Abstract:
A solenoid pump and associated hydraulic circuitry are intended for use in automatic transmissions capable of engine start stop (ESS) operation. In a first embodiment, a solenoid pump provides pressurized hydraulic fluid to respective inputs of two way check valves. The other inputs are provided with controlled hydraulic fluid from a transmission valve body. The outputs of the check valves are provided to those hydraulically operated torque transmitting devices associated with first gear. The solenoid pump is activated when the transmission is in gear and the engine is stopped to maintain hydraulic pressure in those actuators associated with first gear in order that a first gear vehicle launch may be quickly and smoothly achieved when the engine is restarted. A second, similar embodiment provides hydraulic fluid to actuators associated with reverse gear. A third embodiment includes a solenoid pump and a latching solenoid valve both communicating with a hydraulic supply between a variable output solenoid valve and a hydraulic actuator in an automatic transmission which maintains clutch pressure by compensating for leaks in the hydraulic components. In a fourth embodiment, a solenoid pump provides pressurized hydraulic fluid to the exhaust backfill circuits of one or more hydraulic operators in an automatic transmission.

Description:
FIELD 
       [0001]    The present disclosure relates to pumps for maintaining pressure in hydraulic systems of automatic transmissions during the stop phase of engine start stop (ESS) operation and more particularly solenoid pumps and hydraulic circuits for maintaining pressure in hydraulic torque transmitting devices of automatic transmissions during the stop phase of engine start stop (ESS) operation. 
       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]    One of the many operational schemes for passenger cars and light trucks that is under extensive study and development in response to ever increasing consumer demands and federal mileage requirements is referred to as engine start stop (ESS). This operational scheme generally involves shutting of the gasoline, Diesel or flex fuel engine whenever the vehicle is stopped in traffic, that is, whenever the vehicle is in gear but stationary for longer than a short, predetermined time, such as occurs at a traffic light. 
         [0004]    While this operational scheme has a direct and positive impact on fuel consumption, especially for vehicles driven in cities and suburbs, it is not without complications from an engineering standpoint. For example, since the engine output/transmission input shaft does not rotate during the stop phase, automatic transmissions relying for their operation upon pressurized hydraulic fluid may temporarily lose pressure and thus gear and clutch selection and control. This shortcoming can, however, be overcome by incorporating hydraulic accumulators in the hydraulic control circuit at strategic locations. Alternatively, electrically driven gear and vane pumps may be incorporated into the transmission&#39;s hydraulic circuit to provide the required minimum pressure and flow while the engine is off. Both of these approaches have been utilized successfully. 
         [0005]    It is apparent, however, that both of the above-recited solutions comprehend the incorporation of additional components which add both to the weight and cost of the transmission and vehicle drive train. Accordingly, it is also apparent that improvements directed to the problem of maintaining hydraulic flow and pressure in an automatic transmission during periods of engine inactivity in ESS applications are both desirable and worthwhile. The present invention is so directed. 
       SUMMARY 
       [0006]    The present invention provides an electromagnetic solenoid pump and associated hydraulic circuitry for use in an automatic transmission associated with an engine start stop (ESS) drive train. In a first embodiment, a solenoid pump provides pressurized hydraulic fluid (transmission oil) to respective inputs of one or more two way check valves. The other inputs are provided with controlled hydraulic fluid from the transmission valve body. The outputs of the check valves are provided to respective hydraulically operated torque transmitting devices such as clutches or brakes associated with first gear. The solenoid pump is activated when the transmission is in gear and the engine or prime mover is stopped to maintain hydraulic pressure on the torque transmitting devices in order that a vehicle launch in first gear may be quickly and smoothly achieved when the engine is restarted. 
         [0007]    In a second embodiment, similar to the first embodiment, a solenoid pump and one or more two way check valves provide pressurized hydraulic fluid from either one or more outputs of the valve body or the solenoid pump to respective hydraulic actuators associated with torque transmitting devices which achieve or engage reverse gear. 
