Internal combustion engine fuel system with inverse model control of fuel supply pump

A feedforward control system for an electrically operated fuel injection pump for an internal combustion engine includes a controller for determining required fuel pressure and flow rate to be delivered by the pump and for using the determined fuel pressure and flow rate to determine a variable operating voltage for the pump. The variable operating voltage may be delivered as a pulsewidth modulated voltage, with the system being used to operate the pump in an open loop fashion.

BACKGROUND OF THE INVENTION 
This invention relates to a system and method for operating an electrically 
powered pump used for supplying fuel to electronically controlled fuel 
injectors in an internal combustion engine. 
DESCRIPTION OF THE PRIOR ART 
Conventional electronic fuel injection systems use an electrically powered 
pump which is controlled at a constant speed to supply fuel to the fuel 
injectors. The pump pushes much more fuel than is usually needed from the 
fuel storage tank to the injectors, and as a consequence, most of the fuel 
is bypassed. Other known systems sense fuel system pressure and input this 
signal to an electronic engine controller, which then controls the speed 
at which the pump is operated. The system of the present invention, 
however, uses an inverse fuel pump model to offload fuel pump control from 
the engine controller's feedback control system; instead a feedforward 
system is employed to control the pump. The present system is said to be 
an inverse model because the inputs are fuel pressure and fuel flow rate 
and the output is a duty cycle or other type of variable operating voltage 
for the fuel pump. By offloading work from the feedback portion of the 
electronic engine controller, better control may be achieved without 
excessively high feedback gains. Such high gains are generally associated 
with system instability and unwanted oscillatory response. The present 
system avoids such disadvantages. 
SUMMARY OF THE INVENTION 
A feedforward control system for an electrically operated fuel injection 
pump for an internal combustion engine includes means for determining the 
required fuel pressure and flow rate to be delivered by the pump, means 
for using the determined fuel pressure and flow rate to determine a 
variable operating voltage for the pump, and means for supplying the 
determined variable operating voltage to the pump. The means for 
determining voltage may comprise means for calculating a pulsewidth 
modulated voltage to be applied to the pump. The calculated pulsewidth may 
be adjusted to correct for variations in the voltage available for 
operating the pump and variations in the temperature of the fuel being 
pumped. If desired, the actual fuel pressure from the pump may be compared 
with desired pressure and the results of the comparison used for adjusting 
the variable operating voltage supplied to the pump. 
According to another aspect of the present invention, means for using the 
determined fuel pressure and flow rate to determine a variable operating 
voltage for the pump may comprise a lookup table having fuel pressure and 
flow rate as independent variables and pump supply voltage as a dependent 
variable. 
Alternatively, a means for using determined fuel pressure and flow rate to 
determine the variable operating voltage for the pump may comprise an 
arithmetic processor using fuel pressure and flow as independent variables 
and having pump operating voltage as its output. The arithmetic processor 
may also utilize pump supply voltage and fuel temperatures as independent 
variables. As another alternative, the arithmetic processor may 
incorporate a set of linear differential equations having fuel pressure, 
fuel flow rate, pump supply voltage, and fuel temperature as independent 
variables, with the equations yielding a pump voltage value required to 
maintain the desired fuel pressure.

