A starter assembly for a combustion engine

Abstract

A starter assembly is described comprising a starter motor provided with a starter shaft, and a driven wheel engaged with the starter shaft. The driven wheel is rotatably mounted on a driven wheel shaft adapted to be mounted in at least one respective seat. The driven wheel is, in turn, connected to a starter transmission configured to operate on the drive shaft and allow starting-up the engine, in which at least one support bushing is provided between the driven wheel shaft and the driven wheel.

Description

A STARTER ASSEMBLY FOR A COMBUSTION ENGINEDESCRIPTIONTECHNICAL FIELD

[0001] The invention relates to an improved starter assembly for a combustion engine of a motorvehicle. In particular, it relates to a starter assembly intended for two-or three- wheeled motorvehicles, such as scooters or other rideable saddle vehicles.PRIOR ART

[0002] In the field of motorvehicles, in particular, those of the rideable saddle type, such as motorcycles, scooters, and similar vehicles with two or three wheels equipped with a combustion engine, the use of a starter assembly that is actuated by the user to start the combustion engine, is well known.

[0003] The starter assembly consists of an electric motor that, by means of a dedicated transmission, acts on the drive shaft. In a consolidated configuration, the electric motor is associated with an idler wheel, which modifies the transmission ratio. This idler wheel is connected to a starter ring gear that transfers the motion to a freewheel mechanism. The latter receives the energy from the electric motor and transmits it to the drive shaft, thus allowing the start-up of the engine.

[0004] In starter assemblies of the prior art, significant noise is observed when the combustion engine is started. This phenomenon is predominantly due to the impact and stress of the mechanical components at start-up. Furthermore, while the starter motor is operating, the generated vibrations propagate in the transmission assembly, with particular emphasis on the parts of the casing which enclose said assembly. The vibrations, in this case, may cause stresses that adversely affect the duration and the overall efficiency of the system.

[0005] Over time, such vibrations may cause malfunctions in the transmissionassembly and in the starter assembly, preventing the start-up of the combustion engine.SUMMARY

[0006] It is, therefore, an object of the present invention to provide an improved starter assembly, which makes it possible to solve the drawbacks of the prior art.

[0007] It is a further object of the present invention to provide an improved starter assembly, which is structurally simple and reliable, attenuating vibrations and the acoustic impact perceived by the user at start-up of the combustion engine.

[0008] These and other objects are reached by an improved starter assembly that comprises a starter motor provided with a starter shaft, and a driven wheel engaged with the starter shaft. The driven wheel is rotatably mounted on a driven wheel shaft adapted to be mounted in at least one respective seat. The driven wheel is, in turn, connected to a starter transmission configured to operate on the drive shaft and allow engine start-up.

[0009] In particular, at least one support bushing is provided between the driven wheel shaft and the driven wheel. The driven wheel comprises a mounting hole through which the driven wheel is fitted on the driven wheel shaft. The at least one support bushing is integrally mounted in the mounting hole of the driven wheel. The assembly formed by the driven wheel and the at least one mounting bushing is rotatably mounted on the driven wheel shaft.

[0010] Preferably, the starter motor is keyed on a casing that encloses a transmission assembly associated with the combustion engine. The driven wheel shaft is supported in at least one mounting seat formed on the casing.

[0011] The casing comprises a first casing portion on the transmission assembly side, a second casing portion on the flywheel side, and a third casing portion defining a cover on the flywheel side.

[0012] In a first embodiment, the driven wheel shaft is supported by a single support seat, resulting mounted in a cantilevered manner. A first and a second support bushing are preferably provided, each having a respective flange portion, the first and second support bushings being fitted into the mounting hole of the driven wheel, so that the respective flange portions are external and mutually opposed, defining lateralabutments external to the mounting hole in which the driven wheel is arranged.

[0013] In particular, the joining of the support bushings in the mounting hole of the driven wheel is obtained by interference coupling. Interference coupling means a joining in which the dimensions of the two parts, namely the cylindrical surface of the bushing and of the mounting hole, are designed so that their tolerance creates a coupling force greater than zero, when they are mounted. The obtained joining produces a very rigid and stable connection, without the need for additional components.

[0014] In this manner, the pair of support bushings ensures a precise coupling of the driven wheel on the driven wheel shaft, which determines a more stable rotation of the driven wheel, limiting oscillations. This determines better reliability, precision and efficiency in the motion transmission kinematic chain, with a reduction of vibrations and noise. Furthermore, the flange portions laterally retaining the driven wheel optimize the stability thereof in the axial direction, ensuring correct alignment with the starter shaft from which it receives motion.

