Variable cam phaser apparatus

Abstract

 A cam phaser apparatus comprises a first ring gear (4) connectable to a driven member, for example a camshaft (8), a second ring gear (2) connectable to a driving member, for example a cam sprocket (6) or pulley, said first (4) and second (2) ring gears being coaxially arranged alongside one another, said first ring gear (4) having a different number of teeth than said second ring gear (2), and at least one first planetary gear (16,18) supported on a planetary gear carrier (14), said at least one first planetary gear engaging both said first (4) and second (2) ring gears to transfer a driving torque therebetween, said planetary gear carrier (14) being connected to an actuator (22) for rotating the planetary gear carrier (14) or applying a braking torque and/or a motoring torque to said planetary gear carrier (14).

Description

[0001] 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.

[0002] 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.

[0003] 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, in particular during engine start up when the oil is cold, due to temperature related viscosity changes of the oil.

[0004] Whilst attempts have been made to design electrically actuated variable cam phase arrangement, such usually require a 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. Such triple shaft systems typically require a large packaging envelope and difficult assembly and servicing procedures, in particular in relation to the connection of the cam phaser to the camshaft.

[0005] 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.

[0006] Typically, where such planetary gear 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 ring carrier) and a second shaft is connected to the camshaft (typically the planet carrier) to comprise a driven member, the remaining third shaft (typically the sun gear) 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).

[0007] The actuator is typically an electric motor that is mechanically linked to the reduction gearset by means of a mechanical coupling.

[0008] According to the present invention there is provided a cam phaser apparatus for transferring a driving torque from a driving member to a driven member and for selectively adjusting the angular relationship between the drive and driven members, said apparatus comprising a first ring gear connectable to said driven member, for example a camshaft , a second ring gear connectable to said driving member, for example a cam sprocket or pulley, said first and second ring gears being coaxially arranged alongside one another, said first ring gear having a different number of teeth than said second ring gear, and at least one planetary gear supported on a planetary gear carrier, said at least one planetary gear engaging both said first and second ring gears to transfer a driving torque therebetween, said planetary gear carrier being connected to an actuator for rotating the planetary gear carrier or applying a braking torque and/or a motoring torque to said gear carrier to rotate said at least one first planetary gear with respect to said first and second ring gears to vary the angular relationship between the first and second ring gears.

[0009] Preferably said first and second ring gears have the same gear diameter.

[0010] Preferably the first and second rings gears and said at least one first planetary gear have a gear profile adapted to permit said at least one first planetary gear to rotatably mesh with both said first and second ring gears.

[0011] The first ring gear may have two gear teeth more or less than the second ring gear to give a reduction ratio of 50:1. In such embodiment, two of said first planetary gears may be mounted on said carrier at locations spaced 180° from each other. In one embodiment said first ring gear is provided with 102 teeth and said second ring gear is provided with 100 teeth

[0012] Where greater torque capability is required, one or more intermediate planetary gears may be mounted on the carrier, said one or more intermediate planetary gears having a first gear segment meshing with said first ring gear and a second gear segment meshing with said second ring gear, said first and second gear segments having gear profiles radially offset from each other. Said one or more intermediate planetary gears may be provided at equi-spaced locations between said first planetary gears, wherein the gear offset between the first and second gear segments of the intermediate planetary gears is equal to 1/2 tooth.

[0013] Preferably said planetary gear carrier and said second ring gear are rotatably supported on said first ring gear to enable the resulting gear assembly to be mounted directly onto a camshaft. Preferably the gear assembly is mounted to the camshaft using a single central mounting bolt.

[0014] Preferably a cam sprocket or pulley is mounted on or formed integrally with said second ring gear.

[0015] Preferred embodiments 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 part sectional view of a cam phaser apparatus according to an embodiment of the present invention;

Fig. 2 is an exploded view of the gear components of the cam phaser apparatus of Fig. 1;

Fig. 3 is a sectional view of a cam phaser apparatus according to a second embodiment of the present invention;

Fig. 4 is a perspective view of the main planetary gears of the cam phaser apparatus of Fig. 4; and

Fig. 5 is a perspective view of the further or intermediate planetary gears of the cam phaser of Fig. 4.

