Abstract:
The invention relates to a control system, especially a hydraulic control system for a transmission, including a valve assembly, especially a directional valve assembly, designed for controlling a cooling system for a clutch and for ensuring a minimum level of pressure and suctioning function of a pump.

Description:
TECHNICAL FIELD 
   The invention relates to a control system including a valve assembly. More specifically, the present invention relates to a hydraulic control system for a transmission, including a directional valve assembly and designed for controlling a cooling system for a clutch and for ensuring a minimum level of pressure and the suctioning function of a pump. 
   BACKGROUND 
   In conventional control systems for transmissions, a first valve for cooling the clutch and a second valve for ensuring a minimum level of pressure and suctioning function of the pump are used in the cooling system return line. 
   SUMMARY 
   The object of the invention is to optimize the known control system with respect to production costs and function. 
   The object is attained with a control system, especially a hydraulic control system for a transmission, including a valve assembly, especially a directional valve assembly, designed for controlling a cooling system for a clutch and for ensuring a minimum level of pressure and suctioning function of a pump. One exemplary valve assembly includes only a single valve with which the cooling system for the clutch ensures the minimum level of pressure and the suctioning function of the pump. The use of a single valve significantly reduces production costs. Furthermore, the structural space required to hold the control system in the engine compartment of a motor vehicle is reduced. 
   One embodiment of the control system is characterized in that the valve includes a first actuating piston and a second actuating piston, which are housed in a valve chamber such that they can slide. The valve includes several, specifically at least seven, ports, at least one of which is connected to each of the clutch cooling system, a return line from the clutch cooling system, the pump, or a source of pilot pressure. It is particularly advantageous if one port is connected to the source of pilot pressure, one port is connected to the pump, one port is connected to the return line from the clutch cooling system, and at least one port, especially several ports, is or are connected to the clutch cooling system. 
   A further embodiment is characterized in that the clutch cooling system is connected to a first, a second, a third, and a fourth port on the valve chamber. This results in a multitude of control possibilities that have proven operationally advantageous. 
   A further embodiment of the control system is characterized in that the first port in the clutch cooling system is connected to a first end face of the first actuating piston. Via the first port in the clutch cooling system, pressure can be applied to the first end face of the first actuating piston, in order to shift it from a first position to a second position. 
   A further embodiment of the control system is characterized in that the first port in the clutch cooling system is connected to the second port in the clutch cooling system, for example via a connecting line, and the second clutch cooling system port is connected to the return line from the clutch cooling system. In this manner, the first end face of the first actuating piston can be acted upon by pressure from the return line of the clutch cooling system. 
   A further embodiment of the control system is characterized in that a spring presses against a second end face of the first actuating piston, which is opposite the first end face, thus the spring is coiled between the second end face of the first actuating piston and a first end face of the second actuating piston such that when the force of pressure acting against the first end face of the first actuating piston becomes greater than the spring force acting against the second end face of the first actuating piston, the first actuating piston is shifted from a first position to a second position, thus opening up a connection between the return line from the clutch cooling system and the pump port. In this manner the pumped fluid is recirculated from the return line of the clutch cooling system into the suction tract of the pump. 
   A further embodiment of the control system is characterized in that a second end face of the second actuating piston, which is arranged opposite the first end face of the second actuating piston, can be acted upon by the pilot pressure via the port from the pilot pressure source, in order to shift the second actuating piston such that a connection between the third and the fourth ports in the clutch cooling system is opened up. In this manner, the clutch cooling system is activated. 
   A further embodiment of the control system is characterized in that an aperture is located in a connecting line between the third and the fourth ports in the clutch cooling system. The aperture serves to feed a small volume flow to the clutch for purposes of lubrication. 
   A further embodiment of the control system is characterized in that a driver extends from the second end face of the first actuating piston, in the direction of the lengthwise axis of the first actuating piston. The driver serves to guide the spring, which is preferably designed as a helical compression spring. 
   A further embodiment of the control system is characterized in that an especially cap-shaped, shiftable separator element is arranged between the first and the second actuating pistons and serves to divide the space that houses the first actuating piston from the space that houses the second actuating piston. In this manner, different levels of pressure can be realized in the spaces that house the first and the second actuating pistons. 
