Abstract:
Method and apparatus for automatically replenishing additives lost from the lubricating oil of an IC engine, by injecting controlled quantities of the additive into the oil. The amount and frequency of injection is controlled by either the operating conditions of the oil (e.g. its thermal history), or changes the properties of the oil (e.g. its electrochemical activity, or dielectric constant).

Description:
TECHNICAL FIELD 
     This invention relates generally to lubrication systems for internal combustion engines, and more particularly to method and apparatus for automatically replenishing additives to the system&#39;s lubricating oil that are lost during the operation of the engine. 
     BACKGROUND OF THE INVENTION 
     Internal combustion (IC) engines (e.g. spark-, or compression-, ignition engines) have a plurality of moving parts that require lubrication to prevent damage to the engine. Typically, such engines are provided with a lubrication system comprising a sump (a.k.a. crankcase or oil pan) that collects oil that drains from the moving parts, a plurality of passageways in the engine&#39;s block and head for delivering oil to the moving parts, and a pump for pumping oil from the sump through the passageways to the moving parts. A filter is commonly located downstream of the pump to remove unwanted particulates from the circulating oil. 
     The oil used to lubricate internal combustion engines typically contains one or more perishable, life-extending additives. By “perishable” additive is meant an oil additive that either degrades, evaporates, is consumed or is otherwise lost during operation of the engine, and needs replenishing if the oil is to be effective. By “life-extending” additive is meant an additive that forestalls the degradation of the oil, and maintains its effectiveness for an extended period of time. Additives commonly used with lubricating oils include varying amounts of such things as anti-oxidants (e.g. ca. 0.5%-2.0% by wt. aromatic nitrogen compounds), ashless dispersants (e.g. ca. 2%-10% by wt. polyisobutenyl succinimides), wear retardants (e.g. ca. 0.5-2.0% by wt. zinc dithiophosphates), and detergents (e.g. ca. 2-10% by wt. overbased sulfonates), inter alia. Zinc dithiophosphate (ZDP) also functions as an anti-oxidant. The detergents and dispersants are used to neutralize acids and suspend dirt particles that come mainly from blow-by gases (i.e. gases that pass the rings during combustion). The wear retardants, or anti-wear additives, form a sacrificial, protective film on the metal surfaces to protect the metal from wear. The anti-oxidants prevent oxidation of the oil at normal (i.e. 60° C.-130° C.) oil temperatures, and even more so at high (above 130° C.) oil temperatures such as can occur, for example, when operating the engine under severe conditions (e.g. a car/truck pulling a heavy trailer up a steep grade on a hot day). In this later regard, oil oxidizes more rapidly at temperatures above 130° C., than at normal operating temperatures. With increased oil oxidation, comes an undesirable increase in oil viscosity. The anti-oxidants retard oxidation of the oil, but are consumed in the course thereof, and hence are lost from the oil over time—especially at the higher temperatures where the oil is most susceptible to oxidation. The other additives while less sensitive to temperature, are nonetheless lost from the oil over time, usually as a direct function of engine speed and power. 
     Engine and vehicle manufacturers recommend that the oil be changed at regular intervals to keep additive levels up. For example, General Motors Corporation, assignee of the present invention, recommends for some of its vehicles that: (1) under normal driving conditions, the oil in its gasoline engines should be changed every seventy five hundred (7,500) miles or 12 months which ever comes first; and (2) under severe operating conditions (e.g. frequent short trips in freezing weather, extended idling, trailer towing, driving in dusty areas, frequent stop &amp; go driving, etc.) the oil should be changed every three months or three thousand (3000) miles. Many vehicle operators forget to change their engine oil regularly, which can be detrimental to the engine. Accordingly, most automobile manufacturers have included oil change warning/reminder systems in their vehicles. One such oil change warning/reminder system is described in U.S. Pat. No. 4,742,476 Schwartz et al. , which is assigned to the Assignee of the present invention, and is intended to be incorporated herein by reference. 