         [0008]    A third embodiment includes a solenoid pump, a pressure sensor and a latching solenoid all communicating with a hydraulic circuit between a variable output solenoid and a hydraulic actuator associated with a torque transmitting device in an automatic transmission which maintains actuator pressure by compensating for or overcoming leakage of the hydraulic components when the transmission is in gear and the engine is stopped. 
         [0009]    In a fourth embodiment, a solenoid pump provides pressurized hydraulic fluid to the exhaust backfill circuit of one or more hydraulic actuators of torque transmitting devices in an automatic transmission when the transmission is in gear and the engine is stopped. 
         [0010]    Thus it is an aspect of the present invention to provide a solenoid pump to maintain pressure in hydraulic circuits in an automatic transmission utilized in an engine start stop (ESS) application when the engine is stopped and the transmission is in gear. 
         [0011]    It is a further aspect of the present invention to provide a hydraulic circuit for an automatic transmission utilized in an engine start stop application having a solenoid pump and one or more two way check valves which supply pressurized hydraulic fluid to respective hydraulic actuators from either the solenoid pump or the transmission valve body. 
         [0012]    It is a still further aspect of the present invention to provide a hydraulic circuit for an automatic transmission utilized in an engine start stop application having a solenoid pump and one or more two way check valves which supply pressurized hydraulic fluid to respective hydraulic actuators associated with first gear from either the solenoid pump or the transmission valve body. 
         [0013]    It is a still further aspect of the present invention to provide a hydraulic circuit for an automatic transmission utilized in an engine start stop application having a solenoid pump and one or more two way check valves which supply pressurized hydraulic fluid to respective hydraulic actuators associated with reverse gear from either the solenoid pump or the transmission valve body. 
         [0014]    It is a still further aspect of the present invention to provide a hydraulic circuit for an automatic transmission utilized in an engine start stop application having a solenoid pump and one or more two way check valves which supply pressurized hydraulic fluid to respective hydraulic actuators from the solenoid pump during engine off periods when the transmission is in gear. 
         [0015]    It is a still further aspect of the present invention to provide a hydraulic circuit for an automatic transmission utilized in an engine start stop application having a solenoid pump and latching solenoid both communicating with a hydraulic supply between a variable output solenoid and a hydraulic actuator in an automatic transmission which maintains pressure in the hydraulic supply. 
         [0016]    It is a still further aspect of the present invention to provide a hydraulic circuit for an automatic transmission utilized in an engine start stop application having a solenoid pump which provides pressurized hydraulic fluid to the exhaust backfill circuits of one or more hydraulic actuators of hydraulic torque transmitting devices in an automatic transmission. 
         [0017]    It is a still further aspect of the present invention to provide a hydraulic circuit for an automatic transmission utilized in an engine start stop application having a solenoid pump which provides pressurized hydraulic fluid to the exhaust backfill circuits of one or more hydraulic actuators of clutches and brakes in an automatic transmission. 
         [0018]    Further aspects, 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 
         [0019]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0020]      FIG. 1  is a full, sectional view of a solenoid pump utilized in an automatic transmission intended for engine start stop operation according to the present invention in a de-energized (at rest) position or state; 
           [0021]      FIG. 2  is a diagrammatic view of a first hydraulic circuit for an automatic transmission including a solenoid pump, a pair of check valves and a pair of hydraulically operated torque transmitting devices according to the present invention; 
           [0022]      FIG. 3  is a diagrammatic view of a second hydraulic circuit for an automatic transmission including a solenoid pump, a check valve and a hydraulically operated reverse gear torque transmitting device according to the present invention; 
           [0023]      FIG. 4  is a diagrammatic view of a third hydraulic circuit for an automatic transmission including a solenoid pump, a pressure sensor and a latching solenoid valve according to the present invention; and 
           [0024]      FIG. 5  is a diagrammatic view of a fourth hydraulic circuit for an automatic transmission including a solenoid pump and a control valve in an automatic transmission exhaust backfill circuit according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0026]    With reference to  FIG. 1 , a typical and exemplary solenoid pump utilized in the present invention is illustrated and generally designated by the reference number  10 . The solenoid pump  10  includes a generally tubular or cylindrical housing  12  which is closed at both ends by circular discs or plates  14 . The housing  12  receives an electromagnetic coil  20  which is wound on an insulating bobbin  22 . An electrical lead or leads  24  pass through the housing  12  in a suitable insulating feed-through  26  and provide electrical energy to the electromagnetic coil  20 . 
