Module system for manufacturing two and three stable positions fluid-operated actuators

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 is manufactured from a blank. The blank includes at least one opening for a cover and is identical for the variants of the two and three stable position actuator, and is at least prepared for the arrangement of a first pressure duct, a second pressure duct, and a first cylinder diameter of the cylinder housing.

BACKGROUND AND SUMMARY

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 anda first cylinder diameter of said cylinder housing.

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.

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.

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.

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.

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.

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.

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.

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.

DETAILED DESCRIPTION

FIG. 1shows a simplified longitudinal section of a fluid-operated actuator101with 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 housing102, piston103, piston rod104and cover105. The cylinder housing102and the cover105are axially connected in a not showed way. Thereby, the cylinder housing102, piston rod104and cover105will enclose a left pressure chamber106and a right pressure chamber107on either side of the piston103. The cylinder housing102has a left supply duct108and a right supply duct109that are in fluid connection with the left pressure chamber106and right pressure chamber107, respectively. Valves (not shown) connect the left supply duct108and right supply duct109to either a pressure supply or to an exhaust of ambient pressure.

InFIG. 1the right supply duct109is connected to the pressure supply. Thereby, the right pressure chamber107is filled with pressurized fluid and a fluid pressure acts on the piston103. The left supply duct108is connected to the exhaust, and hence there is ambient pressure in the left pressure chamber106. So, the piston103and piston rod104are urged to move to the left. The leftwards motion is stopped when the left end stop abutment103aof the piston103comes into contact with the mating part of the cover105. This represents the left stable position of the actuator101. Similarly, if the left supply duct108were connected to the pressure supply and the right supply duct109were connected to the exhaust, then the piston103and piston rod104would be urged to the right. The right stable position would then be reached when the right end stop abutment103bof the piston103is in contact with the mating part of the cylinder housing102.

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 piston103and piston rod104, need to be centred and kept substantially coaxial with the mating parts of the cylinder housing102and cover105. 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, inFIG. 1there is a static sealing device111(e.g. o-ring or gasket) to prevent leakage between the cylinder housing102and cover105from the left pressure chamber106. Moreover, a left rod sealing device112prevents leakage between the cover105and piston rod104. Similarly, a right rod sealing device113prevents leakage between the cylinder housing102and piston rod104from the right pressure chamber107.

Finally, a piston sealing device114on the outer periphery of the piston103prevents leakage between the pressure chambers106and107.

In the right pressure chamber107, the fluid pressure acts on the piston103on an effective ring-shaped area defined by a cylinder-piston system diameter103dand a piston rod diameter104d. The actuator101has its piston rod104extending out of the cylinder housing102and cover105on 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 diameter103d.

FIGS. 2a,2band2cshow a prior art fluid-operated actuator210with three stable positions. A cylinder housing202and a cover205enclose a main piston203, which is fixedly attached to a piston rod204, and a ring piston221. The cylinder housing202, main piston203and piston rod204enclose a left pressure chamber206where the pressure can act on the main piston203on an effective ring-shaped area defined by a main cylinder-piston system diameter203dand a piston rod diameter204d. The ring piston221is located on the outside of an axial extension203eof the main piston203. The axial motion of the ring piston221is limited by diameter steps in the cylinder housing202, main piston203and cover205. A right pressure chamber207is enclosed by the cylinder housing202, main piston203, piston rod204, cover205, and ring piston221. A pressure in the right pressure chamber207will act on the ring piston221on an effective ring-shaped area defined by an outer cylinder-piston system diameter221d(between the cylinder housing202and ring piston221) and an inner cylinder-piston system diameter221i(between the ring piston221and axial extension203eof the main piston203). Furthermore, a pressure in the right pressure chamber207will act on the main piston203on an effective ring-shaped area defined by the inner cylinder-piston system diameter221iand the main cylinder-piston system diameter203dand a piston rod diameter204d. Between the left pressure chamber206and the right pressure chamber207there is an intermediate pressure chamber222enclosed by the cylinder housing202, main piston203and ring piston221.

The left pressure chamber206is in fluid connection with a left supply duct208. Similarly, the right pressure chamber207is in fluid connection with a right supply duct209. Valves (not shown)’ connect the supply ducts208and209to either a pressure supply or to an exhaust of ambient pressure. The intermediate chamber222is not to be pressurized; hence a breathing duct223in the cylinder housing202connects it to ambient pressure.

A static sealing device211prevents leakage between the cylinder housing202and cover205from the left pressure chamber206. A left rod sealing device212prevents leakage between the cylinder housing202and piston rod204. Similarly, a right rod sealing device213prevents leakage between the cover205and piston rod204from the right pressure chamber207. A main piston sealing device214on the outer periphery of the main piston203prevents leakage between the left pressure chamber206and the intermediate chamber222at the main cylinder-piston system diameter203d. On the ring piston221there are two sealing devices that prevent leakage between the right pressure chamber207and the intermediate chamber222; an inner ring piston sealing device215at the inner cylinder-piston system diameter221iand an outer ring piston sealing device216at the outer cylinder-piston system diameter221d.

InFIG. 2athe left pressure chamber206is pressurized. The fluid pressure will urge the main piston203and piston rod204to the right. A right stable position is reached when the right end stop abutment203bof the main piston203is in contact with the mating part of the cover205.

InFIG. 2bthe right pressure chamber207is pressurized. The fluid pressure has urged the main piston203and piston rod204to a left stable where the left end stop abutment203aof the main piston203is in contact with the mating part of the cylinder housing202.

