FIELD OF TECHNOLOGY The present invention relates to a drive arrangement intended for a fuel pump fitted on a combustion engine, a combustion engine with such a drive arrangement, and a vehicle with such a drive arrangement.

BACKGROUND OF THE INVENTION AND PRIOR ART

Combustion engines, such as diesel engines or Otto engines, are used in several types of applications and vehicles today, e.g. in heavy goods vehicles such as trucks or buses, passenger cars, motor boats, vessels, ferries or ships. Combustion engines are also used in industrial engines and/or motor powered industrial robots, power plants, such as electric power plants comprising a diesel generator, and in locomotives.

Combustion engines may be operated with e.g. diesel or petrol. Such engines are equipped with a fuel system to transport fuel from one or several fuel tanks to the combustion engine's injection system. The fuel system comprises one or several fuel pumps, which may be driven mechanically by the combustion engine or be driven by an electric motor. The fuel pumps create a fuel flow and pressure to transport the fuel to the combustion engine's injection system, which supplies the fuel to the combustion engine's combustion chamber.

The injection system suitably comprises a high pressure fuel pump with a pressure accumulator, which high pressure fuel pump is usually operated via a mechanical connection with the combustion engine. The mechanical connection may e.g. comprise a cogwheel transmission or a chain transmission. The operation of the high pressure fuel pump via the mechanical connection between the combustion engine and the high pressure fuel pump may, due to the component parts, cause noise, which may be experienced as disruptive to the environment. In order to fulfil the noise restrictions applicable within the automotive industry, it is desirable to minimise the noise level in a vehicle to the greatest extent possible. Different methods and systems have been proposed in prior art to operate a fuel pump. For example, in document US 201 1 /0005500 A1 , a transmission device for a combustion engine is displayed, wherein a high pressure fuel pump is operated by the combustion engine's crank shaft by a chain transmission system. In this manner, a drive system which is flexible, but which re- quires a special design of the combustion engine and which has a relatively short life, is achieved for the high pressure fuel pump.

Furthermore, in documents US1067424 and US201 1/0209680 a system for fuel injection to a combustion engine is described, wherein a fuel pump is op- erated by the combustion engine's crank shaft via a gear train transmission system comprising several cogwheels, which may cause disrupting noise.

Despite prior art solutions in the area, there remains a need to further develop a drive system for a fuel pump, which contributes to attenuating the noise lev- els.

SUMMARY OF THE INVENTION

The objective of the present invention is to achieve a drive arrangement for a fuel pump, which minimises noise levels.

The objective of the invention is also to achieve a drive arrangement for a fuel pump, which is compact and space-saving. Another objective of the invention is to achieve a drive arrangement for a fuel pump, which is robust, hard-wearing and durable, and which has a relatively long life. These objectives are achieved with a drive arrangement defined in claim 1 .

According to the invention, the objectives above are achieved with a drive arrangement intended for a fuel pump fitted on a combustion engine, wherein the drive arrangement comprises a first cogwheel arranged on a crank shaft of the combustion engine, and a second cogwheel arranged on a drive shaft of the fuel pump, whereat the crank shaft and the drive shaft are parallel to each other. Furthermore, the first cogwheel and the second cogwheel are arranged in direct engagement with each other. The invention also relates to a combustion engine and a vehicle comprising the arrangement described above.

DETAILED DESCRIPTION OF THE INVENTION The invention is described below with reference to the drive arrangement, which is generally described above.

The drive arrangement is suitably arranged in connection with the combustion engine and the fuel pump. The drive arrangement suitably consists of a gear transmission, which transfers power from the combustion engine's crank shaft to the fuel pump's drive shaft, and hence drives the fuel pump.

