Abstract:
A hydraulic control system includes a primary sump and an auxiliary sump. When the transmission fluid is warm, fluid remains in the auxiliary sump reducing the volume of oil in circulation throughout the transmission to reduce parasitic losses. An oil control valve is designed to block flow of oil from the auxiliary sump to the primary sump when the fluid is warm and to allow flow when the fluid is cold. The oil control valve also responds to transmission line pressure. At moderate temperatures, fluid is held in the auxiliary sump when the engine is running but drains back to the primary sump when the engine is off.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to the field of automotive transmission hydraulic control systems. More particularly, the disclosure pertains to a hydraulic control system having an auxiliary sump. 
       BACKGROUND 
       [0002]    Many automotive transmissions utilize pressurized lubrication. A pump draws fluid from a sump and forces the fluid through lubrication passageways in gearbox components. The lubrication passageways are carefully designed to ensure that fluid reaches all of the parts that require lubrication. The fluid is then discharged from the gearbox components by a combination of gravitational forces and centrifugal forces generated by rotating components. Eventually, the fluid flows back to the sump which is located at the lowest point in the transmission housing. A sufficient quantity of fluid must be present to ensure that the sump does not become empty. The quantity required is typically dictated by cold operating conditions because the fluid has much higher viscosity when cold and therefore takes longer to drain back to the sump. 
         [0003]    If the fluid level in the sump is high, some of the rotating components of the gearbox may extend into the fluid. When that happens, the fluid resists the movement of the components. The engine must generate additional torque to overcome the additional parasitic drag, increasing fuel consumption. Furthermore, the churning that results when rotating components move through the fluid may result in small air bubbles forming in the oil. These air bubbles make the fluid less effective. Excessively high fluid level is most likely to occur at higher temperature because the fluid drains back to the sump quickly so a small fraction of the fluid is in transit. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    A transmission hydraulic control system includes a primary sump, an auxiliary sump, and an oil control valve. The oil control valve passively restricts flow from the auxiliary sump to the primary sump when the fluid temperature exceeds a threshold. The threshold varies depending upon whether the engine is running or not. Excess flow may be vented to the auxiliary sump. An engine driven pump draws fluid from the primary sump and pressurizes the fluid to a line pressure. The oil control valve may utilize line pressure as an indicator of whether or not the engine is running. 
         [0005]    An oil control valve includes a housing and first and second sliding spools. The housing defines four ports, one connected to line pressure, one connected to the auxiliary sump, and one connected to the primary sump. A wax motor separates the two spools by a distance that depends upon the temperature of fluid in the fourth port. The position of the first spool is determined by the line pressure which biases the spool toward the second spool. When the line pressure is above a threshold, the first spool may move against a shoulder of the housing. The shoulder may be created by using a smaller diameter for the second spool than for the first spool. The second spool is biased by a spring. The second spool is configured to permit flow between the auxiliary sump and primary sump in certain positions and to block the flow in other positions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic representation of transmission hydraulic network. 
           [0007]      FIG. 2  is a cross sectional view of an oil control valve when fluid is colder and an engine is off. 
           [0008]      FIG. 3  is a cross sectional view of an oil control valve when fluid is colder and an engine is on. 
           [0009]      FIG. 4  is a cross sectional view of an oil control valve when fluid is at moderate temperature and an engine is on. 
           [0010]      FIG. 5  is a cross sectional view of an oil control valve when fluid is at moderate temperature and an engine is off. 
           [0011]      FIG. 6  is a cross sectional view of an oil control valve when fluid is at normal operating temperature and an engine is off. 
