EP0647772B1 - Cylinder bloc and bearing journal of crankshaft for low noise level internal combustion engine - Google Patents

Description

The present invention relates to an internal combustion engine intended in particular to equip road vehicles, both motor vehicles and heavy goods vehicles.

Currently, for the sake of preserving the environment and increasing user comfort, vehicle manufacturers are increasingly seeking to use engines that are as environmentally friendly as possible. Research mainly focuses on the reduction of harmful exhaust gas emissions (engines (clean engines) and the reduction of silent noise emission levels).

To reduce the level of engine noise emissions, a certain number of technical solutions have been proposed by reducing the vibrations transferred from the engine pistons to the engine casing. One solution is to stiffen the crankshaft bearings of the engine by mechanically connecting the caps of the crankshaft bearings together. Another solution consists in increasing the surface covered by the oil pan according to the principle of "enveloping bowl" by decoupling the oil pan from the cylinder block to reduce its coefficient of sound radiation.

Also known from European Patent No. 0 435 847 (AVL) is an internal combustion engine which has a rigid external structure laterally surrounding the cylinder block and the crankshaft bearings. The upper part of the external structure is fixed to the cylinder head of the engine. The lower part of the external structure is stiffened by a frame in the form of a ladder placed horizontally below the crankshaft bearings. An oil pan in the form of a bowl is fixed to the side flanges of the external structure. This document provides for a seal between the cylinder head, the cylinder block and the external structure in order to decouple them acoustically for high frequencies and to reduce the level of vibration of the external structure. The oil pan attached to the exterior structure further reduces noise from the entire engine.

This engine design aims to dissipate vibrational energy of the rigid internal structure by an external structure added and rigidified in order to act on all the paths of vibration propagation towards the outside. However, the vibratory energy of the parts is much higher than the acoustic energy radiated by these parts due to their vibrations. From this point of view, the engine structure described in the aforementioned AVL document is not an optimal and effective solution for reducing the level of engine noise emissions.

The object of the present invention is to provide an engine structure with improved vibroacoustic performance, that is to say with a significant reduction in the levels of noise emissions to the outside.

The object of the invention is also to simplify the structure of the engine necessary for the reduction of noise emissions by favoring particular paths of propagation of vibrations in order to effect effective damping.

The object of the invention is further to propose an engine with a rigid internal structure for holding forces, and an external structure integrating the function of an oil bowl which is mechanically decoupled from the internal structure, so as to provide treatment effective both acoustically and mechanically in terms of engine vibration.

The internal combustion engine includes a cylinder head mounted above an elongated cylinder block, and crankshaft bearings mounted below and along the cylinder block. According to the invention, the cylinder block has two side hanging skirts which extend down the lateral sides of the cylinder block. The hanging skirts move slightly downwards so as not to come into direct mechanical contact with the crankshaft bearings. Each crankshaft bearing has a bearing cap which can be removed from the bearing base. The bearing caps are connected together by two parallel stiffening bars to make all the crankshaft bearings rigid. An oil pan in the form of a large bowl is suspended in suspension on two longitudinal side flanges of the cylinder block located above the hanging skirts.

In this way, the vibrations of the cylinder block propagate along a privileged path formed by the two hanging skirts which radiate by their lower free end. It is then possible to dampen the vibrations of the lower ends of the hanging skirts by an appropriate damping means. A simple solution consists in connecting, using damping elements, the lower end of the hanging skirts to the crankshaft bearings which are reinforced by the stiffening bars.

The damping elements can be constituted by viscous dampers, preferably non-linear, to allow better damping efficiency without significantly increasing the stiffness of the damper in operation. Such shock absorbers work dynamically to dampen the vibrations of the hanging skirts. Experience shows that the damping result is satisfactory with an oil film at rest having a thickness less than or equal to 50 times the amplitude of the lateral displacements of the lower end of the pendant skirts due to vibrations. It is thus possible to mechanically effectively dampen the vibrations of the motor.

The large bowl which is mounted decoupled from the rigid structure of the motor is preferably flexible in order to allow good absorption of the vibrations of the motor. This bowl is preferably made of composite materials and constitutes an acoustic screen for noise vis-à-vis the outside of the engine.

Thanks to the invention, it is possible to significantly reduce the level of noise emissions from the engine by means of a mechanical treatment of vibrations by means of hanging skirts and dynamic dampers, and also by an acoustic treatment by means of the large bowl. flexible oil, decoupled from the rigid structure of the engine.

