CA1047140A - Exhaust gas sensor failure detection system - Google Patents
Exhaust gas sensor failure detection systemInfo
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- CA1047140A CA1047140A CA297,286A CA297286A CA1047140A CA 1047140 A CA1047140 A CA 1047140A CA 297286 A CA297286 A CA 297286A CA 1047140 A CA1047140 A CA 1047140A
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- exhaust gas
- engine
- gas sensor
- signal
- detection system
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- Testing Of Engines (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a fuel injection system for internal combustion engines an exhaust gas sensor is periodically tested under controlled engine operating conditions for the purpose of detecting any failures in this sensor. The failure detection system generates an electrical signal in response to a failed sensor which signal is used to inform the engine operator of the failure of the sensor.
In a fuel injection system for internal combustion engines an exhaust gas sensor is periodically tested under controlled engine operating conditions for the purpose of detecting any failures in this sensor. The failure detection system generates an electrical signal in response to a failed sensor which signal is used to inform the engine operator of the failure of the sensor.
Description
:~47~L~O
This invention relates to fuel lnjection systems in general and in particular to systems for detecting the failure of particular components of the system~
This application is related to applicantls copending applications Serial No. 228,799, filed June 9, 1975 and Serial No. 229,123, filed June 11, 1975.
Description of the Prior Art The use of exhaust gas sensor in exhaust systems of internal combustion engines for controlling the air~fuel ratio to the engine is well known as exhibited in the patent 3,745,768 issued to Zechnall et al. and entitied "Apparatus To Control The Proportion Of Air and Fuel In The Air/Fuel Mixture Of Internal Combustion Engines." In this parti-cular patent an oxygen analyzer or exhaust gas sensor is responsive to the oxygen present in the exhaust gas of an internal combustion engine. A siynal is generated by the sensor indicatiny whether or not oxygen is present in the exhaust gas and this signal is supplied to an electronic control unit for controlling or supplying in-formation to control the amount of fuel injected into the cylinders of the internal combustion engine. I-f the sensor indicates that oxygen is present in the exhaust gas the sensor signal will supply information to the control unit to increase the amount of fuel supplied to the internal combustion engine. Conversely, if the sensor indicates a lack of oxygen in the exhaust gas it will supply information tending to reduce the amount of fuel supplied to the cylinder.
This invention relates to fuel lnjection systems in general and in particular to systems for detecting the failure of particular components of the system~
This application is related to applicantls copending applications Serial No. 228,799, filed June 9, 1975 and Serial No. 229,123, filed June 11, 1975.
Description of the Prior Art The use of exhaust gas sensor in exhaust systems of internal combustion engines for controlling the air~fuel ratio to the engine is well known as exhibited in the patent 3,745,768 issued to Zechnall et al. and entitied "Apparatus To Control The Proportion Of Air and Fuel In The Air/Fuel Mixture Of Internal Combustion Engines." In this parti-cular patent an oxygen analyzer or exhaust gas sensor is responsive to the oxygen present in the exhaust gas of an internal combustion engine. A siynal is generated by the sensor indicatiny whether or not oxygen is present in the exhaust gas and this signal is supplied to an electronic control unit for controlling or supplying in-formation to control the amount of fuel injected into the cylinders of the internal combustion engine. I-f the sensor indicates that oxygen is present in the exhaust gas the sensor signal will supply information to the control unit to increase the amount of fuel supplied to the internal combustion engine. Conversely, if the sensor indicates a lack of oxygen in the exhaust gas it will supply information tending to reduce the amount of fuel supplied to the cylinder.
- 2 -1~7~L40 Such control is necessary for an internal combustion engine to improve the performance of the engine and to control the ~uality of the exhaust gas components in the exhaust gas of an internal combustion engine.
- The use of exhaust yas sensors in the exhaust lines of furnaces is likewise old in the art. Again the purpose of such sensors in the exhaust lines is to control the operation of the furnace for better performance and economy.
Oxygen sensors are used in the steel making processes to determine the amount of oxygen contained in the molten steel in the process of manufac~ure. These sensors generate signals which are applied to a control unit to control the process in the steel making.
In such instances of the prior art, detection of a failed sensor has been primarily one of observation by an operator such as by the ultimate failure o~ a component such as a converter downstream of the sensor or the physical destruction of the sensor by the environment in which it is placed. Constant or periodic monitoring of the output voltage of the sensor under controlled conditions has been required in order to determine whether or not the sensor is operating or performing correctly.
In fuel management systems for internal combustion engines it is necessary to accurately control the fuel/air ratio entering the engine in order to control the products of combustion as they appear in the exhaust gases. It is desired in internal combustion engines to control the amount of unburnt hydrocarbons and carbon monoxides in the exhaust sas by regulating the fuel/air mixture to the cylinder of the engine.
Nitrogen compounds in the exhaust gases are another undesirable component which may be neutralized by a catalytic converter placed downstream of the gas sensor. With the gas sensor controlling the fuel/air ratio into the engine thereby controlling hydrocarbons and carbon monoxide in the exhaust gas the catalytic converter need only have a single bed for neutralizing nitrogen compounds.
- The use of exhaust yas sensors in the exhaust lines of furnaces is likewise old in the art. Again the purpose of such sensors in the exhaust lines is to control the operation of the furnace for better performance and economy.
Oxygen sensors are used in the steel making processes to determine the amount of oxygen contained in the molten steel in the process of manufac~ure. These sensors generate signals which are applied to a control unit to control the process in the steel making.
In such instances of the prior art, detection of a failed sensor has been primarily one of observation by an operator such as by the ultimate failure o~ a component such as a converter downstream of the sensor or the physical destruction of the sensor by the environment in which it is placed. Constant or periodic monitoring of the output voltage of the sensor under controlled conditions has been required in order to determine whether or not the sensor is operating or performing correctly.
In fuel management systems for internal combustion engines it is necessary to accurately control the fuel/air ratio entering the engine in order to control the products of combustion as they appear in the exhaust gases. It is desired in internal combustion engines to control the amount of unburnt hydrocarbons and carbon monoxides in the exhaust sas by regulating the fuel/air mixture to the cylinder of the engine.
Nitrogen compounds in the exhaust gases are another undesirable component which may be neutralized by a catalytic converter placed downstream of the gas sensor. With the gas sensor controlling the fuel/air ratio into the engine thereby controlling hydrocarbons and carbon monoxide in the exhaust gas the catalytic converter need only have a single bed for neutralizing nitrogen compounds.
-3-SUMMARY OF INVENTION
An exhaust gas sensor failure detection system is described comprising: sensor signal shaping means electrically connected to the exhaust gas sènsor for generating rectangular shaped voltage waveforms having a first voltage level representing one range of ex-haust gases and a second voltage level representing a second range of exhaust gases; means for sensing the switching of the rectangu-lar shaped voltage waveform between the first voltage level and the secQ-nd voltage level and generating a triggering signal substan-tially coincident with the switching; a multivibrator responsive tothe triggering signal for generating an output pulse having a pre-determined time interval; test control circuit means responsive to at least one engine operating parameter for generating a first elec-trical signal when the engine is operating within a predetermined range of the parameter and a second electrical signal when the en-gine is operating other than the predetermined range; capacitive means electrically responsive to the first electrical signal and to the multivibrator for charging and discharging according to the out-put pulse; and capacitive charge level sensor electrically connected to the capacitive means and responsive to a predetermined charge level for generating and maintaining an exhaust gas failure detec-tion signal.
