Engine cooling system

Abstract: An engine cooling system for inducing a stream of cold air via a radiator fan (18) toward the rear part of a vehicle so as to cool a vehicle engine (3), which includes catalysts (10,12) downstream of an exhaust manifold (6). The radiator fan (18) is displaced in front the engine (3) so that substantially no cold airstreams from the radiator fan (18) directly strike the exhaust manifold (6). Thus, exhaust emissions are prevented from being excessively cooled, so that the catalysts (10,12) can become active to purify the exhaust emissions reliably. The engine cooling system is effective to keep the catalysts (10,12) active when the engine (3) is in the partial cylinder operation mode in which the exhaust emissions tend to be lowered in the temperature.

Description: Field of the Invention This invention relates to an engine cooling system for a front engine vehicle by means of a radiator and airstreams induced by a radiator fan and by the motion of the automobile. Description of the Related Art Generally, a front engine vehicle directly induces a stream of cold air to its engine body by its motion. Furthermore, the engine is indirectly cooled by a radiator positioned in front of the engine, through which water is conducted, and across which airstreams are induced by a fan. When running at a speed above a preset value, such a front engine vehicle can sufficiently induce a cold airstream to cool its engine. Conversely, when running at a very low speed or when out of motion, the vehicle cannot induce a cold airstream to the engine body, which leaves the engine hot. To prevent such a problem, the vehicle is usually equipped with a fan between the radiator and the engine. The fan is operated by the rotational force of the engine, or by a motor. In this arrangement, the fan conducts a cold airstream to the engine and the radiator so as to reliably cool the engine body. At present, there are known vehicle engines which can assume a partial cylinder operation mode by disconnecting a part of cylinders so as to accomplish the reduction of an output and a substantial saving of fuel. A control unit for such a vehicle engine selects a suitable operation mode based on various engine operation data. For instance, when the partial cylinder operation mode is selected, the control unit provides a variable valve operating mechanism with a command for this mode. In response to the command, the variable valve operating mechanism interrupts the operation of intake and exhaust valves associated with the cylinders to be disconnected. In addition, the control unit sends this command to a fuel supply system, which suspends the fuel supply to the disconnected cylinders. In the partial cylinder operation mode, the engine produces fewer thermal energies than those in the full cylinder operation mode. Therefore, exhaust emissions are efficiently heat-radiated in a exhaust pipe, so that they tend to be extensively cooled. The engine exhaust emissions usually include noxious substances such as carbon monoxide CO, hydrocarbons HC, and nitrogen oxides NOx. The exhaust emissions should be free from these substances when they are discharged into the atmosphere. For this purpose, three-way catalysts are disposed in the exhaust system of a popular gasoline-fueled engine so as to remove CO, HC and NOx from the exhaust emissions. Furthermore, a diesel engine includes the three-way catalyst so as to purify nitrogen oxides NOx. The three-way catalyst has to be at its active temperature where it can effectively reduce and oxidize CO, HC and NOx so as to make these substance nontoxic, as shown in Fig. 5 of the accompanying drawings. Fig. 5 shows purification efficiencies of the three-way catalyst of a platinum group, which is used in a gasoline-fueled engine operating at a speed of 2400 rpm and an intake air pressure of -300 mmHg. The air-fuel ratio is maintained between 14.6 and 14.7. It can be seen that the purification efficiency of 50% can be attained for each of CO, HC and NOx when the exhaust emissions are in the temperature range of 340°C to 350°C (e.g. the efficient and active temperature). It is known that the reduction catalyst becomes active to reduce NOx when the exhaust emissions have the foregoing temperature. Therefore, it is very important to maintain the exhaust emissions sufficiently hot to activate the catalyst. The exhaust emissions extensively vary their temperature according to the operating conditions of the engine, airstreams induced by the motion of the vehicle, heat radiation from an exhaust manifold cooled by airstreams from the radiator fan, ambient temperature, and so on. Especially, the temperature of the exhaust emissions tends to become low at the time of engine start-up, a low output, or a low ambient temperature. If heat-radiation is enhanced from the exhaust manifold which is cooled by airstreams induced by the motion of the vehicle and by the radiator fan, it is very difficult to keep the exhaust emissions sufficiently hot to activate the catalyst. Therefore, when activated at the initial stage of engine start-up, the three-way catalyst, a NOx catalyst, or a small front catalyst near a combustion chamber cannot oxide or reduce CO, HC and NOx in the exhaust emissions so as to make these substances substantially nontoxic. This