   The invention also relates to a transmission having a control system as described above. In conventional hydraulic control systems for transmissions, among other things, a valve for the cooling of the clutch and a valve for ensuring a minimum level of pressure and the suctioning function of the pump in the cooling system return line are built in. With the present invention, the two valve functions are combined in a single valve, which may also be described as a minimum pressure retaining valve with a shifting function for the cooling system. 
   Further advantages, characterizing features, and details of the invention are disclosed in the following description, in which, with reference to the drawings, an exemplary embodiment is specified in detail. In this, each of the characterizing features mentioned in the claims and in the description can be considered critical to the invention on its own or in any combination. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the present invention will be more readily apparent from the following detailed description and drawings of the illustrative embodiments of the invention wherein like reference numbers refer to similar elements and in which: 
       FIG. 1  is a side sectional view of a valve in its initial position, according to the present invention; 
       FIG. 2  is a side sectional view of the valve of  FIG. 1  in its operating position; and 
       FIG. 3  is a side sectional view of the valve of  FIG. 1  in a third operating position, in which the clutch cooling system is activated. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a valve chamber  1  of a valve as specified in the invention, intended for the hydraulic control of a transmission, is schematically represented. In the valve chamber  1 , a first actuating piston  11  and a second  12  actuating piston are housed such that they can slide. The first actuating piston  11  is equipped at one end with a circular cylindrical section  14 , and at its other end with a circular cylindrical section  15 . Between the two circular cylindrical sections  14  and  15  is a center section  16 , also circular cylindrical, and having a smaller outside diameter. The transition sections between the circular cylindrical sections  14 ,  15  and the center section  16  are curved. At the open end of the circular cylindrical section  14  is a first end face  17  of the first actuating piston  11 . At the open end of the circular cylindrical section  15  is a second end face  22  of the first actuating piston  11 . 
   The second actuating piston  12  is equipped at one end with a circular cylindrical section  18  that has a constant outside diameter. Attached to the circular cylindrical section  18  is a section  19 , which has a decreasing outside diameter. The section  19  is in turn followed by a circular cylindrical section  20 , which has a constant outside diameter. Attached to the other end of the second actuating piston  12  is a section  21 , which has an increasing outside diameter, and whose dimensions correspond to those of the section  19 . The second actuating piston  12 , like the first actuating piston  11 , has a larger outside diameter at its two ends compared to its center. 
   Arranged on the second end face  22  of the first actuating piston  11  is a driver  23 . The driver  23  includes first a circular cylindrical section with a constant outside diameter, then a tapered section, and at its open end, a circular cylindrical section with a reduced outside diameter. The driver  23  serves to fasten and guide a helical compression spring  24 , which is positioned over the driver  23 . An end of the helical compression spring  24  lies against the second end face  22  of the first actuating piston  11 . The other end of the helical compression spring  24  lies inside and against a cap-shaped separator element  25 , which is housed inside the valve chamber  1  such that it can slide. Against the outer side of the cap-shaped separator element  25  lies a first end face  26 , which is formed on the open end of the second actuating piston  12 . At the open end of the circular cylindrical section  18  of the second actuating piston  12  is a second end face  27 . The first actuating piston  11  has a narrower outside diameter than the second actuating piston  12 . 
   Four ports  31 ,  32 ,  33 , and  34  are provided on the valve chamber  1 , all of which are connected to the clutch cooling system. The ports  31  through  34  are also referred to as the first, second, third, and fourth clutch cooling system ports. The first  31  and the second  32  clutch cooling system ports are connected to one another via a connecting line  36 . The second  32  and the third  33  clutch cooling system ports are connected to one another via a connecting line  37 . The third  33  and the fourth  34  clutch cooling system ports are connected to one another via a line  38 , in which an aperture  40  is positioned. A line  39  leads from the fourth clutch cooling system port  34  to the clutch cooling system. 
   In addition, a port  42  is provided on the valve chamber  1  and is connected via a line  43  to the cooling system return line. Furthermore, a port  46  is provided on the valve chamber  1 , and is connected via a line  47  to the suctioning tract of the pump. Via a port  49 , the space that houses the helical compression spring  24  is connected to a tank. Via the port  49  it is ensured that the space that houses the compression spring  24  remains pressureless. Finally, the valve chamber  1  is equipped with a port  50 , which is connected via a line  51  to a source of pilot pressure. 
