preferably also aliowing for any recent acceleration or deceleration.

It is a further object yet further to improve the accuracy of the system either by including an accelerator for the vertical plane to detect if the vehicle is travelling uphill or downhill, or to include a link to the vehicle braking system to distinguish between genuine braking and a slowing down due to an outside influence, such as a hill.

It is an object to yet further improve the accuracy of the system by coupling any or several additional transducers which give signals indicative of engine revolutions, engine temperature, manifold vacuum, choke, setting, application of brakes, or gear engaged in such ways as, via calibration and computation internal to the device, to appropriately raise or lower the fuel consumption figure displayed to the driver.

It is an object of the invention to be able to provide an instantaneous display of a fuel consumption rate which is a function of a reference value or values of fuel consumption, the current speed of the vehicle, and recent changes in speed, including acceleration and deceleration.

It is another object to provide a system in which the aforesaid instantaneous fuel consumption rates are stored, using suitable memory, so as to be able to provide a cumulative or mean value for fuel consumption.

It is a further object to provide a system which will give a display (including prediction) of the cost of travel either for car sharing purposes or as information available to the driver so as to encourage driving economy, in any or all of the following ways; a) fuel cost, since reset b) fuel + distance cost, since reset c) instantaneous fuel cost (not predicted) d) instantaneous fuel + distance cost (not predicted).

It is yet another object of the invention to provide a system in which the calculation of mean fuel consumption per unit distance is effected using a keyboard to enter into the system details of fuel purchases and using the single distance transducer. This provides a suitable method for calculating the reference value referred to above.

With the present invention one can provide a continuous display of fuel consumption efficiency at all reasonable speeds and compensate for acceleration and deceleration at those speeds.

It is an object of the present invention to use a single pulse train from a transducer for sensing distance and to use it, in combination with a value for fuel cost per unit distance derived directly or via machine computation internal to the device, to display a journey fuel cost or a combined journey fuel cost plus other distance charge reflecting non-fuel related costs. A journey is any trip or group of trips as measured since the stored measure of distance has been reset to the zero datum.

It is a preferred feature of this invention that the fuel consumption figure, used to calculate the measure or value of fuel used over a certain distance, is determined by entering into the device, e.g. via a keyboard, details of the addition of fuel to the fuel tank. This improved method of determining average fuel consumption has the virtues of economy, since no fuel transducer is required, and of accuracy. The measurement of fuel through the pumps at garages is of a much higher level of accuracy than is the measurement by the types of flow meter generally used in vehicles.

It is a further feature of the keyboard entry of data into the device that should the user become familiar with average consumption rate produced by this method, or tire of entering this data regularly, then the average fuel consumption figure is directly alterable from the keyboard. This has the advantage of retaining or setting or setting up an average MPG figure for use with other parts of the devices, e.g.

that which determines the quantity of fuel estimated to have been used over a particular distance, without the inconvenience of entering the data concerning fuel additions to the tank.

The present invention has a number of advantages over known systems and devices.

Firstly, it can provide a single continuous signal to the driver which represents the combined effect of speed and change in speed on fuel consumption. This is unlike the "new car sale" mpg information in that it is retained during the use of the device; and also unlike the acceleration-based devices which give a discontinuous signal.

Secondly, since a distance transducer is required in some form for a vehicle's odometer then, in the limiting case, no additional transducer is required for the operation of this invention where the vehicles speedometer, odometer and kinetic mpg meter all share the same transducer and/or are outputs of the same computing device. This has the advantage of economy as reliable flow meters are, for example, expensive elements of a conventional mpg meter. Also, this offers the possibility of building a vehicle speedometer which also displays kinetic MPG, all in the same unit.

Thirdly, there is a need to insert a flow meter into the fuel line. Such a flow meter can cause, or suffer from a variety of problems, including the formation of vapour bubbles during hot weather. The meter may also partially block the fuel pipe, thereby impeding fuel flow. A further disadvantage with the use of flow meters is that they monitor the flow of fuel into the carburettor which is a pulsating flow and so requires smoothing so as to present the driver with an averaged value of fuel consumption. However this smoothing takes time and so there is a delay in providing the driver with information concerning his driving behaviour.

