US 3903853 A
Description (OCR text may contain errors)
Kizler et al.
1 EXHAUST EMISSION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES  Inventors: Harald Killer; Peter .Iiirgen Schmidt, both of Schwieberdingen. Germany  Assignee: Robert Bosch G.m.b.I-l.,
GerlingenSchillerhohe, Germany  Filed: Dec. 13, 1973 [21} App]. No.: 424,621
 Foreign Application Priority Data Jan. 12, 1973 Germany 2301353  US. Cl. 123/32 EA; 60/276; 60/285; 123/ 1 19 R  Int. Cl. F028 3/00  Field of Search 60/276, 285; 323/40; 123/32 EA. 119 R  References Cited UNITED STATES PATENTS 3.624.493 11/1971 Gately .1 323/40 3.759.232 9/1973 Wahl ct a1. .1 60/276 3.782.347 1/1974 Schmidt et a1 60/276 3.815.561 6/1974 Seitz 60/276 Sept. 9, 1975  ABSTRACT T0 render operation of an electronic control system connected to a sensing gauge essentially independent of fluctuations in supply voltage. and to provide an operator indication of malfunction of the system, the output from an oxygen sensor. located in the exhaust stream of the engine is applied as one leg of a bridge circuit. the other leg being supplied with a source of reference potential; the other branch is formed of a pair of resistors, an operational amplifier, connected as a comparator-threshold switch is connected across the diagonals of the bridge to provide an output signal when the sensing signal deviates from the reference; a high-resistance (with respect to the sensing element) connection is made from the supply source to the sensor so that. in case of failure of the sensor. a voltage will be applied to the bridge simulating a sensing signal and resulting in an output from the control system which commands the air-fuel composition to be very lean.
15 Claims, 1 Drawing Figure EXHAUST EMISSION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES The present invention relates to an exhaust emission control system for internal combustion engines, and more particularly to a system to decrease the noxious components therefrom, which includes an integrating controller which is eonnectable to a fuel-air mixing device, such as a carburetor, or a fuel injection system, and controls the mixing device to adjust the relative proportion of air and fuel to a predetermined value.
Control of the mass ratio of air-fuel, so-called )t-control, can be carried out by measuring the emission of exhaust gases from the internal combustion engine. A component, for example oxygen in the exhaust gases is sensed and an electrical signal is obtained representative of the presence, or absence of oxygen in the exhaust gases. The electrical signal is then applied to a control amplifier which, in turn, controls the fuel-air mixture regulating device to hold the mixture at a value which is just below stoichiometric value, If the exhaust composition is just slightly reducing, that is, is just below stoichiometric value, the composition of the exhaust gases is particularly advantageous with respect to emission of noxious components, since the noxious components can be limited to a minimum value, by di rect emission, or catalytic conversion. Holding the exhaust gases at a slightly reducing value permits use of a single catalytic reactor for treatment of the exhaust gases and removal of almost all noxious components.
It is an object of the present invention to provide an electronic control system to control the air number A, which is particularly suitable for use in automotive vehicles.
Automotive vehicles supply their own electrical power, usually by means of altcrnators connected over rectifying networks to a battery. The supply voltage from the battery, that is, the terminal voltage of the electrical system of an automotive vehicle can vary widely, depending on temperature, loading, maintenance, and condition of the battery, as well as of the various components which are connected thereto.
It is a further object of the present invention to provide a control system in which the control effects are independent of fluctuations in supply voltage, typically automotive vehicle battery voltage. Further, the system, desirably, should be simple to construct, typically by using integrated circuits, and should be so arranged that an indication is available to the operator if the sensing element should fail or malfunction. so that the operator will cause the vehicle to be repaired, for replacement of the sensing element, and thus reestablishing of proper control operation thereof, for minimum exhaust emission.
SUBJECT MATTER OF THE PRESENT INVENTION Briefly, a bridge circuit is provided, forming a connecting circuit and connected to or forming part of the entire integrating control amplifier to which the sensor is connected as one branch thereof; another branch is connected to a source of reference voltage, for exam ple a portion of the supply voltage, stabilized, for example, by a Zener diode. An operational amplifier is connected across the diagonals of the bridge. If the sensing voltage from the sensing element differs from a predetermined value, as determined by the reference voltage, so that the bridge becomes unbalanced, an output signal is applied from the operational amplifier, which will thus function as a threshold switch, to command an integrating amplifier to integrate in one direction, or the other. depending on the setting of the threshold switch. The supply voltage, being applied across the bridge, thus may vary within wide limits without affecting the output of the bridge.
