Vehicle engine idle speed governor with unsymmetric correction rates

A vehicle engine has a throttle stop positionable in response to an actuator command signal to determine engine idle speed. Apparatus is provided to generate a speed error signal having both an absolute value and a further characteristic indicative of high or low speed; and further apparatus is provided including a memory effective to store actuator command signals corresponding to specific speed error signals and speed correction apparatus effective to obtain an actuator command signal from the memory corresponding to each speed error signal and supply the actuator command signal to the throttle stop positioning apparatus to correct engine idle speed in the direction of a predetermined desired engine idle speed. The actuator command signals corresponding to at least the largest low speed error signals have absolute values effective to produce a greater throttle stop movement than the actuator command signals corresponding to the high speed error signals of the same absolute value, so that the control responds at a faster rate to large low speed errors than to equivalently large high speed errors.

This invention relates to idle speed control systems for motor vehicles and 
particularly those having a closed loop on engine idle speed. Systems of 
this type help provide the accurate control of engine operation necessary 
to achieve the most stringent vehicle emissions and fuel economy goals. 
A number of characteristics of such closed loop idle speed control systems 
may combine to create a problem in engine operation. An operating motor 
vehicle engine is characterized by a maximum speed of response to any 
attempt to change its engine speed. Electrical speed control apparatus is 
capable of responding to a speed error and moving a throttle stop for a 
predetermined distance in a direction to correct the error at a rate 
significantly faster than the engine can respond to the new position of 
the throttle stop. This may tend to cause overshoot in the response of the 
system to idle speed errors if the response of the control apparatus is 
not compensated in some manner. 
Another characteristic of a motor vehicle engine idle speed control 
apparatus is the fact that such apparatus attempts to maintain vehicle 
engine speed at or very near the lowest speed at which the engine will 
operate. This characteristic differentiates idle speed control systems 
from all other vehicle or vehicle engine control systems. In view of this 
characteristic, the speed of engine operation at idle must not be allowed 
to fall very far below the predetermined idle speed or to remain below 
said predetermined idle speed for any appreciable length of time, in order 
that the engine does not stall. It may be desirable, consequently, to have 
an unsymmetrical response to engine idle speed errors: that is, the 
control system may respond very quickly to a low idle speed error 
situation in order to get engine speed up before the engine stalls but 
respond more slowly or in lesser degree to a high speed error situation so 
that overshoot does not carry the engine into a low idle speed situation 
where stall may occur. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of this invention to provide an improved closed 
loop control system effective to maintain the vehicle engine idle speed 
substantially at a predetermined idle speed with a reduced tendency toward 
engine stall. 
It is a further object of this invention to provide a closed loop vehicle 
engine idle speed control apparatus which, at least for large speed 
errors, has a greater response to a low speed error and a smaller response 
to a high speed error in order to prevent engine stall. 
In particular, this invention provides apparatus including a throttle stop, 
actuator means effective to position the throttle stop in response to 
actuator command signals, apparatus effective to generate speed error 
signals, a memory effective to store predetermined actuator command 
signals corresponding to individual high and low speed error signals and 
apparatus effective to obtain, from the memory, actuator command signals 
corresponding to the generated speed error signals and supply the actuator 
command signals to the actuator apparatus in closed loop operation to 
maintain vehicle engine idle speed substantially at a predetermined 
reference. The actuator command signals in the memory corresponding to at 
least the largest low speed error signals have values effective to produce 
a greater throttle stop movement than the actuator command signals 
corresponding to the high speed error signals of the same absolute value. 
Further details and advantages of this invention will be apparent from the 
accompanying drawings and following description of a preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a vehicle engine 10 includes air and fuel induction 
apparatus 11 and a standard crankshaft, not shown, which is characterized, 
during engine operation, by a rotational speed which is commonly termed 
engine speed. The apparatus of FIG. 1 further includes engine speed 
measuring apparatus 12, which is adapted to measure said engine speed and 
generate a signal indicative thereof to an idle speed control 15, which is 
adapted to control the idle speed of engine 10. 
FIG. 2 shows a portion of the air and fuel induction control system 11 of 
engine 10 in greater detail. A throttle body housing 20 defines an 
induction throat 21 which includes a rotatable throttle blade 22 effective 
to control the flow of air therethrough. Throttle blade 22 is mounted on a 
throttle shaft 24 which has rigidly attached thereto a link 25 effective 
to control the angular position of throttle blade 22 within throat 21. 
Link 25 is normally biased by a spring 26 in the direction of a throttle 
stop 28 but is adapted to be pulled away from said throttle stop 28 by 
linkage, not shown, in response to movement of a throttle pedal 29. 
Additional apparatus, not shown, adds fuel to the air inducted through 
induction throat 21 in predetermined proportion so that the position of 
throttle blade 22 partly determines the idle speed of engine 10 when link 
25 abuts the throttle stop 28. The air and fuel induction apparatus may 
comprise a carburetor, throttle body injection apparatus or port injection 
apparatus of any known type that conforms with the above description. 
Throttle stop 28 is movable and attached to a throttle stop actuator 30 
which is a pulsed motor with a linear output. Actuator 30 is effective to 
move throttle stop 28 in either one of two directions to open or close 
throttle blade 22 while electric power is supplied to said actuator and to 
hold throttle stop 28 in a fixed position when power is not so supplied. 