The efficiency of the mechanical treatment of vibrations can be further increased by creating internal pockets in the hanging skirts. In these internal pockets, a granular material is introduced which by dry friction between the grains allows vibration damping. Thus, the vibrations are first damped in the rigid structure at the level of the hanging skirts before being damped a second time by the dynamic dampers at the ends of the hanging skirts. It is also possible, in certain cases, to remove the damping elements and to keep only the damping by inclusion of a granular material in the hanging skirts, if such damping is sufficient for the use of the engine.

According to a variant of the invention, the hanging skirts in the form of plates can be replaced by a succession of hanging beams. These hanging beams preferably have different characteristics from one another (length, section), so as to constitute as many tuned dynamic absorbers. It is then advisable to damp the hanging beams sufficiently to cover the entire frequency spectrum (vibrations) to be treated with a reasonable number of beams. This damping can be provided by as many dynamic dampers as hanging beams mounted at the free ends of these beams, and / or by introducing granular materials into the internal pockets of the hanging beams. The use of separate shock absorbers associated individually with each hanging beam has the additional advantage of greatly reducing the acoustic radiation coefficient of the hanging skirts, thereby reducing noise transfer by air.

According to another variant of the invention, perforated openwork skirts can be produced so as to reduce the rigid surfaces for transferring vibrations and consequently reduce the coefficient of acoustic radiation of the pendant skirts.

• la figure 1 est une vue schématique en perspective d'un moteur à combustion interne avec la jupe pendante selon un premier mode de réalisation de l'invention,
• la figure 2 est une vue schématique en coupe transversale du moteur selon la figure 1,
• la figure 3 est une vue en perspective du moteur selon un second mode de réalisation de l'invention, et
• la figure 4 est une vue schématique en perspective du moteur selon un troisième mode de réalisation de l'invention.

The invention will be better understood from the study of a few embodiments taken by way of non-limiting examples and illustrated by appended drawings, in which:

• FIG. 1 is a schematic perspective view of an internal combustion engine with the pendant skirt according to a first embodiment of the invention,
• FIG. 2 is a schematic cross-sectional view of the engine according to FIG. 1,
• FIG. 3 is a perspective view of the engine according to a second embodiment of the invention, and
• Figure 4 is a schematic perspective view of the engine according to a third embodiment of the invention.

To simplify the representation, the engine oil pan is not illustrated in FIGS. 1, 3 and 4. Internal combustion engines are well known to those skilled in the art (see for example European patent n ° 0 435 847 cited above) and will not be described in detail. Thereafter, we will only describe the structure of the engine directly concerned by the present invention.

As illustrated in FIGS. 1 and 2, the internal combustion engine comprises a cylinder head 1 mounted above an elongated cylinder block 2. The cylinder block comprises several cylinders 2a in which pistons, not shown, slide. The cylinder block 2 has interior channels 2b in which a cylinder block coolant circulates. Below the cylinder block 2 are several crankshaft bearings 3 aligned along the cylinder block 2. Each bearing 3 is in the form of a vertical plate in two parts: a base 3a integral with the cylinder block 2 and a cap 3b mounted removably on the base 3a. A not shown crankshaft is supported by the crankshaft bearings 3 and driven by the not shown pistons of the engine in order to actuate a gearbox not shown of the vehicle.

The lateral sides of the cylinder block 2 are extended downwards by two hanging skirts 4 in the form of a plate. The hanging skirts 4 are integral with the cylinder block 2 and deviate slightly to the side so as not to come into direct contact with the crankshaft bearings 3. The hanging skirts 4 may have internal pockets 4a into which is introduced a granular material 5 (pumice, sand, etc.), the usefulness of which will be described later.

Two stiffening bars 6 parallel and longitudinal are mounted on the bearing caps 3b of the crankshaft 3 for example by means of bolts 7. The bearing caps 3b have a substantially inverted U shape whose ends of the branches are integral with the stiffening bars 6. Thus, two stiffening beams are obtained for the crankshaft bearings 3.

The cylinder block 2 laterally has two longitudinal flanges 2c to allow the fixing of an oil pan 8 in the form of a large bowl of flexible material. Oil 9 in the oil pan 8 is intended for the lubrication of the engine, and is recycled by means of a suitable circuit not shown. At the side flanges 2c there are four lateral hooking elements 10 allowing the engine to be hooked into the chassis of the vehicle, not shown.

