Abstract:
An automatic transmission lubrication control system includes a modulating, spring biased spool valve and feedback circuit. One end of the spool valve is supplied with line pressure hydraulic fluid. The valve spool modulates a flow of lubricating hydraulic fluid from the cooler and its position is determined by a force balance between the line pressure, the regulated fluid output pressure to the lubrication system and the force of the biasing spring. In a reduced lubrication state, a signal from a transmission control module opens a solenoid valve to provide high pressure fluid to a three way check valve which closes the feedback circuit and applies high pressure fluid to the opposite end of the valve spool. This action moves the valve spool to a travel limit, closing off flow from the cooler. Hydraulic fluid from the torque converter feed is then routed to the lubrication system.

Description:
FIELD 
       [0001]    The present disclosure relates to lubrication controls for automatic transmissions and more particularly to a lubrication control system for an automatic transmission which reduces lubrication flow under low speed and power conditions. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    In motor vehicle automatic transmissions, it is necessary to constantly provide a flow of lubricating transmission fluid to a significant number of rotating components. Determining the necessary lubrication flow which may also be defined as a minimum or sufficient flow for a given component or group of components is critical. Providing such necessary flow is a challenge since it must be maintained throughout the operating speed range of the transmission. Accordingly, flow control devices such as orifices and passageways are sized to provide sufficient flow at high RPM in spite of the fact that, so sized, they will provide excessive flow at low RPM. While this worst case engineering solution fully satisfies the lubrication requirement, an acknowledged consequence is that energy is wasted providing the unnecessarily high flow at low RPM. Specifically, such excess flow causes increased parasitic losses from the internal components of the transmission such as open clutches, bearings, bushings, rotating shells and the like. These parasitic losses result in increased fuel consumption. 
         [0004]    It goes without saying that a design arrived at through compromise is more problematic. Attempting to find a middle ground between minimum necessary flow at high RPM and excessive flow at low RPM will, in all likelihood, result in components at least marginally starved for lubrication at high RPM which may compromise performance and service life. 
         [0005]    The foregoing summary of the state of the automatic transmission lubrication art suggests that improvements in this art would be desirable and the present invention is so directed. 
       SUMMARY 
       [0006]    The present invention provides an automatic transmission lubrication control system having a modulating, spring biased spool valve and a feedback circuit. One end face of the spool valve is supplied with line pressure hydraulic fluid. In a first operating state, the valve spool modulates the flow of lubricating hydraulic fluid returning from a transmission cooler and its position is determined by a force balance between the line pressure, the regulated fluid output pressure to the lubrication system and the force of the spool biasing compression spring. In a second, reduced lubrication state, a signal from the transmission control module (TCM) opens a solenoid valve to provide high pressure hydraulic fluid to a three way check valve which closes the feedback loop and applies the high pressure fluid to the end of the valve spool biased by the biasing compression spring. This action moves the valve spool to a travel limit position, closing off flow from the cooler to the lubrication system and returning it to the sump. Lubricating hydraulic fluid from the torque converter feed is then routed to the lubrication system to satisfy the transmission lubrication requirements at lower transmission speeds. Several orifices are disposed in various fluid flow paths to provide flow restrictions which provide improved control of fluid flow. A lubrication flow switch is provided with pressurized hydraulic fluid in the first state which is exhausted in the second state and signals the TCM that the lubrication control system is operating in the first, high flow state or the second, low flow state. 
         [0007]    Thus it is an object of the present invention to provide a lubrication control system for an automatic transmission. 
         [0008]    It is a further object of the present invention to provide a lubrication control system for an automatic transmission having a spool valve and a three way check valve. 
         [0009]    It is a still further object of the present invention to provide a lubrication control system for an automatic transmission having a spring biased spool valve and a three way check valve. 
         [0010]    It is a still further object of the present invention to provide a lubrication control system for an automatic transmission having a first larger flow orifice for higher speed operating conditions and a second smaller flow orifice for lower speed operating conditions. 
         [0011]    It is a still further object of the present invention to provide a lubrication control system for an automatic transmission having a pressure switch which provides a signal to a transmission control module regarding the state of operation of the lubrication control system. 
