Method and apparatus for measuring fuel consumption in internal combustion engines

The relative fuel consumption of an internal combustion engine, i.e., the fuel consumption per unit time or unit distance, is determined on the basis of measurements to ascertain the exhaust gas temperature. Based on the existing functional relationship between the exhaust gas temperature and fuel consumption, the measured exhaust gas temperature is combined with a signal related to engine speed and is used to provide a datum related to the fuel consumption per unit time. A transducer which detects the distance traveled by the vehicle is used to control an integrating circuit which generates a signal related to the fuel consumption per unit distance traveled. The signals may be used for visual displays to the operator or automatic control of other engine subsystems, for example exhaust gas recycle systems or fuel supply systems.

BACKGROUND OF THE INVENTION 
The invention relates broadly to internal combustion engines. More 
particularly, the invention relates to a method and an apparatus for 
measuring and monitoring the consumption of fuel in an internal combustion 
engine. The fuel consumption is monitored by an apparatus which employs no 
moving parts, thereby eliminating many potential sources of error. 
In known mechanisms and devices for measuring fuel consumption, there is 
included a mechanically operating flow rate meter, usually a miniature 
turbine or some other rotating device, disposed within the fuel channel 
and equipped with indicators, for example signal generators which are 
coupled to the rotating shaft. The rotational speed of the shaft is 
related to the flow rate of fuel which may then be translated into a 
measurement of the fuel consumption per unit time or per distance 
traveled. 
The known systems which include a rotating member have the disadvantages of 
relatively high constructional expense, poor reliability, and short and 
long term error sources, for example bearing wear and others. 
OBJECT AND SUMMARY OF THE INVENTION 
It is thus a principal object of the invention to provide a method and an 
apparatus for measuring and indicating the prevailing fuel consumption 
without the use of moving mechanical parts, thereby eliminating sources of 
error due to mechanical characteristics. It is a further object of the 
invention to provide a fuel flow measurement apparatus which operates 
externally of the hydraulic fuel line and thereby eliminates the necessity 
for hydraulic connections and possible leakages. 
These and other objects are attained according to the invention by 
providing a method and apparatus in which the measurement of the exhaust 
gas temperature is the basic measurement performed for a measurement of 
the fuel consumption. In particular, the invention provides a measurement 
of the exhaust gas temperature in immediate proximity of the exhaust 
valves of the engine. The invention further provides a processing of the 
signal received from the exhaust gas temperature sensor on the basis of 
engine speed to determine the fuel consumption per unit time and/or the 
measurement of the distance traveled by the vehicle so as to permit 
measurement of the fuel consumption per unit distance traveled. It is a 
feature of the method and apparatus of the present invention that they may 
be used not only for informing the operator of the motor vehicle of the 
prevailing fuel consumption but also for purposes of automatic control, 
for example to control the injected fuel quantity. 
It is a feature of the present invention that the apparatus required to 
perform the method can be easily embodied as an integrated electronic 
circuit. 
In one embodiment of the invention, each of the exhaust valves of the 
engine has associated with it an individual exhaust gas temperature 
sensor, the signals of these sensors being averaged to provide an input 
signal for the apparatus. 
The invention will be better understood as well as further objects and 
advantages thereof become more apparent from the ensuing detailed 
description of a preferred exemplary embodiment taken in conjunction with 
the drawing.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a general diagram illustrating an internal combustion engine 10 
provided with an induction tube 11 including a throttle valve 12 and an 
exhaust gas manifold 17 leading to an exhaust pipe 13. FIG. 1 further 
shows a temperature sensor 16 located in the exhaust manifold 17, a first 
rpm transducer 18 for generating a signal related to engine speed and a 
further speed transducer 19 shown in association with a vehicle wheel 20 
for generating a signal related to the wheel speed or the distance 
traveled by the vehicle over the road. The signals from the various 
transducers, i.e., the temperature signal .theta., the engine speed signal 
"n" and the distance signal "s" are seen to be applied to the inputs of a 
general electronic controller 15 which generates a signal that is 
indicative of the fuel flow rate as a function of time or distance. 
The electronic controller 15 will be described in greater detail below in 
conjunction with the illustrations of FIGS. 3 and 4a. The practical 
possibility of deriving information regarding the fuel flow or fuel 
consumption on the basis of the exhaust gas temperature is evident from 
the family of curves shown in FIG. 2. The diagram of FIG. 2 shows the 
exhaust gas temperature as a function of the fuel consumption per engine 
stroke with each of the four curves shown representing a single constant 
engine speed. It will be noticed that the variation of exhaust gas 
temperature as a function of fuel consumption per engine stroke is linear 
and that, moreover, the various curves related to different engine speeds 
are substantially parallel, i.e., have substantially the same slopes. 
Accordingly, it is possible to make a unique determination of the fuel 
consumption with only a measurement of the exhaust gases and one 
additional measurement, namely the engine speed. 
