Abstract:
A power-assisted gear shifting device ( 118 ) for a multi-speed step-change transmission ( 102 ) having a step-down design. The power-assisted gear shifting device ( 118 ) comprises a plurality of auxiliary units. Each one of the auxiliary units comprises a plurality of valves ( 4, 5, 6, 7 ), a shift cylinder ( 1 ), a piston ( 2 ) and a gear shifting element ( 2 A). Each one of the shift cylinders ( 1 ) accommodates one piston ( 2 ) which is axially movable along a guiding rail ( 9 ) by hydraulic fluid controlled by the plurality of valves ( 4, 5, 6, 7 ). The piston ( 2 ) is connected to a gear shifting element ( 2 A) which facilitates torque transmission.

Description:
FIELD OF THE INVENTION 
     The invention relates to a gear shifting device for a multi-speed step-change transmission. 
     BACKGROUND OF THE INVENTION 
     EP O 541 035 discloses a gear shifting device for multi-speed step-change transmissions having valves and shift cylinders in which pistons actuated by a control fluid are located. Shift rods are attached to the shift cylinders which via gear shifting elements act upon parts of the transmission to create a torque-transmitting connection. A shift rod actuates here parts that belong to an auxiliary unit. 
     The shift rods have great weight which unfavorably contributes to the total weight of the transmission and must be accelerated or decelerated by the gear shifting device upon each gear shifting operation. 
     The problem on which this invention is based is to disclose a gear shifting device which eliminates the disadvantages of existing gear shifting devices. 
     SUMMARY OF THE INVENTION 
     It is proposed to provide for each auxiliary unit of a step-change transmission one unit comprising the valves, shift cylinders, pistons and gear shifting elements. Contrary to gear shifting devices known already, this whole gear shifting device sits in the immediate proximity of the auxiliary unit. An auxiliary unit is preferably comprised of two gear wheels disposed side by side in the transmission and can be alternately engaged in the torque transmission. An auxiliary unit, however, can only consist of one engageable gear wheel in the torque transmission when, e.g. two gear wheels opposite each other need not be engaged when shifting to a reverse gear ratio. 
     By virtue of a compact unit arrangement, it is possible to eliminate connecting elements between the gear shifting elements, preferably formed by shift forks or shift levers, and the shift cylinders and pistons. As already mentioned, such connecting elements are essentially shift rods made of steel which, to a great extent, contribute to the total weight of the transmission. The reaction times between the command that triggers a gear shift and the movement of the gear shifting elements are abbreviated by the elimination of the bulky shift rods to be moved, it is an advantageous development thereby it is possible to use the pulsed 2/2 way valves as triggering valves. It is thus possible, when engaging the gear wheels in a torque-transmitting connection, to adapt shifting force and shifting time. The adaptation preferably consists in the valves being loaded at a higher frequency when engaging than when disengaging the connection. In another advantageous development the pulsed valves are operated with a voltage amounting to a multiple of the standard voltage of the valve. To adapt the pulsed valves, a displacement measuring device is advantageously used, which indicates the actual position of the piston in relation to the shift cylinder. The displacement measuring device is preferably placed within the shift cylinder, but it can also be provided in a position outside the shift cylinder, where it is connected with the movable part of the unit. 
     In another advantageous development, the piston of the gear shifting unit is situated upon a piston rod, upon which it is axially movable. On the piston rod, it is possible to provide, without hindering each other, the pistons of the gear shifting units of several auxiliary units. The units for each auxiliary unit are preferably disposed in a row. 
     In another advantageous development, several gear shifting units, of which each gear shifting unit belongs to a respective auxiliary unit, are comprised in one part. The part can be assembled separately from the transmission and then be adapted and attached to the transmission as a unit. This also makes it possible to separately produce and test a complete gear shifting device independent of the type of transmission concerned. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In another advantageous development, the gear shifting units have stop which dampen the impact of the pistons on the edges of the shift cylinders. The stops can be provided within the shift cylinder or also outside on a part of the gear shifting units connected with the piston. The invention is described in detail with the aid of drawings. The drawings show: 
     FIG. 1 is a transmission with gear shifting devices; 
     FIG. 2 is an arrangement of gear shifting devices in a row; and 
     FIG. 3 is a representation of a gear shifting device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 diagrammatically shows a representation of a transmission  102  in a vehicle (not shown here). The transmission  102  has a clutch bell housing  104 , a main gear  106  and an auxiliary gear  108 , in addition to an input shaft  110  and an output shaft  112  with output flange  114 . On the main gear  106  is provided one part  116 . In the arrangement shown here, part  116  shows three separate gear shifting devices  118 ,  120  and  122 . The gear shifting device  118 , shown by way of example, engages with a shift fork  124  in a sliding sleeve  126  which is axially movable along a shaft  128  and non-rotatably connected with the shaft  128 . By displacement of the sliding sleeve  126 , it can be connected either with the gear wheel  130  or the gear wheel  132  to create a torque transmission. The gear shifting devices  118 ,  120  and  122  are connected with a control device  136 , via electric lines  134 , such as an electronic transmission computer or a vehicle master. The gear shifting devices  118 ,  120  and  122  are likewise connected via lines  140  with a pressure source  138  for a control fluid. 
     FIG. 2 shows a segment of the housing of transmission  102  where, in a part  116 , are comprised the gear shifting devices  118 ,  120  and  122 . The part  116  is fastened to the transmission  102  by means of connecting elements  144 . To the gear shifting devices  118 ,  120  and  122 , lead lines  140 , for supply of the control fluid, and electric lines  134 , for connection with the control device  136 . 
     FIG. 3 shows a fundamental representation of a gear shifting device  18  for an automatic transmission in vehicles with displacement measuring devices and pulse-sensitive directional valves in longitudinal section, which has one shift cylinder  1  formed by two parts  1 A and  1 B and one piston  2 . 
     The moved weights can be considerably reduced by the configuration of shift cylinder  1  in two parts  1 A and  1 B. 
