Temperature-compensated engine fuel delivery

A fuel delivery system for an internal combustion engine that includes a fuel pump responsive to application of electrical power for delivering fuel under pressure to the engine. A pressure sensor supplies a pressure signal as a function of fuel pump output pressure. Electrical circuitry is responsive to the pressure signal for applying electrical power to the pump. A temperature sensor is operatively coupled to the circuitry for automatically varying the pump power signal to increase fuel pump output pressure when temperature at the temperature sensor exceeds preselected threshold temperature.

The present invention is directed to fuel delivery systems for internal 
combustion engines, and more particularly to a system and method for 
improving engine performance at high engine/fuel temperatures. 
BACKGROUND AND OBJECTS OF THE INVENTION 
It has heretofore been proposed to supply fuel to an internal combustion 
engine by means of a pressure-controlled electric-motor fuel pump and a 
one-way or non-return fuel line that connects the pump to fuel injectors 
at the engine. For example, U.S. Pat. No. 4,951,636 discloses a fuel 
delivery system for internal combustion engines in which an electric-motor 
fuel pump supplies fuel under pressure to one or more fuel injectors 
carried by the engine. An engine air intake manifold is carried by the 
engine and supplied with combustion air. A pressure sensor is responsive 
to a pressure differential between the fuel injector and the air intake 
manifold for controlling a pulse width modulated drive signal applied to 
the fuel pump so as to maintain substantially constant pressure 
differential between the fuel and combustion air across the injector. U.S. 
Pat. Nos. 5,001,934, 5,044,344 and 5,148,792 disclose other internal 
combustion engine fuel delivery systems in which fuel delivery is 
responsive to fuel pressure. 
Among the many design criteria for internal combustion engine fuel delivery 
systems is the ability to provide sufficient fuel at high engine/fuel 
temperature conditions for starting and operation of the engine. A typical 
"hot soak" test for fuel delivery systems is to operate an automobile at 
high ambient temperature until the engine is hot, and then terminate 
operation of the engine, and therefore the engine cooling system, while 
maintaining high ambient temperature so that the engine temperature and 
temperature under the automobile hood increase significantly. Under these 
conditions, fuel within the engine fuel rail may vaporize. When it is then 
attempted to operate the automobile, the engine may fail to start, or if 
started may fail to idle or run smoothly. It is a general object of the 
present invention to provide a fuel delivery system and method for 
internal combustion engines that yield satisfactory performance under 
normal operating conditions and provide improved performance at high 
engine/fuel temperature conditions as compared with the prior art, and 
that are economical to manufacture and implement in a mass production 
environment. It is a more specific object of the present invention to 
provide a fuel delivery system and method of the described character that 
improve hot restart, idling and drive-away performance. 
SUMMARY OF THE INVENTION 
Fuel pressure is controlled at an internal combustion engine in accordance 
with a presently preferred embodiment of the invention by sensing fuel 
temperature both above and below a preselected temperature threshold. 
Below the temperature threshold, a preselected substantially constant fuel 
pressure characteristic is maintained at the engine, such as a 
substantially constant pressure differential across the fuel injector(s) 
as taught by the patent noted above. Above the temperature threshold, fuel 
pressure at the engine is automatically increased over and above the 
preselected temperature characteristic. Such pressure increase preferably 
is a preselected function of temperature, either a step-function pressure 
increase at the preselected temperature threshold, or a gradual (e.g., 
linear) pressure-increase as a function of temperature between the 
preselected temperature threshold and a second higher temperature 
threshold. In this way, fuel pressure is automatically increased at the 
engine under high engine/fuel temperature conditions, improving 
hot-restart of the engine, and reducing rough idle and drive-away stumble 
under extremely hot conditions. 
A fuel delivery system for an internal combustion engine in accordance with 
the preferred embodiments of the invention includes a fuel pump responsive 
to application of electrical power for delivering fuel under pressure to 
the engine. A pressure sensor supplies a pressure signal as a function of 
fuel pump output pressure. Electrical circuitry is responsive to the 
pressure signal for applying electrical power to the pump. A temperature 
sensor is operatively coupled to the circuitry for automatically varying 
the pump power signal to increase fuel pump output pressure when 
temperature at the temperature sensor exceeds the preselected threshold 
temperature. The temperature sensor preferably is responsive to fuel 
temperature, but alternatively may be responsive to ambient under-hood 
temperature around the engine. The temperature sensor may be integral with 
the pressure sensor for automatically modifying the pressure signal above 
the preselected temperature threshold. Alternatively, the temperature 
sensor may comprise a separate sensor element that provides an electrical 
temperature signal employed by the pump power control circuitry for 
modifying the pressure sensor signal, which is the primary pump control 
signal of the delivery system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 illustrates a fuel delivery system 10 in accordance with the present 
invention as comprising a fuel rail 12 that receives fuel under pressure 
from an electric-motor fuel pump 14 (FIG. 2), and a combustion air intake 
manifold 16 that receives combustion air at atmospheric pressure through 
an intake filter (not shown) or at elevated pressure from a turbocharger 
(also not shown). One or more fuel injectors 18 are disposed between fuel 
rail 12 and air manifold 16, and are responsive to electrical signals from 
an engine control unit or the like for delivering fuel under pressure from 
rail 12 into manifold 16 adjacent to the intake ports of associated 
cylinders. A control unit 20 is mounted on fuel rail 12 within an 
enclosure 22. Unit 20 includes a pressure sensor 24 having a first input 
responsive to pressure of fuel within rail 12, and a second or reference 
input connected to air manifold 16 by a conduit 26 so as to be responsive 
to air pressure within manifold 16. A temperature sensor 28 is disposed 
within enclosure 22, and is responsive to temperature of fuel within rail 
12. Pressure sensor 24 and temperature sensor 28 provide corresponding 
electrical signals to a compensation circuit 30, which receives electrical 
power from the automobile electrical system represented by a battery 32, 
and supplies a control signal to the pump drive circuitry (FIG. 2) for 
applying electrical power to pump 14. 
