GB2557659A

GB2557659A - Wastegate actuator assembly

Info

Publication number: GB2557659A
Application number: GB1621296.1A
Authority: GB
Inventors: Bourqui Yvan
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2016-12-14
Filing date: 2016-12-14
Publication date: 2018-06-27
Also published as: GB201621296D0

Abstract

A wastegate actuator assembly 10 for controlling a wastegate in a turbocharged engine system comprising an electric motor 12, a control valve, and a drive transmission train 16 which connects the motors output shaft 14 to the valve. The transmission train comprises non-circular gears which provide variable ratios. A further aspect of the invention provides a compound gear 18, consisting of a spur gear 22 attached to one of the arcuate gears 24. In this case the output gear 20 is non-circular. The non-circular gears may have a spiral pitch. A wastegate unit, turbocharged engine system and methods of controlling a wastegate in a turbocharged engine system are also provided. The methods disclose transmission arrangements that allow the motor to apply a high gear ratio, and high torque at the output, during closure and a low ratio, and torque, during opening. This provides a valve with a fast response during long strokes and regulations phases whilst providing a high holding torque when the valve is closed using a small current draw.

Description

(71) Applicant(s):

Johnson Electric S.A.

Freiburgstrasse 33, Murten CH-3280, Switzerland (72) Inventor(s):

Yvan Bourqui

(51) INT CL:
F02B 37/18 (2006.01) F16K 31/53 (2006.01)	F16K 31/04 (2006.01)
(56) Documents Cited: GB 2514374 A US 20130028714 A1	JP 2007002846 A US 20040060349 A1
(58) Field of Search: INT CL F02B, F16K Other: EPODOC & WPI

(74) Agent and/or Address for Service:

Albright IP Limited

County House, Bayshill Road, CHELTENHAM, Gloucestershire, GL50 3BA, United Kingdom (54) Title of the Invention: Wastegate actuator assembly

Abstract Title: Variable torque wastegate actuator assembly (57) A wastegate actuator assembly 10 for controlling a wastegate in a turbocharged engine system comprising an electric motor 12, a control valve, and a drive transmission train 16 which connects the motor’s output shaft 14 to the valve. The transmission train comprises non-circular gears which provide variable ratios. A further aspect of the invention provides a compound gear 18, consisting of a spur gear 22 attached to one of the arcuate gears 24. In this case the output gear 20 is non-circular. The non-circular gears may have a spiral pitch.

A wastegate unit, turbocharged engine system and methods of controlling a wastegate in a turbocharged engine system are also provided. The methods disclose transmission arrangements that allow the motor to apply a high gear ratio, and high torque at the output, during closure and a low ratio, and torque, during opening. This provides a valve with a fast response during long strokes and regulations phases whilst providing a high holding torque when the valve is closed using a small current draw.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

1303 18

FIG. 2b

FIG. 3

W03 18

FIG. 4a

FIG. 4b

1303 18

116 _A_.

'Ί

FIG. 6

Wastegate Actuator Assembly

The present invention relates to a wastegate actuator assembly, preferably, but not necessarily exclusively for controlling a wastegate in a turbocharged engine system. The invention also relates to a turbocharged engine system, to a wastegate control actuator for controlling a wastegate in a turbocharged engine system, and to a method of controlling a wastegate in a turbocharged engine system.

A wastegate is a valve in a, typically turbocharged, engine system, which is designed to divert exhaust gases away from the turbine in a turbocharger of the system. This regulates the turbine speed of the turbine, which also then regulates the speed of rotation of the compressor in the system. The wastegate is able to regulate the maximum boost pressure of the turbocharged engine system.

In order to operate effectively, an actuator which controls the valve must provide a fast response early in its stroke, in particular during long strokes and regulation phases of the turbocharged engine system, whilst also providing a high holding torque when the valve is closed using only a small current draw, so as to prevent overheating of the actuator. These two requirements are opposed to one another; fast response is achieved with a low torque system.

The high torque requirement in the closed condition is also an issue. Normal operating conditions for the wastegate are at elevated temperatures, and the valve is often kept closed for long durations. Under these conditions, it is common for the electric motor maintaining the closed condition to overheat and therefore fail.

The present invention seeks to provide a wastegate actuator assembly in which a balance can be struck between a high output torque during a closed condition of the wastegate, and a low output torque during long strokes and regulation phases of the turbocharged engine systems.