Fourthly, the device or system of the present invention can display to the driver a signal corresponding to the loss of energy associated with deceleration normally caused by friction whilst braking. In other systems this energy loss is not displayed at the time of braking but only displayed when accelerating back to the original speed. This again introduces a delay in the feedback of information required to increase fuel economy.

It is a further feature of the preferred embodiment of the device of the present invention, as compared with other travel cost recorders and displays, that the length of a proposed journey may be entered into the device and a cost of that journey computed from the currently held mileage and fuel consumption rates held in the device. Thus, an estimate will be available of journey costs before undertaking a journey. This will aid the driver in making an important decision as to whether an alternative mode of transport is cheaper or whether the journey is desirable at that cost.

The computation of the driver performance figure, displayed and continuously updated during driving, requires a pulse train from the distance transducer and a source of regular time pulses. The latter are available from the integrated circuit of a microprocessor used to compute the displayed results, or may be generated by some other source such as a crystal oscillator.

This pulse train or pulse trains is/are then used to calculate some measure of speed and change in speed. This speed information may then be displayed to the driver in units determined by a reference value and in a manner determined by an equation or equations encoded in the computation equipment of the device. The function of the equation is to produce a displayed result which will encourage the driver to drive at a lower speed and with less acceleration or braking. Where an additional transducer for sensing engine revolutions is fitted to the device the displayed result will function to encourage driving with the most appropriate gear engaged.

It is the intention of the invention to supply a continuously updated signal, e.g. by a digital display, by which a driver may be informed of the combined effects of speed and changes in speed. With the reference value being a measure of fuel consumption of the vehicle, the displayed result of the computation will also be a fuel consumption value, hereinafter called "kinetic MPG", appropriate to that speed and to the recent history of acceleration, and to the accuracy or appropriateness of the equations used in the computation with respect to the particular vehicle to which the device is fitted.

By providing an improved metering or display system which displays and/or records the performance of the vehicle relative to a reference value of performance and independent of the current speed of the vehicle and recent vehicle speeds, the comparison of current and recent vehicle speeds allows the determination of acceleration and selection of appropriate modes in the computation undertaken by the device.

Because the device can measure display and record vehicle performance using a single transducer, namely a distance transducer, this minimises production costs and minimises transducer wear or failure.

It is a feature of this invention that the display and metering of the vehicle performance so as to include the effect of braking, acceleration, or travel at various speeds, is capable of use in conjunction with existing methods of fuel consumption measurement in vehicle.

In a preferred embodiment of the invention, the reference value is the known average fuel consumption rate of the vehicle measured, for example, in units of miles per gallon, and established by the vehicle owner over an appropriate period of time or group of journeys, or taken from a published source, or determined by some other method. It is known that fuel consumption is generally higher at high speeds, higher due to higher rates of acceleration, and higher where vehicle braking occurs. Fuel consumption as measured in MPG is zero when the vehicle is stationary. Thus, although generally fuel consumption will decrease if the vehicle travels at higher speeds, fuel consumption per mile will increase with increasing speed as the vehicle accelerates from rest where, by definition, MPG equals zero.Thus, at least three regions of performance can be distinguished relative to the reference value of the average MPG of the vehicle; (i) at speeds close to zero a region of below average MPG, (ii) at high speeds a region of below average MPG, and (iii) an intermediate peak MPG above average at some intermediate speed. Thus, of necessity, there will be at least two speeds at which intantaneous MPG will equal the average MPG; one will be slower than the peak MPG speed and one higher. Data from the first of these regions may or may not be displayed to the driver.

It is necessary for the functioning of the device to have some method of determining the vehicle's current speed and then, by means of computation, using the current speed and the reference value of mean MPG, a value of MPG at that speed can be calculated. The accuracy of that value depends on (a) how the reference value has been obtained, and (b) on the precision with which the equation for the relationship between vehicle speed and fuel consumption at that speed has been determined or calibrated for the particular vehicle.

