US3923016A

US3923016A - Electronic fuel injection apparatus for a fuel injection

Info

Publication number: US3923016A
Application number: US468527A
Authority: US
Inventors: Yoshikazu Hoshi
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1973-05-09
Filing date: 1974-05-09
Publication date: 1975-12-02
Anticipated expiration: 1992-12-02
Also published as: JPS50229A

Abstract

In a closed-loop fuel injection apparatus for an internal combustion engine which comprises an air detector for measuring air flow into the engine, an oxygen detector for measuring the oxygen quantity in the exhaust gas from the engine, and a fuel control means for determining the fuel amount in accordance with the outputs of the air detector and the oxygen detector. The output of the oxygen detector is integrated by a capacitor and the amount of injection fuel is determined by the product of the charging quantity of the capacitor and the output of the air detector.

Description

United States Patent Hoshi Dec. 2, 1975 [541 ELECTRONIC FUEL INJECTION 3,824,967 7/1974 Gordon l23/32 EA APPARATUS FOR A FUEL INJECTION 3,831,564 8/]974 Schmidt et al. 123/32 EA 75 l t 1 Y h'k H h, H't h', J I nven or OS I azu OS I lac l apan Primary Examiner-Charles J. Myhre [73] A Ig H p n Assistant ExaminerJoseph A. Cangelosi [22] Filed: May 9 1974 Attorney, Agent, or FirmCraig & Antonelli [21] Appl. No.: 468,527

[57] ABSTRACT [30] Foreign Application Priority Data In a closed-loop fuel injection apparatus for an internal combust1on eng1ne wh1ch compr1ses an an detec- May 9, 1973 Japan 48-50731 tor for measurmg a1r flow mto the engme, an oxygen 52 us. c1 123/32 EA; 123/119 R detector for measurmg quamty the 2 haust gas from the engtne, and a fuel control means [51] Int. Cl. F02D 5/02 [58] Field of Search 123/32 EA for determmmg the fuel amount 1n accordance w1th the outputs of the air detector and the oxygen detec- [56] References Cited tor. The output of the oxygen detector is integrated by a capac1tor and the amount of 1n3ect1on fuel 1s deter- UNITED STATES PATENTS mined by the product of the charging quantity of the 3,745,768 7/1973 Zechnall ct al 123/32 EA apacitor and the output of the air detector. 3,782,347 I/l974 Schmidt ct al.. 123/32 EA 3,815,56l 6/l974 Seitz 123/32 EA 10 Claims, 6 Drawing Figures AIR FLOW F D T E ECTOR 35 41 45 l 3 VALVE FUEL TEMPERATURE 25 27 CQNTROLLER VALVE SENSOR CHARGING DISCHARGING VALVE FUEL CIRCUlT CIRCUIT CONTROLLER VALVE 5 37 5 61 f 31 43 447 PULSE GENERATOR FF 1 I F F I9 MONOSIABLE INTEGRATE 2| MULTIVIBRATOR CIRCUIT 5 w '3 H TEMPERATURE /9 L SENSOR COMPARING CIRCUIT 7 OXYGEN I SENSOR US. Patent 'Dec. 2, 1975 Sheet 2 of3 3,923,016

CRANK ANGLE W 0 540 0 |80 OUTPUT OF PULSE GENERATOR 1 I Y l OUTPUT 0F FLIP-FLOP 29 (B) OUTPUT OF CHARGE (c) a DISCHARGE CIRCUITS OPEN OPEN FUEL INJECTION VALVE 45 (D) OPEN FUEL INJECTION VALVE 47 (E) E 55 y 572 5: EC FF 2 a H l o 58 T t E O 0 O O O 0 CRANK ANGLE 0 30 360 540 0 I80 (A) H6. 5 CONTACT CONTACT (F) oUTPUT OF CHARGE amscRAReE CIRCUIT EUEL- INJECTION VALVE (D) US. Patent Dec. 2, 1975 Sheet 3 of 3 ELECTRONIC FUEL INJECTION APPARATUS FOR A FUEL INJECTION Background of the Invention accordance with quantity of oxygen in the exhaust gas.

