WO2000017610A1

WO2000017610A1 - Method and apparatus for estimating fuel consumption for a vehicle

Info

Publication number: WO2000017610A1
Application number: PCT/SE1999/001542
Authority: WO
Inventors: Peter Paeglis
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 1998-09-08
Filing date: 1999-09-06
Publication date: 2000-03-30
Anticipated expiration: 2001-03-08
Also published as: SE9803029D0; SE9803029L

Abstract

The present invention relates to a method and an arrangement for estimating the fuel consumption of a vehicle with an engine. The vehicle incorporates a control unit (1) which by means of values representing the engine's speed and the position of a throttle control (3) calculates the fuel quantity to be supplied to the engine in order to obtain a desired torque and which controls an injection pump (7) with the object of supplying said calculated fuel quantity. The fuel quantity consumed is measured at least once. The measured fuel quantity consumed and the calculated fuel quantity are compared and a calibration parameter is determined, after which the fuel consumption is continuously estimated by applying said calibration parameter to correct the calculated fuel quantity.

Description

Method and apparatus for estimating fuel consumption for a vehicle

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The invention relates to a method and an arrangement for estimating the fuel consumption of a vehicle according respectively to the preamble to patent claim 1 and the preamble to patent claim 11.

GB 2 090000, DE 2 440 398, US 4444 047 and US 4475 380 have made methods and arrangements known for measuring the fuel consumption of vehicles by estimating fuel consumption by means of values representing engine speed and throttle control position.

These known methods assume that a calculated quantity of fuel which a control unit is intended to supply to the engine by means of an injection pump is actually supplied in practice. However, the calculated fuel quantity is not always entirely correct in practice. These methods thus provide a fuel consumption estimate which is not sufficiently accurate for determining, e.g. in laboratory measurements, the fuel consumption of a vehicle.

Other known methods for fuel consumption estimation employ volumetric flowmeters which measure the volume of the fuel which is led from the vehicle's fuel tank. This involves a return flow of fuel from an injection pump via a cooler and back to the injection pump without passing through the fuel tank. The disadvantage of such a system is that said volumetric flow is influenced by the temperature and pressure of the fuel.

Moreover, equipment has to be provided, e.g. in the form of sensors, and such equipment may be expensive while at the same time causing in the fuel flow system an encroachment which may of itself influence the accuracy of fuel consumption measurement.

SUMMARY OF THE INVENTION

The object of the present invention is to make possible very exact estimation of the fuel consumption of a vehicle. A further endeavour is to achieve such estimation by using information which is already available from existing equipment in the vehicle. This object is achieved by the method mentioned in the introduction through the features indicated in the characterising part of patent claim 1. Comparison at least once of measured and calculated fuel quantity provides an estimate of the degree of error in the calculated fuel quantity, an error which can be expressed by means of a calibration - parameter. Thus the fuel consumption can thereafter continue to be estimated with great accuracy by applying said calibration parameter to correct the fuel quantity calculated.

According to a preferred embodiment of the invention the fuel quantity consumed is measured by establishing the volume consumed from the vehicle's fuel tank. By this means the vehicle's actual fuel consumption can be measured fairly exactly. The fuel quantity consumed is preferably measured by establishing the fuel quantity which has to be supplied to the vehicle's tank after the end of a period of operation in order to restore the fuel level in the tank to the same level as at the beginning of the period of operation. Such measurement of the fuel quantity in the tank involves only conventional fuel tank equipment with a flowmeter which indicates the fuel quantity put into the tank, and the possibility of refuelling being carried out to a specific level in the tank. Such a level may in its simplest form correspond to a completely full fuel tank. Said calibration parameter may therefore incorporate a second calibration constant calculated as the ratio between said measured fuel quantity added and the calculated fuel quantity for the period of operation. The fuel consumption thereafter is estimated by applying said second calibration constant to correct the corresponding calculated fuel quantity. The result is correction for a constant percentage error which is also expected to continue to occur during operation of the vehicle. A very good estimate of the actual fuel consumption can thereby be obtained.