DETAILED OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1, a fuel injection system includes a plurality of fuel 
injectors 10, which are supplied by fuel via fuel pump 22. Fuel pump 22 
receives fuel from fuel tank 20. The signals required to operate fuel pump 
22 are output by electronic engine controller 12. The electronic engine 
controller is a microprocessor controller of the type known to those 
skilled in the art of engine controls and used to operate such functions 
as fuel injector pulsewidth, engine spark timimg, EGR control, evaporative 
emissions control purging, and transmission gear selection. 
Electronic controller 12 receives inputs from voltage sensor 14, which 
determines battery voltage or pump supply voltage available to fuel pump 
22, as well as temperature sensor 16 which measures the temperature of the 
fuel being pumped by fuel pump 22. A variety of engine sensors 18 provides 
information to electronic engine controller 12 for variables such as 
engine speed, engine load, engine coolant temperature, EGR rate, air/fuel 
ratio, mass air flow, and other operating parameters. From these 
parameters, a desired fuel pump pressure, p, and flow rate, q, are 
selected according to any of the known algorithms for determining desired 
fuel pump pressure and flow. The desired values of p and q are entered 
into a lookup table 24, which is contained within controller 12, and the 
value of duty cycle is read out. If desired, the sensed values for pump 
supply voltage and fuel temperature may be used to modify the duty cycle 
extracted from Table 24. This may be done by performing a simple 
comparison of the sensed voltage and temperature with reference values, or 
two dimensions could be added to look-up Table 24 to make a 
four-dimensional table so as to directly account for the sensed values of 
voltage and temperature. In the event that it is desired to run a system 
having an inverse model feedforward feature according to the present 
invention with feedback of fuel pressure, fuel pressure sensor 26 may be 
employed to sense the value of the pressure at the injectors, or across 
the injectors, and to feed this value back to controller 12 so that the 
controller will be able to alter the duty cycle accordingly. Such a 
system, including feedback of fuel pressure, will help to offload the 
feedback portion of the engine controller by providing the initial pump 
signal in a feedforward or open loop manner. 
FIG. 2 illustrates a second embodiment of the present invention in which 
the output of voltage sensor 14 and temperature sensor 16 are used to 
correct the duty cycle extracted from Table 24 in a manner which varies 
from that previously discussed. As shown in box 28, the sensed actual 
voltage, V.sub.act, is used to correct the value of v.sub.e, which is the 
output extracted from lookup table 24. Effectively, v.sub.e, which is the 
desired effective voltage, at the pumps, is used in the ratio V.sub.e 
/V.sub.act, and this ratio (which is clipped between zero and one) is the 
duty cycle which is supplied to the fuel pump. As one example of the 
present embodiment, if v.sub.e is 11 volts and V.sub.act is 10 volts, the 
ratio of v.sub.e /v.sub.act will be 1.1. This value is clipped to 1 and 
the duty cycle to the pump is 100%. If, on the other hand, v.sub.e is 8 
volts and v.sub.act is 10 volts, the ratio of v.sub.e /v.sub.act will be 
0.8 and the duty cycle to the pump is 80%. 
Box 30 of FIG. 2 illustrates a correction factor to account for changes in 
fuel temperature. A corrected flow, q.sub.c, is the output of box 30, with 
a desired flow, q.sub.d, being input along with T.sub.f, or sensed fuel 
temperature, as furnished by temperature sensor 16. Corrected flow is 
given by the equation: 
EQU q.sub.c =q.sub.d +q.sub.x x(T.sub.f -T.sub.ref) 
where: 
q.sub.d =desired flow; 
q.sub.x =a constant; and 
T.sub.ref =a reference temperature. 
As an alternative to the use of a lookup table for determining the 
effective voltage or the duty cycle needed for the fuel pump in a system 
according to the present invention, the means for determining a variable 
operating voltage for the pump from the determined fuel pressure and flow 
rate may include an arithmetic processor using fuel pressure and flow rate 
as independent variables as well as at least fuel temperature and pump 
supply voltage. This could be achieved by using an equation having the 
following form: 
##EQU1## 
where: a.sub.n =f.sub.n (V.sub.act, T.sub.inlet), etc. 
b.sub.n =f.sub.n (V.sub.act, T.sub.inlet), etc. 
c.sub.n =f.sub.n (V.sub.act, T.sub.inlet), etc. 
p=pumping system output pressure 
q=pumping system output flow 
V.sub.act =V.sub.batt -voltage drop to and within pump driver=high side 
switching voltage available at the pump 
T.sub.inlet =pump inlet temperature 
A second type of arithmetic processor could incorporate a set of linear 
differential equations having fuel pressure, fuel flow rate, pump supply 
voltage and fuel temperature as independent variables. These equations 
will yield a pump voltage value required to maintain the desired fuel 
pressure. The linear differential equations could be expressed as follows: 
EQU x(t)=A(V.sub.act, T.sub.inlet)x(t)+B(V.sub.act, T.sub.inlet)u(t) 
EQU y(t)=Cx(t)+Du(t) 
where: 
t=time 
x(t)=dynamic states of the inverse model 
x(t)=derivative of x(t) with respect to time 
u(t)=(q p), 
y(t)=required pump command to maintain injector pressure 
V.sub.act =the high side of the duty cycle 
T.sub.inlet =pump inlet temperature. 
q=pump output flow rate 
p=pump output pressure 
A, B, C, and D=matrices of coefficients defining the model's dynamics 
The dynamic form of the inverse model as expressed by the linear 
differential equations above is desirable because it may be employed to 
account for dynamic or transient pump data across a range of values of 
pump supply voltage fuel temperature and pressure and flow rate. Standard 
system identification techniques such as recursive least squares may be 
used to fit dynamic flow data to the inverse model's A, B, C and D 
matrices. In general the present system may be implemented by collecting 
pumping test data under various conditions accounting for a range of 
values of supply voltage, fuel temperature, fuel pressure and flow rate.