WO2012104264A2

WO2012104264A2 - Vehicle power management apparatus and method

Info

Publication number: WO2012104264A2
Application number: PCT/EP2012/051484
Authority: WO
Inventors: Alan Armstrong; Kevin COCKINGS; Michael DECOCK; Ian Smith
Original assignee: Land Rover
Priority date: 2011-02-01
Filing date: 2012-01-31
Publication date: 2012-08-09
Also published as: GB2488968A; GB201101702D0; WO2012104264A3

Abstract

Embodiments of the invention provide electrical power management apparatus for a motor vehicle comprising: a primary power storage device for powering an engine starter device; a vehicle electrical load; a secondary power storage device for powering the vehicle electrical load; and a solid state primary diode portion coupled between the primary power storage device and the vehicle electrical load, the primary diode portion being operable to allow a flow of current in a forward direction therethrough from the primary power storage device to the vehicle electrical load when the starter device is not in use and to prevent a flow of current in a reverse direction therethrough from the secondary power storage device to the engine starter device when the starter is in use.

Description

VEHICLE POWER MANAGEMENT APPARATUS AND METHOD

FIELD OF THE INVENTION The present invention relates to apparatus and a method for controlling an electrical power supply of a vehicle. In particular but not exclusively the invention relates to apparatus and a method for controlling charging and discharging of one or more power storage devices of the vehicle. BACKGROUND

FIG. 1 shows an example of a known vehicle power management apparatus 100 in which a primary battery 1 1 1 and a starter motor 107 are provided for starting an engine (not shown). An engine-driven alternator 105 is provided for recharging the battery 1 1 1.

The primary battery 1 1 1 may be selectively coupled to and decoupled from electrical loads 121 of the vehicle other than the starter motor 107 by means of a primary electromechanical contactor 131 . Thus the primary battery 1 1 1 may be used to power the electrical loads 121 when the primary contactor 131 is closed.

It is to be understood that the electrical loads 121 include loads that cannot remain connected to the primary battery 1 1 1 when the engine is being cranked. This is because the drop in voltage across the primary battery 1 1 1 during cranking can result in malfunction of the loads 121 . For example, certain types of electrical systems may be caused to reset when their power supply falls below a threshold level. Alternatively or in addition the systems may lose data such as settings data and/or experience reduced performance. Thus, when the engine is being cranked the primary contactor 131 is opened to isolate the loads 121 from the primary battery 1 1 1. Accordingly, a secondary battery 1 12 is provided in order to power the loads 121 when the primary battery 1 1 1 is being used to power the starter motor 107.

The secondary battery 1 12 may be isolated from the loads 121 by means of a secondary contactor 132 when required.

The primary and secondary contactors 131 , 132 are controlled by a dual battery module (DBM) 163 which is in turn controlled by a gateway module (GWM) 161 . In a typical method of operation, when it is required to crank the engine the secondary contactor 132 is closed and subsequently the primary contactor 131 is opened in order to permit the secondary battery 1 12 to provide power to the loads 121 during cranking. Once the engine is running, the primary and secondary contactors 131 , 132 may both be held in the closed state in order to recharge the secondary battery 1 12.

It is an aim of embodiments of the invention to provide an improved vehicle power management apparatus.

STATEMENT OF THE INVENTION

Aspects of the invention provide an apparatus and a method as claimed in the appended claims.

According to one aspect of the invention there is provided electrical power management apparatus for a motor vehicle comprising: a primary power storage device for powering an engine starter device; a vehicle electrical load; a secondary power storage device for powering the vehicle electrical load; and a solid state primary diode portion coupled between the primary power storage device and the vehicle electrical load, the primary diode portion being operable to allow a flow of current in a forward direction therethrough from the primary power storage device to the vehicle electrical load when the starter device is not in use and to prevent a flow of current in a reverse direction therethrough from the secondary power storage device to the engine starter device when the starter is in use.

Embodiments of the invention have the advantage that the amount of power consumed by the apparatus when controlling the vehicle to start may be reduced relative to known power management apparatus employing electromechanical contactors.

Furthermore, a speed with which the apparatus may be configured for starting of the vehicle may be increased due to the greater speed of operation of solid state switching devices relative to electromechanical devices. Still furthermore, a reliability of the apparatus is increased by the use of solid state devices relative to electromechanical devices. Advantageously, the primary diode portion may comprise a primary transistor portion comprising at least one transistor device, the at least one transistor device having a first terminal, a second terminal and a third terminal coupled to respective first, second and third nodes of the primary transistor portion, the second and third nodes being coupled between the primary power storage device and the vehicle electrical load, the primary transistor portion being operable to control an amount of current flowing between the second and third nodes by means of the first node.