According to a first aspect of the invention, there is provided a wastegate actuator assembly for controlling a wastegate in a turbocharged engine system, the wastegate actuator assembly comprising: an electric motor having an output shaft; a wastegate control valve; and a drive transmission train which connects the output shaft of the electric motor to the wastegate control valve, the drive transmission train comprising a compound gear having first and second compound gear elements and an output gear which is coupled to the wastegate control valve, wherein the first compound gear element is a spur gear which is directly or indirectly engagable with the output shaft, and the second compound gear element and output gear are non-circular gears which are engagable to provide a variable gear ratio.

The provision of a variable gear ratio between the components of the drive transmission train ensures that a low torque for rapid motion can be achieved for the wastegate control valve, but that a high torque is maintained in the closed condition of the wastegate control valve without requiring a high current. This allows for a more compact arrangement to be created, with few gear components required in order to achieve the desired gear ratios, whilst also minimising the risk of motor overheating since the current draw is much smaller than that for a standard actuator.

Preferably, each of the second compound gear element and output gear may have spiral pitch paths.

The complementarily formed spiral pitches of the output gear and second compound gear element represents an advantageous mechanism by which the variable gear ratio can be achieved, since the two gear will naturally and neatly intermesh as they rotate in tandem.

Optionally, the output gear may have a truncated angular extent, in which case, the angular extent may be between 90 and 180 degrees. The assembly may also further comprise a cranked linkage between the output gear and wastegate control valve.

The truncation of the output gear and the provision of a cranked onward linkage all lead to the ability to provide a more compact actuator arrangement, minimising material cost in the manufacture of the actuator, whilst also improving the ability for the actuator to be integrated into smaller turbocharged engine systems.

The output shaft may include a pinion gear engagable with the first compound gear element. Said pinion gear may be a helical evoloid pinion gear, the first compound gear element being a complementary evoloid gear. Alternatively, there may be least one intermediate gear which interconnects the pinion gear and first compound gear element.

An evoloid gear arrangement advantageously allows for a high initial gear ratio to be maintained, which may beneficially further reduce the current draw on the system, further reducing the likelihood of overheating for the motor. Furthermore, the helical evoloid gear further reduces the lateral extent of the gear train, since it is more compact than a traditional star pinion gear, which may in turn lead to a more compact wastegate actuator assembly, whilst achieving a high relative torque. Torque transmission via a helical evoloid gear may also be improved relative to a traditional pinion gear, as there is a lower propensity for jumping or slippage between adjacent gears.

In one preferred embodiment, the second compound gear element may be positioned on a side of the first compound gear element which is proximal the electric motor.

The positioning of the second compound gear element may allow for the direction of the wastegate control output of the actuator to be selected; in this instance, output in the direction of the electric motor. This may allow for a relatively compact arrangement to be created, since the onward linkage will be adjacent to the electric motor, rather than projecting outwardly from an opposite side of the actuator housing.

According to a second aspect of the invention, there is provided a wastegate unit for a turbocharged engine system, the wastegate unit comprising a wastegate having a wastegate body including an inlet port and an outlet port, a wastegate valve positioned between the inlet and outlet ports, and an exhaust-gas-manifold connector engagable with the inlet port and which can be attached to an exhaust gas manifold, and a wastegate actuator assembly in accordance with the first aspect of the invention which controls the flow of exhaust gas from the outlet port of the wastegate.

According to a third aspect of the invention, there is provided a turbocharged engine system having a combustion engine, a turbocharger turbine which is engagable with a combustion chamber of the combustion engine, an exhaust gas manifold which is connected to an inlet of the turbocharger turbine, and a wastegate unit in accordance with the second aspect of the invention, the exhaust-gas-manifold connector being engaged with the exhaust gas manifold to allow controllable release of exhaust gas from the exhaust gas manifold prior to entry into the turbocharger turbine.

According to a fourth aspect of the invention, there is provided wastegate control actuator for controlling a wastegate in a turbocharged engine system comprising: an electric motor having an output shaft; a drive transmission train comprising a gear coupling to the output shaft, a compound gear comprising a first and second compound gear elements, and an output gear which is coupled to a wastegate control output for controlling a wastegate control valve; and an actuator housing within which the electric motor and drive transmission train are contained; wherein the first compound gear element is a spur gear which engages with the gear coupling, and the second compound gear element and output gear are non-circular gears which are engagable to provide a variable gear ratio.