A further equation for acceleration, and an equation or equations for deceleration, are incorporated in embodiments of this invention to control the displayed and/or metered value of performance relative to the value at a particular speed. Both acceleration and deceleration of a specified degree lower the displayed and/or metered value of performance.

It is chosen that low levels of deceleration do not lower the displayed and/or metered value where these levels of deceleration correspond to the vehicle coming to rest on a flat surface without the driver braking.

The levels of accuracy required of the device differ depending upon whether it is used as a display or as a meter. Where used as a display, the requirement is that the driver receives a clear signal which shows how driving at high speeds, how braking and acceleration, can all negatively affect the fuel consumption of the vehicle. Where such a device is used for metering, i.e. by adding the instantaneous performance values over time, then either the determination of average MPG from speed and changes in speed must be carefully calibrated, at regular intervals of time and/or for the particular vehicle, or the principles by which the cumulative result is obtained must be specified; thus the cumulative units are not gallons or average MPG but a cumulative performance criterion or mean performance criterion of precise derivation.

MPG as a reference may be derived in many ways. It may be derived by transducers such as a fuel flow meter or transducer which indicates the level or amount of fuel contained in the fuel tank and other methods of using transducers to determine average fuel consumption described above, and so be changed automatically from time to time due to the state of tune of the engine or the prevailing vehicle or travelling conditions.The reference value may be determined by calculation from fuel purchases and so, again, updated from time to time; or it may be defined once only for a particular vehicle and that value retained over the time for which the device or system is used in that vehicle, and where different reference values can be set by selection of a setting on a multiple position switch or switches; or it may be defined by the direct entry of a reference value; or it may be defined by restriction of the device to a single reference value which cannot be altered except by changing the components or reprogramming them after temporary removal from the device.

The methods of determining current speed in order to determine the displayed and/or metered performance value are twofold in basic form. The first is to detect some moving part of the vehicle so as to obtain from a measure of the movement of that part a measurement of the distance travelled by the vehicle. Such methods include sensors on a vehicle speedometer part, any rotating part of the axle, wheel drive shaft, or transmission assembly. Alternatively, one can detect the engine revolution rate, determine which gear is engaged by comparing road speed with engine speed, and use these values.

Secondly, one can use accelerometers in an approximately horizontal plane to detect change in speed and, via computation, determine current speed. Acceieration in an approximately vertical plane is used in one embodiment of the invention to determine acceleration or deceleration due to climbing or descending hills and to adjust the displayed output of performance accordingly.

Other reference criteria include the display of cost per unit distance of fuel consumed as a function of speed and change of speed. In one embodiment of the invention the device display and/or meter fuel consumption is given in units of fuel per unit distance, e.g. litres per 100 kilometres, and/or cost of fuel per unit distance, e.g. pence per 1 0 miles, and/or display consumption of fuel as units of fuel per unit distance.

Other reference criteria may be of a purely symbolic nature with a performance mean of, say, 10 units. In this embodiment, the displayed and/or metered value responds in an exactly similar way to speed and change in speed as if the reference value were a mean fuel consumption rate, but the actual value displayed is symbolic and not quantitatively defined. In one embodiment the peak vehicle performance corresponds to a value above the mean of, say, 10, and is thus dimensioned in units of distance per unit of fuel, whilst in a second embodiment peak vehicle performance corresponds to a value below the mean and is thus dimensioned in units of fuel per unit distance.

The display of the driver performance information may be in any one of several ways, e.g. a digital display, an analogue display of a scalar value on a dial or bar, or a syntactical display using words such as "poor", "good", "average". The driver performance information may be displayed in conjunction with other information on a single or separate display, e.g. a digital display of cumulative travel costs and analogue display of driver performance.

The quantity of fuel added to the tank, and the unit cost of fuel, can be determined from any of the following methods using a keyboard for data entry.

