EP2009254A1

EP2009254A1 - Variable cam phaser apparatus

Info

Publication number: EP2009254A1
Application number: EP07252598A
Authority: EP
Inventors: Philippe-Siad Farah; Manfred Kolkman
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2007-06-27
Filing date: 2007-06-27
Publication date: 2008-12-31

Abstract

A cam phaser apparatus comprising a triple member gear system for transferring a driving torque from a drive member (20) to a driven member (21) and for selectively adjusting the angular relationship between the drive (20) and driven members (21), said triple member gear system comprising a first member (10) comprising a driving part of said triple member gear system connectable to a camshaft, a second member (12) comprising a driven part of said triple member gear system connectable to a cam sprocket or pulley, and a third member (13) comprising an adjusting means of said triple member gear system, said third member being connected to an actuator (4) for rotating said third member (13) or applying a braking torque and/or a motoring torque to said third member (13) to vary the angular relationship between the first (10) and second (12) members, wherein the actuator (4) comprises an electric motor (4) having a rotor and a stator, the rotor being is directly connected to on the third member (13).

Description

The present invention relates to a cam phaser apparatus, particularly, but not exclusively a variable cam phaser apparatus used in valve trains of automobile engines.
It is desirable to be able to adjust the cam phase (i.e. the angular relationship between the crankshaft and the camshaft) of engines during engine operation in order to vary the timing of the opening and closing of the inlet and/or exhaust valves to improve engine performance, emissions and/or fuel consumption. Various types of arrangements exist that are capable of achieving this adjustment. Such systems are required to efficiently convert rotational movement from the crankshaft into rotational movement of the camshaft whilst allowing dislocation between these rotational movements in order to allow variation of the cam phase.
Current systems typically utilise hydraulic actuators using high pressure oil to enable relative angular displacement between drive and driven members (e.g. cam sprocket or pulley and camshaft) of the valve train. Such systems have difficulty operating at extremes of temperature, or low engine speed, in particular during engine start up when the oil pressure is too low to allow hydraulic actuation.
Whilst attempts have been made to design electrically actuated variable cam phase arrangement, such usually require a reduction gearset comprising a complex triple shaft arrangement such as planetary gears or a harmonic drive arrangement and an actuator, typically an electric motor, for adjusting the cam phase.
Examples of triple shaft reduction gearset systems suitable for use with a cam phaser comprise planetary gear systems, with a sun gear, planetary gears mounted on a planet carrier and ring gear, or harmonic drive systems, with a wave generator, flex-spline and circular spline.
Another form of triple member reduction gearset system equivalent to a planetary gear system comprises a magnetic gear having an outer ring comprising a plurality of magnets (equivalent to the ring gear), a concentric inner ring comprising a plurality of circumferentially spaced magnets (equivalent to a sun gear) and an intermediate ring or carrier member mounted in an annular space between said outer and inner rings and comprising a plurality of circumferentially spaced pole pieces (equivalent to planetary carrier upon which a plurality of planetary gears are mounted).
Typically, where such triple shaft reduction gearset systems are applied to a cam phaser of an engine, one shaft is connected to the cam sprocket or pulley to comprise a drive member (typically the planet carrier or circular spline) and a second shaft is connected to the camshaft (typically the ring gear or the flex-spline) to comprise a driven member, the remaining third shaft (typically the sun gear or wave generator) being connected to an actuator, in the form of an electric motor, for varying the cam phase (i.e. the angular relationship between the drive and driven members).
The actuator is typically an electric motor that is mechanically linked to the reduction gearset by means of a mechanical coupling. Fig. 1 illustrates such a known system wherein the reduction gearset system is mounted on the camshaft of the engine as a first unit and the actuator is mounted on the engine (on the cylinder head or a side cover of the engine) in a second step. In order to accommodate misalignment between the actuator and the reduction gearset it is normally necessary to provide an alignment coupling, such as an Oldham coupling, to link the actuator to the reduction gearset.
Due to the requirement for the alignment coupling and the need for support bearings for the electric motor of the actuator, the overall length and packaging requirements of such a known cam phaser assembly is greater than that of an equivalent hydraulic vane type cam phaser. The need for an alignment coupling also add cost, can create noise issues and cam be subject to rapid wear.
According to the present invention there is provided a cam phaser apparatus comprising a triple member gear system, such as a planetary gear system, harmonic drive or magnetic gear, for transferring a driving torque from a drive member to a driven member and for selectively adjusting the angular relationship between the drive and driven members, said triple member gear system comprising a first member connectable to said driven member, a second member connectable to said drive member, and a third member comprising an adjusting means of said triple member gear system, said third member being connected to an actuator for rotating said third member or applying a braking torque and/or a motoring torque to said third member to vary the angular relationship between the first and second members, wherein the actuator comprises an electric motor having a rotor and a stator, the rotor being directly connected to or mounted on the third member.
Preferably the rotor is mounted on the third member to form an integral part of the triple member gear system.
In a preferred embodiment, the actuator comprises an axial air-gap type electric motor comprising stator fixedly mounted with respect to the engine and a rotor mounted on said third member to be rotatable therewith, said rotor and stator being coaxially spaced from one another and in facing relationship, one of said rotor and stator being provided with a plurality magnetic pole portions provided on a side face thereof arranged on a circle, the other of the rotor and stator having means for creating a rotating magnetic field.
Preferably the cam phaser further comprises further comprising a selectively actuable coupling means for selectively coupling two of said first, second and third members. Preferably said coupling means is associated with the actuator.
In a preferred embodiment, said coupling means comprises first and second rotatably mounted coaxial coupling members, a first coupling member mounted on the rotor of the actuator and a second coupling member connected to the second member of the triple member gear system, said first and second coupling members being radially or axially spaced apart from one another, one of said first and second coupling members comprising at least one magnetically conductive region and the other of said first and second members incorporating means for selectively generating a magnetic flux to constrain the first and second members to rotate together.
Preferably said first and second coupling members of said coupling means respectively comprise concentrically arranged inner and outer rotors having a radial gap therebetween, the inner rotor being formed on a peripheral region of the rotor of the actuator.
Alternatively the coupling means may comprise a selectively actuable mechanical coupling, such as a mechanical clutch arrangement.
Embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic view of a known cam phaser apparatus; and
Fig. 2 is a schematic view of a cam phaser apparatus according to a first embodiment of the present invention.

