State of the art Turbocompound units are used for utilising part of the energy content of the exhaust gases from a combustion engine. To this end, the unit is situated in the exhaust line so that the exhaust gases drive a power turbine of the unit. The latter, by means of its shaft, two sets of mechanical gears and a hydraulic coupling, provides the engine's power transmission with extra power as a result of the output shaft of the unit being designed to cooperate with the engine's flywheel.

In the case of a turbocharged engine with turbine-driven inlet air compressor, the power turbine of the turbocompound unit is situated downstream from the turbocharging unit.

A conventional turbocompound unit incorporates a first set of gears between the power turbine and the hydraulic coupling. A second set of gears is situated after the hydraulic coupling and includes a gearwheel on the unit's output shaft and an intermediate gear between this and a crankshaft gearwheel which is rigidly connected to the engine's flywheel. The conventional turbocompound unit is fastened by its housing to the outside of a flywheel casing which encloses the flywheel, the intermediate gear and the crankshaft gearwheel. The unit's output shaft passes through a recess in the casing.

Turbocompound technology involves a source for increasing the power and reducing the fuel consumption of combustion engines, particularly in the case of turbocharged diesel engines for heavy vehicles. However, the technology has been called into question not only on the basis of the additional cost of the unit but also because of problems of

operational reliability. In particular, experience has revealed limited service life of the mechanical gear after the hydraulic coupling, involving gearwheel damage requiring inspection, repair and sometimes unit replacement.

Objects and most important characteristics of the invention One object of this invention is to indicate a housing for a turbocompound unit, together with a turbocompound unit, which solves or reduces the problems of the state of the art and provides a reliable and long-lasting solution whereby the need for repairs can be reduced.

This object is achieved according to the invention with a housing for a turbocompound unit of the kind mentioned in the introduction having the features indicated in the characterising part of patent claim 1.

The housing thus being provided with means for oriented fastening to the engine block and not, as in conventional technology, to the flywheel casing prevents incorrect engagement between the gearwheel on the turbocompound unit's output shaft and cooperating gearwheels. This is because placing the unit on the engine block gives the unit's output shaft an alignment which corresponds in parallelism with the gearwheels with which the output shaft's gearwheel has to engage. This contrasts with a unit which, according to conventional technology, is attached to the flywheel casing and is therefore subject to bending movements and vibrations which occur during operation between the engine and the vehicle's gearbox. These movements have been found to affect gear engagement precision and hence gradually in serious cases to lead to gear damage. The invention results instead in more reliable gear engagement and substantially longer service life.

The incorporation in the housing of guide elements not only in the region of the output shaft for cooperation with the transmission plate but also in the form of contact surfaces in a region at a distance therefrom results in the fastening being stable, while at the same time the machining tolerances can be kept reasonable, particularly as regards machining the engine block's aligning surfaces. This is a great advantage in that the machining can

be carried out with such conventional equipment as is used for other machining of the engine block. Thus no special machining will be required. This is mainly because situating the fastening points at a substantial distance from one another means lower tolerance requirements. The point is that if the distance between the fastening points was small in the shaft direction of the housing, a corresponding small positional deviation would be tolerated, whereas fastening points situated at a greater distance from one another allow a greater degree of tolerance as regards positional deviation.

According to a preferred aspect of the invention, the housing includes contact surfaces in at least two mutually substantially perpendicular planes, for cooperation with corresponding aligning surfaces on the engine block. This further provides the possibility of reliable and appropriate alignment of the housing on the engine block.

A particular advantage is that, according to one aspect of the invention, at least one contact surface cooperates with an aligning spigot, thereby further reducing the engine block machining required. Machining is thus reduced to forming an aligned spigot hole.

It is in particular preferable that two contact surfaces be arranged to accommodate the aligning spigot between them. This results in particularly reliable guidance of the housing before tightening by means of threaded connections or the like. It is most preferable that the contact surfaces be arranged according to claim 6, whereby alignment is easy to achieve by moving the housing in the output shaft direction so that the groove encloses the spigot.

It is preferable that the guide element in the region of the output shaft should consist of a protruding bearing abutment for a bearing for that shaft. In particular, it is preferable that said bearing abutment should incorporate a circular cylindrical outer surface constituting a guide surface for guidance cooperation with a guide hole in the transmission plate. This results inter alia in manufacturing advantages as regards the machining of this guide element.

It is preferable that the first contact surfaces be situated substantially opposite to the output shaft, resulting in maximum reduction of manufacturing tolerance requirements.

