Abstract:
A heat transfer apparatus for use in measuring a rheological property of a test sample includes a receptacle for receiving the test sample and a heat conveying member in heat transfer relation to receptacle. The heat conveying member has internal passages extending substantially equidistantly from one another through at least a portion of the heat conveying member to provide for counter-flowing circulation of a fluid. A cold cranking simulator includes a hybrid heat transfer system having heat exchanging elements in heat transfer relation to the receptacle responsive to electric current to transfer heat to or from the receptacle. The cold cranking simulator further includes a heat conveying member having internal passages providing for counter-flowing circulation of a fluid.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a cold cranking simulator for rheological testing of a liquid sample and, more particularly, to a cold cranking simulator having a hybrid system for transferring heat to or from a liquid sample.  
         BACKGROUND OF THE INVENTION  
         [0002]    Engine oil protects the moving parts of an engine by providing a lubricating coating to reduce friction generated by the moving parts. The ability of the engine oil to properly lubricate the moving parts of the engine is largely dependent on rheological properties of the oil, in particular the viscosity of the engine oil. In general terms, viscosity is a measure of resistance of a fluid to flow. In an engine, the oil fills the narrow spaces between the parts and clings to both moving and non-moving parts. The tendency of the oil to remain in contact with both the moving and non-moving parts creates internal frictional forces within the oil. These internal forces must be overcome before relative movement between the parts can occur. The internal forces within the oil will vary in proportion to the viscosity of the oil and will increase with increasing viscosity. Additionally, for a given blend of engine lubricating oil, the viscosity will not remain constant, but will vary as a function of temperature, becoming much more viscous in cold temperatures. The resulting increased frictional forces associated with the increased viscosity renders engine operation or “cranking” more difficult in low temperature conditions.  
           [0003]    Known rheological test devices include devices known as “cold-cranking simulators” which are used to test engine oils at low temperatures under simulated engine starting conditions for compliance with the Society of Automotive Engineers (SAE) Standard J300. The testing of oils using these devices is governed by the American Society for Testing and Materials (ASTM) D5293 “Standard Test Method for Apparent Viscosity of Engine Oils Between −5 and −35° C. Using the Cold-Cranking Simulator.” A cold cranking simulator measures the apparent viscosity of an engine oil by measuring the resistance to rotation imposed on a rotor by a sample of oil delivered into a narrow annular space between the rotor and a non-moving stator. The cold cranking simulator therefore differs in operation from devices such as capillary viscometers which measure flow rate of a fixed volume of a fluid through an orifice. The results of testing on a sample of engine oil using a cold cranking simulator are called the “cranking viscosity” of the engine oil.  
           [0004]    An example of a cold cranking simulator is shown in U.S. Pat. No. 4,472,963 to Gyer. A sample of oil is introduced into a narrow annular space between a rotatably supported rotor and fixed stator. A probe is located within the stator to monitor the temperature of the stator. Methanol from a cold bath is circulated through coolant conduits in the stator to cool the stator. The methanol in the cold bath is maintained at a constant predetermined temperature differential below the test temperature. The methanol is introduced into the stator through a valve which is periodically opened and closed to control flow of coolant. A control system is responsive to the temperature from the stator probe to adjust the on-to-off time of the valve thereby controlling the amount of methanol delivered to the stator. Methanol is also heated to just below boiling in a separate hot bath for circulation through the coolant passages of the stator between tests to facilitate removal of the tested sample. The heated methanol facilitates the removal of the tested sample by reducing the viscosity of the oil thereby reducing the resistance of the oil to flow.  
           [0005]    Methanol is a flammable and highly toxic substance. The storage and handling of the methanol in the baths and in the circulating system of the cold cranking simulator of the &#39;963 patent therefore represents a threat to health and safety. The safety concerns raised by the use of methanol in the &#39;963 patent are further increased by the use of the hot bath in which the flammable methanol is heated to close to its boiling point. Furthermore, heat transfer provided by the circulating methanol is inefficient and limits the rate at which the stator is cooled. The inefficiencies inherent in the circulating methanol also limit the responsiveness of the system to changing heat transfer requirements resulting in imprecision in the temperature control provided by the system.  
