Abstract:
The invention concerns an automated transmission, for example a multi-stage motor-vehicle shift transmission, with at least one controllable actuating drive provided as a gear actuator ( 26 ) to engage and disengage a gear of the transmission or as a clutch actuator ( 7 ) to engage and disengage an associated automated engine clutch, and an automated friction clutch, for example an automated engine clutch arranged in the drivetrain of a motor vehicle between a drive engine and a transmission, with a controllable actuating drive provided as the clutch actuator ( 7 ) for engaging and disengaging the friction clutch. 
     To improve the controllability and achieve a longer service life while reducing production costs, it is proposed to use as the actuating drive ( 7, 26 ) a pneumatic muscle ( 8, 8.1, 8.2 ) with a hose body ( 9 ) made of a fluidically impermeable and elastic material with a lattice network ( 10 ) of tension-resistant fibers arranged in the outer area on the hose body ( 9 ), and with end pieces ( 11   a,    11   b ) that close off the hose body ( 9 ) axially at its ends.

Description:
[0001]    This application is a national stage completion of PCT/EP2006/011024 filed Nov. 17, 2006, which claims priority from German Application Serial No. 10 2005 055 210.2 filed Nov. 19, 2005. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns an automated shift transmission, in particular a multi-stage motor vehicle shift transmission, with at least one controllable actuating drive provided as a gear actuator to engage and disengage a gear of the transmission or as a clutch actuator to engage and disengage an associated automated engine clutch. 
         [0003]    The invention also concerns an automated friction clutch, in particular an engine clutch arranged in the drivetrain of a motor vehicle between a drive engine and a transmission with a controllable actuating drive provided as the clutch actuator for engaging and disengaging the friction clutch. 
       BACKGROUND OF THE INVENTION 
       [0004]    In motor vehicles of both the passenger and commercial vehicle sectors, the use of automated transmissions is increasing, due to their relatively low weight, compact dimensions and high transmission efficiency resulting from their automated shift processes, they offer great operating comfort and, by using corresponding ecological shift control programs, they reduce the fuel consumption of the vehicle concerned. Associated with each automated transmission there is on the drive unit side thereof, as the engine clutch, an automated friction clutch usually made as a single disk dry clutch which, for starting and shift processes, is automatically engaged or disengaged by an associated clutch actuator. 
         [0005]    Semi-automatic transmissions are also known in which gearshifts are carried out directly by the driver by way of shift actuating and shift transfer elements such as a shift lever, shift linkages and transmission-internal shift shafts and shift bars, while the engine clutch upstream therefrom on the drive input side is automatically actuated, i.e., disengaged or engaged, by a clutch actuator in coordination with the shift process. 
         [0006]    Until now the actuating drives used are mainly hydraulic or pneumatic operating cylinders and electric motor or electromagnetic drives. Although operating cylinders that can be actuated by a pressure medium, via associated controlled magnetic valves, are indeed tried, tested and fully developed, their operating principle is such that because of a pre-filling phase and a long signal chain from the associated electronic control unit through the magnetic valve to the operating cylinder concerned, their response behavior is relatively poor, which can be unfavorable for the control of rapid shift processes. 
         [0007]    Although it is true that electric actuating drives show fundamentally more rapid response behavior, owing to the marked hysteresis behavior associated with the magnetization, they are not suitable for rapid changes of the direction of movement. All these actuating drive structures have in common that they are relatively heavy; they entail high production costs because they contain numerous high-precision mechanical components and, since they incorporate running and sealing surfaces and/or rotary bearings affected by friction, they have a service life limited because of wear, and also demand a certain amount of effort and expenditure for maintenance and repair. 
         [0008]    Against this background, the purpose of the present invention is to propose an actuating drive for an automated transmission and an automated friction clutch which, while having a simple and inexpensive structure, shows improved control behavior and has a longer service life. 
         [0009]    This objective is achieved by an automated transmission with at least one controllable actuating drive, which is provided as a gear actuator for engaging and disengaging a gear of the transmission or as a clutch actuator for engaging and disengaging an associated automated engine clutch. In addition, it is provided that the actuating drive is made as a pneumatic muscle with a hose body made of a fluidically impermeable and elastic material with a lattice network of tension-resistant fibers arranged in the outer area on the hose body and with end pieces that close off the hose body at its ends. 
