GB2466488A

GB2466488A - I.c. engine cooling fan drive train

Info

Publication number: GB2466488A
Application number: GB0823371A
Authority: GB
Inventors: David Joseph Nuttall; David Ralph Smith; David Adamson
Original assignee: Leyland Trucks Ltd
Current assignee: Leyland Trucks Ltd
Priority date: 2008-12-23
Filing date: 2008-12-23
Publication date: 2010-06-30
Anticipated expiration: 2028-12-23
Also published as: GB0823371D0; GB2466488B

Abstract

An engine assembly comprises an internal combustion engine 2, a fan 3 for pulling air through a heat exchanging radiator, and a fan drive train arrangement 5-10 for effecting rotation of the fan 3 indirectly from the crankshaft of the engine. Intermediate in the fan drive train 5-10 is a first pulley 7 which is coaxial with the fan 3 and which is rotatably mounted on a support 11, 12, 14, 16 fixed relative to the engine 2. The support may include a bridging plate 14 which spans across one end of the crankshaft. The fan drive train may include pulleys 5, 6, 7, drive belts S, 9 and a viscous coupling 10. The drive train arrangement 5-10 is adapted to rotate the first pulley 7 at higher rotational speed than the crankshaft and therefore provide for increased cooling duty.

Description

ENGINE ASSEMBLY

The present invention relates to an engine assembly and more particularly to such an assembly comprised of an internal combustion engine provided with an engine-driven cooling fan for drawing air through a radiator. The invention relates more particularly, but not necessarily exclusively, to an engine assembly for a light or medium duty truck or lorry of the so-called "cab over" type, i.e. one in which the engine assembly is mounted beneath the driver's cab and may be accessed by tilting the cab forward about an axis parallel to the axles of the vehicle.

Environmental legislation continues to impose ever more stringent requirements on exhaust gas emissions from vehicles (e.g. trucks and lorries) powered by an internal combustion engine. In particular requirements are imposed for reduction of emissions of gases such as NOX, hydrocarbons and carbon monoxide as well as particulate materials (e.g. from diesel fuelled vehicles). Various strategies are employed for meeting the emission targets including Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR). The latter technique (EGR) involves supplying exhaust gas back into the engine so as to effect a reduction in at least some of the aforementioned components. However a consequence of the EGR technique is that the engine becomes hotter as compared to the case where there is no EGR. As a result, a higher cooling duty is imposed on the engine's cooling system so a greater amount of heat must be dissipated by the radiator of the vehicle. In principle, one solution is to use a larger radiator. Alternatively or additionally a larger fan or increased fan speed may be used for supplying cooling air to the radiator at a greater rate.

However in certain types of vehicles the amount of free space available in the engine compartment may be very limited and insufficient for a larger radiator and/or larger fan.

Thus, for example, in so-called "cab-over" vehicles, the undersurface of the cab defines an upper contour for the "packaging space" for the engine and this contour is spaced a relatively short distance from the upper regions of the engine.

There is insufficient surplus space to increase the size of the fan (which is usually mounted on the crankshaft for light and medium duty trucks) and/or the size of the radiator. Thus there will be a difficulty meeting forthcoming, increasingly stringent emission targets by using EGR with current designs of engine assemblies for "cab-over" vehicles.

It is therefore an object of the present invention to obviate or mitigate the above mentioned disadvantage.

According to the present invention there is provided an engine assembly comprising an internal combustion engine, a fan for drawing air through a radiator, and a fan device train arrangement for effecting rotation of the fan indirectly from the crankshaft of the engine wherein intermediate in the fan drive train is a first pulley which is coaxial with the fan and which is rotatably mounted on a support fixed relative to the engine, and wherein the drive train arrangement is adapted to rotate the first pulley at higher rotational speed than the crankshaft.

In accordance with the invention, the fan is not mounted on the crankshaft but is driven indirectly from the crankshaft by a fan drive train arrangement. This drive arrangement incorporates a pulley (the "first" pulley) which is coaxial with the fan and which is rotatably mounted on a support fixed relative to the engine. The fan drive train arrangement is such that the first pulley is driven at a higher rotation speed than the crankshaft. Thus the fan may be rotated at a higher speed (and therefore provide additional cooling duty) as compared to the case where the fan is mounted on the crankshaft.