           [0006]    The temperature control provided by the &#39;963 system is further limited as a result of temperature variations necessarily created along the flow path of the circulating fluid. The circulation of a coolant fluid through a heat conveying member for the purposes of heat transfer between the member and the fluid inherently results in a variation in temperature along the path of the circulating coolant fluid as heat is added or removed from the coolant medium. Circulating systems of prior art cold cranking simulators, such as the simulator of U.S. Pat. No. 4,472,963 to Gyer, direct coolant fluid between an inlet located at a first side of the stator to an outlet located on an opposite side of the stator. The coolant fluid is directed in the conduits of the &#39;963 simulator in a unidirectional circulation of the coolant fluid in which, at any given location of the stator, coolant is being directed in a single direction. As chilled methanol is directed about the stator, heat added to the methanol from the stator will raise the temperature of the methanol between the inlet and the outlet. As a result, temperature gradients will be created across the stator between the coolant inlet and outlet.  
           [0007]    What is needed is a heat transfer system for varying the temperature of a test sample in a cold cranking simulator which provides for increased precision and uniformity in sample temperature control by increased responsiveness to changing heat transfer requirements and limitation of temperature gradients across the test sample.  
         SUMMARY OF THE INVENTION  
         [0008]    According to the present invention, there is provided a heat transfer apparatus for use in measuring a Theological property of a test sample. The apparatus includes a receptacle for receiving the test sample and a heat conveying member in heat transfer relation to the receptacle. The heat conveying member has internal passages which extend substantially equidistant from one another through at least a portion of the heat conveying member to provide for a counter-flowing circulation of a fluid.  
           [0009]    According to an embodiment of the invention the heat conveying member includes heat sinks interconnected to form an assembly of heat sinks. Tubular members extend between adjoining heat sinks to connect internal passages of adjoining heat sinks.  
           [0010]    According to an embodiment of the invention, there is provided a cold cranking simulator. The cold cranking simulator includes a receptacle for receiving a sample of oil. The cold cranking simulator further includes a hybrid heat transfer system having at least one heat exchanging element in heat transfer relation to the receptacle and responsive to electric current to transfer heat to or from the receptacle. The cold cranking simulator further includes a heat conveying member in heat transfer relation to the heat exchanging element to provide for transfer of heat to or from the heat exchanging element. The heat conveying member includes internal passages which extend substantially equidistant from one another through at least a portion of the heat conveying member to provide for a counter-flowing circulation of a fluid. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.  
         [0012]    [0012]FIG. 1 is a perspective view of the test cell of a cold cranking simulator according to the present invention;  
         [0013]    [0013]FIG. 2 is a top plan view of the test cell of FIG. 1 (rotated 90°);  
         [0014]    [0014]FIG. 3 is a sectional view taken along the lines  3 - 3  of FIG. 2;  
         [0015]    [0015]FIG. 4 is a sectional view taken along the lines  4 - 4  of FIG. 2; and  
         [0016]    [0016]FIG. 5 is a schematic illustration of the counter-flowing series of passages provided in the test cell of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Referring to the drawings where like numerals identify like elements, there is shown a test cell  10  of a cold cranking simulator according to the present invention for use in rheological testing of a sample of oil at low temperatures under governing standards identified in ASTM D 5293. The cold cranking simulator is used to simulate automobile engine starting conditions in cold temperatures and determines an apparent viscosity, known as the “cranking” viscosity, by measuring the resistance to rotation imposed on a rotor by a sample of oil delivered into a narrow annular space between the rotor and a non-moving stator. In the manner to be described, the test cell  10  transfers heat to and from the test cell and provides for uniform test sample temperature and precision control over temperature within 0.01° C. for test temperatures as low as −40° C. The precision of the temperature control system is facilitated by a heat transfer system capable of rapidly responding to changing heat transfer requirements. Furthermore, the test cell utilizes a highly compact arrangement of parts leading to space saving efficiencies and economy of materials.  
