US3885537A - Road load modulated exhaust gas recirculation system - Google Patents

Abstract

The carburetor has an exhaust gas recirculation vacuum port (EGR) located above the closed position of the throttle valve, the vacuum providing a signal to an EGR valve to open it upon the attainment of a predetermined vacuum level to pass exhaust gases into the engine intake manifold, the vacuum line containing a pair of flow restrictors and an air bleed device to at times bleed air into the vacuum line to cause the EGR valve to schedule EGR flow at a rate proportional to load during part throttle operations.

Description

[4 1 May 27, 1975 ROAD LOAD MODULATED EXHAUST GAS RECIRCULATION SYSTEM Primary ExaminerWendell E. Burns Attorney, Agent, or FirmR0bert E. McCollum; Keith L. Zerschling [75] Inventor: Roy E. Diehl, Livonia, Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[57] ABSTRACT The carburetor has an exhaust gas recirculation vac- 22 Filed: Nov. 5, 1973 [21] App]. No.: 413,159

uum port (EGR) located above the closed position of the throttle valve, the vacuum providing a signal to an EGR valve to open it upon the attainment of a prede- [52] U.S. 123/119 A termined vacuum level to pass exhaust gases into the engine intake manifold, the vacuum line containing a [58] Field of pair of flow restrictors and an air bleed device to at times bleed air into the vacuum line to cause the EGR valve to schedule EGR flow at. a rate proportional to load during part throttle operations [56] References Cited UNITED STATES PATENTS 3,783,847 1/1974 Kolody............................123/119A 3D 3,796,049 3/1974 Hayashi...... ...................123/119A 40mm "awmg ROAD LOAI) MODULATEI) EXHAUST GAS RECIRCULATION SYSTEM This invention relates, in general, to an internal combustion engine. More particularly, it relates to a system for controlling the recirculation of exhaust gases back into the engine through the intake manifold.

Devices are known for recirculating a portion of the exhaust gases to control the emission of unburned hydrocarbons and lower the output of oxides of nitrogen. These devices have included valving to prevent recirculation of the exhaust gases at undesired times and generally are controlled by movement of the carburetor throttle valve to prevent recirculation during engine idle and wide-open throttle operations. This is desirable because at engine idle, exhaust gas scavenging is inefficient, while at wide-open throttle position, maximum power is limited by the availability of oxygen.

It is an object of this invention to provide an exhaust gas recirculation (EGR) system of the above type that affords a finer control of the recirculation of gases by means of apparatus that schedules EGR flow better in proportion to load during part throttle and cruising operations.

It is a further object of the invention to provide an EGR valve for opening and closing a duct containing exhaust gases for their recirculation into an engine, the valve being moved to open the duct by a signal force that is determined by the level of manifold vacuum in a port (EGR port) traversed by the carburetor throttle valve, and controlled by means that at times lowers the EGR signal force below its true value by means of an air bleed to better proportion EGR flow to engine load, as indicated by manifold vacuum changes.

Another object of the invention is to improve engine drivability by reducing exhaust gas recirculation during light engine loads when the recirculation required to control NO, output, for example, generally is less than that which is usually scheduled.

Other objects, features and advantages of the invention would become more apparent upon reference to the succeeding detailed description thereof, and to the drawings illustrating a preferred embodiment thereof, wherein;

FIG. 1 is a cross-sectional view of a portion of an internal combustion engine and associated carburetor embodying the invention;

FIG. 2 is a cross-sectional view taken on a plane indicated by and viewed in the direction of the arrows 2-2 of FIG. 1; and

FIG. 3 is a schematic illustration of the control portion of the invention.

FIG. 1 illustrates a portion of one-half of a twobarrel carburetor of a known downdraft type. It has an air horn section 12, a main body portion 14, and a throttle body 16, joined by suitable means not shown. The carburetor has the usual air/fuel induction passage 18 open at their upper ends 20 to fresh air from the conventional air cleaner, not shown. The passages 18 have the usual fixed area venturies 22 cooperating with booster venturies 24 through which the main supply of fuel is induced,.by means not shown.

Flow of air and fuel through induction passages 18 is controlled by a pair of throttle valve plates 26 each fixed on a shaft 28 rotatably mounted in the side walls of the carburetor body.