Finally, inFIG. 2cboth the left pressure camber206and right pressure chamber207are pressurized. A middle stable position is thereby reached when the ring piston221mates with a housing diameter step abutment202ain the cylinder housing202and with a piston diameter step abutment203aon the main piston203. The pressure in the left pressure chamber206, acting between diameters203dand204d, cannot alone push the main piston203to the right of this position, since that would lift the ring piston221off the housing diameter step abutment202a. That motion would be counteracted by the pressure in the right pressure chamber207that acts on the larger area between diameters221dand204d. Analogously, a motion of the main piston203to the left of the middle stable position would axially separate the ring piston221from the piston diameter step abutment203a. Thus, the pressure in the right pressure chamber207, acting between diameters221iand204d, cannot alone push the main piston203left of the middle stable position, since that would be counteracted by the left pressure chamber206whose pressure acts on the larger area between diameters203dand204d.

FIG. 3shows a fluid-operated actuator301with three stable positions that is a variant of the plain actuator101inFIG. 1, and thus part of the inventive module system. The cylinder housing102ahas been modified with an additional breathing duct323for the intermediate chamber322. A cover305is fixedly attached to, mated against or, preferably, integral with a ring-shaped protrusion305p, whose inner periphery forms the cylinder-piston sealing diameter303dfor the left pressure chamber306and main piston303with sealing device314. There is a cover supply duct305cin the cover305that provides a fluid connection between the left supply duct108and the left pressure chamber306. A cover abutment305adefines the middle stable position for a ring piston321. Leakage from the supply ducts108and305care prevented by static sealing devices111and111a. The original cylinder-piston system diameter103dof the cylinder housing102serves in the variant102aas the sealing diameter for the static sealing device111aand as the cylinder-piston system diameter for the right pressure chamber307and outer sealing device316of the ring piston321. An inner sealing device315acts at cylinder-piston system diameter321ion an extension303eof the main piston303.

The difference between the original cylinder housing102of the plain actuator101and the cylinder housing102ais minimal. The breathing duct323for the intermediate chamber322has been added in the cylinder housing102a. Thereby, according to the invention, the same blank can be used for both cylinder housings102and102a. 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 housings102and102aare integrated with other parts, for instance a gear-shift control unit in a vehicle transmission, and, hence, would require complex and expensive tooling.

In the fluid-operated actuator301inFIG. 3the cylinder-piston system diameter103dof the cylinder housing102ais used for the outer sealing device316of ring piston321as well as for the static sealing device111a. That may facilitate the manufacturing of the cylinder housing blank and the machining thereof. However, edges and burrs may occur where the breathing duct323ends at the cylinder-piston system diameter103d. This will pose a risk of damaging the outer sealing device316at the assembly, when the seal surface will pass over the end of the breathing duct323.

This is solved in the modified actuator401inFIG. 4, which actuator also forms part of the inventive module system. There, the cylinder housing102bhas a larger diameter102dwhere the breathing duct423for the intermediate chamber422ends. Hence, the risk of damaging the outer sealing device316at the assembly has been reduced greatly. Furthermore, the diameter102dcould be used for both static sealing devices111and111bbetween the cover405and the cylinder housing102b. Then, the static sealing devices111and111bcould be identical, which would save costs.

The ring piston421in the actuator401has been made wider than the corresponding ring piston321inFIG. 3. Thereby, several advantages have been gained. Firstly, the large cylindrical surface with diameter103din the cylinder housings102,102aand102bhas been used, so the volume of the right pressure chamber407has been minimized, which may improve the dynamic performance of the actuator401. Secondly, it is no longer possible for the ring piston421to move that far to the right from the position inFIG. 4that the inner sealing device315would no longer be in contact with the extension303eof the main piston303. Thirdly, the larger width of the ring piston421has made it possible to locate the sealing devices315and316, with integrated guiding devices, significantly axially apart from each other. That will improve the stability against misalignment for the ring piston421.

FIG. 5shows a further modified actuator501of the variant with three stable positions. Actuator501also forms part of the inventive module system. There, the ring piston521has been extended axially inside the ring-shaped protrusion505pof the cover505. Thereby, the guiding devices are axially located even further apart than the actuator401inFIG. 4. Moreover, the inner sealing and guiding device has been separated into a pure sealing device515s, acting on the inner cylinder-piston system diameter321i, and a guiding device515gthat acts on the inside of the ring-shaped protrusion505p. The guiding device515gthereby acts on the main cylinder-piston system diameter303d, which is larger and possibly stiffer than for the corresponding sealing and guiding device315inFIG. 3. Furthermore, with the ring piston521extending axially inside the ring-shaped protrusion505p, the sealing device515swill be in contact with the extension503eof the main piston503even for the most extreme relative positions of the main piston503and ring piston521.

FIG. 5also shows two alternative breathing ducts for connecting the intermediate chamber522to ambient pressure. There is a cover breathing duct523cin the cover505and a piston rod breathing duct composed of a mainly radial duct523pin main piston503and a mainly axial duct523rin piston rod504. With any of these breathing ducts, the cylinder housing102, as a finished part, can be identical for actuator variants with two and three stable positions.

FIG. 6shows another embodiment of a piston rod breathing duct in an actuator601of the variant with three stable positions, which actuator also forms part of the inventive module system. A substantially radial duct623pthrough the main piston603and piston rod604is formed, at least in part, by a hollow pin630that fixedly connects the main piston603to the piston rod604. The duct623pis in fluid connection with a substantially axial duct623rin the piston rod604. This fluid connection could be achieved with, e.g., a slot or a radial hole630hin the hollow pin630. A corresponding ring piston is here numbered621. Also in this case the cylinder housing102, as a finished part, can be identical for actuator variants with two and three stable positions.

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.

Finally, in a preferred embodiment the actuator is arranged for controlling a splitter or range section in a vehicle transmission.

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.