US3805642A

US3805642A - Throttle controlled by engine vacuum

Info

Publication number: US3805642A
Application number: US00262615A
Authority: US
Inventors: M Danek; R Haas
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1972-06-14
Filing date: 1972-06-14
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23

Abstract

A throttle control device has a three-position diaphragm actuator controlled by induction vacuum through a solenoid valve to provide increased idle speed in high drive ratio or in reverse, a low idle speed and other drive ratios with a controlled throttle closing rate.

Description

United States Patent [191 Danek et al.

THROTTLE CONTROLLED BY ENGINE VACUUM Inventors: Michael J. Danek, Laingsburg;

Ronald H. Haas, Okemos, both of Mich.

General Motors Corporation, Detroit, Mich.

Filed: June 14, 1972 Appl. No.: 262,615

Assignee:

U.S. Cl 74/860, 74/873 Int. Cl B60k 21/00, F02d 11/08 Field of Search 74/860, 873

References Cited UNITED STATES PATENTS 11/1950 Weinberger 123/108 X Apr. 23, 1974 2,762,235 9/1956 Olson et al 74/873 2,913,921 11/1959 Gordon 74/873 2,915,914 12/1959 Burnell et al. 74/873 2,976,743 3/1961 Gordon et a1 74/873 3,556,064 [/1971 Tasuku et al. 74/860 X Primary Examiner-Benjamin W. Wyche Assistant Examiner.1. Reep Attorney, Agent, or Firm-Arthur N. Krein [5 7] ABSTRACT A throttle control device has a three-position diaphragm actuator controlled by induction vacuum through a solenoid valve to provide increased idle speed in high drive ratio or in reverse, a low idle speed and other drive ratios with a controlled throttle closing rate.

4 Claims, 2 Drawing Figures 1 THROTTLE CONTROLLED BY ENGINE VACUUM This invention relates to a throttle control system and, in particular, to a throttle control system having a three-position vacuum actuated throttle stop arrangement to maintain appropriate engine idling speeds and to control throttle return to prevent rapid closure of the throttle valve.

It is known to provide an ignition timing control system of the type in which a solenoid valve is disposed in the vacuum conduit between the induction passage and a distributor vacuum advance unit, the solenoid valve being energized through a switch when the transmission is in a low drive ratio mode of operation to prevent vacuum advance of the ignition timing whereas, when the transmission is in the high drive ratio mode of operation, the solenoid valve is 'de-energized to open the vacuum conduit to permit vacuum advance of the ignition timing. Such a control system, known commercially as a Transmission Controlled Spark system has proved effective to maximize fuel economy and engine performance while helping to reduce the emission of undesirable engine exhaust gas constituents.

Another feature adopted on recent engines has been an increase in idle air flow to improve combustion under high speed closed throttle decelerating conditions. This increase has been accomplished by limiting closure of the throttle to what may be termed a fast idle position.

It is therefore an object of this invention to provide a throttle control device to maintain increased idle speeds under certain engine operating conditions and to control throttle closure at a predetermined rate whereby to reduce deceleration exhaust emissions and to prevent hot stalling.

Another object of this invention is to provide a throttle control device to maintain increased engine idle speed when the engine is driving a transmission at a high drive ratio or in reverse while permitting controlled throttle closing when the engine is driving a transmission in the lower drive ratios.

These and other objects of the invention are attained by means. of a three-position spring biased diaphragm valved actuator operated by induction vacuum through a solenoid valve to limit throttle closure with transmission in high or reverse drive ratio and vacuum applied and, permitting slow closure of the throttle to its slow idle position with no vacuum applied or in other drive ratios at a closing rate controlled by the flow of air through orifices.

For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a throttle control and ignition timing control arrangement with a solenoid valve disposed in the vacuum conduit between the induction passage and the throttlecontrol and ignition timing control, the solenoid valve being connected through a switch which senses the transmission drive ratio, the actuator of the throttle control unit shown in a retracted position; and,

FIG. 2 is an enlarged sectional view of the throttle control arrangement taken along line 2-2 of FIG. 1,

showing the stem of the actuator of this unit fully extended.

