US3705571A

US3705571A - Hot start auxiliary circuit for electronic fuel control system

Info

Publication number: US3705571A
Application number: US125097A
Authority: US
Inventors: John W Horn; Todd L Rachel
Original assignee: Bendix Corp
Current assignee: Bendix Corp; Siemens Automotive LP
Priority date: 1971-03-17
Filing date: 1971-03-17
Publication date: 1972-12-12
Anticipated expiration: 1989-12-12

Abstract

An auxiliary circuit for an electronic fuel control system to facilitate hot starting of the associated engine is disclosed herein. The circuit is responsive to engine temperature above a selected level and is operative to lengthen fuel injection control pulses by an amount calculated by the circuitry to be necessary to purge the injectors and the fuel supply conduits of any vapors forming as a result of excessive engine compartment temperatures. The circuit comprises a first means to generate a signal indicative of the temperature condition and a second means to translate this signal into an appropriate voltage for application to the main computing portion of the electronic fuel control system.

Description

United States Patent Horn et al.

[54] HOT START AUXILIARY CIRCUIT FOR ELECTRONIC FUEL CONTROL SYSTEM [72] Inventors: John W. Horn; Todd L. Rachel,

both of Elmira, N.Y.

[73] Assignee: The Bendix Corporation [22] Filed: March 17, 1971 [21] Appl. No.: 125,097

[52] US. Cl. ..123/32 EA, 123/179 L [51] Int. Cl ..F02n 11/08 [58] Field of Search ..123/32 EA, 179 L, 179 G [56] References Cited UNITED STATES PATENTS 3,616,784 11/1971 Barr ..123/32 EA 3,614,945 10/1971 Schlagmuller et a1. ..l23/179 G 3,504,657 4/1970 Eichler et al ..l23/32 EA [451 Dec. 12,1972

Primary Examiner-Laurence M. Goodridge Attorney-Robert A. Benziger and Flame, Hartz, Smith & Thompson [5 7] ABSTRACT An auxiliary circuit for an electronic fuel control system to facilitate hot starting of the associated engine is disclosed herein. The circuit is responsive to engine temperature above a selected level and is operative to lengthen fuel injection control pulses by an amount calculated by the circuitry to be necessary to purge the injectors and the fuel supply conduits of any vapors forming as a result of excessive engine compartment temperatures. The circuit comprises a first means to generate a signal indicative of the temperature condition and a second means to translate this signal into an appropriate voltage for application to the main computing portion of the electronic fuel control system.

11 Claims, 3 Drawing Figures PATENTEDHEB 12 I972 3, 705 571 sum 1 or 2 FIGURE 3 TEMPERATURE SENSOR BATTERY ELECTRONIC TIMING CONTROL PICKUP UNIT FIGURE JOHN w. HORN TODD 1.. RACHEL INVENTORS BY QMAW PATENTEB DEC 12 m2 SHEET 2 BF 2 ALTERNATE A JOHN-W. HORN FIGURE 2 TODD L. RACHEL INVENTORJ' BY QM HOT START AUXILIARY CIRCUIT FOR ELECTRONIC FUEL CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is related to the field of fuel control systems in general and in particular to the field of electronic fuel control systems adapted for use with internal combustion reciprocating piston engines.

2. Description of the Prior Art The prior art is generally concerned with fuel control systems which are adapted to provide fuel for engine operation at the stoichiometric fuel/air ratio, or which operate in the rich mode. By rich mode is meant that the fuel/air ratio for the engine is adjusted to contain more fuel than would be required for operation at the stoichiometric point. Conversely, lean mode denotes operation at a fuel/air ratio which contains less fuel than would be required for operation at the stoichiometric point.

In systems which operate in the rich mode, starting the vehicle under a condition of heat soak did not present any great problem because the leaning out of the fuel caused by the formation of fuel vapor will not lower the fuel/air ratio below a point at which the engine would start. Thus, the teachings of the prior art are not adequate to provide for the situation of vehicle engine operation in the lean mode. The leaning out of the air/fuel ratio which is caused by the formation of fuel vapor under condition of heat soak is sufficiently extreme so that the mixture is no longer combustible with sufficient force and energy to start the engine. It is, therefore, an object of the present invention to provide a circuit means which will recognize a condition of heat soak and which will provide adequate compensation for the main computing circuitry so that additional quantities of fuel and vapor are injected thereby maintaining the fuel/air ratio at a sufficiently high value so that starting may be undertaken. It is a further object of the present invention to provide such a circuit in a simple and economical form for altering signals already present within the main computing portion of the electronic circuitry. It is a still further object of the present invention to provide such a circuit which may utilize the signal indicative of engine temperature which is already present within the main computing portion of the electronic fuel control system.