DESCRIPTION OF THE DRAWINGS
In the Drawings Fig. 1 is a block diagram of the sensor operational detec-tion system as may be used in a fuel injection system for an inter-nal combustion engine;
Fig. 2 is an electrical schematic of the system of Fig. l;
Fig. 3 is an electrical schematic including voltage wave-forms of the transition detector, multivibrator and transitioninterval indicator circuits of Fig. 2;
Fig. 4 is a schematic including waveforms oE the thermal time constant simulator oE Fig. 2;
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~L~ 73L~0 Fig. 5 is a block diagram and partial circuit schematic illustratiny a generation of RPM signals for the system of Fig. 1.
DETAILED DESCRIPTION
Referring to the Figs. by the characters of reference there is illustrated in Fig. 1 a schematic of the preferred embodiment of the sensor operational detection system according to the present invention. The system comprises an exhaust gas sensor 10, a transition detector 12, a multi-vibrator 14, a transition interval indicator 16, a test control circuit means 18, a fuel control unit 20, an injection control means 22, an indicator level sensor 24, and a failure latching means 26. The test control circuit means 18 is responsive to at least one predetermined engine operating condition and in the preferred embodiment it is responsive to an electrical signal Z8 representing fuel ~lowing, an electrical signal 30 representing the speed of the engine in RPM, an electrical signal 32 representing the.
throttle position, and an electrical signal 34 representing the engine temperature. In response to these four parameters a test enable signal is provided to the transition interval indica~or 16.
In the system of Fig. 1, the exhaust gas sensor 10 is a sensor which is positioned in the exhaust system of an internal combustion engine and is responsive to the chemical composition o~ the exhaust gas Flowing through the system. In the preferred embodiment the exhaust gas sensor 10 ~Ftq 3) is an oxygen gas sensor which is capable of generating an output signal 3 having a first voltage level in the presence of oxygen in the exhaust gas and a second voltage level in the absence of oxygen in the exhaust gas.
Such a signal is illustrated in the waveshape A of.Fig. 3. Other gas sensors may be used that are responsive to other constituent gases or characteristics of the exhaust and in response to these particular characteristics will generate a voltage level signal having at least a first and second voltage level for indicating the presence or the relative amount or the propor~ion of the sensed parameter in the exhaust gas.
:1~47~40 The output signal 36 of the exhaust gas sensor 10 is electrically connected to the transition detector 12 which is responsive to the shift in the voltage levels of the output signal 36 of the exhaust gas sensor 10.
In response to the output signal 36 the transition detector 12 generates a first electrical signal 38J~which is substantially a rectangular waveshape signal switching between greater voltage levels than the ou~put signal 36 from the exhaust gas sensor 10. Such a si~nal is illustrated in the waveshape D of Fig. 3.
In the preferred embodiment, the output signal 38 of the transition detector 12 is electrically connected to a monostable multivibrator 14 which in the pre~erred embodiment is responsive to a negative trigger signal for generating a negative pulse. The pulse time duration 40 of the multi-vibrator output signal is independent of the pulse time duration of first electrical signal 38 from the transition detector 12.
The test control means of Fig. 1 in the preferred embodiment is responsive to the combination of four predetermined engine operat;ng conditions. As will hereinafter be shown, the test enabling signal generated from the test control circuit means 18 is present only when the internal combustion engine is operated at predetermined operational conditions.
2Q One condition is that the eng;ne must be up to operating temperature as determined by means such as a coolant temperature sensor not shown ~ ~enerating a temperature signal 34. Another condition is that the engine has been operating under a load condition for a sufficient period of time so that the thermal time constants of the several elements of the system will not have an adverse effect on the fuel flow processing in the engine.
This condition is satisfied by the connection of the electrical signal 28 representing fuel flowing to the thermal time constant simulator ~2 which ~s illustrated in detail in Fig. ~. After these two temperature considera-tions are satisfied the test control circuit means 18 is then responsive to the electrical signal 30 representing speed of the cranksha~t o~ the engine which is generated by means of the circuit illustrated in Flg. 5.
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In addition to the above temperature and speed conditions, it has been found that in order to accurately test an oxygen gas sensor lO in the exhaust system of an internal combustion engine it is necessary that the test be conducted when the engine is in a reasonably steady state condition.
This steady state condition is such that the system is responsive to controlled engine operation of the internal combustion engine thereby controlling the chemical composition of the exhaust gas. One such steady state condition is that of idle engine operation. Since an engine under a relatively heavy load may have the same crankshaft rotation as that in the idle condition, it is necessary to detect the position of the throttle valve to determine which of the two conditions prevail. In the test control circuit means 18, the throttle signal 32 is an electrical signal repre-senting when the throttle valve is closed or not closed. In this manner therefore the system of Fig. l will test the operation of the exhaust gas sensor 10 during hot engine idle conditions and will detect failures only during this operational mode.
The transition interval indicator 16 is enabled by a signal from the clamp 44 and the comparator 46 of the test control circuit ~eans 18 and is responsive to the output signal of the multivibrator 14. Since the multivibrator generates a signal each time that the exhaust gas sensor 10 makes the transition from the first voltage level to the second voltage 1evel the transition interval indicator 16 indicates by means of a variable voltage stored on an indicator such as a capacitor means 48, the time between successive transitions. I~ the exhaust gas sensor 10 is working properly the interval between transitions is relatively short and the variable voltage level of the indicator 48 is relatively low. However, if the exhaust gas sensor l~ is not responsive to changes in the composition of the exhaust gas, the interval between transitions becomes great and the variable voltage level on the indicator 48 becomes higher and higher.
:~47~L40 The output of the transition interval indicatoi^ 16 is electrically connected to a fuel control unit 20 which in turn generates electrical signals controlling the injection control means 22. The output of the injection control means controls one or more electrically operated fuel injectors or groups of injectors 50. The fuel control unit 20 responding to the output from the transition interval indicator 16 will vary in a predetermined relationship the timing of the fuel injector means. It is a function of these three units, 16, 20, and 22 to alter the injection time of at least one injector or one group of injectors in such a manner ~o that the chemistry of the exhaust gas will change. In the preferred embodiment, the fuel control unit 20 will reduce the injection control time for the one injector or one group of injectors thereby causing a lean ~xhaust gas to flow past the exhaust gas sensor 10. In response to this lean exhaust gas the sensor 10 will generate a signal to the fuel control unit 20 in an attempt to enrichen the fuel mixture and position the exhaust gas composition on the rich s;de of stoichiometric point. It is this switching back and forth across the stoichiometric point which the exhaust gas sensor responds by generating its output signal 36 having first and second voltage levels. If ~he exhaust gas sensor 10 does not respond to the changes in the fuel mixture then the transition interval indicator 16 will generate by means of a high voltage signal on the capacitor means 48 that the interval between successive transitions is great.
This high voltage level is sensed by an indicator level sensor 24 and generates a signal to activate a failure latching means 26. Once activated, the failure latching means will generate a failure signal to warn the operator of the internal combustion engine that the exhaust gas sensor 10 is not operating properly. This failure signal may take many forms such as lights or buzzers in the operator's compartment of the internal combustion engine or may under certain conditions cause the internal combustion engine to malfunction. One such operating condition ~1~47~
occurs at idle speed and the failure latching means, ;n an electron;c fuel injection system hav;ng at least two groups of ;njectors, may cause one group of injectors to per;odically misfire or not open thereby causing an extreme rough idle operating condition for the internal combustion engine. Such condition will be such that the internal combustion engine is capable of operating but it is suFficiently annoying to cause the operator to investigate and have the exhaust gas sensor 10 repaired or replaced.