According to a fifth aspect of the invention, there is provided a method of controlling a wastegate in a turbocharged engine system, the method comprising the steps of: a] providing a wastegate actuator assembly, preferably in accordance with the first aspect of the invention; and b] arranging the second compound gear element and output gear such that when a closure actuation is applied by the electric motor, a high gear ratio is effected to impart a high torque at the output gear, and that when an opening actuation is applied by the electric motor, a low gear ratio is effected to impart a low torque at the output gear.

According to a sixth aspect of the invention, there is provided a compact wastegate actuator assembly for controlling a wastegate in a turbocharged engine system, the compact wastegate actuator assembly comprising: an electric motor having an output shaft; a wastegate control valve; and a drive transmission train which connects the output shaft of the electric motor to the wastegate control valve, the drive transmission train mutually interengagable non-circular gears to provide a variable gear ratio. Preferably each of the non-circular gears may have a spiral pitch path.

According to a seventh aspect of the invention, there is provided a method of controlling a wastegate in a turbocharged engine system, the method comprising the steps of: a] providing a compact wastegate actuator assembly in accordance with the sixth aspect of the invention; and b] arranging the non-circular gears such that when a closure actuation is applied by the electric motor, a high gear ratio is effected to impart a high torque at an output gear of the wastegate actuator assembly, and that when an opening actuation is applied by the electric motor, a low gear ratio is effected to impart a low torque at the said output gear.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective representation of a first embodiment of a wastegate 10 actuator assembly in accordance with the first aspect of the invention with the wastegate control valve omitted for clarity;

Figure 2a shows a plan view of the drive transmission train of the wastegate actuator assembly of Figure 1 in a relatively low-torque stroke-beginning condition;

Figure 2b shows the drive transmission train of Figure 2a in a relatively high15 torque holding condition;

Figure 3 shows a perspective representation of an embodiment of a wastegate control actuator in accordance with the third aspect of the invention;

Figure 4a shows a plan view from above of the wastegate control actuator of Figure 3;

Figure 4b shows a plan view from the side of the wastegate control actuator of

Figure 3;

Figure 5 shows a perspective representation of a second embodiment of a wastegate actuator assembly in accordance with the first aspect of the invention; and

Figure 6 shows a perspective representation of a third embodiment of a wastegate actuator assembly in accordance with the first aspect of the invention with the wastegate control valve omitted for clarity.

Referring to Figure 1, there is indicated a wastegate actuator assembly, referenced globally at 10, which is used to impart a driving force to a wastegate control valve (not shown in Figure 1 for clarity). The wastegate actuator assembly 10 comprises an electric motor 12, preferably a DC electric motor, having an output shaft 14 extending therefrom and a drive transmission train 16 which connects the output shaft 14 of the electric motor 16 to the wastegate control valve.

The drive transmission train 16 comprises more than one non-circular gear element, which preferably include at least a compound gear 18 and an output gear 20, the compound gear 18 and output gear 20 being rotationally communicable with one another. The compound gear 18 is directly or indirectly communicable with the output shaft 14 of the electric motor 12, whereas the output gear 20 is directly or indirectly engagable with the wastegate control valve, preferably for controlling a wastegate in a turbocharged engine system.

The compound gear 18 is formed as a first compound gear element 22, here a spur gear, which is coupled to, and preferably formed with, a second compound gear element 24. It will be appreciated that the compound gear 18 could be formed by the first and second gear elements 22, 24 being pinned together by an axle 26 or similar coupling.

The first compound gear element 22 has a circular profile, and is engagable with the output shaft 14 of the electric motor 12. In the depicted embodiment, the output shaft 14 is formed as a pinion gear, preferably a helical evoloid pinion gear, which is complementarily-toothed to engage with the teeth of the first compound gear element 22, here also formed as an evoloid gear. A helical evoloid arrangement is able to provide a very high gear ratio, which in turn allows for a large torque to be applied to the drive transmission train 16 for a given current applied to the electric motor 12.

