Patent Application
20050120982
1. Field of the Invention
This invention relates to oil distribution systems in compression ignition internal combustion engines, the system having a main gallery, a separate oil gallery for piston cooling nozzles and one or multiple control valves which regulate the oil flow through the separate gallery to the piston cooling nozzles, whereby the system may match the amount of oil distributed with the piston cooling demand.
2. Background Art
In general, diesel engines with pistons made of steel or aluminum require piston-cooling jets as a means of removing heat from the piston during engine operation. However, piston-cooling requirements are not uniform across the engine operating range. Maximum demand for cooling occurs at full loads, at engine speeds ranging from peak torque to rated speed, when engine thermal loading is high. If the emissions control strategy includes running the engine at retarded beginning of injection (BOI) timings, the demand for piston cooling is even higher. The demand for cooling may be greatly diminished when the engine runs at part or low loads, when engine thermal loading is reduced. In the majority of cases, no cooling is required when the engine runs at idle speed. Therefore, previous control distribution systems, particularly single gallery systems, that deliver the oil flow based on the gallery oil pressure alone provide more oil flow than is necessary, introducing additional unwanted parasitic losses that translate into loss of fuel economy.
Most known engines with oil distribution achieve only partial or no control of the oil flow for piston cooling. Some engines with conventional piston cooling nozzles fed from the main oil gallery that control main gallery oil pressure directly by a regulator valve have almost no control of the oil flow through nozzles. The flow increases with engine speed until the regulator valve becomes operational and then remains approximately constant at higher speeds. Some engines with conventional piston cooling nozzles fed from the main oil gallery that control the oil pressure via a regulator valve located at the oil pump discharge have a limited control. The flow increases sharply with engine speed until the regulator valve becomes operational, and then increases at a slower rate at higher speeds.
Engines with piston cooling nozzles fitted with check valves achieve control by turning off the oil flow through nozzles at idle speed, when oil pressure is low. This permits reducing the oil pump size, which otherwise would have been to be designed with higher capacity, and would therefore be larger, heavier, and costlier. In addition, lowering the oil flow requirements at idle reduces parasitic losses and improves the fuel economy at idle (which may amount to up to about 25% of the run-time of a heavy-duty, on-highway engine). However, when the engine is running under heavy load, such control may not be adequate for cooling the pistons.
While the engine speed influences the need for piston cooling to some degree, the control of oil flow with engine speed is not optimum for piston cooling because it still provides excess oil flow at the expense of increased parasitic losses and fuel economy. In fact, this type of control is developed for and targets optimum bearing lubrication, not piston cooling. The oil flow behavior described above is rather a result of this particular design choice. Thus, traditional lubrication systems are designed to provide adequate lubrication and cooling to moving engine parts. Optimizing bearing operation drives the system's control strategy. Current designs control oil flow (and pressure) with engine speed for this purpose. The need to cool pistons via lubricating oil is not common to all engines, being most prevalent in diesel engines. The known piston cooling strategies that rely on engine speed variation are unrelated to engine thermal state (i.e., piston temperature). Moreover, it is not practical to measure piston temperature directly in production engines. Therefore, a major shortcoming of present lubrication designs is that it limits the piston cooling to bearing lubrication requirements.
The present invention overcomes the above-mentioned disadvantages by introducing a separate control method and apparatus for piston cooling with an engine oil distribution system, the separate control regulated by factors reflecting the need for piston cooling. In general, the system provides an oil distribution system for an internal combustion engine with a separate oil gallery dedicated for piston cooling, and at least one electronically controlled valve that would control the oil flow through the above-mentioned gallery. Preferably, the engine's electronic control unit (ECU) actuates the control valve based on the need for removing the heat from the pistons. Preferably, prescribed algorithms trigger response from engine operating or state parameters, for example, other means to estimate the piston thermal loads such as direct measurement of metal temperature elsewhere (cylinder block or cylinder head), coolant temperature, or engine load as given by torque or throttle position. The system improves on previous designs by allowing not only piston cooling oil control at idle speed, or at varying speeds, but control at varying engine loads, so that control can be directly correlated to the cooling needs of the engine's pistons.
At part or low loads, the oil temperature is lower, viscosity slightly higher, and parasitic losses in the lubrication system higher than at full load. The control may be used to reduce, or interrupt, the oil flow through piston-cooling nozzles in accordance to piston cooling requirements, so that the total amount of oil being pumped through oil filter and oil cooler can be reduced, together with the pump power which is not needed. The reduction in the oil flow through the system is important because the flow through piston-cooling nozzles may comprise up to 35-40% of the total oil flow in the system, and important savings in parasitic losses and, ultimately, fuel consumption may be achieved.