Referring now to FIG. 1, an internal combustion engine is illustrated as having a carburetor ll providing an induction passage 12; A throttle 14 is rotatably disposed on a throttle shaft 15 in the induction passage 12 and is controlled by a throttle lever 16 fixed to the shaft 15. A port 17 opens from the induction passage 12 at a location adjacent the edge of the throttle 14. The port 17 is on the upstream side of the throttle 14 when the throttle is in the closed position as illustrated; when throttle 14 is moved to an open position, its illustrated; when throttle 14 is moved to an open position, its edge traverses port 17 and port 17 then senses the vacuum in the induction passage 12 downstream of throttle 14.

The solenoid valve unit 20 and the vacuum advance u ngll rg notdescribed or illustrated indetaflsince they form no part of the invention, and may be of the type illustrated in U.S. Pat. No. 3,584,521 issued June 15, 1971 to Robert S. Tooker and James J. Dawson. The solenoid valve unit 20 has first and second openings 26 and 27 disposed in opposite ends thereof and lateral openings 28 and 30 disposed intermediate the ends. A magnetically responsive valve element 31 having resiliently tipped ends is disposed within the solenoid valve unit and is reciprocal between a pair of valve seats, only one of which is shown, to close eitheropening 26 or opening 27.

A solenoid coil, not shown, is disposed within the solenoid valve unit with one lead 32 of this coil being connected to a voltage source 33 through the engine ignition switch 34. The other lead 35 of the solenoid coil is connected to a switch 36 which opens the circuit when it senses the pressure of the hydraulic fluid used to engage the direct drive clutch initransmission 37 and which closes the circuit to ground in the absence of such pressure. Transmission 37, which is more fully described in the above-identified U.S. Pat. No. 3,584,521, and in U.S. Pat. No. 3,32l,056 issued May 23, 1967 to Frank J. Winchell et al., includes a plurality of drive ratios which are selectively engagable between an input or driven shaft 38 and an output or drive shaft 40. When a lower drive ratio is engaged between driven shaft 38 and drive shaft 40, the speed of the drive shaft 40 is reduced below the speed of the driven shaft 38 to a greater extent than when the high drive ratio is engaged between driven shaft 38 and drive shaft 40.

With this type transmission, the solenoid valve 20 is energized through the switch 36 when the transmission is in a low drive ratio mode of'operation and, when the transmission is in a high drive ratio (direct drive) or in reverse, the solenoid valve 20 is de-energized.

When the solenoid valve unit 20 is energized, the valve element-31 is moved to a position to block the flow through opening 26 and openings 28 and 30 are vented through opening 27 to the atmosphere. If the solenoid valve 20 is de-energized, the valve element 31 is moved to block venting to the atmosphere through opening 27 and opening 26 is placed in communication with openings 28 and 30 to receive a vacuum signal from induction passage 12. Thus, the distributor vacuum advance unit 22 and the throttle control unit 25, to be describedrare vented to the atmosphere in all gears except reverse and direct drive; in reverse and direct drive induction passage 12 pressure is applied to these units.

Referring now to FIG. 2, the throttle control unit 25, of the invention, includes a hollow housing formed as a multi-piece unit including front and rear housing portions 50 and 51, respectively, with the outer periphery of a loose diaphragm 52 sandwiched therebetween. An actuator 53 is slidably journalled at one end in the bore 54 in the front housing portion 50 and at its opposite end is journalled in the enlarged bore 55 in one end of a stepped sleeve 56 which extends through the rear housing portion 51 and is suitably secured thereto. Stepped sleeve 56 is provided with a passage 57 at one end in communication with bore 55 and at its other end in communication with conduit 24.

As shown, the actuator 53 includes a first shaft portion 58 journalled in the bore 54, this first shaft portion terminating at its free end in a stem 60 positioned to engagethe throttle lever 16 fixed to the throttle shaft 15.

At its opposite end, the actuator is provided with a tube shaft portion of reduced diameter journalled in the bore 55 in sleeve 56. The actuator is also provided intermediate itsend with a stepped annular flange portion 62 providing an annular shoulder 62a joining a ratail hereinafter, the front chamber 66 is in communication with either atmosphere or induction pressure. If the front chamber 66 is subjected to induction pressure, the actuator 53 will be moved to the left until the flow through the orifice passages 71 becomes shut off by the O-ring seal 64 covering these passages to establish an intermediate position of the actuator. Then, if the throttle lever 16 is, for example, in open throttle position, out of engagement with the stem 60 of the actuator 53, the spring 65 can then move the actuator 53 further to the left to the fully extended position shown in FIG. 2.

