Electric motor braking system

Abstract

An electric motor braking system 10 (e.g., as part of an eddy current brake) includes an electric motor 11 comprising: a casing 12, a stator 13 and a rotor 14, each of the rotor and stator having a re

Description

TECHNICAL FIELD The present disclosure relates to an electric motor braking system. Aspects of the invention relate to a system, to a brake, to a control system, to a vehicle, to a method and to computer readable instructions. BACKGROUND It is known to employ one or more electric motors to provide motive power to a vehicle. Such vehicles are typically referred to as electric vehicles or EVs. The electric motors may be operated in a regenerative mode of operation during vehicle braking and / or when the vehicle is moving but electrical power is not being delivered to the electric motors. It is beneficial to operate the electric motors in a regenerative mode when the vehicle is moving in order to generate electrical power which may be delivered to the battery to extend the range of the vehicle and to improve overall energy efficiency. In addition, operating the electric motors in a regenerative mode helps to slow down the vehicle resulting in less requirement for mechanical braking. This mode of operation is often referred to as regenerative braking. It is against this background that the present invention has been developed. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide an electric motor braking system, an eddy current brake, a control system for controlling the electric motor braking system, a system comprising the control system and the electric motor braking system, a vehicle comprising any of the above, a method of controlling the electric motor braking system, and computer readable instructions arranged to perform the method as claimed in the appended claims. According to an aspect of the present invention there is provided an electric motor braking system comprising: an electric motor comprising: a casing; a rotor comprising a rotor magnetic field generator, wherein the rotor is configured to rotate about an axis of rotation in use; and a stator comprising a stator magnetic field generator, wherein the rotor and / or stator magnetic field generator is configured to generate a motive magnetic field upon application of an electric current thereto, wherein the rotor is configured to rotate about the axis of rotation in use in response to generation of the or each motive magnetic field; and one or more motor braking magnetic field generators comprising a system for generating a variable magnetic field to retard rotation of the rotor. Optionally, one or more motor braking magnetic field generators are fixed to the casing, the rotor, or the stator. The electric motor braking system of the present invention is advantageous as the electric motor may be slowed more quickly than is possible using regenerative braking alone, and the increase in electric motor based braking further reduces the need for traditional friction braking. The one or more motor braking magnetic field generators may each be fixed to the casing, may each be fixed to the stator, or may each be fixed to the rotor. One or more non-magnetic members may be fixed to the rotor, stator or casing opposite the motor braking magnetic field generators. This helps to reduce additional loads on the motor caused by the interaction of any magnetic motor components and the magnetic field generated by the motor braking magnetic field generators. The non-magnetic members may be fixed to, or integral with, the rotor, stator or casing. Alternatively, the rotor, stator or casing may be fabricated from a non-magnetic material. Optionally each motor braking magnetic field generator comprises a permanent magnet and an actuator, wherein the actuator is configured to move the permanent magnet with respect to the casing, the stator or the rotor. This provides a convenient method of varying the magnetic field in the vicinity of a neighbouring motor component using a permanent magnet with an otherwise non-variable magnetic field. Each motor braking magnetic field generator may optionally comprise an electromagnet. This is advantageous as the magnetic field generated by the electromagnet may be varied without the need for physical movement of a permanent magnet. Each motor braking magnetic field generator may be orientated: radially with respect to the axis of rotation; or parallel to the axis of rotation thereby providing multiple packaging options. In one example, the electric motor braking system comprises at least a pair of motor braking magnetic field generators arranged: radially opposed to one another with respect to the axis of rotation; or longitudinally opposed to one another with respect to the axis of rotation. By providing a greater number of motor braking magnetic field generators the electric motor may be braked more rapidly with less need for friction wheel braking. Optionally the electric motor braking system comprises two or more pairs of motor braking magnetic field generators, wherein a first pair of the motor braking magnetic field generators are radially opposed to one another at a first axial position, and a second pair of the motor braking