WO2010060900A1

WO2010060900A1 - Automotive flywheels

Info

Publication number: WO2010060900A1
Application number: PCT/EP2009/065720
Authority: WO
Inventors: Jacob Koenen
Original assignee: Dsm Ip Assets B.V.
Priority date: 2008-11-26
Filing date: 2009-11-24
Publication date: 2010-06-03

Abstract

The invention relates to a flywheel for arrangement in an internal combustion engine (ICE) in engagement with a starter pinion, comprising a flywheel mass carrying a toothed crown made of a plastic material mounted on the flywheel mass.

Description

AUTOMOTIVE FLYWHEELS

The invention relates to a flywheel or starter ring gear (also denoted as flywheel) for arrangement in an internal combustion engine (ICE). More particular the flywheel is for an ICE with a start / stop system.

Such a flywheel typically comprises a flywheel mass carrying a toothed crown for engagement with a starter pinion of a starter engine. Such a toothed crown typically consists of a rim comprising a series of outwardly oriented teeth, positioned in the circumferential area of the flywheel mass. At present such a toothed crown, which is of relatively large diameter, is made by starting with a strip of high carbon steel, having a square or rectangular cross-section, and cutting it to a preset length. This strip is then rolled into a circular configuration with a major diameter larger than the finished gear size, and the ends are welded together to close the loop. The part is then annealed, coined flat and either coined to size on the minor diameter or bored to size or both. The closed hoops are then loaded onto an expanding type arbor in quantities of around twenty-five and the gear teeth and major diameter are cut using a hobbing machine or gear shaping machine. After gear cutting, the closed ring is then placed in a fixture, formed round, and centered and then weld mounted on a flat or flanged stamped center plate. The flywheel typically consists of metal, which may be a one piece element, or consisting of one or more mass plates, with the toothed crown, secured on the plate(s) by, for example, riveting or seaming.

Flywheels for internal combustion engines use to be integrally of metal, as the only material considered suitable for such heavy duty applications. A flywheel for internal combustion engines made of plastic material is described in French patent No 77 28419. Herein the body of the flywheel, and optionally also the toothed crown as an integrated part thereof, is made of a light weight plastic material. The said flywheel comprises different metal inserts, e.g. the hub with a hole to receive the axle of the engine and a peripheral part to add weight to the flywheel, and optionally also a teethed metal crown. The flywheel is made by overmolding of the various metal parts with the plastic composition. Proper alignment is very critical in such processes, in particular in view of the high revolution speed that are achieved with ICE flywheels

In one embodiment therein the flywheel comprises undulations to equalize movements of vibrations or precession which develop during use of such engines. However, flywheels made of plastic material have never been used on large industrial scale for internal combustion engines.

Internal combustion engines are used, for example, in passenger cars. The flywheel mass generally will be on the driving side while the pinion can be on the gear unit. Alternatively the starter engine comprises a ring gear, with inwardly oriented teeth, planetary gear units and a sun gear, the sun gear driving the pinion. The driving side flywheel or starter ring gear can be fixed to the crankshaft e.g. by means of a plurality of threaded studs. In view of increasing energy prices developments are ongoing for a long time and will continue for energy savings. One such development is focused on ICE for passenger cars having a start / stop system, also known as stop / start systems. A start / stop system is intended to completely stop the engine when the passenger car comes to a stand, for example, for a traffic light, and to restart the engine when the traffic light gives way again. During the stand-still, no energy is consumed. Starting or restarting of an internal combustion engine is generally accompanied with increased noise in the passenger cabine, due to which stopping and restarting the engine at each standstill can become really annoying. Repeatedly stopping and restarting the engine also increases the requirements on the wear and friction properties on the flywheel and pinion since the number of required starts went up from 50,000 to 300,000. The present invention aims to provide a solution for the above problems.

Thus there is a need for flywheels with improved performance, which can be used for these heavy duty application conditions and which contributes to noise reduction.