In operation, the biasing force of spring 65 is such that with equal pressure on opposite sides of the diaphragm 52, the position of the actuator 53, whether ex-- tended, retracted or at an intermediate position therebetween, is determined by the position of the throttle lever 16. That is, with the throttle 14 in slow idle position, the spring 65 should be sufficiently weak so as not to overcome the force of the customary throttle return 7 spring 72. If the throttle 14 is moved from slow idle to dial outward extending shoulder 62b which are adapted to be engaged by the annular bead 52a of the diaphragm. An O-ring seal 63 positioned in a suitable annular groove provided for this purpose in the sleeve 56 is positioned to 'sealingly engage the tube shaft portion 61 of the actuator 53. A second O-ring seal 64 mounted in a suitable annular groove 50aprovided for this purpose in the front housing portion 50 sealingly engages the shaft portion 58. The annular groove 50a is formed at an axial distance, as desired, in the bore 54 to fix the O-ring 64 relative to orifices, to be described, in the first shaft portion 58 of the actuator whereby to form with this shaft. portion 58 a valve arrangement.

I A spring6$ positioned withinthe housing encircles the tube shaft portion 61 with one end abutting an end of the sleeve 56 and its other end abutting the stepped annular flange portion 62 of the actuator 53, to normally bias this actuator toward the left, as seen in FIG. 2, to the extended position shown in this figure.

The disphragm 52 and the stepped annular flange portion62 of the actuator 53 form with the front and rear housing portions 50 and 51 front and rear chambers 66 and 67 on opposite sides of the diaphragm, the rear chamber 67 being exposed to atmospheric air pressure through a sized orifice 68 extending through the rear housing portion 51.

An axial passage 70 extending from the end of tube shaft portion 61 into the first shaft portion 58 of the actuator is adapted to be placed in communication with one ormoreradial orifice passages 71 of predetermined size extending through the wall of the shaft portion.58.

The shaft portion 58 with the axial passage 70 and orifice passages 71 provides a valve arrangement reciprocable in bore 54 to cooperate with the O-ring seal 64 to control the ingress and egress of fluid to front chamber 66. When the actuator 53 is in a retracted position, moved to the extreme right with reference to FIG. 2, the orifice passages 71 are in direct communication with chamber 66 whereby, as described in greater defast idle position or beyond the spring 65 can help to extend the actuator to follow the movement of the throttle lever until the actuator is fully extended whereas, if the throttle is moved from a full throttle to fast idle to slow idle, the throttle lever 16 engages the stem of the actuator to effect movement of it back to its retracted position, this movement being from left to right with reference to FIG. 2.

However, if the throttle 14 is open, port 17 will be subjected to induction vacuum and then when transmission 37 shifts, for example, to high gear, solenoid valve 20 becomes de-energized'so that the vacuumsignal can then be transmitted to cause the ignition timing to be advanced and to cause this vacuum signal to be applied to the front chamber 66 of the throttle control unit 25. With differential pressure on opposite sides of the diaphragm 52, the actuator is rapidly moved to the left until the orifice passages 71 are covered by the O- ring seal 64 to establish an intermediate extended position. However, as previouslydescribed, if the throttle lever 16 is not engaged againstthe'actuator 53, the spring 65 can then effect further movement of the actuator to the extended position shown in FIG. 2. As long as the vacuum pressure is applied to front chamber 66, the actuator 53 will remain extended to act as a fast idle throttle stop so that upon deceleration, the throttle cannot be initially closed beyond a fast idle position, as determined by the intermediate extension of the actuator, as desired. If prior todeceleration the actuator 53 had been fully extended, as the throttle lever 16 engages the stem of the actuator 53, its closure movement to the fast idle position will be controlled since its return is against the biasing action of spring and the differential fluid pressure on opposite sides of the diaphragm 52. This permits the flow of air to the engine necessary for proper combustion when throttle 14 is initially closed to'decelerate the engine.