Description of the Prior Art There is a definite relation between the amount of fuel consumed and the amount of air, since carbon and hydrogen, being elements of fuel, combine with oxygen in accordance with a prescribed relationship. In general, air is introduced into a cylinder by engine suction and the amount of fuel needed is determined in response to the amount of the introduced air or oxygen. However, it is very difficult to measure the amount of air with high accuracy. Therefore, the introduced airfuel ratio can be determined by detecting the characteristics of the exhaust gas and it is possible to compensate the fuel quantity so as to obtain a suitable air-fuel ratio. Still, a conventional injection control apparatus tends to be very complicated.

SUMMARY OF THE INVENTION Objects of the Invention It is an object of the invention to provide a simple fuel control apparatus of the closed-loop type.

It is a further object of the invention to provide a fuel control apparatus of which the operation is very stable.

It is still another object of the invention to provide a fuel control apparatus having a high response.

A fuel control apparatus of the present invention includes an integrating circuit for integrating current in response to the output from an oxygen detector. The output of the integrating circuit compensates for the amount of injected fuel. If the integrating circuit has a large time constant, the operation of the apparatus is very stable, but the response is inferior; for a small time constant, the response is good, but the operation itself is unstable. The integrating operation of the integrating circuit is controlled so as to operate during a predetermined duration independent of engine speed. The time constant of the integrating circuit is small, yet the operation of the injection control apparatus is very stable.

Brief Description of the Drawings FIG. 1 is a blockdiagram of an embodiment of the present invention;

FIG. 2 is an explanatory drawing illustrating the operation state of FIG. 1;

FIG. 3 is a wave form of a charged voltage produced by the charging and discharging circuit of FIG. 1;

FIG. 4 is a modification of a pulse generator 5 and a flip-flop 29 of FIG. 1;

FIG. 5 is an explanatory drawing illustrating the operation state in accordance with the modification of FIG. 4; and

FIG. 6 is a detailed circuit of the block diagram of FIG. 1.

Detailed Description With reference to FIG. 1, an air flow detector 1 serves to detect the average value of air flow from the 2 air filter to an engine cylinder. One of the most frequently used air flow detectors comprises a movable air plate inserted into an air passage and a variable resistor a slidable contact of which is moved by the displacement of the air plate. Therefore, the resistance of the variable resistor represents the average of the air flow and is changed in response to the change of air flow.

A temperature sensor 3 detects the temperature of the engine, and since the amount of fuel to be injected is affected by the temperature of the engine, the sensor 3 is needed to compensate the injected amount of fuel.

A pulse generator 5 generates timing pulses in response to the rotation of the crankshaft. The timing pulse is applied to a flip-flop 29 for generating a duration pulse proportional to the engine operation.

An oxygen sensor 7 detects a characteristic of the exhaust gas, especially the density of oxygen in the exhaust gas. In general, an oxygen sensor consists of a zirconium dioxide and electrodes provided on its surface. When the oxygen density on one side of the zirconium dioxide is different from the density on the other side, a voltage is generated between the two sides in response to the difference of the oxygen density. When.

the one side is inserted into the exhaust gas and the oxygen density on the other side is kept constant, the change of the generated voltage corresponds to the variation of the oxygen density in the exhaust gas.

The temperature sensor 9 is provided to detect the temperature of the oxygen sensor 7. Since the output of the oxygen sensor 7 is also affected by temperature, it is needed to compensate the output voltage. The comparing circuit 11 receives the outputs of the oxygen sensor 7 and the temperature sensor 9. When the oxygen density in the exhaust gas exceeds a predetermined value, a positive current is applied to an integrating circuit 19 through an AND gate 15. When the oxygen density is below a predetermined value, a negative current is applied to the integrating circuit 19 through an inverter 13 and an AND gate 17. When positive current is applied, the output voltage of the integrating circuit 19 is increased, and it is decreased by applying a negative current.

The operation of the gates 15 and 17 are controlled by a monostable multivibrator 21. Since the effect of the oxygen sensor is restricted by the monostable multivibrator 21, the integrating circuit 19 has large time constant.

A current controller 23 serves to control the charging current of a charging circuit 25 in such a way that the differential of the charging current is determined by total differential of the outputs of the air flow detector, the temperature sensor and the integrating circuit. The output of the charging circuit 25 is discharged by a discharging circuit 27, in order to change the charged voltage to a function of time which represents the valve opening duration of the fuel injection valve. It is necessary to identify generating timing of the output of the discharging circuit 27 with fuel injection timing. Therefore, the operations of the charging and discharging circuits are controlled by the flip-flop 29. A flip-flop 31 serves to distribute the output of the discharging circuit 27 to

valve controllers

41 and 43 through

AND gates

35 and 37.