The present invention consists in a flywheel for an internal combustion engine (ICE), comprising a flywheel mass and a toothed crown mounted on the flywheel mass, wherein the toothed crown is made of a plastic material. The inventors have found that plastics can do a great job when used as the material for making the toothed crown. The effect of the flywheel according to the invention is that the noise of the engine during start-ups is reduced while the flywheel can withstand a large number of stop-start cycles without significant wear of the flywheel, without giving in on alignment and rigidity of the flywheel. Another effect is that the toothed crown can be made by simple processes, while for the flywheel mass conventional processes for production can still be used. Furthermore, the lifetime of the flywheel can easily be extended by simply replacing the plastic crown on the flywheel by a new plastic crown, without the need to replace the complete flywheel mass. In one preferred embodiment of the invention, the toothed crown comprises a circumferential reinforcing flange, extending in tangential direction and outwardly in radial direction, being in direct engagement with a part of the teeth of the crown. The effect is that the flywheel can withstand a larger the number of stop-start cycles, or alternatively that the material from which the crown is made can be chosen from a wider range, and/or the width of the teeth can be reduced, while the large number of stop-start cycles that the flywheel can withstand, can be maintained.

The toothed crown may comprise one circumferential reinforcing flange at in the crown, or alternatively two circumferential reinforcing flanges, one at each side of the crown, thereby supporting the teeth of the crown at both lateral sides. With two circumferential reinforcing flanges, the circumferential reinforcing flange positioned at that side of the crown in the direction at the pinion axle, shall extend outwardly in radial direction in such limited extend only that engagement of the teeth of the toothed crown with the pinion is still feasible. While two circumferential reinforcing flanges, one at each side of the crown, are preferred from a mechanical strength and durability point of view, a toothed crown with one circumferential reinforcing flange is easier to produce in a single positive moulding step.

The mechanical strength and durability of the toothed crown may also be enhanced by increasing the width of the teeth of the crown. The width of the teeth may vary widely and suitably is in the range of 3 mm to 5 cm.

Preferably the toothed crown in the flywheel according to the invention has teeth with a width of at least 5 mm, preferably at least 8, or even at least 10 mm. For compactness of the flywheel in the engine space, the width of the teeth is preferably at most 3 cm, or better at most 2.5 cm or even 2.0 cm.

The plastic material that is used for making the toothed crown may be any material that can be suitably shaped in the form of the toothed crown, optionally with one or two circumferential reinforcing flanges, and that has durability properties to be used in gear wheels. In another preferred embodiment of the invention the plastic material has a coefficient of friction (COF) of at most 0.7, measured with the test method according ASTM 3702 at 23^eC with a pressure P of 0.83MPa and a velocity V of 0.51 m/sec, and a tensile fatigue strength (TFS), measured on non-aged, dry as molded (0 wt% water) ISO 527/1 A tensile bars at a temperature of 140 °C under a sinusoidal tensile load at a frequency of 8 HZ, with a ratio between minimum fatigue load and maximum fatigue load of 0.1 , of at least 10MPa for 10⁶ cycles.

The flywheel with a toothed crown made of such a material shows a low noise production during start up and has a long durability with retention of its functionality during its use in an ICE. Moreover, the toothed crown can be designed without circumferential reinforcing flanges alongside the teeth, and with relative small teeth width, while still performing well in noise reduction and durability.

The materials with said properties can be suitably used to make starter crowns with standard dimensions. This has a big advantage for the flywheel producer, since he can do without fundamental changes in the designs. Such standard starter crowns typically have a tooth width of about 1 cm to 2 cm. Although it might be assumed that the material properties requirements might be less with crowns with larger dimensions, but in view of the general trend of space savings and size reduction, it has been a specific goal of the inventors to provide a solution in particular for the standard size and smaller.