   The first clutch cooling system port  31  is connected to the first end face  17  of the first actuating piston  11 . When the first actuating piston  11  is in the position shown in  FIG. 1 , the second clutch cooling system port  32  is connected to the cooling system return line port  42  via the center section  16  of the first actuating piston  11 . However, the second clutch cooling system port  32  can also be closed off by the circular cylindrical section  14  of the first actuating piston  11 . 
   When the valve is in the operating positions shown in  FIGS. 1 and 2 , the section  21  of the second actuating piston  12  in the valve chamber  1  is arranged between the third  33  and the fourth  34  clutch cooling system ports, hence there is no connection between the third  33  and the fourth  34  clutch cooling system ports via the valve chamber  1 . In the valve operating position that is shown in  FIG. 3 , the second actuating piston  12  is shifted such that a connection between the third  33  and the fourth  34  clutch cooling system ports via the valve chamber  1  is opened up. 
   The pilot pressure port  50  is connected to the second end face  27  of the second actuating piston  12 . In the operating position shown in  FIG. 1 , the pump port  46  is closed off by the circular cylindrical section  15  of the first actuating piston  11 . When the first actuating piston  11  is shifted as is shown in  FIGS. 2 and 3 , a connection is opened up between the cooling system return line port  42  and the pump port  46 . 
   In the initial valve position shown in  FIG. 1 , the fluid flowing back from the cooling system flows out of the line  43  via the cooling system return line port  42  to the second clutch cooling system port  32 . From the second clutch cooling system port  32 , the fluid flows through the line  36  and the first clutch cooling system port  31  to the first end face  17  of the first actuating piston  11 . A smaller volume flow of the fluid is directed from the second clutch cooling system port  32  to the clutch via the lines  37 ,  38 ,  39  and the aperture  40 , which has a diameter of approximately 0.8 mm, for the purpose of lubricating the bearings. 
   The fluid is a hydraulic fluid, which is also referred to as hydraulic oil. The hydraulic fluid that acts upon the first end face  17  of the first actuating piston  11  generates a force that opposes the prestressed helical compression spring  24 , which is positioned between the first  11  and the second  12  actuating pistons. When the level of pressure prevailing at the first end face  17  of the first actuating piston  11  or the force of pressure acting against it, becomes greater than the prestressed force of the helical compression spring  24 , then the first actuating piston  11  is shifted toward the second actuating piston  12 . With this shifting of the first actuating piston  11 , as is shown in the  FIGS. 2 and 3 , a connection is opened upon between the cooling system return line port  42  and the pump port  46 . As a result of this, the fluid is forced back out of the cooling system return line  43  via the cooling system return line port  42 , the pump port  46 , and the pump port line  47  to the suctioning tract of the pump (not illustrated here). The difference in pressure between the ports  42  and  46  represents the set minimum pressure of the valve. The valve operating position shown in  FIG. 2  corresponds to the normal driving situation of a motor vehicle. 
   If during operation the clutch becomes severely heated, making it necessary to cool the clutch, then the second end face  27  of the second actuating piston  12  is pressurized with a pilot pressure via the pilot pressure port  50  and the pilot pressure line  51 . The pilot pressure then implements a shifting of the second actuating piston  12  from the position shown in  FIGS. 1 and 2  to the position shown in  FIG. 3 . 
   In  FIG. 3 , it is apparent that the shifting of the second actuating piston  12  toward the first actuating piston  11  effected by the pilot pressure causes the connection between the third clutch cooling system port  33  and the fourth clutch cooling system port  34  to be opened up. This leads to some degree to the formation of a bypass, which bridges the aperture  40  in the line  38 . When the valve is in this position shown in  FIG. 3 , the clutch cooling system is active. 
   The shifting of the second actuating piston  12  toward the first actuating piston  11  further causes an increase in the tension of the helical compression spring  24 . This in turn causes the adjusted minimum pressure of the valve to be increased. This is desirable, because a higher level of pressure is required for cooling the clutch than the minimum level of pressure established beforehand. Beyond a certain pressure level the helical compression spring  24  acts as a block, and the two actuating pistons  11  and  12  act as a single-component slide valve. The adjusted coolant pressure is then established over the difference in diameter between the actuating pistons  11  and  12 . This valve operating position is shown in  FIG. 3  and represents the driving situation when the cooling system is engaged. 
   It will be appreciated by persons skilled in the art that the present invention is not limited to the embodiments described thus far with reference to the accompanying drawings; rather the present invention is limited only by the following claims.