The employment of a transistor device as a diode has the advantage that an amount of power consumed by the device is less than that which would be consumed by a convention diode device in the form of a PN junction or the like. This has the advantage that an amount of power dissipated as heat may be reduced. Furthermore, a size and cost of the apparatus may be reduced since the amount of current required to be handled by the apparatus may be substantial in some embodiments. A conventional diode device of comparable current handling capability to a transistor device or array of transistor devices (see below) is typically more expensive, bulkier and/or heavier in weight.

Further advantageously the primary transistor portion may comprise a plurality of transistor devices having respective first, second and third terminals coupled to the first, second and third nodes respectively such that the devices are connected in parallel with one another.

This feature has the advantage that the amount of current that may flow through the primary transistor portion may be increased according to the required specification of the apparatus by adding further transistor devices in parallel with one another. Any number of transistor devices may be used, the number being determined at least in part according to the amount of current it is required to pass through the primary transistor portion.

The apparatus may be arranged to control the primary transistor portion to function as a diode thereby to prevent the flow of current therethrough in the reverse direction when the starter is in use and to allow the flow of current therethrough in the forward direction when the starter device is not in use.

This has the advantage that sensitive vehicle electrical loads being loads across which the potential must be maintained within a prescribed tolerance may be kept supplied with a potential within this range. When the starter device is in use the potential across the primary power storage device may fall outside of this tolerance. By causing the primary transistor portion to function as a diode a flow of current from the secondary power storage device to the starter device may be prevented thereby maintaining the potential across the load within the prescribed tolerance.

The apparatus may be arranged to control the primary transistor portion to function as a diode responsive to a potential difference between the second and third nodes of the primary transistor portion.

The apparatus may comprise a primary diode controller arranged to control the primary transistor portion to function as a diode.

The apparatus may be operable between an active mode and a standby mode, wherein in the standby mode power to the first node of the primary transistor portion is either reduced or terminated and an amount of power consumed by the apparatus is reduced.

Reference to the supply of power to the first node includes reference to the application of a potential to the first node, the supply of current to the first node and/or the drawing of current from the first node.

The apparatus may further comprise current detection means operable to detect a flow of current through the primary transistor portion in the forward direction, when the apparatus is in the standby mode the apparatus being operable to restore power to the first node responsive to the amount of current flowing through the primary transistor portion in the forward direction.

This feature has the advantage that the amount of current drawn by the apparatus when the vehicle is in the standby mode may be reduced.

The current detection means may comprise a sense resistor.

The apparatus may be arranged to place the primary diode controller in a standby mode when the apparatus is in the standby mode and to place the primary diode controller in an active mode thereby to restore power to the first node when the amount of current flowing through the primary transistor portion in the forward direction exceeds a prescribed value. The primary transistor portion may be coupled between the primary power storage device and the vehicle load such that a body diode of the primary transistor portion is oriented to allow current to flow from the primary power storage device to the vehicle electrical load when power to the first node is terminated.

By body diode is meant the body diode(s) of the at least one transistor device.

This feature has the advantage that a quiescent current required by the load when the apparatus is in the standby mode may be provided through the apparatus without a requirement to provide power to the primary transistor portion. It is to be understood that since the primary transistor portion may consume a not inconsiderable amount of power, reducing the amount of power drawn by the primary transistor portion is desirable when in the standby mode.

The apparatus may be further operable to allow a flow of current through the primary transistor portion in the reverse direction.

This feature has the advantage that power may be supplied to the primary power storage device or engine starter device through the primary transistor portion if required.

The apparatus may comprise a battery charging device operable to supply charge to the primary power storage device to recharge the primary power storage device. The battery charging device may be arranged to be coupled to the primary power storage device through the primary diode portion.

Alternatively or in addition the battery charging device may be arranged to be coupled to the primary power storage device substantially directly and not through the primary diode portion.

Advantageously the apparatus may further comprise a secondary diode portion coupled between the electrical load and the secondary power storage device, the secondary diode portion being operable to allow a flow of current therethrough from the secondary power storage device to the vehicle electrical load when the starter device is in use. The secondary diode portion may be operable to prevent discharge of the secondary power storage device when the starter is not in use.

Alternatively or in addition the secondary diode portion may be operable to couple the secondary power storage device to the battery charging device.

This feature has the advantage that charging of the secondary power storage device may be controlled. The secondary diode portion may be operable to decouple the secondary power storage device from the battery charging device.

This feature has the advantage that charging of the secondary power storage device may be prevented when a state of charge of the secondary power storage device reaches a prescribed value. This has the advantage that a useful operating lifetime of the secondary power storage device may be increased in some embodiments.

Advantageously the secondary diode portion may comprise a secondary transistor portion, the secondary transistor portion comprising at least one transistor device, the at least one transistor device having a first terminal, a second terminal and a third terminal coupled to respective first, second and third nodes of the secondary transistor portion, the second and third nodes being coupled between the secondary power storage device and the vehicle electrical load. The apparatus may be operable to control the secondary transistor portion to function as a diode responsive to a potential difference between the second and third nodes of the secondary transistor portion.

