Abstract:
A fuel consumption rate detecting apparatus comprises a circuit for representing fuel consumption amount per unit time, a pulse generator for generating a pulse signal whose pulse width is inversely proportional to the fuel consumption and whose frequency is inversely proportional to the vehicle speed, and meter circuit for measuring the mean value of the pulse signal, which is, in turn, proportional to the fuel consumption rate.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus for detecting fuel consumption rate of a vehicle in the form of, for example, Km/l, which continuously informs a driver of current fuel consumption rate thereby leading him to accomplish the most economic drive of the vehicle. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a new apparatus for indicating the fuel consumption rate in the form of the ratio of the running distance of the vehicle and the amount of the fuel consumed in such running. 
     It is another object of the present invention to provide an apparatus for detecting the fuel consumption rate which is available not only to a vehicle equipped with an electronically controlled fuel injection system but also the vehicle without such fuel injection system. 
     It is a further object of the present invention to provide an apparatus for detecting fuel consumption rate of a vehicle in which an amount of fuel consumed in a unit time is detected, a pulse signal of the frequency proportional to the vehicle speed and of the pulse width inversely proportional to the amount of fuel consumed in a unit time is generated, and the mean value of said pulse signal is obtained in the form of the ratio of the running distance of the vehicle (Km) and the amount of the fuel consumed (liter) in such running. 
    