would cause serious pollution of the atmosphere. Furthermore, the exhaust emissions have a low temperature when the engine in the partial cylinder operation mode produces fewer thermal energies. Specifically, when the heat-radiation of the exhaust manifold is enhanced by airstreams induced by the radiator fan or by the motion of the vehicle, the exhaust emissions become further cold. Therefore, the catalyst cannot attain its effective temperature to eliminate CO, HD and NOx from the exhaust emissions. This phenomen would also cause serious pollution of the atmosphere. US Patent No. 3,820,327 discloses a temperature regulator applicable to overcoming a problem that a temperature of the catalyst reactor is lowered by induced air flow. Referring to a system shown in Fig. 1 of this document, the system comprises a fan 5 actuated by the vehicle engine, a radiator 4 disposed before the engine, a casing 6 surrounding the fan 5 and circulating cooling air induced by the fan 5, a casing 8 housing a catalyst reactor 1, a flap 9 disposed at an entrance of the casing 8 so as to regulate a flow of cooling air, and a link-rod system 10 for opening and closing the flap 9. When cold-starting is effected, the flap 9 is in the closed position so as to close the casing 8, so cooling air will be released into the atmosphere through an aperture 11, thereby preventing the catalyst reactor 1 from becoming too cold. Under the full running load, the aperture will be closed by the flap 9 such that cooling air will be circulated to the casing 8 so as to prevent the catalyst reactor 1 from becoming too hot. The cooling system requires not only a lot of components such as the casings 6 and 8, flap 9 and link-rod system 10 dedicated thereto but also spaces for disposing the casings 6 and 8 in the engine room. This means that only a limited space is available for auxiliary devices to be installed in the engine room, and that the engine room should be designed considering a number of restrictive factors. Summary of the invention It is the object of the invention to provide an engine cooling system according to the preamble of claim 1 and where the exhaust emissions stay hot without the shortcoming of the cited art. This problem is solved by the features of the characterizing part of claim 1. Preferred embodiments of the invention are illustrated in the dependent claims. Brief Description of the Drawings In all drawing figures, identical parts have identical reference numbers. Fig. 1 is a schematic top plan view showing the configuration of a first engine cooling system for a front engine vehicle having the partial cylinder operation function. Fig. 2 is a side cross-sectional view of the vehicle of Fig. 1. Fig. 3 is an enlarged schematic view showing the main part of the cooling system of Fig. 1. Fig. 4 is a schematic view of a second engine cooling system for the front engine vehicle having the partial cylinder operation function. Fig. 5 is a graph showing purification efficiencies of a three-way catalyst. Description of the Preferred Embodiments According to a first embodiment of the invention, an engine cooling system is applied to an engine 3 which is used for a vehicle of the front drive wheel type and has the partial cylinder operation mode. The engine cooling system is disposed in an engine room 2 at the front part of a vehicle body 1. The engine 3 is an in-line horizontal engine having four cylinders. A radiator 4 is positioned in front of the engine 3 in the direction X shown in Fig. 1. The engine 3 is installed on a main frame (not shown) of the vehicle body with its engine body 5 oriented in the direction Y. The engine body 5 accompanies an exhaust manifold 7 at its front side and an intake manifold 7 at its rear side. The intake manifold 7 is coupled to an intake pipe 8 and an air cleaner 9 in this order. The exhaust manifold 6 communicates with a front catalyst 10 and an exhaust pipe 11. The exhaust pipe 11 extends to a main catalyst 12 and reaches a muffler 13. The front catalyst 10 is positioned just under the exhaust manifold 6, while the main catalyst is positioned in the middle of the exhaust pipe 11. The front catalyst 10 is a well-known oxidation catalyst while the main catalyst 12 is a well-known three-way catalyst. The front catalyst 10 has a relatively small capacity so that it becomes active at an initial stage of the engine start-up period, and can effectively purify the exhaust emissions during this period. Conversely, the main catalyst 12 comprises noble metal such as platinum. When elevated above the effective temperature, the main catalyst 12 can effectively eliminate carbon monoxide CO, hydrocarbons HC and nitrogen oxides NOx from the exhaust emissions of the air-fuel mixture having a ratio near the stoichiometric ratio. The front catalyst 10 may be the three-way catalyst. In the partial cylinder operation mode, the cylinders #2 and #3 are continuously active while the cylinders #1 and #4 remain inactive in the engine 3. The exhaust ports (not shown) of the cylinders #1 and #2 merge while the exhaust ports (not shown) of the cylinders #3 and #4 merge as shown in Fig. 3. These exhaust ports are coupled to two points 111 of forked end of the exhaust pipe 11, so that the exhaust emissions flow through the exhaust pipe 11 to reach the front catalyst 10. As