Patent Publication Number: US-2012039726-A1

Title: Method for operating a hydraulic apparatus of a transmission device

Description:
This application claims priority from German patent application serial no. 10 2010 039 350.9 filed Aug. 16, 2010. 
     FIELD OF THE INVENTION 
     The invention relates to a method for operating a hydraulic apparatus of a transmission device. 
     BACKGROUND OF THE INVENTION 
     A hydraulic system of a transmission for a vehicle having a variable displacement pump designed with a variable output is known from DE 10 2004 008 611 A1; a pilot pressure can be applied to the adjustment device of the pump in order to vary the output, and the pump can generate a changeable flow of hydraulic fluid for the appropriate supply of different consumers of the transmission. Furthermore, the hydraulic system is designed with at least two pressure circuits arranged on the discharge side of the variable displacement pump that are prioritized differently regarding the supply of hydraulic fluid by the pump. Hydraulic fluid is applied directly by the variable displacement pump to a primary pressure circuit with higher priority. In order to limit the pressure of the primary pressure circuit, a pressure control valve that is able to connect the secondary pressure circuit is provided between the discharge side of the variable displacement pump and a lower-priority secondary pressure circuit. In order to control the output of the variable displacement pump as a function of the operating status, a pressure return is configured between the discharge side of the variable displacement pump and the adjusting device of the variable displacement pump. 
     If a change in the operating status in the transmission device is required because a greater volume of hydraulic fluid is needed in the transmission device than is currently being provided by the variable displacement pump in the area of the primary pressure circuit and/or the secondary pressure circuit, the pressure decreases in the primary pressure circuit and/or the secondary pressure circuit, and the variable displacement pump is adjusted to provide greater output by the overall force component impinging on the region of the adjusting device. 
     Disadvantageously, however, the adjustment of the output of the variable displacement pump does not occur until during the change of the operating condition; therefore, the transmission device cannot be operated with the desired spontaneity. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is therefore to provide a method for operating a hydraulic device of the transmission by means of which a transmission device may be actuated with the desired degree of spontaneity. 
     During the method according to the invention for operating a hydraulic device of a transmission having a variable displacement pump that can be supplied with a hydraulic pressure to vary the output in the area of an adjusting device, and having at least two pressure circuits that may be connected to the discharge side of the variable adjustment pump and that are assigned different priorities regarding the supply of hydraulic fluid by the pump, with a pressure control valve being provided between a higher-priority pressure circuit and a lower-priority pressure circuit that is able to connect the lower-priority pressure circuit for the purpose of limiting the pressure of the higher-priority pressure circuit, with a pressure return being provided downstream of the discharge side of the variable displacement pump in the direction of the adjustment device of the variable displacement pump in order to adjust the output of the variable displacement pump as a function of the operating status, if a change in the operating status of the transmission is needed that requires increasing the output of the variable displacement pump relative to the current output, the pressure applied in the region of the adjusting device by the pressure return is correspondingly modified before the change to the operating status. 
     When the operating state needs to change in the transmission device, the output of the variable displacement pump is increased to a specific level using the method according to the invention before changing to the operating state characterized by a need for a greater volume of hydraulic fluid, whereby the transmission device is supplied during the entire change of the operating state with the volume of hydraulic fluid necessary to change the operating state without delay, and the transmission device can be operated with the desired high level of spontaneity. 
     The features indicated in the claims as well as the features indicated in the following exemplary embodiments of the subject matter of the invention are suitable for developing the subject matter of the invention by themselves or in any combination with each other. The combination of a given set of features does not represent a restriction on the development of the subject matter of the invention and is only essentially representative in nature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional advantages and advantageous embodiments of the subject matter of the invention can be found in the claims and subsequent exemplary embodiments, the principle of which is described with reference to the drawing; for the sake of clarity, the same reference characters are used for components with the same design and function in the description of the different embodiments. 