SUMMARY OF THE PRESENT INVENTION The present invention contemplates the addition of circuitry comprised of two major components to sense the condition of temperature of the engine and to adjust a voltage signal which already exists within the main computing portion of the electronic control system to thereby lengthen the individual injection control pulses by which an injector valve means is controlled. By lengthening these pulses, additional incremerits of fuel and fuel vapor will be injected into the engine to be started and will thus increase the fuel/air ratio to a point where the engine can start and be self sustaining.

I-Iot soak is that condition which exists in the time period immediately after the shutting down of an engine which had previously been operating for some period of time. This condition manifests itself by the elevation of the temperature of that engine to a point which may be as high as 260F and, in some engines, may go even higher. Under such a temperature condition, the fuel which then resides within the fuel supply system and injector valves in the vicinity of the engine will be elevated in temperature and fuel vapor bubbles willform therein. By providing the circuitry of the present invention, the injector valves of the engine, during a subsequent high temperature restart, will be maintained in the open position for a period of time longer than would normally be required so that the system may purge itself of the undesirable fuel vapor. In order to provide temperature stability, the control transistor is provided with an equal number of pn junctions between the base electrode and ground and between its control electrode and the source of temperature signal.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a schematic diagram of an electronic fuel control system adapted to a reciprocating-piston internal combustion engine.

FIG. 2 shows, in diagrammatic circuit form, an electronic fuel control main computing circuit.

FIG. 3 shows a circuit diagram for achieving the objects of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, an electronic fuel control system is shown in schematic form. The system is comprised of an electronic control unit, or computing means 10, a manifold pressure sensor 12, a temperature sensor 14, an input timing means 16 and various other sensors denoted as 18. Temperature sensor 14 may sense engine temperature directly or indirectly or may also sense injection temperature directly or in directly. The manifold pressure sensor 12 and the associated other sensors 18 are mounted on throttle body 20. The output of the computing means 10 is coupled to an electromagnetic injector valve member 22 mounted in intake manifold 24 and arranged to provide fuel from tank 26 via pumping means 28 and suitable fuel conduits 30 for delivery to a combustion cylinder 32 of an internal combustion engine otherwise not shown. While the injector valve member 22 is illustrated as delivering a spray of fuel towards an open intake valve 34, it will be understood that this representation is merely illustrative and that other delivery arrangements are known and utilized. Furthermore, it is well-known in the art of electronic fuel control systems that computing means 10 may control an injector valve means comprised of one or more injector valve members 22 arranged to be actuated singly or in groups of varying numbers in a sequential. fashion as well as simultaneously. The computing means is shown here as energized by battery 36 which could be a vehicle battery or a separate battery.

Referring now to FIGS. 1 and 2 and particularly to FIG. 2, an electronic fuel control system main computation circuit is shown. The circuit is shown as being energized by a voltage supply designated as B+ at the various locations noted. In the application of this system to an automotive engine fuel control system, the voltage supply could be the battery 36 and/or battery charging system conventionally used as the vehicles electric power source. The man skilled in the art will recognize that the electrical polarity of the voltage supply could be readily reversed.

The circuit 110 receives, along with the voltage supply, various sensory inputs, in the form of voltage signals in this instance, indicative of various operating parameters of the associated engine. Intake manifold pressure sensor 12 supplies a voltage indicative of manifold pressure, temperature sensor 14 is operative to vary the voltage across the parallel resistance associated therewith to provide a voltage signal indicative of engine temperature and voltage signals indicative of engine speed are received from input timing means 16 at circuit input port 116. This signal may be derived from any source indicative of engine crank angle, but is preferably from the engine s ignition distributor.