In order to insure highly precise measurements, the exhaust gas temperature 
must be monitored in isolation of other disturbing influences. In 
particular, the probe must be so located as to measure a temperature 
unaffected by heat transfer from the exhaust gas to portions of the 
exhaust pipe further downstream. The measurements are also affected by the 
temperature of the fresh air induced by the engine. Accordingly, it is 
suitable to dispose a temperature sensor in the induction tube and to 
perform a correction on the basis of the induction tube temperature signal 
or to base the measurement on the difference of the induction tube air 
temperature and the exhaust gas temperature. 
A further factor affecting the characteristic curves depicted in FIG. 2 is 
the air density, for example due to the atmospheric pressure or altitude. 
The exhaust gas temperature increases with decreasing air density and a 
correction for this influence may be made by disposing a suitably placed 
air pressure sensor or by providing a variable indicator, for example a 
movable bezel which can be adjusted to the prevailing altitude or air 
pressure. 
The fuel consumption measurements and the signals derived in these 
measurements which relate the fuel mass per stroke to the exhaust gas 
temperature can be used for automatic control or forward control of 
several engine processes, for example exhaust gas recycling, transmission 
control, or the like. The particular purpose to which the invention is put 
determines the characteristics and the construction of the temperature 
sensor, in particular its sensitivity or response time. For automatic 
control purposes, the temperature sensor must generally have a very rapid 
response characteristic which, in turn, requires low-mass thermal elements 
or resistance measurement sensors without massive supports. However, this 
requirement must be balanced against the concurrent requirement of being 
resistant to mechanical stresses and thermal stresses. 
If the fuel consumption measurements serve only for informative purposes, 
it is possible to use temperature sensors having substantially less 
sensitivity and longer time constants and these sensors may be constructed 
substantially more robust and may also include protective packaging or 
mountings. Such sensors are, for example, NTC transducers or resistance 
probes made of metal, for example, platinum wires or thin nickel layers 
combined with appropriate electronic circuits to produce the desired 
linear relationship between exhaust gas temperature as a function of the 
specific fuel consumption. 
The specific fuel consumption, i.e., the fuel mass per engine stroke, is 
not usually as important to the vehicle operator as the fuel consumption 
per unit time or the fuel consumption per distance traveled. In order to 
transform the specific fuel consumption into one of the two indications, 
there is required some further electronic processing as will be explained 
below with the aid of FIGS. 3 and 4. 
The block circuit diagram of FIG. 3 is seen to include a correcting circuit 
25 which corrects the signal from the temperature sensor 16 and which has 
control inputs for receiving signals related to engine speed "n", the 
induction tube temperature .theta. and a zero point calibration input 0. 
The output of the correcting circuit 25 is applied to the time constant 
adjusting input of a monostable multivibrator 27 which is triggered at an 
input 28 by the signal from the engine speed transducer 18. Following the 
multivibrator 27 is a low pass filter 29 having an output contact 30 to 
which is connected an indicator 31 of known construction for showing the 
fuel consumption per unit time, i.e., the fuel rate of consumption. 
The circuit shown in FIG. 3 further includes a controllable integrator 35 
having a trigger input 36 connected to the output of an integrating 
control circuit 37 which is engaged by a secondary tachometer 19. The 
integrator circuit integrates the output-signal of the low pass filter 29, 
converted into current by the voltage to current converter 38. Following 
the integrator 35 is a transfer circuit 39 which is connected to control a 
further indicating device 40 which indicates the fuel consumption per unit 
distance traveled. The temperature sensor 16 generates an output signal 
which is related to the temperature surrounding the sensor, i.e., the 
temperature of the exhaust gas from the engine. This signal is corrected 
on the basis of engine speed and induction tube temperature and may be 
suitably shifted to assume a zero calibration. The output signal of the 
correcting circuit 25 constitutes the control variable for the monostable 
multivibrator 27 which is triggered at the frequency of the crankshaft or 
camshaft speed "n". The time constant of the monostable multivibrator 27 
depends on the magnitude of the signal from the transducer 16 and 
determines the pulse width of the output signal of the multivibrator 27 
which, in turn, represents a corrected exhaust gas temperature. The pulse 
width t.sub.i of the output signal of the flip-flop 27 represents a 
particular amount of fuel per engine stroke as represented in the family 
of curves of FIG. 2. This signal is received by the low pass filter 29 
which transforms the series of pulses into an arithmetic average voltage 
which thus represents a fuel consumption per unit time. The relation 
between these variables may be gleaned from the following equation in 
which U.sub.max represents the output signal of the monostable 
multivibrator 27, T is the period of the engine speed signal generated by 
the tachometer 18 and t.sub.i is the pulse width of the pulses from the 
monostable multivibrator 27. 
EQU U=U.sub.max .multidot.(t.sub.i /T).varies.U.sub.max .multidot.(Q.sub.K 
/time) 
The measurement of the fuel consumption as a function of distance traveled 
is made by the functional blocks labeled 19, 37, 35, 39, and 40 in FIG. 3. 