(a) Enter the cost of a unit quantity of fuel (e.g. cost per litre) and the total expenditure on fuel added to the tank.

(b) Enter the unit cost of the unit quantity of fuel and the number of those units of fuel (e.g. litres) added to the tank.

(c) Enter the total cost of fuel added to the tank and the total number of units of fuel (e.g. litres) added to the tank.

(d) Enter the quantity of fuel purchased for a unit of currency (e.g. 1) and either the total quantity of fuel added to the tank or the total cost of fuel added to the tank.

Then, by computation, an average fuel consumption per unit distance estimate can be made by dividing the quantity of fuel added to the tank by the distance travelled, both since a given reset to zero datum. Alternatively, another method is to include details of the volume of the fuel tank, and the current fraction of tank full, entering this information via the keyboard to appropriate electronic stores within the system. A fuel consumption per unit distance calculation can be made whenever the current tank fraction is entered and provided that all additions of fuel to the tank have been recorded. In order to produce accurate cost per unit distance information, this system requires that the vehicle should travel a minimum distance, e.g. 200 miles, or consume a minimum volume of fuel, over which distance and fuel consumption information will be retained.

A description will now be given of the mode of entry of data and selection of data to be displayed by a preferred embodiment of the travel cost display device.

The keyboard preferable includes both a visual display, e.g. an LED display, together with an array of keys which must be pressed in an appropriate sequence in order to view or alter any function or to produce an output. The layout and syntax of a preferred embodiment of keyboard will now be described by way of example and with reference to Fig. 1 of the accompanying drawing which is a schematic representation of a typical keyboard. Fig. 2 is a schematic diagram of the general layout of the device.

Referring to the drawing, it will be seen that the keyboard has a visual display 10, for example an LED display. To the left of the visual display 10 are three horizontally arranged keys 1 2a, 1 2b and 1 2c which are hereinafter referred to as nouns, and which are linked to "distance", "fuel" and "MPG" respectively. There are two further keys, namely a "cost" key 1 4a and a "set" key 1 4b, which can be used in conjunction with the noun keys.

The method of using the keyboard and various function algorithms will now be described.

Only the noun and cost keys are active whilst the car is in motion, and these four keys determine which of six functions are displayed to the driver. The three noun keys are programmed such that only one of them may be on at once, whilst the cost key may be operated in conjunction with the three noun keys to give the following six outputs. Their algorithms are also given as general examples.

Distance = distance since reset Fuel = fuel volume consumed since reset e.g.

distance MPG MPG = algorithm of speed and average MPG to give basic performance MPG' peaking at 30 m.p.h. and equal to average MPG at 20 m.p.h. and 56 m.p.h. Braking and acceleration algorithm is superimposed on to the above, to give the final displayed output of performance MPG.

Distance cost = (Mile cost + fuel cost/MPG) x Distance since reset MPG cost = Fuel cost per 10 miles derived from performance MPG and price per mile of fuel (gal. cost/performance MPG) x 10.

Fuel cost = Cost of fuel used since reset.

MPG Algorithm T = Tank volume F=ygals D, =z miles AD = Distance increment since last MPG calculation AG = Gallons of fuel bought since last MPG calculation.

x = Fraction of tank full.

let M = MPG, let AT = (l-x)T When MPG sequence is entered M Dr + AD F + AG + AT and M is displayed and stored for recall.

Do is reset to DF= yM + ATM In order to function, the device must receive data from the keyboard to calibrate the device and to receive regularly updated information such as the fuel purchase data. Inputting data via the keyboard follows a simple sequence or syntax:

NOUN SET OR NUMBER SET < C J J Thus, the set key is pressed, then the noun or cost key; the noun or cost keys then change their function and become number keys each one rolling corresponding digits on the display 1 0. When the required number has been set up on the display, the set key may be pressed again to enter the value into the device and so complete the data entry sequence.There are four entry sequence beginning with 'set', one for each of the noun or cost keys. The sequence that is being entered is indicated by a small LED associated with each switch. To aid the user, certain messages are displayed at the time of data entry.

