Abstract:
A lubricating oil supply system for internal combustion engine includes an oil reservoir and oil pump connected with a lubrication distribution network including a pressure controller which selectively controls the pressure within the distribution network to at least one pressure value that is less than the maximum pressure produced by a pressure relief valve associated with the oil pump.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an internal combustion engine lubrication system in which pressure within the lubrication system is controlled by both mechanically and electrically operated valves. 
         [0004]    2. Related Art 
         [0005]    Pressure-lubrication has been used with automotive internal combustion engines for many years. Typically, a single pressure relief valve is used to limit the maximum pressure developed by an oil pump. The relief pressure is usually set at a fairly high value, in order to assure that the engine receives adequate lubrication in all operating regimes from idle to maximum speed-load operation. Unfortunately, this causes the lubrication pump&#39;s energy consumption to be higher than would otherwise be ideal, because in many operating regimes, only a reduced volume and pressure of oil is required by the engine. 
         [0006]    US Patent Publication 2002/0083915 discloses a system in which a minimum oil pressure is established by a mechanically operated valve, with an electrically operated valve positioned in the mechanical valve&#39;s relief port such that the system pressure may be increased through closure of the electronically operated valve. This system suffers from the drawback that the electrically operated valve does not have a fail-safe position. In the event that the electrically operated valve fails in an open position, only minimal oil pressure would be available to sustain the engine, and such minimal oil pressure would undoubtedly be inadequate to support the engine during high speed and load operation. On the other hand, if the electrically operated valve fails in a closed position, the resulting excessive oil pressure may damage or destroy the engine by causing the oil filter to rupture, with a consequent loss of all oil overboard. In other words, any failure of the electronic valve could lead to engine failure. In another vein, the reliability of the electrically operated valve is compromised because only unfiltered oil flowing from the oil pump passes through the valve, and foreign matter carried by the unfiltered oil may cause the valve to stick or wear excessively. 
         [0007]    It would be desirable to provide an internal combustion engine lubrication system in which an engine is reliably protected with a high pressure mechanical relief valve, combined with the capability of reducing the oil pressure so as to promote fuel economy improvement during operating regimes in which maximum oil pressure and flow are unneeded. 
       SUMMARY OF THE INVENTION 
       [0008]    According to an aspect of the present invention, a lubricating oil supply system for an internal combustion engine includes an oil reservoir and an oil pump for pressurizing oil from the reservoir. A lubrication distribution network is connected with the oil pump. A pressure relief valve is connected to the distribution network downstream from the oil pump. The pressure relief valve limits oil pressure within the distribution system to a maximum permissible value. A pressure controller operatively connected with the distribution network downstream from the pressure relief valve, and preferably downstream from an oil filter, selectively controls the pressure within the distribution network to at least one pressure value which is less than the maximum pressure produced by the pressure relief valve. 
         [0009]    According to another aspect of the present invention, a pressure controller suitable for use as part of the current oil supply system may include a normally closed control valve placed in series with a low pressure relief valve, with the control valve being operated by an engine controller. Alternatively, the pressure controller may include a normally closed proportional control valve operated by an engine controller. In any event, the pressure relief bypass valve limits the oil pressure within the distribution network to a maximum permissible value by transferring high pressure oil from the outlet of the pump to the oil pump&#39;s inlet, whereas the pressure controller, which is operatively connected with the distribution network downstream from the pressure relief valve, controls the pressure within the distribution network by returning oil from the distribution network to the oil reservoir, with the pressure controller selectively limiting the pressure within the distribution network to a pressure value which is less than the maximum pressure produced by the pressure relief valve. 
         [0010]    It is an advantage of a lubricating oil supply system according to the present invention that engine fuel consumption may be reduced by minimizing parasitic losses associated with the oil pump, while at the same time safeguarding the engine&#39;s integrity, by using a pressure controller with a normally closed valve, such that if the valve fails, the engine oil pressure will be maintained at a safe level for all engine operating modes and regimes. 
         [0011]    It is another advantage of a system according to the present invention that the pressure controller of the present invention may be mounted externally upon the engine, as opposed to the known conventional practice of mounting of relief valves deep inside an engine, such as in an engine oil pump, rendering such valves relatively inaccessible for service purposes. 
         [0012]    It is an advantage of a system according to the present invention that the pressure controller of the present invention may be located downstream from an oil filter, thereby protecting the pressure controller from oil-borne contamination. 
