Valve housing autofretted by means of a shut-off piston

Abstract

Method for producing a valve housing (10) comprising the steps: a) casting a first blank (21) having at least one first fluid channel (11); b) producing a slide bore (14) in the first blank (21) which is circularly cylindrical with respect to a longitudinal axis (13) and which penetrates the first blank (21) over its entire length, the slide bore (14) crossing at least one first fluid channel (11), the slide bore (14) being preliminarily finished by reaming, thereby resulting in a second blank (22); c) inserting a circular cylindrical shut-off piston (30) into the slide bore (14) of the second blank (22), wherein the diameter (31) of the shut-off piston (30) is adapted in a fluid-tight manner to the diameter (15) of the slide bore (14); d) filling a pressure fluid into the at least one first fluid channel (11); e) increasing the pressure of the pressurised fluid to a first pressure which is so high that plastic deformation occurs on an inner wall of the at least one first fluid channel (11), resulting in a third blank (23); f) lowering the pressure of the pressurised fluid to a second pressure which is equal to an ambient pressure; g) removing the pressure fluid and the shut-off piston (30) from the third blank (23); h) Honing the slide bore (14), resulting in the valve housing (10).

Description

[0001] The invention relates to a method for producing a valve housing.

[0002] Valves with autofretted valve housings are known from FR 1 176 960 and WO 2015 / 113 975 A1. The fluid channels in the valve housings are filled with a pressurized fluid, in particular a liquid, which is subjected to such high pressure that plastic deformation occurs on the inner walls of the fluid channels. This creates residual compressive stresses in the material of the valve housing, which results in an increase in fatigue strength.

[0003] From DE 10 2005 008 466 A1 a valve housing of a fuel injection valve is known which is micro-strengthened on the surface by means of autofrettage.

[0004] From DE 10 2009 000 538 A1 a bore intersection in a high-pressure accumulator body between this and a high-pressure channel in an autofretted component is known.

[0005] From DE 10 2009 028 262 A1 a method for increasing the compressive strength of a high-pressure loaded component, in particular a fuel injector for high-pressure fuel injection systems, is known, in which an autofrettage pressure of at least 7 kbar is generated inside an assembly.

[0006] Within the scope of the present invention, a valve housing is to be autofretted which is provided with a high-precision slide bore, as is frequently found in hydraulic valves.

[0007] An advantage of the present invention is that the strength-enhancing effect of autofretting can be applied without compromising the accuracy of the slide bore. Furthermore, the valve housing can easily be sealed tightly enough to generate the high pressure required for autofretting inside the valve housing.

[0008] The method according to the invention comprises the following steps: a) casting a first blank having at least one first fluid channel; b) producing a slide bore in the first blank which is circularly cylindrical with respect to a longitudinal axis and which penetrates the first blank over its entire length, wherein the slide bore crosses at least one first fluid channel, wherein the slide bore is preliminarily finished by reaming, thereby resulting in a second blank; c) inserting a circular cylindrical shut-off piston into the slide bore of the second blank, the diameter of the shut-off piston being adapted in a fluid-tight manner to the diameter of the slide bore; d) filling a pressure fluid into the at least one first fluid channel; e) increasing the pressure of the pressurised fluid to a first pressure which is high enough to cause plastic deformation on an inner wall of the at least one first fluid channel, resulting in a third blank; f) lowering the pressure of the pressurised fluid to a second pressure which is equal to an ambient pressure; g) removing the pressure fluid and the shut-off piston from the third blank; h) Honing the slide bore, which produces the valve body.

[0009] The aforementioned steps are preferably carried out in the stated order. The pressure fluid is preferably a liquid and most preferably hydraulic oil. The pressure fluid is preferably free of gas inclusions, in particular free of air bubbles. The slide bore is preferably drilled or reamed in step b prior to reaming. Most preferably, the slide bore is preformed in the first blank. The at least one first fluid channel is preferably completely filled with pressure fluid. Any connections of the at least one first fluid channel that may be present on the outer surface of the second blank are preferably closed in a fluid-tight manner, most preferably by means of screw plugs.

[0010] Advantageous further developments and improvements of the invention are specified in the dependent claims.

[0011] It can be provided that, within the scope of steps d and e, at least one second fluid channel is provided in the second blank, which is not filled with pressurized fluid, wherein at least one second fluid channel crosses the slide bore at one longitudinal end. During operation of the corresponding valve, the pressure in the tank is preferably present in the at least one second fluid channel, so that no excessive pressure load occurs there. Due to the end-side arrangement of the at least one second fluid channel, the shut-off piston does not need to be excessively long, since it is not necessary, within the scope of the method according to the invention, to close the second fluid channels in a fluid-tight manner.