The circuit 110 is comprised of a first stage indicated generally as 108 and a second stage indicated generally as 109 and is operative to provide two consecutive pulses, of variable duration, through sequential networks to circuit location 118 to thereby control the on time transistor 120. The first pulse is provided via resistor 122 from the first stage 108, that portion of circuit 110 having inputs indicative of engine crank angle and intake manifold pressure. The termination of this pulse initiates a second pulse which is provided via resistor 124 from the second stage 109, that portion of the circuit 110 having an input from the temperature sensor 14. These pulses, received sequentially at circuit location 118, serve to turn transistor 120 on (that is, transistor 120 is triggered into the conduction state) and a relatively low voltage signal is present at circuit output port 126. This port may be connected, through suitable inverters and/or amplifiers to the injector valve means (shown in FIG. 1) such that the selected injector valve means are energized whenever the transistor 120 is on". It is the current practice to use switching means to control which of the injector valve means are coupled to circuit location 126 when the system is used for actuation of less than all injector valve means at any one time. Because the injector valve means are relatively slow acting, compared with the speed of electronic devices, the successive pulses at circuit point 118 will result in the injector valve means remaining open until after the termination of the second pulse.

The duration of the first pulse is controlled by the monostable multivibrator network associated with

transistors

128 and 130. The presence of a pulse received via input port 116 will trigger the multivibrator into its unstable state with transistor 128 in the conducting state and transistor 130 blocked (or in the nonconducting state). The period of time during which transistor 128 is conducting will be controlled by the voltage signal from manifold pressure sensor 12. (Ionduction of transistor 128 will cause the collector l28c thereof to assume a relatively low voltage close to ground or common voltage. This low voltage will cause the base 134b of transistor 134 to assume a low voltage below that required for transistor 134 to be triggered into the conduction state, thus causing transistor 134 to be turned off. The voltage at the collector 1340 will, therefore, rise toward the 13+ value and will be communicated via resistor 122 to circuit location 118 where it will trigger transistor 120 into the on" or conduction state thus imposing a relatively low voltage signal at circuit port 126. As hereinbefore stated, the presence of a low voltage signal at circuit port 126 will cause the selected injector valve means to open. When the voltage signal from the manifold pressure sensor 12 has decayed to the value necessary for the multivibrator to relax or return to its stable condition, transistor 130 will be triggered on and transistor 128 will be turned off. This will, in turn, cause transistor 134 to turn on, transistor 120 to turn off and thereby remove the injector control signal from circuit port 126.

During the period of time that transistor 134 has been held in the nonconducting, or off state, the relatively high voltage at collector 1340 has been applied to the base of transistor 136, triggering the transistor 136 on. The resistor network 138, connected to the voltage supply, acts with transistor 136 as a current source and current flows through the conducting transistor 136 and begins to charge capacitor 140. Simultaneously, transistor 142 has been biased on and, with resistor network 144, constitutes a second current source. Currents from both sources flow into the base of transistor 146 thereby holding this transistor on which results in a low voltage at the collector 1460. This low voltage is communicated to the base of transistor 120 via resistor 124.

When transistor 128 turns off signalling termination of the first pulse, transistor 134 turns on and the potential at the collector 1340 falls to a low value. The current from the current source, comprised of transistor 136 and resistor network 138, now flows through the base of transistor 136 and the capacitor ceases to charge. The capacitor will then have been charged, with the polarity shown in FIG. 2, to a value representative of the duration of the first pulse. However, at the end of the first pulse when transistor 134 is turned on the collector-base junction of transistor 136 is forward biased, thus making the positive side of capacitor 140 only slightly positive with respect to ground as a result of being separated from ground by only a few pn junctions. This will impose a negative voltage on circuit location 148 which will reverse bias diode 150 and transistor 146 will be turned off. This will initiate a high voltage signal from the collector of transistor 146 to circuit location 118 via resistor 124 which signal will re-trigger transistor 120 on and a second injector means control pulse will appear at circuit port 126. The time duration between the first and second pulses will be sufficiently short so that the injector means will not respond to the brief lack of signal.

The duration of the second pulse will be a function of the time required for circuit location 148 to become sufficiently positive for diode 150 to be forward biased. This in turn is a function of the charge on capacitor 140 and the magnitude of the charging current supplied by the current source comprised of transistor 142 and resistor network 144. The charge on capacity 140 is, of course, a function of the duration of the first pulse. However, the rate of charge (i.e., magnitude of the charging current) is a function of the base voltage at transistor 142. This valve is controlled by the

voltage divider networks

152 and 154 with the effect of network 154 being variably controlled by the engine temperature sensor 14.