[0015] In a second embodiment, the driven wheel shaft is shaped to be arranged on a first support seat and a second support seat opposite each other. In such a case, the driven wheel shaft is mounted on opposing supports defined by the respective support seats. Again, in this case, a first and a second support bushing are provided, each having a respective flange portion. The first and the second support bushings are mounted with interference in the driven wheel mounting hole, so that the respective flange portions are opposed to each other outside the driven wheel mounting hole, defining lateral abutments within which the driven wheel is arranged.

[0016] Advantageously, in said second embodiment, a third and a fourth support bushing having a respective flange portion are also provided, in which the third and the fourth support bushings are shaped to be inserted into the first and second support seat of the driven wheel shaft, and in which the respective flange portions of the third and fourth support bushings abut with the flange portions of the first and second support bushings. In this manner, a stable coupling of the driven wheel shaft in the seats opposite one another is obtained, ensuring precise alignment of the rotation axis. At the same time, as in the first embodiment, an axial locking of the driven wheel onthe driven wheel shaft is guaranteed, ensuring a correct coupling with the starter shaft of the starter motor.

[0017] Preferably, the driven wheel is a gear wheel. The starter shaft is provided with a respective gear mounted or formed on the starter shaft itself.

[0018] In particular, the driven wheel meshes with a starter ring gear adapted to be coaxially mounted on the axis of the drive shaft. The starter ring gear acts in combination with a freewheel mechanism for starting-up the combustion engine of the known type.

[0019] Advantageously, the starter assembly is applied to a transmission assembly selected from a CVT transmission or a geared transmission.

[0020] Advantageously, a further support bushing is provided, arranged at an attachment collar of the starter motor. In this manner, the support bushing improves the stability of the starter motor in its interface portion with the transmission assembly, in particular with the casing enclosing the transmission assembly.

[0021] Advantageously, the support bushing is interference-fitted on the collar of the starter motor and, in turn, inserted in an appropriate seat formed on the casing of the transmission assembly. In this manner, the bushing on the starter motor side determines that the starter shaft of the starter motor maintains an aligned position with respect to its own rotation axis C-C, and thus a more correct and stable functional coupling with the driven wheel with which it is directly meshed.

[0022] In particular, the support bushings are made of a plastic material, in particular a rigid plastic material with acoustic insulation properties, e.g., polypropylene, polyamide or the like. In this manner, the plastic material provides acoustic noise reduction properties in addition to mechanical resistance properties.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be better understood with reference to description and the accompanying drawings, which illustrate exemplary and non-limiting embodiments of the invention. More in particular, in the accompanying drawings:Fig. 1 shows a perspective view of a motorcycle, in particular a scooter, on which a starter assembly in accordance with the invention can be installed;Fig. 2 shows an exploded view of the components that constitute a starter assembly mounted on a transmission assembly and respective combustion engine of the vehicle of Fig. 1;Fig. 3 shows an internal front view of a transmission assembly on which a starter assembly in accordance with the invention is arranged;Fig. 4 shows a side section view of the transmission assembly of Fig. 2, which shows a first embodiment of the starter assembly in accordance with the invention;Fig. 5 shows a side section view of the transmission assembly with an implemented starter assembly in accordance with a second embodiment of the invention.DETAILED DESCRIPTION

[0024] Fig. 1 shows, by way of example, a scooter 1 on which a starter assembly 10 (Fig. 2) can be installed according to the present invention. The scooter 1 comprises at least one front steerable wheel 2 controlled by a handlebar 5, a rear wheel 3, a rider station having a saddle 4, a transmission assembly 20 and a combustion engine 30 (Fig.2). The scooter 1 is shown by way of example, as one of the possible motorvehicles on which the starter assembly 10 described herein can be installed.

[0025] Fig. 2 shows an exploded representation of the starter assembly 10 that is arranged on a transmission assembly 20 and acts to start the combustion engine 30, hereinafter just engine 30. The starter assembly 20 can be selected from an automatic CVT transmission (Continuously Variable Transmission) or a gear transmission.

[0026] In particular, the starter assembly 10 comprises a starter motor 12 provided with a starter shaft 13 and a driven wheel 14 engaged with the starter shaft 13. The driven wheel 14 is rotatably mounted on a driven wheel shaft 15,15’ housed in the transmission assembly 20, as described below.