According to another preferred embodiment of the invention, the fuel quantity consumed is measured by establishing the fuel quantity supplied to the engine by one revolution of an injection pump at specific engine speed and load. In this case the fuel quantity consumed per revolution of the injection pump can be measured in an engine test rig by means of a fuel weigher. Such measurement may preferably be carried out with an engine running at no load at idling speed and its normal working temperature, which may for example be for a diesel engine an idling speed of about 500 rpm and a working temperature of 80°C. In this case, said calibration parameter may incorporate a first calibration constant which denotes the difference between the measured and calculated fuel quantity per revolution of the injection pump at said engine speed and load. Thereafter the fuel consumption continues to be estimated by applying said first calibration constant to correct said calculated fuel quantity per revolution of the injection pump. Experience has shown that the error between the calculated fuel quantity supplied per revolution of an injection pump and the measured actual quantity is relatively constant. It is therefore appropriate for the first calibration constant to denote the difference between the measured and calculated fuel quantity per revolution of the injection pump. This known error value being substantially constant and hence substantially independent of the engine's load means that in percentage terms the error will be greater when small fuel quantities are supplied than when large fuel quantities are supplied. Using the first calibration constant to adjust the calculated quantity per revolution of injection pump makes it possible to obtain an accurate estimate of the actual fuel consumption, but in order to further increase the accuracy of fuel consumption estimation a calibration parameter may preferably incorporate both said first and second calibration constants.

According to another preferred embodiment of the invention, information on the distance run by the vehicle is used to calculate the fuel consumption per distance run. Information on the distance run can be obtained from a tachometer or tachograph, in which case the fuel consumption may be expressed in, for example, litres per kilometre. Having the control unit calculate at very short intervals of time the fuel quantity which is to be supplied to the engine makes it possible to estimate a substantially instantaneous fuel consumption. Here again the calculated fuel quantity may be corrected by applying said first calibration constant and/or second calibration constant in order to estimate the instantaneous fuel consumption. The fuel consumption may also be estimated as an average consumption during any desired period. The driver of the vehicle may preferably himself select the beginning and end of such a period.

The present invention also includes an arrangement for fuel consumption estimation according to the above method. The arrangement therefore incorporates a first means designed to measure at least once the fuel quantity consumed, a second means designed to receive values representing the measured fuel quantity consumed and the calculated fuel quantity and to calculate a calibration parameter, and a third means designed to estimate the fuel consumption by applying said calibration parameter to the subsequently calculated fuel quantity. Said first means may consist of measuring equipment for establishing the fuel quantity injected per revolution of an injection pump and/or the fuel quantity consumed from a tank. Said second and third means may consist of one or more computation units which are preferably integral parts of a fuel gauge. Such computation units can therefore estimate a vehicle's fuel consumption with good accuracy. Such an estimated fuel consumption value may thereafter be indicated by a display or other indicating device on the vehicle's instrument panel, including the possibility of indicating both the instantaneous fuel consumption and the average consumption during any desired period.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described as examples below with reference to the attached drawings, in which:

Fig.1 depicts schematically an arrangement according to the invention for estimating the fuel consumption of an engine in a vehicle, and

Fig.2 depicts schematically a method according to the invention for estimating the fuel consumption of an engine in a vehicle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig.1 depicts an arrangement according to the present arrangement for estimating the fuel consumption of a vehicle with an engine. The vehicle may for example consist of a heavy-duty truck driven by a diesel engine. The vehicle incorporates a control unit 1 which is designed to receive a multiplicity of information including a value representing the vehicle's speed, which may be obtained from a tachometer or tachograph 2, a value representing the position of a throttle control 3 and a value representing the engine's speed. Information on the engine's speed may be obtained by means, for example, of a sensor 4 detecting the speed of a flywheel 5 on the engine's output shaft. The control unit 1 uses the values representing the engine's speed and the position of the throttle control 3 to calculate the fuel quantity which has to be supplied to the engine in order to achieve the desired torque. The control unit 1 controls the position of a control rod 6 by means of a voltage. The position of the control rod 6 determines the fuel quantity per revolution ^~" which is to be supplied by an injection pump 7. The equipment described above is conventional and is employed in a large number of existing vehicles.

According to the invention, a computation unit 8 is connected to the control unit 1. The computation unit 8 may be an integral part of a fuel gauge 9 and be designed to receive from the control unit 1 information on the calculated fuel quantity which is instantaneously to be supplied to the engine. The fuel supplied per revolution of the injection pump as calculated by the control unit 1 can be summated in a register in the computation unit 8 so that the calculated fuel quantity supplied during a period of time can be determined.

The calculated fuel quantity which the injection pump 7 is intended to supply to the engine is in practice not always supplied in the correct quantity. One source of error may be that the actual value of the fuel quantity supplied per revolution of the injection pump may differ from the desired calculated fuel quantity. There is also a multiplicity of other sources of error which are more difficult to define and may arise from the particular injection pump 7.