The second compound gear element 24 is formed so as to have a non-circular profile, preferably having a spiral pitch path, that is, having a gradually increasing radius about its perimeter or circumferential extent. At least a portion of the second compound gear element 24 may therefore be formed as a stop 28 to continued rotational motion, which is here a discontinuity at or adjacent to the teeth of the second compound gear element 24.

Preferably, the second compound gear element 24 may be positioned on a side of the first compound gear element 22 which is proximal the electric motor 12. Since the second compound gear element 24 is preferably smaller than the first compound gear element, and therefore will not impede the output shaft 14 of the electric motor 12, this arrangement allows for the volume of the wastegate actuator assembly 10 to be kept to a minimum.

The output gear 20 is also formed as a non-circular gear, and, in the depicted embodiment is formed as a gear having an angularly-truncated extent, thereby allowing the total volume occupied by the in use output gear 20 to be reduced. Preferably, the angular extent of the output gear 20 is between 90 and 180 degrees, although the skilled person will recognise that this may be dependent upon the gear ratio required for engagement with the second compound gear element 24. The teeth of the output gear 20 are formed so as to be complementarily engagable with the teeth of the second compound gear element 24. As with the second compound gear element 24, the output gear 20 also preferably has a spiral pitch path, that is, having a gradually increasing radius about its perimeter or circumferential extent.

A wastegate control output 30 is provided engaged with the output gear 20, here formed as a hub 32 which is engaged with an axle 34 of the output gear 20, and which is directly or indirectly connectable to the wastegate control valve. In the depicted embodiment, the hub 32 is formed so as to have an onward connector 36, visible in Figure 3, which is axially offset with the axle 34 of the output gear 20, which beneficially allows for a cranked connector to be used, rather than an additional and bulky gear train.

The engagement between the compound gear 18 and the output gear 20 is illustrated in detail in Figures 2a and 2b. Figure 2a shows the relative positions of the output gear 20 and second compound gear element 24 at the start of a stroke. The point of contact between the output gear 20 and second compound gear element 24 is here at a maximum radial extent of the second compound gear element 24, indicated as Rgeari, and at a relatively small radial extent of the output gear 20, indicated as Ropg. At this point, the gear ratio is approximately 2.2, and is therefore relatively low. This means that a torque applied to the output gear 20 and therefore to the wastegate control valve is relatively low.

On the other hand, Figure 2b shows the relative positions of the output gear 20 and second compound gear element 24 in a holding condition. The point of contact between the output gear 20 and second compound gear element 24 is here at a relatively small radial extent of the second compound gear element 24, again indicated as R_geari, and at a relatively large radial extent of the output gear 20, again indicated as Ropg. At this point, the gear ratio is approximately 3.3, and is therefore relatively high, being approximately 50% higher than the gear ratio in the stroke start position. This means that a torque applied to the output gear 20 and therefore to the wastegate control valve is relatively high.

The interengagement of the output gear 20 and the second compound gear element 24 therefore is such that the drive transmission train 16 provides a variable gear ratio as rotational force is imparted, altering the application of torque to the wastegate control valve. The conversion ratio is therefore non-constant. When the wastegate control valve is open, during long strokes and regulation phases, the second compound gear element 24 has a large radial extent, whilst the output gear 20 has a relatively small radial extent. Thus, the conversion ratio is low, and the rotational motion is fast with a low output torque. When the wastegate control valve is closed, the reverse is true; the movement is slower and the output torque is higher whilst drawing a low current. This advantageously limits the risk of the electric motor overheating.

An assembled wastegate actuator 50 is shown in Figure 3, and Figures 4a and 4b, which is a relatively compact arrangement. The size of the actuator housing 52 is determined by the total operational volume of the electric motor 12 and the drive transmission train

16. The actuator housing 52 comprising a motor compartment 54, a drive train compartment 56 and an outlet port 58 through which the wastegate control output 30 may project. Additionally, there may also be provided a control electronics input port 60 via which at least a power supply may be connectable with the wastegate actuator 50.

As can be seen, in particular from Figure 4b, the drive train compartment 56 has a relatively shallow depth, reducing the overall bulk of the actuator 50, making it more suitable for incorporation into smaller turbocharged engine systems.

A second embodiment of a wastegate actuator assembly is illustrated in Figure 5, and is 5 indicated globally at 110. Identical or similar components to those described in reference to the first embodiment will be referred to using identical or similar reference numerals, and therefore further detailed description will be omitted for brevity.

