GB2176031A - Interactive idle speed control with direct air control - Google Patents

Abstract

A method of controlling the idling speed of an internal combustion engine 19 includes generating an idle speed error signal which is used to generate a throttle command signal to control throttle airflow as a function of the speed error. A fuel pulse width command signal to control fuel charge is generated as a function of airflow as measured by a manifold pressure sensor 19 or a flow meter, thereby maintaining a desired air/fuel ratio. A spark advance circuit 24 may be additionally employed. <IMAGE>

Description

SPECIFICATION Interactive idle speed control with direct air control This invention relates to a method of controlling the idling speed of an internal combustion engine.

This patent application relates to copending, commonly assigned, patent applications 83-433 entitled "Interactive Spark and Throttle Idle Speed Control" (UK patent application no. 86 07107) and 83-434-1 entitled "Interactive idle Speed Control with a Direct Fuel Control" (UK patent application no. 86 11021).

Various idle speed control systems for internal combustion engines are known. Such systems include some which are primarily mechanical and some which are primarily electronic. One of the goals such ststems have tried to achieve is to provide increased engine idling stability. However, attempts to react rapidly to changing conditions in order to achieve idling stability may cause an overshoot of desired idling speed or other instability.

U.S. Patent 4,328,775 issued to Ironside teaches a closed loop idling control for an internal combustion engine including a difference signal generator which produces an engine speed error signal. This signal passes through a phase compensator and directly controls the ignition timing to provide a fast loop control of speed. Additionally, the engine speed error signal controls the throttle position through an integrator in a series connection with the phase compensator to provide a slow loop which cancels out the engine speed error to avoid increased exhaust contamination.

U.S. Patent 4,338,899 issued to Geiger et al teaches controlling the ignition timing of a spark ignited internal combustion engine charged with a lean air-fuel ratio to have a stabilized idle speed which is approximately equal to a desired idle speed. The ignition timing of the engine is controlled to linearly advance the timing from a nominal retarded condition in proportion to a change in engine speed below the desired speed. The timing advance may be implemented via a constant time delay and has the same ratio to engine speed changes as the ratio of nominal ingition pulse spacing to the desired engine idle speed.

U.S. Patent 4,344,397 issued to Geiger et al teaches stabilizing enging idle speed by a successive three-stage control system which sequentially regulates ignition timing, fuel quantity and air throughput volume.

U.S. Patent 4,142,483 issued to Ironside teaches an internal combustion engine operationtiming control using a programmed read-only memory to produce a multibit digital signal used to determine the instant of operation. One input to the ROM is from a speed counter and the other input to the ROM is from another engine parameter transducer.

The digital output of the ROM is applied to a timing counter. A master clock is used for clocking both the speed counter and the timing counter.

U.S. Patent 4,262,643 issued to Cavil et al teaches a timing control system for an internal combustion engine producing a cyclical control pulse offset from a cyclical engine timing reference pulse. The processing circuit includes a counter connected to a NAND gate for producing a control pulse when the counter reaches a preset count, a monostable device subject to the control pulse for resetting the counter, an oscillator for providing preload pulses to the counter for a predetermined period of time to establish a preload count, and a phase-locked loop subject to the reference pulse for transmitting a fixed number of signal pulses per engine revolution to the counter to increment the preload count until the preset count is reached, whereby the control pulse is produced.

U.S. Patent 4,389,989 issued to Hartig teaches an electronic arrangement for idling stabilization between a signal transmitter for ignition spark formation and an ignition device for internal combustion engines. When engine rotational speed decreases, the ignition time point is advanced below a first engine rotational speed, in which there presently is retarded a pulse obtained from the signal transmitter and, with regard to the contemplated unretarded pulse sequence, is transmitted as an advanced signal to the ignition device whereby the unretarded pulses are emitted externally of the stabiliztion range intermediate the first and a second lower engine rotational speed.

There still remains a need for improved regulation of engine idle speed. In particular, it would be desirable to have faster response to idle speed fluctuations by control of both fuel pulse width and engine air intake volume.

This invention includes a method of controlling the idling speed of an internal combustion engine supplied with a rich air/fuel ratio. The air/fuel ratio is in a range wherein an increased air/fuel ratio corresponds to increased torque.

According to the invention there is provided a method of controlling the idling speed of an internal combustion engine, said method comprising, determining a desired engine idle speed, determining an actual engine idle speed, generating a speed error signal as a function of the difference between a desired engine idle speed and the actual engine idle speed, generating a signal as a function of airflow, generating a fuel pulse width command signal to control fuel charge as a function of an airflow measurement, and generating a throttle command signal, to control throttle air flow, as a function of the speed error signal.

In accordance with such operation, an engine torque is limited by the amount of air supplied and, therefore, the primary control loop is on the throttle position with the fuel control tracking the air control. Air and fuel are controlled simultaneously during speed perturbations. However, under steady state conditions, the fuel pulse width tracks the air charge by the use of a filtered manifold pressure signal.

The invention will now be further described by way of example, with reference to the accompanying drawings, in which; Figure 1 is a block diagram of a method for interactive air fuel and spark idle speed control in ac cordance with an embodiment of this invention; Figure 2 is a more detailed block diagram of phase compensator/ amplifier 14 of Figure 1; Figure 3 is a more detailed block diagram of phase compensator/ amplifier 16 of Figure 1; Figure 4 is a more detailed block diagram of phase compensator/ amplifier 22 of Figure 1; and Figure 5 is a block diagram of an embodiment of Figure 4.

