Internal-combustion engines – Engine speed regulator – Idle speed control
Reexamination Certificate
1999-06-01
2001-03-20
Argenbright, Terry M. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Idle speed control
C123S352000, C123S357000
Reexamination Certificate
active
06202629
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to systems for controlling engine speed in an internal combustion engine. More specifically, the invention concerns systems and methods for accurately maintaining engine speed at low idle speeds.
Engine speed control systems, commonly known as engine speed governors, are well known in the automotive industry. In one type of engine speed governor, commonly known as a cruise control, a constant vehicle speed is maintained for a user-defined input. In this cruise control, or isochronous application, the engine speed is maintained constant regardless of the torque load applied to the vehicle engine.
A typical engine speed control system is depicted in FIG.
1
. Specifically, an engine
10
includes a fuel control system
12
that controls the amount of fuel provided to the engine. The speed of the engine is directly proportional to the quantity of fuel thus provided. The engine
10
can include a speed sensor
15
that produces a signal on signal line
16
corresponding to the actual engine speed, N
ACT
. In a typical engine, engine speed is measured using a pulse train generated by a toothed tone wheel and magnetic pickup arrangement. The magnetic pickup signal is pre-processed by an analog circuit that converts the signals into a pulse train. This pulse train is then fed to a counter/timer, typically included within an engine control module (ECM)
20
. This counter/timer calculates the elapsed time between tone wheel pulses, and the angular velocity is calculated as the known angular spacing between teeth divided by the elapsed time. For use in various engine control routines, the result of this operation can be further conditioned to produce the actual engine speed signal N
ACT
. Details of a suitable engine speed sensor system can be found in U.S. Pat. No. 5,165,271, which disclosure is incorporated herein by reference.
In accordance with this engine control system, an engine control module
20
receives a variety of inputs, including the engine speed signal N
ACT
. In addition, the ECM
20
receives a second signal on line
28
that is produced by a throttle position sensor
29
. More particularly, the throttle position sensor
29
translates the position of the vehicle accelerator pedal to a requested engine speed, N
REF
.
The ECM
20
can include a memory
23
which stores a variety of algorithms and constants necessary for determining the operating conditions of the engine
10
. The ECM
20
also includes a fuel control module
25
that receives the N
ACT
signal
16
, the N
REF
signal
28
and data from the memory
23
to determine an appropriate fueling command to be provided to the fuel system
12
. In particular, the fuel control module
25
incorporates the engine speed governor that operates to modulate the fuel control signal
26
as a function of the difference between the actual engine speed N
ACT
and the expected engine speed N
REF
.
One such engine speed control system is shown in U.S. Pat. No. 5,553,589, owned by the assignee of the present invention. The '589 Patent shows one type of speed control system that includes a variable droop feature. The general components of the speed control system in the '589 Patent, along with other prior art speed governors, is depicted in the control system block diagram FIG.
2
. It is understood that the representations in
FIG. 1 and 2
of this prior engine speed governor are relatively generic and for illustration purposes only. Specific details of the speed control system of the '589 Patent are left to the specification and figures of that patent, which information is incorporated herein by reference.
Turning now to
FIG. 2
, a fuel control module
25
′ is depicted. Specifically, the module
25
′ receives the reference speed signal N
REF
, which is based upon the user controlled throttle position. The actual engine speed N
ACT
is provided on signal line
16
to a summing node
30
. Specifically, the actual engine speed N
ACT
is subtracted from the reference speed value N
REF
to produce a speed error signal
31
, N
ERR
. This error signal
31
is indicative of the difference between the desired engine speed and the actual engine speed. This signal
31
, N
ERR
is provided to a linear controller
32
that applies a transfer function C(s) to the error value. This linear controller can be of a variety of types, but most preferably is a PID controller. In the typical engine control system, the linear controller
32
generates a fuel control signal
26
′ that is provided to the fuel system
12
of the engine
10
. In the prior systems, this fuel control signal corresponds to a degree of actuation of a flow control valve forming part of the fuel control system. In a typical installation, the fuel control signal
26
′ corresponds to a particular volume of fuel per stroke of the fuel control valve.
This fuel control signal
26
′ is provided to the engine
10
, which can be approximated in the control system diagram of
FIG. 2
by a transfer function G(s). The engine transfer function G(s) translates the fuel control signal
26
′ to an actual engine speed N
ACT
.
For any engine speed control system, the engine
10
can be approximated by a transfer function G(s) as represented in the control system diagram of FIG.
3
. In particular, the fuel system
12
of the engine can be represented by a fuel system delay
13
. The delay
13
receives the fuel control signal
26
and translates that signal to a supply of fuel to the engine after a time delay L. This delay corresponds to the activation of the mechanical and fluid components of the fuel control system
12
. The combustion process can be represented by the transfer function k in block
14
. Specifically, the value k corresponds to the translation of fuel to engine torque produced by combustion of the fuel within the engine. In one specific example, the transfer function k can have a value of 5.1.
While the combustion of the fuel generates torque within the engine, this torque bears a predetermined relationship to the actual engine speed. Specifically, the torque load applied to the engine is subtracted from the torque generated at block
14
at summing node
19
. This combined torque is then converted to rotational speed as a function of the inertia of the rotating components of the engine, which is represented by block
17
. In an ideal engine, the actual engine speed N
ACT
would be a function of only those components. However, the rotating components of the engine generate a certain amount of friction torque, which is known to be a function of the engine speed. Thus, a transfer function C(N) is introduced at block
18
in a feedback loop from the output of block
17
to the summing node
19
. This friction torque value is thus subtracted from torque load and the torque produced by combustion of the fuel.
The friction torque represented by the transfer function C(N) is a non-linear function of engine speed. Thus, it is known that one typical speed-torque curve has a hyperbolic shape centered on a specific low engine speed. Above that engine speed, the torque gradually increases. Below that engine speed, the friction torque dramatically increases. This great increase in friction torque is primarily due to the fact that at the lower engine speed oil pressure is lower, which means that less oil is circulating between the rotating components of the engine.
The friction torque transfer function C(N) can be approximated by an equation as a function of engine speed N using a linear regression analysis. Although the torque vs. speed curve is non-linear, the system can be linearized using a differential equation based upon the incremental change in engine speed due to a incremental change in commanded fueling to the fueling system
12
. Thus, the following equation can be developed to simulate the engine
10
, based upon the block diagram of FIG.
3
:
J
·
Δ
N
.
(
t
)
=
k
·
Δ
F
STOKE
(
t
-
L
Sisson Albert E.
Zhu G. George
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