GB2181873A

GB2181873A - Device for indicating the level in the fuel tank of a vehicle

Info

Publication number: GB2181873A
Application number: GB08624612A
Authority: GB
Inventors: Dipl Ing Hans-Jorg Florus; Dipl Ing Detlef Kaminski; Antonio Bucefari
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1985-10-18
Filing date: 1986-10-14
Publication date: 1987-04-29
Also published as: IT1199273B; GB8624612D0; JPH0567164B2; DE3537088C1; JPS62129724A; IT8648564A0; FR2588954A1

Abstract

A device for measuring and indicating the level in the fuel tank of a vehicle includes a level signal generator 2 the output signal from which is recorded and appropriately processed as a function of a distance-travelled signal from a distance-travelled signal generator 3 via a counter 5, and hence also as a function of the travelling speed, in order to generate an indication in a fuel gauge 15 corresponding to the level in the tank. <IMAGE>

Description

SPECIFICATION Device for indicating and measuring the level in the fuel tank of a vehicle The invention concerns a device for measuring and indicating the level in the fuel tank of a vehicle, having a level signal generator adapted to sense the level and a distancetravelled signal generator adapted to sense the distance travelled by the vehicle, the signals from which signal generators are supplied via input ports to an analysis unit for the processing of these signals and the generation of a control signal at an output port thereof, which control signal generates an indication in a fuel gauge corresponding to the level in the tank.

A device of this type is already known (German Patent 3,309,802); this is used as part of a multi-purpose electronic system, for example in an onboard computer. In this system, both the signal from the level signal generator and the signal from the distance travelled generator are supplied to the control device allocated to the fuel level measurement but for reasons which are associated with the determination of particular journey data.

It is the general practice that the level in the fuel tank is indicated continuously to the driver of a vehicle so that the amount available at any moment is visible. From this point of view, the value indicated ought to decrease as the duration of the journey increases, i.e., it should drop steadily with the distance travelled until the tank is refilled (Fig. 1). In current fuel level indicating systems, however, it is found that the indicated value can rise at times during the journey even when the tank has not been refilled. One reason for this misleading erroneous behaviour of the indication lies in the filtering of the signal from the level signal generator.The signal has a variation with time (Fig. 2) which depends on the following parameters: The liquid level in the tank moves greatly due to the travelling motions and the road conditions, and it is not possible, for design reasons, to accommodate the level signal generator at the optimimum signal generator location.

In the devices generally known up to now, the signal from the level signal generator is damped with respect to time by means of a low-pass filter, for example by means of an outlet labyrinth, sheet metal vanes on the float arm of the level signal generator, hydraulic damping at the pivoting point of the signal generator, electronic low-pass circuit, etc.

These methods, however, make only an inadequate allowance for the fact that the level in the fuel tank changes during a particular part of the journey whereas a long time can pass without the level dropping to a noticeable extent. It follows that the indication, which is damped with respect to time, can settle on a signal from the level signal generator which suggests too high a level-for example when stopping on a slope.

The invention seeks therefore to design a device of this generic type in such a way that erroneous indications of the amount of fuel are minimised.

According to the present invention there is provided a device for measuring and indicating the level in the fuel tank of a vehicle, having a level signal generator adapted to sense the level and a distance-travelled signal generator adapted to sense the distance travelled by the vehicle, the signals from which signal generators are supplied via input ports to an analysis unit for the processing of these signals and the generation of a control signal at an output port thereof, which control signal generates an indication in a fuel gauge corresponding to the level in the tank.

A device designated according to the invention, which device records the signal from the level signal generator as a function of the distance travelled and filters it digitally on the basis of a distance scale in such a way that a steadily falling time function is obtained, therefore offers a possibility of generating a meaningful indication because the level in the tank is measured during the journey when measurable changes in the level occurs and very long time damping constants can be generated because the signal from the level signal generator is analysed in terms of the distance travelled.

The constant distance-travelled signal may be generated each time a specified distance of between 100 m and 300 m, preferably 200m is travelled.

The digital filter may be designated as a recursive filter of nth order with a damping constant of approximately 10 to 30 km. The filter may be a two-stage recursive low pass filter.

One embodiment of the invention will now be described by way of example with reference to the drawing in which: Figure 1 is a diagram which shows the amount of fuel indicated as being in a tank plotted against the distance travelled, Figure 2 shows, on an enlarged scale, a diagram which represents the proportion of the signal from the level signal generator which depends on the distance travelled, plotted against the distance travelled, Figure 3 shows a block diagram of the device according to the invention and Figure 4 shows the associated flow diagram.