     Schwartz et al., supra, recognized that excessive degradation of the oil occurs at its temperature extremes. At low oil temperatures (i.e. below about 60° C.), fuel, water and soot tend to accumulate in the oil, reducing its viscosity and increasing wear. At high oil temperatures (i.e. above about 130° C.), the anti-oxidants are depleted, the oil becomes viscous and acidic due to oxidation and nitration, and insoluble particles are deposited on the engine surfaces as varnish or sludge. Acidic oil has a reduced ability to prevent rust and corrosion. Schwartz et al., supra, predicts remaining oil life based on the thermal history of the oil (i.e. time-at-temperature, where time is determined in terms of either engine-revolutions or mileage driven). More specifically, Schwartz et al. uses a computer/controller that determines when an oil change is needed based on empirical data and measured values of oil temperature and engine speed (revolutions per minute) or miles driven. The number of engine revolutions (or mileage driven) corresponding to the maximum engine oil life that would occur if the vehicle were continuously driven under conditions least degrading to the lubricating ability of the oil is stored in a non-volatile memory location in the controller. The oil&#39;s thermal history is tracked—that is the temperature of the oil is measured, and the duration the oil is at that temperature as recorded while the engine is in operation. In each period of vehicle operation, the stored number is decremented in accordance with an effective engine-revolutions value determined in relation to the product of measured engine revolutions (or mileage driven) and an engine-oil-temperature-based penalty factor that is determined for each engine and oil. When the oil temperature is in an intermediate, ideal range, the penalty factor is set equal to unity, and the effective engine revolution value accumulates at the measured rate. When the oil temperature is outside the ideal range (e.g. 60° C.-130° C.), the penalty factor is set to a value greater than unity in accordance with a predetermined schedule determined for each engine and oil so that the effective engine revolutions value accumulates at a faster rate than the measured rate. The penalty factor to be applied for each temperature and oil is empirically determined for a particular engine, and generally conforms to a stepped trace similar to that designated as “A” of  FIG. 5  hereof. The decremented stored number represents the remaining life of the engine oil which is displayed for the vehicle operator. A visual and/or audible warning indication is given when the stored number is decremented below 10% of its original value, indicating the need for an oil change. Rather than directly measuring the oil temperature, the temperature can be determined indirectly by calculations made from measurements taken on other engine operating conditions (e.g. number of combustion firings, coolant temperature, and engine rotational speed), ala the method discussed in Schwartz et al U.S. Pat. No. 4,847,768, which is intended to be incorporated herein by reference. 
     Sensors have been proposed for directly measuring the condition (i.e. properties) of the oil. For example, Lee et al. U.S. Pat. No. 5,200,027 discloses an oil degradation sensor that uses two roughened, interdigitated electrodes to directly measure the electrochemical properties of the oil. A saw-toothed voltage is applied to the electrodes to generate an electrochemical current that is measured. The magnitude of the measured current is indicative of the condition of the oil—with lower currents indicating newer/fresher oil and higher currents indicating used/degraded oil. Lee et. Al U.S. Pat. No. 5,200,027 is intended to be incorporated herein by reference. Moreover, Meitzer et al. U.S. Pat. No. 4,733,556 (Mar. 29, 1988) teaches method and apparatus for monitoring changes in the dielectric constant of engine oil as an indicator of its remaining useful life. Meitzer et al. U.S. Pat. No. 4,733,556 is intended to be incorporated herein by reference. 
