Abstract:
In a module system for manufacturing variants of two and three stable positions fluid-operated actuators a cylinder housing of both variants of two and three stable positions actuators are manufactured from a blank, including at least one opening for the cover and being identical for the variants of said two and three stable position actuator, and being at least prepared for the arrangement of:
       a first pressure duct,   a second pressure duct, and   a first cylinder diameter of the cylinder housing, thus decreasing manufacturing costs.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to actuators operated by fluid pressure, and more particularly to a manufacturing module system for having variants thereof with two and three stable positions. 
         [0002]    Fluid-operated actuators, that is, actuators that are operated with fluid pressure are widely used. Some examples are hydraulic cylinders in excavators and pneumatic cylinders in production automation equipment. In transmissions for heavy trucks and buses, pneumatic actuators are often used for automation, fully or in part, of the gear shifting. 
         [0003]    Simplified, a simple fluid-operated actuator is composed of a cylinder housing, at least one cover and a piston that is fixedly connected to a piston rod. The piston is located inside the cylinder housing and cover. Thereby two pressure chambers are created, one on each side of the piston. A sealing arrangement allows a difference in pressure between these chambers. By applying fluid pressure in either chamber, force is applied on the piston that will urge to move. The cylinder housing and cover allow axial motion of the piston and piston rod between two end positions. These end positions will be referred to as stable positions. They correspond to equilibrium positions when fluid pressure is applied in either chamber. 
         [0004]    For special purposes, more complex fluid-operated actuators have been developed. More than two stable positions have been achieved by means of more chambers and additional coaxial pistons. These additional pistons have a limited axial motion possible relative to both the cylinder housing and the piston rod. 
         [0005]    A typical transmission for a heavy truck is shown in EP1035357. In order to achieve a large number of useful gear ratios with a limited number of gearwheels, the transmission is composed of three main functional units; a splitter section 34, a main section 35 and a range section 38. The splitter section provides two possible paths of transmitting the power from an input shaft 2 to a countershaft 4. Which of these paths that is active is determined by a double-acting tooth clutch (“synchronised coupling”) 12. The main section 35 provides several possible paths of transmitting the power from the countershaft 4 to a main shaft (“intermediate shaft”) 3. A number of tooth clutches 18, 20 and 32 can be engaged, one at a time, to make these paths active. Finally, the range section 38 can be regarded as a two-speed gearbox that is connected in series with the main section 35. The range section has a speed reduction gear, normally referred to as low range, and a direct gear, high range, that has no speed change. The position of a tooth clutch sleeve 44 determines which range gear that is active. 
         [0006]    In most heavy truck transmissions, the splitter section and the range section are operated by pneumatic actuators. Conventionally, the tooth clutch in the splitter section has two stable positions, one for each of said paths. Likewise, the range section tooth clutch conventionally has two stable positions, one for high range and one for low range. Thus, in the conventional case the splitter section and the range section can each be operated by a simple pneumatic actuator that has two stable positions. 
         [0007]    In recent years, solutions have been presented that would make it advantageous in some cases to use a middle, neutral, position in the splitter section or the range section. EP1035357 presents a splitter section with a neutral position that is used to reduce the risk of damaging the transmission at some inappropriate shifts. However, such a device would not be necessary for some designs of gear lever and shift pattern for the main section. Neither would it be required for automated variants of the transmission in question. 
         [0008]    Furthermore, EP1055845 presents a range section that has a neutral position. This is used to reduce the effort at manual main section shifts, and it enables the use of smaller and less costly tooth clutches. It would also facilitate the use of simple centrifugal clutches, like the one presented in US-2004/0262115, since the clutch does not need to be disengaged during a main section shift. However, the shift time might increase, and the use in automated variants can be questioned. 
         [0009]    In conclusion, splitter sections and range sections with a neutral position may not be used in all variants of a heavy truck transmission family. In some cases, it would make sense to use the simpler conventional design with two stable positions and no neutral position. 