In the depicted arrangement, the output shaft 114 of the electric motor 112 of the wastegate actuator assembly 110 is formed so as to have a toothed pinion gear 138 which is directly engagable with teeth of the first compound gear element 122 of the compound gear 118.

The second compound gear element 124 is here formed so as to be largely identical to that of the first embodiment; however, the output gear 120 is formed as a full spiral gear, rather than an angularly-truncated gear. In this instance, at least part of the perimeter of the output gear 120 may be non-toothed, since the full angular extent is not able to fully engage with the second compound gear element 124, given the gear ratios available. It will be appreciated, however, that this may not necessarily be always the case; the second compound gear element 124 could feasibly be formed so as to be larger than the output gear 120, thereby reversing the gear ratios, in which case the full angular extent of the second compound gear element 124 would not engage with the output gear 120.

The output gear 120 is coupled to a cranked linkage 140, which indirectly couples the output gear 120 to the wastegate control valve 142. Such an arrangement may have space-saving advantages over a comparable gear-based drive train when imparting the driving force to the wastegate control valve 142.

A third embodiment of the wastegate actuator assembly is illustrated in Figure 6, and indicated globally at 210. As before, identical or similar components to those described in reference to the first embodiment will be referred to using identical or similar reference numerals, and therefore further detailed description will be omitted for brevity.

This particular embodiment illustrates how an indirect coupling of the compound gear 218 to the output shaft 214 of the electric motor 212 may be achieved. A further, intermediate gear 244, preferably a compound gear, may be provided which transfers the rotational motion of the output shaft 214 to the first compound gear element 222. This arrangement may allow the second compound gear element 224 of the compound gear 218 to be provided on a side of the first compound gear element 222 which is distal to the electric motor 212.

In turn, the output gear 220 may be provided so as to be positioned on the said distal side of the first compound gear element 222 so as to engage with the second compound gear element 220. This may be a more convenient arrangement if the wastegate control output 232 needs to be on the opposite side of the actuator housing than the electric motor 212, for whatever reason.

A wastegate unit may therefore be provided which utilises any variant of the previously described wastegate actuator assembly 10, 110, 210, and which comprises a wastegate having a wastegate body which includes an inlet port, an outlet port, and a wastegate valve positioned between the inlet and the outlet port. The wastegate valve may be provided as a diaphragm assembly which is insertable inside the wastegate body, but any suitable valve could be considered in the wastegate unit. An exhaust-gas-manifold connector, such as a screw-threaded connector, can be provided to allow the wastegate unit to be affixed to an exhaust gas manifold, typically provided as pipes or conduit which run from the exhaust of a standard combustion engine.

In use, the wastegate unit may be provided as part of a turbocharged engine system having a combustion engine, and a turbocharger turbine which is engagable with a combustion chamber of the combustion engine. An exhaust gas manifold, which preferably extends from an exhaust of the combustion engine, is connected to an inlet of the turbocharger turbine. The wastegate unit as described above may then be coupled to the exhaust gas manifold via the exhaust-gas-manifold connector to allow controllable release of exhaust gas from the exhaust gas manifold prior to entry into the turbocharger turbine. Driving of additional gas through the turbine can therefore be achieved by control of the wastegate, allowing the performance of the combustion engine to be boosted.

The advantage of a wastegate formed as described above is that the whole unit can be formed so as to be more compact, due to the compact arrangement of the actuator assembly. This may allow for the wastegate to be positioned in otherwise awkward positions which may not be achievable with a larger wastegate.

It is therefore possible to provide a wastegate actuator assembly in which the coupling between the gears of the drive transmission train has a variable gear ratio such that there is a fast response, and therefore low torque, at the beginning of the stroke, and a high closing and holding torque in a closed condition of the assembly whilst using a low current. This advantageously allows for a much smaller actuator to be created, having fewer gear stages which could fail, resulting in a compact and reliable arrangement for turbocharged engine systems. This can be achieved by providing a gear train in which non-circular gears are included, thereby imparting the variable gear ratio through the wastegate actuator assembly.