     It has been proposed to extend the time period between oil changes by simply adding excess quantities of the additives to the oil to insure that a sufficient amount of additive is present at all times. Moreover, it has been proposed to periodically add the additives to the oil regardless of the oil&#39;s usage history. Others have proposed other techniques for adding makeup quantities of additives to the oil. Rohde U.S. Pat. No. 4,066,559 fills an additive-permeable, polyolefin container with the additive, and immerses the container in the oil. At elevated temperatures, the additive diffuses through the wall of the container into the oil. The rate at which the additive diffuses out of the container is reduced as the volume of the additive in the container is reduced, and there is no way provided to replenish the additive in the container when the additive content is depleted. DeJovine U.S. Pat. No. 4,144,166, Lefebvre U.S. Pat. No. 5,591,330 and Lefebvre et al U.S. Pat. No. 5,718,258 provide a soluble composite comprising oil additives embedded in an oil-soluble polymer matrix. Oil passing over the composite (e.g. in an oil filter or other canister) dissolves the matrix polymer, and releases the additives into the oil. The dissolved matrix material contaminates the oil, and retards subsequent dissolution over time. All of these techniques have the prospect of adding too much additive to the oil which has a negative affect on vehicle fuel economy and tailpipe emissions. Accordingly, it is desirable to have controlled addition of the additives so as to keep the additive concentration in the oil within prescribed limits. 
     SUMMARY OF THE INVENTION 
     The present invention prolongs the useful life of IC engine lubricating oil, and extends the time period between needed oil changes by adding makeup quantities of additives to the oil at essentially the same rate as they are depleted from the oil so as to keep the additive concentration in the oil in a prescribed range over a prolonged period of time. More specifically, the present invention contemplates method and apparatus for prolonging the useful life of an IC engine&#39;s lubricating oil by replacing perishable, life-extending additives as they are lost from the oil during engine use. Process-wise the invention comprises: storing a replenishable supply of liquid additive-concentrate (hereafter concentrate) proximate the engine, which concentrate has a concentration of additive greater then the concentration of the additive in the oil; operating the engine under a certain operating condition or conditions (e.g. temperature, power, speed etc.); and injecting the liquid concentrate into the oil at a rate controlled by that operating condition so as to replenish the lost additive at substantially the rate it is lost from the oil. The injection pressure may be provided by a pump, by a hydraulic head of the concentrate in the additive supply system, or by engine-produced pressures (e.g. exhaust gases). 
     According to one embodiment of the invention, the depletion rate of a particular additive from the oil is determined empirically under a certain engine-operating condition (e.g. temperature, power. etc.) when the engine is running. To determine when more additive is needed in an engine in service, this engine-operating condition is monitored (i.e. by direct measurement, or indirectly by calculation) to determine from the empirical data when a predetermined amount of the additive has been lost from the oil. When the monitored condition indicates that the predetermined amount of additive has been lost, a dose (i.e. a predetermined quantity) of the concentrate is injected into the oil (i.e. “X” quantity of concentrate is added when “Y” amount of additive has been lost). 
     According to another embodiment of the invention, the method for prolonging the useful life of the lubricating oil comprises sensing a physical property of the oil that is indicative of the degradation of the additive in the oil (e.g. its electrochemical activity, or dielectric constant), and injecting a dose of the concentrate into the oil when the sensing indicates that the degradation has reached a predetermined amount (e.g. X quantity of concentrate is added when the oil has degraded 10%). 
     According to still another embodiment, the additive is an anti-oxidant, and the concentrate thereof is injected into the oil at a trickle rate determined by the viscosity of the concentrate, the temperature of the oil, the size of the orifice(s) through which the concentrate flows, and the hydraulic head of concentrate. 
     The invention further comprehends apparatus for effecting the aforesaid method. Apparatus-wise, the invention involves a lubrication system for an internal combustion engine that comprises: a sump for collecting oil drained from the engine&#39;s moving parts; a plurality of passageways in the engine for delivering oil to the moving parts; a pump for pumping the oil from the sump into the passageways to lubricate the moving parts; a reservoir containing a concentrate having a concentration of additive therein that is greater then the concentration of the additive in the oil; a nozzle for injecting the additive-concentrate into the oil; a conduit communicating the reservoir and the nozzle for conducting the concentrate from the reservoir to the nozzle; and a pressurizer for applying sufficient pressure on the concentrate to inject it into the oil to replenish additive lost from the oil. In one embodiment, the presuurizer for the concentrate is a second pump, and a sensor is provided to monitor an engine operating condition (e.g. temperature) and report it to a controller that signals activation of the second pump to pump the additive-concentrate into the oil when the monitored condition so warrants. According to another embodiment of the invention, the nozzle comprises a solenoid-operated valve, a sensor monitors an operating condition of the engine and reports it to a controller which, in turn, signals opening of the valve to inject the concentrate into the oil when the monitored condition so warrants. Alternatively, the sensor may comprise a sensor that monitors the condition of the oil (e.g. its electrochemical activity or its changing dielectric constant) and triggers injection of concentrate into the oil when the oil has degraded a predetermined amount. 