The invention will be described by way of example with reference to the accompanying drawings, wherein the single FIGURE is a schematic, fragmentary circuit diagram of an integrating control amplifier which is controlled by a bridge output and in which the exhaust sensor supplies a signal to one arm, or branch of the bridge.
An oxygen sensor 1 is located in sensing relation to the exhaust gases of an internal combustion engine (not shown). A suitable sensor is described in US. Pat. No. 3,841 ,987, such a sensor has a metallic housing forming an electrical connection with the chassis of the ve hicle in which the engine is located, and an additional connection terminal. The output of sensor I provides an electrical signal which is a characteristic of the composition of the gases within the exhaust from the inter nal combustion engine. The oxygen sensor is, preferably, enclosed in a shield, schematically indicated at I, suitable structures are shown in US. Pat. Nos. 3,597,345 and 3,546,086. The control circuit is powered from supply buses 3, I0, connected, for example, to the battery circuit of an internal combustion engine, or any other suitable d-c circuit which may be subject to voltage fluctuations.
The electrical signal from sensor 1 is applied to the base of a transistor 2 connected as an emitter follower. The collector of transistor 2 is directly connected to bus 3; the emitter of the transistor 2 is connected over a resistor 4 to ajunction JI. The collector-emitter path of transistor 2 and the series connected resistor 4 form one leg of a first branch ofa bridge 5. A second leg of the branch of the bridge 5 is formed by the series circuit of the collector-emitter path of a second transistor 6 and a resistor 7. The base of transistor 6 is connected to a voltage divider formed by resistors 8, 9, connected over a common resistor 12 between supply buses 10 and 3. Resistor 9 is adjustable. The two resistors 8, 9 have a Zener diode II connected in parallel thereto.
The third and fourth legs of the bridge 5, forming the second branch, are formed by a resistor I3, connected to the common bus 3 and a resistor I4 connected to the common bus I0, both being connected to junction J2, which forms, together with junction J], the diagonal connection of the bridge.
The diagonal of the bridge is connected to an operational amplifier I5, junction J2 being connected over coupling resistor 17 with the direct, or noninverting input, and junction .11 being connected over coupling resistor I6 to the inverting input of the operational amplifier I5. An output resistor 18 is connected to the output of the operational amplifier l5, and connected to the common supply 10. The output of the operational amplifier I5 is further connected to a junction point of two base resistors 19, 20 for transistors 2I, 22., respectively. Transistors 21, 22 have their emitters connected to respective tap points of two serially connected voltage dividers formed of resistors 23, 24, 25. 26, respectively. The transistors 21, 22 vary the trans fer of the voltage swing derived from operational amplifier l5, and thus can change the voltage difference of the output signal being derived from the operational amplifier l5 and further connected to an integrating amplifier. The emitter of transistor 21 is connected to the junction between resistors 23, 24; the emitter of transistor 22 is connected to the junction between resistors 25, 26. The collectors of the two transistors 21, 22 are connected together. The jointly connected collectors of transistors 21, 22 are connected over a selector switch 27 with an input or coupling resistor 28 of an operational amplifier 29, which functions as an integrator, having an integrating capacitor 30 connected between its output and its inverting input, to which the coupling resistor 28 is likewise connected. Switch 27 can selectively connect resistors 28, 31, or 32 as coupling resistors (rather than only the resistor 28) to the inverting input of operational amplifier 29. The direct, or non-inverting input of operational amplifier 29 is connected over a coupling resistor 33 with the junction of resistors 24, 25. The output of the operational amplifier 29 is connected over a resistor 34 to the common supply bus and, further, to an output terminal 29'. The output terminal 29 can be used to control, if necessary over an additional power amplifier, the air-fuel mixture of an internal combustion engine, for example by providing a position output which influences supply of fuel, or air to the internal combustion engine, or by modifying the injection period of fuel injection valves in the fuel injection system.
Operation: The output sensing signal from sensor 1 is connected into the first branch of the bridge 5 over transistor 2. This electrical signal, which is representative of the composition of the exhaust gases of the internal combustion engine, forms the actual value for the control circuit. The sensors 1 have a high internal resistance when the temperature in the exhaust gases is still low. Thus, the control circuit must have high input resistance and, therefore, transistor 2 is operated as an emitter-follower and, together with its load resistor 4, provides the necessary input resistance for the circuit.