       They show: 
         FIG. 1A  highly schematic circuit diagram of a first embodiment of a hydraulic device having three pressure circuits with different priorities and a pressure return that is operated according to the invention; 
         FIG. 2  A representation of a second embodiment of a hydraulic device corresponding to  FIG. 1 ; 
         FIG. 3  A circuit diagram of another exemplary embodiment of a hydraulic device in which a valve unit of an adjusting device of a variable displacement pump is designed as a control valve; 
         FIG. 4  A representation of another embodiment of a hydraulic device corresponding to  FIG. 3 ; 
         FIG. 5  Another hydraulic device that can be operated according to the invention; and 
         FIG. 6  Another embodiment of a hydraulic device that can be actuated according to the invention; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a circuit diagram of a hydraulic device  1  of a transmission device (not shown) for a vehicle. The hydraulic device  1  comprises a variable displacement pump  2  that is designed with a variable output and that can be supplied with a hydraulic pressure p_B in order to vary the output in the region of an adjusting device  3 . Two pressure circuits PK and SK are arranged on the discharge side of the variable displacement pump  2  that have different priorities with regard to the supply of hydraulic fluid by the pump. In order to limit the pressure p_PK of the primary pressure circuit PK, a pressure control valve  4  is provided between the higher-priority pressure circuit PK—or the primary pressure circuit—and the lower-priority pressure circuit SK—or the secondary pressure circuit that can connect the lower-priority secondary pressure circuit SK or in the region of which the primary pressure circuit PK may be connected to the secondary pressure circuit SK. In the region of an interface S 1 , consumers are supplied with pressure p_PK from the primary pressure circuit PK and actuated depending on the operating status. 
     In order to adjust the output of the variable displacement pump  2  as needed, a pressure return  5  is provided downstream of the discharge side of the variable displacement pump  2  that branches toward the adjusting device  3  of the variable displacement pump  2  in the area of the pressure control valve  4 . Furthermore, a valve  6  is provided downstream of the pressure control valve  4 , in the region of which a flow q_KS of a third pressure circuit TK, or cooling and lubricating fluid circuit may be adjusted. 
     The variable displacement pump  2  is designed in the present case as a vane pump whose adjusting ring  7  can be supplied in the region of an effective area  26  with the pressure p_B that is applied via the pressure return  5  and resisted by a spring device  8  acting on another effective area  26 . Depending on the current application, the variable displacement pump  2  can also have another suitable pump design with an adjustable displacement volume. 
     The spring force of the spring device  8  is applied to the adjusting ring  7  of the variable displacement pump  2  such that the variable displacement pump  2  is pivoted toward high outputs when the hydraulic pressure p_B of the pressure return  5  is low, with the variable displacement pump  2  or its output being increasingly reduced against the spring force of the spring device  8  when the values of the hydraulic pressure p_B are high. 
     Upstream of the variable displacement pump  2 , a line L 1  branches from the pressure return  5  toward a valve device  9  of the adjusting device  3 , the pressure return  5  being connected, via the line L 1 , to a low-pressure area  12  via a first aperture  10  or a second aperture  11  depending on a switch position of the valve device  9 , the low-pressure area being upstream of the fluid pan for the transmission device. The valve device  9  designed as a switching valve  9  in the embodiment of the hydraulic device  1  according to  FIG. 1  is supplied in the region of an effective area  13  with a pilot pressure p_VS 15  by a pressure adjuster  15  against a spring device  14 , with the line L 1  in the switching device of the valve device  9  shown in  FIG. 1  being connected, via the first aperture  10 , to the low-pressure area  12 . 
     If the valve device  9  or its valve spool  27  is moved proceeding by the pilot pressure p_VS 15  of the pressure adjuster  15  from its first switching position into its shifted second switching position against the spring device  14 , the line L 1  is connected, via the second aperture  11 , to the low-pressure area  12 . The aperture diameter of the first aperture  10  is greater in the present case than the aperture diameter of the second aperture  11 , whereby a larger leakage flow flows out of the pressure return  5  through line L 1  toward the low-pressure area  12  when the first aperture  10  is open than is the case when the second aperture  11  is opened on the valve device side. 