[0027] The driven wheel 14 is, in turn, connected to a starter transmission 16 (not shown in detail), which acts on the drive shaft, the axis of which is indicated by reference A (Fig. 2), and allows starting-up the engine 30, according to a constructionof the known type (not described in detail). For example, the starter transmission 16 either is or comprises a starter ring gear 16 mounted on axis A of the drive shaft.

[0028] In particular, the driven wheel 14 meshes with the starter ring gear 16 mounted on axis A of the drive shaft. The starter ring gear 16 acts in combination with a freewheel mechanism (not shown and of the known type) for starting-up the engine 30. When the starter motor 12 begins to rotate, it transmits motion to the driven wheel 14, which performs a transmission reduction, which, in turn, sets the starter ring gear 16 into rotation, transmitting it to the drive shaft by means of the freewheel mechanism. The freewheel mechanism disengages once the rotational speed of the drive shaft exceeds the rotational speed of the freewheel. In other words, the freewheel allows the rotation in a single direction, but prevents reverse rotation. When the engine is started-up, the freewheel mechanism is such that the starter motor (that supplies the force to begin the rotation of the engine) rotates without the engine itself being involved in rotation. This occurs by virtue of the temporary separation of the freewheel. Once the engine has reached a sufficient speed for self start-up, the freewheel disengages, allowing the autonomous operation of the engine. When the engine is started-up, the freewheel disengages from the starter motor and from the starter transmission.

[0029] It is observed that, according to the prior art, this transmission chain between the starter motor 12 and the starter ring gear 16 generates undesired vibrations on the transmission assembly 20, in particular on the casing 21,22,23 of the transmission assembly 20.

[0030] According to the present invention, at least one support bushing 51,52,54,55 is provided interposed between the driven wheel 14 and the driven wheel shaft 15,15’.

[0031] Structurally, the driven wheel 14 comprises a mounting hole 14a through which it is fitted onto the driven wheel shaft 15,15’. The mounting hole 14a is substantially the circular opening through which the driven wheel 14 is fitted onto the driven wheel shaft 15,15’. The at least one support bushing 51,52,54,55 is integrally mounted in the mounting hole 14a of the driven wheel 14. The assembly formed by the driven wheel 14 and by the at least one mounting bushing 51,52,54,55 is rotatably mounted on the driven wheel shaft 15,15’.

[0032] The support bushing 51, 52, 54, 55 has a tubular section that is inserted in the mounting hole 14a. Between the tubular section and the mounting hole 14a there is minimum tolerance, which implies that the joining of the support bushing 51,52,54,55 in the mounting hole 14a occurs by interference coupling.

[0033] In the following embodiments, the starter assembly 10 according to the present invention is applied to a transmission assembly 20 of the CVT type.

[0034] As known, a CVT transmission is a system that offers a continuous variation of the transmission ratio, without using fixed gears. This type of transmission uses two pulleys (one connected to the engine and the other to the rear wheel) and a belt connecting them.

[0035] The CVT transmission assembly 20, as better shown in Fig. 2, is enclosed in a casing 21,22,23. The casing comprises a first casing portion 21, hereinafter also referred to as half-casing 21 on the transmission side, a second casing portion 22, hereinafter also referred to as half-casing 22 on the flywheel side, and a third casing portion 23, hereinafter referred to as cover 23 on the flywheel side. Such reference numerals have been introduced to better clarify the following description and are references known to a person skilled in the art.

[0036] In particular, as shown in a first embodiment of Fig. 4, the driven wheel shaft 15 is configured to be mounted in a cantilevered manner on a casing portion 22 on the flywheel side. The driven wheel shaft 15 defines a driven rotation axis B-B.

[0037] Structurally, the driven wheel shaft 15 is inserted, for a stretch 15a, into a mounting seat 22a formed in the second casing portion 22. The remaining part of the shaft 15b is cantilevered. The driven wheel shaft 15 is in contact only with the casing portion 22 on the flywheel side. Bushings 51,52 integral with the mounting hole 14a of the driven wheel 14 are fitted in the cantilevered shaft portion 15b. The bushings 51,52 are mounted with interference in the mounting hole 14a of the driven wheel 14. In this manner, the driven wheel 14 and the bushings 51,52 integrally rotate about the driven wheel shaft 15.