         [0010]    So, there is a need for a way to enable variants with two or three stable positions of fluid-operated actuators in a cost-efficient way. According to an aspect of the present invention, substantially the same blank is used for the cylinder housings of the actuator variants with two and three stable positions. In a first embodiment the invention is characterized in that said blank comprises at least one opening for said cover and that it is identical for said variants of said two and three stable position actuator, and that the blank is at least prepared for the arrangement of:
       a first pressure duct,   a second pressure duct and   a first cylinder diameter of said cylinder housing.       
 
         [0014]    It can be noted that the cylinder housing in general is a large and fairly expensive part whose blank requires a complex and costly tool. The cylinder housing blank can be, for instance, cast, forged, extruded, pressed or injection moulded. The blank will be finished to a cylinder housing by means of operations like milling and honing of cylinder and sealing surfaces, drilling of access ducts to the pressure chambers, and making fastening arrangements for the cover. If the same blank can be used for different actuator variants, the costs for tooling can be reduced, and higher production volumes of the blank can be achieved. According to another embodiment of the invention it is also possible that at least one of said first and second pressure ducts and said first cylinder diameter are finally produced with same set of tools creating same dimensions for said at least one of said first and second pressure ducts and said first cylinder diameter respectively in both said two and three stable position variants. According to a further developed embodiment of the invention the same set of tools can be used in both said two and three stable position variants, thus creating same dimensions for said first and second pressure duct and said first cylinder diameter respectively for all variants. 
         [0015]    In a preferred embodiment, the actuator is an integrated part of an actuator unit that comprise, for instance, sensors, other actuators and valves that control the flow of pressurised fluid to the pressure chambers. The cylinder housing is part of a large housing whose blank requires very high tooling costs. Thereby, it is of particular advantage to avoid variants of the blank. 
         [0016]    In another preferred embodiment, the variant with three stable positions is designed with a main piston, which is fixedly attached to the piston rod, and a ring piston with limited axial motion relative to the main piston. There are three cylinder-piston system diameters, one small between said main and ring pistons, one larger for the main piston alone, and one even larger for the ring piston alone. This largest diameter is identical to the cylinder-piston diameter of the variant with two stable positions. This gives a compact design with substantially equal actuator strokes between the end positions for the variants with two and three stable positions. 
         [0017]    In still another preferred embodiment, there is a ring-shaped protrusion in the cover for the variant with three stable positions. The inner periphery of this protrusion serves as the outer part of a cylinder-piston system for the main piston and one of the pressure chambers. A duct between the inner and outer peripheries form a part of the supply duct to said pressure chamber. The outer periphery of the protrusion also forms part of sealing devices between an intermediate chamber, said supply duct and the ambient air. With this design, the required different cylinder-piston diameters are achieved in a convenient way. 
         [0018]    In yet another preferred embodiment, on said outer periphery between said supply duct and said intermediate chamber, the sealing device has a larger diameter than the cylinder-piston system diameter of the variant with two stable positions. Thereby, said intermediate chamber can have a breathing duct in the cylinder housing that will not risk damaging the sealing device of said large-diameter cylinder-piston system of said ring piston. 
         [0019]    In a further preferred embodiment, the devices that guide and centre the axial motion of said ring piston are axially spaced apart. This will improve the stability of that motion. 
         [0020]    In an additional preferred embodiment, the breathing duct for the intermediate chamber is located in the cover. Thereby, the cylinder housing can be the same for both two and three stable position variants. 
         [0021]    In an alternative preferred embodiment, the breathing duct is located in the main piston and piston rod. The cylinder housing can be the same for both two and three stable position variants here, too. Moreover, if the main piston is attached to the piston rod with a hollow pin, that pin could be a part of the breathing duct. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention will be exemplified by means of the enclosed drawings. 
           [0023]      FIG. 1  shows a schematic longitudinal section of a typical fluid-operated actuator with two stable positions, which as such is an example of prior art, but which also is part of the inventive module system. 