         [0012]    Further objects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0013]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0014]      FIG. 1  is a diagrammatic view of an automatic transmission incorporating the lubrication control system of the present invention; 
           [0015]      FIG. 2  is a schematic view of a lubrication control system for an automatic transmission according to the present invention in a normal flow, i.e., higher speed, operating state; 
           [0016]      FIG. 3  is a schematic view of a lubrication control system for an automatic transmission according to the present invention in a reduced flow, i.e., lower speed, operating state; and 
           [0017]      FIG. 4  is a graph presenting operating conditions in a conventional automatic transmission lubrication circuit versus a transmission lubrication circuit according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0019]    With reference now to  FIG. 1 , an exemplary automatic transmission is illustrated and generally designated by the reference number  10 . The automatic transmission  10  includes a cast metal housing  12  having various openings, surfaces, flanges and passageways which receive, locate and support the numerous components of the automatic transmission  10 . Among these components are an input shaft  14  and an output shaft  16 . Supplied with rotational power from a component of the automatic transmission  10  is a hydraulic fluid pump  20 . Typically, the hydraulic pump  20  will be a gerotor or gear pump coupled to an inlet or suction line  22  which draws hydraulic fluid through a filter  24  disposed in a sump  26  at the bottom of the housing  12  of the automatic transmission  10 . 
         [0020]    The hydraulic pump  20  supplies hydraulic fluid under pressure in an outlet or supply line  28  to various components within the automatic transmission  10  such as a pressure regulator (not illustrated) and a lubrication control assembly  30  disposed within the housing  12  of the automatic transmission  10 . The lubrication control assembly  30  also receives pressurized hydraulic fluid from a cooler  32  (illustrated in  FIG. 2 ) in a return line  34 . The cooler  32  is typically located remotely from the automatic transmission  10  in a heat absorbing medium. The hydraulic fluid output of the lubrication control assembly  30  is provided to a lubrication manifold  36  which is essentially a plurality of lines or passageways which distribute the hydraulic fluid to various components of the automatic transmission  10 . A sump return line  38  returns hydraulic fluid not provided to the lubrication manifold  36  to the sump  26 . 
         [0021]    Referring now to  FIGS. 1 and 2 , the lubrication control assembly  30  according to the present invention includes a multiple port spool or control valve  40  including a housing or valve body  42  which slidably receives a multiple piston or land valve spool  44 . As illustrated in  FIG. 2 , the valve spool  44  is in a first, modulating or operating high volume position in which it supplies a volume flow rate of pressurized hydraulic fluid to the lubrication manifold  36  of the automatic transmission  10  associated with high operating speeds. The valve spool  44  is biased to a second, low flow or at rest position to the left in the valve body  42  by a compression spring  46 . 
         [0022]    The valve body  42  defines a first, inlet port  42 A which receives hydraulic fluid in the return line  34  from the transmission cooler  32 . In the first or high volume modulating position of the valve spool  44 , the pistons or lands of the valve spool  44  direct the hydraulic fluid to a first outlet port  42 B which communicates with a first high volume supply orifice  52  sized to provide a volume rate of flow of hydraulic fluid sufficient to satisfy the requirements of the automatic transmission  10  at higher speeds. The output of the high volume orifice  52  flows to the lubrication manifold  36 . Hydraulic fluid flow from the first outlet port  42 B is also provided through a line  54  and a first control orifice  56  to a first port  60 A of a three way check valve  60 . The second port  60 B of the three way check valve  60  is connected through a second control orifice  62  to a first control port  42 C of the valve body  42 . The first control port  42 C communicates with a first control chamber  64  which contains the compression spring  46 . A third port  60 C of the three way check valve  60  communicates through a third control orifice  66  with a control valve  68  actuated by the transmission control module (TCM)  70 . As will be explained in more detail below, when low speed and reduced lubrication requirements are sensed, the transmission control module  70  provides an override signal which actuates the control valve  68  which, in turn, provides pressurized hydraulic fluid to the third port  60 C of the three way check valve  60 . 
         [0023]    A second control port  42 D communicating with a second control chamber  72  at the end of the valve spool  44  opposite the first control chamber  64  is connected to the outlet or supply line  28  of the hydraulic pump  20  through a fourth control orifice  74 . The pressure in the second control chamber  72  will vary with the speed of the hydraulic pump  20  and other variables and may typically range from 300 to 2100 kPa. 