[0038] This first embodiment proves particularly advantageous also for the mounting of the driven wheel shaft 15 in a cantilevered manner. Indeed, in this manner the drivenwheel shaft 15 is in contact only with a portion of the casing, in particular the half casing 22 on the flywheel side. Accordingly, there being no support at the free end of the driven wheel shaft 15, no transmission of vibrations occurs toward the third casing portion 23, namely, the casing on the flywheel side. This embodiment avoids (even without the aid of the support bushings) a transmission of vibrations toward the cover 23.

[0039] In particular, the support bushings 51 and 52 are mounted from mutually opposite sides in the mounting hole 14a. Each support bushing 51,52 comprises a flange portion 51’, 52’. The flange portion 51’ of the bushing 51 on the casing side 22 contacts, on the side opposite the driven wheel 14, a shoulder defined around the mounting seat 22a. The bushing 52 on the outer side comprises a flange portion 52’ oriented opposite the flange portion 51’ of the bushing on the half casing side 22. The flange portions 51’, 52’, external to the mounting hole 14a, contact the driven wheel 14, retaining it laterally. A first and a second bushing 51,52 are provided for the sake of ease of joining of the various parts on the driven wheel shaft 15. In this manner, it is concretely possible, e.g., by adapting the size of the mounting hole 14a of the driven wheel 14, to provide the bushings 51,52 also on a starter assembly 10 which does not include them, so as to solve the technical drawbacks described in the introductory part.

[0040] In this manner, the support bushings 51 and 52 allow reducing the vibrations transmitted from the starter motor 12 toward the driven wheel 14, and consequently toward the starter ring gear 16 and freewheel mechanism thereof. The vibrations are also damped on the casing 21,22,23 that houses the transmission assembly 20. The reduction of vibrations determines a decrease in noise of the starter assembly 10 at engine start-up. From real tests, under identical conditions, a noise reduction between 5 and 10 decibels has been observed.

[0041] In functional terms, the starter motor 12 rotates at a speed of about 12,000 rpm. The driven wheel 14, which has the functionality of varying the transmission ratio of the starter motor 12, is subjected to high mechanical stress; therefore, the shaft 15,15’ of the driven wheel 14 mounted on the support bushings 51,52 is more stable when absorbing the vibrations, thus determining a reduction of the acoustic impact perceived by the user.

[0042] In a second embodiment, shown in Fig. 5, the driven wheel shaft 15’ is supported between two ends forming part, respectively, of the second casing portion 22 and of the third casing portion 23. Therefore, in this case, the driven wheel shaft 15’ has two respective mounting seats 22a’ ,23a’ formed in the casing 22 on the flywheel side and in the cover 23 on the flywheel side, respectively. Advantageously, two pairs of bushings 53,54 and 55,56 are provided, arranged at the ends of the driven wheel shaft 15’.

[0043] In detail, for each end of the driven wheel shaft 15’, bushings 53 and 56 are inserted in the respective mounting seat 22a’ ,23a’. The further bushings 54 and 55 are opposite the latter, and mounted with interference in the mounting hole 14a of the driven wheel 14. As in the previous embodiment, each support bushing is provided with a respective flange portion 53’, 56’ and 54’ and 55’ and also in this embodiment the flange portions 54’, 55’ of the bushings 54,55 are opposed to each other so as to laterally embrace the driven wheel 14. Practically, the flange portions 54’, 55’ limit an axial movement of the driven wheel 14 on the driven wheel shaft 15. The flange portions 54’, 55’, in turn, abut with the other respective flange portions 53’, 56’. In this manner, the driven wheel shaft 15’ is supported in the mounting seats 22a’ ,23a’ with the interposition of respective support bushings, and the driven wheel 14 is, in turn, supported by respective support bushings 54,55 that interface with the driven wheel shaft 15’. This configuration attenuates the vibrations generated by the starter motor 12, reducing the impact transmitted to the driven wheel 14 and the corresponding driven wheel shaft 15’, thus preventing oscillation phenomena and ensuring a motion transmission free of instability.

[0044] For both embodiments illustrated with reference to Figs. 4 and 5, a further support bushing 58 is provided, arranged at an attachment collar 12' of the starter motor 12. In this manner, the support bushing 58 improves the stability of the starter motor 12 in its interface portion with the casing 21,22,23, in particular with the second casing portion 22. The support bushing 58 is interference-fitted onto the collar 12’ of the starter motor 12 and, in turn, inserted into an engagement seat 28a (Figs. 4 and 5). The optimized mounting of the starter motor 12 on the casing 22, by means of the support bushing 58, ensures greater stability, allowing the starter shaft 13 to maintain precise alignment with respect to its rotation axis C-C, preventing oscillations induced by highrotational speed. Thus, the kinematic chain formed among the starter shaft 13, the driven wheel 14 and the starterring gear 16 is functionally more stable, attenuating the vibrations between the gears and the propagation of such vibrations throughout the transmission assembly, which cause noise and undesired fluctuations in the casing perceived by the user.