magnetic field generators are radially opposed to one another at a second axial position. Alternatively, a first pair of the motor braking magnetic field generators are longitudinally opposed to one another at a first radial position, and a second pair of the motor braking magnetic field generators are longitudinally opposed to one another at a second radial position. Placement of the pairs of motor braking magnetic field generators at spaced axial or radial locations allows for the forces applied to the electric motor during braking to be evenly distributed. Where the one or more motor braking magnetic field generators comprise an electromagnet, the one or more motor braking magnetic field generators may be configured to receive electrical power directly or indirectly from the electric motor when it is operating in a regenerative braking mode. This provides an efficient use of the regenerative electrical power. The regenerative electrical power may be provided directly to the motor braking magnetic field generators without first passing through a battery or other electrical storage device to reduce efficiency losses. In another aspect of the present invention there is provided an eddy current brake comprising the electric motor braking system of any preceding claim. In a further aspect of the present invention there is provided a control system for controlling an electric motor braking system as described above, the control system comprising one or more processors collectively configured to: receive a first input signal indicative of a motor braking request; issue one or more control signals comprising instructions to operate the electric motor in a regenerative mode and provide power to the one or more motor braking magnetic field generators. The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to: receive a first input signal indicative of a motor braking request; issue one or more control signals comprising instructions to operate the electric motor in a regenerative mode and provide power to the one or more motor braking magnetic field generators. The control system facilitates the efficient use of regenerative power to energise the motor braking magnetic field generators. The one or more instructing control signals may comprise an instruction to provide regenerative power to the one or more motor braking magnetic field generators directly from the electric motor operating in a regenerative mode. This helps to reduce efficiency losses which may result from routing the power via an intermediate power storage device such as a battery. Optionally the control system may be configured to: receive a second input signal indicative of the operational state of a vehicle battery; determine in dependence on the second input signal if the vehicle battery is in an operational state conducive to the receipt of charging power; if it is determined that the vehicle battery is in an operational state conducive to the receipt of charging power, the one or more control signals comprise an instruction to direct at least a portion of the power generated by the electric motor operating in regenerative mode to the vehicle battery; and if it is determined that the vehicle battery is not in an operational state conducive to the receipt of charging power, the one or more control signals comprise an instruction to direct at least a portion of the power generated by the electric motor operating in regenerative mode to the to the one or more motor braking magnetic field generators. This aspect of the control system beneficially prioritises charging of the vehicle battery. In an alternative arrangement, the control system may be configured to prioritise supply of regenerative power to the motor braking magnetic field generators. The control system may be configured to: determine in dependence on the second input signal if the vehicle battery is limited to a maximum charge rate; receive a third input signal indicative of the quantum of power generated by the motor operating in regenerative mode; if the vehicle battery is limited to a maximum charge rate, determine in dependence on the third input signal if the quantum of power generated by the motor exceeds the maximum charge rate; and if the quantum of power generated by the motor exceeds the maximum charge rate, issue one or more control signals comprising instructions to charge the battery with a first portion of the regenerative power, and divert the remainder of the regenerative power to the one or more motor braking magnetic field generators. Alternatively, if the quantum of regenerative power generated by the motor exceeds the maximum charge rate, the control system may determine that the vehicle battery is not in an operational state conducive to the receipt of charging power. In a still further aspect of the present invention there is provided a system comprising the electric motor braking system and the control system described above. In yet another aspect of the present invention there is provided a vehicle comprising the electric motor braking system, the eddy current brake, the control system, or the system described above. In a yet further aspect of the present invention there is provided a method of controlling the electric motor braking system described above, the method comprising: receiving a first input signal indicative of a motor braking request; issuing one or more control signals comprising an instruction to operate the electric motor in a regenerative mode and providing power to the one or more motor braking magnetic field generators. In another aspect of the present invention there is provided a computer readable instructions which, when executed by a computer, are arranged to perform the method described above. