GB2519163A

GB2519163A - Cylinder head of an internal combustion engine

Info

Publication number: GB2519163A
Application number: GB1318137.5A
Authority: GB
Inventors: Winfried Krebs; Carsten Tauscher
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2013-10-14
Filing date: 2013-10-14
Publication date: 2015-04-15
Also published as: GB201318137D0

Abstract

A cylinder head assembly 10 of an internal combustion engine 110 comprises a cylinder head 130, a cylinder head cover 510, a camshaft 135 and a camshaft bearing 500, wherein the camshaft bearing 500 is integrated in the cylinder head cover 510 and the material of the camshaft bearing has the same coefficient of thermal expansion of the material of the camshaft. The camshaft bearing may be casted in during casting of the cylinder head cover, eg by high pressure die casting (HPDC). Alternatively, the camshaft bearing may be pressed in a boss of the cylinder head cover. The camshaft bearing may be a steel or cast iron bushing. The camshaft bearing lubrication oil supply bore 520 may be integrated, eg cast or drilled, in the cylinder head cover.

Description

CYLINDER HEAD OF AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a cylinder head of an internal combustion engine. The invention is particularly related to cylinder heads, comprising one or more camshaft having camshaft bearings of the "closed" type.

BACKGROUND

It is known that In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket. In most engines, the head also provides space for the passages that feed air and fuel to the cylinder, and that allow the exhaust to escape. The head can also be a place to mount the valves, spark plugs, and fuel injectors. Often, the camshaft is also contained within the cylinder head. The camshaft may be seated centrally between each offset row of inlet and exhaust valves, and also utilizing rocker arms, or the camshaft may be seated directly above the valves eliminating the rocker arms and utilizing bucket' tappets.

In standard design for cylinder heads the camshaft bearings, normally sliding bearings, are realized in two parts, an upper bearing cap, as separate element, and a lower bearing cap, which is casted together with the cylinder head. The two parts are joined together by fastening means, for example by means of bolts. The clearance between the cylinder head, better the camshaft bearing, and the camshaft has a remarkable value. In fact, being normally the cylinder head made of aluminium and the camshaft made of steel, these two components have a different coefficient of thermal expansion. Since normally an internal combustion engine should run, according to the specification, up to -40°C, it is mandatory to ensure a correct clearance between camshaft and cylinder head at such extreme low temperature value and this means to significantly increase the clearance at normal ambient temperature.

Of course, a bigger clearance is worsening the "noise, vibration, and harshness" (NVH) of the engine, due to stronger impacts of the camshaft against the cylinder head; the bigger clearance also determines a higher oil flow-rate and consequently a higher oil consumption; moreover, a bigger clearance increases the mechanical losses and consequently the fuel consumption of the engine.

Therefore a need exists for a new cylinder head design, which does not suffer of the above inconvenience.

An object of an embodiment of the invention is to provide a new design of a cylinder head assembly, according to which a smaller clearance between camshaft and cylinder head can be defined, in order to improve NVH performance, oil and fuel consumption.

These objects are achieved by a cylinder head assembly and by an internal combustion engine, having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a cylinder head assembly of an internal combustion engine, the cylinder head assembly comprising a cylinder head, a cylinder head cover, a camshaft and a camshaft bearing, wherein a camshaft bearing is integrated in a cylinder head cover and the material of the camshaft bearing has the same coefficient of thermal expansion of the material of the camshaft.

An advantage of this embodiment is that if the material of the camshaft and the material of the camshaft bearing have the same coefficient of thermal expansion, then it is possible to have a constant clearance between camshaft and camshaft bearing as a function of the external temperature. And, as a consequence a smaller clearance value can be adopted whose reduction is about 25% of the standard value, which is beneficial for improving the NVH performance and reducing oil and fuel consumption.

According to another embodiment, said camshaft bearing is casted in during a casting process of the cylinder head cover.

An advantage of this embodiment is that, normally, the cylinder head cover is casted by using a technique known as Thigh pressure die casting" (HPDC) and the camshaft bearing can be casted together with the head cover.

According to a further embodiment, said camshaft bearing is pressed in a boss of the cylinder head cover.

An advantage of this embodiment is to provide an alternative assembly of the bearing. In fact, the camshaft bearing can be assembled on the cylinder head cover by pressing it inside the cover. Conveniently, a suitable boss can be obtained in the cylinder head cover1 to insert the bearing inside it.

According to still another embodiment said camshaft bearing is a steel bushing.

An advantage of this embodiment is that also the camshaft is made of steel and, therefore, the use of a steel bushing as bearing ensures that bearing and camshaft have the same coefficient of thermal expansion.

According to a still further embodiment, said camshaft bearing is a cast iron bushing.

An advantage of this embodiment is that cast iron and steel have almost the same coefficient of thermal expansion and therefore the use of a steel bushing as bearing ensures that bearing and camshaft have the same coefficient of thermal expansion.

