A motor assembly with overrunning clutch

Abstract

A motor assembly 10 comprising an electric motor and an overrunning clutch 30 arranged within the motor assembly 10, where in a shaft 36 of the overrunning clutch 30 is adapted to engage with an external engine, the shaft 36 being connected to an inner part of the overrunning clutch 30, and an outer part of the overrunning clutch 30 is adapted to engage with a rotor shaft 24 of the electric motor. The engagements may be though ridges and splines 28 and the overrunning clutch 30 may be a freewheel or sprag clutch.

Description

The present inventive concept relates to motor assemblies, for example for use with drives for vehicles and vessels. Background to the invention Traditionally and for many decades, vehicles and vessels have been driven by internal combustion engines (ICEs) of various types and designs according to the requirements. More recently, environmental concerns have led to the development of alternative drive arrangements with the aim of reducing fossil fuel consumption and accompanying pollution and greenhouse gases. Electric-only drives have been found useful in certain circumstances - for example road-going vehicles. However, electric-only drives require large energy stores which currently tend to be heavy. Hybrid drives, where an electric motor is supplied by energy stored in a battery and / or electricity generated by an ICE, are also commonplace in road-going vehicles. However, hybrid drives are complex and space-inefficient. Hybrid drives are not suitable where space is at a premium, especially when the drive shaft space is restricted. Hybrid drives also tend to have a separate clutch. One particular example in which space is at a premium is in vessels such as boats, where traditionally the drive is close to the load, e.g. the propellor. The present inventive concept aims to provide a more efficient and environmentally appropriate arrangement - without requiring a comprehensive redesign of the intended vehicle or vessel. It also provides potential for retro-fitting to an existing vehicle or vessel. Summary of the invention The present inventive concept provides a motor assembly, the motor assembly comprising an electric motor and an overrunning clutch arranged within the motor assembly, wherein a shaft of the overrunning clutch is adapted to engage with an external engine, the shaft being connected to an inner part of the overrunning clutch, and an outer part of the overrunning clutch is adapted to engage with a rotor shaft of the electric motor. The overrunning clutch may be arranged within a hollow tubular portion of the assembly and coaxially with the rotor shaft of the electrical motor. The overrunning clutch may be a freewheel clutch. The overrunning clutch may be a sprag clutch. The motor assembly may engage with an external engine by way of mechanical connection to a part of the external engine, for example a flywheel. The external engine may be an internal combustion engine (ICE). Preferably, the hollow tubular portion of the assembly forms part of the rotor shaft of the electric motor. The hollow tubular portion of the assembly may be the rotor shaft of the electric motor. Preferably the said hollow tubular portion comprises engagement portions suitable for engagement with corresponding engagement portions of an external load. Such an external load may comprise, for example, a gearbox. The engagement portions may comprise ridges or splines or the like. Ridges or splines are intended to provide efficient torque transfer whilst maintaining angular correspondence between the tubular portion of the motor assembly and an external load. The overrunning clutch is preferably arranged so that the clutch slips when the rotor shaft of the electric motor is turning faster than the shaft in at least one rotational sense. The underlying inventive concept, therefore, is the provision of an overrunning clutch within a motor assembly. Compared with previously known electric motor arrangements, the present inventive concept provides a hollow region where a drive shaft would normally not provide a space in which an overrunning clutch could be located. Thus the present arrangement provides space advantages over previously known arrangements as well as efficiencies in the transfer of torque from an engine to an electric motor but not in the reverse direction. This facilitates configurations of traditional ICE and electric power drives in vehicles and vessels, for example, which were not feasible previously. This provides opportunities for reducing fuel consumption and thus the environmental impact of power drives in situations where other forms of impact reduction are not suitable. The present inventive concept enables a shortening of overall axial length of connection between an external engine and an external load, whilst providing sufficient transmission of torque to drive a vehicle or vessel. This is important where space is at a premium, for example in vehicles and vessels. Especially, the present inventive concept facilitates a setup where an ICE and an electric motor can each provide torque to a load, such as a gearbox or propellor etc. in line with one another. For example, a setup can be provided in which in a first mode the ICE can drive the electric motor to generate electricity when needed and / or in turn provide torque to the load, and in a second mode the same electric motor can draw electricity to provide torque to the load. Crucially, when in this second mode, the overrunning clutch of the present inventive concept prevents the electric motor from driving the ICE - which would be inefficient, counterproductive and could result in damage to the ICE. The present inventive concept can be used with a range of engines and vehicle / vessel configurations. The motor assembly can optionally be provided as a retro-fit device. Preferably, such a retro-fit device has dimensions adapted to fit components of an existing configuration for which it is to engage with. Detailed description of exemplaiy embodiments Exemplary embodiments of the present inventive concept will now be described in further detail, with reference to the accompanying drawings. Figure 1 shows an exploded view of an exemplary embodiment of the assembly of the present inventive concept. Figure 2 shows the same assembly as shown in Figure 1, in its assembled form. Figure 3 shows the same assembly as shown in Figures 1 and 2, in cross section perpendicular to the axis of the assembly. Figure 4 shows the same assembly as shown in Figures 1 to 3, in cross section along the axis of the assembly. Figure 5 shows how an exemplary embodiment of a motor assembly of the present inventive concept could be arranged within a wider system. In Figure 1, the assembly 10 has an electric motor (only key rotor elements of which are shown) which