shown in Fig. 3, the engine 3 includes, in its valve operating system, a variable valve operating mechanism M for selectively operating the intake and exhaust valves. The variable valve operating mechanism M is controlled by a hydraulic switching circuit 14, which is controlled by a controller 15. When the full cylinder operation mode is selected, the controller 15 turns off the variable valve operating mechanism M, i.e. controls the mechanism M via the hydraulic switching circuit 14 in a manner such that the cylinders #1 to #4 are active. Further, the controller 15 provides the fuel supply system with the command for the full cylinder operation mode. In response to this command, the fuel supply system supplies fuel to all the four cylinders. Conversely, when the partial cylinder operation mode is selected, the controller 15 turns on the variable valve operating mechanism M, i.e. controls the mechanism M so as to operate only the cylinders #2 and #3 and disconnect the cylinders #1 and #4 via the hydraulic switching circuit 14. Further, the controller 15 provides the fuel supply system with the partial cylinder operation command, so that fuel is supplied only to the cylinders #2 and #3 via their associated injectors (not shown). The variable valve operating mechanism M is described in the co-pending Japanese patent application No. Hei 2-182131 entitled VALVE SYSTEM FOR MOTOR VEHICLE filed on July 10, 1990 (laid open under No. 4-72403). Referring to Fig. 1, the radiator 4 is placed in front of the engine 3 in the engine room 2. The radiator 4 communicates with a water jacket (not shown) of the engine body 5 so as to circulate the cooling water thereto. When circulating through a radiator core (not shown), a warmed cooling water is cooled by airstreams a (induced by the radiator fan, and called "radiator airstreams a " hereinafter) and airstreams b (induced by the motion of the vehicle, and called "incoming airstreams b " hereinafter). The radiator 4 has a width B1 across the vehicle body in the direction Y, and is shaped to cover the front areas of the engine body 5, a clutch 16 and a transmission 17. The radiator 4 is substantially as high as the engine body 5 as shown by B2 in Fig. 2. A radiator fan 18 is positioned behind the radiator 4. The radiator fan 18 leads cold airstreams via the radiator 4 toward the engine 3. A fan shroud 19 is disposed to surround the radiator fan 18 so as to guide the cold airstreams. The radiator fan 18 and a fan motor 20 are supported at the center of the shroud by suitable brackets 21. The motor 20 is controlled by the controller 15. The shroud 19 is placed only on the right half area of the radiator 4 (Figs. 1 and 3), i.e. the shroud is placed in a manner such that the center of the radiator fan 18 is offset by the distance S from the front center of the exhaust manifold 6. Therefore, when the radiator fan 18 is active, the radiator airstreams a are guided by the shroud 19 toward the clutch 16 and the transmission 17 but do not touch the exhaust manifold 6 of the engine body 5 as shown in Fig. 3. It is possible to place a heat exchanger for an air-conditioner in front of the radiator 4 at a position (shown by long and short dash lines) opposite to the radiator fan 18 as shown in Figs. 1 and 2. In operation, when the engine 3 undergoes a cold start, the radiator fan 18 remains inactive. The controller 15 actuates the radiator fan 18 at a proper timing after the completion of the cold start period of the engine. Thereafter, the radiator airstreams a are guided by the fan 18 via the shroud 19 toward the clutch 16 and the transmission 17, but do not directly flow toward the exhaust manifold 6 and the outer wall of the front catalyst 10 which is just under the exhaust manifold 10. Assume that the engine 3 is set in the partial cylinder operation mode under this condition, so that the total energies produced by the engine are accordingly reduced, which causes the exhaust emissions to be lower in their temperature. Since the radiator airstreams a are however made to flow wide of the exhaust manifold 6, the exhaust emissions are not further lowered in their temperature. Therefore, both the front catalyst 10 and the main catalyst 12 become active during the engine start-up period and can remain active to eliminate noxious substances effectively from the exhaust emissions. During the motion of the vehicle, incoming air-streams b are induced to the entire area of the radiator 4, i.e. width B1 in Fig. 3, so as to cool the exhaust manifold 6, clutch 16 and transmission 17. The more rapidly the vehicle runs, the more incoming airstreams b flow toward the engine. Thus, the exhaust system can be sufficiently cooled during the high speed motion of the vehicle. Conversely, the slower the vehicle, the fewer incoming airstreams b flow to the engine. The exhaust emissions are not excessively cooled during the motion of the vehicle, so that the front and main catalysts 10 and 12 can function effectively. Substantially no incoming airstreams b reach the engine during a very slow running or non-running of the vehicle. In such a case, the controller 15 provides the radiator fan 18 with a command to cool the engine at proper timings each time the engine cooling water exceeds the preset temperature. Thus, radiator airstreams a are conducted to the