Abstract:
A transmission having a plurality of shifting elements which are selectively engaged and disengaged when a gearshift is carried out, and a plurality of gearsets which, depending on the shifting position of the shifting elements produce a defined transmission ratio, and a shifting oil system which supplies the shifting elements with oil in order to operate them and a cooling and lubricating oil system which supplies assemblies of the transmission with oil for cooling and/or lubricating. From the shifting oil provided by the shifting oil system, a partial stream of oil can be tapped off for cooling and/or lubricating the shifting elements, such that a quantity of cooling and lubricating oil that is or can be supplied by the cooling and lubricating oil system can be reduced to the quantity required for cooling and/or lubricating those assemblies of the transmission which do not contain the shifting elements.

Description:
This application claims priority from German patent application serial no. 10 2013 212 428.7 filed Jun. 27, 2013. 
     FIELD OF THE INVENTION 
     The invention concerns a transmission of a motor vehicle. In addition the invention concerns a method for operating a motor vehicle transmission. 
     BACKGROUND OF THE INVENTION 
     A motor vehicle transmission comprises a plurality of shifting elements and a number of gearsets, such that in each engaged gear of the transmission a first number of shifting elements are closed or engaged and a second number of shifting elements are open or disengaged. Depending on the shifting positions of the shifting elements and hence depending on the gear engaged, the gearsets of the transmission produce a defined gear ratio. The shifting elements of such a transmission can be in the form of frictional shifting elements such as clutches and/or brakes, or in the form of interlocking shifting elements such as claws. Furthermore, a transmission of a motor vehicle comprises a shifting oil system and a cooling and lubricating oil system. By means of the shifting oil system, the shifting elements can be acted upon with shifting oil, to close them. By means of the cooling and lubricating oil system the assemblies of the transmission, for example its gearsets and bearings, can be acted upon by cooling and lubricating oil. 
     In known transmissions the cooling and lubricating oil system of the transmission serves to supply all the assemblies of the transmission with cooling and lubricating oil, in particular the gearsets, bearings and shifting elements. On the other hand the transmission&#39;s shifting oil system serves exclusively to supply the shifting elements with shifting oil. In such transmissions the shifting elements, even when they are closed or open and therefore when they are not undergoing a shifting process, are still permanently or continually supplied by the cooling and lubricating oil system with cooling and lubricating oil, i.e. even at times when relatively little heat energy is being generated at those shifting elements. This continual cooling and lubrication of the shifting elements even when they are in a closed or open condition results in relatively substantial splash losses in the transmission. Moreover, an oil pump that provides the volume flow of the cooling and lubricating oil in the cooling and lubricating oil system has to be relatively large. 
     Transmissions with functionally separate oil systems, i.e. a shifting oil system which serves exclusively to supply the shifting elements with shifting oil and a cooling and lubricating oil system which serves to supply the gearsets, bearings and shifting elements with cooling and lubricating oil, are known from DE 10 2004 027 113A1 and also from DE 10 2011 081 006 A1. 
     SUMMARY OF THE INVENTION 
     Starting from there, the purpose of the present invention is to provide a new type of motor vehicle transmission and a method for its operation. 
     This objective is achieved by a transmission as described below. 
     According to the invention, from the shifting oil supplied by the shifting oil system a partial stream can be tapped off as necessary for cooling and/or lubricating the shifting elements, so that a quantity of cooling and lubricating oil that is or can be provided by the cooling and lubricating oil system can be reduced to the quantity required for cooling and/or lubricating those assemblies of the transmission which do not contain the shifting elements. 
     Since, according to the invention, from the shifting oil supplied by the shifting oil system a partial stream of shifting oil can be tapped off as necessary for cooling and/or lubricating the shifting elements, the cooling and lubricating oil system can be made smaller, in particular with a smaller oil pump. The quantity of cooling and lubricating oil that is or can be provided by the cooling and lubricating oil system is reduced to the quantity required for cooling and/or lubricating those assemblies of the transmission which do not contain shifting elements, i.e. to the maximum quantity of cooling and lubricating oil required for cooling and/or lubricating the gearsets and bearings. If more cooling and lubricating oil is needed, then from the shifting oil supplied by the shifting oil system a partial shifting oil stream can be tapped off as required for cooling and/or lubricating the shifting elements, i.e. whenever this is made necessary by the generation of heat at the shifting elements of the transmission as a result of carrying out shifting operations. Compared with conventional transmissions splash losses in the transmission can be reduced thereby. 