[0012] The first pressure can be at least 1000 bar and preferably at least 1400 bar. These values ​​achieve the desired increase in fatigue strength. The upper limit of the first pressure is preferably selected such that the second blank does not fracture to the extent that the first and / or second fluid channels become leaky.

[0013] It can be provided that the shut-off piston comprises at least a first part, which is designed in the form of a hollow cylinder, wherein a clamping device is accommodated inside the first part, with which at least one longitudinal end of the first part can be clamped against the slide bore. Preferably, in step c, said at least one longitudinal end of the first part is clamped against the slide bore by means of the clamping device.

[0014] It can be provided that the clamping device extends through the first part over its entire length, wherein both longitudinal ends of the first part, which are opposite in the direction of the longitudinal axis, can be clamped against the slide bore by means of the clamping device. Preferably, in step c, the aforementioned opposite longitudinal ends of the first part are clamped against the slide bore by means of the clamping device.

[0015] The clamping device may comprise a second and a third part, each of which rests with an outer conical surface on the inside of opposite longitudinal ends of the first part. The first part preferably has inner conical surfaces adapted to the outer conical surfaces.

[0016] The clamping device may comprise a screw bolt that passes through the second part and is screwed into the third part, with the screw bolt at least indirectly abutting the second part with a head. A washer, for example, may be arranged between the head and the second part.

[0017] The shut-off piston can be provided with two first parts arranged at opposite ends of a common clamping device. The corresponding first parts can thus be designed to have a comparatively high degree of elasticity. This improves the sealing effect.

[0018] It can be provided that the two first parts each rest on an associated outer conical surface of the clamping device.

[0019] It may be provided that between step g and step h the slide bore of the third blank is drilled and / or reamed.

[0020] It may be provided that the honing process in step h is carried out in several processing stages, with the grain size of the honing tool in question decreasing with each processing stage. Preferably, three processing stages are carried out.

[0021] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0022] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a second blank with inserted shut-off piston; Fig. 2 a second embodiment of a shut-off piston; Fig. 2a an enlarged section of Fig. 2; and Fig. 3 a flow diagram of a method according to the invention.

[0023] Fig. 1 shows a valve housing 10 or a corresponding second blank 22 with an inserted shut-off piston 30. The valve housing 10 has a circular-cylindrical slide bore 14 with respect to a longitudinal axis 13, which in the finished valve accommodates a control slide (not shown) that is movable in the direction of the longitudinal axis 13. Within the scope of the method according to the invention, the slide bore 14 is machined with high precision so that almost no pressure fluid can pass between the control slide and the slide bore. A plurality of first and a plurality of second fluid channels 11; 12 are provided in the valve housing 10. In the present case, all fluid channels 11; 12 intersect the slide bore 14, so that different fluid connections between the fluid channels 11; 12 can be set by moving the said control slide. However, it is also conceivable for fluid channels to be present that do not intersect the slide bore 14.

[0024] The two second fluid channels 12 located at opposite ends of the slide bore 14 in the direction of the longitudinal axis 13 are preferably only subjected to the comparatively low pressure in the tank during operation of the finished valve. The method according to the invention does not need to be applied there, since the strength of untreated cast iron is typically sufficient to withstand the pressures occurring there over the long term. In contrast, the first fluid channels 11 located in the central region of the slide bore 14 are subjected to very high pressures during operation of the finished valve, which pressures also constantly change. The first fluid channels 11 are therefore subjected to fatigue stress. The valve housing 10 is preferably designed to be operationally strong with regard to the pressure stresses expected during operation. It has been shown that this goal is often unattainable with untreated cast iron.Accordingly, within the scope of the present invention, a method for increasing operational strength is used, which is referred to as autofrettage. Such a method is described, for example, on the website that was accessible on November 11, 2016, at the internet address https: / / de.wikipedia.org / wiki / Autofrettage. Furthermore, valves in which this method is used are known from FR 1 176 960 or WO 2015 / 113 975 A1. The fluid channels in the valve housings are filled with a pressurized fluid, in particular a liquid, which is subjected to such high pressure that plastic deformation occurs on the inner walls of the fluid channels. This creates residual compressive stresses in the material of the valve housing, which result in an increase in fatigue strength.