     In the embodiment shown, the piston  2 , designed as a gear shifting element, moves between the fixed cylinder parts  1 A and  1 B. 
     The piston  2  is designed in one piece with a shift fork  2 A whereby connecting elements between piston  2  and one other gear shifting element such as the shift fork  2 A or a possible shift lever are not needed. The connection between piston  2  and shift fork  2 A is thus sturdy and designed with the shortest path. 
     In another design (not shown), it is possible in the exact same manner that cylinder parts  1 A and  1 B be connected with shift fork  2 A, the cylinder parts  1 A and  1 B carrying out the movement relative to piston  2 . 
     As a result of the constructionally very advantageous design of shift cylinder  1 , namely, in a divided design consisting of two parts  1 A and  1 B, the cylinder parts  1 A and  1 B can thus serve as gear shifting elements, whereby a variable configuration of the transmission is possible. 
     To detect the position of piston  2  in shift cylinder  1 , or between cylinder parts  1 A and  1 B, according to FIG. 3, displacement measuring device  3  is attached parallel to the displacement axis of piston  2 , such as inductive path sensors, which are connected with a control device  136 , which, depending on the position of piston  2  detected by the inductive path sensors, relays electronic control signals to pulse-sensitive valves  4 ,  5 ,  6  and  7 . 
     The piston  2  has a guide shoulder  2 B by which it is led into a recess  8  formed in each one of the cylinder parts  1 A and  1 B. Both the cylinder parts  1 A and  1 B and piston  2  are situated around a rail  9  which extends axially through cylinder parts  1 A and  1 B and the piston  2  in the direction of movement of piston  2 . 
     The arrangement of the cylinder parts  1 A and  1 B of shift cylinder  1  and of piston  2  on rail  9  has a main advantage that thereby a row of shift cylinders can be easily situated in a small space, especially the reduced number of parts and the easy assembly bringing decisive cost advantage. The control for all gear shifting devices of a transmission can in principle be attached to said rail  9 . 
     Referring to FIG. 3, the cylinder parts  1 A and  1 B are installed firmly preassembled, but obviously they can also be fixed in an installed state depending on the tolerances of the vehicle. 
     To shift piston  2  in shift cylinder  1 , a pneumatic or hydraulic pressure medium is fed from an external pressure source  138 , via pressure lines  10  and  11 . In each pressure line  10  and  11 , two electromagnetic 2/2-way valves  4 ,  5  and  6 ,  7  are interposed, which control the through flow of the pressure medium through pressure lines  10  and  11  in such a manner the piston  2  moves at a speed corresponding to an optimal speed found empirically or via a simulation in this path position. The mode of valve control can be adapted specifically to the transmission depending on the weights to be shifted. 
     The pulse-sensitive valves  4 ,  5 ,  6  and  7  are designed for a continuous operation at 4 volts but here are operated with 24 volt pulses. Due to control of the pulse vales  4 ,  5 ,  6  and  7  with strong current pulses, they react very quickly. The pulse valves  4 ,  5 ,  6  and  7  are controlled, via the control device  136 , depending on the position of piston  2  in shift cylinder  1 , that has been detected by displacement measuring device  3 . According to the position of the piston  2 , different electric pulses are delivered to pulse valves  4 ,  5 ,  6  and  7 , the pulse valves opening with a pre-defined high pulse frequency and closing with a pre-defined low pulse frequency. Thus in shift cylinder  1 , the through flow of pressure medium is changed, which sets in motion piston  2  in shift cylinder  1 , and therewith also changes the speed of piston  2  during the gear shifting operation. The control of pulse valves  4 ,  5 ,  6  and  7  is so designed that all pulse-sensitive valves can be controlled separately, against each other or with each other. Thereby different speeds result for the piston and thus also different dynamic forces. 
     To illustrate the mode of operation of the gear shifting device, a shifting cycle is described in principle. 
     If in a gear shifting operation, the pressure medium is supplied through line  10  to the gear shifting device, pulse valve  5 , which has the function of a feed valve, opens, while pulse valve  4 , designed as drain valve, closes. The pressure medium thus reaches, via line  10 , through the cylinder part  1 A, into the working chamber  12  of piston  2 , and moves piston  2 , from stop surface  13  on cylinder part  1 A, in the direction of stop surface  14  in the cylinder part  1 B, lying opposite the stop surface  13 . 
     At the beginning of a transmission synchronization phase, shortly before its impact on stop surface  14 , piston  2  remains in a locked position, the pressure medium load of piston  2  considerably increasing due to the further supply of pressure medium through line  10 . 
     The portion of the piston working chamber  12  that lies in the direction of movement of piston  2 , is relieved during the whole gear shifting operation via pressure line  11 , and open valve  6 , designed as a drain valve. At the same time, pulse valve  7 , that serves to supply the pressure medium, is closed. 
     At the end of the synchronization process, piston  2  is unlocked whereby it sets moving again in the direction of its end position on stop surface  14 , doing this at higher speed due to the high pressure medium load during the synchronization process. The existing position of piston  2  is detected by the displacement measuring device  3 , which via electric pulses, controls pulse valves  6  and  7  in a manner such that pulse valve  6 , serving as a vent, is closed, with the result that a so-called cushion of pressure medium drastically reduces the movement of piston  2  on the last short path portion to stop surface  14 . The pressure supply, via pulse valve  5  to pressure line  10 , has already been adjusted during or toward the end of the brief stoppage of piston  2 , during the synchronization phase of the transmission, by closing feed valve  5 . To bring piston  2  to its end position, despite the pressure-medium cushion between piston  2  and stop surface  14 , pulse valve  6  is shifted to an open position, by the displacement measuring device  3 , immediately before the impact of piston  2  on stop surface  14 , so that the pressure medium located between piston  2  and stop surface  14  can escape via pressure line  11 , and so piston  2  not spring back when its strikes on stop surface  14 . 
     For reversing, the shift cycle is the same, in the inverse direction, pulse valves  5  and  6  are closed, the gear shifting device is loaded with pressure via pressure line  11  and open valve  7 , and relieved via open pulse valve  4  and pressure line  10 . 
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 Reference numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 shift cylinder 
                 106 
                 main gear 
               