     In order to operate a transmission device designed with the hydraulic device  1  according to  FIG. 1  at a high level of efficiency over the entire operating range and simultaneously make the variable displacement pump  2  available with a highly dynamic output adjustment, the valve device  9  is moved into its second switching position in which the line L 1  is connected, via the smaller aperture, or second aperture  11 , to the low-pressure area  12  when the transmission device or a vehicle drivetrain designed with the transmission device is in static mode, during which a lower flow of hydraulic fluid is provided by the hydraulic device  1 . 
     During a dynamic change of the operating state during which a high flow volume of hydraulic fluid is provided via the hydraulic device  1  or its variable displacement pump  2  within a short time, the valve device  9  is moved into the switching position shown in  FIG. 1 , and the line L 1  is connected, via the first, larger aperture  10 , to the low-pressure area  12 . Then a higher flow volume of leakage fluid flows, via line L 1 , toward the low-pressure area  12 , and the pressure p_B applied in the area of the adjusting device  3  or at the adjusting ring  7  decreases, at a higher gradient than if the second aperture  11  were open, to a level at which the variable displacement pump  2  is pivoted by the spring device  8  in the direction of higher outputs against the pressure p_B. 
     With a relatively simple design, a dynamic adjustment of the flow of the variable displacement pump  2  is thus achieved as a function of the operating state, and a minimum output of the variable displacement pump  2  is achieved during static operation that only marginally restricts the efficiency of a transmission device, and the transmission device can be operated with an overall high degree of efficiency. 
     The hydraulic device  1  fundamentally maximizes potential economy since only a very small leakage flow arises the area of the pressure return  5  when a transmission device is in static mode, i.e., in particular when the output shaft is at a constant rotational speed, when the main pressure p_PK in the primary pressure circuit PK is substantially constant, when the transmission device is in a mode where it is not shifted, or during an operating state of the vehicle drivetrain in which basically no actions occur in the transmission device that generate a strong need for a high volume of hydraulic fluid. Consequently, when the necessary primary and secondary pressure levels are reached, the variable displacement pump  2  switches to the position in which the output flow is reduced. 
     The pump input power is optimally reduced by minimizing the demand in the area of the secondary pressure circuit SK of the hydraulic device  1  in addition to the demand for leakage fluid originating from the pressure return  5  toward the low-pressure area  12 . This is the case, for example, when the amount of cooling and lubricating fluid required in the third pressure circuit TK is minimal at low transmission loads. 
     In order to limit the hydraulic pressure p_B applied to the adjusting device  3  via the pressure return  5  to a maximum above which the functioning of the variable displacement pump  2  would be irreversibly damaged under certain circumstances, a pressure control valve  16  is provided upstream from the variable displacement pump  2  or the adjusting ring  7 , the pressure limiting valve being designed in the present case as a check valve and opening upon a preset pressure threshold, with the pressure return  5  being connected to the low-pressure area  12  in a unrestricted fashion in this region when the pressure-control valve  16  is open. 
     Both the pressure control valve  4  and the valve  6  designed as a combination of a pressure control valve and pressure-reducing valve can be fed a pilot pressure p_VS 15  in the manner shown in  FIG. 1 , the pilot pressure being adjustable in the area of the pressure adjuster  15 , with the pressure p_PK in the primary pressure circuit PK and the pressure p_SK of the secondary pressure circuit SK being adjustable depending on the pilot pressure p_VS 15 . If the hydraulic fluid flow q_KS in the third pressure circuit TK is adjusted independently of the pilot pressure p_VS 15  of the pressure adjuster  15 , a separate pressure adjuster  17  is assigned to the valve  6  and fed the pilot pressure p_VS 17  that is adjustable there, with the connection between the valve  6  and the pressure adjuster  15  then being disconnected. 
     In addition to switching the valve device  9 , the output of the variable displacement pump  2  can also be varied in the hydraulic system  1  according to  FIG. 1  by correspondingly changing the flow of lubricant and cooling fluid q_KS in the third pressure circuit TK; for example, if a change in operating state is needed in the transmission device that requires a greater amount of hydraulic fluid to be provided by the hydraulic device  1  or the variable displacement pump  2 , the pilot pressure p_VS 15  or p_VS 17  is elevated and the flow of coolant and lubricating fluid q_KS is increased. Consequently, more hydraulic fluid is guided from the secondary circuit SK via the valve  6  toward the third pressure circuit TK, and less hydraulic fluid is fed into the pressure return, and the pressure p_B decreases. The variable displacement pump  2  then pivots toward a higher output. 