Advantageously the apparatus may comprise a secondary diode controller operable to control the secondary transistor portion to function as a diode whereby current may flow only in a forward direction through the secondary transistor portion, the apparatus being further operable to override the secondary diode controller thereby to allow a flow of current in a reverse direction through the secondary transistor portion opposite the forward direction when required.

The apparatus may further comprise current detection means operable to detect a flow of current through the secondary transistor portion. Advantageously the current detection means comprises a sense resistor in series with the secondary transistor portion. The apparatus may be arranged to place the secondary diode controller in a standby mode wherein power to the first node is terminated when the apparatus is in the standby mode and to place the secondary diode controller in an active mode wherein power to the first node is restored when the amount of current flowing through the secondary transistor portion in the forward direction exceeds a prescribed value.

The forward direction may correspond to a direction from the secondary power storage device to the load.

This feature has the advantage that when it is required to provide current to the load, for example during cranking of the engine, if the secondary diode controller is in the standby mode it may assume automatically the active mode.

When in the active mode, the secondary diode controller may control the secondary transistor portion automatically to supply current to the vehicle load if the potential across the primary power storage device falls, thereby preventing a disruption of power supply to the load.

Alternatively the forward direction may correspond to a direction from the load to the secondary power storage device.

This feature has the advantage that if the state of charge of the secondary power storage device falls, for example following supply of power to the load during cranking, the secondary power storage device may automatically be recharged. Furthermore, discharge of the secondary power storage device when the vehicle is in the standby mode (for example discharge in the forward direction through a body diode of the secondary transistor portion) may be prevented, thereby preserving the state of charge of the secondary power storage device. This is because current is prevented from flowing in the reverse direction through the secondary diode portion.

Advantageously the at least one transistor device of the primary transistor portion may comprise a metal oxide semiconductor field effect transistor (MOSFET) device. In an embodiment the first terminal of the at least one transistor device of the primary transistor portion corresponds to a gate terminal and the first node of the primary transistor portion corresponds to a gate node, the second terminal of the at least one transistor device of the primary transistor portion corresponds to a source terminal and the second node of the primary transistor portion corresponds to a source node, and the third terminal of the at least one transistor device of the primary transistor portion corresponds to a drain terminal and the third node of the primary transistor portion corresponds to a drain node.

Advantageously the secondary transistor portion may comprise at least one transistor device.

In an embodiment the first terminal of the at least one transistor device of the secondary transistor portion corresponds to a gate terminal and the first node of the secondary transistor portion corresponds to a gate node, the second terminal of the at least one transistor device of the secondary transistor portion corresponds to a source terminal and the second node of the secondary transistor portion corresponds to a source node, the third terminal of the at least one transistor device of the secondary transistor portion corresponds to a drain terminal and the third node of the secondary transistor portion corresponds to a drain node.

Advantageously the at least one transistor device of the secondary transistor portion comprises a metal oxide semiconductor field effect transistor (MOSFET) device.

In a further aspect of the invention there is provided a method of controlling a motor vehicle comprising: allowing by means of a primary diode portion a flow of current in a forward direction from a primary power storage device to a vehicle electrical load when an engine starter device is not in use and preventing by means of the primary diode portion a flow of current in a reverse direction from a secondary power storage device to the engine starter device when the starter is in use.

Advantageously the method may comprise the step of allowing current to flow through the primary diode portion responsive to a potential difference between a pair of nodes of the primary diode portion connected between the primary power storage device and the vehicle electrical load. The step of allowing current to flow through the primary diode portion responsive to a potential difference between the pair of nodes of the primary diode portion may be performed by means of a primary diode portion controller. The method may comprise the step of controlling the primary diode portion controller to assume a standby mode, the step of controlling the primary diode portion controller to assume the standby mode comprising the step of terminating a supply of power to a control node of the primary diode portion not being one of said pair of nodes of the primary diode portion.

The method may comprise the step of detecting a flow of current through the primary diode portion, when the primary diode portion is in the standby mode the method comprising restoring power to the control node of the primary diode portion responsive to the amount of current flowing in the forward direction therethrough.

Advantageously the method may comprise the step of allowing a quiescent current to flow from the primary power storage device to the vehicle electrical load through the primary diode portion when a supply of power is terminated to the control node. The method may comprise the step of allowing a flow of current through the primary diode portion in the reverse direction.

The method may comprise the step of supplying charge by means of a battery charging device to the primary power storage device to recharge the primary power storage device.

Optionally the method comprises the step of supplying charge by means of the battery charging device to the primary power storage device through the primary diode portion. Alternatively or in addition the method may comprise the step of supplying charge by means of the battery charging device to the primary power storage device substantially directly and not through the primary diode portion.