The invention relates to a method which is intended to estimate fuel consumption on the basis of the fuel quantity supplied to the engine as calculated by the control unit 1. Making such an estimate of fuel consumption with great accuracy involves catering for the influence of said sources of error. This may be done by means of a calibration parameter.

To estimate such a calibration parameter, the actual fuel quantity consumed V2 may be measured by establishing the fuel quantity which has to be supplied to the vehicle's fuel tank after a period of operation in order to restore the fuel level in the tank to the same level as at the beginning of the period of operation. This fuel quantity V2 is most easily measured between two full refuellings of the tank. The measured fuel quantity V2 and the calculated fuel quantity which has been supplied during the period of operation can be compared to arrive at a ratio between the measured fuel quantity V2 and the calculated fuel quantity. This ratio may be used as a second calibration constant K2. This constant K2 may be calculated in the computation unit 8 after information on the measured fuet quantity V2 has been provided. K2 is calculated as the ratio between the calculated summated fuel quantity during the period and said measured fuel quantity V2. Thereafter the computation unit 8 will estimate the fuel consumption by applying said second calibration constant K2 to correct the fuel quantity calculated in the control unit. Such a calibration constant K2 corrects generically all types of sources of error.

A known source of error arising from the injection pump 7 is that it does not supply exactly per revolution the fuel quantity which has been calculated by the control unit 1. Experience has shown that the difference between the calculated fuel quantity and the measured injected fuel quantity is substantially constant per revolution of the injection pump 7 and is therefore independent of the quantity of fuel injected per revolution. This source of error will therefore in percentage terms be greatest at low injection quantities and decrease progressively at larger injection quantities. Being aware of this makes it clear that the second calibration constant K2 will not always provide exact adjustment of the calculated fuel quantity. If, for example, the calibration constant K2 is determined during a period of operation at high engine load, i.e. with a large value for fuel quantity supplied per revolution of the injection pump 7, the calibration constant K2 will not provide accurate correction of a fuel quantity calculated at low engine load, i.e. with a small fuel injection quantity per revolution of the injection pump 7. For this reason, a first calibration constant Kl may be determined to denote the difference between the measured and calculated fuel quantity per revolution of the injection pump 7. This first calibration constant Kl is preferably determined with the engine running at no load at a normal idling speed and a normal working temperature, which for a diesel engine corresponds to an idling speed of 500 rpm and a working temperature of 80°C. The actual fuel quantity supplied per revolution of the injection pump 7 may be measured in an engine test rig by fuel weigher. This value VI may be supplied to the computing unit 7 and the first calibration constant Kl be thereby determined. Being provided with knowledge of the calibration constants Kl and K2, the computation unit 8 estimates the subsequent fuel consumption by applying said calibration constants Kl and K2 to correct the fuel consumption calculated by the control unit 1. The computation unit 8 can thus provide a very accurate estimate of the actual fuel consumption. ^~

Fig.2 depicts schematically a method for fuel consumption estimation according to the present invention. The method is initiated, at reference 10, by the vehicle's fuel tank being filled with fuel. Reference 11 represents the commencement of measurement of the fuel quantity injected into the engine running at no load at an idling speed of 500 rpm and an engine temperature of 80°C, values which correspond respectively to normal idling speed and normal working temperature. The fuel quantity VI per revolution of the injection pump 7 is measured in an engine test rig with fuel weigher. The fuel quantity initiated by the control unit 1 and intended to be supplied to the engine per revolution of the injection pump 7 is also determined. In cases where the computing unit 8 cannot directly receive the value representing the fuel quantity calculated by the control unit, this calculated fuel quantity may be determined indirectly by reading an average value of the position of the control rod 6 at said idling speed. The calibration constant Kl is then determined at reference 12 as the difference between the measured VI and the calculated fuel quantity per revolution of the injection pump 7. The calibration constant Kl is thereafter used by the computation unit 8 to estimate the fuel consumption.

At reference 13, the vehicle is fully refuelled, after which the vehicle, at reference 14, is operated for a period. During this period of operation, the fuel quantity calculated by the control unit 1 is continuously summated in a register situated in the computation unit 8. At the end of the period of operation, the calculated fuel quantity supplied during the period of operation is thus stored in that register.

