Fuel supply indicator arrangement for a motor vehicle fuel tank

A fuel supply indicator arrangement for a motor vehicle fuel tank includes a device for generating a fuel consumption signal to measure the fuel consumption of an internal combustion engine. A fuel supply indication is provided by an end position switch arrangement in the fuel tank including several end position switches located above a fuel withdrawal point at heights corresponding to predetermined fill levels, the end position switch arrangement being of such configuration that it emits an end position switch signal depending on which of the end position switches is immersed in fuel, and an electric circuit calculates a value for the fuel supply indication from the fuel consumption signal and the end position switch signals.

BACKGROUND OF THE INVENTION
 This invention relates to fuel supply indicators for motor vehicle fuel
 tanks which include a fuel consumption detector to measure the fuel
 consumption of an internal combustion engine.
 Conventional motor vehicle fuel tanks include a fuel level detector for a
 fuel supply indicator. The fuel level detector is a lever or dip tube
 sensor with a float that rises and falls with the fuel level. This
 reciprocating motion varies a resistance by way of a contact bridge or
 linkage and consequently varies a current in a circuit, and the current is
 measured by an instrument which is used to indicate fuel level or fuel
 supply. The scale of the instrument in the circuit is calibrated in fuel
 volume. However, one disadvantage of this arrangement is that the fuel
 supply indication depends also on the inclination of the vehicle, so that
 a faulty fuel supply indication may result if the vehicle is inclined.
 Also, with a multichamber fuel tank, a plurality of lever or dip tube
 sensors is required, with a corresponding increase in cost. Moreover,
 these sensors only provide indications with gaps of up to five liters.
 U.S. Pat. Nos. 4,307,452 and 4,546,648 disclose arrangements for measuring
 the consumption of fuel by an internal combustion engine but those
 arrangements provide no indication of the fill level of a fuel tank.
 SUMMARY OF THE INVENTION
 Accordingly, it is an object of the present invention to provide a fuel
 supply indicator arrangement for a motor vehicle fuel tank which overcomes
 disadvantages of the prior art.
 Another object of the invention is to provide a fuel supply indicator
 arrangement producing an improved fuel supply indication which is more
 reliable in every operating condition of the vehicle.
 These and other objects of the invention are attained by providing a fuel
 supply indicator which includes an end position switch arrangement having
 at least one end position switch located above a fuel withdrawal point in
 a fuel tank at a height corresponding to a predetermined fill level, the
 end position switch arrangement having a configuration such that it
 provides an end position switch signal dependent upon whether or not an
 end position switch is immersed in the fuel, along with an electric
 circuit that computes a value for the fuel supply indicator from a fuel
 consumption signal combined with each end position switch signal.
 This arrangement has the advantage that an exact and reliable indication of
 the current fuel supply in the fuel tank is obtained in a simple and
 economical manner. The fuel supply indicator according to the invention is
 essentially independent of any rated volume of the fuel tank. Instead, the
 end position switch arrangement, with one or more end position switches,
 defines fixed points at which the fill level of the fuel tank is reliably
 indicated. Between these fixed points, the fuel consumption signal is used
 to provide an accurate fuel supply indication, since that signal is used
 to determine a volume of fuel withdrawn over time.
 In order to provide the vehicle driver with information regarding current
 operating parameters of a motor vehicle in especially advantageous manner,
 an indicating instrument is provided that is connected to the electric
 circuit to display a value representing the fuel consumption and/or a
 value representing the fuel supply.
 In an especially preferred embodiment, the electric circuit is an
 electronic circuit, in particular a microprocessor or a data processing
 device.
 For an empty fuel tank warning, the end position switch arrangement
 includes an end position switch for indicating "Empty", which is located
 at a first height above the fuel withdrawal point which corresponds to a
 minimal fill level of the fuel tank. This ensures that, even with an
 "Empty" indication, a certain volume of fuel will remain available for
 operation of the engine.