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of an electric vehicle drivetrain layout; Figure 2 shows a schematic representation of an electric motor braking system; Figure 3 shows a block diagram depicting a simplified example of a system such as may be adapted in accordance with an embodiment of the invention; Figure 4 shows a flow chart depicting a method such as may be adapted in accordance with an embodiment of the invention; Figure 5 shows a schematic representation of an alternative electric motor braking system; Figure 6 shows a schematic representation of an alternative motor braking magnetic field generator; and Figure 7 shows a vehicle in accordance with an embodiment of the invention. DETAILED DESCRIPTION A vehicle 400 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 7. As shown in Figure 7, a system 90 for controlling an electric motor braking system 10 is installed in the vehicle 400. The system 90 comprises a control system 50 and an electric motor braking system 10. The system 90 forms part of a vehicle power supply system 95 comprising a battery 8 which is configured to provide electrical power to the electric motor braking system 10. The control system 50 controls the delivery of electrical power to the electric motor braking system 10. Figure 1 shows a schematic representation of an electric vehicle drivetrain 1 comprising the vehicle power supply system 95, a front axle 2, and a rear axle 4. Wheels 5 are located at either end of the front 2 and rear 4 axles. The front axle 2 is driven by an electric motor 11 which forms part of the electric motor braking system 10 as described in greater detail below. In the example shown in Figure 1, only the front axle 2 is driven. However, in an alternative example, the rear axle 4 may be driven by the electric motor 11, or both the front 2 and rear 4 axles may be driven by separate electric motors 11 one or both of which may comprise an electric motor braking system 10. The battery 8 supplies electrical power to the electric motor braking system 10 via power transmission cable 7. The control system 50 is operatively connected to the electric motor braking system 10 and the battery 8 by a wired or wireless data connection 9. The control system 50 controls the operation of the electric motor 11 and the electric motor braking system 10 as will be described in greater detail below. Figure 2 shows a schematic representation of an electric motor braking system 10. The electric motor braking system 10 comprises an electric motor 11 which comprises a casing 12, a stator 13 and a rotor 14. A driveshaft 15 with an axis of rotation 16 is connected to the rotor 14 and configured to rotate therewith. The driveshaft 15 provides drive to the front axle 2. The stator 13 comprises magnetic field generator such as a permanent magnet or electromagnetic coil, and the rotor 14 comprises a magnetic field generator such as a permanent magnet or electromagnetic coil as is well known in the art. In the example shown in Figure 2, the electric motor braking system 10 comprises four motor braking magnetic field generators 20 which are orientated parallel to the axis of rotation 16. The motor braking magnetic field generators 20 are arranged in two pairs with each motor braking magnetic field generator 20 arranged longitudinally opposed to another motor braking magnetic field generator 20 and radially spaced from the axis of rotation 16. The motor braking magnetic field generators 20 are fixed to the stator 13. In other examples (not shown) the motor braking magnetic field generators 20 may be fixed to the casing 12, or the rotor 14. In this example, the rotor 14 comprises a pair of aluminium annular members 17 which are fixedly attached to the rotor 14 and configured to rotate therewith. Each of the motor braking magnetic field generators 20 are positioned opposite one or the other of the annular members 17. It will be understood that the annular members 17 may comprise any suitable non-magnetic material as an alternative to aluminium. Each motor braking magnetic field generator 20 comprises a system for generating a variable magnetic field. In the example of Figure 2 the motor braking magnetic field generators 20 comprise electromagnets whose magnetic field is varied in use by varying the electrical current that is provided to the electromagnets. The control system 50 controls the electrical current supplied to the electromagnets as described in greater detail below. The motor braking magnetic field generators 20 are configured to receive electrical power from the vehicle battery 8. The motor braking magnetic field generators 20 are also configured to receive electrical power directly from the motor 11 when the motor 11 is