         [0010]    The objective concerning the automated friction clutch is achieved by an automated friction clutch with a controllable actuating drive serving as a clutch actuator for engaging and disengaging the friction clutch. The actuating drive is made as a pneumatic muscle with a hose body made of a fluidically impermeable and elastic material with a lattice network of tension-resistant fibers arranged in the outer area on the hose body and with end pieces that close off the hose body at its ends. 
         [0011]    The lattice network on the hose bodies is preferably made as a diamond-shaped mesh. 
         [0012]    The pneumatic muscle, often called a Fluidic Muscle, has long been known in itself. For example, reference can be made here to EP 0 161 750 B1 by the company Bridgestone and to publications and product descriptions of the company Festo (“Pneumatic muscle works like a real one”, Technische Rundschau [Technical Magazine] 2, 2003, page 12). Such pneumatic muscles, however, have never so far been used in the automotive sector. But there is nothing to prevent the use of pneumatic muscles in motor vehicles if an appropriately oil- and gasoline-resistant elastomeric plastic is used for the hose body. 
         [0013]    The function of the pneumatic muscle is based on the fact that when a pressure medium, such as compressed air, flows into the hose body, the latter expands radially and, due to the effect of the relatively inextensible fibers of the lattice network, it becomes axially shorter. By virtue of this effect, a controlled feed of the pressure medium can produce a comparatively large tensile force, far greater than that of a pneumatic operating cylinder of comparable size. 
         [0014]    Furthermore, the pneumatic muscle operates largely without friction and, therefore, shows very good response behavior without stick-slip effects. Since there are no friction-affected, articulation bearings and sealing surfaces, the pneumatic muscle is completely maintenance-free in operational service and has a very long service life. Compared with hydraulic and pneumatic operating cylinders and with electric-motor or electromagnetic actuating drives, the pneumatic muscle is considerably lighter and can also be produced more cheaply. 
         [0015]    The closed structure of the pneumatic muscle is particularly well suited for difficult service conditions, such as exposure to dirt and water. Since heavy commercial vehicles are, in any case, provided with compressed air units, the pneumatic muscle can be used in such vehicles without much effort, i.e., both simply and inexpensively. The lattice network, preferably with a diamond-shaped mesh, can be arranged over the outside wall of the hose body as described in EP 0 161 750 B1 or it can be embedded in the material of the hose body as in the MAS pneumatic muscle from the Festo Company. 
       SUMMARY OF THE INVENTION 
       [0016]    Thanks to the large actuating force it produces and its rapid response behavior, the pneumatic muscle is particularly suitable as a clutch actuator for an automated engine clutch made as a dry clutch actuated by way of a release lever, via a release bearing, that acts in opposition to a contact pressure spring (membrane spring). For this the pneumatic muscle is expediently arranged on the tension side of the release lever, orientated substantially parallel to the movement direction of the release bearing with its end piece on the lever side articulated to the release lever and with its end piece opposite from the lever attached on the housing side. In such a case, the actuating path of the pneumatic muscle extends with a suitable lever ratio, between full engagement of the friction clutch in the rest position and full disengagement of the clutch. 
         [0017]    However, the pneumatic muscle is also suitable as a gear actuator of an automatic transmission, for example in a motor vehicle. Thus, in the case of a shift mechanism having two shift positions and that can be actuated, via an operating sleeve, by way of a shift element made as a gearshift fork or shift rocker, the pneumatic muscle can be arranged substantially parallel to the movement direction of the operating sleeve on the tension side of the shift element relative to a neutral position with its end piece on the shift element side connected to the element and with its end piece facing away from the element attached on the housing side. 
         [0018]    In this way, the concerned operating sleeve can be shifted back and forth by the pneumatic muscle, between two positions in which the gear is disengaged or engaged respectively. Since the pneumatic muscle is a purely tensioning element, the return of the operating sleeve to the neutral position, when the muscle is not pressurized, is expediently accomplished by a restoring spring, which can be a compression spring arranged on the same side of the shift element or as a tension spring arranged on the opposite side of the shift element. 