Referring to Fig. 3, there is illustrated in schematic form the circuitry for the transition detector 12, the multivibrator 14, and the transition interval indicator 16. Additionally, Fig. 3 shows voltage waveshapes taken at several po;nts in the circuitry which are identified by ùpper case letters. As previously indicated it is a function of these three units 12, 14 and 16 to respond to the operation of the exhaust gas sensor 10 to alter the injection time of at least one injector or one group of injectors in such a manner that the exhaust gas chemistry w;ll change. The input signal labelled A is typical of the output signal 36 received from an exhaust gas sensor 10 or its associated amplifier. This pulse is applied through a filter network 51 and 52 to the input of an emitter follower transistor 53 in the transition detector 12. As shown by the pulse waveform B the resistor capacitor input filter 51,52 removes the relatively high frequency signals or noise on the output signal 36 from the exhaust gas sensor 10. The output of the emitter follower transistor 53 labelled C, is supplied to the input of the second stage 54 of the transition detector. In the waveshapes of Fig. 3 the typical voltage levels for the signals are indicated. As therefore seen in the first stage 53, the output signal 36 of the exhaust gas sensor 10 drives the first stage 53 into saturation by the negative transition of the output signal from the sensor 10.
The second stage 54 of the transition detector 12 has lts emitter 55 biased by a voltage divider 56 co~prising a pair of g ~7~
resistors 57 and 58 electrically connected across the source of supply.
In the preferred embodiment the voltage on the emitter 5~ of the transistor 54 is approximately 200 millivolts. The output of the second stage 54 is a relatively sharp rectangular wave pulse 38 switching between the voltage level of the supply and the saturation voltage drop across the transistor 54 plus the bias on the emitter 55. It is a function of this second stage 54 to complete the shaping and raise the power gain of the signal 36 from the exhaust gas sensor.
The multivibrator stage in the preferred embodiment is a monostable or one-shot multivibrator ~ormed from an integrated circuit comparator 59 and its feedback network comprising a series resistor 60 and capacitor 61. The output signal 38 of the second stage 54 of the transition detector is capacitively coupled by means of a capacitor 62 to the inverting input 63 of the comparator 59.
The noninverting input 64 of the comparator 59 is biased through a resistor 65 from the voltage source A~. With reference to waveshapes E and F on Fig. 3 it is seen that the multivibrator 14 is responsive to a negative trigger signa1 on its noninverting inpLIt 64 for generating a negative pulse. This negative pulse has a predetermined time duration 40 which is independent of the time duration of the input pulse 3~ from the second stage 54 of the transition detector 16.
As illustrated in waveshape ~, the input signal to the comparator ~9 at its noninverting input 64 is charged back up to the supply voltage with a time constant which is determined by the resistance 60 in feedback circuit of the comparator and the series resistor 65 from ~he source of supply and the capacitor 61.
The transition interval indicator 16 in the preferred embodiment is an asymetrical integrator in that its charging and discharging paths are in parallel but operate with different time constants. It is the 3~ voltage level on the capacitor ~8 which is sensed by the indicator level sensor 24 to determine or detect the failure of the exhaust ~as sensor 10.
~L¢34 7 1 ~
The charging circuit for the capacitor q8 comprises a resistor 66 electrically connected to the output of the multivibrator l~ and through this resistor the capacitor ~8 attempts to charge to the normally high voltage level output of the comparator 59. The discharging circuit for the capacitor 48 is a resistor 67 and a diode 68 electrically connected in series to the output of the comparator 59. ~owever, the diode 68 is electrically connected in the circuit so as to block the flow of charging current to the capacitor 48. The respective values of the two resistors 66 and 67 determine the time constants ~or their respective circuit. In the preferred embodiment the discharge time constant is much smaller than the charging time constant. As an example the resistance value of the charging resistor 66 is 8 times the resistance value of the discharging resistor 67.
Referring to the waveshape G of Fig. 3 there is shown the slow charging voltage for the capacitor 48 which is determined by the charging resistor 66. In the preferred embodiment this time constant is approxi-mately fifteen seconds. When the multivibrator 14 generates its pulse illustrated in waveshape F the capacitor 48 discharges through its discharge network for the duration of the pulse. In the preferred embodiment the output pulse time 40 of the multivibrator 14 is approximately forty milliseconds and the discharge time constant for the capacitor 48 is approximately three seconds.
Thus it is seen for the circuit illustrated in Fig. 3 with power applied to the circuit a capacitor 48 will attempt to charge up through its charging resistor 66 to the output of the comparator 59. Since the nonmal output of the comparator 59 is approximately equal to the source voltage, the voltage on the capacitor ~ would eventually be equal to the source voltage. HowèYer, as will hereinafter be shown, the test control circuit means 18 provides a clamping signal on the capacitor 48 preventing 3~ ~t from being charged. With an exhaust gas sensor lO electrically connected ~o the input of the transition detector l2 and having a characteristic -~Lq~7 ~L-g~0 waveshape as shown in wave~orm A of Fig. 3 the capacitor 4~ will attempt to discharge in response to positive yoing transition of the sensor output signal 36. For the purposes of failure detection a predetermined voltage level 69 is selected such as that indicated on waveshape G and if the voltage on the capacitor 48 attains that level 69 the indicator level sensor 2~ will generate a signal indicating that the sensor 10 has not generated a waveshape 36 similar to that shown on waveshape A of Fig. 3.
Referring to Fig. 4 there is illustrated a circuit schematic and waveforms ~or the thermal time constant simulator 42 of the test control circuit means 18 of Fig. 1. It is the function of the simulator 42 to develop a voltage signal after a predetermined period of time, which is not real time but operation time, to indicate that the temperature of the several components of the fuel flowing processing system including the exhaust gas and the exhaust gas sensor are sufficiently high. In particular the exhaust gas sensor 10 of the preferred embodiment must be at a relatively high temperature in order to operate properly. The thermal time constant simulator 42 is essentially an asy~etrical integrator having a capacitor 7~, a charging resistor 71 and a discharging resistor 72 so that the charging and discharging time constants are much different. Electrically connected to the asymetrical integrator is a transistor switch member 73 which is responsive to a signal 28 repre~enting the time that the fuel is f~owing in the system. When the transistor 73 is driven into conduction, the capacitor 70 will discharge through its series resistor 72 and diode 74 combination thereby lowering the voltage level on the inverting input 75 of the comparator 46.
Referring to the waveshape A of Fig. 4 which is the input wave-shape signal 28 to the base of the transistor 73, the waveshape is illustrated as being substantially a rectangular waveshape having both a Yarying pulse width duration and a varying time period between pulses.
In the preferred embodiment the presence of a pulse indicates that the ~uel is flowing throu~h the injector into the cylinder and the absence of a pulse indicates that the injector is closed. The time duration between 4714~
pulses is essentially a function of the operating speed of the engine and therefore when the engine is operating at idle speed the pulses are much further apart than when the engine is operating under load conditions.
The time constant simulator 42 will not allow the capacitor 70 to discharge to an operating voltage level in Reference 76 with the engine operating continuously at idle condition, This is illustrated by the waveshape C
wherein it is shown that the capacitor 7~ will begin to discharge when the collector 77 of the input transistor 73 is essentially at ground level.
If the internal combustion engine is operating continuously at an idle condition it has been found that the temperature of the exhaust gas sensor 10 will decrease below a preferred operating level. The time constants of the charge and discharge circuits of the capacitor 70 of Fig. 4 are such that the voltage at the inverting input 75 of the comparator 46 will remain sufficiently close to the supply voltage thereby indicating that the system is not in condition for performing the test.