         [0024]    It will thus be appreciated that the axial position of the valve spool  44  and the hydraulic fluid flow to the lubrication manifold  36  will be the result of a force balance between the pump pressure within the second control chamber  72  tending to translate the valve spool  44  to the right in  FIG. 2  and the feedback pressure in the line  54 , the three way check valve  60  and the first control chamber  64 , combined with the force of the compression spring  46  which together tend to translate the valve spool  44  to the left. 
         [0025]    The multiple port spool or control valve  40  includes additional ports which are not involved in the normal, regulated operating state. They include a second inlet port  42 E which is adjacent the first inlet port  42 A and which receives hydraulic fluid flow through a fifth control orifice  76  from the return line  34 . A torque converter feed line  78  provides hydraulic fluid through a second low volume supply orifice  82  and thence to a third inlet port  42 F. A sixth control orifice or pair of orifices  84  also provide hydraulic fluid from the torque converter feed line  78  through another feed line  86  to a lubrication pressure switch  88  and a fourth inlet port  42 G. The lubrication pressure switch  88  provides a signal to the transmission control module  70  that relatively high pressure exists in the feed line  86  which indicates that the fourth inlet port  42 G is closed, thus confirming to the transmission control module  70  that the valve spool  44  is in its normal, regulated operating position. 
         [0026]    Referring now to  FIG. 3 , the reduced lubrication flow operating state of the lubrication control assembly  30  is illustrated. It will be apparent that in this operating state, the valve spool  44  has moved to its leftmost limit of travel as illustrated in  FIG. 3 . This translation has occurred as a consequence of the transmission control module  70  sensing operating conditions in which reduced lubrication flow is appropriate. In this situation, the transmission control module  70  provides a signal to the control valve  68  to open it, thereby providing pressurized hydraulic fluid through the third control orifice  66  to the third port  60 C of the three way control valve  60 . The ball check thus moves to close off the port  60 A and the hydraulic fluid flows through the second control orifice  62  and fills the first control chamber  64 . The combined force of the hydraulic fluid and the compression spring  46  cause the valve spool  44  to translate to its full, left travel limit. 
         [0027]    In this position, the lands of the valve spool  44  provide communication between the third inlet port  42 F and the first outlet port  42 B. The second low volume supply orifice  82  is significantly smaller than the first high volume supply orifice  52  and thus the flow of hydraulic fluid to the lubrication manifold  36  is significantly reduced. Also in this position of the valve spool  44 , the second inlet port  42 E is in communication with a first exhaust port  42 H and the sump return line  38  which returns hydraulic fluid from the cooler  32  to the sump  26 . This feature ensures that full cooler flow and thus maximum cooling are available at all times, regardless of the quantity of fluid passing through the lubrication manifold  36 . Finally, the lands of the valve spool  44  provide communication between the fourth inlet port  42 G and a second exhaust port  42 J which communicates with the sump  26  through the sump return line  38 . Since the sixth control orifices  84  limit the hydraulic fluid flow in the feed line  86 , the pressure drops and the lubrication pressure switch  88  changes state, indicating to the transmission control module  70  that the lubrication control assembly  30  and specifically the valve spool  44  is operating in its reduced flow state. 
         [0028]    Referring now to  FIG. 4 , plots of various operating conditions in a conventional automatic transmission lubrication circuit versus a transmission lubrication circuit according to the present invention are presented. The X (horizontal) axis delineates increasing line pressure, that is, hydraulic pressure in the outlet or supply line  28  from the hydraulic pump  20 . The left Y (vertical) axis presents increasing lubrication feed pressure to the lubrication manifold  36  and the right Y (vertical) axis presents actual hydraulic fluid flow in liters per minute. 
         [0029]    The lubrication control system according to the present invention provides several advantages over prior art systems. First of all, it is estimated that reducing hydraulic fluid flow during low power operation may achieve a 1% improvement in fuel economy. Second of all, all hydraulic fluid, whether is it used for lubrication or is bypassed directly back to the sump, passes through the transmission cooler. Thus, maximum transmission fluid cooling is always provided. Last of all, unless the control valve  68  is activated, the normal and fail-safe operating condition is higher volume, regulated flow lubrication. In this regard, the lubrication pressure switch  88  confirms to the transmission control module  70  correspondence between commanded and actual operating conditions. 
         [0030]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention and the following claims.