     The pilot pressure p_VS 15  or p_VS 17  is elevated at a time at which the increased hydraulic fluid flow demand does not yet exist in the transmission device, although such demand is highly probable given the need for changing the operating state. 
     Alternately or additionally, in other versions of the above-described procedure for increasing the output of the variable displacement pump  2  in the exemplary embodiments of the hydraulic device  1  shown in the drawing depending on its present use, a hydraulic fluid consumer is activated in one of the pressure circuits PK, SK, and/or TK and/or a leakage fluid flow is activated in one of the pressure circuits, or simultaneously in a plurality of pressure circuits PK, SK and/or TK, preferably by supplying a consumer, such as a pressure adjuster with leakage, with hydraulic fluid, by elevating a flow of cooling fluid of a startup clutch or a double clutch system or the like, which reduces the flow of hydraulic fluid in the pressure return  5  as well as the pressure p_B. 
     Once the change of the operating state is instigated in the transmission device, the previous need for a greater volume of hydraulic fluid is reduced, for example, by deactivating the consumer that was additionally activated beforehand and/or by reducing the previously increased leakage flow, whereby the elevated delivery rate in the region of the variable displacement pump  2  is fully available for immediately implementing the change in operating state characterized by a need for a greater volume of hydraulic fluid, such as a gear shift during which a hydraulically actuatable shift element within a flow of force in the transmission device is connected by being fed pressure coming from the primary pressure circuit PK. 
     A second embodiment corresponding to  FIG. 1  is shown in  FIG. 2 , the second embodiment of the hydraulic device  1  essentially corresponding to the first embodiment shown in  FIG. 1 . For this reason, only the differences between the two embodiments in  FIG. 1  and  FIG. 2  will be discussed in the following description; with regard to the additional functionality of the hydraulic device  1  in  FIG. 2 , reference is made to the description of  FIG. 1 . 
     The hydraulic device  1  according to  FIG. 2  is designed without the pressure control valve  16  in the area of the pressure return  5 . Furthermore, the valve device  9  of the adjusting device  3  is moved from the switching position shown in  FIG. 2  into its shifted switching position not by the pressure adjuster  15  but by means of another pilot pressure p_VS 18  adjustable in the area of another pressure adjuster  18  to connect to the pressure return  5  to the low-pressure area  12  either via the first aperture  10  or the second aperture  11 . 
     In the third embodiment of the hydraulic device  1  shown in  FIG. 3 , the valve device  9  of the adjusting device  3  is designed as a control valve that can be supplied with the pressure p_B which, in the area of a first effective area  19  of a valve spool  27  of the valve device  9 , is applied by the pressure return  5  and is resisted by a spring device  20 . Downstream of the first effective area  19  of the valve spool  27  of the valve device  9  is a throttle device  21  in the region of which the pressure p_B is reduced by a specific factor, the pressure p_B 21  that is throttled in relation to pressure p_B being applied to a second effective surface  22  of the valve spool  27  of the valve device against which the spring device  20  also impinges. Furthermore, the low-pressure area  12  is provided downstream of the throttle device  21 , whereby the hydraulic fluid guided through the throttle device  21  is discharged in the direction of the low-pressure area  12  as a flow of leakage fluid. 
     The valve device  9  designed with seven control edges  91  to  97  is coupled to the intake side  23  of the variable displacement pump  2  in the region of the fourth control edge  94 , and to the discharge side  24  of the variable displacement pump  2  in the region of the control edges  92  and  96 . The effective surface  25  of the adjusting ring  7  of the variable displacement pump  2  against which the spring device  8  also impinges can be supplied with pressure via the fifth control edge  95  of the valve device  9 , whereas in the area of the other effective surface  26  of the adjusting ring  7  a pressure counteracting the spring device  8  can be applied to the adjusting ring  7  of the variable displacement pump  2  via the third control edge  93  of the valve device  9 . 
