GB2035618A

GB2035618A - Vehicle internal combustion engine idle speed governor

Info

Publication number: GB2035618A
Application number: GB7934534A
Authority: GB
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 1978-10-23
Filing date: 1979-10-04
Publication date: 1980-06-18
Also published as: FR2439874A1; GB2035618B; JPS5557639A; CA1127273A; DE2940545C2; DE2940545A1; FR2439874B1

Abstract

A vehicle engine has a throttle stop positionable in response to an actuator command signal to determine engine idle speed. Apparatus 12,34,40,41,42 is provided to generate a speed error signal having both an absolute value and a further characteristic indicative whether the speed is high or low; and further apparatus is provided including a memory 44,45 effective to store actuator command signals corresponding to specific speed error signals and speed correction apparatus 34,46,47,48 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 speed error signals below the desired speed have absolute values which produce a greater throttle stop movement than those corresponding to the speed error signals above the desired speed and having the same absolute value. Thus the control responds at a faster rate to large errors when the idle speed is too low than to equivalently large errors when it is too high. <IMAGE>

Description

SPECIFICATION Vehicle internal combustion engine idle speed governor This invention relates to idle speed control systems for motor vehicle internal combustion engines, 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 directon 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 repsond 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.

A motor vehicle internal combustion engine speed control system according to the present invention includes an engine throttle stop, actuator means effective to position the throttle stop in response to actuator comand signals, apparatus effective to generate engine speed error signals, a memory effective to store predetermined actuator command signals corresponding to individual high and low engine speed error signals and apparatus effective to obtain, from the memory, actuator command signals corresponding to the generated engine 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 ofthe same absolute value.

A preferred embodiment of this invention is hereinafter described with reference to the accompanying drawings in which: Figure 1 is a schematic view of a vehicle engine with an idle speed control according to this invention; Figure 2 is a schematic view of a portion of the air and fuel induction apparatus for the engine of Figure 1; Figure 3 is a block diagram showing timing aparatus for the idle speed control used with the engine of Figure 1; Figure 4 is a block diagram of an idle speed control for use with the engine of Figure 1; and Figure 5 is a sample, in tabular form, of certain actuator command signals corresponding to specific speed error signals as stored in the memory apparatus of the idle speed control of Figure 4.

Figure 1 shows a vehicle engine 10 which 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 Figure 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.

Figure 2 shows a portion of the air and fuel induction control system 11 of engine 10 in greater detail. Athrottle body housing 20 defines an induction throat 21 which includes a rotatable throttle blade 22 effective to control the flow of air there through. 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 positon 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 carburettor, 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 of the stepping motor variety. 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 stepping 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 stood 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.

Figure 3 shows timing apparatus for the idle speed control 15 of Figure 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 Figure 3. When throttle switch 32 is open, AND gate 37 is disabled and program counter 34 is not so triggered.

Figure 4 shows a block diagram of the idle speed control 15, which is controlled by the timing apparatus of Figure 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 42 provides, upon 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 conected 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 flag register to control the polarity of 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 clockpulses from clock 33 and terminates actuator power driver 48 when that count reaches 0.

Figure 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 greater than the predetermined idle speed. It can be seen that although for positive or negative absolute speed error numbers of 4 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 Figures 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.

Claims

1. Avehicle internal combustion engine having fuel induction and control means including a throttle for controlling the fuel flow rate to the engine and a throttle stop for determining the engine idle throttle position, and in which an engine idle speed governing apparatus comprises:: an actuator effective to position the throttle stop in response to an actuator command signal, said actuator being capable of movement, at least in the direction of decreasing engine speed, at a faster rate than the engine itself can decrease its speed; apparatus effective to generate a speed error signal having an absolute value proportional to the difference between engine speed and a predetermined reference and a further characteristic indicative of high or low speed, respectively, for speeds greater than the reference or speeds less than the reference;; memory apparatus effective to store predetermined actuator command signals corresponding to individual high and low speed error signals, the actuator command signals coresponding to at least the largest low speed error signals having values effective to produce a greater throttle stop movemenu than the actuator command signals corresponding to the high speed error signals of the same absolute value; and apparatus effective to obtain from the memory apparatus the actuator command signal corresponding to the speed error signal and to provide the actuator command signal to the actuator to generate a throttle stop movement to return engine idle speed toward the reference by an amount determined at least in part by the value of the actuator command signal, so that at least large corrective throttle stop movement is smaller in the correction of high engine idle speed than in the correction of low engine idle speed.

New claims or amendments to claims filed on 13 February 1980 New or amended claims:

2. An idle speed control mechanism for use with an internal combustion engine having means to vary the flow of air into the engine, said control mechanism comprises: means responsive to engine speed and effective to indicate the magnitude and sense of the deviation thereof from a predetermined reference idle speed; means effective in response to said last means to increase said air flow when engine speed is below the reference and to decrease said air flow when engine speed is above the reference, the amount of said air flow increase for deviations above said reference in excess of a minimum being greater than the amount of said air flow decrease for deviations below said reference of the same magnitude below said reference.

3. An idle speed control mechanism according to claim 2 in which the amount of the difference between said air flow increase and decrease for deviations of the same magnitude progressively increases for a substantial range of deviation beyond said minimum.