Referring now to FIG. 2, it will be observed that there is a circuit location designated point A within the second state computing means 109 of the main computing circuitry 110. Similarly, there exists a point designated alternate A and that portion of the circuitry which controls the bias applied to one of the inductances within pressure sensor 12. The significance of these locations will become apparent from consideration of FIG. 3 described in detail hereinbelow.

Referring now to FIG. 3, the hot starting circuit of the present invention is illustrated in a preferred form as circuit 200. Circuit 200 consists of first transistor stage 202, second transistor stage 204,

control resistors

206, 208, 210, 212, 214 and 216 blocking diode 218 and voltage level establishing diode means 220. Circuit 200 is adapted to receive a signal indicative of engine temperature at circuit port 222. This signal may come, for instance, from the terminal of temperature sensor 14 which is shown as a thermistor and which may be located in the water jacket of a water cooled engine, or it may come from a temperature sensor which senses the temperature of the injector valve means 22, or of the fuel within the fuel supply conduit 30, or from any other convenient source of temperature which may be indicative of a hot soak fuel vaporization condition within the fuel supply system in the vicinity of the engine. Circuit 200 further includes a terminal denoted as A which may be directly coupled to either circuit location A, or Alternate A within the main computing circuit 110. As shown within main computing circuit 110, location A is within the second stage 109 while location Alternate A is within the first stage 108. By connecting the circuit 200 to location A, the hot starting correction will be applied only to the second of the two pulses generated by the main computing circuit110. Connection of circuit 200 to the Alternate A location in the first stage 108 will result in a correction factor being applied to both the pulses produced by the first stage 108 and by the second stage 109.

OPERATION In all operational modes, terminal 222 will receive a voltage from the temperature sensor which is indicative of the instantaneous engine operating temperature. For normal operation, this voltage will be sufficiently high that blocking diode 218 will be reverse biased and transistor 202 will be turned off. The signal received at terminal 222 will drip as the temperature of the engine goes up. When a hot soak situation occurs, the signal received at terminal 222 will be sufficiently low that diode 218 will be forward biased and transistor 202 will begin to conduct. The particular voltage level at which this will occur will be determine as a function of the relative values of

resistors

206, and 210 and the effect of diode means 220 and resistor 216. Diode means 220 will establish the base of transistor 202 at a relatively fixed voltage level above the voltage effect obtained by voltage divider network consisting of

resistors

210 and 216. The diode means 220 are included to provide that the same number of pn junctions are available to influence the reference voltage applied to the base of transistor 202 as are present to influence the voltage signal indicative of temperature. It is known that the voltage drop across a pn junction varies relatively broadly as a function of temperature and providrun ing diode means 220 insures that, since circuit 200 may be at ambient temperature, the wide variations in ambient temperature will not affect the ability of circuit 200 to recognize and respond to a hot soak condition. Since, in this embodiment,two pn junctions are present between the base of transistor 202 and terminal 222, diode means 220 inserts two pn junctions between the base of transistor 202 and ground. Thus, this circuitry is virtually free of any influence due to variations in ambient temperature and turn on of transistor 202 can be stabilized to respond to a selected or predetermined hot soak condition. By suitably adjusting the values of

resistors

210 and 216, the reference voltage at the base of transistor 202 can be readily established so that the transistor will go into conduction whenever the voltage received at terminal 222 drops to a point indicative of the hot soak condition. In this regard, of course, the resistance value of resistor 206 will be of importance.

As long as transistor 202 is not in conduction, the voltage at the collector terminal thereof will be substantially the same as the B+ voltage being applied to the circuit. However, when transistor 202 begins to conduct, the voltage at the collector terminal of transistor 202 will drop to a value which is a function of the amount of collector current flowing and this collector current will be in turn a function of the instantaneous voltage received at terminal 222. The collector voltage will be applied via resistor 214 to the base of transistor 204 and, so long as the voltage at the base of transistor 204 is less than the 3+ or supply voltage, transistor 204 will also conduct and the voltage appearing at terminal A will be affected thereby. The amount of this effect will be controlled by the extent of conduc tion of

transistors

202 and 204 and this will be applied at the selected portion of circuit 1.10 in FIG. 2 to vary the injection command pulses being controlled thereby.

