Abstract:
A signal proportional to a vehicle speed is applied to one input terminal of a differential amplifier, and the output of the differential amplifier is fed back to the other input terminal of the differential amplifier via a switch the on-time of which is proportional to consumed fuel. Then, the output of the differential amplifier is taken out as a fuel consumption signal for informing a vehicle driver the momentary fuel consumption of the vehicle on a voltmeter or ammeter.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an analog fuel consumption signal generator for vehicles for indicating the amount of instantaneous fuel consumption. 
     It is important for economic driving of a vehicle that the driver may be informed of the instantaneous fuel consumption of a vehicle. 
     DESCRIPTION OF THE PRIOR ART 
     The conventional vehicle fuel consumption indicator counts the distance the vehicle ran consuming a constant amount of fuel and generates a digital signal of the counted distance as a fuel consumption. 
     However, since the conventional indicator finally indicates analog value by a pointer, it requires a complex digital-to-analog (D/A) converter for converting the digital signal to an analog signal. 
     Moreover, since the time during which a constant amount of fuel is consumed is dependent upon the running condition of vehicle, the period of time required for an indication is different for each new indication. Furthermore, the conventional indicator generally needs the results of dividing the vehicle speed by the amount of fuel consumption per unit time, and therefore the circuit arrangement thereof is complicated by various restrictions. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an analog fuel consumption signal generator for a vehicle for easily indicating the amount of instantaneous fuel consumption of a vehicle and informing the driver of the instantaneous fuel consumption of a vehicle by applying a signal proportional to vehicle speed to one input terminal of a differential amplifier, feeding the output of the differential amplifier back to the other input terminal of the differential amplifier via a switch the on-time of which is proportional to the consumed fuel, and using the output of the differential amplifier as a fuel consumption signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a basic diagram of the analog fuel consumption signal generator according to this invention. 
     FIG. 2 is an electrical circuit diagram of one embodiment of the invention. 
     FIG. 3 is an electrical circuit diagram of another embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be explained with reference to the preferred embodiments in conjunction with the accompanying drawings. 
     Referring to FIG. 1, there is shown a frequency-to-voltage (f-V) converter 1 for converting the frequency of a vehicle speed pulse to an analog voltage. This converter 1 generates at a point a a voltage V 1  proportional to the vehicle speed, v, that is, V 1  ∝v. Shown at 2 is a differential amplifier, which produces at a point b a voltage of G 1  (V 1  -V 2 ), where V 2  is the voltage at a point d and G 1  the gain. Shown at 3 is a constant current circuit which produces a current proportional to the voltage at point b and has trans conductance of G 2 . Shown at 4 is a switch the on-period T ON  of which is proportional to the consumption of fuel per unit time. R represents a grounded resistor. The current at point c is given by G 1  G 2  (V 1  -V 2 ) when the voltages at points a and d are V 1  and V 2 , respectively. The current Id at point d is given by ##EQU1## Following Eq. (2) is derived from Eq. (1) ##EQU2## If, now, the condition of ##EQU3## is satisfied, Eq. (2) can be approximated to ##EQU4## because the 1/R in Eq. (2) can be neglected. In other words, the potential at point b corresponds to the fuel consumption. 
     FIG. 2 is a circuit diagram of one embodiment of the analog consumption signal generator for a vehicle having a electronic fuel injection system according to the invention. 
     In FIG. 2, the voltage 12 V of a power supply 5 is regulated to 6 V by a voltage regulator 6. Shown at 7 is a reed switch for generating a vehicle speed pulse. This reed switch 7 is turned on and off by a rotary-type permanent magnet (not shown) mounted on a meter cable in accordance with the speed of a vehicle thereby to detect the vehicle speed. The amount of fuel consumed is detected from a signal of the valve opening time of a fuel injector at the junction e between the injector coil 9 of the fuel injection system and a transistor TR8 for driving the injector. 