 Preferably, the end position switch for the "Empty" indication is mounted
 on a fuel withdrawal unit in the fuel tank.
 For a reserve warning indication, the end position switch arrangement
 includes a "Reserve" end position switch for a reserve indication, located
 at a second height above the fuel withdrawal point corresponding to a fill
 level of the fuel tank at or below which a reserve warning signal, such as
 for example a reserve warning light, is activated.
 Desirably, the end position switch for the "Reserve" indication may be
 mounted on a fuel withdrawal unit in the fuel tank.
 For an indication of a full fuel tank, the end position switch arrangement
 includes "Full" end position switch for a "Full" indication, located at a
 third height above the fuel withdrawal point corresponding to a maximum
 fill level of the fuel tank.
 In a preferred embodiment the end position switch for the "Full" indication
 is located on a quick vent nipple in the fuel tank so that the end
 position switch for the "Full" indication is always at a defined distance
 from a component which causes termination of operation of a filling
 nozzle. Thus, in each operating condition, a reliable "Full" indication is
 always assured.
 For example, in the case of fuel tanks having several compartments, the end
 position switch arrangement includes one additional end position switch
 located at a fourth height above the fuel withdrawal point which is
 between the first and third heights.
 Preferably, the first height is lower than the second height and the second
 height is lower than the third height.
 A simple and dependable construction is achieved by providing a holder for
 each end position switch welded into the fuel tank.
 To further enhance the accuracy of the fuel supply indication, a fuel flow
 volume measuring device, such as a through flow meter which emits a fuel
 fill signal to the electric circuit corresponding to the quantity of fuel
 that has flowed through the nozzle, is provided in a filling nozzle of the
 fuel tank and the electric circuit calculates the value for the fuel
 supply indication taking account of the fuel fill signal.
 A further improvement in accuracy of the fuel supply indication when the
 vehicle is inclined is achieved by providing an inclination sensor that
 ascertains an angle of inclination of the vehicle, or of the direction of
 gravity, and provides a corresponding inclination signal to the electric
 circuit, and an electric circuit which calculates the value of the fuel
 supply indication taking account of the inclination signal.

DESCRIPTION OF PREFERRED EMBODIMENTS
 An important aspect of the invention is the evaluation of several signals
 from different signal-generating instruments arranged in or on a fuel tank
 system of a motor vehicle. In the typical embodiment of the invention
 shown in the drawing a fuel tank having a fuel supply indicator includes a
 fuel tank 10, a tank nozzle 12, a fuel withdrawal unit 14 and a quick-vent
 nipple 16 with a vent system 18. A dotted line 17 corresponds to a minimal
 fill level of the tank and a dotted line 19 designates a maximum fill
 level of the fuel tank 10.
 The fuel withdrawal unit 14 withdraws fuel from the fuel tank 10 by way of
 a fuel line 20 to a fuel injection system or carburetor 24 of an internal
 combustion engine (not shown). A second fuel line 22 returns excess fuel
 from the carburetor or injection system back into the fuel tank 10, thus
 assuring that the carburetor or fuel infection system 24 and fuel
 injection valves (not shown), are always supplied with cool fuel.
 In addition, an integrated circuit or processor 26 receives a fuel
 combustion signal 30 from a device 28 which measures fuel consumption. In
 the illustrated embodiment, the device 28 is integrated into the fuel
 injection system 24. The processor 26 receives signals from various end
 position switches that generate corresponding end position switch signals
 which inform the processor whether or not the corresponding end position
 switch is immersed in fuel. In the illustrated embodiment, the following
 end position switches are provided.
 A first end position switch 32 for an "Empty" indication is located at a
 first height above a fuel withdrawal or fuel pump intake point 34 of the
 fuel withdrawal unit 14 and is mounted on that unit. This ensures that,
 even when an empty fuel tank is indicated, some fuel will remain available
 for delivery to the fuel injection system 24.