         [0013]    Other advantages, as well as features of the present invention, will become apparent to the reader of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic representation of an internal combustion engine having a lubricating oil supply system according to the present invention. 
           [0015]      FIG. 2  is a schematic representation of an engine lubrication supply system according to an aspect of the present invention, operating at a high pressure condition. 
           [0016]      FIG. 3  is similar to  FIG. 2  but shows a system of  FIGS. 1 and 2  operating in a low pressure condition, as opposed to the higher pressure operation shown in  FIG. 2 . 
           [0017]      FIG. 4  shows an embodiment of the present system having a proportional pressure control relief valve. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    As shown in  FIG. 1 , an engine,  10 , has an oil reservoir,  14 , extending below a cylinder block,  28 , and a cylinder head,  26 . A lubrication distribution network,  22 , is connected with an oil pump  18 . Those skilled in the art will appreciate in view of this disclosure that oil pump  18  could comprise either a gerotor type pump either driven concentrically by an engine crankshaft, or a gear pump or gerotor pump, typically mounted to the engine&#39;s cylinder block and driven by either a camshaft or another rotating component of the engine, or yet other types of pump arrangements. Such detail is committed to those wishing to employ the inventive oil supply system described and claimed herein. 
         [0019]    The present lubricating oil supply system includes not only oil reservoir  14 , oil pump  18 , and lubrication distribution network  22 , but also a high pressure relief valve,  34 , employed to limit the oil pressure within distribution network  22  to a maximum permissible value. In other words, pressure relief valve  34  clips the oil pressure to a predetermined maximum value. This protects, for example, oil filter  38  from destruction were the oil pressure to be too high during cold operation at higher engine speeds. 
         [0020]    The present system also includes a control valve,  42 , which is part of a pressure controller. Control valve  42  and a low pressure relief valve,  46 , are operatively connected with distribution network  22  downstream from high pressure relief valve  34  and preferably downstream from oil filter  38 . As shown in  FIGS. 1 ,  2 , and  3 , control valve  42  is placed in series with low pressure relief valve  46 . When controller  50  provides an appropriate signal, control valve  42  opens, and the oil pressure within lubrication distribution network  22  is controlled by low pressure relief valve  46  to a lower maximum pressure which is less than the pressure allowed by valve  34 . This is shown in  FIG. 3 . In this manner, oil pump  18  is required to do less work because oil is pumped against a lower head. Because control valve  42  is normally closed, a loss of signal from controller  50  will merely cause the lubrication system to revert to a maximum pressure system controlled solely by pressure relief valve  34 . This protects the integrity of engine  10 . This state is shown in  FIG. 2 . 
         [0021]    Although oil is bypassed at a lower pressure by valves  42  and  46 , adequate oil pressure is provided to cylinder head  26  and to crankshaft bearings  30  because valve  42  is opened by controller  50  only during the several operating regimes in which it is not necessary to provide maximum oil pressure to sustain appropriate engine life. In fact, in many operating regimes such as those characterized by operation at less than half of the engine&#39;s maximum load, oil pressure may be significantly reduced while still providing adequate lubrication to the engine. 
         [0022]      FIG. 4  shows an embodiment of the present invention in which a proportional control valve,  48 , is operated by controller  50 . As its name implies, valve  48 , working with controller  50 , provides a tailored, but reduced, oil pressure which is intended to increase engine fuel economy by providing no more pressure than is needed to sustain the life of the engine&#39;s bearings and other lubrication using devices. As with the other embodiments of this invention, proportional control valve  48  is a normally closed device, such that if the power fails between controller  50  and valve  48  or the signal is lost, valve  48  will close, thereby allowing the engine to be operated with only relief valve  34  being active, with valve  34  holding the engine oil pressure at a higher safe value. In general, according to a preferred embodiment, controller  50  will operate valve  48  as a function of at least engine operating speed, or at least engine operating speed, oil temperature and engine load. 
         [0023]    Valves  42 ,  46 , and  48 , as the case may be, are preferably mounted to an external surface of engine  10 , such as an outer surface of cylinder block  28 . Such external mounting is shown in  FIG. 1 . This will permit relatively easy access to valves  42  and  46 , or  48  for the purposes of repair or adjustment, without the necessity of removing engine hardware such as the oil pan or front cover. 
         [0024]    The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention. Accordingly the scope of legal protection afforded this invention can only be determined by studying the following claims.