         [0019]    In the case of a corresponding shift mechanism having three shift positions, it is advantageous to arrange two pneumatic muscles, one on each side of the shift element and orientated substantially parallel to the movement direction of the operating sleeve, each with its end piece on the element side connected to the shift element and its end piece facing away from the element attached on the housing side. The operating sleeve can then be moved between the shift positions G1 (first gear engaged), N (neutral, gears disengaged) and G2 (second gear engaged) so that the disengagement of a gear advantageously takes place, respectively, when the (engaging) muscle is unpressurized in addition to the elastic effect of the hose body concerned and the muscle on the opposite side is pressurized, which substantially accelerates the disengagement. 
         [0020]    In a further preferred embodiment of a shift mechanism having two shift positions and that can be actuated via an operating sleeve by a shift rocker, the shift rocker is solidly attached to a tilt lever orientated substantially parallel to the movement direction of the operating sleeve and able to pivot about a pivot axis orientated normal to the said direction. 
         [0021]    In this case, the pneumatic muscle is arranged on the tension side of the tilt lever a distance away from the pivot axis relative to a neutral position, orientated substantially normal to the movement direction of the operating sleeve, with its end piece on the lever side articulated to the tilt lever and with its end piece remote from the lever attached on the housing side. The operating sleeve concerned can be moved by the pneumatic muscle, between the shift positions N (neutral, gear disengaged) and G (gear engaged), and the desired force and path ratio can be produced by an appropriate choice of the lever ratio, between the tilt lever and the shift rocker. 
         [0022]    In a corresponding shift mechanism with three shift positions and a shift rocker again solidly attached to a tilt lever orientated substantially parallel to the movement direction of the operating sleeve and able to pivot about a pivot axis orientated normal or perpendicularly to the direction, it is preferable to arrange respective pneumatic muscles with opposite action directions opposite one another, a distance away from the pivot axis and orientated essentially normal to the movement direction of the operating sleeve. The end pieces of these pneumatic muscles are each articulated to the tilt lever on the side facing the lever and attached on the housing side at the ends remote from the tilt lever. 
         [0023]    In this case, the two pneumatic muscles can optionally be arranged relative to the shift rocker on the same side of the tilt lever and relative to the pivot axis at opposite ends of the tilt lever, i.e., both on the side of the tilt lever facing towards or facing away from the transmission shaft. 
         [0024]    In another embodiment, the two pneumatic muscles can be arranged relative to the shift rocker on opposite sides of the tilt lever and relative to the pivot axis at the same end of the tilt lever, i.e., on a side of the tilt lever facing towards the transmission shaft and a side of the tilt lever facing away from the transmission shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
           [0026]      FIG. 1A  is a schematic representation of a clutch actuator device with the clutch engaged; 
           [0027]      FIG. 1B  is the clutch actuator of  FIG. 1A  with the clutch disengaged; 
           [0028]      FIG. 2A  is a schematic representation of a shift mechanism with two shift positions, the gear being disengaged; 
           [0029]      FIG. 2B  is the shift mechanism of  FIG. 2A  with gear engaged; 
           [0030]      FIG. 3A  is a schematic representation of a first shift mechanism having three shift positions, the gears being disengaged; 
           [0031]      FIG. 3B  is the shift mechanism of  FIG. 3A  with one gear engaged; 
           [0032]      FIG. 4A  is a schematic representation of a second shift mechanism having three shift positions, the gears being disengaged, and 
           [0033]      FIG. 4B  is the shift mechanism of  FIG. 4A  with one gear engaged. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    A clutch actuator mechanism  1 , represented in  FIGS. 1A and 1B , for a single-disk dry clutch with membrane spring (not shown in more detail), comprises a release lever  2  mounted at one end to pivot on a pivot bearing  3  fixed to a housing, engaged approximately in the middle by way of two carrier bolts  4  arranged radially opposite one another with a release bearing  6  mounted to move axially on a guide sleeve  5  fixed to the housing, and connected at its other end to a clutch actuator  7 . 
