GB2447029A - Sintered steel component with layer of Fe3O4 - Google Patents

Abstract

A method of manufacturing a moving part capable of providing a liquid seal by forming the part from sintered steel and forming a layer of Fe304 on the sintered steel. The iron oxide layer is formed by steam treatment. Parts made by this process can include a coupling for a vehicle engine fuel injector, a viscous fan for an internal combustion engine cooling system, an oil seal retainer for end sealing a vehicle crankshaft, differential transmission, gearbox, axle, driveshaft, hub or transfer case, or a vacuum pump in a vehicle braking system.

Description

IMPROVEMENTS IN OR RELATING TO LIQUID SEALS

The present invention relates to a method of manufacturing a moving part that has a surface capable of providing a liquid seal in use and, more particularly, to rotating parts for vehicle engine that provide such surfaces.

There are many different situations with the automotive industry in which there is a requirement to maintain a liquid seal. Amongst these varied applications, there are several examples of situations in which a moving, typically rotating, part traverses a boundary between a liquid filled area and a non-liquid filled, or dry, area or between areas containing dissimilar liquids that must be kept separate.

These parts are typically made by machining from a single billet of material. The billet must have a minimum diameter that is at least equal to the maximum diameter of the finished part. This process produces a considerable amount of wastage in the form of scrap material. For complex shapes the machining process requires frequent resetting of the machine because it has to be re-set for each new face. Each face is then ground in order to give a sufficiently polished surface finish for a liquid seal to be formed. This process is very time intensive and therefore costly.

In order to form a liquid seal within an engine sub-system, the connecting part is typically provided with a rubber gasket or seal. Any unevenness on the surface abutting the rubber seal will result in the premature deterioration of the rubber seal.

Many engine sub-systems are supplied as sealed units and, in these circumstances, it may not be possible to replace a damaged rubber seal. Instead, the entire sub-system must be replaced. Unevenness on the surface abutting the rubber seal may therefore decrease the effective lifetime of the sub-system as a whole. This may also adversely affect other subsystems or components of the engine due to oil or coolant-loss.

Alternatively, it is known to use a soft metal pressed insert fabricated from copper, phosphor-bronze or a similar material, in order to provide a sufficiently smooth surface to form an effective seal.

The method of the present invention aims to provide a substantial reduction in the complexity of the process by which such parts are manufactured.

According to the present invention there is provided a method of manufacturing a moving part capable of providing a liquid seal, the method comprising the steps of: forming the part from sintereci steel; forming a layer of Fe304 to provide a surface finish on the sintered part that is capable of providing a liquid seal.

The manufacture of such parts using a combination of sintering and steam treatment is considerably more cost effective than previously used machining and grinding methods. In addition, when a part is machined, the performance of the part depends critically on the tolerances of each individual face. As each face has to be machined separately, each one could be subject to an error in the positioning of the machine.

In contrast, the sintering process of the present invention is a single step of sintering to produce the majority of the facets of the part. This results in a much more reliable process.

The method may further comprise the step of machining complex structures, such as keyways, and screw threads within the part. These structures cannot be created by sintering, but they account for a very small proportion of the surfaces of the part and do not include the surfaces that provide a liquid seal.

Furthermore, according to the present invention there is provided a moving part providing a liquid seal for use in a vehicle engine, the part comprising: a sintered body; and a steam treated surface finish for providing the liquid seal. The moving part may be a rotating part.

The part may be, inter ails, a coupling for an injection pump for a fuel injection unit in a diesel engine; a viscous fan from a radiator system of an internal combustion engine; a water pump for use in an internal combustion engine; an oil seal retainer for use in dosing the ends of a vehicle crankshaft; an oil seal retainer for sealing a differential transmission, gearbox or transfer case; or a vacuum pump for use in the braking system of a vehicle.