 A second end position switch 36 for a "Reserve" indication is located at a
 second height above a fuel withdrawal or fuel pump intake point 34 of the
 fuel withdrawal unit 14. This switch 36 is mounted on the fuel delivery
 unit 14 and defines a fill level of the fuel tank 10 at or below which a
 reserve warning light goes on, signaling the driver of the motor vehicle
 that fuel must be added.
 A third end position switch 38 for a "Full" indication is located at a
 third height above a fuel withdrawal fuel or pump intake point 34 of the
 fuel withdrawal unit 14. This end position switch 38 is mounted on the
 quick-vent valve 16 and is welded together with that value into the fuel
 tank 10. In this way, the end position switch 38 is always at a defined
 vertical distance from a component defining a fueling switch-off point,
 and a "Full" indication is always assured.
 Other additional end position switches 40 are arranged above the fuel
 withdrawal point 34 at different heights between the first and third
 heights. Such additional end position switches 40 are especially required
 in the case of multi-compartment fuel tanks.
 Thus, each individual end position switch 32, 36, 38 and 40 delivers a
 signal corresponding to a quite specific height, indicating a particular
 fill condition of the fuel tank. The end position switches 32, 36, 38 and
 40 thus define fixed points for the fill level of the fuel tank 10. Fill
 levels between these fixed points are calculated by the processor 26 using
 the fuel consumption signal 30. For example, the first height may
 correspond to a fill level from 0 to 5 liters or from 0 to 7 liters, and
 the second height to a fill level from 5 to 15 liters or 7 to 10 liters of
 fuel.
 As the fuel tank 10 is being filled up, the end position switches 32, 36,
 38 and 40, which are activated successively as the fuel level rises,
 inform the processor 26 as to the current fill level. To determine a
 precise fill level between any two of the end switches 32, 36, 38 and 40
 upon completion of a filling, a through flow measuring instrument 42 is
 provided in the tank nozzle 12, by which a volume of fuel which has flowed
 through, or been "tanked", can be determined. Using the flow volume
 measured after the last activation of an end position switch 32, 36, 38 or
 40, the processor 26 can calculate a fill level lying between two of the
 end position switches 32, 36, 38 and 40, or above or below the end
 position switches 32 or 38, respectively. In this way, it is not necessary
 that the through flow meter 42 should measure an exact value for a large
 volume to be measured. Instead, it may measure relatively inaccurately,
 since only small readings of the through flow volume become relevant at
 any one time. The through flow meter 42 operates, for example, like a
 volume meter of a tank column at a refueling station, and is preferably a
 component or pipe carrying fuel and arranged in the tank nozzle 12 or at
 some other point in the recovery fuel path.
 As the fuel tank 10 is gradually emptied during operation of the internal
 combustion engine, the processor 26 calculates the current fill condition
 of the fuel tank from the respective end position switch signals together
 with the fuel consumption signal 30 and supplies a corresponding signal to
 an indicator 44 which is readable by an operator.
 An inclination sensor in the withdrawal unit 14 generates a corresponding
 correction signal taking account of the fact that the same fill condition
 of the fuel tank can be represented by different end position switch
 signals at the processor 26 depending on whether the vehicle is inclined.
 The processor 26 performs a logic combination of all the aforesaid signals
 and, with suitable software, produces an output signal for the indicator
 44 which may, for example, be in the form of a `combi` instrument.
 In an uncalibrated initial condition, the processor 26 need only wait until
 the fill level of fuel in the fuel tank 10 passes one of the end position
 switches 32, 36, 38 and 40, preferably one of the additional end position
 switches 40. At that point, an automatic self-calibration of the system
 will take place according to the invention.
 Although the invention has been described herein with reference to specific
 embodiments, many modifications and variations therein will readily occur
 to those skilled in the art. Accordingly, all such variations and
 modifications are included within the intended scope of the invention.