[0016] As illustrated in Figs. 1 and 2, a cam phaser apparatus according to an embodiment of the present invention comprises coaxial input and output ring gears 2, 4, the input ring gear 2 being drivingly connected to a cam pulley or sprocket 6 and the output ring gear 4 being drivingly connected to a camshaft 8. The output ring gear 4 is rotatably supported by the input ring gear 2. The input ring gear 2 and output ring gear 4 are providing with cooperating end-stops 9,10 to limit the maximum phasing angle between the gears.

[0017] Each of the input and output ring gears 2,4 have inwardly facing gear teeth provided on the inner periphery thereof, the gear teeth of the input ring gear 2 being arranged on a first contact circle and the gear teeth of the output ring gear 4 being arranged on a second contact circle coaxial with and of equal diameter to said first circle.

[0018] A planetary carrier 14 is rotatably mounted on the input ring gear 2 by means of a bearing and supports a pair of equally spaced planetary gears 16,18 each planetary gear meshing with the gear teeth of both the input and output ring gears 2,4 to enable torque to be transferred between the input and output ring gears 2,4 via the gear teeth.

[0019] The planetary carrier 14 is drivingly engaged by the control shaft 20 of a rotary actuator 22 (e.g. an electric motor) to provide a motoring or braking torque to the planetary carrier 14 to adjust the cam phase, as will be described below. The body of the actuator 22 is mounted upon the cylinder head of the engine (not shown).

[0020] In order to adjust the phase between the input and output ring gears 2,4, the input ring gear 2 is provided with a different number of teeth than the output ring gear 4 such that rotation of the planetary carrier 14 with respect to the input ring gear 2, and thus rotation of the planetary gears 16,18, varies the angular relationship between the input and output ring gears 2,4. In the described embodiment, the input ring gear 2 is provided with 102 teeth while the output ring gear 4 is provided with 100 teeth to give a reduction ration of 50:1. A high reduction ratio is required to match the torque capability of the electrical actuator with the torque loading of the camshaft.

[0021] The lower the desired reduction ratio, the easier it will be to install more planetary gears with a single teeth segment. For example, by providing an input ring gear 2 with three more or less teeth than the output ring gear 4 (e.g. 102/99) gives a reduction ratio 33:1 and allows usage of 3 euqally spaced planetary gears. However, this will increase the torque requirements of the actuator and make is much bigger.

[0022] The gear teeth profiles of the planetary gears 16,18 and the ring gears 2,4 are corrected to compensate for the slightly different pitch diameter of the gear teeth of the input ring gear 2 compared to those of the output ring gear 4 due to the unequal number of gear teeth therebetween.

[0023] In a second embodiment of the present invention, as illustrated in Figs. 3 to 5, where greater torque transference capacity is required than that which can be achieved by the main planetary gears 16,18, intermediate planetary gears 30,32 may be provided at intermediate locations between the main planetary gears 16,18.

[0024] To compensate for the phase difference between the teeth of the input and output ring gears 2,4 at such intermediate locations due to the unequal numbers of teeth therebetween, the intermediate planetary gears 30,32 are provided with a first gear segment 34 adapted to mesh with the teeth 10 of the input ring gear 2 and a second gear segment 36 adapted to mesh with the teeth 12 of the second ring gear 4, the teeth of the first gear segment 34 being radially offset with respect to the teeth of the second gear segment 36, as illustrated in Fig. 5. Where such intermediate planetary gears 30,32 are located equidistant between said main planetary gears 16,18, such gear offset will be equal to half a gear tooth.

[0025] The cam phaser according to the present invention can be mounted directly on the end of the camshaft 8 without requiring additional support structures and thus provides a more compact arrangement than prior art devices. The absence of a sun gear enables access to the end of the camshaft 8 to enable the cam phaser to be bolted directly to the end of the camshaft by a single centre bolt 40, greatly facilitating assembly.

[0026] As shown in Fig. 2, the inner periphery of the planetary carrier 14 can be provided with a simply keyway arrangement 15 to enable the output shaft 20 of the actuator to be easily drivingly engaged with the planetary carrier 14.