The command value, that is, the value which the air number A should have, and to which the air-fuel mixture is to be controlled so that the exhaust gases from the engine will have a predetermined composition, is formed by means of Zener diode l l. The resulting signal is applied over the voltage divider formed of resistors 8, 9 and transistor 6 into the second arm of the branch of bridge 5. The command value can be adjusted by adjusting resistor 9. Transistors 2 and 6, in the first branch of the bridge, are of opposite conductivity type, and so connected that they are temperaturecompensating.
The comparison circuit for the command value and actual value is connected as a bridge, and thus is essentially independent of variations in supply voltage. supplied over the common lines 3, 10. The bridge is in balance, that is, command and actual values are equal, if the collector-emitter paths of transistors 2, and 6 have the same voltage thereacross. This is the case if the output signal from sensor 1, and the commanded value which the signal should have are equal. if the command value and actual value deviate, a voltage will appear across the diagonal terminals 11, J2 of the bridge. Let it be assumed that the output voltage of the sensing signal from sensor 1, that is, the actual value is greater than the commanded value. The inverting input to the operational amplifier will have a higher voltage applied than at the direct, or non-inverting input. Operational amplifier l5, functioning as a comparator circuit, provides an output signal which will be approximately at the voltage of the supply line 3. In the opposite case, that is if the actual value is smaller than the commanded value, the output signal of operational amplifier 15 will jump to a voltage which corresponds approximately to that of supply line 10.
The voltage swing or voltage jump at the input to integrator 29, 30 is decreased by an intermediately connected circuit 40, which includes transistors 21, 22. The voltage jump is decreased and, therefore, the capacitance value of integrating capacitor 30 can be decreased. The output signal of operational amplifier 15 controls either the one or the other of transistors 21, 22 to be in conductive condition, the other, or the one transistor, then, being blocked. A signal will be applied over the respectively conductive transistor to the input network of the integrator 21, 30 which has a smaller voltage swing than that of the output signal of the operational amplifier.
Selector switch 27 is provided in order to change the time constant of the integrator 29, 30. The output signal of the integrator 29, 30 then controls a suitable control element in such a manner that the air-fuel mixture applied to the internal combustion engine is so changed that it corresponds to a predetermined commanded ratio, resulting in exhaust of minimum noxious components. Switch 27 is shown schematically; the actual construction of the switch can be different. The switch 27 can be a controlled semiconductor switch; or, for example transistors in series with resistors corresponding to schematically indicated resistors 28, 31, 32 can be used. The transistors are selectively rendered conductive in accordance with desired integration time constants, as explained in US. Pat. No. 3,782,347 (with reference to FIG. 4 thereof and specification col. 5, paragraph at line 42, and relating to the network of resistor 38, and the transistor 45 resistor 46 circuit).
If the sensor 1 fails, then the circuit is so arranged that the operation of the engine will deteriorate to such an extent that the operator of the vehicle will notice the deterioration and will be forced to service or maintain the vehicle, for example by replacing the sensor. To so change the output of the circuit when sensor 1 fails, a resistor 35 is connected between the sensor 1 and the common supply line 10.
When sensor 1 fails, no more voltage will be supplied therefrom. This is normally, due to the operation of the sensor, an indication of lean mixture being sensed. The control circuit would then operate in such a manner that the air-fuel mixture is commanded to supply a richer mixture to the engine. Resistor 35 is provided in order to avoid supplying too rich a mixture to the engine. Upon failure of sensor 1, resistor 35 supplies an electrical signal to the base of transistor 2, which simulates the signal which would be derived from an operative sensor 1 if the air-fuel mixture were too rich. Thus, the control circuit will tend to command the system to supply only a leaner mixture (to counteract the simulated rich" mixture signal). The resistor 35 has a value which is relatively high with respect to the internal resistance of sensor 1, when the sensor is at operating temperature. Under normal conditions, when the sensor is at operating temperature, it is of low resistance. The device operates reliably if the relative value of resistor 35 is so high with respect to the resistance of sensor 1 that hardly any appreciable or noticeable load is applied by resistor 35 on sensor 1, in all operating ranges of the internal combustion engine, and particularly under idling conditions.
Various changes and modifications may be made within the scope of the inventive concept.