     Depending on the overall force component that is applied to the valve spool  27  of the valve device  9  and is adjusted depending on the actuating pressure p_B applied to the first effective surface  19 , the throttled pressure p_B 21  applied to the second effective surface  22 , and the spring force of the spring device  20 , the third control edge  93  is either connected to the second control edge  92  or the fourth control edge  94 , and the fifth control edge  95  is connected to the sixth control edge  96  or fourth control edge  94 . This means that, depending on the position of the valve spool  27 , the effective surface  25  of the adjusting ring  7  is either supplied with the pressure from the intake side  23  or the pressure from the discharge side  24  of the variable displacement pump  2 , whereas the pressure from the discharge side  24  or pressure from the intake side  23  is applied to the effective surface  26  of the adjusting ring  7 . 
     In contrast to the two embodiments of the hydraulic device  1  shown in  FIG. 1  and  FIG. 2 , the hydraulic pressure p_B applied via the pressure return  5  is not directly used to adjust the output of the variable displacement pump  2 . The hydraulic fluid flowing through the pressure return  5  represents a control flow for the valve device  9 , thus making it easy to reduce to a minimum the volume flow of hydraulic fluid flowing through the pressure return  5 . The overall adjusting force that must be applied to the adjusting ring  7  against the spring device  8  in order to adjust the variable displacement pump  2  is taken directly from the discharge side  24  of the variable displacement pump  2  or is set by the pressure applied there, thus enabling the variable displacement pump  2  to operate with a low power loss and high dynamic adjustment. 
     In the third embodiment of the hydraulic device  1  shown in  FIG. 3 , the pressure return  5  branches off of another pressure control valve  28  that is located downstream of the pressure valve  4  and in the region of which the pressure p_SK of the secondary pressure circuit SK is adjusted. As the pressure p_SK of the secondary circuit SK rises, the leakage flow of fluid decreases in the area of the pressure return  5 , and the output of the variable displacement pump  2  increases. 
     The pressure p_SK of the secondary pressure circuit SK is thus lowered in the above-described manner when there is a need to change the operating state in the transmission device for which an increase is anticipated in the volume of hydraulic fluid required from the amount currently provided by the variable displacement pump  2 , by correspondingly actuating an additional valve unit  29  downstream of the additional pressure control valve  28  originating from a pressure adjuster  30  assigned to the valve unit  29  with pilot pressure p_VS 30 , and by means of the associated increase in the lubrication and coolant flow q_KS in the third pressure circuit TK, whereby the variable displacement pump  2  is adjusted toward higher displacement volumes due to the reduced pressure p_B in the pressure return  5  and corresponding actuation of the valve device  9 . 
       FIG. 4  shows a representation of a fourth embodiment of the hydraulic device  1  corresponding to  FIG. 3  that only partially differs from the embodiment of the hydraulic device  1  shown in  FIG. 3  so that essentially only the differences between the hydraulic device  1  in  FIG. 4  and the hydraulic device  1  in  FIG. 3  will be discussed in the following description; in regard to the additional functions, reference is made to the description of  FIG. 3 . 
     The hydraulic device  1  according to  FIG. 4  is designed without the additional pressure control valve  28  of the hydraulic device  1  according to  FIG. 3 , and the valve device  9  is supplied in the area of the second effective surface  22  with the pilot pressure p_VS 15  of the pressure adjuster  15 , by means of which the pressure control valve  4  is also controlled in order to connect the pressure chamber  25  of the variable displacement pump  2  to the intake side  23  or the discharge side  24  of the variable displacement pump  2 , whereas the other pressure chamber  26  is operatively connected to the discharge side  24  or the intake side  23  of the variable displacement pump  2 . As the hydraulic pressure p_B in the pressure return  5  decreases, the output of the variable displacement pump  2  increases. 
