GB2204915A

GB2204915A - I.c. engine exhaust gas recirculation control

Info

Publication number: GB2204915A
Application number: GB08711170A
Authority: GB
Inventors: Keith Charles Ransom
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1987-05-12
Filing date: 1987-05-12
Publication date: 1988-11-23
Also published as: WO1988008928A1; GB8711170D0

Abstract

An exhaust gas recirculation system has a vacuum controlled valve (16) in the recirculation passage (14). The vacuum for operating the valve is supplied from the intake manifold (10) and is regulated by [a] a modified vacuum signal (30) provided from a closed loop electronic vacuum regulator (32), and [b] pressure signals picked up from opposite sides of a restriction (26) placed in the recirculation passage.

Description

Exhaust gas recirculation This invention relates to exhaust gas recirculation for internal combustion engines.

Exhaust gas recirculation is a known technique which is of significant importance in reducing undesirable emissions from internal combustion engines. A proportion of the exhaust gas is recirculated through a passage to the intake side of the engine, and mixed with the incoming air or fuel/air mixture.

Exhaust gas recirculation is often referred to by the acronym EGR, and this designation will be used in this specification.

According to a first aspect of the present invention there is provided an exhaust gas recirculation system for an internal combustion engine which has an intake manifold, an exhaust manifold, an EGR passage between the two manifolds and a vacuum operated EGR valve for controlling exhaust gas flow through the passage, wherein the passage contains a flow restriction upstream of the EGR valve, and wherein a vacuum regulator for providing a vacuum signal to operate the EGR valve is connected across the restriction, the vacuum regulator being connected to a vacuum supply and receiving control inputs from both sides of the restriction, from atmosphere and from a vacuum source controlled in accordance with predetermined relationships between engine operating parameters.

The vacuum source is preferably derived from the intake manifold vacuum modified by an electronic vacuum regulator controlled from an engine management module.

According to a second aspect of the invention, there is provided an exhaust gas recirculation system for an internal combustion engine, the system comprising an engine intake manifold, an exhaust manifold, an EGk passage between the two manifolds, a vacuum operated EGR valve for controlling exhaust gas flow through the passage, a flow restriction in the passage which produces a pressure drop when exhaust gas flows through the passage, and an electronic module which receives engine operating information and outputs a signal for controlling the EGR valve, the system being arranged so that there is a predetermined relationship between the pressure drop across the restriction and the output signal from the module.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an EGR system in accordance with the invention; and Figure 2 shows a section through a vacuum regulator for use in the system of Figure 1.

In Figure 1, the intake manifold of an engine (not shown) is designated 10 and the exhaust manifold is designated 12. An EGR passage 14 is connected between the two manifolds, and an EGR valve 16 is fitted in the passage 14 to control gas flow through the passage.

The opening and closing of the valve 16, together with the respective pressure prevailing in the manifolds, controls the flow of exhaust gas recirculated to the intake flow.

The EGR valve 16 is a vacuum controlled valve and receives a vacuum control signal from a line 18. The vacuum appearing in line 18 is set by a vacuum regulator 20.

The regulator itself is shown in more detail in Figure but Figure 1 shows that the regulator has connections 22 and 24 to the EGR passage 14 at opposite sides of a restriction 26 in the passage; connection 28 to the intake manifold, being a vacuum supply; connection 30 to an electronic vacuum regulator 32 and a connection 34 to atmosphere. The electronic regulator 32 receives intake manifold vacuum from a line 33, and modifies his in accordance with an electrical control signal on a line .35, to produce a regulated vacuum supplied along the line 30 to the regulator 20.

Inside the regulator 20, a valve member 36 shuttles between two valve seats 38 and 40. The valve member is supported between two diaphragms 42 and 44, and a compression spring 46 provides a continually present biasing force acting on the diaphragm/valve member assembly.