     In still another embodiment: the concentrate comprises an anti-oxidant, and is formulated to have a viscosity that decreases as its temperature increases; the pressurizer is a hydraulic head of liquid concentrate behind the nozzle; and the nozzle includes at least one orifice immersed in the oil and sized to inject the concentrate into the oil at increasing rates as the temperature of the oil increases. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will better be understood when considered in the light of the following detailed description of certain specific embodiments thereof which is given hereafter in conjunction with the several drawings in which: 
         FIG. 1  schematically depicts one embodiment of the present invention; 
         FIG. 2  schematically depicts another embodiment of the present invention; 
         FIG. 3  schematically depicts still another embodiment of the present invention; 
         FIG. 4  is an isometric view of an IC engine crankcase according to a preferred embodiment of the present invention; and 
         FIG. 5  are plots of oil temperature vs. (1) penalty factors, and (2) additive makeup flow rate for one example of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1-3  depict an IC engine  2  having a V-block  4 , a pair of heads  6  and  8  and an oil pan/crankcase  10 . The engine  2  internally includes a lubrication system  12  (here depicted external to the engine) comprising an oil sump  14  in the crankcase  10 , an oil pump  16  for circulating the oil through the lubrication system, an oil filter  18  for removing unwanted particulates from the oil, and a plumbing system  20  communicating the sump  14 , pump  16  and filter  18  to a network of oil passages (not shown) within the engine  2  for directing the oil to the various moving parts of the engine that require lubrication. 
       FIG. 1  depicts one embodiment of the invention wherein the crankcase  10  includes a sensor  22  for sensing a condition of the oil (e.g. its temperature, electrochemical activity, dielectric constant etc.) and reporting it to a controller  24  via signal  26 . Based on empirically generated data, and using lookup tables and the like, the controller  24  determines when makeup additive is needed when the controller  24  determines that makeup additive is needed, it sends a signal  28  that energizes a pump  30  for a duration of time sufficient to pump a predetermined quantity of concentrate  32  from a reservoir  34  to injection nozzle  36  located somewhere in the lubrication system (here shown, by way of example, to be in the crankcase  10 ). The reservoir  34  is located proximate the engine  2 , and may be either inside or outside of the crankcase  10 , as will be discussed in more detail hereinafter in conjunction with  FIG. 4. A  liquid level sensor  46  in the reservoir  34  alerts the engine operator when the concentrate  32  in the reservoir  34  is low, and needs replenishing. 
       FIG. 2  shows another embodiment of the invention. The embodiment shown if  FIG. 2  is similar to that shown in  FIG. 1  except instead of energizing the pump  30  to deliver a predetermined quantity of additive-concentrate to the oil in the lubrication system, the output of the pump  30  is plumbed to (1) circulate concentrate  32  to and from the reservoir  34  under pressure, and (2) divert some of the circulating concentrate to a solenoid-operated injector valve  38  (akin to a fuel injector commonly found in IC engine fuel systems) located somewhere in the lubrication system (here shown at the crankcase  10 ). In this embodiment, the controller  24  controls the pulse width (i.e. open time) or the frequency of opening of the injector valve  38 . Higher oil temperatures will cause the valve to open more frequently. Alternatively, the pump  30  may be eliminated, and the hydraulic head of concentrate in the reservoir  34  used to provide the pressure needed to inject the concentrate into the oil when the injector valve  38  is opened. 
