Patent Application
20140109884
The present disclosure relates generally to internal combustion gas engines and more particularly to exhaust gas recirculation systems for such engines.
Exhaust gas recirculation (EGR) is used in many internal combustion (IC) engines, and particularly gasoline and diesel engines. In an EGR system, a portion of an engine's exhaust gas is recirculated back to the engine cylinders. Therefore, at a time when a cylinder allows fuel, oxygen and other combustion products into the combustion chamber for ignition, vehicle exhaust is also allowed to enter the chamber.
The introduction of vehicle exhaust into the combustion chamber has a number of consequences. One consequence is that the introduced exhaust displaces the amount of combustible matter in the chamber. Because the exhaust gases have already combusted, the recirculated gases do not burn again when introduced to the chamber. This results in a chemical slowing and cooling of the combustion process by several hundred degrees Fahrenheit. Thus, combustion of material in the cylinder results in a same pressure being exerted against the cylinder piston as results from combustion without the recycled exhaust, but at a lower temperature. The lower temperature leads to a reduced formation rate for nitrous oxide emissions. Thus, the EGR technique results in less pollutants being emitted in an engine's exhaust.
Additionally, the introduction of recirculated exhaust gas into an engine cylinder allows for an increase in engine performance and fuel economy. As the combustion chamber temperature is reduced, the potential for harmful “engine knock” or engine detonation is also reduced. Engine detonation occurs when the fuel and air mixture in a cylinder ignite prematurely due to high pressure and heat. In engine detonation, instead of an associated spark plug controlling when a cylinder's fuel is ignited, the ignition occurs spontaneously, often causing damage to the cylinder. However, when the combustion chamber temperature is reduced due to EGR, the potential for engine detonation is also reduced. This allows vehicle manufacturers to program more aggressive (and hence, more efficient) timing routines into an associated spark timing program. Because of the aggressive timing routines, the vehicle's power control module (PCM) has a greater advance notice and thus more time to take measures to prevent engine detonation. The aggressive timing routines can also result in higher cylinder pressures leading to increased torque and power output for the vehicle. For these and additional reasons, high levels of EGR are especially useful when applied to turbocharged or supercharged engines.
There is a large amount of heat energy contained in the exhaust gas due to its extremely high temperature and high flow rate during certain driving conditions. In a vehicle with non-cooled EGR, the heat energy in the exhaust is “wasted” out of the tailpipe. In the conventional EGR system 10 illustrated in
In one form, the present disclosure provides an engine coolant heating system for a vehicle. The system comprises an exhaust gas recirculation cooler having an input for receiving exhaust gas from an engine and an output for outputting cooled exhaust gas; an exhaust gas recirculation valve connected between an input of an intake manifold and the output of the exhaust gas recirculation cooler; and at least one additional valve connected at least between the input of the exhaust gas recirculation cooler, an output of the exhaust gas recirculation cooler and an exhaust output. The at least one additional valve is for configuring the system in a first configuration whereby a portion of the exhaust gas from the engine is passed through the cooler before a predetermined amount of cooled exhaust gas is passed through the exhaust gas recirculation valve to the intake manifold, and for configuring the system in a second configuration whereby substantially all of the exhaust gas from the engine is passed through the cooler before the predetermined amount of cooled exhaust gas is passed through the exhaust gas recirculation valve to the intake manifold.
The present disclosure also provides method of recirculating exhaust gas output from an engine. The method comprises configuring an exhaust gas recirculation valve and at least one additional valve into a first configuration whereby a portion of exhaust gas output from the engine is passed through an exhaust gas recirculation cooler before a predetermined amount of cooled exhaust gas is passed through the exhaust gas recirculation valve to an intake manifold; and configuring the exhaust gas recirculation valve and the at least one additional valve into a second configuration whereby substantially all of the exhaust gas output from the engine is passed through the cooler before the predetermined amount of cooled exhaust gas is passed through the exhaust gas recirculation valve to the intake manifold.
In one embodiment, the at least one additional valve is a single multi-position valve having a first position corresponding to the first configuration and a second position corresponding to the second configuration.
In another embodiment, the at least one additional valve comprises a first valve connected between the input of the cooler and the exhaust output; and a second valve connected between a connection of an output of the first valve and the exhaust output and a connection between the output of the cooler and an input of the exhaust gas recirculation valve. The first valve causes substantially all of the exhaust gas from the engine to be passed through the cooler in the second configuration. The second valve causes no cooled exhaust gas to pass to the exhaust output in the first configuration and a second predetermined portion of cooled exhaust gas to pass to the exhaust output in the second configuration.
In another embodiment, the predetermined amount of cooled exhaust gas is less than or equal to 40% of the cooled exhaust gas. In another embodiment, the portion of the exhaust gas is less than or equal to 40% of the exhaust gas.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description, including disclosed embodiments and drawings, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the invention, its application or use. Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention.
According to the principles disclosed herein, and as discussed below, engine coolant heating systems that improve waste heat recovery are disclosed and include a piped connection between the outlet of an EGR cooler and the main exhaust pipe leading to the vehicle's tailpipe. The systems also include a system of valves in the exhaust stream that direct the flow of exhaust appropriately given the specific driving conditions.