has components including a rotor 14, magnets 16, tube nuts 18, a retaining ring 20, and a target ring 22. The electric motor has a rotor shaft 24 which has a hollow tubular portion 26 formed within it. The hollow tubular portion 26 may be provided with a splined region 28 at at least one end thereof, for engagement with a part of an external load, such as a shaft thereof. In this exemplary embodiment, the overrunning clutch is a sprag clutch 30. The hollow tubular portion 26 also accommodates and engages an outer freewheel clutch unit 32 of a sprag clutch 30. An inner part 34 of the sprag clutch 30 is joined to a sprag shaft 36 which can engage with an external engine. The assembly 10 also has a seal ring 38, lip seals 40, 42, snap rings 44, 46 and socket head screws 48. The outer part 32 of the sprag clutch 30 is connected to the hollow tubular portion 36 of the electric motor by a press fit connection. The inner part 34 of the sprag clutch 30 is connected to the sprag shaft 36 by a press fit connection. Using a press fit to connect the two parts of the sprag clutch 30 to the respective hollow tubular portion 36 and sprag shaft 36 provides for substantially equal pressure on the sprag clutch 30 from both sides thereof. Alternatively, pawls and ball races could be fitted to run on hardened faces of the respective shafts. Elements of the electric motor can be held together in place by tube nuts 18 and socket head screws 48 passing through the other elements and being attached together. Such an attachment can be further improved by providing an adhesive. The key components of the assembly 10 are arranged co-axially along an axis of the assembly X. As can be seen in Figure 1, the electric motor, the sprag clutch 30, the rotor shaft 24 and the sprag shaft 36 are co-axial along the axis X of the assembly 10. The sprag clutch 30 is configured so that, in use, when the sprag shaft 36 (and thus the inner part 34 of the sprag clutch 30) is rotating faster than the outer part 34 of the sprag clutch 30 in the rotational sense of the configured drive then the sprag engages, transferring torque from the sprag shaft 36 to the inner part 34 of the sprag clutch, and in turn to the rotor shaft 24 of the electric motor. When the rotor shaft 24 is rotating faster than the sprag shaft 36, then the sprag clutch 30 slips so that torque transference is significantly reduced. The result is that the electric motor does not tend to transfer torque to the sprag shaft 36 and onwards to an external engine. In Figure 2, the same assembly 10 as shown in Figure 1, and described above, is shown in its assembled form. Certain components are not labelled, to aid clarity. The electric motor (again only key rotor elements of which are shown) has the sprag clutch 30 arranged within it, so that only certain parts of the sprag clutch 30 are seen in Figure 2 - for example where they extend from the electric motor. On one side of the electric motor, the splined region 28 of the hollow tubular portion 26 extends from the sprag clutch 30 and electric motor for engagement with an external load. On the other side, the sprag shaft 36 extends from the sprag clutch 30 for engagement with an external engine. The key components of the assembly 10 are arranged co-axially along an axis of the assembly X. As can be seen in Figure 2, the electric motor, the sprag clutch 30, the tubular portion 26 and the sprag shaft 36 are co-axial along the axis X of the assembly 10. In use, the sprag shaft 36 can turn the sprag clutch 30 and thus the electric motor when the sprag shaft 36 is rotating faster than the electric motor in the configured rotational sense. When the electric motor is rotating faster than the sprag shaft 36, the sprag clutch 30 slips so that torque transference is significantly reduced. In Figure 3, a cross section view of the same assembly 10 as shown in Figures 1 and 2 is shown. Certain components are not labelled, to aid clarity. The electric motor (again only key rotor elements of which are shown) has the sprag clutch 30 arranged within it, with the outer part 32 in connection with the hollow tubular portion 26 of the motor. The inner part 34 of the sprag clutch 30 is joined to the sprag shaft 36. The sprag clutch 30 is arranged at one side of the hollow tubular portion 26, so that the sprag shaft 36 extends from one end thereof. At the other side of hollow tubular portion 26 is the splined region 28 which is for engagement with an external load. The electric motor, the sprag clutch 30, the tubular portion 26 and the sprag shaft 36 are co-axial along the axis X of the assembly 10. As can be seen especially in Figures 2 and 3, the assembly 10 provides a compact arrangement so that axial space requirements are reduced compared with previous arrangements. For example, with reference to Figure 3, the length of the embodiment shown, i.e. the length of assembly 10 between the opening of the hollow tubular portion 26 on the left-hand side of the drawing and the end of the sprag shaft 36 on the right-hand side of the drawing is approx. 160 mm. The overall diameter of the embodiment, whose largest dimension is the outer surface of the rotor is approx. 320 mm. In Figure 4, an alternative cross section view of the same assembly 10 is shown, along the axis X of the assembly. Certain components are not labelled, to aid clarity. The electric motor, the sprag clutch 30, the tubular portion 26 and the sprag shaft 36 are co-axial along the axis X of the assembly 10. In Figure 5, an exemplary assembly 10 is shown within a wider system. The system has an internal combustion engine (ICE) E and a load L which includes a gearbox and other parts. Only certain components of the assembly 10 are labelled, to aid clarity. The sprag shaft 36 is connected to a flywheel F of the engine E to transfer torque from the engine E to the sprag clutch 30. On the other side of the assembly 10, the load L can engage with the hollow tubular portion 26 by way of a gearbox shaft S. The sprag clutch 30 is configured so that, in use, when the sprag shaft 36 (and thus the inner part 34 of the sprag clutch 30) is rotating faster than the outer part 34 of the sprag clutch 30 in the rotational sense of the configured drive - when the engine E is providing torque - then the sprag engages, transferring torque from the sprag shaft 36 to the inner part 34 of the sprag clutch, and in turn to the rotor shaft 24 of the electric motor. When the rotor shaft 24 is rotating faster than the sprag shaft 36, then the sprag clutch 30 slips so that torque transference is significantly reduced. The result is that the electric motor does not tend to transfer torque to the sprag shaft 36 and onwards to the engine E. Thus, the load L can be driven by the engine E or the electric motor but torque is generally not transferred from the electric motor to the engine E.