After transmission 37 downshifts to a lower drive ratio, solenoid valve unit 20 is energized and actuator 53 is then permitted to retract from the intermediate position to its retracted position, in a manner to be described. Throttle 14 is then permitted to close at a controlled rate to the slow idle position determined by the usual curb idle adjustment screw, not shown. Preferably, the throttle reaches this slow idle position just prior to full retraction of the actuator. In this position of the throttle, air flow is limited to that required for proper idle operation.

When the throttle is closed, as at idle and during deceleration, the port 17 is subjected to the essentially atmospheric pressure above throttle 14 so that no vacuum signals are provided to either ,the vacuum advance unit 22 or to the throttle control unit 25.

When transmission 37 is in one of the lower drive ratio modes of operation, switch 36 will cause the'solenoid valve 20 to be energized so that both the vacuum advance unit 22 and the throttle control unit 25 are vented to the atmosphere through their connections by conduits 21 and 24, respectively, to the openings 28 and 30, respectively, in communication wwth opening 27 in the solenoid valve.

With the actuator 53 at an intermediate position and with vacuum pressure no longer applied to the front chamber 66 and instead, this chamber is now vented to the atmosphere as described above so that when the throttle lever 16 contacts it, and is rotated in a clockwise direction toward slow idle, that is, to the position shown in FIG. 1, the actuator 53 is slowly allowed to retract to its retracted position, with the actuator moving to he right, with reference to FIG. 2, to its retracted position, with the rate of return of the actuator to this position being governed by the size of the orifices, that is, the orifice 68 in communication with rear chamber 67 and the orifice passages 71 in the actuator 53, the front chamber 66 being slowly vented to the atmosphere through these latter orifice passages 71 via conduit 24 and through the passage 27 in the solenoid valve 20.

Thus, the subject throttle control system provides a fast idle carburetor throttlesetting for reverse or high gear closed throttle deceleration with a slow idle carburetor throttle setting for engine operation at idle speed, with dashpot action from the extended position of the actuator to the slow idle position of the throttle as the actuator is forced toward its retracted position. Proper combustion is thereby enhanced .during high gear closed throttle deceleration.

In the embodiment "disclosed, the subject throttle control has been combined with a Transmission Controlled Spark system to assure reduction in emission of undesirable exhaust gas constituents. By combining the throttle control with the Transmission Controlled Spark system, the cost and complexity of the entire system is held to a minimum.

It should be appreciated that in a transmission where the drive ratio is changed manually rather than through the use of hydraulic pressure, switch 36 may be arranged to be operated by the usual transmission shift linkage rather than by hydraulic pressure, as disclosed. Further, it should also be appreciated that the solenoid valve unit 20 may be replaced by other valve mechanisms which are similarlyoperated in accordance with transmission drive ratios.

What is claimed is:

1. A throttle control for an internal combustion engine having a throttle movable by a throttle lever between open, fast idle and slow idle positions to vary engine speed, the throttle lever having a spring associated therewith to normally bias the throttle lever in a direction to move the throttle toward the slow idle position, comprising an actuator having a shaft portion adapted to be moved between a retracted position to an extended position with an intermediate position therebetween to engage said throttle lever to control the movement of said throttle lever from said open position to said slow idle position, a housing, a flexible diaphragm dividing said housing into atmospheric and vacuum chambers, said actuator being operatively connected to and extending through said diaphragm and having said shaft portion slidably received in said housing, seal means mounted in said housing in sealing engagement with said shaft portion, means biasing said diaphragm actuator toward said extended position, inlet means including orifice means in said shaft portion of said actuator in communication with said vacuum chamber when said actuator is between said retracted position and said intermediate position, said seal means blocking flow from said orifice means to said vacuum chamber when said actuator is between said intermediate position and said extended position, means to apply engine vacuum to said vacuum chamber through said inlet means to effect movement to and hold said actuator at said intermediate position, said means including transmission controlled means to interrupt engine vacuum to said vacuum chamber and to vent said vacuum chamber to the atmosphere via said orifice means at a controlled rate. 1 j