    
     DESCRIPTION OF THE DRAWING 
     FIG. 1 is the circuit diagram of a first embodiment according to the present invention, 
     FIG. 2 is a front view of the indicator shown in FIG. 1, 
     FIGS. 3 and 4 are graphs showing characteristic curves of the computing circuit in FIG. 1, 
     FIG. 5 (a), (b), (c), (d) and (e) show respective voltage characteristic curves on the specific portions of the circuit shown in FIG. 1, 
     FIG. 6 is a voltage characteristic curve of the pulse signal flowing through indicator shown in FIG. 1, and 
     FIG. 7 shows the circuit diagram of a second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, a vehicle speed detector 1 generates a speed pulse signal of the frequency proportional to vehicle speed, which, for example, is incorporated into a speed meter. The vehicle speed detector 1 comprises a magnet 1a carried on a speed meter cable and a reed switch 1b disposed in the vicinity of the rotating locus of the magnet 1a. The magnet 1a and the reed switch 1b are so constructed that the reed switch opens and closes four times each turn. When the vehicle speed is 60 Km/H, for example, it opens and closes 637 × 4 times in a minute. A computing circuit 2 computes the fuel consumption speed from injection pulses applied on an electromagnetic valve 20b by a controlling circuit 20a of an electronically controlled fuel injection system which is well known. The computing circuit comprises bias resistors 2a and 2b, an input transistor 2c, its collector resistor 2d, an inverting transistor 2e, its collector resistor 2f, a diode 2g, a charging and discharging transistor 2h, a charging resistor 2i, a capacitor 2j, an operational amplifier 2k and resistors 2l and 2m for defining an amplitude of the operational amplifier 2k. When the transistor 2e is made nonconductive, the capacitor is charged through the resistor 2f, diode 2g and resistor 2i and, at the same time, through the resistors 2h. When the transistor 2e is made conductive, on the other hand, the capacitor 2j is discharged through the resistor 2h and the transistor 2e. The electromagnetic valve 20b is opened only during the high level of the injection pulse to inject fuel in proportion to the duration of the high level pulse. An operation circuit 3 provides, in synchronism with the speed pulse signal, a pulse signal which is inversely proportional to the fuel consumption speed. The operation circuit 3 comprises a R-S flip-flop circuit 3a, a transistor 3b, a capacitor 3c, a resistor 3d, an operational amplifier 3e, input resistors 3f and 3g, a voltage dividing resistor 3h and a comparator 3i. The R-S flip-flop circuit is operated in response to the vehicle speed pulse signal. When the flip-flop circuit is set, the transistor 3b is made nonconductive. The operational amplifier 3c forms an integration circuit in combination with the capacitor 3c. The comparator 3i generates a comparison signal which becomes low and, in turn, resets the R-S flip-flop circuit when the output voltage of the integration circuit exceeds a predetermined voltage. The duration in which the flip-flop circuit is kept set by one of the vehicle speed pulses until it is reset by the succeeding comparison signal is so determined that the flip-flop circuit has been reset by the time when the next one of the vehicle speed pulses is applied to the flip-flop circuit 3a. A meter circuit 4 measures the mean value of the pulse signal current which is an output signal of the R-S flip-flop circuit 3a. The meter circuit 4 comprises an output transistor 4a, a current limiting resistor 4b, a smoothing capacitor 4c, an indicator for indicating the fuel consumption rate 4d. The indicator 4d which is of a moving coil type as shown in FIG. 2 indicates the mean current flowing through the current limiting resistor 4b. Connected to the meter circuit 4 is a battery 5, which is generally regulated at a constant voltage. 
     In operation, when an engine of a vehicle starts, the electronically controlled fuel injection system 20 generates an injection pulse signal in synchronism with the rotation of the engine and drives the electromagnetic valve 20b to open, which, in turn, supplies fuel to the engine under a constant pressure. The injection pulse signal is further applied to the computer circuit 2 at the terminal 2n to effect the input transistor 2c and the inverting transistor 2e to thereby charge and discharge the capacitor 2j. When the terminal 2n is brought to the high level by the injecting pulse signal, the input transistor 2c is made conductive and the inverting transistor 2e is made nonconductive, whereby the capacitor 2j is charged through the resistor 2f, the diode 2g and the resistor 2i and in parallel therewith the resistor 2h. 
     When, on the other hand, the input terminal 2n is brought to the low level, the input transistor 2c is made nonconductive and the inverting transistor 2e is made conductive, whereby the capacitor 2j is discharged through the resistor 2h and the transistor 2e. The mean value of the capacitor voltage varies with the rotation of the engine and, also, the valve opening period, as shown in FIG. 3. From the figure, it is apparent that the mean value of the capacitor voltage is proportional to the product of the valve opening period and the engine rotation, which represents fuel consumption speed. The capacitor voltage is then inverted by the inverting amplifier comprising the operational amplifier 2k, the negative resistor 2l and the input resistor 2m to get a negative voltage which is proportional to the product of the valve opening period and the number of the engine rotation as shown in FIG. 4. 
     In the case the vehicle is running, the vehicle speed pulse signal shown in FIG. 5 (a) whose frequency is proportional to the vehicle speed is applied to the R-S flip-flop circuit 3a, which is set to generate the low level voltage at its Q output terminal as shown in FIG. 5 (b). The low level voltage of the Q output terminal, in turn, renders the transistor 3b nonconductive to cause the integrator comprising the capacitor 3c, resistor 3d and operational amplifier 3e to integrate the output signal of the computer circuit 2. As shown in FIG. 5 (d), the integrated signal voltage increases with a gradient proportional to the fuel consumption speed which corresponds to the output voltage of the computer circuit. When the integrated signal voltage exceeds a predetermined voltage defined by the comparator 3i, a low level comparison signal shown in FIG. 5 (e) appears to thereby reset the flip-flop circuit 3a. Consequently, the voltage of the Q output terminal becomes high to thereby render the transistor 3b conductive and the capacitor 3 c discharges in an instant. Thus, the output of the comparator 3i returns to the high level, which resets the R-S flip-flop 3a to the original state. Since the Q output terminal of the R-S flip-flop circuit 3a maintains the high level during the period from when it is set until it is reset as shown in FIG. 5 (c), the time duration of the output pulse is inversely proportional to the fuel consumption speed. 
     The output pulse signal which is generated by the operation circuit 3 at the terminal Q of the flip-flop circuit every time the vehicle speed pulse signal is applied thereto is applied to the meter circuit 4 in which the output transistor 4a switches on and off according to the output pulse signal of the operation circuit 3 the current flowing through the ampere meter 4d in the manner shown in FIG. 6. 
     When one cycle of the applied output pulse is assumed T (sec.), its pulse width is t (sec.), the resistance of the current limiting resistor is R (Ω), the internal resistance of the amperemeter is r (Ω) and the battery voltage is E (V), then the mean value of the current I is expressed as follows: 
     