           [0012]      FIG. 7  is a cross sectional view of an oil control valve when fluid is at normal operating temperature and an engine is on. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0014]    A transmission hydraulic control system is illustrated schematically in  FIG. 1 . Bold lines represent the flow of mechanical power. Solid lines represent the flow of hydraulic fluid. One solid line may represent multiple fluid circuits. Dotted lines represent control signals. Power is provided by engine  10  which drives the impeller of torque converter  12 . Torque converter  12  transmits torque from an impeller to a turbine whenever the impeller rotates faster than the turbine. This is beneficial when the vehicle must accelerate from a stationary condition. To transmit torque, torque converter  12  must be filled with fluid. Torque converter  12  may also include a bypass clutch that, when engaged, transmits power from the impeller to the turbine without requiring a speed difference. The bypass clutch may be engaged by providing pressurized fluid. The fluid for these functions is provided by valve body  14  via fluid circuits  16 . The turbine of torque converter  12  is fixed to the input shaft of gearbox  18 . Gearbox  18  establishes various speed ratios based on current driving conditions. At low vehicle speeds and high torque demands, gearbox  18  multiplies the torque and reduces the speed. For cruising, gearbox  18  multiplies the speed such that the engine can operate at a low speed that is quiet and efficient. The gearbox speed ratio may be established by providing pressurized fluid to a subset of clutches via fluid circuits  20 . Fluid may flow in either direction through circuits  16  and  20 . Additionally, fluid flows at relatively low pressure through lubrication circuit  22  to gearbox  18  and then returns to primary sump  24 . Fluid return flow path  26  represents the interior of the transmission housing. Primary sump  24  is located at the lowest point in the housing such that gravity causes the fluid to return to the sump. 
         [0015]    Pressurized fluid is provided by pump  28 , which draws fluid from primary sump  24  and transmits the fluid to valve body  14  via line pressure circuit  30 . The power required to pressurize the fluid comes from engine  10 . Whenever the pressure in line pressure circuit  30  exceeds a desired value, regulator valve  32  diverts some flow to auxiliary sump  34  via circuit  36  to relieve the excess pressure. Valve body may also exhaust excess fluid to auxiliary sump  34  via circuit  38 . Auxiliary sump  34  is located higher than primary sump  24  and is located such that the rotating components of gearbox  18  do not move through any fluid that may be in auxiliary sump  34 . Storing fluid in auxiliary sump  34  reduces the volume of fluid in primary sump  24 . Ideally, the volume of fluid in auxiliary sump  34  is managed such that sufficient fluid remains in primary sump  24  yet the fluid level in primary sump  24  is lower than the lowest rotating components. To increase the volume of oil in primary sump  24 , oil control valve  40  opens to permit flow through circuits  42  and  44 . To decrease the volume of oil in primary sump  24 , oil control valve  40  closes such that fluid pumped out of primary sump  24  by pump  28  builds up in auxiliary sump  34 . When the volume of fluid in auxiliary sump  34  exceeds the sump capacity, it overflows and returns to primary sump  24  via the housing. 
         [0016]    An oil control valve, like other types of valves, may be either passively controlled or actively controlled. When an actively controlled valve is utilized, a controller must determine the appropriate state of the valve based on sensors and then command the valve to open or close accordingly. For example, an actively controlled valve may be actuated by a solenoid that exerts a force in response to an electrical current regulated by the controller. In addition to the cost of the solenoid itself, active control increases costs because the controller must include a driver circuit to regulate the electrical current. A passively controlled valve, on the other hand, changes state from open to closed and from closed to open without a command from a controller. 
         [0017]    The state of oil control valve  40  depends upon temperature control signal  46  and engine operation control signal  48 . Temperature control signal  46  indicates a representative temperature of the fluid. In  FIG. 1 , temperature control signal  46  is implemented by routing circuit  36  through oil control valve  40 . Other circuits could be selected for this purpose as long as the temperature of fluid in the circuit is representative. Circuits that are segregated as the fluid changes temperature are less appropriate for this purpose. Also, circuits that may be evacuated some of the time should be avoided. Engine operation control signal  48  is implemented by exposing oil control valve  40  to line pressure circuit  30 . When the engine is not running, the pump does not rotate and the pressure in circuit  30  rapidly falls to near zero. When the engine is running, the pressure in circuit  30  is above a minimum line pressure threshold. 