The method may comprise the step of providing a flow of current from the secondary power storage device to the vehicle electrical load when the starter device is in use through a secondary diode portion. Advantageously the method may comprise the step of preventing discharge of the secondary power storage device when the starter is not in use by means of the secondary diode portion. Optionally the method comprises the step of providing charge to the secondary power storage device from the battery charging device by means of the secondary diode portion.

The method may comprise the step of decoupling the battery charging device from the secondary power storage device by means of the secondary diode portion.

Advantageously the method may comprise the step of allowing current to flow through the secondary diode portion in a forward direction responsive to a potential difference between a pair of nodes of the secondary diode portion connected between the secondary power storage device and the vehicle electrical load.

Optionally the step of allowing current to flow through the secondary diode portion responsive to a potential difference between the pair of nodes of the secondary diode portion is performed by means of a secondary diode portion controller.

Advantageously the method may comprise the step of controlling the secondary diode portion controller to assume a standby mode, the step of controlling the secondary diode portion controller to assume the standby mode comprising the step of terminating a supply of power to a control node of the secondary diode portion not being one of said pair of nodes of the secondary diode portion.

The method may comprise the step of allowing a quiescent current to flow through the secondary diode portion in the forward direction when a supply of power is terminated to the control node thereof.

Advantageously the method may comprise the step of detecting a flow of current through the secondary diode portion, when the secondary diode portion is in the standby mode the method comprising restoring power to the control node of the secondary diode portion responsive to the amount of current flowing therethrough in the forward direction.

The method may comprise the step of allowing a flow of current through the secondary diode portion in a reverse direction opposite the forward direction. The forward direction may correspond to a direction from the secondary power storage device to the load. Alternatively the forward direction may correspond to a direction from the load to the secondary power storage device.

Advantageously the primary diode portion may comprise at least one transistor device. The secondary diode portion may comprise at least one transistor device.

Within the scope of this application it is envisaged that the various aspects, embodiments, examples and alternatives, and in particular the features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination thereof. For example, features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which:

FIGURE 1 is a schematic illustration of a known power management apparatus of a motor vehicle;

FIGURE 2 is a schematic illustration of a power management apparatus according to an embodiment of the invention; FIGURE 3 is a schematic illustration of a power management apparatus according to a further embodiment of the invention;

FIGURE 4 is a schematic illustration of a power management apparatus according to a still further embodiment of the invention; and

FIGURE 5 is a schematic illustration of a portion of a power management apparatus according to an alternative embodiment of the invention. DETAILED DESCRIPTION FIG. 2 shows a power supply control apparatus 200 of a vehicle according to an embodiment of the present invention.

The apparatus 200 has a power management module 230 coupled to a 12V primary battery 21 1 that is arranged to supply power to a starter motor 207 when it is required to crank an engine of the vehicle (not shown).

The power management module 230 has a LIN (Local Interconnect Network) processor 234 coupled to a gateway module (GWM) 261. The GWM 261 is arranged to provide control signals to the LIN processor 234 in order to control the power management module 230.

In the embodiment shown an engine-driven alternator 205 is coupled to the primary battery 21 1 via a primary MOSFET module 231 of the power management module 230 in order to allow charging of the battery 21 1 by the alternator 205 as described below.

The alternator 205 is coupled in parallel with electrical loads 220 of the vehicle and a 12V secondary battery 212. The loads 220 include sensitive loads such as one or more electronic control units (ECUs) of the vehicle and other loads that store settings data in volatile memory. It is to be understood that it is important to ensure that the sensitive loads 220 receive a continuous supply of electrical potential above a prescribed threshold in order to prevent malfunction or loss of data.

The alternator 205 and loads 220 are coupled to the secondary battery 212 by means of a secondary MOSFET module 232.

As discussed with respect to the prior art arrangement of FIG. 1 , it is to be understood that when the engine is cranked by means of the starter motor 207 a drop in the electrical potential across the primary battery 21 1 occurs. In order to prevent a corresponding drop in potential across the loads 220, the primary and secondary MOSFET modules 231 , 232 are each arranged to act to allow current to flow therethrough in only one direction, i.e. to behave as diodes. Thus, the primary MOSFET module 231 is arranged only to allow current to flow from the primary battery 21 1 to the loads 220 whilst the secondary battery is arranged only to allow current to flow from the secondary battery 212 to the loads 220. In the event that a drop in potential across the primary battery 21 1 occurs, a corresponding drop in potential across the loads 220 is prevented because as the potential across the loads 220 falls, the secondary MOSFET module 232 begins to conduct, causing current to flow from the secondary battery 212 to the loads 220. Since the primary MOSFET module 231 is also arranged to act as a diode, the drop in potential across the primary battery 21 1 acts to cause a 'reverse bias' potential to be applied across the primary MOSFET module 231. The primary MOSFET module 231 therefore assumes a non-conducting condition such that current is not permitted to flow therethrough from the secondary battery 212 to the starter motor 207.