The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

1. A wastegate actuator assembly for controlling a wastegate in a turbocharged engine system, the wastegate actuator assembly comprising:

an electric motor having an output shaft; a wastegate control valve; and a drive transmission train which connects the output shaft of the electric motor to the wastegate control valve, the drive transmission train comprising a compound gear having first and second compound gear elements and an output gear which is coupled to the wastegate control valve, wherein the first compound gear element is a spur gear which is directly or indirectly engagable with the output shaft, and the second compound gear element and output gear are non-circular gears which are engagable to provide a variable gear ratio.

2. A wastegate actuator assembly as claimed in claim 1, wherein each of the second compound gear element and output gear have spiral pitch paths.

3. A wastegate actuator assembly as claimed in claim 1 or claim 2, wherein the output gear has a truncated angular extent.

4. A wastegate actuator assembly as claimed in claim 3, wherein the output gear has an angular extent of between 90 and 180 degrees.

5. A wastegate actuator assembly as claimed in any one of the preceding claims, further comprising a cranked linkage between the output gear and wastegate control valve.

6. A wastegate actuator assembly as claimed in any one of the preceding claims, wherein the output shaft includes a pinion gear engagable with the first compound gear element.

7. A wastegate actuator assembly as claimed in claim 6, wherein the pinion gear is a helical evoloid pinion gear, the first compound gear element being a complementary evoloid gear.

8. A wastegate actuator assembly as claimed in claim 6, further comprising at least one intermediate gear which interconnects the pinion gear and first compound gear element.

9. A wastegate actuator assembly as claimed in any one of the preceding claims, wherein the second compound gear element is positioned on a side of the first compound gear element which is proximal the electric motor.

10. A wastegate unit for a turbocharged engine system, the wastegate unit comprising a wastegate having a wastegate body including an inlet port and an outlet port, a wastegate valve positioned between the inlet and outlet ports, and an exhaustgas-manifold connector engagable with the inlet port and which can be attached to an exhaust gas manifold, and a wastegate actuator assembly as claimed in any one of the preceding claims which controls the flow of exhaust gas from the outlet port of the wastegate.

11. A turbocharged engine system having a combustion engine, a turbocharger turbine which is engagable with a combustion chamber of the combustion engine, an exhaust gas manifold which is connected to an inlet of the turbocharger turbine, and a wastegate unit as claimed in claim 10, the exhaust-gas-manifold connector being engaged with the exhaust gas manifold to allow controllable release of exhaust gas from the exhaust gas manifold prior to entry into the turbocharger turbine.

12. A wastegate control actuator for controlling a wastegate in a turbocharged engine system, the wastegate control actuator comprising:

an electric motor having an output shaft;

a drive transmission train comprising a gear coupling to the output shaft, a compound gear comprising a first and second compound gear elements, and an output gear which is coupled to a wastegate control output for controlling a wastegate control valve; and an actuator housing within which the electric motor and drive transmission train are contained;

wherein the first compound gear element is a spur gear which engages with the gear coupling, and the second compound gear element and output gear are non-circular gears which are engagable to provide a variable gear ratio.

13. A method of controlling a wastegate in a turbocharged engine system, the method comprising the steps of

a] providing a wastegate actuator assembly as claimed in any one of claims 1 to 9; and

b] arranging the second compound gear element and output gear such that when a closure actuation is applied by the electric motor, a high gear ratio is effected to impart a high torque at the output gear, and that when an opening actuation is applied by the electric motor, a low gear ratio is effected to impart a low torque at the output gear.

14. A compact wastegate actuator assembly for controlling a wastegate in a turbocharged engine system, the compact wastegate actuator assembly comprising:

an electric motor having an output shaft; a wastegate control valve; and a drive transmission train which connects the output shaft of the electric motor to the wastegate control valve, the drive transmission train mutually interengagable non-circular gears to provide a variable gear ratio.

15. A compact wastegate actuator assembly as claimed in claim 14, wherein each of the non-circular gears have spiral pitch paths.

16. A method of controlling a wastegate in a turbocharged engine system, the method comprising the steps of:

a] providing a compact wastegate actuator assembly as claimed in claim 14 or claim 15; and

b] arranging the non-circular gears such that when a closure actuation is applied by the electric motor, a high gear ratio is effected to impart a high torque at an output gear of the wastegate actuator assembly, and that when an opening actuation is applied by the electric motor, a low gear ratio is effected to impart a

5 low torque at the said output gear.

Intellectual

Property

Office

Application No: GB 1621296.1 Examiner: Nicholas Wigley