2. A throttle control mechanism for an internal combustion engine having an induction passage with a throttle therein for controlling air flow for combustion in theengine, a spring biased throttle lever connected to the throttle, said engine further having an associated transmission with an input connected to the engine and an output connected to a load and variable ratio drive means driving the output from the input, the variable ratio drive means providing high and low drive ratios and reverse, said throttle control comprising a housing, a diaphragm and an actuator positioned to form with said housing a first chamber and a second chamber, said actuator. being journalled in said housing for axial movement between a retracted position and an extended position with an intermediate position therebetween with one end of saidactuatorextending from said housing for engagement by said throttlelever, spring means positioned in said second chamber to normally bias said actuator toward said extended position while permitting retraction of said actuator by said throttle lever from said extended position to said intermediate position and then from said intermediate position to said retracted position as the pressure in said first chamber and said second chamber are equalized, said actuator being adapted to be retained in said intermediate position when vacuum signals are applied to said firstchamber to thereby limit throttle closing to a fast idle position, a vacuum conduit means operatively connected between said first chamber and said induction passage at a position upstream of said throttle when said throttle is in a closed position and downstream of said throttle when said throttle is openfor the transmission of vacuum signals to said first chamber, valve means in said conduit between said first chamber and said induction passage movable between a closed position wherein transmission of vacuum signals is prevented and said valve means is in communication with the atmosphere and an open position wherein transmission of vacuum signals is permitted, valve operating means connected to said valve means to control movement of said valve means as a function of the drive ratios provided by said transmission, said vacuum conduit means including orifice means in said actuator in communication with said first chamber as said actuator is moved axially between said retracted position and said intermediate position and out of communication with said first chamber as said actuator is moved axially between said intermediate position and said extended position.

3. A throttle control mechanism according to claim 2 including seal means positioned in said housing to sealingly engage said actuator to block the flow from said orifice means when said actuator is at said intermediate position with said seal means then positioned between said orifice meansand said first chamber.

4. In combination with an intermal combustion engine having an induction passage for air flow to the engine, a throttle in said induction passage for controlling air flow therethrough, said throttle being movable between open, fast idle and slow idle positions, a throttle lever connected to said throttle for controlling the position thereof and having a spring associated therewith to normally bias said throttle to said slow idle position, an associated transmission with an input connected to said engine and an output connected to a load and with variable ratio drive means driving said output from said input, a throttle control unit for controlling the position of said throttle, conduit means including a valve means controlled by said transmission drive mode connected to said induction passage upstream of said throttle when said throttle is in a closed position and downstream of said throttle when said throttle is open and to said throttle control unit for transmitting vacuum signals from said induction passage to said throttle control, said throttle control unit including a housing means having a bore therein, an actuator having a shaft sage.

means slidably mounted in said bore with one end thereof extending from said bore for engagement with said throttle lever, an O-ring seal positioned within saidbore to sealingly engage said shaft means, a diaphragm mounted within said housing in position to sealingly engage said actuator to form with said housing a first chamber and a second chamber with said first chamber in communication with said bore, an orifice in said housing for venting said second chamber to the atmosphere, passage means including at least one radial orifice passage through said shaft means of said actuator in communication with said conduit means, said actuator being movable axially between a retracted position and an extended position with an intermediate position therebetween, said radial orifice passage being in communication with said first chamber during movement of said actuator from said retracted position to said intermediate position as determined by closing off flow through said radial orifice passage by said O-ring seal, spring means operatively connected to said actuator to normally bias said actuator toward said extended position, said valve means including a first passage in communication with said induction passage and a second passage in communication with the atmosphere and a valve element movable from a first position to permit the transmission of vacuum signals from said induction passage to said first chamber, to a second position to block the flow of vacuum signals from said induction passage and to place said passage means in communication with the atmosphere through said second pas-

Claims

1. A throttle control for an internal combustion engine having a throttle movable by a throttle lever between open, fast idle and slow idle positions to vary engine speed, the throttle lever having a spring associated therewith to normally bias the throttle lever in a direction to move the throttle toward the slow idle position, comprising an actuator having a shaft portion adapted to be moved between a retracted position to an extended position with an intermediate position therebetween to engage said throttle lever to control the movement of said throttle lever from said open position to said slow idle position, a housing, a flexible diaphragm dividing said housing into atmospheric and vacuum chambers, said actuator being operatively connected to and extending through said diaphragm and having said shaft portion slidably received in said housing, seal means mounted in said housing in sealing engagement with said shaft portion, means biasing said diaphragm actuator toward said extended position, inlet means including orifice means in said shaft portion of said actuator in communication with said vacuum chamber when said actuator is between said retracted position and said intermediate position, said seal means blocking flow from said orifice means to said vacuum chamber when said actuator is between said intermediate position and said extended position, means to apply engine vacuum to said vacuum chamber through said inlet means to effect movement to and hold said actuator at said intermediate position, said means including transmission controlled means to interrupt engine vacuum to said vacuum chamber and to vent said vacuum chamber to the atmosphere via said orifice means at a controlled rate.