An example of a part manufactured according to the present invention will now be described, by way of example only with reference to the following drawings in which: Figure 1 shows an axial view of a coupling for a fuel pump manufactured according to the method of the present invention; Figure 2 shows a cross sectional view of the coupling shown in Figure 1; Figure 3 shows a perspective view of the coupling shown in Figures 1 and 2; Figure 4 shows the coupling of Figures 1 to 3 in context with those parts to which it is most closely attached, in use; Figure 5 shows an exploded view of the relevant part of a diesel engine showing the position of the coupling of Figures 1 to 3, in use; Figures 6a to 6e show a series of 30X magnification view of sintered parts with and without machining, pre-and post-durability testing; Figure 7 shows a viscous fan from a radiator system of an internal combustion engine; Figures 8a and 8b show exterior and interior views of a water pump for use in an internal combustion engine; Figure 9 shows an oil seal retainer for use in closing the ends of a vehicle crankshaft; Figure 10 shows an oil seal retainer for sealing a differential transmission, gearbox or transfer case; and Figure 11 shows a vacuum pump for use in the braking system of a vehicle.

Sintering is a method for making objects from a suitable, typically metallic powder by heating the material (below its melting point) until its particles adhere to each other and then applying pressure. Sintering is traditionally used for manufacturing ceramic objects and sintered bronze is frequently used as a material for bearings. Sintered bronze is suitable for use in bearings since its porosity allows lubricants to flow through it. In the case of materials with high melting points such as Teflon and tungsten, sintering is used when there is no alternative manufacturing technique. In these cases very low porosity is desirable and can often be achieved.

In most cases the density of a collection of grains increases as material flows into voids, causing a decrease in overall volume. Mass movements that occur during sintering consist of the reduction of total porosity by repacking. In the final stages, metal atoms move along crystal boundaries to the walls of internal pores, redistributing mass from the internal bulk of the object and smoothing pore walls.

Surface tension is the driving force for this movement.

Steam treatment is a term of art that refers generally to a coating technique that is typically employed when a part needs to be hardened. When handling ferrous parts, the technique generally results in the deposition of a uniform 2 -10 pm layer of Fe304, or "black iron" onto the entirety part. The resulting part has a black appearance and, in addition to an increased hardness1 it is also known to be more resistant to corrosion than a similar part that has not been so treated.

Fe304 is a crystalline solid which means that a surface formed from Fe304 is smooth and has a low porosity.

Figures 1 to 5 show a coupling 10 for the type of fuel pump used in a diesel engine.

The coupling 10 is fabricated from, for example, M1040 steel. The grade of steel is chosen to be suitable for the particular application. The choice is a compromise between cost and weight to produce a part suitable for the mechanical loads whilst still providing a sufficient safety margin.

The coupling 10 is shown in isolation in Figures 1, 2 and 3. The coupling 10 comprises a flange 12 and a boss or hub 13. The flange and hub 13 both have a circular cross-section. The manufacturing tolerance on the diameter of the hub 13 is extremely tight to ensure that the coupling 10 is capable of interfacing to provide an effective seal.

Figure 4 shows the coupling 10 in the context of a fuel pump system 15 including a fuel pump 18. Figure 5 contextualises the fuel pump system 15 within the engine as a whole. The coupling 10 is driven to rotate by the insertion of a shaft 16 into a keyed conical hole 11 with a keyway 19. The shaft 16 is also keyed and rotation results when a key is provided in joining the respective keyways 19. The hole 11 tapers through the hub 13 and at least partially through the flange 12. The coupling separates a liquid filled area A from a non-liquid filled area B. The seal is provided on the liquid filled side A of the coupling 10, by a rubber seal 17 which is provided on the hub 13. Holes 14 are provided through the flange 12 to enable the coupling 10 to interface with other engine parts in the non-liquid filled area B. The coupling 10 is manufactured in a three-step process comprising first producing the part by sintering, then steam treating the sintered part and finally machining the keyway 19 and tapping the holes in the flange 12. The steam treatment is used to harden the surface; reduce the porosity and improve the corrosion resistance of the part. Typically it would be necessary to grind the surface in order to provide a surface that is sufficiently smooth to provide a liquid seal. However, steam treating the surface obviates the need for any grinding.

Looking at a microscopic level the cross-section of a machined part consists of a series of regularly spaced and shaped peaks. In contrast, the surface resulting from the steam treatment has an almost completely smooth surface with occasional microscopic peaks that result from random positioning of crystals. The smooth surface results in a much larger proportion of the surface area being available for interfacing with the seal. The occasional peaks are typically worn away by the interfacing part before any damage occurs to that part. The smooth surface provides an advantage for both the lifetime of the seal and the slip torque of the keyed conical hole 11.