In Fig. 4 the input to the noninverting input 80 oF the comparator 46 is indicated as being a particular reference voltage 76 which level is in the preferred embodiment somewhat less than the supply voltage. When the voltage at the output of the capacitor 70 or at the inverting input 75 falls below the reference voltage 76 the output signal 78 of the comparator 49 will switch as shown on waveshape D. In the preferred embodiment and as illustrated in Fig. 2 the output stage 79 of the comparator 46 is an uncommitted collector of a grounded emitter NPN
transistor. When the voltage on the inverting input 75 of the comparator 46 2~ falls below the voltage level of the noninverting input 80 of the comparator 46 this output transistor 79 functioning as a clamping circuit means is turned off removing the ground clamp and essentially connects the output of the comparator 46 to the voltage level of the component electrically connected to the collector. In the preferred embodiment as illustrated in Fig. 2 this is the capacitor ~8 in the transition indicator means 16, or the clamping diode 44 from the temperature circuit.
~LC~7 ~
When power is initially supplied to the circuit of Fig. 4 the voltage at the output of the capacitor 70 is essentially equal to the supply voltage and will remain there until the voltage signal at the input to the transistor 73 occurs at a sufficiently fast repetition rate. The discharge time constant of the capacitor 70 in the preferred embodiment is approximately twenty seconds and the charging time constant is approximately sixty seconds. The pulse width duration of the input pulses to the transistor 73 varies in time from approxinlately five milliseconds to fifteen milliseconds and the time period between pulses is typically on the order of fifty milliseconds.
It is previously indicated that one of the test conditions which is supplied to the test control circuit means 18 is an electrical signal 30 indicating the speed of the engine. As previously indicateds in the operation of the sensor detection system it is desired to test the sensor 10 and detect any failures only during idle speed conditions. The RPM signal 30 in the preferred embodiment is a series of negative pulses of a predetermined pulse time duration wherein the pulse repetition frequency or the time between the pulses varies inYersely as to rpm. Thus at idle speeds the time between pulses is much longer than at high speeds. In Fig. 2 the signal 30 is supplied through a resistor 81 to a capacitor 82 and supplies or contributes to maintaining the voltage 76 on the noninverting input 80 of the comparator 46 of Fig. 4. Thus, under high speed condition, the capacitor 82 is not charged up inasmuch as the negative pulses from the rpm signal 30 occur very rapidly and operate to discharge the capacitor 82 to ground.
Referring to Fig. 5 there is a partial block diagràm and electrical schematic of the circuit for generating the rpm signal 30 as used in Flg. 2.
The timing generator 84 is responsive to the rotation of the crankshaft 86 of the engine and generates a pair of pulse trains 87 and 88, labelled waYeforms A and B in Fig. 5. The time between consecuti~e pulses in either 47~L4(~
pulse train is proportional to the speed of the crankshaft 86 and the faster the crankshaft rotates, the shorter the time or the closer together the pulses become. These pulses are supplied to a flip-flop 90 and one output is connected to a pulse generator 92 for generating pulses 94 having a predetermined width or time duration in response to the pulse trains 87 and 88 from the timing generator 84. These pulses 94 as shown in waveform D o~ Fig.5 are supplied to a transistor 96 which when turned on operates to discharge a timing capacitor 98. I~laveform E of Fig. 5 shows the waveform at the output of the timing capacitor 98 which is connected to noninverting input of a comparator 100. The output of the comparator 100 is a plurality of negative going pulses 30 having a predetermined pulse time duration but having a time between pulses which is inversely proportional to the speed of the engine.
Referring to Fig. 2 one of the other conditions applied to the test control circuit means 18 is an electrical signal 32 representin~ the position of the throttle valve in the throttle body of the engine. As previously indicated it is a function of the system to detect failures in the exhaust gas sensor 10 only during idle conditions. When the throttle is closed indicating idle condition, the voltage level on the throttle input is at a high voltage le~el and allows the capacitor 82 to charge to this level. As shown in Fig. 1 it is a combination of the rpm signal 30 and the throttle position signal 32 which operate to determine the idle state of the engine. In essence, these two signals 30 and 32 are combined together forming a logical AND gate.
The other test condition which must be present is the indication of the engine ~emperature. This signal 34 is generated by means of a coolant temperature sensor generating a high voltage output signal when the cool~nt exceeds a predetermined temperature. This waveshape 34 as indicated on Fig. ~, switches from a low to a high voltage level when the temperature exceeds a predetermlned temperature. This signal is electrically connected to the ou~put of the comparator by means o~ the clamping diode 44.
-lS-~47~4~
As illustrated in Fig. 2 the output of the comparator 46 in the test control circuit means 1~ is an open col1ector ~IP~ tnansistor 79. The temperature signal 34 from the coolant temperature is supplied through the clamping diode 44 to the collector of the transistor 79 clamping it to ground when the coolant temperature is below the predetermine~ level.
However, when all the conditions for detection are present, the voltage level of the noninverting input 80 of the comparator 46 as a result o~ the throttle position signal 32 and the speed of the enyine is high if the engine is in idle condition. llhen the operating temperature of the exhaust system is above a predetermined level of temperature the voltage level on the inverting input 75 of the comparator 46 is lower than the voltage level to the noninverting input 80 causing the output transistor 79 to be ~riven out of conduction removing the clamping voltage fro~ the capacitor 48 in the transition interval indicator 16. This allows the capacitor ~8 to charge to the output of the multivibrator 14 and when the voltage level on the capacitor 48 exceeds the predetermined level as determined by the bias voltage of the transistor 102 of the ;ndicator level sensor 24 a failure latching signal will be generated.
Referring to Fig. 2 the indicator level sensor 24 comprises the transistor 102 having its input biased to a predetermined voltage level.
This voltage level is determined by a voltage divider 104 comprising a pair of resistors 105 and 106 electrically connected across the supply voltage. In the preferred embodiment ~hen the voltage on the emitter 108 of the transistor 102 exceeds the bias voltage on the base 109, the transistor 102 is driven into conduction and the voltage is applied to the collector 110 of the transistor 102.
The cutput or collector of the transistor 102 in the indicator level sensor 24 is electrically connected to a failure latching means 26 for generating a signal representing the failure of the exhaust gas sensor.
The failure latching circuit comprises a pair of transistors 112 and 11~
wherein the first transistor 112 has its emitter lead electrically connected ~16-1~47~4~) to the base lO9 lead of the indicator level sensor transistor 102 and its collector lead electrically connected to the collector llO of the ind1cator level sensor transistor 102. The second transistor 114 has its base electrically connected to the collector of the ~irst transistor 112 and its emitter is grounded. Thus, the two transistors 112 and 114 are connected in a latching circuit. The base of the second transistor 11~ is biased through a resistor to ground therefore when the transistor 102 in the sensor circuit is driven into conduction this applies the voltage on the base lead of the second transistor 114 of the latching circuit driving it into conduction. Through the co-operation and operation oF the two transistors 112 and 114 the collector lead of the second transistor 114 has a voltage level impressed thereon which will be maintained until po~er is removed from the circuit. This voltage level will be present regardless of succeeding operations of the transition interval indicator 16 or the test control circuit means 18.
Referring more particularly to Fig. 2, the fuel control unit 20 controls the selection of which injector group 50 is to be fired and controls the injector timing control unit 22 to determine the time durat-on that the injector is to be operated. A constant current source ll~ is selectively coupled to each injector group 50 by means such as a flip-flop 118 receiving control signals from the control unit 120. In response to the signal on the capacitor 48 of the transition interval indicator unit 16, a control circuit represented by a transistor 122 having a resistor 124 and a diode 126 serially connected to its emitter and to the output of the flip-flop 118 provides a voltage mismatch for the current source 116 thereby effecting the amount of current supplied to the fuel control pulse generating circuitry only during the injection cycle of one of the injector groups. In the preferred embodiment this voltage mismatch circuit causes an increase in the current to the fuel control pulse generating circuitry only during the ~njection cycle o~ the one injector group thereby causing the ~njector group to operate on a shorter p~lse width. This in effect will cause a lean fuel L7~
mixture to be injected into the cylinders controlled by the particular in~ector group. It is through the action of this particular circuit that will cause the exhaust gas to switch back and forth over the stoichiometric fuel air ratio.