In the preferred embodiment, engine thermal load, as suggested by fluid or metal temperature, or by engine torque or load, may be the determining factor, rather than engine speed. The invention also leads to improvements in the design and operation of oil coolers controlled by thermatic valves (also known as “oil thermostats”). Current designs that use an oil thermostat attempt to regulate the oil cooling in the oil cooler by varying the amount of oil flow being passed and cooled through the cooler as a function of oil temperature. In general, a desired oil temperature is a temperature that should be controlled to fall in between a minimum and maximum value. If the oil is overheated, its decrease in viscosity jeopardizes proper bearing lubrication and may lead to catastrophic engine failure in short time. There are also long term effects through increased oxidation rates at high temperatures, and oil properties deteriorations are mitigated through reduced oil change intervals, with negative implications on life-cycle costs and environment. Therefore, oil coolers are used to maintain the oil temperatures below the maximum limit, especially on heavy and medium duty diesel engines. If the oil temperature falls below a minimum value due to overcooling, or in winter (at low ambient temperatures), oil viscosity increases along with pumping losses and impacts negatively the fuel economy. However, with the present invention a designer may supply the piston cooling circuit, for example, the “separate gallery” only, with cooled oil at all operating conditions and ambient temperatures, and regulate the oil flow to the piston cooling jets according to prescribed algorithms, while the temperature of oil fed to the engine continues to be regulated by the temperature controlled oil cooler. A modified or a controlled oil cooler may also be employed to provide this advantage.
The invention may reduce the cost of improving piston cooling by allowing one or more control valves to regulate the flow to piston banks, for example, two valves, each controlling flow to a bank of pistons. The invention also may reduce the cylinder-to-cylinder variation in piston cooling oil flow, compared to designs where other oil consumers are fed off the main gallery or the flow is biased toward one end of the gallery. By decoupling the objective of optimized bearings lubrication oil flow control as related to engine speed, from optimized piston cooling objective via oil control responsive to engine thermal state, the present invention provides improved performance and efficiency in the design and operation of the engine.
The present invention will be more clearly understood by reference to the following detailed description of a preferred embodiment when read in conjunction with the accompanying drawing, in which like reference characters refer to like parts throughout the views, and in which
Referring first to
In such a lubricating oil system 24, an oil pump 31 delivers lubricating oil from a supply sump 26 through a manifold 27 that distributes the oil to numerous locations throughout the engine 10. Preferably, the manifold 27 includes passages 32 leading to an oil cooler 28 (
As better shown in
In the preferred embodiment, a separate gallery 52 is coupled to the manifold 48 at fork 54 where fluid may be delivered both to the main gallery 50 and the separate gallery 52. Preferably, control valve 56 is coupled in the passageway leading to the separate gallery 52. The valve 56 is responsive to signals from the electronic control module 60. The electronic control module 60 may be programmed to control the valve 56, for example, a solenoid valve, as desired. For example, a preferred algorithm will control the valve for opening as a function of the load applied to the engine or as a function of engine temperature, preferably sensed as coolant temperature or directly measured metal temperature. Thus, unlike speed dependent lubrication zones that may require additional lubricating oil due to high velocity displacement of parts or turbulent fluid flow that may increase the need for additional lubrication at high speed, the valve 56 may be closed at high speed separating the gallery 52 when the speed is high, and the load is light or metal temperature low. Since a light load allows the pistons to be cooled in another way (i.e., reduced cooling requirements), the high lubrication requirements of other zones throughout the system may be handled by the main gallery 50 and flow to gallery 52 closed, without requiring additional or larger size pump 31 in the system. Due to reduced oil flow demand overall for the engine, required hydraulic power to pump the oil is diminished, power consumed by the oil pump decreases, and the fuel consumption is reduced. Preferably, when the valve 56 adjusts fluid flow as a function of engine load, the opening of the valve correlates with increasing load applied to the engine.
This invention provides control flexibility for handling cooling problems such as a condition known as “hot idle”. When a vehicle stops at a traffic light after a long period of functioning at high loads and speeds, the engine is still hot, and the pistons require cooling via oil sprays for a certain additional amount of time, but the engine is at idle, running at very low speed and low oil pressures. If the engine was equipped with previously known, mechanical-style check valves for each individual nozzles, they would be closed due to low gallery oil pressure (at idle) and no oil cooling would be provided to pistons. In the preferred embodiment with the computer controlled valve 56, the control overcomes the previous design deficient for cooling through the flexibility of adjusting valve opening and, thus enhancing or decreasing piston cooling as desired for each situation.
As a result, the invention may provide for separate conditioning or independent delivery of the oil to piston cooling nozzles. The invention improves the cooling by responding to cooling needs directly, rather than responding to speed or lubrication distribution governed by speed and lubrication needs. The valve 56 provides improved control of the delivery so that pump efficiency is increased and power requirements are reduced. For example, the separate gallery 52 may be positioned outside the hot engine block or the valve may couple the gallery 52 to additional cooling or treatment passages. In addition, piston cooling may be improved over previously known systems.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention as defined in the claims.