In the embodiment of FIG. 2 the primary and secondary MOSFET modules 231 , 232 each comprise a set of eight MOSFET devices coupled in parallel. The source electrodes of each set of diodes are connected to one another at a common node S1 , S2 respectively. The respective gate electrodes are coupled to one another at common nodes G1 , G2 and the drain electrodes are coupled to one another at common nodes D1 , D2. Application of a potential to the gate electrode of one MOSFET device of a given module 231 , 232 is therefore arranged to be applied to the gate electrode of each of the devices of the given module 231 , 232. Each MOSFET module 231 , 232 has an ideal diode controller (IDC) IDC1 , IDC2 associated therewith. A first ideal diode controller IDC1 has a first input terminal coupled to the sources of the MOSFET devices of the primary MOSFET module 231 at a source node S1 and a second input terminal coupled to the drains of the MOSFET devices at a drain node D1 . IDC1 is therefore able to measure a potential fet1_source_vlts at node S1 and a potential fet1_drain_vlts at node D1 .

When IDC1 determines that the potential difference between nodes S1 and D1 is positive, i.e. the potential across the primary battery 21 1 is greater than that across the loads 220, IDC1 controls the MOSFET devices of the primary module 231 to assume a conducting condition, allowing current to flow in a 'forward' direction from the primary battery 21 1 to the loads 220. However, when the potential across the primary battery 21 1 is less than that across the loads 220 IDC1 controls the MOSFET devices of the primary module 231 to assume a non-conducting condition whereby current is prevented from flowing in a 'reverse' direction from the loads 220 (or secondary battery 212) to the primary battery 21 1 or starter motor 207.

The secondary MOSFET module 232 is configured to operate in a similar manner. Thus, a second ideal diode controller IDC2 is arranged to compare a potential fet2_source_vlts of the sources of the MOSFET devices of the module 232 at node S2 with a potential fet2_drain_vlts of the drains of the MOSFET devices of the module 232 at node D2. If the potential at node S2 is greater than the potential at node D2, IDC2 controls the MOSFET devices of the secondary MOSFET module 232 to assume the conducting condition. This allows current to flow in a 'forward' direction from the secondary battery 212 to the loads 220.

If the reverse condition exists, i.e. the potential at node D2 is greater than that at node S2, IDC2 is configured to control the secondary MOSFET module 232 to assume a nonconducting condition in which current is prevented from flowing in the 'reverse' direction through the module 232.

As shown in FIG. 2 the ideal diode controllers IDC1 , IDC 2 are connected to their respective MOSFET module 231 , 232 by means of a respective logical OR gate OR2, OR4. The OR gates OR2, OR4 are configured to perform a logical 'OR' function between input signals provided thereto. One signal is provided by the respective IDC (IDC1 or IDC2) and the other by a respective battery charge request signal batt1_chrg_req, batt2_chrg_req. Thus, the respective battery charge requests are operable (independently of one another) to override the respective signals from the I DCs IDC1 , IDC2 thereby to cause the respective modules 231 , 232 to conduct. Thus the modules 231 , 232 are each operable to allow current to flow in the 'reverse' direction therethrough when it is required. It is to be understood that in the embodiment of FIG. 2 this feature allows the respective batteries 21 1 , 212 to be charged by the alternator 205 when required.

Thus, when it is required to charge the primary battery 21 1 the GWM 261 controls the LIN processor 234 to control the batt1_chrg_req signal line to assume a HIGH state thereby forcing the MOSFET devices of the primary MOSFT module 231 to assume the conducting condition. Similarly, when it is required to charge the secondary battery 212 the GWM 261 controls the LIN processor 234 to control the batt2_chrg_req signal line to assume a HIGH state thereby forcing the MOSFET devices of the secondary MOSFT module 232 to assume the conducting condition.

It is to be understood that it is desirable that the amount of power consumed by the power management module 230 be as low as possible when the vehicle is in a standby mode (or 'shutdown' condition) when the vehicle is parked. This is so as to maximise a length of time for which the primary battery 21 1 is able to retain sufficient charge to restart the engine when it is required to do so.

It is to be understood that the ideal diode controllers IDC1 , IDC2 consume a not insignificant amount of power when they are active (and not in a standby mode) and supplying current to the respective MOSFET modules 231 , 232. Thus, the GWM 261 is configured to control the power management module 230 to place the first and second ideal diode controllers IDC1 , IDC2 in the standby mode when the vehicle enters the shutdown condition. In the standby mode power is not consumed to a significant extent by the IDCs or the MOSFET modules 231 , 232. As discussed below, this does not prevent supply of a 'quiescent' (or 'standby') current through the primary MOSFET module 231 to loads 220 requiring power when the vehicle is in the shutdown condition.