Fuel valves

45 and 47 are driven by the

valve controllers

41 and 43, respectively.

With reference now to FIG. 2, the operation of the circuit depicted in FIG. 1 will be explained. For purposes of simplification, it will assumed that the output of the temperature sensor 3 is negligible.

The output of the air flow detector 1 corresponds to an average of the air flow in an air passage (not shown) as explained previously. Since the quantity of air introduced into one of the cylinders of the engine is determined by the opening time of an air-intake valve and the air flow quantity therethrough, it is possible to represent the quantity of air in the cylinder by the electrical output of the air flow detector 1 during the valve opening. Since the flip-flop 29 is operated by the output of the pulse generator 5, which is connected to the toggle input of the flip-flop, the duration of the pulse from the flip-flop 29 will be proportional to the valve opening.

As is shown in FIG. 2, in each 180 rotation of the crankshaft, a pulse will be produced by the pulse generator 5, the duration of the pulse being a portion of the 180 rotation. This is shown at curve (A) in FIG. 2.

The set output of flip-flop 29 is shown at (B) in FIG. 2, this output appearing on line 61 shown in FIG. 1. Of course, the reset output will appear on line 62 at periods alternating between the set output of flipflop 29.

Now, since the set output of the flip-flop 29 is connected to the charging circuit 25, during the generation of the output on line 61, i.e., signal (B) of FIG. 2, the charging circuit will store a charge in accordance with the output of the air flow detector 21, which is connected to the charging circuit by way of current controller 23. This charged voltage represents the quantity of air introduced into a cylinder.

Since the quantity of fuel injection is controlled by the opening time of

fuel valve

45 or 47, shown in FIG. 1, it is necessary to produce a signal as a function of time, which becomes the basis of the opening time of the

fuel valve

45 or 47. Then, the charged voltage is discharged with a predetermined current value by the discharging circuit 27.

Namely, as is shown at (C) in FIG. 2, the charging circuit 25 produces a ramp output corresponding to the output of the air flow detector 1 during the time that the set output of flip-flop 29 is high. Then, by the way of the reset output of the flip-flop 29, on line 62, discharging circuit 27 is activated and the charge previously stored in charging circuit 25 is discharged during a period of time t, i.e., during the period of time of the negatively sloped ramp of signal (C) of FIG. 2.

The output of the discharging circuit 27 is coupled by way of AND gates and 36 to the

respective valve controllers

41 and 43 for the

fuel valves

45 and 47, respectively. Connected to the other respective inputs of the AND gates are the set and reset outputs of the flip-flop 31, which is connected by way of

lines

61 and 62 to the set and reset outputs of flip-flop 29.

As a result, during alternate periods of time that the discharging circuit supplies the negatively-sloped ramp output, the

fuel injection valves

45 and 47 will be correspondingly alternately opened, as shown at (D) and (E) of FIG. 2.

The current to be charged is also effected by the output of the integrating circuit 19 which represents a characteristic of the exhaust gas. As a result, the charging current is represented as a function of the air flow in the air passage and the amount of oxygen in the exhaust gas. The discharging time will be affected by the output of the integrating circuit 19 and the quantity of injected fuel is compensated by the density of oxygen in the exhaust gas.

With reference to FIG. 3, which depicts the respective positiveand negative-sloped wave form (C) of FIG. 2, the tangent of the angle a is determined as a function of the outputs of the air flow detector 1, the temperature sensor 3 and the integrating circuit 19, all of which are supplied to the current controller 23. The duration of the negatively-sloped ramp, i.e., time t, is proportional to the opening time of the air-intake valve of the engine. Thus, the tangent B is constant and is determined by the discharging current. While tan a is changed by the output of the integrating circuit, it is possible to change tan B in response to the characteristics of the exhaust gas, in order to compensate the quantity of injected fuel.

In some instances, one fuel valve may be employed to simultaneously supply fuel to two cylinders. In this case, the quantity of injected fuel must be doubled. This necessity is achieved by doubling the charging time of the charging circuit 25.