Thereafter the vehicle's fuel tank is fully refuelled, at reference 15, and the fuel quantity supplied is measured. The fuel quantity supplied thus corresponds to the fuel quantity V2 consumed during said period of operation, since the tank has been restored to the same filling level as at the beginning of the period of operation. The calibration constant K2 representing the ratio between the measured V2 and the calculated fuel quantity consumed during said period of operation is then determined at reference 16. This constant K2 is thereafter stored in the computation unit 8 for subsequent correction of the fuel quantity calculated by the control unit 1. To ensure that the calibration constant K2 is given an accurate value, the method according to references 14 to 16 may be repeated a number of times. -

Thereafter, the vehicle may, at reference 17, continue to run with the fuel consumption being estimated by the computation unit 8 by applying said calibration constants Kl and K2 to adjust the fuel quantity calculated by the control unit 1. The fuel gauge 9 can thus indicate an accurate estimate of the momentary fuel consumption, as also the average consumption during a period of operation.

The invention is in no way limited to the embodiments described but may be varied freely within the scopes of the patent claims. There is for example the possibility of calculating other calibration parameters than the calibration constants Kl and K2 described above, in order to adjust a calculated fuel consumption with the object of achieving an accurate estimate of the actual fuel consumption of a vehicle.

Instead of obtaining signals representing various vehicle parameters directly from various sensors, the same signals may be obtained from other control systems in the vehicle in which these signals are already available, either as directly measured values or as values calculated on the basis of other measured values/parameters.

The invention is concerned with how fuel consumption can be determined with great accuracy, as is for example particularly desirable in the case of laboratory measurements or in cases where it is possible to adopt the particular measures required for ensuring a high degree of measurement accuracy. The invention may also be used as an accessory on serious-manufactured vehicles in order to provide the driver with information on the vehicle's fuel consumption continuously during the life of the vehicle. In such cases the arrangement may advantageously be supplemented by a display unit on the vehicle's instrument panel to display the vehicle's fuel consumption.

Claims

PATENT CLAIMS

1. Method for estimating the fuel consumption of a vehicle, where the vehicle incorporates an engine and a control unit (1) which by means of values representing the engine's speed and the position of a throttle control (3) calculates the fuel quantity to be supplied to the engine and which controls an injection pump (7) with the object of supplying said calculated fuel quantity, characterised in that the fuel quantity consumed is measured at least once , that the measured fuel quantity consumed and the calculated fuel quantity are compared and a calibration parameter is determined, and that the fuel consumption is estimated by applying said calibration parameter to correct the calculated fuel quantity.

2. Method according to claim 1, characterised in that the fuel quantity consumed V2 is measured by measuring the volume consumed from the vehicle's fuel tank.

3. Method according to claim 2, characterised in that the fuel quantity consumed V2 is measured by measuring the fuel quantity which has to be supplied to the vehicle's fuel tank after a period of operation in order to restore the fuel level in the tank to the same level as at the beginning of the period of operation.

4. Method according to any one of the foregoing claims, characterised in that said calibration parameter incorporates a second calibration constant K2 which is calculated as the ratio between said measured fuel quantity V2 and said calculated fuel quantity, and that the fuel consumption is thereafter estimated by said second calibration constant K2 being applied to correct the calculated fuel quantity.

5. Method according to any one of the foregoing claims, characterised in that the fuel quantity consumed is measured by establishing the fuel quantity VI which is supplied to the engine by one revolution of an injection pump at specific engine speed and load.

6. Method according to claim 5, characterised in that said fuel quantity VI is determined at idling speed.

7. Method according to claim 5 or 6, characterised in that said calibration parameter incorporates a first calibration constant Kl which represents the difference - between the measured VI and the calculated fuel quantity per revolution of the injection pump at said engine speed and load, and that the fuel consumption continues thereafter to be estimated by said first calibration constant Kl being applied to correct said calculated fuel quantity per revolution of the injection pump.

8. Method according to any one of the foregoing claims, characterised in that information is provided concerning the distance run by the vehicle and that the fuel consumption is estimated per distance run.

9. Method according to claim 8, characterised in that an instantaneous fuel consumption is estimated.

10. Method according to claim 8 or 9, characterised in that an average consumption during any desired period is estimated.

11. Arrangement for estimating the fuel consumption of a vehicle, where the vehicle incorporates an engine and a control unit (1) which by means of values representing the engine's speed and the position of a throttle control (3) is designed to calculate the fuel quantity to be supplied to the engine in order to achieve the desired engine torque and which controls an injection pump (7) with the object of supplying said calculated fuel quantity, characterised in that a first means is designed to measure at least once the fuel quantity consumed, that a second means is designed to receive values representing the measured fuel quantity consumed and the calculated fuel quantity and to calculate a calibration parameter, and that a third means is designed to estimate the fuel consumption by applying said calibration parameter to correct the fuel quantity thereafter continuously calculated.