operating in a regenerative mode of operation. Alternatively, the motor braking magnetic field generators 20 may be configured to receive electrical power only from the vehicle battery such that regenerative power generated by the motor 11 when operating in a regenerative mode is directed to the battery 8 for use throughout the vehicle, including providing power to the motor braking magnetic field generators 20. In operation, when a braking request is made, a variable electric current is supplied to the motor braking magnetic field generators 20 such that a variable magnetic field is generated by each of the braking magnetic field generators 20. The variable magnetic fields extend into the material of the annular members 17 and induce eddy currents within the material of the annular members 17. In accordance with Lenz’s law, the direction of the induced eddy currents is such that the magnetic field created by the induced eddy currents acts to oppose changes in the variable magnetic fields generated by the motor braking magnetic field generators 20. Consequently, the rotation of the electric motor is braked. The electric motor braking system 10 therefore comprises an eddy current brake. Figure 3 shows a block diagram depicting a simplified example of a control system 50 such as may be adapted in accordance with an embodiment of the invention. In particular, Figure 3 shows a control system 50 for controlling the electric motor braking system 10. The control system 50 comprises a controller 110, although it will be appreciated that this is merely illustrative and that the control system 50 may comprise more than one controller. The controller 110 comprises processing means 120 and memory means 130. The processing means 120 may be one or more electronic processing device 120 which operably executes computer-readable instructions. The memory means 130 may be one or more memory device 130. The memory means 130 is electrically coupled to the processing means 120. The memory means 130 is configured to store instructions, and the processing means 120 is configured to access the memory means 130 and execute the instructions stored thereon. The controller 110 comprises an input means 140 and an output means 150. The input means 140 may comprise an electrical input 140 of the controller 110. The output means 150 may comprise an electrical output 150 of the controller 110. It will be appreciated that this is merely illustrative and that the controller 110 may comprise more than one input means and more than on output means. The input 140 is arranged to receive a motor braking request signal 141 from a Vehicle Control Unit (not shown) of the vehicle 400, or from a braking sensor (not shown) which is configured to detect braking actions made by a driver. The input 140 is also arranged to receive a battery operational state signal 142. The motor braking request signal 141 and the battery operational state signal 142 are electrical signals which are indicative of a motor braking request and the operational state of the battery 8 respectively. The output 150 is arranged to output a motor control signal 151 comprising instructions to operate the electric motor in a regenerative mode. The output 150 is also arranged to output a power control signal 152 comprising instructions to supply power to the motor braking magnetic field generators 20. The controller 110 is configured to use the motor braking request signal 141 and the battery operational state signal 142, together with the instructions stored in the memory means 130, to determine the motor control signal 151 and the power control signal 152. If the controller 110 is determines that the battery 8 is in an operational state conducive to the receipt of charging power, the power control signal 152 comprises an instruction to direct at least a portion of the power generated by the electric motor 11 operating in regenerative mode to the battery 8. Alternatively, if it is determined that the battery 8 is not in an operational state conducive to the receipt of charging power, the power control signal 152 comprises an instruction to direct at least a portion of the power generated by the electric motor 11 operating in regenerative mode to the to the motor braking magnetic field generators 20. In one example, the control system 50 may be configured to receive a regenerative power input signal indicative of the quantum of power generated by the motor 11 when operating in regenerative mode. In this example, the controller 110 is configured to determine, in dependence on the battery operational state signal 142, if the battery 8 is limited to a maximum charge rate. If the battery 8 is limited to a maximum charge rate, the controller 110 is configured to determine, in dependence on the regenerative power input signal, if the quantum of power generated by the motor 11 exceeds the maximum charge rate. If it does, the controller 110 is configured to issue a power control signal 152 comprising instructions to direct power up to the maximum charge rate of the battery 8 to the battery 8, and to direct at least part of the remaining powerto the motor braking magnetic field generators 20. Figure 4 illustrates a method 100 according to an embodiment