Many such motors are known to those skilled in the art of automatic 
control systems. The polarity of the power so supplied can determine the 
direction of throttle stop movement and the length of time in which said 
power is supplied can determine the length of throttle stop movement. 
Actuator 30 further includes a throttle switch 32 which is mechanically 
closed by the force of link 25 against throttle stop 28. Throttle switch 
32 may be physically mounted on the tip of throttle stop 28 as a contact 
switch or may be mechanically contained within the main body of actuator 
30; and it functions to generate a signal by closing when link 25 contacts 
throttle stop 28 and thus when the engine 10 is in an idle condition. 
FIG. 3 shows timing apparatus for the idle speed control 15 of FIG. 1. The 
timing apparatus comprises a clock 33 which produces constant time pulses 
at a very fast rate to the clock input of a program counter 34. The pulses 
from clock 33 are further provided to a divider 36 which reduces the 
frequency of clock 33 to a much lower frequency and supplies pulses at the 
lower frequency to one input of an AND gate 37. The other input of AND 
gate 37 receives the signal from throttle switch 32 indicating an engine 
idle condition; and the output of AND gate 37 is connected to the trigger 
input of program counter 34. 
In operation, when throttle switch 32 is closed due to an engine idle 
condition, AND gate 37 is enabled to pass the pulses from divider 36 to 
repetitively trigger program counter 34 to count clock pulses from clock 
33 and generate output pulses in time with said clock pulses consecutively 
on a plurality of output lines numbered 1-7 in FIG. 3. When throttle 
switch 32 is open, AND gate 37 is disabled and program counter 34 is not 
so triggered. 
FIG. 4 shows a block diagram of the idle speed control 15, which is 
controlled by the timing apparatus of FIG. 3. Engine speed measuring 
apparatus 12, which may include analog to digital converting means, is 
connected to provide a binary digital number indicative of sampled engine 
speed to a register 40 upon the receipt of a pulse on output line 1 of 
program counter 34. Command speed apparatus 41 provides, upon the receipt 
of a pulse on output line 2 of program counter 34, a binary digital number 
representative of a desired engine idle speed through subtract apparatus 
42 to register 40, with the result that the number from command speed 
apparatus 41 is subtracted from the engine speed number already in 
register 40 and the result is a speed error signal stored in register 40. 
In the simplest case, command speed apparatus 41 could provide a single 
constant number representing a constant desired engine idle speed. 
However, command speed apparatus 41 may also be provided with one or more 
environmental or engine operating condition inputs and include computing 
and/or memory table lookup means for generating a number representing a 
desired engine idle speed which varies with engine operating or 
environmental conditions. 
The idle speed control 15 includes a memory which can be a read only memory 
or ROM 44 and further includes a memory address register 45. Register 40 
is connected to provide its contents to address register 45 upon the 
receipt of a pulse on output line 3 of program counter 34. This contents 
is a binary digital number with a sign bit which represents a speed error 
signal having an absolute value determined by all the bits of the number 
except the sign bit and a characteristic indicative of high or low speed 
represented by the sign bit. Address register 45 is connected to designate 
a particular address in ROM 44; and ROM 44 is connected to register 40 to 
provide the contents of the address indicated in address register 45 upon 
the receipt of a pulse on output line 4 of program counter 34. The 
contents of this memory location in ROM 44 comprises an actuator command 
number comprising a plurality of bits indicating a length of time for 
power to be applied to actuator 30 and at least one additional bit 
indicating a motor direction or polarity of applied power. 
Idle speed control 15 further includes an output counter 46, a motor 
direction register 47 and an actuator power driver 48. Register 40 is 
connected to provide its contents less the sign bit to the load input of 
output counter 46 upon the receipt of a pulse from output line 5 of 
program counter 34. Register 40 is further adapted to provide its sign bit 
to motor direction register 47 upon the receipt of a pulse from output 
line 6 of program counter 34. Motor direction register 47 serves as a flat 
register to control the polarity or direction of power supplied by 
actuator power and driver 48 to actuator 30. Output counter 46 is adapted 
to control the beginning and end of the actual application of power from 
actuator power driver 48 to actuator 30, beginning with a trigger input 
pulse from output line 7 of program counter 34. Output counter 46 is a 
down counter which counts clock pulses from clock 33 and terminates 
actuator power driver 48 when that count reaches 0. 
FIG. 5 shows, in tabular form, selected absolute values of the actuator 
command numbers, stored in ROM 44, which numbers determine the correction 
pulse width for actuator power, and identifies the corresponding positive 
and negative speed error numbers which serve as addresses for ROM 44. The 
negative speed error numbers correspond to speeds less than the 
predetermined idle speed; while the positive speed error numbers 
correspond to speeds greater than the predetermined idle speed. It can be 
seen that, although for positive or negative absolute speed error numbers 
of 4 of the actuator command number is 15, for greater absolute speed 
error numbers the actuator command number becomes greater for negative 
speed errors than for positive speed errors. This will result in a longer 
power pulse to the actuator for negative speed errors in accordance with 
the objects of the invention. 
Although there are many embodiments of this invention that will occur to 
those skilled in the art of engine idle speed control, this invention was 
reduced to practice using a digital microcomputer with a stored program 
which converted the hardware into the equivalent of the apparatus shown in 
FIGS. 3 and 4. The apparatus in these Figures is simplified for 
convenience, but those familiar with digital computing apparatus will 
recognize the elements and could easily program any particular digital 
microcomputer to create the equivalent apparatus. Therefore, this 
invention should be limited only by the claims which follow.