           [0024]      FIGS. 2   a ,  2   b  and  2   c  show a schematic longitudinal section of a typical fluid-operated prior art actuator with three stable positions in each of these three stable positions. 
           [0025]      FIG. 3  shows an embodiment of the invention with a ring-shaped protrusion on the cover. 
           [0026]      FIG. 4  shows an embodiment of the invention where the ring piston has its guiding devices located at different axial positions and where there is an increased diameter for the sealing device between the intermediate chamber and the pressure duct to the left pressure chamber. 
           [0027]      FIG. 5  shows an embodiment of the invention with modified ring piston and with breathing ducts for the intermediate chamber located in the cover and in the main piston and piston rod. 
           [0028]      FIG. 6  shows an embodiment of the invention where the main piston is attached to the piston rod with a hollow pin that forms a part of the breathing duct for the intermediate chamber. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  shows a simplified longitudinal section of a fluid-operated actuator  101  with two stable positions, which actuator forms a part of the inventive module system and which as such can be regarded as conventional technique, comprising a cylinder housing  102 , piston  103 , piston rod  104  and cover  105 . The cylinder housing  102  and the cover  105  are axially connected in a not showed way. Thereby, the cylinder housing  102 , piston rod  104  and cover  105  will enclose a left pressure chamber  106  and a right pressure chamber  107  on either side of the piston  103 . The cylinder housing  102  has a left supply duct  108  and a right supply duct  109  that are in fluid connection with the left pressure chamber  106  and right pressure chamber  107 , respectively. Valves (not shown) connect the left supply duct  108  and right supply duct  109  to either a pressure supply or to an exhaust of ambient pressure. 
         [0030]    In  FIG. 1  the right supply duct  109  is connected to the pressure supply. Thereby, the right pressure chamber  107  is filled with pressurized fluid and a fluid pressure acts on the piston  103 . The left supply duct  108  is connected to the exhaust, and hence there is ambient pressure in the left pressure chamber  106 . So, the piston  103  and piston rod  104  are urged to move to the left. The leftwards motion is stopped when the left end stop abutment  103   a  of the piston  103  comes into contact with the mating part of the cover  105 . This represents the left stable position of the actuator  101 . Similarly, if the left supply duct  108  were connected to the pressure supply and the right supply duct  109  were connected to the exhaust, then the piston  103  and piston rod  104  would be urged to the right. The right stable position would then be reached when the right end stop abutment  103   b  of the piston  103  is in contact with the mating part of the cylinder housing  102 . 
         [0031]    In order to prevent leakage between the pressure chambers and the surroundings, sealing devices are required. Sealing devices can be of any of different available types, as readily known by a person skilled in the art, for instance elastomeric lip seal type. Furthermore, for proper function the axially moving parts, as the piston  103  and piston rod  104 , need to be centred and kept substantially coaxial with the mating parts of the cylinder housing  102  and cover  105 . This is achieved by means of guiding devices that can be of various types, for instance polymeric guide bands or ball bushings, as would be known by a person skilled in the art. A sealing device may be integrated with a guiding device, but may also be separate. In case of separate, non-integrated, sealing and guiding devices, they may be located close to each other or wide apart. They may even act on different surfaces, as would be recognized by a person skilled in the art. In the figures of the present document, the guiding devices are left out, for simplicity, or can be regarded as integrated in the sealing devices, where appropriate. So, in  FIG. 1  there is a static sealing device  111  (e.g. o-ring or gasket) to prevent leakage between the cylinder housing  102  and cover  105  from the left pressure chamber  106 . Moreover, a left rod sealing device  112  prevents leakage between the cover  105  and piston rod  104 . Similarly, a right rod sealing device  113  prevents leakage between the cylinder housing  102  and piston rod  104  from the right pressure chamber  107 . 
         [0032]    Finally, a piston sealing device  114  on the outer periphery of the piston  103  prevents leakage between the pressure chambers  106  and  107 . 