By arranging the first cogwheel and the second cogwheel in direct engagement with each other, a drive arrangement which minimises noise levels is achieved. By arranging the first and the second cogwheel in direct engagement with each other, so that the cogs of the first cogwheel and the cogs of the second cogwheel are in engagement with each other, no intermediate wheels are required between the first and the second cogwheels. In pinion gears vibrations arise, caused by variations in the cog loads acting on the cogwheels at engagement, and these vibrations cause noise. The cog loads may vary in size, direction and point of impact, and are determined by e.g. the cogwheel's radius, torque and inertia. Intermediate wheels are doubly impacted by cog loads, since they are in engagement with at least two cogwheels/intermediate wheels and thus have at least two gear meshes. A gear mesh is defined as the direct connection/engagement between two cogwheels/intermediate wheels. By reducing the number of intermediate wheels in the drive arrangement, ac- cording to the present invention, the number of gear meshes between the fuel pump and the combustion engine is minimised, and direct drive of the fuel pump via the combustion engine's crank shaft is achieved. Thus, a drive arrangement for a fuel pump is achieved, which minimises the noise level and which is compact and space-saving.

By reducing the number of cogwheels/intermediate wheels in engagement with the second cogwheel arranged in the fuel pump, a fuel pump drive arrangement is achieved, which is robust, hard-wearing and durable and which thus has a relatively long life.

The fuel pump is preferably a separate unit fitted on the combustion engine. By using a separate fuel pump instead of a fuel pump integrated with the combustion engine, service and maintenance of the fuel pump is facilitated. Similarly, service and maintenance is facilitated by the drive arrangement, since it is easy to dismantle and replace the fuel pump, its drive shaft and the second cogwheel of the drive arrangement. By using a separate/external fuel pump, a flexible and user-friendly drive arrangement intended for a fuel pump is thus achieved. The fuel pump's drive shaft, on which the second cogwheel is arranged, and the combustion engine's crank shaft, on which the first cogwheel is arranged, are parallel with each other. Suitably, the drive arrangement according to the present invention entails a noise reduction of between 3-6 dB from the gear transmission, in comparison with prior art constructions with intermediate wheels.

The first cogwheel preferably has a diameter, which is at least as large as the diameter of the second cogwheel. Alternatively, the first cogwheel is larger than the second cogwheel, which entails an up-shift. Alternatively, the first cogwheel may be smaller than the second cogwheel. Preferably, the relation- ship between the first cogwheel and the second cogwheel is such that the ratio between the second cogwheel's (the cogwheel on the fuel pump's drive shaft) rotation speed and the first cogwheel's (the cogwheel on the crank shaft) rotation speed is between 0.8-2, more preferably 1 -2. A large diameter of the first and the second cogwheels entails that the cog loads acting on the cogwheels, as well as the gap (the clearance of the herringbone teeth) in the gear mesh, may be reduced. Accordingly, a drive arrangement for a fuel pump is achieved, which minimises noise levels.

The play in the gear mesh, also referred to as the angular backlash, is calcu- lated using the formula below:

tan a? = - r

where x is the distance between two teeth and r is the radius of the cogwheel. The angular backlash is preferably smaller than 0.5 degrees and x is preferably smaller than 0.5 mm. The formula shows that the larger the cogwheel's radius, the lower angular backlash, and therefore the noise level. A larger cogwheel also has a larger inertia and torque, which reduces the cog loads acting on the cogwheel, and the noise levels may therefore be reduced.

Suitably, the first cogwheel has a diameter between 1 50-300 mm, preferably 200-260 mm, more preferably 240 mm. Suitably, the second cogwheel has a diameter between 1 50-300 mm, preferably 200-260 mm, more preferably 240 mm.

Suitably, a flywheel is arranged in the combustion engine's crank shaft adja- cent to the first cogwheel. The flywheel is suitably arranged at the crank shaft's rear edge. At the crank shaft's rear edge the flywheel is also in connection with a gearbox, a generator or a pump in the vehicle. The first cogwheel, and thus the second cogwheel, are suitably arranged adjacent to the flywheel at the crank shaft's rear edge. The flywheel's inertia entails that the crank shaft is more flexible in its front edge than in its rear edge. When the first cogwheel is arranged at a stable section of the crank shaft, the risk of cog load variations in the engagement between the first and the second cogwheels is reduced. Accordingly, a lower noise level is obtained when the first cogwheel is arranged on the crank shaft adjacent to the flywheel at the rear edge of the crank shaft, than when the first cogwheel is arranged at the front edge of the crank shaft. Adjacent means that the second cogwheel is arranged within a distance of up to approximately 800 mm from the flywheel, seen along the crank shaft's elongation. Preferably, at least one intermediate wheel is arranged in connection with the first cogwheel. The at least one intermediate wheel is suitably also arranged in connection with a third cogwheel on a camshaft of the combustion engine. The at least one intermediate wheel is suitably arranged in direct engagement with the first cogwheel and the third cogwheel. In this manner, the combustion en- gine's crank shaft drives both the fuel pump and the combustion engine's camshaft.