As noted above, some of the loads 220 still require power to be supplied to them when the vehicle is in the shutdown condition. The MOSFET devices of the primary and secondary MOSFET modules 231 , 232 are able inherently to allow a nominal current to flow therethrough in a forward direction from the respective battery 21 1 , 212 to the loads 220 when no current is supplied to the gate nodes G1 , G2 of the MOSFET modules 231 , 232 respectively. It is to be understood that this is because the MOSFET devices of each module 231 , 232 may be considered to comprise a 'body diode' coupled between the source and the drain terminals. It is this feature of the MOSFET devices that allows current to flow from source node S1 to drain node D1 when no current is supplied to gate node G1 and from source node S2 to drain node D2 when no current is supplied to gate node G2. However, it is to be understood that the 'body diode' of a MOSFET device has limited current capacity before heating of the MOSFET device to a not insignificant level can occur, resulting in energy loss due to heating and damage to the device. It is to be understood that whilst the vehicle is in the standby mode the amount of current drawn by the loads 220 may rise occasionally to levels that would cause damage to either MOSFET module 231 , 232 if the required current were to be supplied through one or both of the modules 231 , 232 without providing a current to the gate nodes G1 , G2.

The amount of current drawn by the loads 220 may rise whilst the vehicle is in the standby mode for example if a central locking control module of the vehicle receives a signal to unlock doors of the vehicle, if a burglar alarm of the vehicle is triggered, a tracking device transmits a location or other signal, and/or one or more other devices or systems of the vehicle are active such that the total amount of current drawn by the loads 220 exceeds a prescribed threshold value.

The prescribed value may be set to be a value below that at which damage to the first MOSFET module 231 may occur but which is above the value of quiescent current expected to be drawn by the loads 220 when the vehicle is in the shutdown mode and the loads 220 are in a standby mode.

Accordingly, if the vehicle is in the standby mode and the current drawn by the loads 220 exceeds the prescribed threshold value the power management module 230 controls IDC1 to become active. Once active, IDC1 detects automatically that current is flowing through the MOSFET module 231 from the primary battery 21 1 to the loads 220 and controls the MOSFET module 231 to allow current to flow therethrough from node S1 to node D1 .

In order to detect when the current flowing through the primary MOSFET module 231 exceeds the prescribed threshold level, a first sense resistor R1 and a first comparator CP1 are provided. The first sense resistor R1 is coupled in series with the primary MOSFET module 231 such that current flowing through the primary MOSFET module 231 also flows through sense resistor R1 . The first comparator CP1 is arranged to measure a potential drop across R1 . If the potential drop across R1 is above a prescribed voltage threshold value indicating that an amount of current flowing from the primary battery 21 1 to the loads 220 exceeds a prescribed current threshold value, the first comparator CP1 is configured to provide a control signal to the first ideal diode controller IDC1 via a first OR gate OR1 to IDC1 to 'wake up', i.e. to assume the active mode and perform its intended function

Accordingly, when the vehicle is in the standby mode and IDC1 is in the standby condition, the first comparator CP1 monitors the amount of current flowing from the primary battery 21 1 to the loads 220 by monitoring the potential difference across R1. When the amount of current flowing through R1 exceeds the threshold value the comparator CP1 provides a control signal to IDC1 to cause IDC1 to become active and provide power to the primary MOSFET module 231 as described above.

It is to be understood that in the embodiment of FIG. 2 the power management module 230 is configured to control operation of the secondary MOSFET module 232 in a similar manner to the primary MOSFET module 231 when the vehicle is in the shutdown condition.

Accordingly, the power management module is provided with a second sense resistor R2 and a second comparator CP2 configured to control the secondary MOSFET module 232. The second sense resistor R2 is coupled in series with the secondary MOSFET module 232 and the second comparator CP2 is configured to activate IDC2 when the current flowing through the second sense resistor R2 exceeds a prescribed value.

It is to be understood that in normal operation of the power management module 230, the secondary battery 212 is controlled only to provide power to the loads 220 when the engine is being cranked by the starter motor 207. In normal operation, when the engine is being cranked the vehicle will not be in the shutdown state and therefore both the first and second ideal diode controllers IDC1 , IDC2 would be active and not in their standby modes.

However, it is to be understood that the embodiment of FIG. 2 has the feature that if the engine is cranked and IDC2 is not active but in standby mode (for example due to a failure to provide a control signal to awake IDC2) the amount of current flowing through R2 will typically exceed the threshold value above which the second comparator activates IDC2. Accordingly, it can be seen that IDC2 would be automatically activated when the engine is cranked in order to maintain power to the loads 220 via the secondary battery 212. It is to be understood that, in some embodiments, whilst it is unlikely that IDC2 would be in the standby condition when the engine is cranked the feature that IDC2 would be activated automatically may be advantageous in certain circumstances. For example, in the event of a malfunction of the vehicle, for example of a function of the GWM 261 or power management module 230 in which IDC2 were not activated when the vehicle was no longer in the standby condition, power to the loads 220 would be preserved.