               
                 1A 
                 cylinder part 
                 108 
                 auxiliary transmission 
               
               
                 1B 
                 cylinder part 
                 110 
                 input shaft 
               
               
                 2 
                 piston 
                 112 
                 output shaft 
               
               
                 2A 
                 shift fork 
                 114 
                 output flange 
               
               
                 2B 
                 guide shoulder 
                 116 
                 gear shifting device 
               
               
                 3 
                 displacement measuring device 
                 118 
                 gear shifting device 
               
               
                 4 
                 pulse-sensitive valve 
                 120 
                 gear shifting device 
               
               
                 5 
                 pulse-sensitive valve 
                 122 
                 gear shifting device 
               
               
                 6 
                 pulse-sensitive valve 
                 124 
                 shift fork 
               
               
                 7 
                 pulse-sensitive valve 
                 126 
                 sliding sleeve 
               
               
                 8 
                 recess 
                 128 
                 shaft 
               
               
                 9 
                 guiding rail 
                 130 
                 gear wheel 
               
               
                 10 
                 pressure line 
                 132 
                 gear wheel 
               
               
                 11 
                 pressure line 
                 134 
                 line 
               
               
                 12 
                 working chamber of the piston 
                 136 
                 control device 
               
               
                 13 
                 stop surface 
                 138 
                 pressure source 
               
               
                 14 
                 stop surface 
                 140 
                 line 
               
               
                 102 
                 transmission 
                 144 
                 connecting element 
               
               
                 104 
                 clutch bell housing