FR2919026A1 - Exhaust gas re-injecting device for supercharged internal combustion engine of vehicle, has heat evacuation duct with cooling fins connecting bypass control valve to cooler, and bypass duct surrounded by thermally insulating substance - Google Patents

Abstract

The present invention relates to an exhaust gas reinjection device, allowing better control of the temperature of the exhaust gas reinjected including through a conduit (22) equipped with cooling fins connecting a valve (21) bypass a cooler (23), a bypass duct (24) being surrounded by a thermally insulating substance.

Description

The invention relates to the invention

  field of internal combustion engines. The present invention relates more particularly to a device for reinjecting exhaust gases, for example, in a supercharged engine. The exhaust gas return devices, also referred to as EGR, are generally equipped with a cooling system for cooling the exhaust gas. Controlling this cooling improves the performance of the EGR device which aims to reduce the nitrogen oxide content of the exhaust gas to comply with anti-pollution standards, while maintaining a satisfactory combustion stability. A commonly used EGR device includes, for example, a cooler, also called a heat exchanger, communicating with a cooling circuit receiving the engine coolant. In order to control the temperature of the reinjected exhaust gases, the cooler of the EGR device is associated with a bypass duct, also called EGR bypass. This bypass is generally integrated in the heat exchanger, that is to say that the exhaust gases are diverted to the side of the exchanger. To effectively control the temperature, the cooling capacity of the heat exchanger is generally optimized. However a heat exchanger with a high cooling capacity will have a large volume and makes the engine less compact.

  In addition, the heat exchangers are optimized for an operating point at a determined optimum flow rate of the exhaust gas. The optimum flow rate is generally a high flow rate for very hot operating points, the temperature control for intermediate operating points then being very approximate.

  The present invention aims to mitigate one or more

  disadvantages of the prior art, by creating a device for reinjection of gases

  exhaust system to effectively control the temperature of

  exhaust gas reinjected, circulating from the exhaust circuit to the intake circuit.

  This objective is achieved by means of an exhaust gas reinjection device comprising a cooler and a first bypass duct of the cooler, the first bypass duct being supplied with exhaust gas from an exhaust circuit by a first bypass valve, the cooler and the first bypass duct being connected to a second exhaust gas return control valve in an intake circuit, characterized in that a second duct equipped with cooling fins connects the first bypass valve to the cooler and in that the first bypass duct is surrounded by a thermally insulating substance.

  According to another feature, the thermally insulating substance of the first bypass duct is an air gap held in a double wall of the first duct.

  According to another feature, the thermally insulating substance of the first bypass duct is formed by a layer of a thermally insulating material disposed around the first bypass duct, against its outer surface.

  According to another feature, a stream of heat removal air is directed to the second duct equipped with cooling fins.

  The invention, its characteristics and its advantages will appear more clearly on reading the description given with reference to the figures referenced below: FIG. 1 represents a schematic view of an example of an exhaust gas recirculation device according to the invention, installed between the intake circuit and the exhaust circuit of an engine; FIG. 2 represents a perspective view of an exemplary bypass duct with an insulating layer according to the invention; FIG. 3 represents a perspective view of an example of a bypass duct with a double wall enclosing an insulating air layer; FIG. 4 is a diagram showing the heat exchanges between the supply duct of the cooler, the cooler and the environment under the bonnet; FIG. 5 represents the arrangement of an exhaust gas reinjection device 10 according to a high-pressure architecture; - Figure 6 shows the disposition of an exhaust gas reinjection device according to a low pressure architecture. The invention will now be described with reference to the figures mentioned above. The air for supplying the internal combustion engine is, for example, sucked by a compressor (11) of a turbocharger (10, 11, 17). The compressor (11) is rotated by a turbine (17) of the turbocharger, the turbine (17) and the compressor (11) being integral with a rotating shaft (10). In a nonlimiting manner, the compressed air at the outlet of the compressor (11) passes through a cooler (12) which discharges heat, for example, into the air or into a cooling liquid. The compressed and cooled air, at the outlet of the cooler (12), for example meets a flap (13) controlled by an actuator (131) in an open or closed position, to increase or decrease, respectively, the fresh air flow. In a nonlimiting manner, exhaust gases passing through an exhaust gas reinjection control valve (25) are mixed with the fresh air and then injected into the inlet distributor (14). The exhaust gas feed control valve (25) is, for example, positioned in the open or closed position by an actuator (251). The actuators (131, 251 and 211 respectively) receive, for example, control signals (s131, s251 and s211 respectively) produced by a control unit (100). The control unit (100) produces, for example, a control (s251) for closing the exhaust gas return valve (25), in a supply mode of the intake distributor, in fresh air only. The control unit (100) produces, for example, a control (s251) for the total or partial opening of the exhaust gas return valve (25), in a supply mode of the intake distributor, in fresh air mixed with reinjected exhaust.