For the purpose of rotating the first pulley at a higher rotational speed than the crankshaft, the fan drive train arrangement may incorporate a second pulley assembly rotatably supported on the engine casing. This second pulley assembly may be driven by a first endless belt for effecting rotation of the second pulley assembly from the crankshaft of the engine. Rotary motion of the second pulley assembly to the aforementioned first pulley may be transmitted by means of a further endless belt.

It will be appreciated that the diameters of the first pulley and the second pulley assembly are selected so as to provide a desired, increased rotational speed of the first pulley compared to the crankshaft.

In preferred embodiments of the invention, the rotational axis of the second pulley assembly is above that of the first pulley and lies in the same vertical plane.

In further preferred embodiments of the invention, the fan drive train arrangement incorporates a fan speed modulator device (e.g. a conventional viscous coupling) having a drive input and a drive output. The fan is mounted on the drive output and the first pulley is connected to the drive input of the modulator device. In this way, the rotational speed of the fan may be varied (e.g. dependent on the engine temperature) as compared to the rotational speed of the pulley. Whilst it will generally be the case that the fan speed modulator device effects rotation of the fan (albeit at a different speed from that of the first pulley), it is also contemplated within the invention that the fan speed modulator device may be one which selectively either transmits drive to the fan or not at all. In other words the fan speed modulator device may be one which causes the fan to be "on" (i.e. to rotate) or to be "off' (i.e. not to rotate). In such a case the fan speed modulator device may, in effect, be a clutch.

Engine assemblies in accordance with the invention are eminently suitable for incorporation in "cab-over" type vehicles, particularly for the case where the first pulley and the fan are coaxial with the crankshaft. It is thus possible to use the same size fan as would normally be used in the vehicle but driven at a higher rotational speed so as to be capable of providing additional cooling duty. Thus the invention may with advantage be employed in "cab over" vehicles which embody Exhaust Gas Recirculation for reducing exhaust emissions.

The invention will be further described by way of example only with reference to the accompanying drawings, in which: Fig 1 is an exploded view of one embodiment of engine assembly in accordance with the invention; The engine assembly 1 illustrated in Fig 1 is comprised of an internal combustion (e.g. diesel) engine 2 associated with an engine driven fan 3 positioned and arranged for drawing air through a radiator (not shown) which forms part of the cooling system of the engine assembly 1. Engine 2 is of generally conventional construction and so will not be described further in detail save to mention for the purposes of the following description that it incorporates a crankshaft 4 provided, at its end seen in Fig 1 with a crankshaft damper 13. Both the crankshaft 4 and crankshaft damper 13 may be of conventional construction.

As described in more detail below, the fan 3 is driven from the crankshaft (not shown) of the engine 2 via an arrangement of: (i) rotatable pulleys 5, 6 and 7; (ii) drive belts 8 and 9; and (iii) a viscous coupling fan drive 10.

Pulley 7 (the "first" pulley) is mounted on a fixed bracket arrangement secured to the casing of engine 2. More particularly, the bracket arrangement is comprised of: (a) two side plates 11 and 12 secured using bolts to the engine casing one on each side of the end of the crankshaft 4 and projecting beyond the crankshaft damper 13, and (b) a bridging plate 14 secured by an arrangement of threaded fastener devices (schematically illustrated by reference numeral 15) to the forward edges of side-plates 11 and 12 so as to be bridged across, but spaced from, the crankshaft damper 13 of the crankshaft 4.

As clearly depicted in Fig 1, a stub shaft 16 is secured to, and projects from, the frontal face of plate 14 so as to be coaxial with the rotational axis of the crankshaft. It is on this stub shaft 16 that the aforementioned pulley 7 is rotatably mounted, for which purposes any suitable type of bearing arrangement may be used.

