Spin-on Filter Concept for Future Engine and Vehicle Generations

Spin-on filters have proven themselves to be robust filters over decades in many areas of oil and fuel filtration. The filter change and in particular the removal of the spin-on filter requires force and is often only possible with the aid of a strap wrench or similar special tool. The bayonet lock developed by Mann+Hummel for the mounting of spin-on filters sets new standards for easy servicing and reduction of service costs.

Spin-on Filters for Industry and Automotive Applications

For a long time, spin-on filters have been state of the art for engine-related filtration tasks. They are used as robust filter units for oil, hydraulic and fuel filtration. A spin-on filter consists of a sheet metal filter housing which closes with a solid thread cover. Using the thread cover, the spin-on filter is screwed onto the engine or filter head. The sealing is made with an axial seal which presses onto the surface area of the flange when the thread cover is screwed on. The sealing between the dirty and clean side of the filter is made via the screw thread.

The filter element is located in the filter housing and the fluid to be filtered flows from the outside to the inside. Depending on the filtration requirements, the integration of all common types of filter media is possible: cellulose-based media, high performance media with glass fibers or synthetic fibers. The modular design of the filter also allows the integration of functions such as a bypass valve, anti-drain membrane or check valve on the clean side.

Spin-on filters are available in a wide range of sizes with diameters from 70 to 140 mm and lengths from 60 to 300 mm. The design is based on a modular system which enables the filter to be configured for different requirements through simple adjustments. In combination with standard filter heads, a filter system can easily be composed and an economic solution found, even for lower production volumes. The integration of additional functions as found in complex liquid filter modules requires a similar effort.

During servicing, a disadvantage of the simple design becomes apparent. The axial seal means that the force required for disassembly is sometimes very high. A special wrench is often needed to unscrew the spin-on filter from the filter head or engine flange. The further development of this design which has proven itself and which has been optimized over decades represented a big challenge. The targets for the further development of the spin-on filter into a modern product were:

• quick removal and fitting of the filter during a service without the need for tools

• prevention of the mounting of non- approved filters

• comparable mechanical robustness, to enable a one to one replacement

• only low additional costs compared to the conventional spin-on filter

• modular system to enable comparable product diversity

• unchanged installation space requirement

• no restrictions regarding use of various filter media.

These development targets were implemented in the new Wavelock system.

Design

The main design of the Wavelock system is largely comparable to the conventional spin-on filter. Figure 1 shows a cross- section of the system. The fluid to be filtered flows axially through the filter head into the filter and flows through the filter element from the outside to the inside. The cleaned fluid flows out of the filter through its center. The sealing to the environment and between the dirty and clean side of the filter element respectively is made with a radial O-ring. Depending on the respective requirements, the modular design can be used to integrate additional functions such as a filter bypass valve or an anti-drain membrane. The Wavelock spin-on filter does not require additional space for fitting or removal.

Figure 1

Cross-section of the Wavelock system (© Mann+Hummel)

Connection of the Spin-on Filter to the Flange

The key innovation of the Wavelock spin-on filter is the design of the connection of the spin-on filter to the flange on the filter head. A bayonet concept with three bayonet wings was developed to enable quick and easy service with fitting or removal carried out simply by a 90° rotation. The bayonet wings on the flange side are designed with a horizontal contact surface. The counter contour of the filter, which is also horizontal, is placed against this surface and transmits the active working forces. The pre-stressing between the filter flange and the spin-on filter is generated by a three-winged spring which presses the filter to the contact surface.

In order to enable easy and reliable fitting, the bayonet wings are designed with a lead-in chamfer and with a recess geometry on the filter side. The lead-in chamfer ensures that the spin-on filter can be positioned to precisely find the closing position without having to apply axial pressure. After a 90° rotation the bayonet is locked in the end position and the recess geometry on the filter side prevents an unintended opening of the connection during operation. The snap-in of the recess geometry can be clearly heard and felt to ensure secure fitting during servicing. An end stop integrated in the bayonet wings of the spin-on filter prevents rotation beyond the final position. The bayonet ring on the flange side is attached to the engine flange or the filter head and at the same time holds the wire spring in place. The bayonet ring on the filter side is firmly attached to the spin-on filter through the seaming ring.