[0045] Structurally, the support bushing 58 comprises a respective flange portion 58’. The flange portion 58’ is facing the side of the starter motor 12 and is interposed between the peripheral edges of the engagement seat 28a and the starter motor wall defined by the collar 12’.

[0046] In a preferred embodiment, all the support bushings are made of a plastic material, in particular, rigid plastic material with acoustic insulation properties, e.g., polypropylene, polyamide, or the like.

[0047] In all the embodiments described, the starter device 10 is of simple construction and extremely effective in reducing vibrations and noise perceived by the user at start-up of the combustion engine; the latter aspect increases reliability and perceived quality.

[0048] Exemplary embodiments have been described above and are illustrated in the accompanying drawings. Those skilled in the art will understand that various modifications, omissions, and additions can be made to what is expressly described herein, without departing from the scope of the invention, as defined in the following claims.

Claims

Claims1. A starter assembly (10) for a combustion engine (30) comprising:-> a starter motor (12) having a starter shaft (13);-i a driven wheel (14) rotatably connected to the starter shaft (13);the driven wheel (14) being, in turn, connected to a starter transmission (16) configured to operate on a drive shaft (A) of said combustion engine (30) and allow its starting-up, said driven wheel (14) comprising a mounting hole (14a); wherein the driven wheel (14) is rotatably mounted on a driven wheel shaft (15,15’), wherein at least one support bushing (51,52,54,55) is provided between the driven wheel shaft (15,15’) and the driven wheel (14); wherein a first support bushing (51) and a second support bushing (52) are provided mounted on said driven wheel shaft (15), each support bushing (51,52) having a respective flange portion (51’, 52”), the first and second support bushings (51,52) being mounted in the mounting hole (14a) of the driven wheel (14), so that the respective flange portions (51’, 52’) are opposite each other and external to the mounting hole (14a), defining lateral abutments within which the driven wheel (14) is arranged.

2. A starter assembly (10) according to claim 1, wherein the at least one support bushing (51,52,54,55) is integrally mounted in the mounting hole (14a) of the driven wheel (14) with which it is rotatably mounted on the driven wheel shaft (15,15').

3. A starter assembly (10) according to claims 1 or 2, wherein the starter motor (12,12’) is keyed onto a casing (21,22,23) that encloses a transmission assembly (20) of said combustion engine (30), and wherein said driven wheel shaft (15,15’) is supported in at least one mounting seat (22a, 22a’ ,23a’) formed on said casing (20).

4. A starter assembly (10) according to claim 3, wherein said driven wheel shaft (15) is mounted in a single mounting seat (22a) formed on said casing (21,22,23), so that said driven wheel shaft (15) is arranged in a cantilevered manner.

5. A starter assembly (10) according to claim 3, wherein the driven wheel shaft (15') is shaped to be arranged on a first support seat (22a') and a second support seat(23a') opposite each other formed on said casing (21,22,23), and wherein a first support bushing (54) and a second support bushing (55) are provided, each having a respective flange portion (54', 55'), the first and second support bushings (54,55) being mounted in the mounting hole (14a) of the driven wheel (14), so that the respective flange portions (54', 55') are opposite each other and external to the mounting hole (14a), defining lateral abutments within which the driven wheel (14) is arranged.

6. A starter assembly (10) according to claim 5, wherein a third support bushing (53) and a fourth support bushing (56) having a respective flange portion (53', 56') are also provided, wherein the third and fourth support bushings (53,56) are shaped to be inserted in the first (22a’) and second (23 a’) support seats of the driven wheel shaft (15'), and wherein the respective flange portions (53', 56') of the third and fourth support bushings (53,56) abut with the flange portions (54', 55’) of the first and second support bushings (54,55).

7. A starter assembly (10) according to any of the preceding claims, wherein a further support bushing (58) is provided mounted between an attachment collar (12’) of the starter motor (12) and an engagement seat (28a) of said attachment collar (12’).

8. A transmission assembly (20) related to a combustion engine (30), said transmission assembly (20) comprising a starter assembly (10) according to any one of the claims from 1 to 7.

9. A transmission assembly (20) according to claim 8, selected from: a CVT transmission or a gear transmission.

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