         [0035]    The clutch actuator  7  is made as a pneumatic muscle  8  with an elastic hose body  9 , with a diamond-meshed lattice network  10  made of tension-resistant fibers arranged in the outer area on the hose body  9 , and with end pieces  11   a ,  11   b  that close off the hose body  9  at its ends. The pneumatic muscle  8  is arranged on the tension side of the release lever  2 , orientated substantially parallel to a movement direction  12  of the release bearing  6 , with its end piece  11   b  articulated to the release lever  2  and with its end piece  11   a  remote from the lever attached solidly to a supporting component  13  fixed onto the housing. The end piece  11   a , remote from the lever, is provided with a fitting  14  for the connection of a pressure hose  15  coming from a compressed air supply. Opposite the muscle  8 , a tension spring  16  is arranged and connected at one end to the release lever  2  and at the other end to the supporting component  13 . 
         [0036]      FIG. 1A  shows the engaged, actuating-force-free condition of the clutch actuator mechanism  1  in which the release bearing  6  is in its rest position E, the membrane spring is stressed and the friction clutch is, therefore, fully engaged or closed. In this condition, the pneumatic muscle  8  is not pressurized. 
         [0037]    In  FIG. 1B , the disengaged condition of the clutch actuator mechanism  1  is shown in which the release bearing  6  is in a disengaging position A, the membrane spring is not stressed and the friction clutch is, therefore, fully disengaged or open. For this, the pneumatic muscle  8  has been filled with a pressure medium, in particular compressed air, whereby the hose body  9  has been expanded radially and becomes axially shorter because of the action of the lattice network  10 . This results in an axial actuating force  17  which, as a releasing force, has pivoted or moved the release lever  2  and thus also the release bearing  6  against a restoring force  18  of the membrane spring to the disengaging position A. The friction clutch can be engaged again when the pressure in the muscle  8  is released, essentially due to the restoring force of the membrane spring and also the restoring force of the tension spring  16  that acts as a restoring spring. 
         [0038]    In contrast,  FIGS. 2   a  and  2   b  show a shift mechanism  19 . 1  of a transmission (not shown in more detail), which comprises a shifting fork  21  attached solidly to a shift bar  20 . By way of two carrier bolts  22 , arranged radially opposite one another, the shifting fork  21  is engaged with a shifting sleeve  24  mounted to move axially on a transmission shaft  23 . The fork  21  has two shift positions N in which an associated gear is disengaged, and G, in which the gear concerned is engaged. 
         [0039]    The shift bar  20  is directed parallel to the transmission shaft  23  and is mounted to move axially in two radial bearings  25   a ,  25   b  fixed on the housing. On the tension side of the shifting fork  21 , relative to a neutral position N of the shifting sleeve  24 , is arranged a gear actuator  26  made as a pneumatic muscle  8 , which is orientated substantially parallel to a movement direction  27  of the shifting sleeve  24 , with its end piece  11   b  on the fork side connected to the shift bar  20  and with its end piece  11   a , remote from the fork, solidly attached to a holding fixture  28  fixed on the housing. The end piece  11 , a remote from the fork, is provided with the fitting  14  for the connection of the pressure hose  15  from a compressed air supply. Between the shifting fork  21  and the radial bearing  25   a  on the drive side, a compression spring  29  is arranged on the shift bar  20 . 
         [0040]      FIG. 2A  shows the actuation-force-free, neutral condition of the shift mechanism  19 . 1  in which the shifting sleeve  24  is in the neutral position N, in which the associated gear is disengaged. 
         [0041]      FIG. 2B  shows the shift condition of the shift mechanism  19 . 1  in which the shifting sleeve  24  is in a shift position G in which the associated gear is engaged. For this, the pneumatic muscle  8  has been activated by filling with a pressure medium, in particular compressed air, whereby the hose body  9  has been made shorter and the axial actuating force  17  has been produced under the effect of which the shifting sleeve  24 , by way of the shift bar  20  and the shifting fork  21 , has been moved out of the neutral position N to the shift position G and the gear concerned has consequently been engaged. This has also stressed the compression spring  29 . The gear is disengaged again when the pressure in the muscle  8  is released, essentially due to the restoring force  18  of the compression spring  29  acting as a restoring spring. 
         [0042]    In a second preferred embodiment, according to  FIGS. 3   a  and  3   b , a shift mechanism  19 . 2  comprises a shift rocker  30  mounted in a bearing component  31  fixed on the housing to pivot about a pivot axis  32  positioned normal to the movement direction  27  of a shifting sleeve  24 ′, being engaged by way of two carrier bolts  22  with the shifting sleeve  24 ′ mounted to move axially on the transmission shaft  23 , and being connected with two pneumatic muscles  8 . 1 ,  8 . 2  which constitute the gear actuator  26 . 