The throttle body 16 is flanged as indicated for bolt ing to the top of the engine intake manifold 30, with a spacer element 32 located between. Manifold 30 has a number of vertical risers or bores 34 that are aligned for cooperation with the discharge end of the carburetor induction passages 18. The risers 34 extend at right angles at their lower ends 36 for passage of the mixture out of the plane of the figure to the intake valves of the engine.

The exhaust manifolding part of the engine cylinder head is indicated partially at 38, and includes an exhaust gas crossover passage 40. The latter passes from the exhaust manifold, not shown, on one side of the engine to the opposite side beneath the manifold trunks 36 to provide the usual hot spot beneath the carburetor to better vaporize the air/fuel mixture.

As best seen in FIG. 2, the spacer 32 is provided with a worm-like recess 42 that is connected directly to crossover passage 40 by a bore 44. Also connected to passage 42 is a passage 46 alternately blocked or connected to a central bore or passage 48 communicating with the risers 34 through a pair of ports 50. Mounted to one side of the spacer is a cup shaped boss 52 forming a chamber 54 through which passages 46 and 48 are interconnected.

As described above, it is necessary and desirable to provide some sort of control to prevent the recirculation of exhaust gases at undesirable times. For this purpose, passage 46 normally is closed by a valve 56 that is moved to an open position by a servo 58. The servo includes a hollow outer shell 64 containing an annular flexible diaphragm 66. The latter divides the interior into an air chamber 68 and a signal vacuum chamber 70. Chamber 68 is connected to atmospheric pressure through a vent 72, while chamber 70 is connected to a vacuum signal forcethrough a line 74. The stem of valve 56 is fixed to a pair of retainers 76 secured to diaphragm 66. They serve as a seat for a compression spring 77 normally biasing the valve to its closed position. The stem slidably and sealingly projects through a plate 78 closing chamger 54.

As shown in FIG. 1, the carburetor contains an exhaust gas recirculating (EGR) port 80 that is located above the closed position of throttle valve 26, to be traversed by the edge of the throttle valve as it moves open. The pressure in port 80 thereby varies from atmospheric to the manifold vacuum level as a function of the opening of throttle valve 28. Port 80 is connected to a passage 86.

Passage 86 is connected to servo vacuum line 74 through apparatus that at times lowers the vacuum signal to a different value at the servo than exists at port 80, for a purpose to be described. More specifically, line 86 contains a pair of fixed area orifices or flow restricting devices 90 and 92 interconnected by a passage 94. The line 74 is connected to passage 94.

Downstream of orifice 92 is a manifold vacuum controlled air bleed device 84. It has an outer housing 98 divided into two chambers 1(l 0 and 102 by an annular flexible diaphragm 104. The lower shell portion is formed with two passages 106 and 108. Passage 108 is formed at its chamber end with a conical seat 110 cooperating with the diaphragm 104 acting as a valve seat and valve combination, respectively. A compression spring 112 is seated between a spacer 1 l4 riveted to the diaphragm and an adjustable stop 116. Adjusting the stop will change the spring preload to a desired level.

The air bleed device controls the bleed of air into EGR vacuum line 94 as a function of manifold vacuum level. Chamber 100 is connected by a passage 118 to a manifold vacuum port 120 located below the closed position of throttle valve 28. Lower passage 106 is vented to atmosphere, while passage 108 is connected to the downstream side of the flow restrictor 92. If the force of spring 112 is chosen, for example, to be such as to keep diaphragm 104 against seat 110 until the manifold vacuum rises above 7 inches Hg., then the diaphragm will block off the bleed of air into passage 108 for all vacuum levels below 7 inches Hg.

Therefore, when manifold vacuum in high enough, i.e., above 7 inches Hg, such as it is during cruising conditions, to pull diaphragm 104 up against stop 116, air will be bled into line 108 from line 106. This air then passes through orifice 92 and bleeds the vacuum in line 74. The signal vacuum at EGR port 80 is sensed at full value in line 86 to orifice 90, where it is reduced across the orifice due to the air bled into line 74.

The vacuum level in line 74, therefore, is reduced proportional to the size of the restrictors or orifices 90 and 92, the size of which can be a matter of choice to provide the desired vacuum level schedule. For example, if the orifices are of equal size, then the vacuum signal force in line 74 will be one-half of the true value at the EGR port 80. If orifice 90 has a flow area of two times that of orifice 92, then the vacuum signal force in line 74 will be about two-thirds that of the EGR port vacuum level.