[0025] In the Fig. 1, the problem arises that autofretting would impair the accuracy of the slide bore. An advantage of the present invention is that the strength-enhancing effect of autofretting can be applied, with only minimal impairment of the accuracy of the slide bore. Furthermore, the valve housing can be easily sealed so tightly that the high initial pressure required for autofretting can be generated inside the valve housing. For this purpose, preferably all openings of the fluid channels 11; 12 that open onto the outer surface 18 of the valve housing 10 are sealed fluid-tight or provided with a fluid-tight pressurized fluid supply. This is readily possible with the various connections 16; 17 of the valve housing 10, to which pipes, hoses, or screw-in valves are to be connected anyway during later operation of the finished valve.Corresponding internal threads are preferably provided there, which can be used for fluid-tight closure. The slide bore 14, in contrast, is purely circular-cylindrical.

[0026] In order to seal the slide bore 14 in a fluid-tight manner, the shut-off piston 30 is provided. This is designed as a circular cylinder, similar to a control slide, with its diameter 31 being adapted in a fluid-tight manner to the diameter 15 of the slide bore. As can be seen from the explanations regarding Fig. 2, the shut-off piston 30 is not inserted into the highly precisely machined slide bore 14. Instead, it is inserted into a second blank 22, the slide bore of which is only reamed, not honed. Accordingly, it is possible that minor leaks may occur between the shut-off piston 30 and the slide bore 14, which can lead to a greater or lesser loss of pressure fluid during the autofretting process.

[0027] To prevent these leaks, the shut-off piston is provided with a tensioning device 32. The shut-off piston 30 comprises a first part 40, which is in the form of a hollow cylinder having a first bore 41 on the inside, which is circularly cylindrical with respect to the longitudinal axis 13. At its two opposite ends in the direction of the longitudinal axis 13, the first bore 41 is each provided with an inner conical surface 42, which is circularly conical with respect to the longitudinal axis 13. A second and a third part 50; 60, each with a matching outer conical surface 51; 61, rest there. The second part 50 has a second bore 52, which is circularly cylindrical with respect to the longitudinal axis 13 and through which a screw bolt 70 passes. The head 71 of the screw bolt 70 rests on the outside of the second part 50 with respect to the longitudinal axis 13. The outer diameter of the second part 50 is preferably equal to the diameter of the head 71.The screw bolt 70 has an external thread 72, which is screwed into an internal thread 62 on the third part 60. The third part 60 and the head 71 of the screw bolt 70 each have a hexagon socket 63; 73 or other rotational drive means, so that they can be rotated relative to one another using adapted screwing tools. By tightening the screw bolt 70, the second and third parts 50; 60 are moved towards one another. Due to the engagement between the outer conical surfaces 51; 61 and the inner conical surfaces 42, the two longitudinal ends of the first part 40 are elastically deformed radially outward, so that they are pressed against the slide bore 14. In this area, a complete seal of the slide bore 14 can thus be achieved. The sealing effect can be further improved by using sealing elements (not shown) made of an elastomer, for example O-rings.

[0028] As from Fig. 1, the aforementioned region is located between the inner first fluid channels 11 and the outer second fluid channels 12. The second fluid channels 12 are accordingly not covered by the sealing effect of the shut-off piston 30. The two connections designated by reference numeral 17 are provided in this case for receiving a screw-in valve, for example, a pressure relief valve. A closure part is preferably used there, which is designed such that the fluid connection between the respective first fluid channel 11 and the respective second fluid channel 12 is interrupted.

[0029] Fig. 2 shows a second embodiment of a shut-off piston 30'. Fig. 2a shows an enlarged section of Fig. 2. The shut-off piston 30' has two first parts 40', which are arranged at opposite longitudinal ends of the tensioning device 32'. Compared to the first embodiment, the first parts 40' are designed to be significantly smaller, so that they have a higher elasticity. Accordingly, inaccuracies in the slide bore can be better compensated. In return, it is accepted that the sealing is only carried out over a short area along the longitudinal axis 13 and not, as in the first embodiment, along the entire length of the first part (No. 40 in Fig. 1). Accordingly, the slide bore (No. 14 in Fig. 1) less protected from the pressure of the pressurized fluid.

[0030] The optional step of the procedure (No. 80 in Fig. 3) is hardly avoidable with this shut-off piston 30'.