         [0043]    The shifting sleeve  24 ′ has three shift positions, G 1  in which a first gear is engaged, G 2  in which a second gear is engaged and the central, neutral position N in which both gears are disengaged. The two pneumatic muscles  8 . 1  and  8 . 2  are arranged on either side of the shift rocker  30 , each orientated substantially parallel to the movement direction  27  of the shifting sleeve  24 ′, in such a manner that the respective end pieces  11 . 1   b  and  11 . 2   b , facing the rocker, are articulated to the shift rocker  30  and end pieces  11 . 1   a ,  11 . 2   a , remote from the rocker, are attached to the bearing component  31 . The end pieces  11 . 1   a ,  11 . 2   a  remote from the rocker are provided with respective fittings  14 . 1  and  14 . 2  for the connection of pressure hoses  15 . 1  and  15 . 2  from a compressed air supply. 
         [0044]      FIG. 3A  shows the actuating-force-free, neutral condition of the shift mechanism  19 . 2  in which the shifting sleeve  24 ′ is in the neutral position N and both of the associated gears are disengaged. 
         [0045]      FIG. 3B  shows the shift condition of the shift mechanism  19 . 2 , in which the shifting sleeve  24 ′ is in shift position G 2 , in which the second gear concerned is engaged. For this, the diagonally opposite pneumatic muscle  8 . 1  has been activated by filling with compressed air, whereas the other muscle  8 . 2  is still unpressurized. The axial shortening of the hose body  9  of the opposite muscle  8 . 1  produces an axial actuating force  17  under the effect of which the shifting sleeve  24 ′ has been moved by way of the shift rocker  30  from the neutral position N to the shift position G 2  so that the second gear has been engaged. During this, the other muscle  8 . 2  has been elastically extended, whereby a restoring force  18 ′ has been produced. The second gear can be disengaged when the pressure in the muscle  8 . 1  is released, solely due to the restoring force  18 ′ of the other muscle  8 . 2 , but this is expediently brought about much more rapidly by pressurizing the muscle  8 . 2 . 
         [0046]    In a further preferred embodiment of a shift mechanism  19 . 3 , shown in  FIGS. 4A and 4B , a shift rocker  30 ′ is connected solidly to a tilt lever  33  which is orientated substantially parallel to the movement direction  27  of the shifting sleeve  24 ′ which has three shift positions (G 1 , N, G 2 ) and which is mounted to pivot together with the shift rocker  30 ′ about a pivot axis  32  positioned approximately centrally and directed normal to the direction in a bearing component  31 ′ fixed on the housing. 
         [0047]    At its two ends, opposite one another relative to the shift rocker  30 ′, the tilt lever  33  is respectively connected to pneumatic muscles  8 . 1 ,  8 . 2  constituting a gear actuator  26 , the muscles  8 . 1  and  8 . 2  each being orientated substantially perpendicularly to the movement direction  27  of the shifting sleeve  24 ′, being articulated to the tilt lever  33  by their end pieces  11 . 1   b ,  11 . 2   b  on the lever side, and being attached to the bearing component  31 ′ by their respective end pieces  11 . 1   a  and  11 . 2   a  remote from the lever. The end pieces  11 . a  and  11 . 2   a  remote from the lever are each provided with fitting  14 . 1  and  14 . 2  for the connection of the pressure hose  15 . 1 ,  15 . 2  from a compressed air source. 
         [0048]      FIG. 4A  shows the actuating-force-free, neutral condition of the shift mechanism  19 . 3  in which the shifting sleeve  24 ′ is in the neutral position and both of the associated gears are disengaged. 
         [0049]      FIG. 4B  shows the shift condition of the shift mechanism  19 . 3  in which the shifting sleeve  24 ′ is in shift position G 2  in which the second gear is engaged. For that purpose, this time the pneumatic muscle  8 . 2 , arranged on the side of shift position G 2 , has been activated by filling with compressed air, whereas the other muscle  8 . 1  is still left unpressurized. Owing to the axial shortening of this hose body  9  of the muscle  8 . 2  concerned an axial actuating force  17  is produced, under whose effect the shifting sleeve  24 ′ has been moved by the tilt lever  33  and the shift rocker  30 ′ from the neutral position N to shift position G 2  so that the second gear has been engaged. The other muscle  8   x   1  has been elastically extended, whereby the restoring force  18 ′ has been produced. The second gear can be disengaged again by releasing the pressure in the muscle  8 . 2  and by the restoring force  18 ′ of the other muscle  8 . 1  alone, although this muscle  8 . 1  is expediently controlled essentially by pressurizing it. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Reference numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 clutch actuator mechanism 
               