More specifically, referring to FIG. 4, switches 51 and 52 are provided to operate in synchronism with the rotation of the crankshaft to produce pulses, the same as the output of the flip-flop 29. The flip-flop 55 doubles the pulse duration of the

switches

51 and 55 and the

output

57 and 58 of the flip-flop 55 are supplied to

lines

61 and 62 of FIG. 1. Since the duration of the pulses supplied to the charging circuit 25 is doubled, the operation time of the charging circuit is doubled as shown in FIG. 5.

In FIG. 5, the wave forms A) (D') correspond to the wave forms (A) (D) in FIG. 2, with the wave forms for each of the lines of flip-flop 55 shown at (B') and (8).

Referring now to FIG. 6, a detailed circuit diagram of portions of the circuit of FIG. 1 are shown. In the figure, portion 111, corresponding to block 11 of FIG. 1, compares the output of an oxygen sensor with a predetermined level. Circuit portion 1 19 is an integrating circuit, corresponding to block 19 of FIG. 1, portion 123 is a current controller, corresponding to block 23 of FIG. 1, portion 121 is a monostable multivibrator, corresponding to block 21 of FIG. 1, portion 129 is a pulse generator, corresponding to pulse generator 5 of FIG. 1, and portion 127 is a charging and discharging circuit, corresponding to

blocks

25 and 27 of FIG. 1.

A voltage supply potential is connected to terminal 151 and the output of the oxygen sensor (not shown) is applied to terminal 153 and amplified by field-effect transistor 155, the gate resistance of which is very large. The output of the transistor 155 is applied to

operational amplifiers

163 and 165. When the output of the transistor 155 exceeds a predetermined level established by the variable resistor 159, the output of the operational amplifier 165 will turn transistor 169 off. On the other hand, when the output of the field-effect transistor 155 is below the predetermined level set by resistor 157, the output of the operational amplifier 163 will turn transistor 167 of Since the voltage generated by the oxygen sensor changes in response to variations in temperature, a temperature sensor 161 is provided in series with the

variable resistors

157 and 159, in order to stabilize the predetermined levels set by the

variable resistors

157 and 159.

Now, when transistor 169 is off," the potential at the terminal 151 will be resistively coupled to the base of transistor 177 which, in conjunction with transistor 179, will turn transistor 181 on, thereby discharging capacitor 175 therethrough.

When the transistor 167 is off, as a result of the potential applied to terminal 151 being resistively coupled to the base of transistor 171, transistor 173, which is resistively connected to the collector of transistor 171, will be turned on, thereby providing a charging path through the transistor 173 to the capacitor 175 to charge the same. The voltage across transistor 175 is amplified by transistor 183 and supplied to the base of the transistor 191.

A diode 187, variable resistor 189, transistor 191, resistor 193 and temperature detector'195, for detecting the temperature of the engine, are connected in series between the voltage source terminal 151 and ground. The arm of the variable resistor 189 is displaced by the air-plate which receives the air flow. The output line 197 will supply the voltage which changes as a function of the air flow, the voltage across capacitor 175 and the temperature of the engine, to the base of transistor 227, the operation of which will be discussed hereinafter.

During the rotation of the crankshaft of the engine, switch

terminal contacts

201 and 202 will alternately open and close. When the switch 201 is open, transistor 205 will be on, and transistor 185 will be on. When transistor 185 is turned on, the voltage at the collector thereof will become high, thereby forcing the voltage on line 197 to a high level, so that the operation of the charging circuit within circuit portion 127 is interrupted.

1n the monostable multivibrator 121, transistors 211 and 212 are operated in response to the voltage on the collector of transistor 207 within pulse generator circuit 129.

Transistors

215 and 216 provide the output of the transistors 167 and 169 to the integrating circuit when the trigger from the switch 201 is applied to the base of the transistor 212.

Within the charging and discharging circuit 127, transistors 221 and 223 operate as a monostable multivibrator. Transistor 227 and capacitor 225 operate as the charging circuit portion, while transistor 229 and capacitor 225 operate as discharging circuit. The charging current of the capacitor 225 is determined by the voltage supplied to the base of the transistor 227 by way of line 197, as discussed above. The discharging current is determined by the voltage applied to the base of the transistor 229, which is determined in accordance with the voltage across variable resistor 231, a slidable arm of which is supplied to the base of transistor 229.