         [0018]    As seen in FIGS.  1 - 4 , the cold cranking simulator includes a cylindrical rotor  14  which is supported for rotation by shaft  16 . The rotor  14  is concentrically located within the opening of a hollow cylindrical stator  18 . The outer surface  20  of the rotor  14  and the inner surface  22  of the stator  18  are closely toleranced and precisely machined such that a narrow annular space  24  may be maintained between the rotor  14  and the stator  18  by the cold cranking simulator as the rotor  14  is rotated within the stator  18 . The annular space  24  simulates the spaces between closely fitting moving parts of an engine to provide for measurement of the cranking viscosity of the oil sample under low temperatures.  
         [0019]    The test cell  10  includes a block  26  preferably made of a highly thermally conductive metal such as copper to facilitate heat transfer through the block  26 . The block  26  includes a central bore  28  extending from an upper surface of the block defining a cavity which serves as a receptacle for the test cell  10  in which the sample of oil to be tested is received. As seen in FIG. 4, the stator  18  is positioned within the cavity of block  26  and aligned to the block by a pin  30  extending from the stator  18 . The pin  30  in the stator  18  is received in a hole  32  formed in a surface of the block  26  at the terminal end of the central bore  28 . The block  26  also includes a counterbored passage  34  extending from a lower surface of the block and communicating with the central bore  28 . A sample of oil to be tested is introduced into the annular space  24  between the rotor  14  and stator  18  through the counterbored passage  34  and is cooled to a test temperature by the temperature control system of test cell  10 . The viscosity of the oil sample is then tested by the cold cranking simulator in the well known manner by measuring the resistance to rotation of the rotor  14  that is imposed on the rotor by the oil sample located in the annular space  24 .  
         [0020]    As seen in FIG. 3, the test cell  10  includes a temperature probe  33  which is inserted in a notch formed in the outer surface  35  of the stator  18  such that the probe confronts the block  26  at the interface between the stator  18  and the block  26 . This positions the probe  33  in temperature monitoring proximity to the stator  18  in which the sample of oil will be received. The probe  33  is electrically connected by wire, shown extending from the stator  18 , to a control system for test cell  10  for transmission of an electrical signal representing the interface temperature as measured by the probe  33 . As will be described in greater detail, the control system of test cell  10  is responsive to the reported temperature from probe  33  to adjust the heat transfer provided by test cell  10 , thereby controlling sample temperature. Locating the temperature probe  33  at the interface between the stator  18  and the block  26  rather than fully within the stator  18  or the block  26  enhances the responsiveness of the test cell  10  to changes in thermal load thereby facilitating precise temperature control.  
         [0021]    The test cell  10  of the cold cranking simulator includes a hybrid heat transfer system in which heat transfer from the block  26  to cool the test sample is provided by a first heat transfer system  36 . The heat transfer provided by the first heat transfer system  36  is adjustable to provide for control over the temperature of the sample. The hybrid heat transfer system of the test cell  10  further includes a second heat transfer system  38  which functions to convey the heat which has been removed from block  26  by the controllable first heat transfer system  36 .  
         [0022]    The first heat transfer system  36  includes thermoelectric modules  40  each of which is positioned to extend along one of four planar side surfaces  42  of the block  26 . The thermoelectric modules  40  use a principal known as the “Peltier effect” in which electrical current is directed through the modules by the first heat transfer system  36  to establish opposite hot and cold surfaces of the modules  40 . In the normal operating mode of the first heat transfer system in which the modules  40  are used to cool the test sample, the current is directed through the modules  40  such that the hot surfaces of the modules  40  established by the first heat transfer system  36  are surfaces  44  on the outermost sides of the modules.  