According to the present invention, the first cogwheel is arranged on the combustion engine's crank shaft. Furthermore, a first intermediate wheel is suitably arranged in direct engagement with the first cogwheel, which intermediate wheel also is in direct engagement with a second intermediate wheel. The second intermediate wheel is suitably arranged in direct engagement with a third intermediate wheel, which third intermediate wheel also is in direct engagement with a third and a fourth cogwheel. The third cogwheel is suitably arranged on a first camshaft of the combustion engine, and the fourth cogwheel is arranged on a second camshaft of the combustion engine. In this manner, the combustion engine's crank shaft drives both the fuel pump and both camshafts.

According to one aspect of the present invention, the second cogwheel arranged in the fuel pump is only in engagement with the first cogwheel. By minimising the number of gear meshes with the second cogwheel arranged in the fuel pump, the angular amplitude and the load in the gear meshes are minimised. The noise levels are thus reduced.

The fuel pump connected with the combustion engine is preferably a high pressure pump.

According to one aspect of the present invention, a drive arrangement is provided, which is intended for a fuel pump fitted on a combustion engine, wherein the combustion engine is preferably a diesel engine.

Other advantages of the invention are set out below in the detailed description of the invention's example embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description, as an example, of preferred embodiments of the invention with reference to the enclosed drawings, in which: Fig. 1 shows a schematic side view of a vehicle, comprising a drive arrangement intended for a fuel pump fitted in a combustion engine according to one embodiment of the present invention, Fig. 2 shows a fuel pump fitted in a combustion engine.

Fig. 3a shows a side view of a drive arrangement according to one em- bodiment of the present invention,

Fig. 3b shows the drive arrangement according to Fig. 3a seen straight from the rear in the vehicle's driving direction. Fig. 4 schematically shows a view of a drive arrangement according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE IN- VENTION

Fig. 1 shows a schematic side view of a vehicle 1 , which comprises a drive arrangement 2 for a fuel pump 20, connected with a combustion engine 4 according to the present invention. The combustion engine 4 is connected to a gearbox 8, which is connected to the driving wheels 10 of the vehicle 1 via a transmission. The vehicle also comprises a chassis 12.

Fig. 2 shows a combustion engine 4 with a crank shaft 26. A fuel pump 20 is fitted on the combustion engine 4. The fuel pump is thus a separate unit, which has been fitted on the combustion engine 4. The fuel pump 20 is operated with a drive arrangement 2, which is described in further detail in Figs. 3a and 3b.