The internal structure of the engine constituted by the cylinder head 1, the cylinder block 2, the crankshaft bearings 3, the hanging skirts 4 and the stiffening bars 6 is rigid. The external structure of the motor constituted by the large bowl 8 is flexible and mechanically decoupled from the rigid internal structure. The stiffening bars 6 make it possible to stiffen the crankshaft bearings 3 in a solid block to prevent their vibrations caused by the operation of the engine (movement of the pistons in the cylinders and movement of the crankshaft). The vibrations of the cylinder block 2 are mechanically propagated by the hanging skirts 4, the free lower end of which radiates. The granular material 5 contained in the internal pockets 4a of the skirts 4 makes it possible to dampen the vibrations by dry friction between the grains of the material.

Damping elements 11 are provided between the caps 3b of crankshaft bearings 3 and the lower end of the hanging skirts 4, in order to dampen the vibrations radiated by said free ends. The damping elements 11 are dynamic dampers, for example viscous of a non-linear nature. Thus, the rigid internal structure of the engine ensures good reduction of vibrations, direct sources of noise emissions.

The large bowl 8 is mechanically decoupled from the rigid internal structure so that the vibrations of the internal structure of the engine are not transferred to the external environment. The large bowl 8 is preferably made of flexible material, for example composite, and constitutes an acoustic screen which encloses the internal structure with their mechanical vibrations and sound emissions.

It is possible to further improve the vibroacoustic performance of the motor by modifying the structure of the hanging skirts 4. One solution consists in replacing skirts in the form of a plate with several hanging beams 4b (FIG. 3). These beams 4b have different dimensions to constitute dynamic absorbers frequency tuned vibrations. The damping of these beams 4b should take account of the characteristics of each beam in order to effectively cover the whole spectrum of vibrations to be treated. Solutions for including granular materials in the skirts 4 and / or dynamic dampers at the ends of the beams 4b can be used. Having tuned beams and dynamically damped, greatly reduced the acoustic radiation coefficient of the skirts 4 as a whole.

Another solution (FIG. 4) consists in providing lateral openings 4c in the hanging skirts 4. This also makes it possible to reduce the coefficient of acoustic radiation of the hanging skirts 4.

Claims (11)

1. An internal combustion engine comprising a cylinder head (1), an elongate cylinder block (2), crankshaft bearings (3) below the cylinder block and an oil sump (8), characterised in that the cylinder block is extended downwards by two lateral hanging skirts (4) which do not come into direct contact with the crankshaft bearings, in that the crankshaft bearings have cap pieces (3b) which are connected mechanically to one another by two parallel stiffening bars (6) and in that the oil sump (8) is in the form of a large tank fixed by suspension on two lateral flanges (2c) along the cylinder block above the hanging skirts.
2. An engine as claimed in claim 1, characterised in that the lower free ends of the hanging skirts (4) are connected to the bearing cap piece (3b) by means of shock absorber members (11).
3. An engine as claimed in claim 2, characterised in that the shock absorber members are formed by non-linear viscous shock absorbers.
4. An engine as claimed in claim 3, characterised in that the thickness of the oil film of the shock absorbers is lower than or equal to 50 times the amplitude of the displacements of the free end of the hanging skirts due to vibration.
5. An engine as claimed in one of the preceding claims, characterised in that the hanging skirts comprise inner pockets (4a) containing a granular material (5).
6. An engine as claimed in one of the preceding claims, characterised in that the hanging skirts are formed by a plurality of beams (4b) hanging along the cylinder block.
7. An engine as claimed in claim 6, characterised in that the hanging beams (4b) have different dimensions and form dynamic absorbers frequency tuned to cover the spectrum of the vibrations transferred from the cylinder block to the hanging skirts.
8. An engine as claimed in one of claims 1 to 5, characterised in that the hanging skirts (4) have lateral openings (4c).
9. An engine as claimed in one of the preceding claims, characterised in that the oil sump (8) is made from flexible material.
10. An engine as claimed in one of the preceding claims, characterised in that the oil sump (8) is made from a composite material.
11. An engine as claimed in one of the preceding claims, characterised in that the oil sump (8) is mechanically decoupled from the structure of the block.

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