It is to be understood that the embodiment of FIG. 2 has the feature that when the engine is cranked, the power management module 230 controls automatically the primary and secondary MOSFET modules 231 , 232 to prevent a voltage drop across the loads 220 by preventing flow of current in the reverse direction through the primary MOSFET module 231 from node D1 to node S1 and allowing current flow through the secondary MOSFET module 233 from node S2 to node D2. In other words, substantially no external signals are required to be provided to the power management module 230 in order to prepare the power management module 230 for cranking.

In some embodiments, this feature has the advantage of reducing the time required to prepare the apparatus 200 for engine cranking thereby reducing a time required to start the engine once an engine controller is instructed to start the engine.

Alternatively or in addition, in some embodiments this feature has the advantage of reducing a load on a communications network of the vehicle.

As noted above, it is to be understood that in the event that a situation arises in which IDC2 fails to be activated, the second comparator CP2 provides the required control signal to IDC2 to activate IDC2 and the secondary MOSFET module 232 is controlled by IDC2 to allow current to flow from the secondary battery 212 to the loads 220.

It is to be further understood that in some embodiments non-sensitive loads 221 being loads that can remain connected across the primary battery 21 1 when the starter motor 207 is cranked may be connected in parallel with the primary battery 21 1 at a node between the primary battery 21 1 and the primary MOSFET module 231 . That is, loads that do not present a problem if the potential across them falls below 12V, for example to around 6V such as during cranking, may remain connected to the primary battery 21 1 during cranking. It is to be understood that in a normal running mode of the vehicle with the engine on, the alternator 205 may be used to power the loads 220 and charge the primary and secondary batteries 21 1 , 212. Thus one or both of the battery charge request signals batt1_chrg_req, batt2_chrg_req may be controlled to assume the logical HIGH condition to allow the corresponding MOSFET module 231 , 232 to assume an ON condition in which bi-directional current flow is permitted therethrough.

Thus, if the batt1_chrg_req signal is HIGH, the primary MOSFET module 231 allows current to flow from the alternator 205 to the primary battery 21 1 in a reverse direction through the module 231. If the batt2_chrg_req signal is HIGH, the secondary MOSFET module 232 allows current to flow through the module 232 in the reverse direction from the alternator 205 to the secondary battery 212.

Once the secondary battery 212 has reached a sufficiently high state of charge (SoC), the GWM 261 controls the power management module 230 to cause the secondary MOSFET module 232 to be placed back under the control of the second ideal diode controller IDC2, i.e. the batt2_chrg_req signal line assumes a logical LOW condition. Further charging of the secondary battery 212 is thereby prevented. Similarly, when the primary battery 21 1 has reached a sufficiently high SoC the GWM may control the power management apparatus 230 to cause the batt1_chrg req signal line to assume a logical LOW condition to prevent further charging of the primary battery 21 1 . It is to be understood that in order to minimise an amount of current consumed by the power management module 230 when the vehicle is in the shutdown mode the LIN processor 234 is arranged to assume a standby condition when the vehicle is in this mode. The LIN processor 234 sets a logical state of an output signal line 'LIN awake' according to the condition of the processor 234.

When the processor 234 is in the standby condition the LIN awake signal line is set LOW. Thus the first ideal diode controller IDC1 will only become active if the current flowing through sense resistor R1 exceeds a prescribed value or the LIN_awake signal line subsequently assumes a HIGH state. If t e LIN processor 234 becomes active, the LIN awake signal line is set HIGH and OR1 controls the ideal diode controller IDC1 to become active regardless of the state of the potential across R1. The first ideal diode controller IDC1 also provides a feedback current signal 'fetl curr feedb' to the LIN processor 234. The LIN processor 234 in turn communicates this signal to the gateway module 261 .

It is to be understood that embodiments of the present invention have the advantage that a time required to control the power management module 230 to start the engine of the vehicle is less than that of the prior art arrangement of FIG. 1 in which mechanical contactors are employed.

This is at least in part through the use of solid state MOSFET devices rather than electromechanical contactors.

Operation of the power supply control apparatus 200 of FIG. 2 will now be described with reference to a vehicle having a key-based accessory control and engine start system. It is to be understood that other types of accessory control and engine start arrangements are also useful.

When the key is turned to switch the vehicle from an OFF state to an ACC state in which accessories of the vehicle may be used (such as an infotainment system), the gateway module 261 is configured to control the power management module 230 to assume an operational condition in which the LIN processor 234 is switched ON.

IDC1 is therefore switched ON (via the LIN_awake signal line and OR1 ) and the primary MOSFET module 231 is controlled to behave as an ideal diode by means of IDC1. Power for the loads 220 is thus provided by the primary battery 21 1 .