A second level of data entry is used to calibrate the device. This is achieved by holding the set key depressed for a given number of seconds and changing from 'set' mode to 'calibration' mode. This change is indicated on the device by initially displaying the word 'set' and then displaying the word 'cal' when calibration mode is entered. There are four calibration data entry sequences, one for each of the noun or cost keys.

KEY SEQUENCES Calibration Sequences Press 'set' key display SET after 4 seconds display CAL and enter calibration mode; thus; Set (4 seconds): noun or cost: number: set Cal Cost = Sets distance cost per unit distance (e.g. pence/mile) Cal MPG = Sets mean MPG. This is also a way of viewing the previous calculation of MPG by the tank fraction method, i.e. it shares the same storage location.

Cal Fuel = Sets tank volume.

Cal Distance = sets the number of pulses per unit distance coming from speedo.

Set Sequences Set: noun or cost: number: set Set Distance = This set distance to zero and fuel used to zero on trip display. Rolling over from zero sets up (i) trip distance elapsed.

Set Fuel = enters the new fuel purchase in money using sequence set: fuel: number: set, then displays number*: set, where the cost per unit volume is entered.

(*The previous unit cost of fuel is displayed for amendments , is a blank Figure on the display).

Claims (14)

1. A vehicle fuel consumption indicator system comprising a transducer which provides a measure of distance travelled by the vehicle, computing means receiving the output of said transducer and arranged to compute road speed therefrom, storage means arranged to hold one or more reference values of fuel consumption, in-vehicle keying means by means of which reference data or updating data can be entered and fed to said computing means and/or said storage means, said computing means being arranged to compute, using at least said reference value or values, the instantaneous fuel consumption, and display means providing a continuously updated indication of said instantaneous fuel consumption.

2. A vehicle fuel consumption indicator system comprising a transducer which provides an output signal representative of road speed, computing means receiving the output of said transducer, storage means arranged to hold one or more reference values of fuel consumption, in-vehicle keying means by means of which reference data or updating data can be entered and fed to said computing means and/or said storage means, said computing means being arranged to compute, using at least said reference value or values, the instantaneous fuel consumption, and display means providing a continuously updated indication of said instantaneous fuel consumption.

3. A system as claimed in claim 1 or 2, in which the computed value of fuel consumption is dependent on immediately preceding changes in vehicle speed.

4. A system as claimed in any preceding claim, in which the computed value of fuel consumption is dependent on acceleration of the vehicle.

5. A system as claimed in any preceding claim, in which the computer value of fuel consumption is dependent on deceleration of the vehicle.

6. A system as claimed in any preceding claim, which includes an accelerometer responsive to movements in a vertical plane and connected to said computing means thereby to vary the computation if the vehicle is travelling uphill or downhill.

7. A system as claimed in any preceding claim, in which said computing means receives signals from the vehicle braking system and is responsive to application of the brakes.

8. A system as claimed in any preceding claim, which includes a further transducer providing signals indicative of engine speed.

9. A system as claimed in any preceding claim, which includes one or more further transducers providing for said computing means a signal or signals indicative of engine temperature and/or manifold vacuum and/or choke setting and/or engaged gear setting.

10. A system as claimed in any preceding claim, in which said display means comprises a metering display providing an indication of the cumulative, average value of fuel consumption.

11. A system as claimed in any preceding claim, in which said display means can produce a display of travel costs.

1 2. A system as claimed in claim 11, in which the travel cost display is capable of displaying the actual or predicted fuel cost for a given journey, and/or the actual or predicted total cost of fuel plus a distance charge reflecting non-fuel related costs for a given journey.

13. A system as claimed in any preceding claim, in which keying means comprises a first set of three keys respectively associated with distance, fuel and fuel consumption, a key associated with cost, and a setting key.

14. A system as claimed in claim 13, in which the setting key is also operable as a calibration key in a second mode.

1 5. A vehicle fuel consumption indicator system substantially as hereinbefore described with reference to the accompanying drawing.