A camshaft adjuster for adjusting the phase position of a camshaft relative to a crankshaft, in particular a hydraulic camshaft adjuster. A camshaft bearing area provided in the camshaft adjuster is designed as a roller bearing.

This application is a 371 of PCT/EP2009/059371 filed Jul. 21, 2009, which in turn claims the priority of DE 10 2008 039 038.0 filed Aug. 21, 2008, the priority of both applications is hereby claimed and both applications are incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a camshaft adjuster of an internal combustion engine, in particular a hydraulic camshaft adjuster.

BACKGROUND OF THE INVENTION

Nowadays, use is widely made of the hydraulic phase or camshaft adjuster, having an oscillating or rotary motor known from the field of hydraulics. Said oscillating motor phase adjuster is operated with engine oil pressure. The phase adjuster is conventionally situated on the ends of the camshaft in the power transmission path. The hydraulic camshaft adjuster is supplied with pressurized oil by means of the oil pump of the engine, Oil guiding ducts are provided in the camshaft for the supply to the actuator. By means of electronically controlled valves, the hydraulic oil is conveyed into the oil pressure chambers of the oscillating motor, and an adjustment of the phase position of the camshaft relative to the crankshaft is thereby attained. That side of the camshaft which faces toward the camshaft adjuster is mounted in a plain bearing on account of the hydraulic oil supply which is usually conducted through the camshaft. For the mounting of the camshaft at the end side, use is usually made of bushes or bearing blocks.

DE 100 02 512 A1 describes a cylinder head for a valve-controlled internal combustion engine, in which cylinder head are provided bearing seats for the inlet and outlet camshafts. On the side of the hydraulic camshaft adjuster, a bearing bush is provided in the bearing seat in order to compensate for the assembly recesses required in the bearing seat and to permit the supply of hydraulic oil to the camshaft adjuster in the bearing point. The hearing bush has two openings, which are arranged axially adjacent to one another, for the two-duct supply of oil to the camshaft adjuster, and a lubricant opening for the lubrication of the bearing point.

DE 10 2004 053 572 B4 describes a hydraulic camshaft adjuster having a two-duct oil guide in the camshaft. Two oil guiding ducts are provided within the camshaft, via which oil guiding ducts hydraulic oil is supplied to in each case one oil pressure chamber (depending on the desired adjusting direction). The oil guiding ducts extend through the camshaft and via external lines to an oil pump and an oil control valve.

DE 198 17 319 A1 describes a hydraulic camshaft adjuster in which a central control slide is provided in order to supply hydraulic oil to the working chambers of the vane-type adjuster. The central control slide replaces the external valve and is integrated, as a 4/2 directional control valve, into the central fastening screw for the camshaft, as a result of which only one radial oil guiding duct is required in the camshaft, and the axial structural length of the camshaft adjuster is reduced.

Various documents, such as for example DE 10 2005 059 841 A1 or DE 197 52 381 A1, are concerned inter alia with the lubrication of bearing points for camshafts.

Depending on the rotational speed range of the engine and the temperature, mechanical friction losses in the engine alone nowadays amount to up to 30 percent, and therefore account for a significant proportion of fuel consumption. The main sources of friction losses in the engine are the piston assemblies, the bearings of the engine shafts, and the valve drive components.

It is therefore the object of the invention to optimize a camshaft bearing point at the side of a hydraulic camshaft adjuster with regard to the occurring friction losses.

SUMMARY OF THE INVENTION

According to the invention, the object is achieved by arranging a rolling bearing in a bearing point for a camshaft of a hydraulic camshaft adjuster. The rolling bearing is preferably a ball bearing.

The advantages of the invention can be considered in particular to be that mechanical friction losses and undesired noise generation in the combustion engine can be further reduced.

The bearing point according to the invention of the camshaft can particularly advantageously be applied to a vane-type adjuster with a central supply of pressure medium by means of a control slide. By dispensing with a radial oil guiding duct in the camshaft, the installation space gained can be used for arranging a rolling bearing. The invention may however also be applied to camshaft adjusters with axial oil guiding ducts.

In another advantageous embodiment, the supply of hydraulic oil into the adjuster takes place at the side facing away from the camshaft. In this case, too, an oil guiding duct in the camshaft is not required, and this reduces the axial installation space and nevertheless allows the camshaft to be mounted using rolling bearings.

DETAILED DESCRIPTION OF THE INVENTION

The FIGURE shows a camshaft adjuster01. In a known way, the camshaft adjuster is designed as a vane-type adjuster and is arranged in the cylinder head of an internal combustion engine. The camshaft adjuster comprises an outer rotor02which is connected to a sprocket03for conjoint rotation therewith.

The sprocket03is connected via a chain to a crankshaft, and is driven by the latter (not illustrated) during the operation of the internal combustion engine.

The camshaft adjuster01also comprises an inner rotor04which is connected to a camshaft06for conjoint rotation therewith. The fastening of the inner rotor04to the camshaft06is realized by means of a central screw07.

Radially aligned vanes08which engage one into the other are provided on the outer rotor02and on the inner rotor04, which vanes, in annular sectors, form in each case two pressure chambers09for the adjustment in the “early” and “late” directions. For adjustment, depending on the desired adjusting direction, hydraulic oil is pumped into one of the pressure chambers09, as a result of which a relative rotation between the inner rotor04and outer rotor02, and therefore an adjustment of the phase position of the camshaft06relative to the sprocket03and therefore relative to the crankshaft, takes place.

In the basic position—typically a “late” control time in the case of inlet valve adjustment and an “early” control time in the case of outlet valve adjustment—a locking element (not illustrated) locks the adjuster when the engine is shut down. During operation, said locking action is released hydraulically.

A control slide11is arranged in the central screw07, coaxially with the longitudinal axis thereof. The control slide11can be moved axially by means of an actuating drive12. The actuating drive12is preferably an actuating magnet which moves an armature13.

The control slide11, with its annular ducts14and with radial bores16in the central screw07, forms a multi-way valve by means of which the flow of the hydraulic oil to one or the other pressure chamber09is controlled and an adjustment is thereby realized.

In the event of an axial movement of the control slide11, therefore, the oil pressure is switched between the pressure chambers09. The pressure chamber09in each case not charged with oil pressure is connected to the return line.

Ducts17are provided in the inner rotor04, which ducts permit the flow of hydraulic oil from a radial duct18of the camshaft06via an axial duct19to the pressure chambers09via the control slide11.

To fix a control time position, the control slide11is held by the force of a spring21in a basic position, in which the connections of all the ducts are separated from one another.

According to the invention, a rolling bearing22is preferably arranged adjacent to the radial duct18in the camshaft bearing point23of the cylinder head.

In another embodiment of the invention, the supply of hydraulic oil may take place via an axial duct in the camshaft06. In this way, further installation space can be saved in the axial direction and the camshaft can nevertheless be mounted using rolling bearings.

The mounting, according to the invention, of the camshaft in a rolling bearing at the adjuster side may also be applied to other camshaft adjusters if the axial installation space is available.

LIST OF REFERENCE NUMERALS