Preferably, the COF of the material is at most 0.6 or at most 0.5 and also preferably the tensile fatigue limit (TFS) is at least 25, 30 or even 40MPa at 10⁶ cycles. The lower the COF is and the larger the residual tensile fatigue strength is, the larger the number of stop-start cycles is that the flywheel can withstand. The material used for the crown also preferably has a Charpy impact resistance measured according to test method ISO179/1 ell of at least 45 kJ/m2, resulting in a better overall performance.

The advantage of the starter crown with the preferred material properties is that either the crown can be designed with a smaller tooth width and/or the crown shows a longer service.

The plastic material comprises a polymer. The polymer can be considered as the primary component. Suitably, the polymer is a thermoset polymer or a thermoplastic polymer. Suitable thermoplastic polymers include liquid crystalline polyesters, polyimides, thermoplastic polyesters and thermoplastic polyamides, preferably semi-crystalline thermoplastic polyesters and semi-crystalline thermoplastic polyamides. These semi-crystalline polymers preferably have a melting point of at least 240⁰C, more preferably at least 260⁰C and still more preferably at least 280⁰C. With the term melting point (temperature) is herein understood the temperature, measured according to ASTM D3418-97 by DSC with a heating rate of 10°C/min, falling in the melting range and showing the highest melting rate.

The liquid crystalline polyesters suitably consists of (1 ) diacid residues consisting essentially of (i) cyclohexanedicarboxylic acid residues and (ii) other diacid residues, 2,6-naphthalene-dicarboxylic acid residues, or a mixture thereof; (2) diol residues consisting essentially of hydroquinone residues, 4,4'-biphenol residues or a mixture therof; and, optionally (3) p-hydroxybenzoic acid residues. In the above definition, the moles of diol residues are equal to the moles of diacid residues and the total of the (1 ), (2) and (3) mole percentages is equal to 100. The liquid crystalline polyesters have melting points determined by differential scanning calorimetry equal to or less than 360⁰C.

Examples of suitable semi-crystalline thermoplastic polyesters are PET, PBN, and PEN. Examples of suitable semi-crystalline thermoplastic polyamides include aliphatic polyamides, such as PA6, PA66 and PA46, and semi-aromatic polyamides based on terephthalic acid, such as PA66/6T, PA9T and derivatives thereof.

A wide variety of polyimides are suitable for use according to the invention, including those described in U.S. Patent No. 3,179,614, the teachings of which are incorporated herein by reference. The polyimides described therein are prepared from at least one diamine and at least one anhydride. Preferred diamines, which can be used, include m-phenylene diamine (MPD), p-phenylene diamine (PPD), oxydianiline (ODA), mehtylene dianiline (MDA), and toluene diamine (TDA). Preferred anhydrides, which can be used to include benzophenone tetracarboxylic dianhydride (BTDA), biphenyl dianhydride (BPDA), trimellitic anhydride (TMA), pyromellictic dianhydride (PMDA), maleic anhydride (MA), and nadic anhydride (NA).

Next to the polymer, the plastic material may comprise other components, such as fillers, reinforcing agents, and one or more additives. Preferably the plastic material comprises a lubricating additive, more preferably a lubricating additive in combination with either a filler or a reinforcing agent, or a combination thereof.

Suitable fillers that can be used in the plastic material for the toothed crown are graphite, mica, and molybdenum disulphide (MoS₂). As reinforcing agent, can be used, for example, glass fibres, carbon fibres and aramid fibres.

For the lubricating additive may be chosen a polymer, for example, fluoroelastomers, such as Teflon, and maleic acid anhydride modifications thereof, rubbers and polyolefines, and maleic acid anhydride modifications thereof, such as maleic acid anhydride modified polyethylene, polypropylene or PE/PP rubber. Preferably the lubricating additive is a maleic acid anhydride polymer.

Preferably, the composition of the plastic material and the combination of components therein are chosen such that the plastic material has a heat distortion temperature (HDT-A) of at least 190⁰C, measured according to ISO 75- 2, and a nominal 0.45 MPa stress applied (HDT-B), of at least 280⁰C; idem ISO 75-2, nominal 1.80 MPa stress applied (HDT-A). The HDT herein is measured on pre-dried samples having a residual moisture content of at most 0.01 wt%, relative to the total weight of the plastic material. The residual moisture content was measured by Karl fisher titration ISO method 15512.