As illustrated in Fig 1, a known cam phaser apparatus includes a first member 1 of a triple member reduction gearset system A, said first member 1 being connected to the camshaft of the engine. In the case of a planetary gear system, such first member 1 could be the planet carrier and planetary gears. In the case of a harmonic drive, the first member 1 could be the circular spline. In the case of a magnetic gear, the first member 1 could be the intermediate ring or pole pieces.
A second member 2 of the triple member gear system is connected to a crankshaft of the engine via a pulley or cam sprocket and an endless belt or chain. In the case of a planetary gear system the second member 2 could be the ring gear. In the case of a harmonic drive, the second member 2 could be the flex-spline. In the case of a magnetic gear, the second member 2 could be the outer ring.
A third member 3 of the triple member gear system is connected to an electric motor 4 for altering the cam phase of the engine. In the case of a planetary gear system, the third member 3 could be the sun gear. In the case of a harmonic drive, the third member 3 could be the wave generator. In the case of a magnetic gear, the third member 3 could be the inner ring. The housing of the motor is fixed with respect to the cylinder head while the rotor of the motor rotates with the camshaft.
When it is desired to advance the cam phase of the camshaft, a braking torque is applied to the third member 3 by the electric motor 4 to decelerate the third member 3, thus advancing the camshaft angle with respect to the crankshaft.
When it is desired to retard the cam phase of the cam shaft, a motoring torque is applied to the third member 3 by the electric motor to accelerate the third member 3, thus retarding the camshaft angle with respect to the crankshaft.
When no advance is required, a magnetic coupling means 5 is provided between the second member 2 and the third member 3 to selectively couple the second and third members 2,3 together, causing all three member to rotate together at the same speed.
In order to accommodate misalignment between the reduction gearset system A and the electric motor 4, an alignment coupling 6, typically an Oldham coupling, is provided for transferring a driving torque between the electric motor 4 and the reduction gearset system. Such coupling 6 increases the cost and complexity of the system, increases the space taken by the cam phaser apparatus and may lead to problems of wear and increased maintenance issues. Furthermore, the self contained electric motor 4 requires support bearings and a separate housing, further increasing the size of the cam phaser apparatus.
In an embodiment of the present invention, as illustrated in Fig 2, the actuator is integrated into the reduction gearset system through the use of an axial air-gap type electric motor.
As with the prior art, the cam phaser apparatus includes a first member 10 of a triple member reduction gearset system, said first member 10 being connected to the camshaft 21 of the engine. In the case of a planetary gear system, such first member 10 could be the planet carrier and planetary gears. In the case of a harmonic drive, the first member 10 could be the circular spline. In the case of a magnetic gear, the first member 10 could be the intermediate ring or pole pieces.
A second member 12 of the triple member gear system is connected to a crankshaft of the engine via a pulley or cam sprocket 20 and an endless belt or chain. In the case of a planetary gear system the second member 12 could be the ring gear. In the case of a harmonic drive, the second member 12 could be the flex-spline. In the case of a magnetic gear, the second member 12 could be the outer ring.
A third member 13 of the triple member gear system is drivingly connected to an actuator as will be described below for altering the cam phase of the engine. In the case of a planetary gear system, the third member 13 could be the sun gear. In the case of a harmonic drive, the third member 13 could be the wave generator. In the case of a magnetic gear, the third member 13 could be the inner ring. The housing of the motor is fixed with respect to the cylinder head of the engine while the rotor of the motor rotates with the camshaft.
When it is desired to advance the cam phase of the camshaft, a braking torque is applied to the third member 13 by the actuator to decelerate the third member 13, thus advancing the camshaft angle with respect to the crankshaft.
When it is desired to retard the cam phase of the cam shaft, a motoring torque is applied to the third member 13 by the actuator to accelerate the third member 13, thus retarding the camshaft angle with respect to the crankshaft.
Position sensors may be provided to allow the relative position of the first, second and/or third members to provide a feedback control signal to control the operation of the cam phaser apparatus.
In order to reduce the size of the cam phaser apparatus and to obviate the need for an alignment coupling or for additional actuator support bearings, an axial air-gap electric motor 25 is utilised as the actuator, a stator 26 of the motor being fixed to the cylinder head of the engine or an adjacent engine cover and the rotor 27 of the motor being mounted on the third member 13, the rotor and stator being coaxially arrange and aligned with the vehicle camshaft. Such axial air-gap electric motors are known, albeit not in relation to cam phaser systems, and thus will not be described in more detail.
A magnetic coupling means 15 is provided between the second member 12 and the third member 13 to selectively couple the second and third members 2,3 together, causing all three member to rotate together at the same speed, an inner rotor member 30 of the magnetic coupling 15 being mounted on the peripheral edge of the rotor 27 of the motor 25. Alternatively, a small motoring torque may be applied to the rotor to maintain the rotor speed at the same speed as the camshaft to maintain a given cam timing.
The direct mounting of the rotor 27 of the motor 25 on the third member of the triple member gear system obviates the need for separate motor support bearings. The provision of an axial air-gap between the rotor 27 and the stator 26 avoids the need for precise axial alignment between the rotor and stator and thus avoids the need for an alignment coupling between the rotor and the third member of the triple member gear system. Thus a more compact and reliable cam phaser system is produced.
The magnetic coupling may be omitted if desired, in which case, when no phase adjustment is required, the speed of the third member shall be synchronised with the speed of the second member. To achieve such synchronisation, a small current may be supplied to the actuating motor to compensate for frictional losses.
Various modifications and variations to the described embodiments of the inventions will be apparent to those skilled in the art without departing from the scope of the invention as defined in the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments.