The sealing between the filter head and the spin-on filter is realized with two radial O-rings, Figure 2. The sealing to the environment is realized via an O-ring attached to the external seal holder. The sealing between the dirty and clean side is established by the second O-ring which is attached to a plastic spacer on the center tube of the filter element and lies in a radial position at the outlet port. This robust design with pressurized sealing also seals reliably at high pressures and can compensate relative movements in the application. As there is no thread present in the flow area of the fluid, the component cleanliness is considerably increased. Shavings or wear particles from the thread manufacture or fitting process cannot enter the fluid.

Figure 2

Layout and design of the Wavelock bayonet lock (© Mann+Hummel)

Implementation of the Development Targets

The most important requirement for the spin-on filters is that servicing can be carried out without the need for tools. The filter change is to take place by hand without the aid of equipment and therefore much quicker. For servicing without tools the removal torque must not exceed 20 Nm. This is made possible by perfect matching of the materials of the bayonet rings, the design of the radial seals and the spring rate of the wire spring. This target is met with torques of approximately 12 Nm for fitting and maximum 20 Nm for the removal. Figure 3 shows the comparison of the fitting torques of a Wavelock spin-on filter and a comparable conventional spin-on filter. As the total number of components for the bayonet connection is greater than with a conventional spin-on filter, the manufacturing costs for the filter are higher. The application and the resulting improvement in servicing, however, compensate these additional costs.

Figure 3

Comparison of the fitting and removal torque of Wavelock spin-on filters and conventional spin-on filters of the size W962 after aging (© Mann+Hummel)

Design and Validation

The mechanical loads which arise during operation with the Wavelock system through vibration and static and dynamic internal pressure pose a big challenge for the design. For cost reasons, only manufacturing processes that can be implemented in large series are suitable for the production of the highly stressed components. Therefore, the bayonet rings on the filter and flange are punched and formed from steel sheet. The design has to be adjusted to the forming process and load peaks have to be avoided in the area where the forming is more extreme.

In order to meet these requirements at a reasonable cost, the complete development and process of optimization was supported with simulations. The dynamic and static simulation of the mechanical load of the components was linked to the simulation of the forming process in the production. This enabled a design which fully matches the robustness of conventional spin-on filters in every respect, Figure 4.

Figure 4

Results of the mechanical load simulation of the bayonet components (components from the head side (left), components from the spin-on side (right)) (© Mann+Hummel)

The vibration resistance of the bayonet system was a challenge for the development team. In order to obtain meaningful results for the necessary improvements in this respect, realistic load profiles were determined and used together with the known requirements as a basis for the simulation and validation of the components. In this way it was possible to optimize all the important design steps virtually, with validation only carried out on the component itself in a final step. The goal of achieving a robustness comparable to conventional spin-on filters was confirmed in the validation process. The examination of components under the same load profiles shows that a direct replacement of the robust spin-on filter with the Wavelock spin-on filter is possible.

Modular Filter System

The design of an interface between the filter and flange is only the first step to develop a successful product. In order to cover a wide range of applications, the Wavelock spin-on filter has to be integrated into an overall design concept which allows to combine different sizes, a wide range of filtration requirements and additional functions in a modular system. The first product family to realize the spin-on filter concept is the modular range of fuel pre-filters, Figure 5.

Figure 5

Modular Wavelock pre-filter system (© Mann+Hummel)

There are three different filter heads for the complete product range in this size: the standard version, a version with a hand-operated pump or with an electric fuel pump. The Wavelock spin-on filter is available in two lengths. The spin-on filters are also available with water separation and will be equipped with a variety of filter media. Finally, with the addition of components such as an electric heater or water sensor, the fuel pre-filter system is suitable for universal use.

Summary

Mann+Hummel has successfully further developed the proven spin-on filter design which has been the standard for decades. The Wavelock design maintains the simplicity and variability of a spin-on filter and also meets the requirements of modern filter systems. During servicing the patented bayonet connection of the Wavelock spin-on filter to the filter flange enables a quick filter change without the need for tools. The radial seals to the environment and between the dirty and clean side of the filter increase the operational reliability. The risk of particle contamination is reduced as no thread is integrated in areas where fluid flows. The Wavelock spin-on filter does not require more space than other available products and also meets the requirements for mechanical durability for the same applications. The integration of the Wavelock design in a modular system is currently being implemented. This includes the possibility of different sizes and the ability to use all filter media currently available.