     The controller for the oil-change warning system of Schwartz et al. U.S. Pat. No. 4,742,476 supra is conveniently adapted for use with the present invention. In this regard, rather than sending an audible or visual signal to the operator that an oil change is needed, Schwartz et al&#39;s controller is programmed to automatically dose the oil with concentrate. For example, in the case of an anti-oxidant additive, dosing will preferably occur when the anti-oxidant concentration in the oil falls below about 10% of its prescribed concentration in the oil. Hence, a suitable controller  24  for the present invention will be essentially the same as that employed by Schwartz et al. and includes conventional computer control elements including a clock, a microcomputer, an analog-to-digital converter (A/D), a counter (CTR), a non-volatile memory, and an input/output device (I/O). The clock provides high frequency pulses to the microcomputer, and all of the elements communicate with each other via an address and control bus and a bi-directional data bus. The analog output of the sensor (e.g. temperature sensor)  22  is applied as an input to A/D where it is converted to a digital format and made available for acquisition via the data bus. The digital pulse train output of an engine speed sensor (not shown) is applied as an input to the counter where it is divided down to a rate of one pulse per engine revolution and made available for acquisition via the data bus. An automatic reset switch is provided that has a digital output that is inputted to the I/O device and is triggered each time the oil is dosed to reset the controller. The digital information for controlling the pump  30 , or injector valve  38 , is outputted as control signal  28  from the I/O device. Eventually, the oil may have to be changed. When it is, the oil change technician, or engine operator, actuates a manual reset switch which is also inputted to the I/O device and resets the controller. 
     The sensors are conventional sensors well known to those skilled in the art. Thus for example, a temperature sensor may be a varistor element housed in a conductive probe positioned in any location (preferably the crankcase) where the measured oil temperature is representative of the temperature of the oil in the mainstream of oil flow. A speed sensor may be a variable reluctance magnetic pickup cooperating with a toothed ferromagnetic wheel coupled to the engine crankshaft. The manual reset switch may be a conventional momentary-contact single-pole-single-throw switch 
       FIG. 3  shows still another embodiment of the invention. The embodiment shown in  FIG. 3  is particularly applicable where the additive is an anti-oxidant (though not limited thereto).  FIG. 3  is similar to  FIGS. 1 and 2  except that the controller  24 , pump  30  (i.e. from  FIGS. 1 and 2 ) and valve  38  are eliminated. Instead, the injection rate of the concentrate  40  is controlled by a combination of (1) the viscosity profile of the concentrate  40 , (2) the engine oil temperature, and (3) size of the orifice in the nozzle  44  through which the concentrate flows. The injection pressure is provided by the hydraulic head of the concentrate  40  in the reservoir  42 . The anti-oxidant makeup rate is determined by the concentration of the anti-oxidant in the concentrate and the flow rate of the concentrate into the oil. Preferably, the anti-oxidant makeup rate (e.g. see trace B of  FIG. 5 ) will vary as a function of oil temperature, and will approximate the rate at which the penalty factor changes as a function of temperature (e.g. see trace A of FIG.  5 ). The reservoir  42  contains a supply of the concentrate  40  at a level  50  above the level  47  of the oil in the sump  14 . A tube  45  connects the reservoir  42  with the nozzle  44 . The reservoir  42  communicates with the crankcase  10 , above the oil level  47  and concentrate level  50 , by a vent tube  48  to maintain the same pressure in the reservoir  42  and the crankcase  10 . As a result, the difference in height between the level  50  of the concentrate  40  in the reservoir  42  and the level  48  of the oil in the crankcase  10  (i.e. the hydraulic head) provides the pressure needed to inject the concentrate  40  into the oil. The concentrate flows through one or more orifices (not shown) in the nozzle  44 , which orifice(s) is/are sized to deliver concentrate to the oil at a trickle only when the temperature of the oil in the sump  14  is greater then a predetermined threshold temperature (e.g. 70° C.). The concentrate is formulated such that its viscosity profile (i.e. viscosity vs. temperature) will cause the concentrate to trickle at increasing rates (and hence deliver more concentrate) through the orifice(s) in the nozzle and into the oil as the temperature of the oil increases above the threshold temperature. Below the threshold temperature, no concentrate will flow. Above, but near the threshold temperature (i.e. up to about 130° C.), concentrate will trickle into the oil very slowly. At higher oil temperatures (i.e. up to 160° C. or more) the concentrate will trickle at a faster rate. 