clutch 16 and the transmission 17. The engine is operating at a very low load or is idling in the partial cylinder operation mode under this condition, so that it produces relatively low energies. Since radiator airstreams a do not directly flow to the exhaust manifold 6 and the outer wall of the front catalyst 10, the exhaust emission flowing through the exhaust manifold 6 are not excessively lowered in their temperature. Thus, both the front catalyst 10 and the main catalyst can function effectively and reliably. An engine cooling system according to a second embodiment will be described referring to Fig. 4. In this embodiment, the cooling system is applied to an in-line vertical four-cylinder engine with the partial cylinder operation mode. This engine 3 includes its crankshaft extending perpendicular to the axle, and the intake manifold 7 which is placed behind the radiator fan 18 and extends to the air cleaner 9. The exhaust manifold 6 extends to the main catalyst 12, and is attached to the engine body 5 at a position which is displaced by the distance S1 from a position which is displaced by the distance 51 from the axis of the radiator fan motor. During the motion of the vehicle, incoming air-streams b are induced to the whole front area B1 of streams b are induced to the whole front area B1 of the radiator 4, and radiator airstreams a are guided by the fan shroud 19 to flow toward the intake manifold 7. In the embodiment, the cooling system is effectively applicable to the in-line vertical engine similarly to the cooling systems of the foregoing embodiment. As described so far, the radiator fan is positioned in front of the engine in a manner such that the radiator airstreams do not directly strike the exhaust manifold of the engine. Thus, the exhaust emissions flowing through the exhaust manifold are prevented from being excessively cooled by the radiator airstreams, thereby allowing the catalysts to be active to eliminate noxious substances from the exhaust emissions. In the foregoing exhaust systems of the engine 3, the front catalyst 10 is disposed just under the exhaust manifold 6 and the main catalyst 12 follows downstream of the front catalyst 10. Alternatively, it is possible that a NOx catalyst may be placed downstream of the exhaust manifold of a diesel engine and the radiator fan may be positioned in front of the exhaust manifold with a certain distance displaced from the front part of the exhaust manifold. According to the invention, the engine 3 includes the variable valve operating mechanism M in its valve system. When the control unit 15 issues the command for the partial cylinder operation mode, the variable valve operating mechanism M activates the valve system accordingly. The fuel supply system provides the active cylinders with fuel in response to the foregoing command. Needless to say, the present invention is effectively applicable to ordinary engines which do not have the partial cylinder operation mode.

Claims: An engine cooling system of an engine (3) with a catalyst downstream of an exhaust manifold (6) and comprising a radiator (4) positioned in front of the engine (3), and a radiator fan (18) inducing air flow from a front part of the vehicle to a rear part thereof, characterized in that the radiator fan (18) is disposed at a position offset from a front side of the exhaust manifold (6) such that the induced airstreams do not directly flow towards the exhaust manifold (6), thereby maintaining the exhaust emissions hot. An engine cooling system as in claim 1, wherein the catalyst is a first catalyst (10) disposed just under the exhaust manifold (7). An engine cooling system as in claim 2, wherein the first catalyst (10) is an oxidation catalyst. An engine cooling system as in claim 2, wherein the first catalyst (10) is a three-way catalyst. An engine cooling system as in claim 1, wherein the engine (3) is a horizontal engine with a crankshaft thereof axially disposed in parallel with an axle. An engine cooling system as in claim 5, wherein the exhaust manifold (7) is positioned in front of the engine (3). An engine cooling system as in claim 1, wherein the catalyst is a second catalyst (12) disposed in the middle of an exhaust pipe (11). An engine cooling system at in claim 7, wherein the second catalyst (12) is a three-way catalyst. An engine cooling system as in claim 1, wherein the engine (3) is a vertical engine with a crankshaft thereof disposed axially perpendicular to an axle. An engine cooling system as in claim 9, wherein the exhaust manifold (7) is coupled to the engine (3) at a side opposite to the radiator fan (18). The engine cooling system as in any one of claims 1 to 10, wherein the engine (3) includes a cylinder cut-out system for appropriately keeping some engine cylinders inoperative.

Inventors: HATANO KIYOSHI, KATAOKA TETSUO, KUBO MASAHIKO, MURATA SHINICHI, HATANO, KIYOSHI, KATAOKA, TETSUO, KUBO, MASAHIKO, MURATA, SHINICHI, HATANO, KIYOSHI C/O MITSUBISHI JIDOSHA KOGYO K.K, Kataoka, Tetsuo, c/o MITSUBISHI JIDOSHA KOGYO K.K, Kubo, Masahiko, c/o MITSUBISHI JIDOSHA KOGYO K.K, Murata, Shinichi, c/o MITSUBISHI JIDOSHA KOGYO K.K
Applicants: MITSUBISHI MOTORS CORP, MITSUBISHI JIDOSHA KOGYO KABUSHIKI KAISHA
Application year: 1993
Main classification: F01P3
IPC codes: F01N3, F01P3, F01P11, B60K11, B60K13