               
                   
                  2 
                 release lever 
               
               
                   
                  3 
                 pivot bearing 
               
               
                   
                  4 
                 carrier bolts 
               
               
                   
                  5 
                 guide sleeve 
               
               
                   
                  6 
                 release bearing 
               
               
                   
                  7 
                 clutch actuator 
               
               
                   
                  8 
                 pneumatic muscle 
               
               
                   
                  8.1 
                 pneumatic muscle 
               
               
                   
                  8.2 
                 pneumatic muscle 
               
               
                   
                  9 
                 hose body 
               
               
                   
                 10 
                 lattice network 
               
               
                   
                 11a 
                 end piece 
               
               
                   
                 11.1a 
                 end piece 
               
               
                   
                 11.2a 
                 end piece 
               
               
                   
                 11b 
                 end piece 
               
               
                   
                 11.1b 
                 end piece 
               
               
                   
                 11.2b 
                 end piece 
               
               
                   
                 12 
                 movement direction (of 6) 
               
               
                   
                 13 
                 supporting component 
               
               
                   
                 14 
                 connection fitting 
               
               
                   
                 14.1 
                 connection fitting 
               
               
                   
                 14.2 
                 connection fitting 
               
               
                   
                 15 
                 pressure hose 
               
               
                   
                 15.1 
                 pressure hose 
               
               
                   
                 15.2 
                 pressure hose 
               
               
                   
                 16 
                 tension spring 
               
               
                   
                 17 
                 axial actuating force 
               
               
                   
                   
                 (due to 8, 8.1, 8.2) 
               
               
                   
                 18 
                 restoring force (due to 16, 29) 
               
               
                   
                 18′ 
                 restoring force (due to 8.1, 8.2) 
               
               
                   
                 19.1 
                 shift mechanism 
               
               
                   
                 19.2 
                 shift mechanism 
               
               
                   
                 19.3 
                 shift mechanism 
               
               
                   
                 20 
                 shift bar 
               
               
                   
                 21 
                 shifting fork 
               
               
                   
                 22 
                 carrier bolts 
               
               
                   
                 23 
                 transmission shaft 
               
               
                   
                 24 
                 shifting sleeve 
               
               
                   
                 24′ 
                 shifting sleeve 
               
               
                   
                 25a 
                 radial bearing 
               
               
                   
                 25b 
                 radial bearing 
               
               
                   
                 26 
                 gear actuator 
               
               
                   
                 27 
                 movement direction (of 24, 24′) 
               
               
                   
                 28 
                 holding fixture 
               
               
                   
                 29 
                 compression spring 
               
               
                   
                 30 
                 shift rocker 
               
               
                   
                 30′ 
                 shift rocker 
               
               
                   
                 31 
                 bearing component 
               
               
                   
                 31′ 
                 bearing component 
               
               
                   
                 32 
                 pivot axis 
               
               
                   
                 33 
                 tilt lever 
               
               
                   
                 A 
                 shift position 
               
               
                   
                   
                 (of 6; clutch disengaged) 
               
               
                   
                 E 
                 shift position 
               
               
                   
                   
                 (of 6; clutch engaged) 
               
               
                   
                 G 
                 shift position 
               
               
                   
                   
                 (of 24; gear engaged) 
               
               
                   
                 G1 
                 shift position 
               
               
                   
                   
                 (of 24′; first gear engaged) 
               
               
                   
                 G2 
                 shift position 
               
               
                   
                   
                 (of 24′; second gear engaged) 
               
               
                   
                 N 
                 shift position 
               
               
                   
                   
                 (of 24, 24′; gear/gears 
               
               
                   
                   
                 disengaged)