     According to an advantageous further development of the invention, for each shifting element the shifting oil system of the transmission comprises a control valve by way of which the shifting oil required for operating the shifting element concerned can be supplied to it, while the partial stream of shifting oil used for cooling and/or lubricating the shifting element can be tapped off downstream of the control valve concerned from the shifting oil supplied to the shifting element concerned. The partial shifting oil stream used for cooling and/or lubricating can be tapped off from the shifting oil to be supplied or that has been supplied to the shifting element concerned upstream of a shifting piston or shifting oil pressure chamber of the shifting element, or in the area of the shifting piston or shifting oil pressure chamber of the shifting element concerned. This further development of the invention is simple to construct and can be implemented with little design modification of the transmission. 
     In an alternative advantageous further development of the invention, for each shifting element the shifting oil system of the transmission has two control valves connected in parallel, namely a first control valve by way of which the shifting oil required for operating the shifting element concerned can be supplied to it from the shifting oil system, and a second control valve by way of which the shifting oil to be used for cooling and/or lubricating the shifting element can be supplied to it from the shifting oil system. This further development of the invention is also simple to construct, but it entails a design modification in the area of the control valves of the shifting oil system of the transmission. 
     Preferably, the partial stream of shifting oil used for cooling and/or lubricating the shifting element concerned can be tapped off from the shifting oil at least while the shifting element is undergoing a shifting operation. If necessary, however, the partial shifting oil stream used for cooling and/or lubricating the shifting element concerned can also be tapped off from the shifting oil even after the shifting process of the shifting element. When a partial shifting oil stream is tapped off for cooling or lubricating the shifting element concerned even after the shifting operation of the shifting element, the shifting element can also be cooled and/or lubricated beyond the actual shifting operation itself. 
     In an advantageous further development a rotational element is associated with each shifting element to promote a uniform distribution of the partial shifting oil stream tapped off from the shifting oil. 
     The method according to the invention is also described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred further developments of the invention emerge from the description given below. Example embodiments of the invention, to which it is not limited, are explained in greater detail with reference to the drawing, which shows: 
         FIG. 1 : An example of a gearset and shifting element layout of a transmission; 
         FIG. 2 : A shifting oil system of a transmission according to the invention; 
         FIG. 3 : An alternative shifting oil system of a transmission according to the invention; 
         FIG. 4 : A detail of a transmission according to the invention in the area of a shifting element; and 
         FIG. 5 : An alternative detail of a transmission according to the invention in the area of a shifting element. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a transmission layout of an example of an automatic transmission of a motor vehicle, wherein a drive aggregate (not shown) can be coupled to a transmission input  1  of the automatic transmission and a drive output of the motor vehicle (not shown) can be coupled to a transmission output  2  of the automatic transmission. 
     The automatic transmission illustrated in  FIG. 1  has a total of eight shafts  3 ,  4 ,  5 ,  6 ,  7 ,  8 ,  9  and  10 , the shaft  3  being a transmission input shaft and the shaft  4  being a transmission output shaft. The shafts  3  to  10  of the automatic transmission in  FIG. 1  are in driving connection, on the one hand by way of gearsets  11 ,  12 ,  13  and  14  and on the other hand by way of transmission-internal shifting elements A, B, C, D and E. 
     The automatic transmission in  FIG. 1  has four gearsets  11 ,  12 ,  13  and  14  and five shifting elements A, B, C, D and E, the shifting elements A and B being in the form of brakes and the shifting elements C, D and E being clutches. With the automatic transmission shown in  FIG. 1  a total of eight forward gears and one reversing gear can be engaged, such that in each of these gears three shifting elements at a time are closed and two shifting elements are open. 