         [0018]      FIG. 2  shows a cross section of oil control valve  40  when the engine is not running and the transmission fluid is cold. Valve bore  60  defines a number of ports  62 ,  64 ,  66 ,  68 , and  70  separated by a number of lands  72 ,  74 ,  76 ,  78 , and  80 . Spool  82  slides axially between lands  76 ,  78 , and  80 . The diameter of spool  82  is less in a central section than near the ends. Spring  84  pushes spool  82  toward the left. Wax motor  86  is inserted into spool  82 . Pin  88  emerges from wax motor  86  by a distance that depends upon the phase of wax. When the wax is in a solid state, as shown in  FIG. 2 , pin  88  extends a small distance. When the wax is heated, it changes to a liquid state and pushes pin  88  out by a greater distance. Spool  90 , which has a larger diameter than spool  82 , slides axially under land  74 . Plug  92  is inserted under land  72  and held in place by plate  94 . 
         [0019]    Port  62  is connected to line pressure circuit  30  which provides the engine operation control signal  48 . Since this signal would be generated regardless of whether the hydraulic circuit has an oil control valve, no additional solenoids are required. As shown in  FIG. 2 , the engine is off so this circuit is not pressurized. Consequently, pin  88  pushes spool  90  to the left against plug  92 . Ports  64  and  70  are both connected to the regulator valve pressure relief circuit  36  which provides temperature control signal  46 . Heat transfer occurs between the fluid and wax motor  86  such that the temperature of the wax closely follows the temperature of the fluid. Since this circuit acts on both ends of spool  82  and the ends have nearly identical areas, the net force imposed is negligible. Port  66  is connected to auxiliary sump  34  via circuit  42  and port  68  is connected to the primary sump  24  via circuit  44 . In the position shown in  FIG. 2 , the reduced diameter section of spool  82  is centered under land  78  providing a flow passage from port  66  to port  68 . Gravity forces fluid to flow from auxiliary sump  34  through oil control valve  40  to primary sump  24 . 
         [0020]      FIG. 3  shows a cross section of oil control valve  40  when the engine is running and the transmission fluid is cold. When the engine is on, line pressure forces spool  90  to the right. Spool  90  forces spool  82  to the right compressing spring  84 . Movement to the right stops when spool  90  encounters shoulder  96 . In the position shown in  FIG. 3 , fluid may still flow from port  66  to port  68  permitting auxiliary sump  34  to drain into primary sump  24 . Since the oil is still cold, this makes the entire volume of oil available ensuring adequate oil even if the oil drains back slowly from gearbox  18 . 
         [0021]      FIGS. 4 and 5  show oil control valve  40  at an intermediate temperature when the engine is on and when the engine is off, respectively. At this temperature, flow is blocked when the engine is on as shown in  FIG. 4  and flow is allowed when the engine is off as shown in  FIG. 5 . This behavior is desired during final test of the transmission. After the transmission is assembled, it is placed on a test stand which performs a variety of test to ensure that all features are functioning properly. For example, the test stand would command various shifts to ensure that the speed ratio changed as commanded. To test that the oil control valve is functioning properly, the test much be of sufficient duration to heat the fluid enough to that the oil begins accumulating in the auxiliary sump. If the temperature at which that occurs is too high, then final test requires a long time. After the test, it is desirable to verify that the oil level is appropriate. Oil control valve  40  allows all of the oil to immediately drain to the primary sump following final test. If the oil control valve did not react to an engine running signal, it would be necessary to wait for the oil to cool down before verifying the oil level in the primary sump. 
         [0022]      FIGS. 6 and 7  show oil control valve  40  at normal operating temperature when the engine is off and when the engine is on, respectively. At this temperature, flow is blocked independent of whether or not the engine is running. This behavior is desirable because some vehicle are programmed to reduce fuel consumption by stopping the engine while waiting at a traffic light and restarting the engine automatically when the driver releases the brake pedal. If the fluid drained from the auxiliary sump to the primary sump while the engine was off, then the transmission parasitic drag would be higher when the engine restarted. 
         [0023]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.