2. A throttle control mechanism for an internal combustion engine having an induction passage with a throttle therein for controlling air flow for combustion in the engine, a spring biased throttle lever connected to the throttle, said engine further having an associated transmission with an input connected to the engine and an output connected to a load and variable ratio drive means driving the output from the input, the variable ratiO drive means providing high and low drive ratios and reverse, said throttle control comprising a housing, a diaphragm and an actuator positioned to form with said housing a first chamber and a second chamber, said actuator being journalled in said housing for axial movement between a retracted position and an extended position with an intermediate position therebetween with one end of said actuator extending from said housing for engagement by said throttle lever, spring means positioned in said second chamber to normally bias said actuator toward said extended position while permitting retraction of said actuator by said throttle lever from said extended position to said intermediate position and then from said intermediate position to said retracted position as the pressure in said first chamber and said second chamber are equalized, said actuator being adapted to be retained in said intermediate position when vacuum signals are applied to said first chamber to thereby limit throttle closing to a fast idle position, a vacuum conduit means operatively connected between said first chamber and said induction passage at a position upstream of said throttle when said throttle is in a closed position and downstream of said throttle when said throttle is open for the transmission of vacuum signals to said first chamber, valve means in said conduit between said first chamber and said induction passage movable between a closed position wherein transmission of vacuum signals is prevented and said valve means is in communication with the atmosphere and an open position wherein transmission of vacuum signals is permitted, valve operating means connected to said valve means to control movement of said valve means as a function of the drive ratios provided by said transmission, said vacuum conduit means including orifice means in said actuator in communication with said first chamber as said actuator is moved axially between said retracted position and said intermediate position and out of communication with said first chamber as said actuator is moved axially between said intermediate position and said extended position.

3. A throttle control mechanism according to claim 2 including seal means positioned in said housing to sealingly engage said actuator to block the flow from said orifice means when said actuator is at said intermediate position with said seal means then positioned between said orifice means and said first chamber.

4. In combination with an intermal combustion engine having an induction passage for air flow to the engine, a throttle in said induction passage for controlling air flow therethrough, said throttle being movable between open, fast idle and slow idle positions, a throttle lever connected to said throttle for controlling the position thereof and having a spring associated therewith to normally bias said throttle to said slow idle position, an associated transmission with an input connected to said engine and an output connected to a load and with variable ratio drive means driving said output from said input, a throttle control unit for controlling the position of said throttle, conduit means including a valve means controlled by said transmission drive mode connected to said induction passage upstream of said throttle when said throttle is in a closed position and downstream of said throttle when said throttle is open and to said throttle control unit for transmitting vacuum signals from said induction passage to said throttle control, said throttle control unit including a housing means having a bore therein, an actuator having a shaft means slidably mounted in said bore with one end thereof extending from said bore for engagement with said throttle lever, an O-ring seal positioned within said bore to sealingly engage said shaft means, a diaphragm mounted within said housing in position to sealingly engage said actuator to form with said housing a first chamber and a second chamber with said first chamber in communication with said bore, an orifice in saiD housing for venting said second chamber to the atmosphere, passage means including at least one radial orifice passage through said shaft means of said actuator in communication with said conduit means, said actuator being movable axially between a retracted position and an extended position with an intermediate position therebetween, said radial orifice passage being in communication with said first chamber during movement of said actuator from said retracted position to said intermediate position as determined by closing off flow through said radial orifice passage by said O-ring seal, spring means operatively connected to said actuator to normally bias said actuator toward said extended position, said valve means including a first passage in communication with said induction passage and a second passage in communication with the atmosphere and a valve element movable from a first position to permit the transmission of vacuum signals from said induction passage to said first chamber, to a second position to block the flow of vacuum signals from said induction passage and to place said passage means in communication with the atmosphere through said second passage.