It is further indicated in Fig~ 2 the signal from the failure latching means 26 is supplied to a timer 128 whose function is to interrupt the injector timing control unit 22. In the preferred embodiment the timer wili supply a signal to the injector timing control unit which in effect will drop the timing signal to one of the injector groups 50. With this timing signal not present to the injector group, fuel will not be supplied to the cylinders from the injectors controlled by that group and the internal combùstion engine will then misoperate.
By unbalancing the signal to one of the injector group 50 such as removing the timing signal the internal combustion engine will operate in a rough mode which will become very annoying to the operator. However, this malfunction will only occur during idle condition and will not effect the operation of the internal combustion engine at times other than idle.
There has thus been shown and described an exhaust gas sensor operational detection system for use in a fuel injection system of an internal combustion engine. Under predetermined engine operating conditions, the detection system will detect an inoperative or failed exhaust sensor and as a result thereof will generate a failure signal for activating some form of warning means to the operator of the engine.
An exhaust gas sensor failure detection system is described comprising: sensor signal shaping means electrically connected to the exhaust gas sènsor for generating rectangular shaped voltage waveforms having a first voltage level representing one range of ex-haust gases and a second voltage level representing a second range of exhaust gases; means for sensing the switching of the rectangu-lar shaped voltage waveform between the first voltage level and the secQ-nd voltage level and generating a triggering signal substan-tially coincident with the switching; a multivibrator responsive tothe triggering signal for generating an output pulse having a pre-determined time interval; test control circuit means responsive to at least one engine operating parameter for generating a first elec-trical signal when the engine is operating within a predetermined range of the parameter and a second electrical signal when the en-gine is operating other than the predetermined range; capacitive means electrically responsive to the first electrical signal and to the multivibrator for charging and discharging according to the out-put pulse; and capacitive charge level sensor electrically connected to the capacitive means and responsive to a predetermined charge level for generating and maintaining an exhaust gas failure detec-tion signal.
DESCRIPTION OF THE DRAWINGS
In the Drawings Fig. 1 is a block diagram of the sensor operational detec-tion system as may be used in a fuel injection system for an inter-nal combustion engine;
Fig. 2 is an electrical schematic of the system of Fig. l;
Fig. 3 is an electrical schematic including voltage wave-forms of the transition detector, multivibrator and transitioninterval indicator circuits of Fig. 2;
Fig. 4 is a schematic including waveforms oE the thermal time constant simulator oE Fig. 2;
;c/~
~L~ 73L~0 Fig. 5 is a block diagram and partial circuit schematic illustratiny a generation of RPM signals for the system of Fig. 1.
DETAILED DESCRIPTION
Referring to the Figs. by the characters of reference there is illustrated in Fig. 1 a schematic of the preferred embodiment of the sensor operational detection system according to the present invention. The system comprises an exhaust gas sensor 10, a transition detector 12, a multi-vibrator 14, a transition interval indicator 16, a test control circuit means 18, a fuel control unit 20, an injection control means 22, an indicator level sensor 24, and a failure latching means 26. The test control circuit means 18 is responsive to at least one predetermined engine operating condition and in the preferred embodiment it is responsive to an electrical signal Z8 representing fuel ~lowing, an electrical signal 30 representing the speed of the engine in RPM, an electrical signal 32 representing the.
throttle position, and an electrical signal 34 representing the engine temperature. In response to these four parameters a test enable signal is provided to the transition interval indica~or 16.
In the system of Fig. 1, the exhaust gas sensor 10 is a sensor which is positioned in the exhaust system of an internal combustion engine and is responsive to the chemical composition o~ the exhaust gas Flowing through the system. In the preferred embodiment the exhaust gas sensor 10 ~Ftq 3) is an oxygen gas sensor which is capable of generating an output signal 3 having a first voltage level in the presence of oxygen in the exhaust gas and a second voltage level in the absence of oxygen in the exhaust gas.
Such a signal is illustrated in the waveshape A of.Fig. 3. Other gas sensors may be used that are responsive to other constituent gases or characteristics of the exhaust and in response to these particular characteristics will generate a voltage level signal having at least a first and second voltage level for indicating the presence or the relative amount or the propor~ion of the sensed parameter in the exhaust gas.
:1~47~40 The output signal 36 of the exhaust gas sensor 10 is electrically connected to the transition detector 12 which is responsive to the shift in the voltage levels of the output signal 36 of the exhaust gas sensor 10.
In response to the output signal 36 the transition detector 12 generates a first electrical signal 38J~which is substantially a rectangular waveshape signal switching between greater voltage levels than the ou~put signal 36 from the exhaust gas sensor 10. Such a si~nal is illustrated in the waveshape D of Fig. 3.
In the preferred embodiment, the output signal 38 of the transition detector 12 is electrically connected to a monostable multivibrator 14 which in the pre~erred embodiment is responsive to a negative trigger signal for generating a negative pulse. The pulse time duration 40 of the multi-vibrator output signal is independent of the pulse time duration of first electrical signal 38 from the transition detector 12.
The test control means of Fig. 1 in the preferred embodiment is responsive to the combination of four predetermined engine operat;ng conditions. As will hereinafter be shown, the test enabling signal generated from the test control circuit means 18 is present only when the internal combustion engine is operated at predetermined operational conditions.
2Q One condition is that the eng;ne must be up to operating temperature as determined by means such as a coolant temperature sensor not shown ~ ~enerating a temperature signal 34. Another condition is that the engine has been operating under a load condition for a sufficient period of time so that the thermal time constants of the several elements of the system will not have an adverse effect on the fuel flow processing in the engine.
This condition is satisfied by the connection of the electrical signal 28 representing fuel flowing to the thermal time constant simulator ~2 which ~s illustrated in detail in Fig. ~. After these two temperature considera-tions are satisfied the test control circuit means 18 is then responsive to the electrical signal 30 representing speed of the cranksha~t o~ the engine which is generated by means of the circuit illustrated in Flg. 5.
i~714~
In addition to the above temperature and speed conditions, it has been found that in order to accurately test an oxygen gas sensor lO in the exhaust system of an internal combustion engine it is necessary that the test be conducted when the engine is in a reasonably steady state condition.
This steady state condition is such that the system is responsive to controlled engine operation of the internal combustion engine thereby controlling the chemical composition of the exhaust gas. One such steady state condition is that of idle engine operation. Since an engine under a relatively heavy load may have the same crankshaft rotation as that in the idle condition, it is necessary to detect the position of the throttle valve to determine which of the two conditions prevail. In the test control circuit means 18, the throttle signal 32 is an electrical signal repre-senting when the throttle valve is closed or not closed. In this manner therefore the system of Fig. l will test the operation of the exhaust gas sensor 10 during hot engine idle conditions and will detect failures only during this operational mode.
The transition interval indicator 16 is enabled by a signal from the clamp 44 and the comparator 46 of the test control circuit ~eans 18 and is responsive to the output signal of the multivibrator 14. Since the multivibrator generates a signal each time that the exhaust gas sensor 10 makes the transition from the first voltage level to the second voltage 1evel the transition interval indicator 16 indicates by means of a variable voltage stored on an indicator such as a capacitor means 48, the time between successive transitions. I~ the exhaust gas sensor 10 is working properly the interval between transitions is relatively short and the variable voltage level of the indicator 48 is relatively low. However, if the exhaust gas sensor l~ is not responsive to changes in the composition of the exhaust gas, the interval between transitions becomes great and the variable voltage level on the indicator 48 becomes higher and higher.