According to another embodiment, the cylinder head assembly also comprises an oil supply system for the camshaft bearing lubrication, which is integrated in the cylinder head cover.

An advantage of this embodiment is that to lubricate the bearing, a standard oil supply system can be used, integrated in the cylinder head cover.

According to a further embodiment said oil supply system is casted in during the casting process of the cylinder head cover.

As mentioned, the cylinder head cover is normally casted and the oil supply system which essentially consists of a bore can be casted together with the head cover.

According to still another embodiment, said oil supply system is drilled in the cylinder head cover.

An advantage of this embodiment is that the oil supply system can simply be drilled in the cylinder head cover.

A further embodiment of the disclosure provides an internal combustion engine equipped with a cylinder head assembly according to one of the previous embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is an axonometric view of a new cylinder head having a cylinder head cover with an integrated camshaft bearing, according to an embodiment of the invention.

Figure 4 is a plane view of the same embodiment of Fig. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the dud 205 and manifold 200. An intercooler 260 disposed in the dud 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VOT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

A detail of the cylinder head assembly 10 according to an embodiment of the present invention is shown in Fig. 3 (axonometric view) and 4 (plane view). In such drawings is shown that the cylinder head assembly 10 comprises a cylinder head 130 and a cylinder head cover 510 having a camshaft bearing 500, which is integrated in the cover. The material of the camshaft bearing has the same coefficient of thermal expansion of the material of the camshaft 135, in order to ensure same thermal deformation of the two components, whatever is the external temperature, even if in extreme condition (about -40°C).

A preferred solution is to integrate the camshaft bearing during the casting process of the cylinder head cover. Normally such casting process is a High Pressure Die Casting (I-IPDC) process. Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity.

As an alternative and if convenient the camshaft bearing is pressed in a boss of the cylinder head cover. Conveniently, a suitable boss can be obtained in the cylinder head cover, to insert the bearing inside it.

A preferred solution is to use a steel or a cast iron bushing to realize the camshaft bearing and to cast it in the cylinder head cover. In principle the integration of the bushing could be done with positive fit or due to closed linkage. In both cases the use of steel or cast iron as material for the camshaft bearings ensures the bearing has the same coefficient of thermal expansion of the camshaft, which is made of steel.

In any case, the back side geometry of the bushing could be realized in a suitable shape, also different form the remaining portion, strongly connected to the integration process.

The oil supply for the camshaft bearings lubrication could be provided through an oil supply system 520, as illustrated in Fig. 3 and 4. The oil supply system can be a standard one and can be integrated in the cylinder head cover. It essentially consists in a bore, having a fluid connection with the main oil supply gallery in the cylinder head. The oil supply system can be casted in during the casting process of the cylinder head cover or even simply drilled in the cylinder head cover.

Summarizing, the present invention provides a new design for a cylinder head assembly according to which the material of the camshaft and the material of the camshaft bearing have the same coefficient of thermal expansion. So acting, it is possible to have a constant clearance between camshaft and camshaft bearing as a function of the external temperature. And, as a consequence a smaller clearance value can be adopted which is beneficial for improving the NVH performance and reducing oil and fuel consumption.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

cylinder head assembly data carrier automotive system 110 internal combustion engine engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector 170 fuetrail fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 camshaft bearing 510 cylinder head cover 520 oil supply system

Claims

CLAIMS1. Cylinder head assembly (10) of an internal combustion engine (110), the cylinder head assembly comprising a cylinder head (130), a cylinder head cover (510), a camshaft (135) and a camshaft bearing (500), wherein the camshaft bearing (500) is integrated in the cylinder head cover (510) and the material of the camshaft bearing has the same coefficient of thermal expansion of the material of the camshaft.
2. Cylinder head assembly according to claim 1, wherein said camshaft bearing (500) is casted in during a casting process of the cylinder head cover (510).
3. Cylinder head assembly according to claim 2, wherein said camshaft bearing (500) is pressed in a boss of the cylinder head cover (510).
4. Cylinder head assembly according to claim 2, wherein said camshaft bearing (500) is a steel bushing.
5. Cylinder head assembly according to claim 2, wherein said camshaft bearing (500) is a cast iron bushing.
6. Cylinder head assembly according to any of the preceding claims, wherein the cylinder head assembly (10) also comprises an oil supply system (520) for the camshaft bearing lubrication, which is integrated in the cylinder head cover (510).
7. Cylinder head assembly according to claim 6, wherein said oil supply system (520) is casted in during the casting process of the cylinder head cover (510).
8. Cylinder head assembly according to claim 6, wherein said oil supply system (520) is drilled in the cylinder head cover (510).
9. Internal combustion engine (110) comprising a cylinder head assembly (10) according to one of the preceding claims.