When the manifold vacuum level is below 7 inches Hg, then the diaphragm 104 remains seated, no air is bled past orifice 92, and the vacuum signal force level in line 74 is the same as the EGR port vacuum level. The delay in buildup of the vacuum signal at the EGR valve by the flow past orifice 90 will be only slight, such as less than one-half of one second, for example. However, to avoid this delay during an EGR valve closing mode, a branch line 122, containing a one-way check valve 124, bypasses the orifice 90 to allow full flow of the then higher pressure at the EGR port in line 86 to line 74. This is desired so the EGR valve will close quickly during decelerations, for example.

As stated initially, the invention is used to reduce the EGR servo vacuum signal to a level below that at the carburetor EGR port 80, at particular modes of engine operation. This improves drivability while maintaining a given NO emission level since the volume of EGR flow called for by the EGR port vacuum level during cruising or light load operations generally is in excess of that actually needed to maintain a low NO, level. Conversely, when the signal is at full value, the NO emissions will be lowered while maintaining a given drivability.

In operation, during engine idle speed and deceleration conditions, the throttle valve is closed, so no EGR flow occurs because EGR port 80 is at substantially atmospheric pressure. This transmitted through line 74 maintains the EGR valve 56 closed. While manifold vacuum is high, above 7 inches Hg, opening of passage 108 to the air in passage 104 is ineffective since the lower chamber 102 in the air bleed device is already at atmospheric pressure.

Assume now that the throttle valve 26 is moved to a slightly open position for light accelerations of the vehicle. The manifold vacuum most likely will not decay below a vacuum level of 7 inches Hg; therefore, the

bleed valve device will remain open, bleeding air into passage 108 and through orifice 92 to the passage 74. At this time, the EGR vacuum in port will be a mod ulated manifold vacuum as the throttle valve traverses the EGR port. The bleed device will decay the EGR vacuum signal force to the EGR valve 56, thus providing only a small amount of EGR flow and one corresponding essentially to the light load operation.

During heavier vehicle accelerations, movement of the throttle valve past the EGR port to a wider open position generally will decay the manifold vacuum to a level below 7 inches Hg. Accordingly, the air bleed device will close, by the diaphragm 104 seating against the conical end of passage 108, so that air no longer is bled into line 74. Accordingly, the EGR vacuum in line 74 will be at its full value, resulting in the EGR valve opening to its maximum flow capacity, which is desired during this condition of operation.

During wide open throttle conditions, the movement of the throttle valve to a nearly vertical position will generally decay the manifold vacuum to nearly zero. This also will put the EGR port at nearly atmospheric pressure, which will then close the EGR valve 56 even though the air bleed device is closed. This condition will continue for so long as it takes the manifold vacuum to recover and begin building up again, at which point the EGR vacuum will then be at its full value to the EGR valve 56 until it reaches a level above 7 inches Hg. At this point, the air bleed device will open and lower the EGR signal vacuum to the EGR valve 56.

During deceleration modes, the one-way check valve opens when the pressure at EGR port 80 goes to atmosphere, or when it becomes greater than the vacuum downstream of the check valve plus the force of the spring closing the check valve, if a spring is used. This is desirable to provide a fast closing of the EGR valve at this time because there is no need for EGR to reduce NO During decelerations, the engine is not producing horsepower and therefore is not producing N0 The air-fuel mixture is already excessively lean during decelerations; therefore, adding EGR would only further hinder its burning.

From the foregoing, it will be seen that the invention provides an EGR flow rate during part load operations that is nearly proportional to engine load so that during maximum accelerations a maximum flow capacity is obtained, whereas during light load operation, only little flow is provided. Likewise, it will be seen that the invention prevents large flow when wide open throttle conditions of operation occur because at that time the EGR port vacuum is nearly zero.

While the invention has been described and illustrated in its preferred embodiment, it will be clear to those skilled in the arts to which it pertains that many changes and modifications may be made thereto without departing from the scope of the invention. For example, it will be clear that the spring force of the air bleed device can be changed as desired to vary the operating characteristics. Also, while the EGR port is shown as located above the closed position of the throttle valve, it will be clear that the port could be located as desired either to straddle the edge of the throttle valve in a closed position, for example, or be located further above the throttle valve than shown so as to delay a buildup of EGR port vacuum until the throttle valve has opened substantially. Other positions may also be possible within the scope of the invention.