         [0027]    Concentrically disposed within the bobbin  22  is a pump assembly  30  which includes a tubular or cylindrical pump body  32 . The cylindrical pump body  32  includes an inlet port  36  at one end and an aligned outlet port  38  at the opposite end. 
         [0028]    The tubular or cylindrical pump body  32  defines an elongate, hollow pumping chamber  40 . Disposed within the pumping chamber  40  is a piston assembly  50 . The piston assembly  50  includes a ferrous, i.e., magnetic, plunger or armature portion  52  and may include a non-magnetic member or body portion  54 , which may be either metallic or non-metallic. The plunger or armature portion  52  and the member or body portion  54  define a through interior axial passageway  60 . The tubular or cylindrical pump body  32  defines a pumping chamber  64  at the lower end of the piston assembly  50 . Between the axial passageway  60  of the piston assembly  50  and the pumping chamber  64  and secured to the end of the non-magnetic member or body portion  54  is a first reed or check valve  72  which is biased against the end of the non-magnetic member or body portion  64  to close off the axial passageway  60 . A second reed or check valve  76  is disposed on a circular plate or baffle  78  within the pumping chamber  64  and is biased to close off the pumping chamber  64  and prevent flow from the outlet port  38  into the pumping chamber  64 . A compression spring  80 , concentrically disposed about the piston assembly  50 , engages a shoulder  82  on the plunger or armature portion  52  and biases the piston assembly  50  upwardly as illustrated in  FIG. 1 , toward the inlet port  36 . 
         [0029]    The operation of the solenoid pump  10  is straightforward. Assuming the solenoid pump  10  is filled with a fluid such as hydraulic fluid or transmission oil, when the electromagnetic coil  20  is energized, the piston assembly  50  translates downwardly in  FIG. 1 , drawing in fluid through the inlet port  36  and forcing fluid in the pumping chamber  64  past the second reed or check valve  76  and out the outlet port  38 . When the electromagnetic coil  20  is de-energized, the first reed or check valve  72  opens and fluid flows from the axial passageway  60 , past the first reed or check valve  72  and into the pumping chamber  64 . The pumping cycle is then repeated as the electromagnetic coil  20  is re-energized. 
         [0030]    Referring now to  FIG. 2 , a first embodiment of a hydraulic control circuit of an automatic transmission  102  is illustrated and generally designated by the reference number  100 . The hydraulic control circuit  100  is disposed within and is a portion of the automatic transmission  102  which typically includes a plurality of planetary gear assemblies arranged in tandem and interconnected by a plurality of rigid members, clutches and brakes (all not illustrated). The automatic transmission  102  includes a sump  104  within which hydraulic fluid (transmission oil) collects. The sump  104  is typically and preferably located at the bottom of the automatic transmission  102 . An inlet or suction line  106  draws hydraulic fluid from the sump  104  and communicates with the inlet port  36  of the solenoid pump  10  described above. An outlet line  112  is connected to the outlet port  54  of the solenoid pump  10  and communicates with a pressure relief valve  114 , a first inlet port  116 A of a first two way check or ball valve  116  and a first inlet port  118 A of a second two way check or ball valve  118 . The pressure relief valve  114  includes a compression spring  122  and a ball or poppet member  124  that opens to release pressure in the outlet line  112  when it exceeds a predetermined value such as 50 to 60 p.s.i. The first two way check or ball valve  116  includes a check ball  126  and the second two way check or ball valve  118  includes a check ball  128 . 