Referring to Figure 1, an interactive air fuel and spark idle control system 10 includes an idle speed error summer 11 and having inputs supplying a desired idle set speed and an actual idle speed which is computed by a speed conputer 12 in response to a signal from a crankshaft position sensor 13. A speed error signal from summer 11 is applied to a phase compensator and amplifier circuit 14 which has an output applied to a summer 15. Another input to summer 15 is applied from a temperature modifier 28. A manifold pressure sensor 17 has an output signal representative of pressure applied to a phase compensator and amplifier 16. The output of phase compensator and amplifier 16 is a pressure compensation signal applied to temperature modifier 28. Temperature modifier 28 also has input signals representative of air temperature and engine coolant temperature.The output of summer 15 is a fuel pulse width control signal which is applied to fuel injector dirver circuit 18 which in turn applies fuel to engine 19.

Engine 19 receives air through an intake manifold and throttle 20. A throttle position servo 21 controls the position of throttle 20 and receives an input from a phase compensator and integrator circuit 22. Compensator and integrator circuit 22 receives as an input the output of summer 11. A spark module and distributor 23 applies a spark to engine 19 and receives an input from a spark advance circuit 24. Spark advance circuit 24 includes computation means for computing a spark advance. Referring to Figure 1, spark advance circuit 24 includes a constant delay spark timing circuit 25 which receives inputs from a crankshaft position sensor 13 and from a delay modification advance circuit 26. Advance circuit 26 receives an input from the output of speed computer 12.

In operation, the method of Figure 1 describes a strategy in which the fuel control follows the air charge density in such a way as to maintain a desired air fuel ratio. In accordance with this invention, the throttle position is varied in proportion to the phase compensated speed error and its time integral to return the engine to its idle set speed.

The spark advance is varied in proportion to the speed error. The fuel pulse width is varied in proportion to the filtered value of manifold pressure, so as to maintain a desired air fuel ratio, when the speed error and its derivative are equal to zero. To improve the transient response of the fuel pulse, the fuel pulse width is also varied in proportion to the phase compensated speed error to provide a stable return to the idle set speed.

As a result, in accordance with this invention, engine torque is air limited and, therefore, the primary control loop is on the throttle position with the fuel control tracking the air control. Advantageously, air and fuel are controlled simultaneously during speed perturbations. Under steady conditions, however, the fuel pulse width tracks the air charge through the filtered manifold signal from filter 16.

Referring to Figure 2, a more detailed depiction of phase compensator/amplifier 14 includes a phase compensator 301 which receives the speed error as an input and applies an output to an amplifier 302. The output of amplifier 302 is the speed effect compensation which is applied to summer 15 of Figure 1.

Referring to Figure 3, a more detailed depiction of phase compensator/amplifier 16 includes a phase compensator 161 which receives the manifold pressure signal as an input and applies an output to an amplifier 162. The output of amplifier 162 is the pressure compensation signal which is applied to temperature modifier 28.

Referring to Figure 4, a more detailed breakdown of compensator/ integrator 22 includes the speed error being applied to the parallel combination of the phase compensator/amplifier 141 and integrator/amplifier 142 whose outputs are both applied to a summer 144. The output of summer 144 is applied to the input of a phase compensator 143 which has as an output the throttle position command signal.

Referring to Figure 5, a particular implementation of phase compensator/integrator block 22 uses a proportional and integration function and omits the phase compensators. In particular, a speed error is applied to the input of a gain amplifier 401 and to the input of the series combination of an integrator 402 and a gain amplifier 403 which is in parallel with gain amplifier 401. The outputs of gain amplifier 401 and gain amplifier 403 are both applied to a summer 404. The output of summer 404 is a throttle position command signal.

It can be appreciated that the manifold pressure sensor 17 of Figure 1 is used with a speed density system when computing airflow by measuring manifold pressure and air temperature. Alternatively, this can be done by using measurements from an air volume flow meter, air temperature and engine rpm or from an air mass flow meter and engine rpm.

Various modifications and variations will no doubt occur to those skilled in the arts to which this invention pertains. For example, the particular calculation of the spark advance may be varied from that disclosed herein. This and all other variations which basically rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention.

Claims (7)

1. A method of controlling the idling speed of an internal combustion engine, said method comprising; determining a desired engine idle speed; determining an actual engine idle speed; generating a speed error signal as a function of the difference between a desired engine idle speed and the actual engine idle speed; generating a signal as a function of airflow; generating a fuel pulse width command signal to control fuel charge as a function of an airflow measurement; and generating a throttle command signal, to control throttle air flow, as a function of the speed error signal.

2. A method as recited in claim 1 further comprising the step of; generating a spark advance in proportion to the speed error signal.

3. A method as recited in claim 2 wherein; generating a throttle command signal includes summing of a first signal proportional to the phase compensated speed error signal and a second signal proportional to the time integral of the speed error signal.

4. A method as recited in claim 3 wherein the step of generating a throttle command signal further includes the step of applying the speed error signal to a series phase compensator.

5. A method as recited in claim 4 within; generating a fuel pulse width command signal includes summing a first signal proportional to the phase compensated speed error signal, and a second signal which is a funtion of air temperature, coolant temperature, and the engine intake manifold pressure.

6. A method as recited in claim 5 whrein said second signal for generating a fuel pulse width command signal includes a phase compensated signal representative of engine intake manifold pressure.

7. A method of controlling the idling speed of an internal combustion engine substantially as her einbefore described with reference to the accom panying drawings.