Claims

1. A motor assembly, the motor assembly comprising an electric motor and an overrunning clutch arranged within the motor assembly, wherein a shaft of the overrunning clutch is adapted to engage with an external engine, the shaft being connected to an inner part of the overrunning clutch, and an outer part of the overrunning clutch is adapted to engage with a rotor shaft of the electric motor.

2. A motor assembly according to claim 1, wherein the overrunning clutch is arranged within a hollow tubular portion of the assembly and coaxially with the rotor shaft of the electrical motor.

3. A motor assembly according to claim 2, wherein the hollow tubular portion of the assembly forms part of the rotor shaft of the electric motor.

4. A motor assembly according to claim 2 or claim 3, wherein the said hollow tubular portion comprises engagement portions suitable for engagement with corresponding engagement portions of an external load.

5. A motor assembly according to claim 4, wherein the engagement portions comprise ridges or splines.

6. A motor assembly according to any preceding claim, wherein the overrunning clutch is arranged so that the clutch slips when the rotor shaft of the electric motor is turning faster than the shaft in at least one rotational sense.

7. A motor assembly according to any preceding claim, wherein the overrunning clutch is a freewheel clutch.

8. A motor assembly according to claim 6, wherein the overrunning clutch is a sprag clutch.

9. A retro-fit device, comprising a motor assembly according to any preceding claim.

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