What is claimed is:

1. An exhaust gas recirculating system for an internal combustion engine, having a throttle valve controlling flow through a carburetor induction passage, comprising, a duct connecting the exhaust gases to the engine intake manifold, a spring closed exhaust gas recirculation (EGR) valve normally closing the duct to prevent recirculation and movable to an open position by a signal vacuum connected thereto, the induction passage containing an exhaust gas recirculating (EGR) port lo cated relative to the throttle valve so as to be at essentially atmospheric pressure at closed throttle positions with decreases in pressure level in proportion to the progressive opening of the throttle valve until EGR port vacuum reaches the level of manifold vacuum, conduit means operatively connecting the EGR port signal vacuum to the valve to move the same, and vacuum signal control means in the conduit means for at times reducing the EGR flow by reducing the level of the EGR vacuum signal at the EGR valve to a value below the value.at the EGR vacuum port, and below the level necessary to maintain the EGR valve open, the control means including an air bleed means responsive to a predetermined mode of operation of the engine for bleeding air into the conduit means, the conduit means including first and second flow restrictors in series flow arrangement with each other, the conduit means connection to the EGR valve being between the flow restrictors, and the air bleed means being located downstream of the restrictor furthest from the EGR port.

2. A system as in claim 1, the air bleed means including an atmospheric air passage, a flexible diaphragm type vacuum valve having spring means biasing the dia' phragm against the air passage closing the same, and means applying engine manifold vacuum to the diaphragm to move the vacuum valve above a predetermined manifold vacuum level to open the air passage and bleed down the EGR vacuum.

3. A system as in claim 1, the: bleed means comprising an air source, second conduit means connecting the air source to the first mentioned conduit means, a spring closed air bleed valve normally blocking the second conduit means, a vacuum servo operably connected to the air bleed valve and movable in response to the attainment of a predetermined manifold vacuum to open the valve and bleed air into the conduit means.

4. A system as in claim 1, including further conduit means between the EGR port and EGR valve bypassing the first flow restrictor and including a one-way check valve means operable upon the pressure level at the EGR port being higher by a predetermined amount than the pressure level at the EGR valve to open and immediately equalize the two pressures.

Claims (4)

1. An exhaust gas recirculating system for an internal combustion engine, having a throttle valve controlling flow through a carburetor induction passage, comprising, a duct connecting the exhaust gases to the engine intake manifold, a spring closed exhaust gas recirculation (EGR) valve normally closing the duct to prevent recirculation and movable to an open position by a signal vacuum connected thereto, the induction passage containing an exhaust gas recirculating (EGR) port located relative to the throttle valve so as to be at essentially atmospheric pressure at closed throttle positions with decreases in pressure level in proportion to the progressive opening of the throttle valve until EGR port vacuum reaches the level of manifold vacuum, conduit means operatively connecting the EGR port signal vacuum to the valve to move the same, and vacuum signal control means in the conduit means for at times reducing the EGR flow by reducing the level of the EGR vacuum signal at the EGR valve to a value below the value at the EGR vacuum port, and below the level necessary to maintain the EGR valve open, the control means including an air bleed means responsive to a predetermined mode of operation of the engine for bleeding air into the conduit means, the conduit means including first and second flow restrictors in series flow arrangement with each other, the conduit means connection to the EGR valve being between the flow restrictors, and the air bleed means being located downstream of the restrictor furthest from the EGR port.

2. A system as in claim 1, the air bleed means including an atmospheric air passage, a flexible diaphragm type vacuum valve having spring means biasing the diaphragm against the air passage closing the same, and means applying engine manifold vacuum to the diaphragm to move the vacuum valve above a predetermined manifold vacuum level to open the air passage and bleed down the EGR vacuum.

3. A system as in claim 1, the bleed means comprising an air source, second conduit means connecting the air source to the first mentioned conduit means, a spring closed air bleed valve normally blocking the second conduit means, a vacuum servo operably connected to the air bleed valve and movable in response to the attainment of a predetermined manifold vacuum to open the valve and bleed air into the conduit means.

4. A system as in claim 1, including further conduit means between the EGR port and EGR valve bypassing the first flow restrictor and including a one-way check valve means operable upon the pressure level at the EGR port being higher by a predetermined amount than the pressure level at the EGR valve to open and immediately equalize the two pressures.

Images