         [0031]    The automatic transmission  102  also includes a valve body  130  which includes various spool and control valves (not illustrated) which operate and cooperate to selectively provide pressurized hydraulic fluid to various torque transmitting devices, such as clutches and brakes, within the automatic transmission  102 . A first output from the valve body  130  in a hydraulic line  132  communicates with a second inlet port  116 B of the first two way check or ball valve  116  and a second output in a hydraulic line  134  communicates with a second inlet port  1188  of the second two way check or ball valve  118 . The first two way check or ball valve  116  also includes an outlet port  116 C and a first hydraulic outlet line  136  which communicates with a cylinder of a first hydraulic actuator  138 . The first hydraulic actuator  138  is associated with and operates one of two torque transmitting devices, such as clutch or brake assemblies, that must be activated or engaged in the automatic transmission  102  to achieve and maintain first gear. The second two way check or ball valve  118  also includes an outlet port  118 C and a second hydraulic line  142  which communicates with a cylinder of a second hydraulic actuator  144 . The second hydraulic actuator  144  is associated with and operates the other of two torque transmitting devices, such as clutch or brake assemblies, that must be activated or engaged in the automatic transmission  102  to achieve and maintain first gear. 
         [0032]    In operation, when the engine or prime mover is operating, pressurized hydraulic fluid from a main hydraulic pump (not illustrated) driven by the engine or prime mover is supplied to the valve body  130  and directed and supplied as necessary to various hydraulic actuators, such as the hydraulic actuators  138  and  144 , to provide sequenced shifts through the available gears of the automatic transmission  102 . In this operational mode, the solenoid pump  10  is not operating and the check balls  126  and  128  move to the left in  FIG. 2  and block or close off the first inlet ports  116 A and  118 A. The pressure relief valve  114  relieves pressure as necessary to ensure closing of the inlet ports  116 A and  118 A. When the prime mover stops and the automatic transmission  102  is in gear, as occurs, for example, when the vehicle is stopped at a traffic light, the main hydraulic pump in the transmission is no longer rotating and thus delivered hydraulic pressure drops. As noted above, however, it is highly desirable that the transmission clutches and/or brakes associated with first gear be maintained in an activated (stroked) or engaged state in order to provide a smooth and prompt launch when the vehicle operator commands it and the prime mover re-starts. Accordingly, when the prime mover shuts down, the solenoid pump  10  is energized and pressurized hydraulic fluid is provided to the first inlet ports  116 A and  118 A of the first and second check valves  116  and  118 . The check balls  126  and  128  thus move to the right and block or close off the second inlet ports  1168  and  1188 . The pressurized hydraulic fluid is thus provided to the first and second hydraulic actuators  138  and  144 , thereby maintaining launch ready engagement of the brake or clutch assemblies associated with first gear. 
         [0033]    It should be appreciated and understood that although only two check valves  116  and  118  and two hydraulic actuators  138  and  144  have been illustrated, this being the number of clutches or brakes necessary to engage or achieve first gear in a typical and exemplary automatic transmission, this is by way of illustration and example only. Should a particular automatic transmission have more or fewer clutches or brakes and associated actuators which are necessary to achieve first gear, the number of check valves and hydraulic lines can readily and easily be increased or decreased to accommodate such other automatic transmission configurations. 
         [0034]    Referring now to  FIG. 3 , a second, similar engine start stop, solenoid pump application and embodiment  200  is illustrated. It is anticipated that, on occasion, a driver may shift from drive to reverse while the prime mover is stopped in traffic, for example, to back up to avoid a stopped or stalled vehicle directly in front. The second embodiment  200  includes the automatic transmission  102 , the sump  104 , the suction line  106 , the solenoid pump  10 , the outlet line  112 , the pressure relief valve  114 , the valve body  130  and a two way check or ball valve  216  having a first inlet port  216 A and a second inlet port  216 B. The first inlet port  216 A of the two way check valve  216  communicates with the outlet line  112  and the second inlet port  216 B communicates with an output of the valve body  130 . The two way check or ball valve  216  also includes a first outlet  216 C and a first hydraulic outlet line  218  which communicates with a cylinder of a reverse hydraulic actuator  220 . The reverse hydraulic actuator  220  is associated with and operates a torque transmitting device, such as a clutch or brake, which achieves or engages reverse gear. It should be understood that if two or more clutches must be engaged to achieve reverse and if one of these reverse clutches is also active in drive, then separate solenoid pumps  10  will be required for each one of the clutches in order to have engine start stop in both drive and reverse. 