In particular, the smooth outer surface of the hub 13 ensures that damage to the seal 17 is reduced, thus increasing the effective life of the fuel pump system 15. At the interface between the keyed conical hole 11 and the shaft, the smooth surface resulting from the steam treatment results in a considerable decrease in the surface friction which, in turn, results in a decrease in heat and wear, thereby Increasing the efficiency of operation of the interface and increasing the durability of the seal.

Figures 6a to 6e show a series of 30X magnification view of sintered parts with or without machining, pre-and post-durability testing.

Figure 6a shows a sintered part at 30X magnification. The porous surface is readily apparent. This surface can be made more uniform by machining, as shown in Figure 6b. This provides a good surface finish, but the surface is porous and is therefore unsuitable for providing a liquid seal.

Figure 6c shows a non-machined sintered part that has been subjected to durability testing. The wear apparent on the surface is typical of that expected in such a test.

Figure 6d shows the sintered part of Figure 6a when it has been steam treated. The surface is very smooth and non-porous. The surface also has a very high surface hardness. Figure 6e shows the part from Figure 6d once it has been subjected to a durability test. It will be readily apparent that the wear is reduced in comparison with the sintered part shown in Figure 6c which had not been steam-treated.

Figure 7 shows a viscous-drive 70 for a cooling fan for an internal combustion engine cooling system. The viscous-drive 70 transmits drive to a cooling fan (not shown) from the engine in response to changes in the ambient air temperature surrounding the body of the viscous-drive. The viscous-drive 70 comprises a housing 71, a bi-metallic controller (not shown), an input shaft (not shown) and an output shaft 72.

The input and output shafts 72 are. separated by the viscous-drive 70. The housing 71 Is secured to the engine or radiator by means of a suitable bracket. The housing 71 is positioned so as to be in the direct path of the air-flow from the cooling fan mounted to the radiator. The housing 71 is designed to transmit any changes in the air temperature to the bi-metalljc controller housed within the housing 71. The periphery of the housing is typically provided with a plurality of fins 73 to increase the surface area to optimise the controller's response to air temperature change.

The housing 71 further comprises at least two internal chambers (not shown), one accommodating the input shaft and one accommodating the output shaft 72. Fluid communication between the two chambers is via a valve (not shown) which is operated by the controller and a return orifice.

The input shaft has a first input or driven end and distal from the input end a plurality of vanes. The output shaft 72 has a driven end surrounded by a plurality of vanes.

Distal from the driven end there is a drive end which is connected to the cooling fan.

The vanes of the input and output shafts are surrounded by a viscous fluid contained within the housing. Fluid communication between the first and second chamber is permitted only via the control valve and the return orifice.

The input shaft is driven by the engine, typically via a belt and pulley. There is no communication of drive from the input shaft to the output shaft if the engine temperature is too low as the bi-metallic controller holds the valve closed.

Once the ambient air temperature exceeds a given threshold the bi-metallic controller opens the valve, allowing a circuit of fluid communication between the two chambers.

A viscous fluid in the first chamber may then pass from the first chamber to the second via the valve, applying a force to the drive vanes on the output shaft and causing the fan to turn. Oil returns to the first chamber via the return orifice thus creating a fluid circuit.

A reliable seal must be provided between the housing and the input and output shafts to prevent a loss of fluid which would be detrimental to performance.

Figures 8a and 8b show, respectively1 the exterior and interior of a water pump 80 for an internal combustion engine cooling system. The water pump 80 is used to pump coolant around the engine and between the engine and the heat exchanger or radiator. The water pump 80 comprises a housing 81, a drive shaft 82 and an impeller 83. The impeller 83 is connected to the drive shaft 82 which is driven by the engine. The drive shaft 82 rotates on bearings and must have a reliable fluid seal between the drive shaft 82 and the housing 81 to prevent loss of coolant or the fluid communication of coolant on one side of the housing 81 and engine lubricant on the other side of the housing 81 which would be detrimental to the engine.