     The transmission layout in  FIG. 1  is shown purely as an example. In addition to frictional shifting elements, interlocking shifting elements can also be present. 
     To carry out a gearshift and thus to carry out a shifting operation, at least one of the previously open shifting elements A, B, C, D and E is opened or disengaged and at least one of the previously closed shifting elements is opened or disengaged. To supply the shifting elements A, B, C, D and E as necessary with the shifting oil they require when undergoing a shifting operation, namely when a shifting element is being engaged or closed, the automatic transmission comprises a shifting oil system  15 . 
     By virtue of the shifting oil system  15 , the shifting elements A, B, C, D and E can be acted upon with shifting oil as necessary to close them, in such manner that each of the shifting elements A, B, C, D and E, of which in  FIG. 2  only the shifting elements A, B, C and D are shown, can be acted upon individually with shifting oil from a central shifting oil line  16  by way of a control valve  17  specifically associated with the shifting element concerned. When shifting oil is needed at the shifting element A, the control valve associated with the shifting element A is opened in order to supply the shifting element A with shifting oil, as necessary, from the central shifting oil line  16 . Thus, from the central shifting oil line  16  a shifting element-specific shifting oil line  18  branches off toward each of the shifting elements, which line  18  is connected to the central shifting oil line  16  when the control valve  17  is open and is cut off from the central shifting oil line  16  when the control valve  17  is closed. 
     In addition to the shifting oil system  15 , the automatic transmission has a cooling and lubricating oil system (not shown), by means of which assemblies of the automatic transmission can be supplied with cooling and lubricating oil for their cooling and/or lubrication. 
     According to the invention, from the shifting oil provided by the shifting oil system  15  a partial stream can be tapped off in the area of each of the shifting elements A, B, C, D and E as necessary for cooling and/or lubricating the shifting elements A, B, C, D and E. A quantity of cooling and lubricating oil that is or can be supplied from the cooling and lubricating oil system can be reduced to the maximum quantity required for cooling and/or lubricating those assemblies of the transmission which do not contain the shifting elements A, B, C, D or E. 
     The cooling and lubricating oil supplied by the cooling and lubricating oil system (not shown) can be used for cooling and/or lubricating the gearsets  11 ,  12 ,  13  and  14  of the automatic transmission, for cooling and/or lubricating the bearings of the automatic transmission and for cooling and/or lubricating the shifting elements A, B, C, D and E of the automatic transmission. 
     If the cooling and lubricating oil required for cooling and/or lubricating the above assemblies of the automatic transmission is larger than the quantity of cooling and lubricating oil that can be provided by the cooling and lubricating oil system, then from the shifting oil supplied by the shifting oil system  15  a partial shifting oil stream is tapped off as necessary for cooling and/or lubricating the shifting elements A, B, C, D and E, and this is done for whichever shifting element or shifting elements where heat energy is actually being generated. 
     In the example embodiment shown in  FIG. 2 , in which the shifting oil system  15  comprises an individual control valve  17  for each shifting element, the partial shifting oil stream used for cooling and/or lubricating the shifting element concerned can be tapped off downstream of the corresponding control valve  17  from the shifting oil supplied to the shifting element concerned, namely according to  FIG. 2  upstream of the shifting element A, B, C, D or E concerned, from the shifting element-specific shifting oil line  18  leading to the shifting element concerned. 
     Thus, as shown in  FIG. 2 , downstream of the control valve  17  and upstream of the shifting element concerned a shifting element-specific cooling and lubricating line  19  branches off from the shifting element-specific shifting oil line  18  leading to the shifting element concerned, by way of which line  19  the partial shifting oil stream tapped off can be supplied to the shifting element concerned for its cooling and/or lubrication. 