         [0035]    Once again, in operation, while the prime mover is operating, conventional control of the reverse hydraulic actuator  220  is achieved by the valve body  130 , through the two way check valve  216 , the pressure relief valve  114  ensuring that pressure is relieved in the hydraulic outlet line  112  so that the check valve  216  can properly and fully close. When the prime mover is stationary and reverse gear is selected, the solenoid pump  10  in energized and the outlet line  218  and the reverse hydraulic actuator  220  begin to be filled and pressurized and stroked such that reverse gear will be fully or substantially fully engaged when the prime mover re-starts. 
         [0036]    It should be appreciated that both the embodiments of  FIGS. 2 and 3  may be utilized together in one automatic transmission  102 , in which case, only one solenoid pump  10  would typically be utilized. 
         [0037]    Referring now to  FIG. 4 , a third application and embodiment  300  of a solenoid pump  10  in an automatic transmission  102  for an engine start stop application is illustrated. A somewhat less critical operational issue in engine start stop applications relates to the loss of pressure in hydraulic circuits utilizing latching solenoids valves which close off or isolate a circuit to maintain hydraulic pressure in the circuit for a period of time when the prime mover is stopped and the transmission is in gear. While the latching solenoid valve may provide positive and complete circuit closure and isolation, small but finite leaks in the hydraulic circuit at interconnections and within the hydraulic actuator may amount to as much as 5 ml/minute. Over even a relatively short period of time, such leaks may result in a reduction or total loss of pressure in a circuit, thereby impairing vehicle launch and operation until full pressure has been restored. 
         [0038]    The third embodiment  300  includes a latching solenoid valve  302  that may be disposed within the valve body  130  with other spool or control valves  332  and  334 , as noted above. A control supply line  336  from the spool or control valves  332  and  334  communicates with and supplies pressurized hydraulic fluid to an inlet port  302 A of the latching solenoid valve  302 . When the latching solenoid  302  is de-energized, such pressurized hydraulic fluid is provided to an outlet port  302 B and a hydraulic line  338 . When the latching solenoid valve  302  is energized, it cuts off the flow of pressurized hydraulic fluid to the outlet port  302 B. A solenoid pump  10 , as described above, which draws hydraulic fluid from the sump  104  is also in fluid communication with hydraulic line  338 . A latching solenoid pressure switch  340  which closes on pressure drop and opens on pressure rise receives electrical power from the circuit that energizes the latching solenoid  302  and selectively provides it to the solenoid pump  10  through an electrical conductor  342  when pressure in the hydraulic line  338  falls below a predetermined value. The hydraulic line  338  terminates in a cylinder  348  of a hydraulic actuator  350  associated with a torque transmitting device, such as a clutch or brake, that must or should be maintained in a pressurized (stroked) condition during periods of stopped prime mover operation while the transmission is in gear, in order to ensure smooth, prompt and acceptable vehicle launches. 
         [0039]    Referring now to  FIG. 5 , a fourth embodiment  400  of a solenoid pump  10  in an automatic transmission  102  for an engine start stop application is illustrated. Here, the solenoid pump  10  is utilized in the exhaust backfill hydraulic circuit. Providing pressurized hydraulic fluid flow to a plurality of actuators also involves exhausting such flow through control valves and return lines to the sump  104  of the transmission  102 . In order to achieve predicable and repeatable operation, it is known that such exhaust or return circuits should not be allowed to operate or return to ambient pressure but should be maintained at a certain minimum pressure, on the order of 5 p.s.i. which allows for the hydraulic circuit to be filled with hydraulic fluid. Once again, in engine start stop applications, maintaining this desired minimum exhaust backfill pressure may not be possible inasmuch as the prime mover which drives the main transmission hydraulic pump will, as noted above, often not be operating while the transmission is still in gear. During engine start stop operation, higher pressure is desired to stroke the clutch pistons against their respective return springs which requires a newer pumping source when the engine or the prime mover and hence the transmission pump is off. 