A duration pulse corresponding to the charging time of the capacitor 225 is produced at the collector of the transistor 223 and supplied by way of output terminal 235 to a valve controller for controlling the operation of a'fuel injection valve.

In the above circuit, the voltage of the capacitor 175 in the integrating circuit 119, which represents the oxygen density in the exhaust gas, compensates the charging current delivered to the capacitor 225 within a charging and discharging circuit portion 127. However, it is possible to compensate the discharging current. In this case, the diode 187, the variable resistor 189, the resistor 193 and the temperature sensor 195 are connected in series between the voltage source terminal 151 and ground. The drain electrode of the field-effect transistor 183 is then connected to the base of transistor 229. The charging current is determined by the air flow average and temperature of the engine, and the 6 discharging current is determined by the voltage across capacitor 175.

While I have shown several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but also contemplates numerous changes and modifications as would be known to those skilled in the art given the present disclosure of the invention, and I therefore do not wish to be limited thereto but intend to cover all such changes and modifications.

What I claim is:

1. An electronic control apparatus for a fuel injection system comprising:

first means for generating a first signal representative of the flow of air supplied to an engine cylinder;

second means for generating pulses in response to the engine rotation;

third means for generating a second signal representative of the level of the quantity of oxygen in the engine exhaust gas;

fourth means, responsive to said second signal, for

generating a third signal representative of the integration of said second signal;

fifth means, coupled to said first means and said fourth means, for generating a charging current in response to said first and third signals;

sixth means, coupled to said second means and said fifth means, for discharging said charging current in response to said pulses generated by said second means;

seventh means, coupled to said sixth means, for generating a fuel injection valve opening signal in accordance with the time required for said charging current to discharge by said sixth means; and

eighth means, responsive to the pulses generated by said second means, for generating a pulse having a predetermined duration, for controlling the operation of said fourth means.

2. An electronic control apparatus according to claim 1, wherein said fourth means includes a comparing circuit which compares said second signal with'a predetermined value and generates one of a positive and negative valued signal in dependence upon said second signal exceeding said predetermined value, and

a charge-discharge circuit which integrates the output of said comparing circuit in response to said predetermined duration pulse generated by said eighth means.

3. An electronic control apparatus according to claim 2, wherein said eighth means comprises a monostable multivibrator.

4. An electronic control apparatus according to claim 2, wherein said fifth means includes a voltage divider network having at least two variable resistance means and an output terminal connected in series across a constant voltage source, the resistance value of one of said variable resistance means being varied in accordance with the voltage integrated by the chargedischarge circuit of said fourth means, and the resistance value of the other of said variable resistance means being varied in accordance with the value of said first signal representative of air flow, the charging current generated by said fifth means varying in response to the voltage at said output terminal.

5. An electronic control apparatus for a fuel injection system comprising:

second means for generating pulses in response to engine rotation;

third means for generating a second signal representative of the quantity of oxygen in the engine enhaust gas;

fourth means for storing or discharging a charge in response to the output of said third means;

fifth means for storing a charge in response to the output of said first means;

sixth means for discharging the charge stored by said fifth means through a resistance means, the value of which is dependent upon the output of said fourth means;

seventh means for activating fuel injection valves in response to the output of said sixth means; and

eighth means comprising a monostable multivibrator for operating said fourth means in response to the pulses generated by said second means.

6. An electronic control apparatus for a fuel injection system comprising:

first means for generating a first signal representative of the flow of air supplied to an engine;

second means for generating pulses in response to the engine rotation;

fourth means, responsive to said second signal, and coupled to said second means, for generating a third signal representative of the integration of said second signal;

fifth means, coupled to said first means, said second means and said fourth means, for generating a fourth signal, a first component of which is representative of the storing of a charge over a first prescribed portion of said engine rotation, and a second component of which is representative of the discharging of said charge during a second prescribed portion of said engine rotation subsequent 8 to said first prescribed portion, in response to said first and third signals; and

sixth means, coupled to said fifth means and said second means, for generating a fuel injection valve opening signal in accordance with the duration of the second component of said fourth signal.