         [0023]    The effective heat transfer provided by the Peltier effect of the thermoelectric modules  40  and the intimate proximity of the modules to the block  26  provides for rapid transfer of heat from the block  26  to the hot sides  44  of the modules  40  and rapid cooling of the test sample in block  26 . Transferring heat from the block  26  by thermoelectric modules adjacent the block  26  also provides for increased responsiveness of the cold cranking simulator to changes in required heat transfer from the block  26  in the following manner. In response to reported temperature by probe  33 , the rate of heat transfer from block  26  may be instantly varied through control over the current which is delivered to the modules  40  by the first heat transfer system  36 . Variation in current delivered to the modules  40  may be accomplished alternatively by variation in on-to-off time of a duty cycle of a set current or by variation in the amperage of the current. Furthermore, because equal current may be delivered to each of the modules  40 , the first heat transfer system provides for a more balanced heat transfer from the block  26  over methanol circulating systems of the prior art. The increased responsiveness and uniformity of heat transfer from the test sample greatly facilitates precision in the control of sample temperature by test cell  10 .  
         [0024]    The Peltier effect of the modules  40  provides for an alternate mode of operation of the modules  40  to that described above. By reversing the direction of the current directed through the modules by the first heat transfer system  36 , the hot and cold surfaces of the modules will be reversed from that described above. In this alternate mode of operation, the hot surfaces of the modules  40  will be surfaces  46  located on the innermost sides of the modules such that heat is directed into the block  26  rather than removed. The alternate mode of operation provides for rapid heating of the block  26 . This is useful for removal of a tested sample because the heating of the sample reduces the viscosity of the oil thereby decreasing the resistance of the oil to flow from the cavity of the test cell  10 . The rapid heating and removal of a tested sample from the test cell  10  by reversal of current provided to the modules  40  eliminates the need for introducing heat from a separate source such as the separate hot methanol baths of prior art devices.  
         [0025]    It should be understood by those skilled in the art that the thermoelectric modules  40  of the foregoing description are not limited to single-stage modules. Depending on the desired test temperature and the cooling capability of available single-stage modules, it may be preferable that the thermoelectric modules  40  comprise multi-stage modules. A multi-stage module, per se well known in the art, has typical application where larger temperature differentials are desired across the thermoelectric module. In a multi-stage module, separate stages, each constituting a separately charged thermoelectric layer, are stacked one on top of another to form the thermoelectric module. Where a multi-stage module is used for the thermoelectric module  40 , reference herein to the “hot” and “cold” side of the module  40  should be understood to refer to either the innermost or outermost surface of the stacked layers depending on which of the alternate heating or cooling modes of operation is applicable.  
         [0026]    The second heat transfer system  38  of the test cell  10  uses a circulating fluid to convey heat away from the test cell  10 . However, in contrast to prior art simulators using circulating methanol, heat transfer with the sample for temperature control is provided by the thermoelectric modules  40  instead of by the circulating fluid. The circulating fluid of the second heat transfer system  38  of test cell  10  functions merely to convey heat away from the hot sides of the modules  40 . As a result, methanol is not required as the circulating fluid. A mixture of water and ethylene glycol, a commonly used engine coolant, provides a suitable circulating fluid for test temperatures down to −40° C. Furthermore, depending on desired test temperature and required heat loads, water alone may be sufficient. The elimination of methanol, a flammable and highly toxic material, enhances operator health and safety.  