[0031] The nuts 93, which are screwed onto the opposite longitudinal ends of the clamping device 32', correspond to the third parts (No. 60 in Fig. 1) of the first embodiment. Compared to the first embodiment, the clamping device 32' has been extended so that both nuts 93 are located outside the valve housing when the shut-off piston 30' is inserted into the valve housing. This allows the nuts 93 to be easily accessible with a wrench. To counteract the corresponding tightening torque, each nut 93 is assigned a hexagon socket 95 in the clamping device 32'.

[0032] The clamping force directed along the longitudinal axis 13 is transmitted from the nut 93 to the associated first part 40' by means of a separate circular-cylindrical sleeve 94. Each first part 40' has an inner conical surface 91, with which it rests against a matching outer conical surface 90 on the clamping device 32'. By tightening the respective nut 93, the first part 40' is thus expanded radially outward, so that it is pressed against the slide bore.

[0033] Fig. Figure 3 shows a flow diagram of a method according to the invention. In step a, a first blank 21 is produced by casting. Cast iron is preferably used as the casting material, although it is also conceivable to use aluminum. The inner shape of the first blank 21, in particular the fluid channels (Nos. 11, 12 in Fig. 1) and a pre-formed slide bore (No. 13 in Fig. 1) are preferably produced using a lost casting core. The outer shape of the first blank 21 can be produced using a lost casting mold or a reusable casting mold. Preferably, all Fig. 1 shown first and second fluid channels are contained in the first blank 21.

[0034] In the following step b, the circular cylindrical slide bore (No. 14 in Fig. 1) is produced, which penetrates the first blank 21 over its entire length. This is preliminarily finished by reaming, resulting in a second blank 22. The slide bore is preferably pre-cast in step a and then bored out. However, it is also conceivable to drill the slide bore out of the solid. The drilled slide bore is then reamed. During reaming, the slide bore is bored out using a reamer with a geometrically defined cutting edge, whereby only a small amount of material is removed. The diameter accuracy achievable in this way is in the range between 20 µm and 50 µm. This accuracy is clearly too low for a finished slide bore. However, it is sufficient to be used with the proposed shut-off piston (No. 30 in Fig. 1) to achieve complete sealing of the valve bore.

[0035] In the following step c, the circular cylindrical shut-off piston (No. 30 in Fig. 1) into the slide bore of the second blank 22. Preferably, the shut-off piston is clamped by means of the clamping device (No. 32 in Fig. 1) is clamped to the slide bore, resulting in a particularly good seal. The shut-off piston is preferably positioned in the slide bore so that all first fluid channels (No. 11 in Fig. 1) are covered fluid-tight by the shut-off piston.

[0036] In the following step d, pressure fluid is filled into the first fluid channels. Preferably, no pressure fluid is filled into the second fluid channels. The various connections (No. 16; 17 in Fig.1) are preferably sealed in a fluid-tight or pressure-tight manner or are provided with a pressure-tight pressure fluid supply. It is conceivable that the connections for this purpose are each provided with an internal thread. The pressure fluid is preferably a liquid, most preferably hydraulic oil. The pressure fluid is preferably free of gas inclusions, in particular free of air bubbles.

[0037] In the subsequent step e, the pressure of the pressurized fluid is increased to a first pressure high enough to cause plastic deformation on the inner walls of the first fluid channels. This results in a third blank 23. The first pressure is preferably at least 1000 bar and most preferably at least 1400 bar. Preferably, the stated values ​​for the first pressure are only slightly exceeded, so that there is no risk of fracture of the second blank.

[0038] In the subsequent step f, the pressure of the pressurized fluid is reduced to a second pressure which is essentially equal to the ambient pressure.

[0039] In the following step g, the pressure fluid and the shut-off piston are removed from the third blank 23.

[0040] Ideally, step h now occurs directly, although this ideal is not always economically achievable. During step e, the pressure of the pressurised fluid also acts, to a greater or lesser extent, on the inner wall of the slide bore. The level of pressure there depends on the quality of the seal between the slide bore and the shut-off piston. The aim of the present invention is to make this seal so good that elastic deformation occurs at the slide bore alone, which completely disappears during step f. However, this goal cannot always be achieved with the required process reliability. As a result, local plastic deformation may occur at the slide bore. Compensating for this requires material removal, which cannot be achieved economically in step h.Therefore, it may be economically expedient to carry out the optional step 80 between steps g and h, in which the slide bore of the third blank 23 is drilled and / or reamed.