         [0033]    In the right pressure chamber  107 , the fluid pressure acts on the piston  103  on an effective ring-shaped area defined by a cylinder-piston system diameter  103   d  and a piston rod diameter  104   d . The actuator  101  has its piston rod  104  extending out of the cylinder housing  102  and cover  105  on both sides. This is a general case, designs where the piston rod extends out on one side, only, are also common. In such a case, the pressure in one of the pressure chambers will act on an effective circular area defined by the cylinder-piston system diameter  103   d.    
         [0034]      FIGS. 2   a ,  2   b  and  2   c  show a prior art fluid-operated actuator  210  with three stable positions. A cylinder housing  202  and a cover  205  enclose a main piston  203 , which is fixedly attached to a piston rod  204 , and a ring piston  221 . The cylinder housing  202 , main piston  203  and piston rod  204  enclose a left pressure chamber  206  where the pressure can act on the main piston  203  on an effective ring-shaped area defined by a main cylinder-piston system diameter  203   d  and a piston rod diameter  204   d . The ring piston  221  is located on the outside of an axial extension  203   e  of the main piston  203 . The axial motion of the ring piston  221  is limited by diameter steps in the cylinder housing  202 , main piston  203  and cover  205 . A right pressure chamber  207  is enclosed by the cylinder housing  202 , main piston  203 , piston rod  204 , cover  205 , and ring piston  221 . A pressure in the right pressure chamber  207  will act on the ring piston  221  on an effective ring-shaped area defined by an outer cylinder-piston system diameter  221   d  (between the cylinder housing  202  and ring piston  221 ) and an inner cylinder-piston system diameter  221   i  (between the ring piston  221  and axial extension  203   e  of the main piston  203 ). Furthermore, a pressure in the right pressure chamber  207  will act on the main piston  203  on an effective ring-shaped area defined by the inner cylinder-piston system diameter  221   i  and the main cylinder-piston system diameter  203   d  and a piston rod diameter  204   d . Between the left pressure chamber  206  and the right pressure chamber  207  there is an intermediate pressure chamber  222  enclosed by the cylinder housing  202 , main piston  203  and ring piston  221 . 
         [0035]    The left pressure chamber  206  is in fluid connection with a left supply duct  208 . Similarly, the right pressure chamber  207  is in fluid connection with a right supply duct  209 . Valves (not shown)’ connect the supply ducts  208  and  209  to either a pressure supply or to an exhaust of ambient pressure. The intermediate chamber  222  is not to be pressurized; hence a breathing duct  223  in the cylinder housing  202  connects it to ambient pressure. 
         [0036]    A static sealing device  211  prevents leakage between the cylinder housing  202  and cover  205  from the left pressure chamber  206 . A left rod sealing device  212  prevents leakage between the cylinder housing  202  and piston rod  204 . Similarly, a right rod sealing device  213  prevents leakage between the cover  205  and piston rod  204  from the right pressure chamber  207 . A main piston sealing device  214  on the outer periphery of the main piston  203  prevents leakage between the left pressure chamber  206  and the intermediate chamber  222  at the main cylinder-piston system diameter  203   d . On the ring piston  221  there are two sealing devices that prevent leakage between the right pressure chamber  207  and the intermediate chamber  222 ; an inner ring piston sealing device  215  at the inner cylinder-piston system diameter  221   i  and an outer ring piston sealing device  216  at the outer cylinder-piston system diameter  221   d.    
         [0037]    In  FIG. 2   a  the left pressure chamber  206  is pressurized. The fluid pressure will urge the main piston  203  and piston rod  204  to the right. A right stable position is reached when the right end stop abutment  203   b  of the main piston  203  is in contact with the mating part of the cover  205 . 
         [0038]    In  FIG. 2   b  the right pressure chamber  207  is pressurized. The fluid pressure has urged the main piston  203  and piston rod  204  to a left stable where the left end stop abutment  203   a  of the main piston  203  is in contact with the mating part of the cylinder housing  202 . 