Fig. 3a shows a drive arrangement 2, intended for a fuel pump 20 fitted in a combustion engine 4 according to one embodiment of the present invention. The fuel pump 20 is a high pressure pump, which supplies fuel at a high pressure to the combustion engine's cylinders (not displayed). The combustion engine 4 comprises a crank shaft 26, on which a first cogwheel 24 is arranged. A drive shaft 22 with a second cogwheel 34 is arranged at the fuel pump 20. The fuel pump 20 is arranged adjacent to the crank shaft 26 of the combustion engine 4, which crank shaft 26 extends in parallel with the drive shaft 22 of the fuel pump 20. The crank shaft 26 has a front end 28 and a rear end 30, wherein a flywheel 32 is arranged at the rear end 30. The first cogwheel 24 is arranged adjacent to the flywheel 32 on the crank shaft 26. The distance between the flywheel 32 and the first cogwheel 24 is in this embodiment example 600 mm, seen along the crank shaft's 26 elongation. The first cogwheel 24 of the crank shaft 26 and the second cogwheel 34 of the drive shaft 22 of the fuel pump 20 are arranged in direct engagement with each other, so that the teeth of the first cogwheel 24 (not displayed) and the teeth of the second cogwheel 34 (not displayed) are in engagement with each other. In this manner, the fuel pump 20 is driven directly by the crank shaft 26 of the combustion engine via the first cogwheel 24. Since the drive arrangement 2 comprises a reduced number of cogwheels, the number of gear meshes between the fuel pump 20 and the crank shaft 26 is minimised, and the noise level is thus minimised. The more gear meshes, the greater the risk of gaps and impact by cog loads, which in turn leads to noise. The inertia of the flywheel 32 entails that the rear end 30 of the crank shaft 26 is more stable than the front end 28. By arranging the first cogwheel 24 on the crank shaft 26 adjacent to the flywheel 32, a stable engagement is achieved, and thereby lower torsion vibration amplitudes, between the first cogwheel 24 and the second cogwheel 34, as the gear mesh is exposed to fewer load variations. Fewer load variations entails fewer vibrations and thus the noise levels caused by the drive arrangement 2 are minimised. Furthermore, the first cogwheel 24 and the second cogwheel 34 are of the same size/diameter, which means that the ratio between the first cogwheel's rotation speed and the second cogwheel's rotation speed is 1 .0, i.e. a gearing of 1 :1 . Since the first cogwheel 24 is at least as large as the second cogwheel 34 in the present invention, the cog loads are reduced and the gap in the gear meshes is minimised. Accordingly, the noise levels caused by the drive arrangement 2 are minimised. A smaller number of larger wheels also entails a robust and durable construction. Figure 3a also shows an intermediate wheel 36 arranged in direct engagement with, on the one hand, the first cogwheel 24 and, on the other hand, a third cogwheel 38 of a camshaft 40 in the combustion engine 4. The camshaft 40 extends in parallel with the crank shaft 26. Accordingly, the camshaft 40 is driven by the crank shaft 26, via the first cog- wheel 24 and the intermediate wheel 36.

Fig. 3b shows the drive arrangement 2 according to Fig. 3a seen in a view straight from the rear in the driving direction of the vehicle 1 . Fig. 4 schematically shows a drive arrangement 2, intended for a fuel pump 20 according to an embodiment of the present invention. The drive arrangement 2 comprises a first cogwheel 24 arranged on the crank shaft 26 (not displayed) of the combustion engine 4 and a second cogwheel 34 arranged on the drive shaft 22 (not displayed) of the fuel pump 20. The first cogwheel 24 and the second cogwheel 34 are arranged in direct engagement with each other. A first intermediate wheel 50 is arranged in engagement with the first cogwheel 24. A second intermediate wheel 52 is arranged in engagement with the first intermediate wheel 50 and a third intermediate wheel 54. The third intermediate wheel 54 is in turn also arranged in engagement with a third cogwheel 56, ar- ranged on a first camshaft (not displayed), and a fourth cogwheel 58 arranged on a second camshaft (not displayed).

The present invention should not be viewed as limited to the example embodiments described above, but modifications and combinations of these may occur within the framework of the enclosed claims. The number of intermediate wheels connected to the first cogwheel may e.g. be any number. The first cogwheel may be as large as the second cogwheel, or larger than the second cogwheel, wherein the ratio between the second cogwheel's (the cogwheel of the fuel pump's drive shaft) rotation speed and the first cogwheel's (the cog- wheel on the crank shaft) rotation speed is between 0.8-2, more preferably 1 - 2. Plain bearings or some other form of bearings may be arranged at the cogwheels and/or intermediate wheels for further noise reduction. The fuel pump may be fitted on e.g. a diesel engine or an Otto engine. The combustion engine may be of a horizontal or vertical model. The vehicle in which the drive arrangement may be arranged may e.g. be a heavy goods vehicle, such as a bus or a truck. The vehicle in which the drive arrangement may be arranged may e.g. be a boat.