Referring to FIG. 2, pressure sensor 24 preferably comprises a 
piezoelectric strain gauge sensor of the type disclosed in above-noted 
U.S. Pat. No. 5,001,934, which provides an electrical signal to an 
amplifier 34 within compensation circuit 30 as a direct function of fuel 
pressure within rail 12. The output of amplifier 34 is fed to the 
inverting input of an amplifier 36, which has its non-inverting input 
connected to receive a reference voltage indicative of desired pump outlet 
fuel pressure under normal operating conditions. The output of amplifier 
36 is fed to a pulse width modulation amplifier 38, which provides a 
control signal to an output power circuit 40. The output of power circuit 
40 alternately switches between high and low digital levels at a frequency 
and/or duty cycle, preferably at fixed and variable duty cycle, that 
varies as a function of desired pump output pressure. Output power circuit 
40 preferably comprises an FET switch that alternately connects and 
disconnects vehicle power source 32 (FIG. 1) to the motor 42 of motor/pump 
14. Motor 42 drives the pump 44 of motor/pump 14 for supplying fuel under 
pressure to fuel rail 12 (FIG. 1) from a fuel supply or tank 46. Combined 
motor/pump 14 may be of the type disclosed in U.S. Pat. Nos. 5,122,039 and 
5,148,792. 
Temperature sensor 28, which may comprise a thermistor or other suitable 
temperature sensor, is connected to a temperature compensation circuit 48 
within compensation circuit 30. Temperature compensation circuit 48 
compares the input signal from temperature sensor 28 with a preselected 
temperature threshold--i.e., preselected as a function of engine design 
parameters and/or desired operating characteristics--and provides a 
temperature compensation signal to the non-inverting input of amplifier 36 
as a preselected function of temperature above the temperature threshold. 
Such preselected function may comprise a step function 50, whereby a 
preselected voltage is added to the reference voltage at the non-inverting 
input of amplifier 36 above the temperature threshold of temperature 
compensation circuit 48, automatically effectively to increase the 
pressure reference level, and thereby automatically to increase the 
effective level of the electrical power signal applied to pump 14 and 
increase pump output pressure. Preferably, the stepped pressure increase 
of pump outlet pressure is on the order of about 15 to 20 percent, such as 
an increase of 10 psi over a nominal fuel pressure of 55 psi when fuel 
temperature reaches a threshold level of 200.degree. F. Alternatively, 
temperature compensation circuit 48 may apply a compensation signal to the 
non-inverting input of amplifier 36 that increases linearly 52 between 
lower and upper temperature thresholds, thereby automatically linearly 
increasing pump outlet pressure as temperature varies between such 
thresholds. For example, pump outlet pressure may automatically be 
increased 10 psi over and above the nominal operating pressure of 55 psi 
as fuel temperature varies between a lower threshold of 100.degree. F. and 
a upper threshold of 250.degree. F. In either event, fuel pressure is 
automatically increased at the engine as a function of engine/fuel 
temperature so as to improve starting, idle and drive-away characteristics 
of the engine under high temperature conditions. 
FIG. 3 illustrates a modification to FIG. 2 in which the temperature sensor 
28a is incorporated in the pressure sensor 24a. Below the preselected 
threshold pressure, pressure sensor 24a operates in the same manner as 
pressure sensor 24 in FIG. 2, providing a signal to amplifier 36 for 
comparison to the preselected reference level to drive PWM amplifier 38 
and the pump motor. Above the temperature threshold setting of sensor 28a, 
sensor 28a alters the operating characteristics of pressure sensor 24a so 
as to vary the pressure sensor output signal automatically, as a step or 
linear function of temperature as described above, as a combined function 
of temperature and pressure. 
FIG. 4 illustrates another modification 56 to the embodiment of FIGS. 1 and 
2 in which pressure sensor 24 is disposed at the fuel pump as disclosed in 
above-noted U.S. Pat. Nos. 5,044,344 and 5,148,792. Temperature sensor 28 
is disposed so as to be responsive to engine temperature or ambient 
under-hood temperature surrounding the engine. Otherwise, operation of the 
embodiment in FIG. 4 is identical to that hereinabove described in 
connection with FIGS. 1 and 2. 
FIG. 5 is a functional block diagram that illustrates operation of all 
embodiments of the invention in FIGS. 1-4. The temperature input is fed to 
temperature compensation function 48, which supplies either a stepped or 
linear compensation characteristic that is summed with the desired 
pressure reference set point. The difference between this sum and the 
output of the pressure sensor or transducer 24 or 24a is fed through 
compensation amplifier 36 to PWM amplifier 38, which drives output circuit 
40 and pump/motor 14. The output pressure of the pump, either at the 
pump(FIG. 4) or at the fuel rail (FIGS. 2 and 3), is monitored by the 
pressure sensor 24 or 24a to provide the pressure sensor signal. 
The pressure reference input to amplifier 36 may be set at the time of 
system manufacture, or may be adjustable by the engine control computer or 
the operator. In the same way, the step-function or linear characteristics 
of temperature compensation circuit 48 may be set at the time of 
manufacture or variable in the field. Non-linear functions 52 and/or 
multiple thresholds and control gradients may be employed. In this 
respect, it will be appreciated that the specific pressure and 
temperatures discussed above are given by way of example only.