         [0039]    Finally, in  FIG. 2   c  both the left pressure camber  206  and right pressure chamber  207  are pressurized. A middle stable position is thereby reached when the ring piston  221  mates with a housing diameter step abutment  202   a  in the cylinder housing  202  and with a piston diameter step abutment  203   a  on the main piston  203 . The pressure in the left pressure chamber  206 , acting between diameters  203   d  and  204   d , cannot alone push the main piston  203  to the right of this position, since that would lift the ring piston  221  off the housing diameter step abutment  202   a . That motion would be counteracted by the pressure in the right pressure chamber  207  that acts on the larger area between diameters  221   d  and  204   d . Analogously, a motion of the main piston  203  to the left of the middle stable position would axially separate the ring piston  221  from the piston diameter step abutment  203   a . Thus, the pressure in the right pressure chamber  207 , acting between diameters  221   i  and  204   d , cannot alone push the main piston  203  left of the middle stable position, since that would be counteracted by the left pressure chamber  206  whose pressure acts on the larger area between diameters  203   d  and  204   d.    
         [0040]      FIG. 3  shows a fluid-operated actuator  301  with three stable positions that is a variant of the plain actuator  101  in  FIG. 1 , and thus part of the inventive module system. The cylinder housing  102   a  has been modified with an additional breathing duct  323  for the intermediate chamber  322 . A cover  305  is fixedly attached to, mated against or, preferably, integral with a ring-shaped protrusion  305   p , whose inner periphery forms the cylinder-piston sealing diameter  303   d  for the left pressure chamber  306  and main piston  303  with sealing device  314 . There is a cover supply duct  305   c  in the cover  305  that provides a fluid connection between the left supply duct  108  and the left pressure chamber  306 . A cover abutment  305   a  defines the middle stable position for a ring piston  321 . Leakage from the supply ducts  108  and  305   c  are prevented by static sealing devices  111  and  111   a . The original cylinder-piston system diameter  103   d  of the cylinder housing  102  serves in the variant  102   a  as the sealing diameter for the static sealing device  111   a  and as the cylinder-piston system diameter for the right pressure chamber  307  and outer sealing device  316  of the ring piston  321 . An inner sealing device  315  acts at cylinder-piston system diameter  321   i  on an extension  303   e  of the main piston  303 . 
         [0041]    The difference between the original cylinder housing  102  of the plain actuator  101  and the cylinder housing  102   a  is minimal. The breathing duct  323  for the intermediate chamber  322  has been added in the cylinder housing  102   a . Thereby, according to the invention, the same blank can be used for both cylinder housings  102  and  102   a . That will save tooling costs and facilitate the use of variants with two and three stable positions. That is especially the case when the cylinder housings  102  and  102   a  are integrated with other parts, for instance a gear-shift control unit in a vehicle transmission, and, hence, would require complex and expensive tooling. 
         [0042]    In the fluid-operated actuator  301  in  FIG. 3  the cylinder-piston system diameter  103   d  of the cylinder housing  102   a  is used for the outer sealing device  316  of ring piston  321  as well as for the static sealing device  111   a . That may facilitate the manufacturing of the cylinder housing blank and the machining thereof. However, edges and burrs may occur where the breathing duct  323  ends at the cylinder-piston system diameter  103   d . This will pose a risk of damaging the outer sealing device  316  at the assembly, when the seal surface will pass over the end of the breathing duct  323 . 
         [0043]    This is solved in the modified actuator  401  in  FIG. 4 , which actuator also forms part of the inventive module system. There, the cylinder housing  102   b  has a larger diameter  102   d  where the breathing duct  423  for the intermediate chamber  422  ends. Hence, the risk of damaging the outer sealing device  316  at the assembly has been reduced greatly. Furthermore, the diameter  102   d  could be used for both static sealing devices  111  and  111   b  between the cover  405  and the cylinder housing  102   b . Then, the static sealing devices  111  and  111   b  could be identical, which would save costs. 