Referring to
Referring to
Thus, one advantage of the disclosed engine coolant heating system 100 is that the three illustrated valves 120, 122, 124 can be controlled such that during coolant warm-up, the EGR cooler 118 has the maximum amount of exhaust flow it can handle, and transfers the maximum amount of heat from the exhaust into the coolant until the target coolant temperature is reached. This allows the waste heat recovery system to get the fullest possible utility out of the exhaust heat energy that would otherwise be wasted out of the tailpipe.
Referring to
The system 200 is designed for use in a turbocharged vehicle. As such, the system 200 also includes a turbo compressor 232 connected between the EGR valve 220 and the intake manifold 12 and a turbo turbine 230 connected between the engine block 14 and the inlet of the catalytic converter 16. It should be appreciated that the recirculated exhaust gas will pass through the compressor 232 before entering the intake manifold 12. It also should be appreciated that engine exhaust will pass through the turbine 230 before entering the catalytic converter 16. Otherwise, the system 200 is operated in the same manner, with the same operating modes, as system 100 discussed above with respect to
When the coolant is already at the optimal operating temperature and there is no need for coolant heating, the three-way valve 326 and the EGR valve 320 are set to allow approximately 40% of the exhaust flow to go through the EGR cooler 318 and then back to then engine 14 (via manifold 12) for re-combustion. The remaining exhaust gas simply continues down the main exhaust pipe and out of the vehicle. When there is a need to rapidly heat up the engine coolant, the three-way valve 326 is set to force 100% of the exhaust flow through the EGR cooler 318. Downstream of the EGR cooler 318, the position of the EGR valve 320 is set to allow up to approximately 40% of the flow to return to the intake manifold 12 while the remainder of the flow passes to the main exhaust pipe and out of the vehicle.
It should be appreciated that any of the systems 100, 200, 300 disclosed herein may be modified to move the catalytic converter 16 downstream of the respective EGR cooler 118, 218, 318. That is, the disclosed systems 100, 200, 300 are not to be limited by the location of the catalytic converter 16 shown in
As shown in the illustrated embodiment, the system 400 also includes an intake manifold 12, an engine block 14, an EGR cooler 418, EGR valve 420, engine back pressure valve 422 and an EGRC bypass valve 424. In this embodiment, the catalytic converter 416 is located downstream of the input to the cooler 418. Moreover, the engine back pressure valve 422 is connected between the exhaust piping to the tailpipe and the outlet of the catalytic converter 416. The EGR bypass valve 424 is still connected between the exhaust piping to the tailpipe and a connection between the outlet of the cooler 418 and an inlet of the EGR valve 420. The opening and closing of the valves 420, 422 and 424 are controlled in the manner discussed above regarding
The disclosed coolant heating systems 100, 200, 300, 400 can be contrasted against typical exhaust waste heat recovery systems, and against typical cooled EGR systems. Typical exhaust waste heat recovery systems involve the use of a separate and dedicated exhaust-to-coolant heat exchanger that is installed directly into the main exhaust pipe. This configuration has many drawbacks. For a vehicle that already has an EGR cooler, this configuration requires a separate and un-related exhaust-to-coolant heater. This second heat exchanger adds unnecessary cost and weight to the vehicle.
In addition, since the separate exhaust-to-coolant heat exchanger is typically installed in the main exhaust pipe near the rear of the vehicle, coolant must be routed along almost the entire length of the vehicle. Even with insulated coolant lines, some of the heat added to the coolant by the exhaust is lost via convection across the long coolant lines. The long coolant lines also increase the pressure drop of the cooling circuit, increasing the load on the coolant pump. Moreover, the nature of a heat exchanger built directly into the main exhaust pipe prevents the use of extended surface area (i.e., fins) on the exhaust side of the heat exchanger. Since the thermal performance of an exhaust-to-coolant heat exchanger is extremely exhaust-side dependent, a heat exchanger without exhaust side fins has much lower thermal efficiency than one that has them
Typical cooled EGR systems utilize an EGR cooler that is sized to meet the cooling demands of the engine's peak power condition, where the exhaust temperatures and flows are highest. In reality, the vehicle spends a very small portion of its life at this peak power condition, which means that the EGR cooler is oversized for the most typical driving conditions. This lack of cooler utility results in wasted money (to buy the large cooler), wasted fuel (due to additional mass), and wasted packaging space—all of which is undesirable.
The disclosed systems 100, 200, 300, 400 have the following advantages over the typical exhaust waste heat recovery systems, and typical cooled EGR systems described above. First, the disclosed systems accomplish EGR cooling and rapid coolant heating within the same heat exchanger. This provides a lower cost and much better fuel economy than the typical exhaust waste heat recovery and cooled EGR systems, which include the separate and dedicated exhaust-to-coolant heat exchanger. Second, the entire coolant heating system 100, 200, 300 disclosed herein is installed directly behind the engine, with coolant hoses less than 1 meter long. This results in minimal convective heat losses in the coolant lines and minimal coolant pressure drop. Moreover, the coolant heater/EGR cooler disclosed herein has brazed fins on the exhaust side for efficiency (e.g., 90-95%).
The disclosed coolant heating systems 100, 200, 300, 400 also increase the utility of their EGR coolers by using it to rapidly warm-up the coolant at engine cold start. What would otherwise be wasted money, fuel, and packaging space is now used for quicker coolant warm-up and a resulting fuel economy improvement, which is extremely beneficial.