:~47~L40 The output of the transition interval indicatoi^ 16 is electrically connected to a fuel control unit 20 which in turn generates electrical signals controlling the injection control means 22. The output of the injection control means controls one or more electrically operated fuel injectors or groups of injectors 50. The fuel control unit 20 responding to the output from the transition interval indicator 16 will vary in a predetermined relationship the timing of the fuel injector means. It is a function of these three units, 16, 20, and 22 to alter the injection time of at least one injector or one group of injectors in such a manner ~o that the chemistry of the exhaust gas will change. In the preferred embodiment, the fuel control unit 20 will reduce the injection control time for the one injector or one group of injectors thereby causing a lean ~xhaust gas to flow past the exhaust gas sensor 10. In response to this lean exhaust gas the sensor 10 will generate a signal to the fuel control unit 20 in an attempt to enrichen the fuel mixture and position the exhaust gas composition on the rich s;de of stoichiometric point. It is this switching back and forth across the stoichiometric point which the exhaust gas sensor responds by generating its output signal 36 having first and second voltage levels. If ~he exhaust gas sensor 10 does not respond to the changes in the fuel mixture then the transition interval indicator 16 will generate by means of a high voltage signal on the capacitor means 48 that the interval between successive transitions is great.
This high voltage level is sensed by an indicator level sensor 24 and generates a signal to activate a failure latching means 26. Once activated, the failure latching means will generate a failure signal to warn the operator of the internal combustion engine that the exhaust gas sensor 10 is not operating properly. This failure signal may take many forms such as lights or buzzers in the operator's compartment of the internal combustion engine or may under certain conditions cause the internal combustion engine to malfunction. One such operating condition ~1~47~
occurs at idle speed and the failure latching means, ;n an electron;c fuel injection system hav;ng at least two groups of ;njectors, may cause one group of injectors to per;odically misfire or not open thereby causing an extreme rough idle operating condition for the internal combustion engine. Such condition will be such that the internal combustion engine is capable of operating but it is suFficiently annoying to cause the operator to investigate and have the exhaust gas sensor 10 repaired or replaced.
Referring to Fig. 3, there is illustrated in schematic form the circuitry for the transition detector 12, the multivibrator 14, and the transition interval indicator 16. Additionally, Fig. 3 shows voltage waveshapes taken at several po;nts in the circuitry which are identified by ùpper case letters. As previously indicated it is a function of these three units 12, 14 and 16 to respond to the operation of the exhaust gas sensor 10 to alter the injection time of at least one injector or one group of injectors in such a manner that the exhaust gas chemistry w;ll change. The input signal labelled A is typical of the output signal 36 received from an exhaust gas sensor 10 or its associated amplifier. This pulse is applied through a filter network 51 and 52 to the input of an emitter follower transistor 53 in the transition detector 12. As shown by the pulse waveform B the resistor capacitor input filter 51,52 removes the relatively high frequency signals or noise on the output signal 36 from the exhaust gas sensor 10. The output of the emitter follower transistor 53 labelled C, is supplied to the input of the second stage 54 of the transition detector. In the waveshapes of Fig. 3 the typical voltage levels for the signals are indicated. As therefore seen in the first stage 53, the output signal 36 of the exhaust gas sensor 10 drives the first stage 53 into saturation by the negative transition of the output signal from the sensor 10.
The second stage 54 of the transition detector 12 has lts emitter 55 biased by a voltage divider 56 co~prising a pair of g ~7~
resistors 57 and 58 electrically connected across the source of supply.
In the preferred embodiment the voltage on the emitter 5~ of the transistor 54 is approximately 200 millivolts. The output of the second stage 54 is a relatively sharp rectangular wave pulse 38 switching between the voltage level of the supply and the saturation voltage drop across the transistor 54 plus the bias on the emitter 55. It is a function of this second stage 54 to complete the shaping and raise the power gain of the signal 36 from the exhaust gas sensor.
The multivibrator stage in the preferred embodiment is a monostable or one-shot multivibrator ~ormed from an integrated circuit comparator 59 and its feedback network comprising a series resistor 60 and capacitor 61. The output signal 38 of the second stage 54 of the transition detector is capacitively coupled by means of a capacitor 62 to the inverting input 63 of the comparator 59.
The noninverting input 64 of the comparator 59 is biased through a resistor 65 from the voltage source A~. With reference to waveshapes E and F on Fig. 3 it is seen that the multivibrator 14 is responsive to a negative trigger signa1 on its noninverting inpLIt 64 for generating a negative pulse. This negative pulse has a predetermined time duration 40 which is independent of the time duration of the input pulse 3~ from the second stage 54 of the transition detector 16.
As illustrated in waveshape ~, the input signal to the comparator ~9 at its noninverting input 64 is charged back up to the supply voltage with a time constant which is determined by the resistance 60 in feedback circuit of the comparator and the series resistor 65 from ~he source of supply and the capacitor 61.
The transition interval indicator 16 in the preferred embodiment is an asymetrical integrator in that its charging and discharging paths are in parallel but operate with different time constants. It is the 3~ voltage level on the capacitor ~8 which is sensed by the indicator level sensor 24 to determine or detect the failure of the exhaust ~as sensor 10.
~L¢34 7 1 ~
The charging circuit for the capacitor q8 comprises a resistor 66 electrically connected to the output of the multivibrator l~ and through this resistor the capacitor ~8 attempts to charge to the normally high voltage level output of the comparator 59. The discharging circuit for the capacitor 48 is a resistor 67 and a diode 68 electrically connected in series to the output of the comparator 59. ~owever, the diode 68 is electrically connected in the circuit so as to block the flow of charging current to the capacitor 48. The respective values of the two resistors 66 and 67 determine the time constants ~or their respective circuit. In the preferred embodiment the discharge time constant is much smaller than the charging time constant. As an example the resistance value of the charging resistor 66 is 8 times the resistance value of the discharging resistor 67.
Referring to the waveshape G of Fig. 3 there is shown the slow charging voltage for the capacitor 48 which is determined by the charging resistor 66. In the preferred embodiment this time constant is approxi-mately fifteen seconds. When the multivibrator 14 generates its pulse illustrated in waveshape F the capacitor 48 discharges through its discharge network for the duration of the pulse. In the preferred embodiment the output pulse time 40 of the multivibrator 14 is approximately forty milliseconds and the discharge time constant for the capacitor 48 is approximately three seconds.
Thus it is seen for the circuit illustrated in Fig. 3 with power applied to the circuit a capacitor 48 will attempt to charge up through its charging resistor 66 to the output of the comparator 59. Since the nonmal output of the comparator 59 is approximately equal to the source voltage, the voltage on the capacitor ~ would eventually be equal to the source voltage. HowèYer, as will hereinafter be shown, the test control circuit means 18 provides a clamping signal on the capacitor 48 preventing 3~ ~t from being charged. With an exhaust gas sensor lO electrically connected ~o the input of the transition detector l2 and having a characteristic -~Lq~7 ~L-g~0 waveshape as shown in wave~orm A of Fig. 3 the capacitor 4~ will attempt to discharge in response to positive yoing transition of the sensor output signal 36. For the purposes of failure detection a predetermined voltage level 69 is selected such as that indicated on waveshape G and if the voltage on the capacitor 48 attains that level 69 the indicator level sensor 2~ will generate a signal indicating that the sensor 10 has not generated a waveshape 36 similar to that shown on waveshape A of Fig. 3.