Claims

A cam phaser apparatus comprising a triple member gear system, such as a planetary gear system, harmonic drive or magnetic gear, for transferring a driving torque from a drive member to a driven member and for selectively adjusting the angular relationship between the drive and driven members, said triple member gear system comprising a first member connectable to said driven member, a second member connectable to said drive member, and a third member comprising an adjusting means of said triple member gear system, said third member being connected to an actuator for rotating said third member or applying a braking torque and/or a motoring torque to said third member to vary the angular relationship between the first and second members, wherein the actuator comprises an electric motor having a rotor and a stator, the rotor being directly connected to or mounted on the third member.
A cam phaser apparatus as claimed in claim 1, wherein the triple member gear system is one of a planetary gear system, a harmonic drive or a magnetic gear system.
A cam phaser apparatus as claimed in any preceding claim, wherein the rotor is mounted on the third member to form an integral part of the triple member gear system.
A cam phaser apparatus as claimed in claim 3, wherein the actuator comprises an axial air-gap type electric motor comprising stator fixedly mounted with respect to the engine and a rotor mounted on said third member to be rotatable therewith, said rotor and stator being coaxially spaced from one another and in facing relationship, one of said rotor and stator being provided with a plurality magnetic pole portions provided on a side face thereof arranged on a circle, the other of the rotor and stator having means for creating a rotating magnetic field.
A cam phaser apparatus as claimed in claim 3 or claim 4, further comprising a selectively actuable coupling means for selectively coupling two of said first, second and third members.
A cam phaser apparatus as claimed in claim 5, wherein said coupling means is associated with the actuator.
A cam phaser apparatus as claimed in claim 6, wherein said coupling means comprises first and second rotatably mounted coaxial coupling members, a first coupling member mounted on the rotor of the actuator and a second coupling member connected to the second member of the triple member gear system, said first and second coupling members being radially or axially spaced apart from one another, one of said first and second coupling members comprising at least one magnetically conductive region and the other of said first and second members incorporating means for selectively generating a magnetic flux to constrain the first and second members to rotate together.
A cam phaser apparatus as claimed in claim 7, wherein said first and second coupling members of said coupling means respectively comprise concentrically arranged inner and outer rotors having a radial gap therebetween, the inner rotor being formed on a peripheral region of the rotor of the actuator.
A cam phaser apparatus as claimed in claim 5, wherein the coupling means comprises a selectively actuable mechanical coupling, such as a mechanical clutch arrangement.