According to a further aspect, the housing also incorporates at least one fastening portion which is intended for fastening to the engine block but is not intended for alignment and abutment against the latter. In this case it is preferable that each fastening portion be intended to cooperate with a positional error compensating device anchored to the engine block. This results in the substantial advantage that the housing can be further stabilised and fixed to the engine block without entailing any greater precision requirements as regards the positions of the cooperating fixing points, usually fixing holes, on the engine block.

Further advantages are achieved by the features indicated in the other dependent claims, and will be indicated in the following description of an embodiment.

Brief description of the drawings An embodiment of the invention will now be described with reference to the drawings, in which: Fig. 1 depicts schematically a turbocompound unit in conjunction with a turbocharged combustion engine.

Fig. 2 depicts part of a housing for a turbocompound unit according to the invention in a first sideview.

Fig. 3 depicts the housing in Fig. 2 viewed from below, and Fig. 4 depicts a section through the housing in Figs. 2 and 3 in cooperation with a transmission plate.

Description of an embodiment In Fig. 1 ref. 1 denotes a turbocharged diesel engine for a heavy vehicle. The engine is equipped in a conventional manner with arrangements for cooling of charge air and radiator fluid. Ref. 2 denotes an engine block and ref. 3 an exhaust manifold which leads the exhaust gases from cylinders of the engine to a turbocharging unit 4. Situated downstream from the turbocharging unit 4, as viewed in the exhaust line, is a power turbine 6 of a turbocompound unit 5.

The power turbine 6 has running from it a turbine shaft 7 for transmitting power generated by the power turbine, via a first gear set 8, to a hydraulic coupling 9 which is inserted to allow speed differences between the input and output shafts of the coupling.

A second gear set 11 is then arranged to further reduce the speed of the turbocompound unit 5 and allow cooperation between the shaft and the flywheel 12. Ref. 13 denotes a casing for the flywheel, a casing which in the conventional solution supports the turbocompound unit 5, a practice which does not apply to the unit according to the invention. For comprehension of the approximate combined gear ratio of the gear sets, it may be stated that the speed of the power turbine may range up to several tens of thousands of revolutions per minute, e. g. 60,000 rpm, while the flywheel speed during normal cruising of the vehicle ranges up to about 1100 rpm.

Fig. 2 depicts a section 14 of a housing for a turbocompound unit according to the invention. In principle, the construction of this unit is the same as the unit in Fig. 1. The same reference notations are used for corresponding parts. A cover (not depicted in this diagram) is intended to be fitted to the surface 14'. The housing also includes a bearing abutment 15 to accommodate a roller bearing for the output shaft. Ref. 16 denotes an oil outlet from the unit.

The unit's housing is designed to cooperate positionally with the engine block for a combustion engine. To this end, the housing incorporates a number of contact portions and guides for cooperation with corresponding aligning surfaces on the engine block.

First contact portions 17 and 20 have respective contact surfaces 18 and 21 which cooperate with first aligning surfaces P1 and P2 respectively on the engine block. These first contact portions 17,20 also constitute fixing portions in that each of them is provided with a drilled hole in which a screw (hinted at by broken lines at 19 and 22 respectively) is inserted to cooperate with a threaded hole in the region of the first aligning surfaces PI and P2.

A second contact portion 23 incorporates an inner groove with laterally situated second contact surfaces 24 for guided cooperation with an aligning spigot 25 which is firmly

fitted in a oriented manner in, and protrudes from, the engine block. It should be noted that the second contact portion 23 does not abut directly against any aligning surface on the engine block but is only indirectly aligned via the spigot 25.

The housing 14 further incorporates a first fastening portion 26 and a second fastening portion 27 which are likewise not intended to abut directly against any aligning surface on the engine block. These fastening lugs are fastened instead at a distance therefrom by means, for example, of a positional error compensating fastening device 35 not further described here such as, for example, that referred to in the applicant's Swedish patent no.

501 741. These fastenings serve to fix and stabilise the housing 14 relative to the engine block after alignment of the contact portions relative to corresponding aligning surfaces or spigots. As may be seen in the diagram, the fastening lugs protrude considerably sideways as viewed from the bearing abutment 15 of the output shaft. This arrangement results in stable fixing to the engine block.

Fig. 3 shows the housing 14 with the bearing abutment 15 as viewed from behind and partly concealed by the boss of the oil outlet 16. It further shows not only fixing portions 26 and 27 but also a flange 29 for connecting a casing for a power turbine to the housing section 14. The diagram shows on the right of the housing section 14 the first and second contact portions 17,20 and 23, and in the case of this latter the delineations of the second contact surfaces 24 are hinted at by broken lines. In this version the groove formed in the second contact portion 23 is open forwards but is ended by a transverse wall 24'.