[0027] In operation, at a constant cam phase, the actuator 22 will be operated at the same speed as the speed of the input ring gear 2. As such, the angular orientation between the input ring gear 2 and the output ring gear 4 is locked and maintained via the planetary gears 16,18.

[0028] When it is desired to advance or retard the cam phase of the engine, a respective motoring or braking torque is applied to the planetary carrier 14 to rotate the planetary carrier 14 with respect to the input ring gear 2, thus rotating the planetary gears 16,18 (and 30,32 in the case of the second embodiment) to adjust the relative angular orientation of the output ring gear 4 with respect to the input ring gear 2 and thus the relative angular orientation between the cam sprocket 6 and the camshaft 8. Position sensors may be provided to detect the relative positions of the input and output ring gears 2,4 to provide a feedback control for the cam phaser.

[0029] Where the input ring gear 2 has more teeth than the output ring gear 4, any acceleration of the actuator 22 (in clockwise direction when looking towards the camshaft) will cause the output ring gear 4 will accelerate with respect to the input ring gear 2 and hence induce a cam phase towards retard position.

[0030] Vice versa, when the rotary actuator 22 is decelerated (braking) the output ring gear 4 will accelerate with respect to the input ring gear 2 and hence induce a cam phase towards advance position.

[0031] Optionally, the input ring gear 2 can have with fewer instead of more teeth that the output ring gear 4. This will invert the cam phase change direction of the camshaft for the same actuator operation.

[0032] Various modifications and variations to the described embodiments of the invention 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

1. A cam phaser apparatus for transferring a driving torque from a driving member to a driven member and for selectively adjusting the angular relationship between the drive and driven members, said apparatus comprising a first ring gear connectable to said driven member, for example a camshaft, a second ring gear connectable to said driving member, for example a cam sprocket or pulley, said first and second ring gears being coaxially arranged alongside one another, said first ring gear having a different number of teeth than said second ring gear, and at least one first planetary gear supported on a planetary gear carrier, said at least one first planetary gear engaging both said first and second ring gears to transfer a driving torque therebetween, said planetary gear carrier being connected to an actuator for rotating the planetary gear carrier or applying a braking torque and/or a motoring torque to said planetary gear carrier to rotate said at least one first planetary gear with respect to said first and second ring gears to vary the angular relationship between the first and second ring gears.

2. A cam phaser as claimed in claim 1, wherein said first and second ring gears have the same gear diameter.

3. A cam phaser as claimed in claim 2, wherein the first and second rings gears and said at least one first planetary gear have a gear profile adapted to permit said at least one first planetary gear to rotatably mesh with both said first and second ring gears.

4. A cam phaser as claimed in any preceding claim, wherein the first ring gear has two gear teeth more or less than the second ring gear to give a reduction ratio of 50:1.

5. A cam phaser as claimed in any of claims 1 to 3, wherein the first ring gear has three gear teeth more or less than the second ring gear to give a reduction ratio of 33:1.

6. A cam phaser as claimed in claim 4, wherein two of said first planetary gears are mounted on said gear carrier at locations spaced 180° from each other.

7. A cam phaser as claimed in claim 6, wherein said first ring gear is provided with 102 teeth and said second ring gear is provided with 100 teeth

8. A cam phaser as claimed in claim 6 or claim 7, wherein one or more intermediate planetary gears are mounted on the planetary gear carrier, said one or more intermediate planetary gears having a first gear segment meshing with said first ring gear and a second gear segment meshing with said second ring gear, said first and second gear segments having gear profiles radially offset from each other.

9. A cam phaser as claimed in claim 8, wherein each of said one or more intermediate planetary gears are provided at equi-spaced locations between said first planetary gears, wherein the gear offset between the first and second gear segments of the intermediate planetary gears is equal to 1/2 tooth.

10. A cam phaser as claimed in any preceding claim, wherein said planetary gear carrier and said second ring gear are rotatably supported on said first ring gear to enable the resulting gear assembly to be mounted directly onto a camshaft.

11. A cam phaser as claimed in claim 10, wherein the gear assembly is mounted to the camshaft using a single central mounting bolt.

Drawing