         [0027]    The incorporation of thermoelectric modules  40  in test cell  10  for controlled heat transfer with the sample simplifies required control of the circulating fluid in contrast to prior art circulating methanol systems. For the simulator disclosed in U.S. Pat. No. 4,472,963 to Gyer, for example, it was necessary that cooling baths be provided to chill the methanol to a set number of degrees below the desired test temperature. Changing test temperatures required corresponding changes in the inlet temperature of the methanol. For test cell  10 , circulation of a water/glycol ethylene mixture from a mechanical chiller at approximately +5° C. provides for sufficient conveyance of heat from the modules  40  of test cell  10  for any test temperature down to −40° C. However, the invention is not limited to circulation of a water/ethylene glycol mixture from a mechanical chiller. Depending on the desired test temperature and required heat load, circulation of fluid from an air-water heat exchanger or circulation of ordinary tap water may be sufficient.  
         [0028]    The second heat transfer system  38  includes an assembly  48  of heat sinks which serves as a heat conveying member for removal of heat from the hot sides of the modules  40 . The heat sinks are made from a thermally conductive material such as aluminum or copper, for example. Each of the heat sinks of the assembly  48  extends adjacent to the outer surface  44  of one of the modules  40  of the first heat transfer system  36  such that the heat sinks collectively surround the modules  40  and block  26 . The assembly  48  of heat sinks includes a rear heat sink  50 , opposite side heat sinks  52 ,  54  and front heat sink  56 . As seen in FIGS. 1 and 2, the side heat sinks  52 ,  54  extend between end portions of the rear heat sink  50  and the front heat sink  56  such that the ends of the side heat sinks confront the end portions of the front and rear heat sinks. The confronting relationship between the side heat sinks  52 ,  54  and the front and rear heat sinks  56 ,  50  results in a highly compact and generally square assembly of heat sinks. The adjoining relationship between the ends of the side heat sinks and the end portions of the front and rear heat sinks facilitates insulation of block  26  which is surrounded by the assembly  48  such that the use of additional insulating material such polyurethane is eliminated. An equally feasible arrangement of heat sinks in which the side heat sinks extend such that the ends of the front and rear heat sinks confront end portions of the side heat sinks would also provide for a compact assembly eliminating the need for additional insulating material.  
         [0029]    The test cell  10  includes a top cover  58  extending between the heat sinks, above the block  26  and the modules  40  of the first heat transfer system  36 . The test cell further includes a bottom cover  60  extending between the heat sinks, below the block  26  and the modules  40 . The top and bottom covers  58 ,  60  are secured to the front, rear and side heat sinks by bolts  62 . The bolts extend through the countersunk openings in the front heat sink  56 , the rear heat sink  50 , and the side heat sinks  52 ,  54  to engage tapped holes in the top and bottom covers  58 ,  60 . The interfit of the top and bottom covers  58 ,  60  between the heat sinks of the assembly  48  provides for an extremely compact and generally cube shaped enclosure surrounding the block  26  and the modules  40  of the first heat transfer system  36 . The compact cube-shaped enclosure provides sufficient insulation for precision controlled test temperatures as low as −40° C. without the need for supplemental insulating material.  
         [0030]    The assembly  48  of heat sinks define internal passages which are interconnected to form series of passages through which the fluid of the second heat transfer system  38  may be circulated. The system of passages includes transversely disposed upper passages  68  and lower passages  70  in each of the side heat sinks  52 ,  54  and front heat sink  56  which, when aligned, form portions of first and second series  72 ,  74  of passages. As seen in the Figures, the upper and lower passages  68 ,  70  extend through the assembly  48 of heat sinks separated from one another by a distance which remains substantially equal. The equidistant spacing of the passages  68 ,  70  provides for a counter-flowing circulation of separated portions of fluid in the passages in the manner to be described in greater detail. Although the equidistant relationship of the preferred passages involves a separation between the upper and lower passages, it is conceivable that the passages could comprise concentric cylindrical passages such that the equidistant spacing between the passages is zero. The rear heat sink  50  includes an arrangement of passages which provides for division of the fluid into separate portions for counter-flowing channeling of the separated portions through the first and second series  72 ,  74  of passages.  