Fig. 4 is a sectional view of the housing section 14 including inter alia the hydraulic coupling 9 and the output shaft 10. The bearing abutment 15 is intended to serve as a guide element for the housing section 14 by means of the peripheral circular cylindrical surface 28. This guide surface 28 is arranged to cooperate with a guide hole 31 formed in a transmission plate 30 which is itself orientedly fastened by means of guide pins (not depicted) to the engine block in the latter's rear region, i. e. in the direction towards the engine's transmission. Also visible in this diagram is a gearwheel 32 which is mounted on the unit's output shaft 10 and forms part of the second gear set, corresponding to that denoted by ref. 11 in Fig. 1.

In the design depicted, the output shaft and, in particular, this gearwheel 32 are well guided by a rolling bearing 33 inserted in the bearing abutment, with the bearing adjacent to the gearwheel. This illustrates the bearing abutment's dual function not only as a bearing seat but also as a guide element for the turbocompound unit. This dual function provides reliable and easy guidance of the housing and, in particular, of the shaft 10 and its gearwheel 32, resulting in reliable engagement with the intermediate gear (not depicted) with which the gearwheel has to cooperate. With advantage, this intermediate gear is supported by a pivot pin fastened to the transmission plate.

Ref. 34 denotes a seal inserted between the housing and the transmission plate. Ref. 14" denotes the previously mentioned cover which in this diagram is fitted to the surface 14' of the housing section 14.

Fitting the turbocompound unit to the combustion engine entails placing the unit's housing 14,14'against the engine block with the contact surfaces 17 and 20 abutting against corresponding aligning surfaces PI and P2 on the engine block (see Fig. 3).

Thereafter, the housing 14,14'is moved in the direction of the arrow A corresponding to leftward movement in Figs. 1 and 4 and movement upwards from the plane of the paper in Fig. 2. The spigot 25 is thus guided in between the second contact surfaces 24 in the groove in the second contact portion 23, and the guide surface 28 of the bearing abutment 15 is guided into the guide hole 31 in the transmission plate 30. When a position of sufficient insertion has been reached, the screws are tightened inside the first contact portions 17 and 20, followed by tightening of the fastening elements which pass through the fastening portions 26 and 27. The result is very good alignment of the turbocompound unit relative to the gearwheels of the second gear set. Such is the case irrespective of whether the engine is subject to powerful vibrations or whether deflections due to deformations occur in the region of the flywheel casing.

It may be mentioned in this context that the suspension points for the engine and the associated transmission in today's vehicles are situated further apart than in previous installations. This fact has made the region of the flywheel casing increasingly unsuitable for fastening the turbocompound unit, owing to the increased deformations arising from this suspension principle.

A great advantage of the solution described is that placing at least the first contact portions and preferably also the second contact portion at a distance from the region for guidance cooperation on the output shaft, and still more preferably at the greatest distance possible in practice therefrom, results in very good alignment precision with moderate tolerance requirements. A slight deviation vertically of, for example, the surfaces PI and P2 causes only a minimal change of direction of the gearwheel 32 of the output shaft 10.

This is a great advantage of the invention in making it possible for the surfaces PI and P2 to be machined by means of machine-tools which are conventionally used in engine manufacture. The machining tolerances for the surfaces thus present only moderate requirements. There is therefore no need of special machines.

The invention may be varied within the scopes of the patent claims. Thus the contact portions may be shaped differently and need not, for example, be directly adjacent to threaded fastening devices. The second contact surfaces may be replaced by a single surface situated at an angle to the surfaces P1, P2, and the aligning spigot 25 may be replaced by some other element, e. g. even by an aligned and machined projecting part of the engine block. The aligning spigot is preferably circular cylindrical, but other shapes may arise, such as cylindrical with some other cross-sectional shape than circular.

The guiding elements in the region of the output shaft may also be of some other kind, although the embodiment depicted is preferable for the reasons stated above. Thus it is possible, with a certain reduction in precision, for the unit housing 14 to cooperate in this region with, for example, a fastening lug on the engine block via a guide element designed otherwise than as an outer surface for a protruding bearing abutment.

The contact portions may also be designed differently, e. g. be arranged further apart laterally and/or constitute a larger area. They may also be separate from fastening devices such as screws. It is essential, however, that they be situated at a substantial distance from the region of the output shaft, and preferably the region of the opposite side of the housing.