To install the system, it is necessary to provide a programmed electronic control circuit (or module) 37 which receives engine management signals relating to engine speed 39 and load 41 and which outputs an EGR setting signal to the electronic regulator 32. There is however no feedback from the EGR system itself to the module 37, which is therefore in an "open loop" situation. The fact that the module only has to be programmed with predetermined speed/load data, and does not need to be capable of interpreting feedback data from the EGR system itself means that the module 37 can be considerably less complex than might otherwise be necessary.

However it is desirable to modify the setting of the EGE valve 16 in accordance with the actual conditions in the EGR system, and this is accomplished by a "closed loop" arrangement using the restriction 26.

The function of the regulator 20 is to provide a suitable vacuum signal to produce the correct flow in the ESE passage by varying the opening of the EGR valve 16. To do this, the source vacuum from the intake manifold (line 28) is suitably regulated to give a value such that a given pressure drop is obtained for a given vacuum in line 30.

The source vacuum is introduced into a chamber 48'in the regulator through connection 28. With the valve member 36 in its middle position, there is communication between the source through 28), the valve through 18) and atmosphere (through 34). If the valve member 36 is in its uppermost position as shown in Figure 2, the source will be closed off and the valve will be held at atmospheric pressure. At the other extreme, the valve member will close against the seat 38 and then the valve 16 will be supplied with full supply vacuum.

Normally however the valve member will shuttle between these two extreme positions and will be controlled by the pressure difference ssP between the pressures in the lines 22 and 24 together with the biasing force of the spring 46 acting in one direction, and the vacuum from the electronic regulator 32 through connection 30 acting in the opposite direction. The value of tP will clearly vary in accordance with the flow rate through the passage 14, and thus the opening of the valve 16 is also controlled, not only by the predetermined parameters in the module 37, but also by the instantaneous conditions in the passage 14.

The EGR system described can be easily calibrated because the (implied) required flow for any engine condition can be set in the module 37, ie it does not rely on knowledge of conditions at which the valve operates.

Claims

1. An exhaust gas recirculation system tor an internal combustion engine which has an intake manifold, an exhaust manifold, an EGR passage between the two manifolds and a vacuum operated EGR valve for controlling exhaust gas flow through the passage, wherein the passage contains a flow restriction upstream of the EGIR valve, and wherein a vacuum regulator for providing a vacuum signal to operate the EGR valve is connected across the restriction, the vacuum regulator being connected to a vacuum supply and receiving control inputs from both sides of the restriction, and from a vacuum source controlled in accordance with predetermined relationships between engine operating parameters.

2. An EGR system as claimed in Claim 1, wherein the vacuum supply is provided by engine intake manifold vacuum.

3. An EGR system as claimed in Claim 1 or Claim 2, wherein the vacuum regulator has a valve member which controls the magnitude of the operating vacuum signal to the valve, and the valve member is influenced by pressure signals acting in opposite directions on the member and derived from pressures sensed at opposite sides of the restriction.

4. An EGR system as claimed in Claim 3, wherein the valve member is also influenced by a spring.

5. An EGR system as claimed in any preceding claim, wherein the controlled vacuum source is derived from the intake manifold vacuum modified by an electronic vacuum regulator connected to an engine management module.

6. An EGR system as claimed in Claim 5, wherein the electronic vacuum regulator is mounted in one housing with the vacuum regulator connected across the restriction.

7. An EGR system as claimed in Claim 5 or Claim 6, wherein the engine management module receives no information fed back from the EGR passage.

8. An exhaust gas recirculation system for an internal combustion engine, the system comprising an engine intake manifold, an exhaust manifold, an EGR passage between the two manifolds, a vacuum operated EGR valve for controlling exhaust gas flow through the passage, a flow restriction in the passage which produces a pressure drop when exhaust gas flows through the passage, and an electronic module which receives engine operating information and outputs a signal for controlling the EGR valve, the system being arranged so that there is a predetermined relationship between the pressure drop across the restriction and the output signal from the module.

9. An EGR system as claimed in any preceding claim, wherein the EGR valve is a poppet valve.

10. An exhaust gas recirculation system, substantially as herein described with reference to the accompanying drawings.