         [0031]    As shown schematically in FIG. 5 fluid is introduced into the test cell through inlet  76 , preferably from a mechanical chiller at a constant temperature +5° C. The rear heat sink  50  includes a passage splitter  78  adjacent inlet  76  which forms separate passages thus dividing the fluid introduced into the cell via inlet  76  into first and second portions. The first portion of the fluid is directed around the test cell  10  in the first series  72  of passages in a clockwise direction while the second portion of the fluid is directed in the second series  74  of passages in a counterclockwise direction. As shown, the passages of the respective series of passages are preferably located above and below one another with respect to the heat sink assembly. The rear heat sink  50  further includes a passage union  80  adjacent an outlet  82  which joins the separate passages of the first and second series  72 ,  74  of passages into a single passage.  
         [0032]    The rear heat sink  50  provides for the division and reunion of the fluid necessary for the counter-flowing circulation of the second heat transfer system in the following manner. As discussed above, the fluid is divided into first and second portions by passage splitter  78 . The first portion is channeled in a lower part of rear heat sink  50  to side heat sink  52 . The first portion is then channeled through the lower passages  70  of side heat sink  52 , front heat sink  56  and side heat sink  54 . The first portion is then channeled in a lower part of rear heat sink  50  to the passage union  80 .  
         [0033]    The second fluid portion created by the passage splitter  78  is initially channeled upwardly from the splitter in an upper part of rear heat sink  50  to side heat sink  54 . The second portion is then channeled through the upper passages  68  in a counterclockwise direction through side heat sink  54 , front heat sink  56  and side heat sink  52 . An angling passage  89  in rear heat sink  50  channels the second portion of fluid to the passage union  80  for merging of the second portion with the first portion. As shown, the angling passage  89  of the second series  74  of passages is located inwardly from the passages of the first series  72  with respect to the rear heat sink  50 . The united flow is then discharged from the test cell  10  through outlet  82 , for return to the mechanical chiller for example.  
         [0034]    In the normal operating mode of the hybrid heat transfer system in which the circulating water mixture is conveying heat away from the thermoelectric modules  40 , the temperature of the first portion of the water mixture will be increased as the fluid is channeled about the test cell  10  in a clockwise direction. Similarly, the temperature of the second portion of the fluid will be increased as the fluid is channeled about the test cell in a counter-clockwise direction. As a result, the average temperature of the two portions of the fluid will be substantially equalized regardless of location around the test cell  10 . In this manner, temperature gradients which would otherwise be formed across the test cell  10  are minimized by the counter-flowing circulation system of test cell  10 . The reduction of temperature gradients across the test cell  10  facilitates uniformity in the sample temperature.  
         [0035]    It is most preferable that the inlet  76  and outlet  82  be located closely to one another as seen in FIGS. 1 and 2. In this manner, the length of transversely disposed passages located above and below one another in the rear heat sink  50  will be maximized thereby facilitating the gradient-reducing function of the divided counter-flowing system of the second heat transfer system  38 .  
         [0036]    The internal passages in the assembly  48  of heat sinks are arranged such that, at each of the interfaces between adjoining heat sinks, each of the internal passages of one heat sink confronts an internal passage of the adjoining heat sink. The second heat transfer system  38  preferably includes tubular members  88  each of which extends between confronting passages of adjoining heat sinks. The tubular members  88  provide passage segments serving to interconnect the otherwise separate passages of the first and second flow pathways  72 ,  74  of the second heat transfer system  38 . A suitable gasket material, such as silicone, can be used to seal the separate heat sinks and connecting tubular members  88 . The use of a single inlet  76  and outlet  82  for the test cell  10  and connecting tubular members  88  to link confronting passages in the heat sinks provides compactness in comparison to the use of separate inlets and outlets for each heat sink connected together by flexible tubing externally of the assembly.  
         [0037]    While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather should be construed in breadth and scope in accordance with the recitation of the appended claims.