     The vehicle speed signal from the reed switch 7 is converted from frequency to the analog voltage by the simple frequency-to-voltage converter 1 formed of resistors R 1  and R 2 , capacitors C 1  and C 2  and diodes D 1  and D 2 . The voltage from the output of the converter 1 is applied to the differential amplifier 2 formed of transistors TR 1  to TR 4  and resistors R 5  to R 7 . The output of the differential amplifier 2 is converted to a current by the constant current circuit 3 formed of a resistor R 10  and a transistor TR 5 . The output current from the constant current circuit 3 charges a smoothing capacitor C 3  via a transistor TR 6  of the switch 4 during the injection time. The voltage across the smoothing capacitor C 3  is applied to the base of the transistor TR 4  as one input terminal of the differential amplifier 2. As a result of this feedback, the differential amplifier 2 produces the base-ground voltage of the transistor TR 3  divided by the on-time of the transistor TR 6 . Thus, a voltmeter 8 connected in the differential amplifier 2 indicates the fuel consumption of a vehicle. In this case, the unit of fuel consumption is 1 km/l or 1 mile/gallon. 
     Table 1 lists the constants of the circuit elements. The resisters R 3 , R 8  and R 11  are used for biasing the transistors TR 3 , TR 4  and TR 5 , respectively. 
     
                       TABLE 1______________________________________TR.sub.1 to TR.sub.4 = 2SC458               R.sub.3, R.sub.8 = 360 kΩTR.sub.5, TR.sub.6 = 2SA733               R.sub.4, R.sub.9 = 3.9 kΩD.sub.1, D.sub.2 = 1SI588               R.sub.5 = 3 kΩC.sub.1 = 0.1 μF R.sub.6, R.sub.7 = 1 kΩC.sub.2 = 47 μF  R.sub.10 = 5.1 kΩC.sub.3 = 22 μF  R.sub.11 = 15 kΩR.sub.1 = 3.9 kΩ               R.sub.12,13 = 100 kΩR.sub.2 = 100 Ω______________________________________ 
    
     The operation of the analog fuel consumption signal generator for a vehicle according to this invention will be explained. 
     In FIG. 2, while a vehicle with such a generator is running, the reed switch 7 thereof repeats turning-on-and-off operation at the rate of 4×637 times/60 km/h. During on-operation of the reed switch 7, the capacitor C 1  discharges and during off-operation thereof, the capacitor C 2  is charged via the diode D 1 . During one off-operation of the reed switch 7, the electricity charged to the capacitor C 1  is moved and the capacitor C 2  discharges via the resistor R 4  to reach an equilibrium state in which it is charged to a voltage proportional to the vehicle speed. 
     The transistors TR 1  and TR 2  serve as a current mirror circuit for supplying a constant current to the emitters of the transistors TR 3  and TR 4 . 
     The transistors TR 3  and TR 4  serve as a differettial amplifier for amplifying the voltage difference between the capacitors C 2  and C 3  so that an amplified voltage difference is produced across the resistor R6. The transistor TR5 which receives this amplified voltage difference at the base provides an electric current proportional to the amplified voltage difference through the collector thereof so that the capacitor C3 is charged by the electric current when the transistor TR6 is rendered conductive. 
     In the electronic fuel injection system employed in this invention, the injection time is proportional to the fuel consumption. During the fuel injection, the transistor TR 8  for driving the injector is turned on, and the transistor TR 6  is similarly conducting. Thus, the on-time T ON  of the transistor TR 6  becomes proportional to the fuel consumption. 
     The voltage across the resistor R 6  as the output of the differential amplifier 2 can be detected by the voltmeter 8, and the scale is proportional to the fuel consumption. 
     FIG. 3 shows another embodiment of the analog fuel consumption signal generator for vehicle according to this invention. Referring to FIG. 3, there are shown a transistor amplifier TR 7  provided in the constant current circuit which is formed of the transistor TR 5  and the resistor R 10  and an indicator 10 such as an ammeter connected to the collector of the transistor TR 7 . The operation of the embodiment of FIG. 3 is the same as that of the embodiment of FIG. 2 except that the fuel consumption of the vehicle is indicated by the ammeter 10 not by the voltmeter 8 as shown in FIG. 2, and thus will not be described. 
     While discrete components are used in the embodiments of the invention as shown in FIGS. 2 and 3, operational amplifiers may be employed as the frequency-voltage (f-V) converter 1 and the differential amplifier 2. 
     In addition, for detection of vehicle speed, a Hall effect element or a photointerrupter can be used in place of the reed switch 7. 
     In accordance with this invention, the voltage proportional to the fuel consumption can be produced at the output end of the differential amplifier by applying a voltage proportional to the vehicle speed to one input terminal of the differential amplifier, converting the output voltage of the differential amplifier to a current and feeding the current back to the other input terminal of the differential amplifier in proportion to the fuel consumption rate. Therefore, the fuel consumption can easily be detected every moment by a voltmeter or the like.