of the invention. The method 100 is a method of controlling the electric motor braking system 10. In a first step 101 a first input signal 141 indicative of a motor braking request is received by the control system 50. In step 102 a control signal 151 comprising an instruction to operate the electric motor 11 in a regenerative mode is issued by the control system 50, and in step 103 power is provided to the motor braking magnetic field generators 20. The method 100 may be performed by the vehicle power supply system 95 illustrated in Figures 1 and 6. In particular, with reference to Figure 3, the memory 130 may comprise computer-readable instructions which, when executed by the processor 120, perform the method 100 according to an embodiment of the invention. Figure 5 shows a schematic representation of an alternative electric motor braking system 210. The electric motor braking system 210 is the same in all respects as the electric motor braking system 10 described above with reference to Figure 2. However, in this example, the electric motor braking system 210 comprises motor braking magnetic field generators 20, and non-magnetic annular members 17, which are orientated radially with respect to the axis of rotation 16. The motor braking magnetic field generators 20 are arranged in two pairs with each motor braking magnetic field generator 20 arranged radially opposed to another motor braking magnetic field generator 20 and longitudinally spaced along the axis of rotation 16. Figure 6 shows an example of an alternative the motor braking magnetic field generator 220. In this example, the motor braking magnetic field generator 220 comprises a housing 224 which contains a permanent magnet 221 mounted on a spindle 222 which is connected to an actuator 223, The actuator 223 is configured to move the permanent magnet with respect to the housing 224 in response to the power control signal 152 issued by the control system 50. Movement of the permanent magnet 221 with respect to the element of the electric motor to which the motor braking magnetic field generator 220 is attached causes a variable magnetic which in turn induces eddy currents and eddy current braking as discussed above. It is not essential that the rotor 14 in either of the electric motor braking systems 10, 210 described above comprise non-magnetic annular members 17. In an alternative example, the main body of the rotor 14 may comprise a magnetic material such a martensitic steel, with or without the addition of non-magnetic annular members 17. Alternatively, the body of the rotor 14 may comprise a non-magnetic material such as aluminium or an austenitic steel. The annular members 17, if present, may comprise any suitable nonmagnetic material. The annular members 17, if present, may be fixed to or integral with the rotor 14. It will be understood that, for each of the example electric motor braking systems 10, 210 described above the motor braking magnetic field generators 20 may be fixed to the casing 12 rather than, or in addition, to the stator 13. In this case the principle of operation remains the same as that described above such that eddy currents are induced in the annular members 17 (or in the material of the rotor if no annular members are present) when the motor braking magnetic field generators 20 are operated to generate a variable magnetic field. It is not necessary that the electric motor braking systems 10, 210 described above comprise four motor braking magnetic field generators 20, or that the motor braking magnetic field generators 20 be arranged in pairs. The number of motor braking magnetic field generators 20 employed may be selected based on braking requirements. It will be appreciated that a minimum of one motor braking magnetic field generator 20 must be provided fixed either the casing 12, the stator 13, or the rotor 14. Furthermore, it is not necessary that the motor braking magnetic field generators 20 be exclusively orientated parallel to the axis of rotation 16, or exclusively orientated radially with respect to the axis of rotation 16. Any other orientation may be used in any combination such that one or more motor braking magnetic field generators 20 may be orientated parallel and / or radially with respect to the axis of rotation 16, while one or more others orientated in another direction. In other alternative examples, the motor braking magnetic field generators 20 may be fixed to the rotor 14 rather than to the casing 12 and / or stator 13. In this case, the variable magnetic fields generated by the motor braking magnetic field generators 20 may either extend into the material of the casing 12 and / or stator 13 (which may comprise magnetic or non-magnetic materials), or into the material of non-magnetic annular members fixed to, or integral with, the stator 13 and / or casing 12 opposite the motor braking magnetic field generators 20. The eddy currents induced within the material of the annular members, casing 12 and / or stator 13 then create a magnetic field which acts to oppose changes in the variable magnetic fields 5 generated by the motor braking magnetic field generators 20 in accordance with Lenz’s law. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. 10