  The gaseous mixture supplying the intake distributor (14) is burned in the combustion chambers (15) of the engine, the exhaust gas leaving the combustion chambers (15) then being recovered in the collector (16) of the combustion chamber. 'exhaust. At the outlet of the exhaust manifold the gases pass through the turbine (17) and drive the turbine (17) in rotation. On the other hand, a part of the gas leaving the exhaust manifold (16) passes through the exhaust gas feed device (2), also called the EGR device, when the valve (25) for controlling the injection of the exhaust gases. exhaust gas is open. The device (2) EGR comprises, in connection with the exhaust circuit, a bypass valve (21), also called a bypass valve. The bypass valve (21) is controlled by an actuator (211) in a determined position. According to the position of the bypass valve (21), the exhaust gases entering the device (2) EGR, are directed towards a first conduit (24) bypass, also called bypass conduit, equipped with means of thermal insulation or to a second conduit (22) for discharging heat and supplying a cooler (23). The bypass valve (21) is, for example, controlled by the control unit (100), in a total bypass position, in which the exhaust gases entering the device (2) EGR, are directed, in total, to the first conduit (24) bypass. Advantageously, the heat loss through the thermally insulated bypass conduit (24) is limited. The exhaust gas will, for example, have a temperature of about 150 ° C higher than the temperature of the exhaust gas circulating in an uninsulated bypass duct. The energy gain is important and the temperature of the re-injected exhaust gas is better controlled.

  In another configuration, the bypass valve (21) is controlled in a total cooling position, in which the exhaust gases at the inlet of the device (2) EGR, are directed entirely towards the second conduit (22). heat evacuation and cooler supply (23). FIG. 4 represents, in a nonlimiting manner, the exchanges of heat between the environment (ENV) of the engine, under the hood of a vehicle, the conduit (22) of supply and the cooler (23). The quantity of heat (El) discharged through the supply duct (22) into the engine environment (ENV) is increased by means of cooling fins of this duct (22). For high or low exhaust gas flow rates, the difference between the temperature (Ti) at the inlet of the supply duct and the temperature (T2) at the outlet of the supply duct (22) is increased by 50 ° C. C. The cooling capacity of the supply duct (22) is increased and advantageously makes it possible to produce the cooler accordingly. The volume of the cooler may, for example, be decreased. In addition, the cooling capacity of the supply duct (22) being increased, the differences between the heat energy (El) evacuated by the supply duct (22) and the heat energy (E2) discharged by the cooler ( 23), for different operating points, are flattened. The differences in energy dissipation (E1) through the conduit (22) supply as a function of the mass flow (Qegr) of the exhaust gas flowing in this conduit (22), are less. Indeed, in the case of a duct devoid of fin, supplying the cooler, the portion of the energy dissipated by the supply duct relative to the total energy dissipated by the cooler and by its supply duct, could go from 20%, for large gas flows, to 65% for low gas flows. Thanks to the cooling fins, these differences are reduced and the precision in the control of the cooling of the exhaust gases is improved. The temperature (T3) at the outlet of the cooler (23) is thus better controlled. In another configuration, the bypass valve (21) is controlled in an intermediate position, in which the exhaust gases entering the device (2) EGR, are directed, in part towards the first duct (24) by- pass and partly to the second conduit (22) for heat removal and supply of the cooler (23). The best control of the energy dissipated during cooling and the limitation of the heat losses through the bypass conduit (24) makes it possible to increase the functional range of the EGR device which allows the reduction of the nitrogen oxide content. exhaust gas while maintaining a satisfactory combustion stability. The cooler with its optimized operating points, usually for very high temperatures, is associated with a heat supply and exhaust duct (22) which improves the performance of the EGR device (2) for the operating points intermediate. At the outlet of the first duct (24) bypass or at the outlet of the cooler (23), the exhaust gases are directed towards the valve (25) for controlling the exhaust gas re-injection. Depending on the more or less large opening of the valve, the amount of exhaust gas reinjected is more or less important. In a nonlimiting manner, the device (2) EGR is supplied with exhaust gas leaving the exhaust manifold (16), these gases being reinjected at the intake manifold inlet (14), as shown in FIG. In this configuration similar to a high pressure exhaust reinjection system, the control program of the valves controlling the reinjection of the exhaust gas will also be similar. Without limitation, in another exemplary embodiment, the device (2) EGR is supplied with exhaust gas leaving a filter (18) particles downstream of the turbine (17), these gases being reinjected input of the compressor (11), as shown in Figure 6. In this configuration similar to a low pressure exhaust gas re-injection system, the control program of the valves controlling the re-injection of the exhaust gas will also be similar. The first bypass duct (24) is surrounded, in a non-limiting manner, by an insulating material as shown in FIG. 2. The partition (241) of the first by-pass duct is, for example, in contact with a thermally insulating material. and heat-resistant, for example in the form of a sheath. This insulating material is, for example, without limitation, a material of ceramic, plastic or glass fiber type. According to another exemplary embodiment, as represented in FIG. 3, the bypass duct (24) comprises a double partition. An insulating air space (244) is, for example, included in a sealed compartment formed by an internal partition (241) of the bypass duct (24) and its external partition (242). The exhaust gases circulating in the portion delimited by the internal partition (241) are thus thermally insulated.