       FIG. 4  illustrates a variant of the invention in which the partial shifting oil stream used for cooling and/or lubricating can be tapped off from the shifting oil being supplied to the shifting element concerned, in the area of the shifting element.  FIG. 4  shows a partial cross-section through an automatic transmission in the area of one of the shifting elements A, B, C, D or E. The shifting element A, B, C, D or E is in the form of a disk packet with outer disks  20  and inner disks  21 , such that the outer disks  20  and the inner disks  21  of the disk packet can be pressed together by applying a control pressure to a shifting piston  22  of the shifting element concerned in order to close the shifting element. The shifting oil required for closing the shifting element is supplied to the shifting piston  22  of the shifting element by way of a shifting element-specific shifting oil line  18  leading to the shifting element, wherein a shifting oil pressure chamber  33  that co-operates with the shifting piston  22 , into which chamber the shifting oil is fed, in delimited by the shifting piston  22  and a disk carrier  25  and by two seals  23  and  24  which seal the shifting piston  22  relative to a housing or disk carrier  25 . 
     If the shifting element is a clutch, the assembly  25  is a disk carrier. If the shifting element is a brake, the assembly  25  is a housing. 
     As shown in  FIG. 4 , a bore is formed in the shifting piston  22 , which branches off from the shifting oil pressure chamber  33  of the shifting piston  22  delimited by the seals  23 ,  24 , so that via the bore  26 , from the shifting oil supplied to the shifting piston  22  a partial stream can be tapped off, which then serves for cooling and/or lubricating the shifting element concerned. 
     As shown in  FIG. 4 , the bore  26 , which passes through the shifting piston  22 , opens into a bore  27  in a ring gear  28  of the transmission, so that by way of this bore  27 , in the ring gear  28  the partial stream tapped off from the shifting oil can be delivered to the shifting element concerned for cooling and/or lubricating it. 
     In the variant shown in  FIG. 4  as well, as in the variant shown in  FIG. 2 , a respective control valve  17  is associated with each shifting element, but in contrast to  FIG. 2  the partial shifting oil stream is tapped off from the shifting oil not upstream of the shifting element concerned, but rather, in the area of the shifting element, namely in the area of the shifting piston  22  or the shifting oil pressure chamber  33  thereof. 
     In the variant of the invention shown in  FIG. 4  the shifting piston  22  and the disk carrier  25 , which together with the seals  23  and  24  define the shifting oil pressure chamber  33  of the shifting element concerned, are configured in such manner that although the partial shifting oil stream used for cooling and/or lubricating the shifting element can be tapped off from the shifting oil via the bore  26  formed in the shifting piston  22  during the shifting process of the shifting element concerned, this cannot be done after the actual shifting process. That is because in the area in which the bore  26  opens into the shifting oil pressure chamber  33  the shifting piston  22  has a projection  29  which, after the displacement of the shifting piston  22  brought about by applying the control pressure, co-operates with a corresponding projection  30  on the disk carrier  25  so as to block off the bore  26 , preventing any further partial stream from being tapped off from the shifting oil. In contrast, in the variant shown in  FIG. 5  the projections  29  and  30 , respectively on the shifting piston  22  and the disk carrier  25 , are absent so that in  FIG. 5 , even after the actual shifting operation a partial stream can be tapped off from the shifting oil in the shifting piston  22  for cooling and/or lubricating the corresponding shifting element. 
     In each case the bore  26  in the shifting piston  22  has dimensions such that it acts as a throttle, so that via the shifting oil line  18  of the shifting element concerned, a larger shifting oil quantity is passed to the shifting piston  22  of the shifting element than the quantity of shifting oil tapped off via the bore  26  in the shifting piston  22  for cooling and/or lubricating the shifting element. 
     It should be mentioned that in the shifting piston  22  of a shifting element more than one bore  26  can be formed in order to tap off the partial stream of shifting oil. 
     In an advantageous further development of the invention, the shifting element illustrated in  FIGS. 4 and 5  can be associated with a rotation element for the uniform distribution of the partial stream tapped off from the shifting oil, in order to distribute the shifting oil tapped off for cooling and/or lubricating the shifting element concerned in a uniform manner. In the example embodiments shown in  FIGS. 4 and 5 , a rotation element of such type is preferably accommodated in a free space  31  formed between the ring gear  28  and the shifting piston  22 , between the bores  26  and  27 . 