Thus it will be appreciated that (as described above) the pulley 7 is rotatably mounted on the fixed bracket arrangement (comprised of the side plates 11, 12 and the bridging plate 14) and is coaxial with the crankshaft 4.

Rotation of the pulley 7 (for rotation of the fan 3) is effected by the aforementioned arrangement of the pulleys 5 and 6 and the belts 8 and 9.

Pulley 5 is rotatably mounted on the engine casing so as to have a rotational axis which lies above and in the same vertical plane as that of pulley 7.

Rotation of pulley 5 is transmitted to further pulley 6 by virtue of the latter being rigidly mounted on the former by means of an adapter 17. More specifically, a rear face (not seen in Fig 1) of adapter 17 is secured by means of threaded fastening devices 1 7a to the front face of pulley 5 whereas a front annular face of adapter 17 is secured to a rear annular face of pulley 6. Effectively therefore pulleys 5 and 6 together form a single, composite pulley unit. As will be appreciated from Fig 1, the arrangement of pulley 5, adapter 17 and pulley 6 is such that the latter is located immediately above pulley 7 with its rotational axis in the same vertical plane.

Endless belt 8 which is driven from the crankshaft passes partially around pulley 5 (as well as additional pulleys 18 and 19 which are not further described since they are not partof the direct drive to the fan 3). It will be appreciated that belt 8 serves to effect rotation of pulley 5 which in turn drives pulley 6 at the same rotational speed.

The belt 9 serves to transmit rotation of pulley 6 to pulley 7. In order to maintain tension in the belt 9 without the need for tensioning device the belt may be an elastomeric polyamide cord V belt 9. However we do not preclude the use of a tensioning device for maintaining belt tension.

It should be appreciated at this point that the radii of pulleys 5, 6 and 7 will be selected so as to ensure that pulley 7 has a rotational speed greater than that of the crankshaft Typically the ratio of the rotational speed of pulley 7 to that of the rotating crankshaft will be 1:1 -1:1.4.

The mechanism by which pulley 7 drives fan 3 will now be described.

In broad outline, viscous coupling 10 has a drive input rotationally associated with the pulley 7 and a drive output on which a fan 3 is mounted. A viscous coupling is of a conventional type (e.g. as available from Borg Warner) whereby rotation of the drive input at a particular rotational speed causes the drive output to rotate at substantially the same or lesser speed as determined by an adjustable mechanism within the viscous coupling 10. This mechanism may, for example, be controlled by a bimetallic strip which is responsive to the heat emitted by the radiator whereby the higher the temperature the greater the rotational output speed of coupling 10 for a given input speed. Alternatively the internal mechanism of viscous coupling 10 may be controlled electronically by a control unit of the vehicle.

Fan 3 is of one piece construction and has fan blades 20 mounted on an annular hub 21 which (as shown in Fig 1) has an inner annular flange 22.

The drive output of coupling 10 is associated with studs 23 by means of which viscous coupling 10 is affixed to the annular flange 22 via the intermediary of a spacer ring 24.

Mounted on stud-like projections 25 of pulley 7 is an adapter 26 having a stub shaft which projects through the (open) central region of fan hub 22 and spacer ring 24 and is connected to drive output of coupling 10.

It will therefore be appreciated from the foregoing description that rotation of pulley 7 (effected as described above) by belt 8, pulleys 6 and 7, and belt 9) drives the rotational input of coupling 10 whereas the drive output of the latter effects rotation of fan 3.

It will be appreciated from the foregoing description that with appropriate selection of the pulleys 5, 6 and 7 the latter may be have a rotational speed which is in a ratio of 1:n to that of the crankshaft, where n is a predetermined value greater than 1. This higher fan rotational speed is able to provide additional cooling air as compared to where a fan of the same size is mounted on the crankshaft. This increase in cooling air is achieved without the need either to re-position the fan higher on the engine or to provide a larger diameter fan. Additionally there is no need for a larger size radiator. The described arrangement is therefore eminently suitable for vehicles such as the "cab-over" type in which the "packaging space" for the engine assembly (limited by the undersurface of the cab) is insufficient to provide such modifications.