Referring to Fig. 4 there is illustrated a circuit schematic and waveforms ~or the thermal time constant simulator 42 of the test control circuit means 18 of Fig. 1. It is the function of the simulator 42 to develop a voltage signal after a predetermined period of time, which is not real time but operation time, to indicate that the temperature of the several components of the fuel flowing processing system including the exhaust gas and the exhaust gas sensor are sufficiently high. In particular the exhaust gas sensor 10 of the preferred embodiment must be at a relatively high temperature in order to operate properly. The thermal time constant simulator 42 is essentially an asy~etrical integrator having a capacitor 7~, a charging resistor 71 and a discharging resistor 72 so that the charging and discharging time constants are much different. Electrically connected to the asymetrical integrator is a transistor switch member 73 which is responsive to a signal 28 repre~enting the time that the fuel is f~owing in the system. When the transistor 73 is driven into conduction, the capacitor 70 will discharge through its series resistor 72 and diode 74 combination thereby lowering the voltage level on the inverting input 75 of the comparator 46.
Referring to the waveshape A of Fig. 4 which is the input wave-shape signal 28 to the base of the transistor 73, the waveshape is illustrated as being substantially a rectangular waveshape having both a Yarying pulse width duration and a varying time period between pulses.
In the preferred embodiment the presence of a pulse indicates that the ~uel is flowing throu~h the injector into the cylinder and the absence of a pulse indicates that the injector is closed. The time duration between 4714~
pulses is essentially a function of the operating speed of the engine and therefore when the engine is operating at idle speed the pulses are much further apart than when the engine is operating under load conditions.
The time constant simulator 42 will not allow the capacitor 70 to discharge to an operating voltage level in Reference 76 with the engine operating continuously at idle condition, This is illustrated by the waveshape C
wherein it is shown that the capacitor 7~ will begin to discharge when the collector 77 of the input transistor 73 is essentially at ground level.
If the internal combustion engine is operating continuously at an idle condition it has been found that the temperature of the exhaust gas sensor 10 will decrease below a preferred operating level. The time constants of the charge and discharge circuits of the capacitor 70 of Fig. 4 are such that the voltage at the inverting input 75 of the comparator 46 will remain sufficiently close to the supply voltage thereby indicating that the system is not in condition for performing the test.
In Fig. 4 the input to the noninverting input 80 oF the comparator 46 is indicated as being a particular reference voltage 76 which level is in the preferred embodiment somewhat less than the supply voltage. When the voltage at the output of the capacitor 70 or at the inverting input 75 falls below the reference voltage 76 the output signal 78 of the comparator 49 will switch as shown on waveshape D. In the preferred embodiment and as illustrated in Fig. 2 the output stage 79 of the comparator 46 is an uncommitted collector of a grounded emitter NPN
transistor. When the voltage on the inverting input 75 of the comparator 46 2~ falls below the voltage level of the noninverting input 80 of the comparator 46 this output transistor 79 functioning as a clamping circuit means is turned off removing the ground clamp and essentially connects the output of the comparator 46 to the voltage level of the component electrically connected to the collector. In the preferred embodiment as illustrated in Fig. 2 this is the capacitor ~8 in the transition indicator means 16, or the clamping diode 44 from the temperature circuit.
~LC~7 ~
When power is initially supplied to the circuit of Fig. 4 the voltage at the output of the capacitor 70 is essentially equal to the supply voltage and will remain there until the voltage signal at the input to the transistor 73 occurs at a sufficiently fast repetition rate. The discharge time constant of the capacitor 70 in the preferred embodiment is approximately twenty seconds and the charging time constant is approximately sixty seconds. The pulse width duration of the input pulses to the transistor 73 varies in time from approxinlately five milliseconds to fifteen milliseconds and the time period between pulses is typically on the order of fifty milliseconds.
It is previously indicated that one of the test conditions which is supplied to the test control circuit means 18 is an electrical signal 30 indicating the speed of the engine. As previously indicateds in the operation of the sensor detection system it is desired to test the sensor 10 and detect any failures only during idle speed conditions. The RPM signal 30 in the preferred embodiment is a series of negative pulses of a predetermined pulse time duration wherein the pulse repetition frequency or the time between the pulses varies inYersely as to rpm. Thus at idle speeds the time between pulses is much longer than at high speeds. In Fig. 2 the signal 30 is supplied through a resistor 81 to a capacitor 82 and supplies or contributes to maintaining the voltage 76 on the noninverting input 80 of the comparator 46 of Fig. 4. Thus, under high speed condition, the capacitor 82 is not charged up inasmuch as the negative pulses from the rpm signal 30 occur very rapidly and operate to discharge the capacitor 82 to ground.
Referring to Fig. 5 there is a partial block diagràm and electrical schematic of the circuit for generating the rpm signal 30 as used in Flg. 2.
The timing generator 84 is responsive to the rotation of the crankshaft 86 of the engine and generates a pair of pulse trains 87 and 88, labelled waYeforms A and B in Fig. 5. The time between consecuti~e pulses in either 47~L4(~
pulse train is proportional to the speed of the crankshaft 86 and the faster the crankshaft rotates, the shorter the time or the closer together the pulses become. These pulses are supplied to a flip-flop 90 and one output is connected to a pulse generator 92 for generating pulses 94 having a predetermined width or time duration in response to the pulse trains 87 and 88 from the timing generator 84. These pulses 94 as shown in waveform D o~ Fig.5 are supplied to a transistor 96 which when turned on operates to discharge a timing capacitor 98. I~laveform E of Fig. 5 shows the waveform at the output of the timing capacitor 98 which is connected to noninverting input of a comparator 100. The output of the comparator 100 is a plurality of negative going pulses 30 having a predetermined pulse time duration but having a time between pulses which is inversely proportional to the speed of the engine.
Referring to Fig. 2 one of the other conditions applied to the test control circuit means 18 is an electrical signal 32 representin~ the position of the throttle valve in the throttle body of the engine. As previously indicated it is a function of the system to detect failures in the exhaust gas sensor 10 only during idle conditions. When the throttle is closed indicating idle condition, the voltage level on the throttle input is at a high voltage le~el and allows the capacitor 82 to charge to this level. As shown in Fig. 1 it is a combination of the rpm signal 30 and the throttle position signal 32 which operate to determine the idle state of the engine. In essence, these two signals 30 and 32 are combined together forming a logical AND gate.
The other test condition which must be present is the indication of the engine ~emperature. This signal 34 is generated by means of a coolant temperature sensor generating a high voltage output signal when the cool~nt exceeds a predetermined temperature. This waveshape 34 as indicated on Fig. ~, switches from a low to a high voltage level when the temperature exceeds a predetermlned temperature. This signal is electrically connected to the ou~put of the comparator by means o~ the clamping diode 44.
-lS-~47~4~
As illustrated in Fig. 2 the output of the comparator 46 in the test control circuit means 1~ is an open col1ector ~IP~ tnansistor 79. The temperature signal 34 from the coolant temperature is supplied through the clamping diode 44 to the collector of the transistor 79 clamping it to ground when the coolant temperature is below the predetermine~ level.
However, when all the conditions for detection are present, the voltage level of the noninverting input 80 of the comparator 46 as a result o~ the throttle position signal 32 and the speed of the enyine is high if the engine is in idle condition. llhen the operating temperature of the exhaust system is above a predetermined level of temperature the voltage level on the inverting input 75 of the comparator 46 is lower than the voltage level to the noninverting input 80 causing the output transistor 79 to be ~riven out of conduction removing the clamping voltage fro~ the capacitor 48 in the transition interval indicator 16. This allows the capacitor ~8 to charge to the output of the multivibrator 14 and when the voltage level on the capacitor 48 exceeds the predetermined level as determined by the bias voltage of the transistor 102 of the ;ndicator level sensor 24 a failure latching signal will be generated.