       FIG. 3  shows a variant of a shifting oil system  15  of a transmission according to the invention, in which two control valves  17 ,  32  connected in parallel are associated with each shifting element. A first control valve  17  serves as necessary for the operation of the shifting element, namely for supplying shifting oil from the central shifting oil line  16  to the shifting element concerned by way of the shifting element-specific shifting oil line  18 . By way of a second control valve  32  connected parallel to the first control valve  17 , the shifting element concerned can be supplied from the central shifting oil line  16 , as necessary, with a partial stream of shifting oil for cooling and/or lubrication, namely via a shifting element-specific cooling and/or lubricating line  19 . Accordingly, in the variant shown in  FIG. 3  as well each shifting element is cooled and/or lubricated as necessary from the shifting oil system  15 , namely by means of a partial stream tapped off from the shifting oil, although in contrast to the variant shown in  FIG. 2 , in the variant in  FIG. 3  two control valves  17  and  32  connected in parallel are provided for each shifting element. These control valves  17  and  32  connected in parallel can be individual control valves, or a dual control valve. 
     In  FIG. 3 , if the opening times of the control valves  17 ,  32  connected in parallel are identical, then each of the shifting elements can be supplied as necessary with the partial stream tapped off from the shifting oil for cooling and/or lubricating the shifting element, both while the shifting process is in progress and also after the actual shifting operation itself. 
     By making the opening time of the control valve  32  shorter, in the variant shown in  FIG. 3  it is also possible to supply the shifting element concerned with a partial stream tapped off from the shifting oil for cooling and/or lubricating the shifting element, exclusively during the actual shifting operation itself. 
     Accordingly, by virtue of the present invention shifting elements of an automatic transmission can be cooled and lubricated as necessary, and this from the shifting oil system  15 , in such manner that from the shifting oil supplied for operating the shifting element concerned a partial stream is tapped off, which is then used for cooling and/or lubricating the shifting element. 
     The cooling and lubricating oil system provides a quantity of cooling and lubricating oil which is the maximum needed for cooling and/or lubricating those assemblies of the transmission which do not contain the shifting elements. If a total quantity of cooling and lubricating oil required for cooling and/or lubricating is larger than the quantity that is or can be supplied by the cooling and lubricating oil system, then the shifting elements are supplied with cooling and lubricating oil from the shifting oil system, namely in that, as necessary for the shifting element concerned, a partial stream of shifting oil is tapped off for cooling and/or lubricating the shifting element concerned. In this way splash losses in the transmission can be reduced. 
     The partial shifting oil stream can be tapped off for cooling and/or lubrication both during and after the closing, and also both during and after the opening of the shifting element A, B, C, D or E concerned, for cooling and/or lubricating the shifting element. However, during and after an opening process the pressure in the shifting oil line  18  leading to the shifting element A, B, C, D or E concerned, or the pressure in the respective shifting oil pressure chamber  33 , must be low enough to ensure that the opened shifting element to be cooled does not close again. If a shifting piston  22  is acted upon by a restoring spring  34 , the actuation force for the shifting piston  22 , which depends on the pressure in the respective shifting oil pressure chamber  33 , must be smaller than the restoring force of the restoring spring  34 . 
     INDEXES 
     
         
           1  Transmission input 
           2  Transmission output 
           3  Shaft 
           4  Shaft 
           5  Shaft 
           6  Shaft 
           7  Shaft 
           8  Shaft 
           9  Shaft 
           10  Shaft 
           11  Gearset 
           12  Gearset 
           13  Gearset 
           14  Gearset 
           15  Shifting oil system 
           16  Shifting oil line 
           17  Control valve 
           18  Shifting oil line 
           19  Cooling and/or lubricating line 
           20  Outer disks 
           21  Inner disks 
           22  Shifting piston 
           23  Seal 
           24  Seal 
           25  Disk carrier/Housing 
           26  Bore 
           27  Bore 
           28  Ring gear 
           29  Projection 
           30  Projection 
           31  Free space 
           32  Control valve 
           33  Shifting oil pressure chamber 
         A Shifting element/Brake 
         B Shifting element/Brake 
         C Shifting element/Clutch 
         D Shifting element/Clutch 
         E Shifting element/Clutch