Such a plastic material may be a thermoplastic polyamide composition comprising

(a) 0.- 99 wt.% of a semi-crystalline polyamide with a melting temperature of at least 250⁰C, (b) 1 - 20 wt.% of either (i) a maleic acid anhydride modified polyolefine or (ii) a maleic acid anhydride modified fluoroelastomer, or a combination of (i) and (ii), and

(c) 0 -40 wt.% fillers and/or fibres, wherein the wt.% of (a), (b) and (c) is relative to the total weight of the plastic material.

An example of such a material is a polyamide composition, comprising 80 wt.% of polyamide-46, 20 wt.% of a maleic acid anhydride modified polyolefine.

The toothed crown for the flywheel according to the invention may be produced by any method that is suitable for making plastic parts. The method may comprise different moulding and shaping steps, and combinations thereof. The toothed crown may for example be obtained by injection moulding of the plastic material or by machining of a ring shaped or flat shaped plastic specimen. A ring shape specimen may be obtained by extrusion moulding of a pipe and cutting or sawing the ring shape specimen there from. Alternatively the toothed crown may be a multicomponent part, which may be produced starting from a metal ring, which can be overmoulded with the polymer composition. Preferably, the toothed crown is integrally made of the polymer composition.

In a preferred process the toothed crown is made by positive injection moulding. With the term positive injection moulding is herein understood that the moulded part is obtained in its final shape and that no post-moulding shaping steps are necessary. Removal of flash, polishing of the part and similar steps are not considered shaping steps, i.e. these do not change the shape of the part.

The flywheel according to the invention comprises, next to the toothed crown, a flywheel mass. Such a flywheel mass typically comprises a hub comprising a hole for receiving the axle of the engine and aligning and positioning and of the flywheel in the right position for engagement with the pinion of the starter engine, a web and a peripheral part, the latter part contributing largely to the mass of the flywheel. The flywheel mass is typically made of metal. In the flywheel according to the invention the toothed crown and the flywheel mass have to be assembled together. This assembly may be accomplished for example by mounting the toothed crown on the flywheel mass by riveting or screwing.

The toothed crown may also be fixed by shrinking or welding, or a combination thereof. Suitably, the toothed crown is in direct engagement with the flywheel mass via a circumferential surface area on the flywheel mass, which area is referred to herein as engagement surface area. This engagement surface area may extend in tangential and axial direction. Preferably, the said circumferential surface area is provided with surface irregularities for mechanical interlocking thereby preventing release of the toothed crown from the flywheel mass. The invention also relates to a toothed crown, for use in a flywheel for an internal combustion engine (ICE), made of a plastic material, and all preferred embodiments thereof as described above.

The invention further relates to an internal combustion engine (ICE) comprising a flywheel or a toothed crown according to the invention and all preferred embodiments thereof as described above. The flywheel suitably is a single mass flywheel or a dual mass flywheel.

In a preferred embodiment, the internal combustion engine (ICE) is a combustion engine with a start / stop system.

In another preferred embodiment, the flywheel in the internal combustion engine (ICE) is a dampened flywheel or a dual clutch flywheel. The invention is further illustrated with the following examples and experiments.

Test methods Melting point

The melting point was measured according to ASTM D3418-97 by DSC with a heating rate of 10°C/min, falling in the melting range and showing the highest melting rate.

Heat distortion temperature HDT

The heat distortion temperature (HDT-B) was measured according to ISO 75-2, nominal 0.45MPa stress applied (HDT-B). The heat distortion temperature (HDT-B) was measured according to ISO 75-2, nominal 1.80MPa stress applied (HDT- A). Prior to measuring the material was pre-dried at 120 °C to a residual moisture level below 0.01 wt%.