Referring to Fig. 2 the indicator level sensor 24 comprises the transistor 102 having its input biased to a predetermined voltage level.
This voltage level is determined by a voltage divider 104 comprising a pair of resistors 105 and 106 electrically connected across the supply voltage. In the preferred embodiment ~hen the voltage on the emitter 108 of the transistor 102 exceeds the bias voltage on the base 109, the transistor 102 is driven into conduction and the voltage is applied to the collector 110 of the transistor 102.
The cutput or collector of the transistor 102 in the indicator level sensor 24 is electrically connected to a failure latching means 26 for generating a signal representing the failure of the exhaust gas sensor.
The failure latching circuit comprises a pair of transistors 112 and 11~
wherein the first transistor 112 has its emitter lead electrically connected ~16-1~47~4~) to the base lO9 lead of the indicator level sensor transistor 102 and its collector lead electrically connected to the collector llO of the ind1cator level sensor transistor 102. The second transistor 114 has its base electrically connected to the collector of the ~irst transistor 112 and its emitter is grounded. Thus, the two transistors 112 and 114 are connected in a latching circuit. The base of the second transistor 11~ is biased through a resistor to ground therefore when the transistor 102 in the sensor circuit is driven into conduction this applies the voltage on the base lead of the second transistor 114 of the latching circuit driving it into conduction. Through the co-operation and operation oF the two transistors 112 and 114 the collector lead of the second transistor 114 has a voltage level impressed thereon which will be maintained until po~er is removed from the circuit. This voltage level will be present regardless of succeeding operations of the transition interval indicator 16 or the test control circuit means 18.
Referring more particularly to Fig. 2, the fuel control unit 20 controls the selection of which injector group 50 is to be fired and controls the injector timing control unit 22 to determine the time durat-on that the injector is to be operated. A constant current source ll~ is selectively coupled to each injector group 50 by means such as a flip-flop 118 receiving control signals from the control unit 120. In response to the signal on the capacitor 48 of the transition interval indicator unit 16, a control circuit represented by a transistor 122 having a resistor 124 and a diode 126 serially connected to its emitter and to the output of the flip-flop 118 provides a voltage mismatch for the current source 116 thereby effecting the amount of current supplied to the fuel control pulse generating circuitry only during the injection cycle of one of the injector groups. In the preferred embodiment this voltage mismatch circuit causes an increase in the current to the fuel control pulse generating circuitry only during the ~njection cycle o~ the one injector group thereby causing the ~njector group to operate on a shorter p~lse width. This in effect will cause a lean fuel L7~
mixture to be injected into the cylinders controlled by the particular in~ector group. It is through the action of this particular circuit that will cause the exhaust gas to switch back and forth over the stoichiometric fuel air ratio.
It is further indicated in Fig~ 2 the signal from the failure latching means 26 is supplied to a timer 128 whose function is to interrupt the injector timing control unit 22. In the preferred embodiment the timer wili supply a signal to the injector timing control unit which in effect will drop the timing signal to one of the injector groups 50. With this timing signal not present to the injector group, fuel will not be supplied to the cylinders from the injectors controlled by that group and the internal combùstion engine will then misoperate.
By unbalancing the signal to one of the injector group 50 such as removing the timing signal the internal combustion engine will operate in a rough mode which will become very annoying to the operator. However, this malfunction will only occur during idle condition and will not effect the operation of the internal combustion engine at times other than idle.
There has thus been shown and described an exhaust gas sensor operational detection system for use in a fuel injection system of an internal combustion engine. Under predetermined engine operating conditions, the detection system will detect an inoperative or failed exhaust sensor and as a result thereof will generate a failure signal for activating some form of warning means to the operator of the engine.
Claims (8)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a fuel injection system for an internal com-bustion engine with electrically controlled fuel injector means, an exhaust gas sensor failure detection system comprising:
sensor signal shaping means electrically connected to the exhaust gas sensor for generating rectangular shaped voltage waveforms having a first voltage level representing one range of exhaust gases and a second voltage level representing a second range of exhaust gases;
means for sensing the switching of said rectangular shaped voltage waveform between said first voltage level and said second voltage level and generating a triggering signal substan-tially coincident with said switching;
a multivibrator responsive to said triggering sig-nal for generating an output pulse having a predetermined time interval;
test control circuit means responsive to at least one engine operating parameter for generating a first electrical signal when the engine is operating within a predetermined range of said parameter and a second electrical signal when the engine Is operating other than said predetermined range;
capacitive means electrically responsive to said first electrical signal and to said multivibrator for charging and discharging according to the said output pulse; and capacitive charge level sensor electrically con-nected to said capacitive means and responsive to a predetermined charge level for generating and maintaining an exhaust gas failure detection signal.
sensor signal shaping means electrically connected to the exhaust gas sensor for generating rectangular shaped voltage waveforms having a first voltage level representing one range of exhaust gases and a second voltage level representing a second range of exhaust gases;
means for sensing the switching of said rectangular shaped voltage waveform between said first voltage level and said second voltage level and generating a triggering signal substan-tially coincident with said switching;
a multivibrator responsive to said triggering sig-nal for generating an output pulse having a predetermined time interval;
test control circuit means responsive to at least one engine operating parameter for generating a first electrical signal when the engine is operating within a predetermined range of said parameter and a second electrical signal when the engine Is operating other than said predetermined range;
capacitive means electrically responsive to said first electrical signal and to said multivibrator for charging and discharging according to the said output pulse; and capacitive charge level sensor electrically con-nected to said capacitive means and responsive to a predetermined charge level for generating and maintaining an exhaust gas failure detection signal.
2. An exhaust gas sensor detection system accord-ing to claim 1 further including control means responsive to said exhaust gas failure detection signal and said first electrical signal for periodically suppressing signals supplied to the electrically controlled fuel injection means thereby causing the internal combustion engine to malfunction.
3. An exhaust gas sensor detection system accord-ing to claim 1 wherein said test control circuit means is responsive to engine speeds for generating said first electrical signal indi-cating idle engine speed.
4. An exhaust gas sensor detection system accord-ing to claim 3 wherein said test control circuit means additionally includes means responsive to engine operating temperature for generating said first electrical signal indicating that the engine is at its operating temperature and operating at idle speed.
5. An exhaust gas sensor detection system accord-ing to claim 4 wherein said test control circuit means additionally include means responsive to a closed throttle position of said engine.
6. An exhaust gas sensor detection system accord-ing to claim 1 wherein capacitive means comprises a capacitor hav-ing separate charging and discharging circuits electrically con-nected in parallel circuit wherein the charging rate is substan-tially different than the discharging rate.
7. An exhaust gas sensor detection system accord-ing to claim 6 wherein said charging circuit comprises a resistor and said discharging circuit comprises a resistor and a diode electrically poled for discharging said capacitive means at a faster rate than the rate for charging said capacitive means.
8. An exhaust gas sensor detection system accord-ing to claim 6 wherein said second electrical signal from said test control circuit means maintains said capacitive means in a discharged condition and said first electrical signal enables said charging and discharging circuits.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/521,310 US3948228A (en) | 1974-11-06 | 1974-11-06 | Exhaust gas sensor operational detection system |
| CA228,838A CA1044780A (en) | 1974-11-06 | 1975-06-09 | Exhaust gas sensor operational detection system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1047140A true CA1047140A (en) | 1979-01-23 |
Family
ID=25667982
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA297,286A Expired CA1047140A (en) | 1974-11-06 | 1978-02-20 | Exhaust gas sensor failure detection system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1047140A (en) |
-
1978
- 1978-02-20 CA CA297,286A patent/CA1047140A/en not_active Expired
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