     In the exemplary embodiment of the hydraulic device  1  shown in  FIG. 4 , the variable displacement pump  2  itself rather than the pump pressure in the region of the discharge side  24  is used to control the pressure in the secondary pressure circuit SK. In contrast to the embodiment of the hydraulic device  1  according to  FIG. 3 , an additional pressure control valve is not necessary, and the adjusting power for the variable displacement pump  2  is in turn taken directly from the discharge side  24  which is therefore available to a large degree. 
     In comparison to the hydraulic device  1  according to  FIG. 3 , the hydraulic device  1  according to  FIG. 4  can be operated in the region of the pressure return  5  without a leakage fluid volume flow toward the low-pressure area  12 , which allows a transmission device designed with the hydraulic device  1  to be operated over the entire operating range with much greater efficiency in comparison to the hydraulic device  1  according to  FIG. 3 . 
     In the embodiments of the hydraulic device  1  according to  FIG. 3  and  FIG. 4 , the maximum pressure difference can be applied to the variable displacement pump  2  or its adjusting ring  7  in the region of the hydraulic device  1 , namely between the intake pressure of the variable displacement pump  2  and the pressure side of the variable displacement pump  2 . The variable displacement pump  2  can hence be adjusted with maximum dynamics. 
       FIG. 5  and  FIG. 6  show two other embodiments of the hydraulic device  1  that are designed without the valve device  9  in the region of the adjusting device  3 , the design of the hydraulic device  1  according to  FIG. 5  otherwise corresponding to the design of the hydraulic device  1  according to  FIG. 3 , and the hydraulic device according to  FIG. 6  having the same components as the hydraulic device  1  according to  FIG. 1 . 
     The pressure p_B applied via the pressure return  5  in the hydraulic devices  1  according to  FIG. 5  and  FIG. 6  is guided in each case to the effective surface  26  of the adjusting ring  7  of the variable displacement pump  2 , the pressure return  5  upstream of the effective surface  26  being connected, via a throttle device  31 , to the low-pressure area  12 . 
     When a change to the operating state in the transmission device is needed that can only be accomplished to the desired degree with a hydraulic fluid requirement that is elevated in comparison to the hydraulic fluid flow for the current output of the variable displacement pump, the pressure p_B applied to the adjusting ring  7  via the pressure return  5  is suitably reduced before the operating state changes in the manner described in  FIG. 1  to  FIG. 4 , for example, by elevating the coolant and lubricating fluid flow q_KS, or by elevating a leakage in the primary pressure circuit PK or in the secondary pressure circuit SK, and the variable displacement pump  2  is adjusted in the direction of higher outputs so that the transmission device can be operated with the desired degree of spontaneity. 
     REFERENCE CHARACTERS 
     
         
           1  Hydraulic device 
           2  Variable displacement pump 
           3  Adjusting device 
           4  Pressure control valve 
           5  Pressure return 
           6  Valve 
           7  Adjusting ring of the variable displacement pump 
           8  Spring device 
           9  Valve device of the adjusting device 
           10  First aperture 
           11  Second aperture 
           12  Low-pressure area 
           13  Effective surface 
           14  Spring device 
           15  Pressure adjuster 
           16  Pressure control valve 
           17  Pressure adjuster 
           18  Pressure adjuster 
           19  Effective surface 
           20  Spring device 
           21  Throttle device 
           22  Second effective surface 
           23  Intake side of the variable displacement pump 
           24  Discharge side of the variable displacement pump 
           25 ,  26  Effective surface of the adjusting ring of the variable displacement pump 
           27  Valve spool of the valve device 
           28  Additional pressure control valve 
           29  Valve unit 
           30  Pressure adjuster 
           31  Throttle device 
           91  to  97  Control edge 
         L 1  Line 
         q_KS Coolant and lubricating fluid 
         PK Primary pressure circuit 
         p_B Hydraulic pressure 
         p_B 21  Throttled hydraulic pressure 
         p_PK Pressure 
         p_SK Pressure 
         p_VS Pilot pressure 
         q_KS Hydraulic fluid volume flow 
         S 1  Interface 
         SK Secondary pressure circuit 
         TK Third pressure circuit