Figure 9 shows an oil seal retainer 90 designed to be affixed to an end of the crankshaft 91 of a vehicle. An engine crankshaft 91 is provided with a primary output end (not shown) and distal from the primary output end is a secondary output end 92 or ancillary drive end. The output from the engine is taken from the primary output end of the crankshaft 91 which drives the vehicle via a gearbox.

Additionally, engine ancillaries such as power steering pumps, cooling fans, alternators, air conditioning compressors and vacuum pumps are driven by the crankshaft 91 via a pulley and serpentine belt system from the secondary output 92.

The crankshaft 91 is supported by bearings within a crankcase (not shown) which contains lubricating oil for the crankshaft 91 and the other moving parts of the engine.

The pulley for the ancillary drive is mounted on the end 92 of the crankshaft 91 that is supported by bearings in the crankcase and protrudes through the crankcase to outside of the engine.

A reliable oil seat is vital at the point where the crankshaft 91 protrudes through the end bearings of the crankcase to support the pulley, to prevent the loss of lubricating oil from the crankcase.

Figure 10 shows an oil seal retainer 100 for sealing differential transmission systems, gearboxes and transfer cases. These devices supply drive torque from an engine to the road wheels of a motor vehicle.

Such devices typically comprise a housing 101, gears mounted on rotating shafts 102 supported by bearings set into the housing 101. The rotating parts require lubrication which is typically provided by a lubricant such as oil contained within the housing 101.

Rotating shafts 102 often need to protrude from the housing 101 in order to receive drive from the engine or another gear drive, or to output drive to the road wheels or another gear drive.

The housing 101 not only provides suitable support for the bearings that carry the rotating shafts 102, but also serves to contain lubricating oil and keep out foreign bodies such as dirt that could damage the gears.

It is vital to provide a reliable oil seal at the point where the rotating shafts 102 protrude from the housing 101 to prevent loss of lubricating oil or the ingress of dirt which would adversely affect the performance of the device.

Figure 11 shows a vacuum pump 110 for the braking system of a motor vehicle. The vacuum pump 110 is typically driven via a pulley driven by a serpentine belt on the side of the vehicle engine. The vacuum pump 110 typically comprises a housing 111, a drive shaft 112 and an impeller (not shown). The impeller is connected to the drive shaft 112 which is driven by the drive pulley on the outside of the housing 111. The drive shaft 112 rotates on bearings and must have a reliable fluid seal between the drive shaft 112 and. the housing 111 to prevent loss of vacuum or lubricant. The loss of vacuum or lubricant would be detrimental to the performance of the braking system.

The rotating parts designed to provide liquid seals in each of the systems illustrated in Figures 7 to 11 respectively can be made using the three-step process of creating the part by sintering and then steam treating the sintered part in order to provide deposit a layer of Fe304 that creates a surface that is sufficiently smooth to provide the liquid seal without requiring machining or any additional surfaces to create the seal. Machining is required only to create any complex internal shapes such as screw-threads and keyways that cannot be created using sintering. Although all of the moving parts illustrated are rotating parts, the skilled man will appreciate that parts designed to execute, for example, reciprocating motion also require the smooth surface finishes provided by the method of the present invention.

Claims (10)

1. A method of manufacturing a moving part capable of providing a liquid seal, the method comprising the steps of: forming the part from sintered steel; forming a layer of Fe304 to provide a surface finish on the sintered part that is capable of providing a liquid seal.

2. The method according to claim 1, further comprising the step of machining complex structures within the part.

3. The method according to claim 2, wherein the structures are selected from a list including keyways and screw-threads.

4. A moving part providing a liquid seal for use in a vehide engine, the part comprising: a sintered body; and a steam treated surface finish for providing the liquid seal.

5. The moving part according to claim 4, wherein the movement is rotational movement.

6. The rotating part according to claim 5, wherein the part is a coupling for a fuel injector in a vehicle engine.

7. The rotating part according to claim 5, wherein the part is a viscous fan from a cooling system of an internal combustion engine.

8. The rotating part according to claim 5, wherein the part is a water pump for use in an internal combustion engine.

9. The rotating part according to claim 5, wherein the part is an oil seal retainer for use In sealing the ends of a vehicle crankshaft, differential transmission, gearbox, axle, driveshaft, hub or transfer case.

10. The rotating part according to claim 5, wherein the part is a vacuum pump for use in the braking system of a vehicle.