The function of these circuits is more easily understood in conjunction 
with the detailed circuit diagram of FIG. 4a and the associated pulse 
diagram of FIG. 4b. 
The circuit diagram of FIG. 4a is a detailed representation of the block 
diagram of FIG. 3 and the blocks of FIG. 3 are generally represented in 
FIG. 4 by dash-dotted lines. The circuit of FIG. 4a shows the temperature 
sensor 16, the correcting circuit 25 embodied here as a controllable 
amplifier, a signal amplifier 50 connected behind the tacho generator 18, 
the voltage-controlled monostable flip-flop 27 as well as the low pass 
filter 29. Following the filter 29 is the voltage-to-current converter 38, 
embodied here as an amplifier-transistor combination with feedback. 
Following the distance tacho generator 19 is a signal amplifier 51 feeding 
an integrating control circuit 37 including a flip-flop 52, a further 
flip-flop 53 and a NAND gate 54. The inputs of the NAND gate 54 receive 
the output signal of the flip-flop 53 and 52, respectively. The integrator 
35 is an operational amplifier 55 with capacitive feedback whose inverting 
input is connected via a resistor 56 and a transistor 57 to a positive 
supply line 58 as well as via a diode 59 to the output of the 
voltage-to-current converter. The junction of the diode 59 and the 
converter 38 is connected to one electrode of a transistor 60 the other 
conductor electrode of which is connected to the aforementioned positive 
supply line 58. The base of the transistor 60 is connected to the junction 
of the output from the flip-flop 52 and the input to the flip-flop 53. The 
output of the NAND gate 54 is connected to the base of the transistor 57. 
The output signal of the integrator 35 behaves in a manner depicted in FIG. 
4b. The illustration shows a first increasing region persisting for a time 
t.sub.k followed by a region at a constant amplitude during a subsequent 
time t.sub.s and followed finally by a region in which the integrating 
capacitor discharges. 
When the integrating capacitor charges, the transistors 57 and 60 are 
blocked and a well-defined current flows from the voltage-to-current 
converter 38 into the capacitor 61 which thereby produces an increase of 
the voltage across the capacitor 61 having a slope "k". For this part of 
the process, the following relation holds: 
EQU k=(.DELTA.U.sub.s /t).varies.current.varies.(Q.sub.k /time) 
The integration proceeds during the time span t.sub.k which is the time 
elapsing between two switching events of the flip-flop and during which 
the vehicle has traveled a particular distance. 
EQU t.sub.K.varies. 1/velocity.varies.time/unit distance 
After the expiration of the time interval t.sub.k the voltage across the 
capacitor 61 is 
EQU U.sub.s =K.multidot.t.sub.K .varies.Q.sub.k /unit distance 
Thus, the value U.sub.s is the desired fuel consumption as a function of 
distance traveled. 
After the expiration of the integration time t.sub.k, the flip-flop 52 
terminates the integration by causing the transistor 60 to conduct and 
thereby assume the flow of the current from the voltage-to-current 
converter 38. For a short time t.sub.s, the duration of which is 
determined by the output signal of the monostable flip-flop 53, the 
voltage across the capacitor 61 remains constant. During this time 
t.sub.s, the voltage across the capacitor is transmitted by a transfer 
circuit 39 to a further capacitor 63 where it remains available for use by 
the subsequent indicating device 40 to show the fuel consumption as a 
function of distance. The transfer circuit 39 may be embodied, for 
example, as an electronic switch 39a, for example an MOS switch, which is 
controlled by the output of the multivibrator 53 and which is connected to 
the aforementioned capacitor 63. The charge in the capacitor 63 and 
therefore the voltage previously held by the capacitor 61 is retained on 
the capacitor 63 until the arrival of the subsequent pulse of duration 
t.sub.s. 
After the expiration of the time t.sub.s, the transistor 57 is opened by 
the NAND gate 54 and causes a discharge of the integrating capacitor 61 to 
a selected initial state from which the integration process begins anew at 
the occurrence of the next triggering of the flip-flop 52. 
The method and apparatus described above for monitoring and measuring the 
fuel consumption in a motor vehicle may be used for any purpose of 
interest. Among these are, for example, indicating the fuel consumption as 
a function of time or distance, but also the automatic control of the 
operation of the engine. When the measured results are used as a control 
signal, the temperature sensor 16 must have fast response times to permit 
rapid and exact automatic control. While the diagram of FIG. 1 shows only 
a single temperature sensor 16 located in the exhaust gas manifold, it may 
be more suitable to provide a temperature sensor at several or even at 
each exhaust valve to generate a median or summed value of the output 
signals from all these sensors to provide a signal input temperature 
signal for the apparatus. 
The foregoing relates to preferred exemplary embodiments of the invention, 
it being understood that other embodiments and variants thereof may be 
possible without departing from the spirit and scope of the invention.