7. An electronic control apparatus for a fuel injection system according to claim 6, wherein said second signal generated by said third means has a first component of a first polarity representative of the density of oxygen in said engine exhaust gas exceeding a prescribed level, and a second component of a second polarity, opposite to said first polarity, representative of the density of oxygen in said engine exhaust gas failing to exceed said predetermined level.

8. An electronic control apparatus for a fuel injection system according to claim 6, wherein the amplitude of the first component of said fourth signal at the termination of said first prescribed portion of said engine rotation is representative of the level of the density of oxygen in said exhaust gas, while the duration of said second component of said fourth signal is representative of the length of time required for the value of charge corresponding to said amplitude to discharge during said second prescribed portion of said engine rotation at a predetermined rate of discharge.

9. An electronic control apparatus for a fuel injection system according to claim 7, wherein the amplitude of the first component of said fourth signal at the termination of said prescribed portion of said engine rotation is representative of the level of the density of oxygen in said exhaust gas, while the duration of said second component of said fourth signal is representative of the length of time required for the value of charge corresponding to said amplitude to discharge during said second prescribed portion of said engine rotation at a predetermined rate of discharge.

10. An electronic control apparatus for a fuel injection system according to claim 6, further including a monostable multivibrator, coupled to the output of said second means, for controlling the operation of said fourth means.

Claims

1. An electronic control apparatus for a fuel injection system comprising: first means for generating a first signal representative of the flow of air supplied to an engine cylinder; second means for generating pulses in response to the engine rotation; third means for generating a second signal representative of the level of the quantity of oxygen in the engine exhaust gas; fourth means, responsive to said second signal, for generating a third signal representative of the integration of said second signal; fifth means, coupled to said first means and said fourth means, for generating a charging current in response to said first and third signals; sixth means, coupled to said second means and said fifth means, for discharging said charging current in response to said pulses generated by said second means; seventh means, coupled to said sixth means, for generating a fuel injection valve opening signal in accordance with the time requireD for said charging current to discharge by said sixth means; and eighth means, responsive to the pulses generated by said second means, for generating a pulse having a predetermined duration, for controlling the operation of said fourth means.

2. An electronic control apparatus according to claim 1, wherein said fourth means includes a comparing circuit which compares said second signal with a predetermined value and generates one of a positive and negative valued signal in dependence upon said second signal exceeding said predetermined value, and a charge-discharge circuit which integrates the output of said comparing circuit in response to said predetermined duration pulse generated by said eighth means.

4. An electronic control apparatus according to claim 2, wherein said fifth means includes a voltage divider network having at least two variable resistance means and an output terminal connected in series across a constant voltage source, the resistance value of one of said variable resistance means being varied in accordance with the voltage integrated by the charge-discharge circuit of said fourth means, and the resistance value of the other of said variable resistance means being varied in accordance with the value of said first signal representative of air flow, the charging current generated by said fifth means varying in response to the voltage at said output terminal.

5. An electronic control apparatus for a fuel injection system comprising: first means for generating a first signal representative of the flow of air supplied to an engine cylinder; second means for generating pulses in response to engine rotation; third means for generating a second signal representative of the quantity of oxygen in the engine enhaust gas; fourth means for storing or discharging a charge in response to the output of said third means; fifth means for storing a charge in response to the output of said first means; sixth means for discharging the charge stored by said fifth means through a resistance means, the value of which is dependent upon the output of said fourth means; seventh means for activating fuel injection valves in response to the output of said sixth means; and eighth means comprising a monostable multivibrator for operating said fourth means in response to the pulses generated by said second means.

6. An electronic control apparatus for a fuel injection system comprising: first means for generating a first signal representative of the flow of air supplied to an engine; second means for generating pulses in response to the engine rotation; third means for generating a second signal representative of the level of the quantity of oxygen in the engine exhaust gas; fourth means, responsive to said second signal, and coupled to said second means, for generating a third signal representative of the integration of said second signal; fifth means, coupled to said first means, said second means and said fourth means, for generating a fourth signal, a first component of which is representative of the storing of a charge over a first prescribed portion of said engine rotation, and a second component of which is representative of the discharging of said charge during a second prescribed portion of said engine rotation subsequent to said first prescribed portion, in response to said first and third signals; and sixth means, coupled to said fifth means and said second means, for generating a fuel injection valve opening signal in accordance with the duration of the second component of said fourth signal.