Referring firstly to Fig. 3 a device, indicated overall by 1, for measuring and indicating the level in the fuel tank of a vehicle consists essentially of a level signal generator 2 sensing the level of fuel in the tank, a distancetravelled signal generator 3 sensing the distance travelled by the vehicle, an analysis unit 4 and a fuel gauge 15. Within the analysis unit 4, which can be designed as a single chip micro-computer, are located, inter alia, a counter 5, a storage element 6, a signal processing stage 7 and a digital filter 8, the analysis unit 4 being itself connected to the battery voltage (at 9 and 10). The analysis unit 4 has three input ports 11, 12 and 13 and an output port 14, the reserve input 11 being here left out of consideration.

The signals from the level signal generator 2 are applied to the input port 12 of the storage element 6, while the distance-travelled signals from the distance-travelled signal generator 3 are supplied via the input port 13 to the counter 5. After a specified constant distance (for example 200 m) has been travelled, i.e., when the counter has received a particular number of distance-travelled signals, the counter generates a constant distance-travelled signal which activates the storage element 6 via a connection 5'.The storage element 6 then records the signal available to it from the level signal generator 2, which signal is supplied via the signal processing stage 7-which takes account of parameters and characteristics specific to vehicle type, such as tank geometry, reiationships in the signal generator itself, wheel geometry, etc.,-to the digital filter 8 after it has been appropriately processed. The digital filter 8 is, for example, designated as a recursive filter of the second order with a damping constant of approximately 30 km; using a filter dimensioned in this way, it is, in particular, possible to indicate even maximum consumptions without any phase displacement worth mentioning of the indication relative to the level in the tank.The filtered output signal then available at the output port 14 is, simultaneously, the control signal for generating the indication in the fuel gauge 15 corresponding to the level in the tank.

Corresponding to the specified constant distance travelled, 200m, in the example quoted, the signal from the level signal generator is therefore recorded every 200m, and the program previously described initiated so that the signals of the level signal generator are filtered as a function of distance travelled. The repetition frequency of the program is therefore dependent on the vehicle speed.

It is only when the vehicle tank is being filled and the vehicle is stationary that the time function of the rising tank level is measured, the variation with time of the signal voltages of the level signal generator, so that the instantaneous level is indicated directly to the driver. This can be done if the assumption is made that the vehicle is at rest when no distance travelled signals are recorded within a period of, for example, 500 ms. After this time, the level is cyclically recorded with a period of 500 ms and a conclusion drawn on whether the tank is being filled or the vehicle is simply not parked horizontally from the variation of the level with time that has been determined.If it is recognise that the vehicle tank is being filled, the indication then follows the fuel level with no appreciable damping, i.e., the indication of the amount of fuel currently in the tank is available to the driver immediately.

Furthermore, if the reserve contact closes when the vehicle is being driven, so that an additional signal is supplied to the analysis unit 4 via the reserve input port 11, the indication is then only switched over to "reserve" when the reserve contact has remained closed without interruption for a distance travelled of, for example, 3 km; this prevents the appearance of an undefined and confusing alternation of the fuel gauge between "fuel level" and "reserve".

The invention does not, however, simply exclude a false indication of the amount of fuel; increased indication accuracy is also obtained so that it is both possible to provide scaling of any given indication in litres and also to effect a digital indication which explicitly indicates the residual amount of fuel.

Claims

1. A device for measuring and indicating the level in the fuel tank of a vehicle, having a level signal generator adapted to sense the level and a distance-travelled signal generator adapted to sense the distance travelled by the vehicle, the signals from which signal generators are supplied via input ports to an analysis unit for the processing of these signals and the generation of a control signal at an output port thereof, which control signal generates an indication in a fuel gauge corresponding to the level in the tank, wherein, in use, the distance-travelled signal of the distance-travelled signal generator is supplied to a counter of the analysis unit, which counter generates a constant distance-travelled signal each time a specified distance has been travelled, the constant distance-travelled signal activates a storage element of the analysis unit to accept the signal available to it from the level signal generator, the accepted signal being supplied via a signal processing stage to a digital filter of the analysis unit, the output signal of which filter forms the control signal.

2. A device according to claim 1, wherein the constant distance-travelled signal is generated each time a specified distance of between 100 m and 300 m is travelled.

3. A device according to claim 2, wherein said specified distance is 200m.

4. A device according to claim 1, wherein the digital filter is designed as a recursive filter of nth order with a damping constant of approximately 10 to 30 km.

5. A device according to claim 1, 2, or 3, wherein the digital filter comprises a twostage recursive low pass filter.

6. A device for measuring and indicating the level in a fuel tank of a vehicle substantially as described herein with reference to the accompanying drawings.