  The second heat sink and cooler supply duct (22) advantageously comprises cooling fins. The second conduit is, for example, a metal conduit, whose outer wall is equipped with cooling fins normally extending on its outer surface, over a predetermined length. In a nonlimiting manner, the fins are parallel to each other. The cooling fins are, for example, plates of a specified thickness and width spaced apart from each other to allow the circulation of air. In another example, the fins are plates, of predetermined thickness, extending normally to its outer surface of the conduit (22) supply and surrounding the conduit (22) supply. Without limitation, the engine environment is arranged so that a stream of air flowing in the engine compartment, passes between the fins of the duct (22) to have a better evacuation of heat in the air. A fan controlled by the control unit (100) for example blows air on the cooling fins. The outer surface of the fins allows a heat exchange between the conduit (22) supply and the air of the engine environment. At the outlet of the second conduit (22), the exhaust gas enters the cooler (23) of the device (2) EGR. Without limitation, this cooler (23) is a water cooler or an air cooler. The thermal insulation of the first duct (24) bypass and the heat removal means of the second duct (22) supplying the cooler (23), allow better control of the temperature of the reinjected exhaust gas. Indeed in a mode of reinjection of hot exhaust gas heat energy of the exhaust gas passing through the first conduit (24) bypass is retained and transmitted to the intake circuit. The heat losses, by the bypass pipe, are thus negligible and independent, for example, the flow of exhaust gas in this conduit (24).

  Conversely, in devices that are not fitted with an isolated bypass duct, the heat losses at the bypass duct imply that the temperature of the re-injected exhaust gases is inaccurate. The inaccuracy is all the less controllable as the heat losses in an uninsulated duct, vary according to the flow.

  It should be obvious to those skilled in the art that the present invention allows embodiments in many other specific forms without departing from the scope of the invention as claimed. Therefore, the present embodiments should be considered by way of illustration but may be modified in the field defined by the scope of the appended claims.

Claims (4)

  An exhaust gas feed device comprising a cooler (23) and a first cooler bypass duct (24), the first bypass duct (24) being fed with exhaust gas from a fuel circuit. exhaust through a first bypass valve (21), the cooler (23) and the first bypass duct (24) being connected to a second exhaust gas return control valve (25) in an intake circuit, characterized in that a second conduit (22) equipped with cooling fins connects the first bypass valve (21) to the cooler (23) and that the first bypass duct (24) is surrounded by a substance (243). , 241) thermally insulating.   2. exhaust gas reinjection device according to claim 1, characterized in that the thermally insulating substance of the first bypass duct (24) is a blade (244) of air held in a double wall (242, 241). the first conduit (24).   3. The exhaust gas reinjection device according to claim 1, characterized in that the thermally insulating substance of the first bypass duct (24) is formed by a layer of a thermally insulating material (243) arranged around the first duct. (24) bypass, against its outer surface.   4. exhaust gas reinjection device according to one of claims 1 to 3, characterized in that a heat evacuation air stream is directed on the second conduit (22) equipped with cooling fins. cooling.