The viscous coupling 10 is able (in accordance with its conventional function) to modulate the speed of fan 3 relative to the rotational speed of pulley 7. Thus, for example when the engine 1 has just been started and is relatively cold then for a given rpm of the engine the coupling 10 may rotate the fan 3 at a lower speed than would be the case if the engine were running at higher temperatures and more cooling air was required for the radiator.

One feature of the illustrated arrangement is that the fan is positioned forwardly than it would otherwise need to be if mounted directly on the crankshaft.

This reduces the distance between the fan and the radiator. However the provision of the spacer ring 24 goes someway to optimising the distance between the radiator and the fan 3 than will be the case if the latter were mounted directly on the viscous coupling 10.

A further feature is that sitting the fan off the engine (i.e. further away from the engine than if it (the fan) were mounted on the crankshaft) allows air to pass around the engine more easily, thus reducing the "blockage effect" caused by the engine "blocking" the path of the heated air from the radiator. This reduction in the "blockage effect" allows heated air to be more readily vacated from the engine space.

It will be appreciated that a number of modifications may be made to the illustrated arrangement. Thus, for example, the fixed bracket arrangement on which the pulley 7 is mounted may be a machined cast part rather than 3 individual plates 11:14 as described above. Alternatively or additionally the pulley 5 may be repositioned so that its rotational axis is not necessarily above that of pulley 7 and/or in the same vertical plane thereof.

Claims

CLAIMS1. An engine assembly comprising an internal combustion engine, a fan for pulling air through a heat exchanging radiator, and a fan device train arrangement for effecting rotation of the fan indirectly from the crankshaft of the engine wherein intermediate in the fan drive train is a first pulley which is coaxial with the fan and which is rotatably mounted on a support fixed relative to the engine, and wherein the drive train arrangement is adapted to rotate the first pulley at higher rotational speed than the crankshaft.
2. An engine assembly as claimed in claim 1 wherein the first pulley is mounted on a bracket arrangement having a part thereof which spans across an end of the crankshaft of the engine.
3. An engine assembly as claimed in claim 2 wherein the first pulley is rotatably mounted on a shaft provided on that part of the bracket arrangement which spans across said end of the crankshaft.
4. An engine assembly as claimed in any one of claims 1 to 3 wherein said first pulley is coaxial with the rotational axis of the crankshaft.
5. An engine assembly as claimed in any one of claims 1 to 4 wherein the fan drive train arrangement incorporates a second pulley assembly rotatably supported on the engine casing, a first endless belt for effecting rotation of the second pulley from the crankshaft of the engine, and a second endless belt for transmitting rotation of the second pulley assembly to the first pulley.
6. An engine assembly as claimed in claim 5 wherein the rotational axis of the second pulley assembly is above that of the first pulley and lies in the same vertical plane.
7. An engine assembly as claimed in claim 5 or 6 wherein the second endless belt is one that does not require a tensioner.
8. An engine assembly as claimed in claim 7 wherein the second endless belt is an elastomeric polyamide cord V belt.
9. An engine assembly as claimed in any one of claims 1 to 8 wherein the fan drive train arrangement incorporates a fan speed modulator device having a drive input and a drive output, the fan is mounted on said drive output, and the first pulley is connected to said input whereby rotational speed of the fan may be varied as compared to the rotational speed of the first pulley.
10. An engine assembly as claimed in claim 9 wherein the modulator device is adapted to fan control speed dependent on the temperature of the engine.
11. An engine assembly as claimed in claim 9 or 10 wherein a spacer is provided between the fan and the modulator device.
12. An engine assembly as claimed in any one of claims 9 to 11 wherein the fan speed modulator device is a viscous coupling.
13. A vehicle incorporating an engine assembly as claimed in any one of claims 1 to 12 for providing motive force for the vehicle.
14. A vehicle as claimed in claim 13 which is of the "cab-over" type in which the cab may be pivoted about a horizontal axis, said engine assembly being mounted below the cab of the vehicle.