While a preferred embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims, and, in some cases, certain features of the invention may be used to advantage without corresponding use of other features. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

I claim:

1. In an electronic fuel control system having a main computing circuit for intermittently energizing at least one injector valve means for the provision of metered quantities of fuel, the improvement comprising:

hot starting circuit means responsive to engine temperatures above a selected level indicative of hot soaking and coupled to the main computing circuit operative to lengthen the time period of energization of the injector valve means.

2. The system as claimed in claim 1 wherein said hot starting circuit means comprises:

control means responsive to engine temperatures operative to produce a signal having a magnitude representative of engine temperature above the selected level; and

amplifier means responsive to said control means signal operative to produce an output signal having a magnitude representative of the desired lengthening.

3. The system as claimed in claim 2 wherein said control means and said amplifier means include solid state electronic devices.

4. The circuit as claimed in claim 3 wherein said control means includes a plurality of pn junctions between the base electrode of the solid state electronic device and the source of temperature and an equal number of pn junctions between the base electrode and ground.

5. A fuel control system for an internal combustion engine comprising: sensor means operative to provide information concerning the engine fuel requirements;

computing means responsive to said sensor means information operative to produce an output signal having a variable characteristic representative of engine fuel requirements;

injector valve means responsive to said variable characteristic operative upon energization to provide precise quantities of fuel for the engine;

said sensor means including temperature sensor means operative to sense engine temperature; and

a hot start circuit responsive to said temperature sensor operative to apply a variable strength signal to said computing means at temperatures above a selected level indicative of hot soaking to alter the variable characteristic of the computing means output signal to controllably enlarge the quantities of fuel being provided to the engine by said injector valve means.

6. The system as claimed in claim 5 wherein said computing means include first and second stages and said second stage computing means is responsive to said first stage computing means and at least one of said first and second stage computing means is responsive to said temperature sensor means and said hot start circuit is coupled to one of said first and second stages.

7. The system as claimed in claim 6 wherein said hot start circuit is coupled to the first stage of said computing means.

8. The system as claimed in claim 6 wherein said hot start circuit is coupled to the second stage of said computing means.

9. The system as claimed in claim 5 wherein said hot start circuit comprises:

10. The system as claimed in claim 9 wherein said control means and said amplifier means include solid state electronic devices.

11. The circuit as claimed in claim 10 wherein said control means includes a plurality of pn junctions between the base electrode of the solid state electronic device and the source of temperature and an equal number of pn junctions between the base electrode and ground.

Claims

1. In an electronic fuel control system having a main computing circuit for intermittently energizing at least one injector valve means for the provision of metered quantities of fuel, the improvement comprising: hot starting circuit means responsive to engine temperatures above a selected level indicative of hot soaking and coupled to the main computing circuit operative to lengthen the time period of energization of the injector valve means.

2. The system as claimed in claim 1 wherein said hot starting circuit means comprises: control means responsive to engine temperatures operative to produce a signal having a magnitude representative of engine temperature above the selected level; and amplifier means responsive to said control means signal operative to produce an output signal having a magnitude representative of the desired lengthening.

5. A fuel control system for an internal combustion engine comprising: sensor means operative to provide information concerning the engine fuel requirements; computing means responsive to said sensor means information operative to produce an output signal having a variable characteristic representative of engine fuel requirements; injector valve means responsive to said variable characteristic operative upon energization to provide precise quantities of fuel for the engine; said sensor means including temperature sensor means operative to sense engine temperature; and a hot start circuit responsive to said temperature sensor operative to apply a variable strength signal to said computing means at temperatures above a selected level indicative of hot soaking to alter the variable characteristic of the computing means output signal to controllably enlarge the quantities of fuel being provided to the engine by said injector valve means.

9. The system as claimed in claim 5 wherein said hot start circuit comprises: control means responsive to engine temperatures operative to produce a signal having a magnitude representative of engine temperature above the selected level; and amplifier means responsive to said control means signal operative to produce an output signal having a magnitude representative of the desired lengthening.