[0041] In step h, the slide bore is honed, resulting in the finished valve housing 10. The corresponding honing tool has a plurality of geometrically undefined cutting edges formed by a plurality of hard grains, which in turn are bound by a binding agent to form essentially rigid honing strips. The honing strips are preferably held in the honing tool such that they align themselves automatically relative to the slide bore. Honing preferably takes place in several, most preferably three, processing stages 81; 82; 83, with the grain size of the respective honing tool decreasing with each processing stage. The diameter accuracy of the finished slide bore is then on the order of 1 µm. Reference symbol a Step a of the procedure b Step b of the procedure c Step c of the procedure d Step d of the procedure e step e of the procedure f Step f of the procedure g Step g of the procedure h Step h of the procedure 10 valve housings 11 first fluid channel 12 second fluid channel 13 Longitudinal axis 14 slide bore 15 Diameter of the slide bore 16 connection 17 Connection 18 Exterior surface 21 first blank 22 second blank 23 third blank 30 shut-off pistons (first embodiment) 30' shut-off piston (second embodiment) 31 Diameter of the shut-off piston 32 Clamping device (first embodiment) 32' clamping device (second embodiment) 40 first part (first embodiment) 40' first part (second embodiment) 41 first borehole 42 inner conical surface 50 second part 51 Outer conical surface 52 second hole 60 third part 61 Outer conical surface 62 internal thread 63 hexagon socket 70 screw bolts 71 Head of the screw bolt 72 external threads 73 hexagon socket 80 optional step of the procedure 81 first processing stage 82 second processing stage 83 third processing stage 90 outer conical surface on the clamping device 91 Inner conical surface on the first part 93 Mother 94 sleeve 95 hexagon socket

Claims

[1] Method for producing a valve housing (10) comprising the steps: a) casting a first blank (21) having at least one first fluid channel (11); b) producing a slide bore (14) in the first blank (21) which is circularly cylindrical with respect to a longitudinal axis (13) and which passes through the first blank (21) over its entire length, the slide bore (14) crossing at least one first fluid channel (11), the slide bore (14) being preliminarily finished by reaming, thereby resulting in a second blank (22); c) inserting a circular cylindrical shut-off piston (30) into the slide bore (14) of the second blank (22), wherein the diameter (31) of the shut-off piston (30) is adapted in a fluid-tight manner to the diameter (15) of the slide bore (14); d) filling a pressure fluid into the at least one first fluid channel (11); e) increasing the pressure of the pressurised fluid to a first pressure which is so high that plastic deformation occurs on an inner wall of the at least one first fluid channel (11), resulting in a third blank (23); f) lowering the pressure of the pressurised fluid to a second pressure which is equal to an ambient pressure; g) removing the pressure fluid and the shut-off piston (30) from the third blank (23); h) Honing the slide bore (14), resulting in the valve housing (10). [2] Method according to claim 1, wherein in the context of steps d and e, at least one second fluid channel (12) is provided in the second blank (22), which is not filled with pressure fluid, wherein at least one second fluid channel (12) crosses the slide bore (14) at one longitudinal end. [3] A method according to any one of the preceding claims, wherein the first pressure is at least 1000 bar and preferably at least 1400 bar. [4] Method according to one of the preceding claims, wherein the shut-off piston (30; 30') comprises at least a first part (40; 40') which is designed in the form of a hollow cylinder, wherein a clamping device (32; 32') is accommodated in the interior of the first part (40; 40'), with which at least one longitudinal end of the first part (40; 40') can be clamped against the slide bore (14). [5] Method according to claim 4, wherein the clamping device (32) passes through the first part (40) over its entire length, wherein both longitudinal ends of the first part (40) opposite in the direction of the longitudinal axis (13) can be clamped against the slide bore by means of the clamping device (32). [6] Method according to claim 5, wherein the clamping device (32) comprises a second and a third part (50; 60), each of which bears internally with an outer conical surface (51; 61) against opposite longitudinal ends of the first part (40). [7] Method according to claim 6, wherein the clamping device (32) comprises a screw bolt (70) which passes through the second part (50) and is screwed into the third part (60), the screw bolt (70) bearing at least indirectly on the second part (50) with a head (71). [8] Method according to claim 4, wherein the shut-off piston (30') has two first parts (40') which are arranged at opposite ends of a common clamping device (32'). [9] Method according to claim 8, wherein the two first parts (40') each bear against an associated outer conical surface (90) of the clamping device (32'). [10] Method according to one of the preceding claims, wherein between step g and step h the slide bore (14) of the third blank (23) is drilled and / or reamed. [11] Method according to one of the preceding claims, wherein the honing in step h is carried out in several processing stages (81; 82; 83), the grain size of the honing tool in question decreasing with each processing stage.

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