         [0040]    In  FIG. 5 , the valve body  130  is seen to include a first variable force solenoid (VFS) valve  402  and a second variable force solenoid (VFS) valve  404 . It will be appreciated that the illustration of two variable force solenoid valves is for purposes of description and example only and that just one or more than two variable force solenoid valves may be utilized in the present invention. Moreover, different solenoid valve configurations or types, other than variable force, may be utilized in the present invention. Each of the variable force solenoid valves  402  and  404  includes at least one inlet port: the first variable force solenoid valve  402  includes an inlet port  402 A and the second variable force solenoid valve  404  includes an inlet port  404 A which are both fed from a pressurized hydraulic supply line  406 . The first variable force solenoid valve  402  also includes a controlled outlet port  402 B which communicates through a hydraulic line  408  with a first hydraulic actuator  410  associated with one of the torque transmitting devices, such as clutches or brakes, typically associated with first gear. The second variable force solenoid valve  404  also includes a controlled outlet port  404 B which communicates through a hydraulic line  418  with a second hydraulic actuator  420  associated with another of the clutches or brakes typically associated with first gear. 
         [0041]    Each of the variable force solenoid valves  402  and  404  includes at least one exhaust port: the first variable force solenoid valve  402  includes an exhaust port  402 C and the second variable force solenoid valve  404  includes an exhaust port  404 C. Both of the exhaust ports  402 C and  404 C communicate with an exhaust backfill hydraulic line  424 . The exhaust backfill hydraulic line  424  terminates at an outlet port  430 B of a control valve  430 . The control valve  430  includes a valve spool  432 , an inlet port  430 A which is in communication with the output of a solenoid pump  10 , as described above, a control port  430 C which is in fluid communication with the hydraulic supply line  406  and an exhaust port  430 D which returns hydraulic fluid to the sump  104 . 
         [0042]    When hydraulic pressure in the line  406  drops below a predetermined value, typically because the prime mover has stopped, and the transmission is in gear, the solenoid pump  10  is energized and the spool  432  which is biased by a compression spring  434  moves upward, closing off the exhaust port  430 D and providing fluid communication between the inlet port  430 A and the outlet port  430 B, thereby providing pressurized hydraulic fluid from the solenoid pump  10  to the exhaust backfill hydraulic line  424  to maintain the desired and minimum necessary hydraulic pressure in the exhaust backfill line  424  to ensure suitable, smooth and repeatable vehicle launches. When the prime mover restarts and the main transmission hydraulic pump again begins operating, the pressure in the line  406  will translate the spool  432  downwardly, closing off the inlet port  430 A and providing communication between the outlet port  430 B and the exhaust port  430 D. When hydraulic pressure in the line  406  is at or above a predetermined system threshold pressure value, the variable force solenoid valves  402  and  404  may again be energized to control engagement of the hydraulic actuators  410  and  420 . 
         [0043]    Once again, it should be appreciated that although only two solenoid control valves, the variable force solenoid valves  402  and  404  are described above, the incorporation of a solenoid pump  10  in an exhaust backfill circuit of an automatic transmission  102  may be associated with only one solenoid valve or more than two solenoid valves. Moreover, the incorporation of a solenoid pump  10  in an exhaust backfill circuit of an automatic transmission  102  may be accompanied by incorporation of additional solenoid pumps  10  as described above with respect to the other embodiments  100 ,  200  and  300 . 
         [0044]    The foregoing description of the invention is merely illustrative and 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.