Coefficient of friction COF

The coefficient of friction was measured according to test method

ASTM 3702, at 23^ with a pressure P 0.83MPa and a velocity V 0.51 m/sec.

Residual tensile fatigue strength

The residual tensile fatigue strength was measured according to the

DSM test method for tensile fatigue, comprising the testing of non-aged, dry as molded

(0 wt% water) 4 mm thick ISO 527/1 A tensile bars under a sinusoidal load with a ratio between minimum fatigue load and maximum fatigue load of 0.1 at a frequency of 8 HZ and a temperature of 140 °C.

The compositions and test results of 2 materials have been collected in table 1 Table 1. Material compositions (in parts by weight) and test results

Both material perform well in the tensile fatigue strength test and are suited for use in the toothed crowns of the flywheels according to the invention. In that respect, the material of Example 2 is even better than that of Example 1 .

Claims

1. A flywheel, for arrangement in an internal combustion engine (ICE), comprising a flywheel mass carrying a toothed crown mounted on the flywheel mass for engagement with a starter pinion of a starter engine, wherein the toothed crown is made of a plastic material.

2. A flywheel according to claim 1 , wherein the plastic material has a coefficient of friction (COF) of at most 0.7, measured with the test method according ASTM 3702 at 23^eC with a pressure P of 0.83MPa and a velocity V of 0.51 m/sec, and a tensile fatigue strength (TFS), measured on non-aged, dry as molded (0 wt% water) ISO 527/1 A tensile bars at a temperature of 140 °C under a sinusoidal tensile load at a frequency of 8 HZ, with a ratio between minimum fatigue load and maximum fatigue load of 0.1 , of at least 10MPa for 10⁶ cycles.

3. A flywheel according to claim 1 or 2, wherein the plastic material comprises either a filler, a reinforcing agent or a lubricating additive, or any combination thereof.

4. A flywheel according to any of claims 1 -3, wherein the plastic material has a heat distortion temperature HDT-A of at least 19CO, measured according to ISO 75-1/-2 on pre-dried samples having a residual moisture content of at most 0.01 wt%.

5. A flywheel according to any of claims 1 -4, wherein the plastic material is a thermoplastic polyamide composition comprising a semi-crystalline polyamide with a melting temperature of at least 250⁹C measured with the test method according to ASTM D3418-97 by DSC with a heating rate of 10°C/min, and either (i) a maleic acid anhydride modified polyolefine or (ii) a maleic acid anhydride modified fluoroelastomer , or (iii) PTFE, or (iv) molybdumdisulfide or (v) glass reinforcement or a combination of (i) (ii),(iii),(iv) or (v).

6. A flywheel according to any of claims 1 -5, wherein the toothed crown is obtained by positive injection moulding of the plastic material or by machining of a ring shaped plastic specimen.

7. A flywheel according to any of claims 1 -6, wherein the toothed crown is in direct engagement with the flywheel mass via a circumferential surface area on the flywheel mass extending in tangential and axial direction, wherein the circumferential surface area is provided with surface irregularities for mechanical interlocking thereby preventing release of the toothed crown from the flywheel mass.

8. A flywheel according to any of claims 1 -7, wherein the toothed crown comprises a circumferential reinforcing flange, extending in tangential direction and outwardly in radial direction, being in direct engagement with a side part of the teeth of the crown.

9. A toothed crown, for use in a flywheel by mounting on a flywheel mass for an internal combustion engine (ICE), made of a plastic material.

10. A toothed crown according to claim 9, wherein the toothed crown comprises a circumferential reinforcing flange according to claim 9, and/or wherein the plastic material is according to any of claims 2-5.

1 1. An internal combustion engine (ICE) comprising a flywheel according to any of claims 1 -8.

12. An internal combustion engine (ICE) according to claim 1 1 , comprising a combustion engine with a start / stop system.

13. An internal combustion engine (ICE) according to claim 1 1 or 12, wherein the flywheel is a dampened flywheel or a dual clutch flywheel.