         [0044]    The ring piston  421  in the actuator  401  has been made wider than the corresponding ring piston  321  in  FIG. 3 . Thereby, several advantages have been gained. Firstly, the large cylindrical surface with diameter  103   d  in the cylinder housings  102 ,  102   a  and  102   b  has been used, so the volume of the right pressure chamber  407  has been minimized, which may improve the dynamic performance of the actuator  401 . Secondly, it is no longer possible for the ring piston  421  to move that far to the right from the position in  FIG. 4  that the inner sealing device  315  would no longer be in contact with the extension  303   e  of the main piston  303 . Thirdly, the larger width of the ring piston  421  has made it possible to locate the sealing devices  315  and  316 , with integrated guiding devices, significantly axially apart from each other. That will improve the stability against misalignment for the ring piston  421 . 
         [0045]      FIG. 5  shows a further modified actuator  501  of the variant with three stable positions. Actuator  501  also forms part of the inventive module system. There, the ring piston  521  has been extended axially inside the ring-shaped protrusion  505   p  of the cover  505 . Thereby, the guiding devices are axially located even further apart than the actuator  401  in  FIG. 4 . Moreover, the inner sealing and guiding device has been separated into a pure sealing device  515   s , acting on the inner cylinder-piston system diameter  321   i , and a guiding device  515   g  that acts on the inside of the ring-shaped protrusion  505   p . The guiding device  515   g  thereby acts on the main cylinder-piston system diameter  303   d , which is larger and possibly stiffer than for the corresponding sealing and guiding device  315  in  FIG. 3 . Furthermore, with the ring piston  521  extending axially inside the ring-shaped protrusion  505   p , the sealing device  515   s  will be in contact with the extension  503   e  of the main piston  503  even for the most extreme relative positions of the main piston  503  and ring piston  521 . 
         [0046]      FIG. 5  also shows two alternative breathing ducts for connecting the intermediate chamber  522  to ambient pressure. There is a cover breathing duct  523   c  in the cover  505  and a piston rod breathing duct composed of a mainly radial duct  523   p  in main piston  503  and a mainly axial duct  523   r  in piston rod  504 . With any of these breathing ducts, the cylinder housing  102 , as a finished part, can be identical for actuator variants with two and three stable positions. 
         [0047]      FIG. 6  shows another embodiment of a piston rod breathing duct in an actuator  601  of the variant with three stable positions, which actuator also forms part of the inventive module system. A substantially radial duct  623   p  through the main piston  603  and piston rod  604  is formed, at least in part, by a hollow pin  630  that fixedly connects the main piston  603  to the piston rod  604 . The duct  623   p  is in fluid connection with a substantially axial duct  623   r  in the piston rod  604 . This fluid connection could be achieved with, e.g., a slot or a radial hole  630   h  in the hollow pin  630 . A corresponding ring piston is here numbered  621 . Also in this case the cylinder housing  102 , as a finished part, can be identical for actuator variants with two and three stable positions. 
         [0048]    According to further embodiments of the invention it is also possible that at least one of said first and second pressure ducts and said first cylinder diameter are finally produced with same set of tools creating same dimensions for said at least one of said first and second pressure ducts and said first cylinder diameter respectively in both said two and three stable position variants. In yet another embodiment of the invention all of said first and second pressure ducts and said first cylinder diameter are finally produced with different sets of tools creating different dimensions for said first and second pressure ducts and said first cylinder diameter respectively, when comparing said two stable position variants with said three stable position variants. However, said blank is still identical for said two and three stable position variants. 
         [0049]    Finally, in a preferred embodiment the actuator is arranged for controlling a splitter or range section in a vehicle transmission. 
         [0050]    Although the present invention has been set forth with a certain degree of particularity, it is understood that various modifications, substitutions and rearrangements of the components are possible without’ departing from the spirit and scope of the invention as hereinafter claimed.