     In all of the embodiments engine-generated pressure (e.g. exhaust gases) may be substituted for the pump or hydraulic head of concentrate. In this regard, exhaust gases may be routed to the reservoir via a pressure regulator to provide the needed injection pressure. Alternatively, the pressure regulator may be eliminated and the reservoir provided with a pressure relief valve that holds the reservoir at the pressure set by the relief valve. 
     Additive concentrations in the lubricating oil will vary with the grade of the oil, and the composition of the specific additive. In general, by weight: (1) anti-oxidants will constitute about 0.5% to about 2.0% of the oil; (2) dispersants will constitute about 2% to about 10% of the oil; (3) wear-retardants will constitute about 0.5% to about 2% of the oil; and (4) detergents will constitute about 2% to about 10% of the oil. 
     Preferably, the concentrate will comprise about 50% by wt. to about 100% by wt.) of at least one anti-oxidant admixed with a mixture of various lubricating oils that, together with the anti-oxidant, provide the desired viscosity profile for a particularly sized nozzle orifice. Concentrate formulations needed to achieve a particular viscosity profile are determined empirically. In this regard, various concentrations of anti-oxidant are mixed with a diluent comprising various proportions of one or more lubricating oils compatible with the engine lubricating oil. The dilutent will preferably comprise different proportions of different single SAE viscosity grade (e.g. SAE 5W-SAE 90W), and/or multi SAE viscosity grades (e.g. 5W30) natural or synthetic lubricating oils. 
       FIG. 4  depicts a preferred implementation of the embodiment shown in  FIG. 3  wherein reservoir  58  containing the concentrate is located inside the oil pan  54  above the level of the oil  56  therein, and is preferably integral with the sidewall  60  of the oil pan. The reservoir  58  will contain a supply of liquid, anti-oxidant concentrate  62  comprising 75% by wt. Of a 50/50 admixture of a phenolic or arylamine anti-oxidant and the balance a mixture of 80% by volume SAE 0W20 viscosity grade oil, and 20% by volume SAE 5W30 viscosity grade oil formulated to have a viscosity profile adapted to provide the temperature-dependant, anti-oxidant flow rate shown in trace “B” of  FIG. 5 , when coupled with a nozzle having an orifice 0.1 mm in diameter. A filler opening  64  provides access to the inside of the reservoir  58  for replenishing the concentrate  62 , as needed. A liquid level sensor  66  is provided through the wall of the reservoir  58  to alert the operator when the concentrate level is low and needs replenishing. A vent tube  68  opens to both the inside of the oil pan  54  and the reservoir  58  to equalize the pressure therebetween. A concentrate supply tube  70  depends from the reservoir  58 , and terminates in a nozzle  72  located beneath the surface  74  of the oil  56  in the oil pan  54 . The reservoir  58  has a relatively large horizontal cross-section compared to the inside diameter of the tube  70 , and the vertical length of the tube  70  is long relative to the depth of the reservoir to minimize the change in pressure of concentrate at the orifice in the nozzle  72 , as the concentrate is consumed, and hence maintain the hydraulic head of the concentrate  62  substantially constant. The nozzle  72  comprises one or more orifices (not shown) sized to cooperate with the viscosity of the concentrate  62  to supply concentrate to the oil  56  at increasing rates as the oil temperature rises over the temperature range 60° C. to 160° C. 
     While the invention has been described in terms of certain specific embodiments thereof, it is not intended to be limited thereto, but rather only to the extent set forth hereafter in the claims which follow.