1. In an internal combustion engine exhaust emission control system, having means (i) sensing the composition of exhaust gases and providing a sensed electrical signal representative of the composition of the exhaust gases,
an integrating control amplifier (29, 30) providing an output signal (29') which is available to command the relative mass ratio (A) of air and fuel being applied to the engine,
and a connection circuit connecting the sensing means and the integrating control amplifier,
the improvement wherein the connecting circuit comprises a bridge circuit (5), said sensing means (1) being connected to one branch of the bridge circuit to provide the sensing signal thereto;
a reference source (6, 7, 8, 9, H) connected into another branch of the bridge circuit and providing a reference signal, with respect to said sensing signal, the other branches of the bridge circuit being formed by balanced impedances (l3, l4);
and an operational amplifier (15) having its respective inverting and direct inputs connected across the diagonal junctions (J1, J2) of the bridge circuit to provide an output signal representative of deviation of the sensed signal from the reference signal.
2. System according to claim 1, wherein the branch of the bridge circuit to which the sensing means (1) is connected includes a transistor (2) connected as an emitter-follower, the sensing means (1) being connected to and controlling conduction of the emitterfollower transistor (2).
3. System according to claim 1, wherein the integrat ing control amplifier (28, 29) is connected to the output of the operational amplifier (l5).
4. System according to claim 1, further comprising connection means (40) having a variable transfer function and connected between the output of the operational amplifier l5) and the integrating control amplifier (28, 29).
5. System according to claim 4, wherein the connection means (40) comprises a balanced transistor network (21, 22) having its emitter-collector paths connected between the source of voltage (3, 23, 24; 25, 26) and its output to the integrating control amplifier (29, 30), and connected to be controlled by the output of the operational amplifier 6. System according to claim 1, wherein the reference source (6, 7, 8, 9, 11) providing the reference signal includes a Zener diode (11) and a transistor (6) is provided, connected in the branch of the bridge circuit to which the reference source is connected, said transistor (6) being connected to be controlled by said Zener diode (l1 7. System according to claim 6, wherein the branch of the bridge circuit to which the sensing means (I) is connected includes a transistor (2) connected in emitter-follower circuit;
and wherein both said transistors (2, 6) are of relatively opposite conductivity type.
8. System according to claim 1, further comprising switch means (27) connected to the input of the integrating amplifier (29, and selectively switching the integrating amplifier to have different integrating time constants.
9. System according to claim 1, comprising a connecting circuit between the sensing means l and the supply circuit for the system, said connecting circuit supplying the bridge, upon failure of said sensing means, with a signal which results in an output signal there from commanding a lean air-fuel mixture.
10. System according to claim 9, wherein the connecting circuit comprises a coupling resistor (35) connecting the terminal of the sensing means which is also connected to the bridge circuit with the supply circuit for the system.
11. System according to claim 10, wherein said coupling resistor (35) has a value which is high with respect to the internal resistance of the sensing means 1 when the sensing means is at operating temperature so as to avoid noticeably loading the sensing means.
12. An internal combustion engines exhaust emission control system comprising means (1) sensing the composition of exhaust gases and providing a sensed electrical signal representative of the composition of exhaust gases;
an integrating control amplifier (29, 30) providing an output signal (29) which is available to command the relative mass ratio (A) of air and fuel being applied to the engine;
and a connecting circuit connecting the sensing means and the integrating control amplifier, said connecting circuit including a bridge circuit (5), one branch of said bridge circuit having a transistor (2) connected as an emitterfollower, the sensing means, (I) being connected to, and controlling the conduction of said emitterfollower transistor (2);
a reference source (6, 7, 8, 9, 11) connected into another branch of the bridge circuit and providing reference signal, the other branches of the bridge circuit being formed by balanced impedences (l3,
and an operational amplifier (15) having its respective inverting and direct in-puts connected across the diagonal junctions (J1, J2) ofthe bridge circuit, said operational amplifier (15) having its out-put connected to the in-put of the integrating control amplifier (29, 30).
13. System according to claim 12, further comprising connection means having a variable transfer function and connected between the output of the operational amplifier (l5) and the integrating control amplifier (28, 29).
14. System according to claim 12, wherein the reference source (6, 7, 8, 9, ll) providing the reference signal includes a Zener diode (11) and a transistor (6) is provided, connected in the branch of the bridge circuit to which the reference source is connected. said transistor (6) being connected to be controlled by said Zener diode (ll and wherein said transistor (6) and the transistor (2) connected in emittenfollower circuit are of relatively opposite conductivity type.
15. System according to claim 12, further comprising a coupling resistor (35) which has a value which is high with respect to the internal resistance of the sensing ure of said sensing means, which results in an output from the bridge, and hence from the operational amplifier commanding the integrating amplifier to provide an output signal representative of a lean air-fuel mixture.