Claims

1. An electric motor braking system comprising:an electric motor comprising:a casing;a rotor comprising a rotor magnetic field generator, wherein the rotor is configured to rotate about an axis of rotation in use; anda stator comprising a stator magnetic field generator, wherein the rotor and / or stator magnetic field generator is configured to generate a motive magnetic field upon application of an electric current thereto, wherein the rotor is configured to rotate about the axis of rotation in use in response to generation of the or each motive magnetic field; andone or more motor braking magnetic field generators fixed to the casing, the rotor, or the stator, wherein the one or more motor braking magnetic field generators comprise a system for generating a variable magnetic field to retard rotation of the rotor.

2. The electric motor braking system of claim 1, wherein each motor braking magnetic fieldgenerator comprises a permanent magnet and an actuator, wherein the actuator is configured to move the permanent magnet with respect to the casing, the stator or the rotor.

3. The electric motor braking system of claim 1 or 2, wherein each motor braking magnetic fieldgenerator comprises an electromagnet.

4. The electric motor braking system of any preceding claim, wherein each motor brakingmagnetic field generator is orientated:radially with respect to the axis of rotation; orparallel to the axis of rotation.

5. The electric motor braking system of any preceding claim, comprising at least a pair of motorbraking magnetic field generators arranged:radially opposed to one another with respect to the axis of rotation; or longitudinally opposed to one another with respect to the axis of rotation.

6. The electric motor braking system of claim 5, comprising two or more pairs of motor brakingmagnetic field generators, wherein a first pair of the motor braking magnetic field generators are radially opposed to one another at a first axial position, and a second pair of the motor braking magnetic field generators are radially opposed to one another at a second axial position.

7. The electric motor braking system of claim 5, comprising two or more pairs of motor brakingmagnetic field generators, wherein a first pair of the motor braking magnetic field generators are longitudinally opposed to one another at a first radial position, and a second pair of the motor braking magnetic field generators are longitudinally opposed to one another at a second radial position.

8. The electric motor braking system of any preceding claim, wherein the one or more motorbraking magnetic field generators comprise an electromagnet, and wherein the electric motor is configured to selectively operate in a regenerative braking mode, wherein the one or more motor braking magnetic field generators are configured to receive electrical power directly or indirectly from the electric motor when operating in a regenerative braking mode.

9. An eddy current brake comprising the electric motor braking system of any preceding claim.

10. A control system for controlling an electric motor braking system according to claim 8 or theeddy current brake according to claim 9, the control system comprising one or more processors collectively configured to:receive a first input signal indicative of a motor braking request;issue one or more control signals comprising instructions to operate the electric motor 11 in a regenerative mode and provide power to the one or more motor braking magnetic field generators.

11. The control system of claim 10, configured to:receive a second input signal indicative of the operational state of a vehicle battery;determine in dependence on the second input signal if the vehicle battery is in an operational state conducive to the receipt of charging power;if it is determined that the vehicle battery is in an operational state conducive to the receipt of charging power, the one or more control signals comprise an instruction to direct at least a portion of the power generated by the electric motor operating in regenerative mode to the vehicle battery; andif it is determined that the vehicle battery is not in an operational state conducive to the receipt of charging power, the one or more control signals comprise an instruction to direct at least a portion of the power generated by the electric motor operating in regenerative mode to the to the one or more motor braking magnetic field generators.

12. A system 90 comprising the electric motor braking system of claim 8 and the control systemof claim 10 or 11.

13. A vehicle comprising the electric motor braking system of any one of claims 1 to 8, the eddycurrent brake of claim 9, the control system of claim 10 or 11, or the system of claim 12.

14. A method of controlling the electric motor braking system of claim 8, the method comprising:receiving a first input signal indicative of a motor braking request;issuing one or more control signals comprising an instruction to operate the electric motor in a regenerative mode and provide power to the one or more motor braking magnetic field generators.

15. Computer readable instructions which, when executed by a computer, are arranged toperform the method according to claim 15.Application No: GB2404595.7Examiner:Contract Unit ExaminerClaims searched: 1-15Date of search: 21 January 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X Y X: 1-7, 9-15; Y: 8 DE 102022205166 Al (BOSCH GmbH) Abstract; claims; figures 1, 2, paragraphs [0030]-[0032], X,Y X: 1-7, 9-15; Y: 8 WO 2024 / 012783 Al (BOSCH GmbH) Abstract; claim 1; figures 1-3. X,Y X: 1-7, 9-15; Y: 8 US 2023 / 0234396 Al (TOMINAGA et al) Abstract; figures 2, 5, paragraphs [0020]-[0075], X Y X: 14, 15; Y: 8 WO 2023 / 147872 Al (VOLVO TRUCK CORP) Abstract; figures 2 &3; page 3, lines 5-8. X,Y X: 14, 15; Y: 8 DE 102021200754 Al (BOSCH GmbH) Abstract; claim 1; figure 2. X Y X: 14, 15; Y: 8 US 2996650 A (ROBERTI et al) Figures 1 &10.Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From B60L 0007 / 28 01 / 01 / 2006 B60L 0007 / 18 01 / 01 / 2006 B60T 0001 / 10 01 / 01 / 2006 H02K 0007 / 104 01 / 01 / 2006 H02K 0007 / 106 01 / 01 / 2006

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