         I = E (t/T) .sup.. (1/R+ n)                                (1) 
    
     When the vehicle speed is assumed Vs (Km/H), then the cycle time T is expressed as follows: 
     
         T = kl (1/Vs)                                              (2) 
    
     where kl is a constant. 
     When the fuel consumption speed is assumed Vf (L/H), then the aforementioned pulse width t is expressed as follows: 
     
         t = k2 (1/Vf)                                              (3) 
    
     where k2 is another constant. 
     In the above expression (1), if another constant k3 is substituted for E (1/R+n) and the expression (2) and (3) are substituted for (t/T), then the mean value of the current I is expressed as follows: 
     
         I = k3 (t/T) = k3 (k2/k1).sup.. (Vs/Vf) = K (Vs/Vf)        (4) 
    
     From the above expression (4), it is apparent that I is proportional to the fuel consumption rate (Km/l). 
     Connected in parallel with the ampere meter 4d is a capacitor 4c for preventing oscillation of the ampere meter 4d in the lower speed range where T&gt;&gt;t. 
     In FIG. 7, there is shown another embodiment according to the present invention, which is used for a vehicle equipped with no electronically controlled fuel injection system. 
     In this embodiment, a detecting circuit 200 is substituted for the computing circuit 2 of the first embodiment. The detecting circuit 200 comprises a conventional oscillating circuit 201 for generating a signal of a predetermined frequency, a transistor 202, a current limiting resistor 203, a differential transformer 204, and a suction vacuum detector 205. The differential transformer 204 is composed of a primary coil 204a, secondary coils 204b and 204c, and a magnetic core 204d. The suction vacuum detector 205 is provided with a bellows for converting suction vacuum into mechanical motion to effect the movement of the magnetic core 204d, whereby the differential transformer 204 generates an electric signal responsive to the movement of the magnetic core 204d. A rectifying circuit 206, which is of the well known construction, rectifies both the output voltages of the secondary coils 204b and 204c. A tachometer 207 which is also well known detects the rotation of the engine and generates a rotational signal of the frequency proportional to the engine rotation. A conventional D-A converter 208 converts in the well known manner the rotational signal into a voltage proportional to the engine rotation, which is applied on a bias resistor 203. An operational amplifier 209, with resistors 210 and 211, inverts the output of the rectifying circuit 206 which corresponds to the product of the suction vacuum and the engine rotation, which is generally known, is proportional to the fuel consumption speed. 
     In operation, the oscillating circuit 201 generates a oscillation signal, which makes the transistor 202 turn on and off. As a result, the primary coil 204a of the differential transformer 204 is energized and deenergized correspondingly, thereby generating voltages responsive to the mechanical motion of the moving core 204d on both the secondary coils 204b and 204c. Those voltages are rectified and smoothed by the rectifying circuit 206 to obtain a direct current signal corresponding to the suction vacuum. If the voltage applied on the resistor 203 is unchanged, the direct current signal becomes proportional to the suction vacuum. However, since the voltage applied to the bias resistor 203 is the output voltage of the D-A converter 208, the direct current voltage of the rectifying circuit 206 is proportional to the product of the engine revolution and the suction vacuum. The polarity of the output of the rectifying circuit 206 is then inverted by the operational amplifier 209 with the resistor 210 and 211 in the same manner as the first embodiment.