Similarly, the LIN_awake signal line also controls the second ideal diode controller IDC2 to switch ON and thereby control the secondary MOSFET module 232 to behave as an ideal diode. When it is required to start the engine of the vehicle, the primary battery 21 1 is employed to power the starter motor 207 to start the engine. It is to be understood that no switching signals are required to be provided to the primary and secondary MOSFET modules 231 , 232 when the starter motor 207 is being used in order to maintain power to the loads 220. This is because the primary and secondary MOSFET modules 231 , 232 remain under the control of their respective ideal diode controllers IDC1 , IDC2. Thus, when the potential across battery 21 1 falls as it powers the starter motor 207 and the amount of current drawn from the secondary battery 212 increases (the secondary MOSFET module being controlled to allow this increase under the control of IDC2), a flow of current from the secondary battery 212 to the starter motor 207 is prevented by the ideal diode behaviour of the primary MOSFET module 231 . Thus the potential across the loads 220 remains substantially at the level of secondary battery 212 (i.e. at a potential of around 12V). It is to be understood that once a signal to start the engine is issued (e.g. by an engine controller or main ECU of the vehicle) it is not necessary to wait for switching of the primary or secondary MOSFET modules 231 , 232 to occur before the starter motor may be switched on. Rather, the starter motor may be switched on substantially immediately. It is to be understood that this feature may be particularly useful in respect of stop/start vehicles that are configured to stop the engine when it is determined that a fuel saving may be made. For example, the engine may be stopped as the vehicle coasts or decelerates during a braking operation. The engine may be restarted when the driver presses the accelerator pedal.

Embodiments of the invention allow cranking of the engine to begin with reduced delay compared with systems employing mechanical contactor devices.

Embodiments of the invention have the further advantage that a reduction in NVH (noise, vibration and harshness) performance due to the presence of mechanical contactors may also be prevented.

Furthermore in the embodiment of FIG. 2 the state of the primary and secondary MOSFET modules 231 , 232 does not need to be changed by means of control signals every time the engine is started or stopped. Thus a requirement to issue control signals to the power management module 230 every time the engine is stopped and restarted may also be substantially eliminated. Once the engine is running, the LIN processor 234 may be controlled to set the batt1_chrg_req signal line HIGH to allow electrical current from the alternator 205 to flow through the primary MOSFET module 231 to recharge the primary battery 21 1 .

Similarly, the LIN processor 234 may be controlled to set the batt2_chrg_req signal line HIGH to allow electrical current from the alternator 205 to flow through the secondary MOSFET module 232 to recharge the secondary battery 212. As noted above, the embodiment of FIG. 2 is advantageous over the prior art arrangement of FIG. 1 at least in part because with the primary and secondary MOSFET modules 231 , 232 both under the control of their respective ideal diode controllers IDC1 , IDC2 (their normal state prior to switching on the engine), the engine may be cranked with the modules 231 , 232 still under the control of IDC1 and IDC2 without a requirement to issue further control signals. The switching delays in respect of contactors 131 , 132 of the prior arrangement of FIG. 1 are therefore eliminated.

Furthermore, as also noted above it is to be understood that the arrangement of FIG. 2 is more tolerant of delays or failures in respect of control of ideal diode controllers IDC1 , IDC2 in preparation for starting the engine.

For example, if engine cranking is commenced when the primary or secondary MOSFET modules 231 , 232 are switched OFF, it is to be understood that power to the loads 220 will be maintained automatically even if the LIN processor 234 remains asleep.

For example, if the secondary MOSFET module 232 is OFF and the potential across the loads 220 falls (due to cranking of the engine as described above), the increase in current drawn through the module 232 will cause the second ideal diode controller IDC2 to switch ON due to the potential drop across R2, causing the second MOSFET module 232 to 'wake up' and behave as an ideal diode.

Similarly, if the primary MOSFET module 231 is in the OFF state when engine cranking is commenced, the module 231 will remain in a non-conducting state thereby preventing a drop in potential across the loads 220.

Thus it is to be understood that the power management module 230 is arranged automatically to preserve a potential of 12V across the loads 220 even if control signals to the primary and secondary MOSFET modules 231 , 232 causing the modules 231 , 232 to behave as ideal diodes fail to be issued or are issued after cranking of the engine by the starter motor 207 has begun. It is to be understood that late issuance of control signals might arise for any one of a number of reasons including for example a software error, a higher than expected demand on the computing capacity of the gateway module 261 , or a higher than expected demand on a communications network of the vehicle. It is to be understood that embodiments of the invention have the advantage that NVH performance of a vehicle having a power management module 230 according to an embodiment of the invention may be enhanced considerably compared with the prior art arrangement of FIG. 1 . Furthermore, a reduced number of control signals from a GWM 261 may be associated with embodiments of the invention compared with the prior art arrangement.

It is to be understood that reference herein to a MOSFET module 231 , 232 is not to be understood as requiring the MOSFET array to be provided as a plug-in or other modular component that is necessarily separable from the remainder of the power management module 230. Rather the MOSFETS of the array of each MOSFET module 231 , 232 may be individually and permanently fixed to a circuit board comprising other components of the power management module 230 such as the LIN processor 234 and one or more other components. Other arrangements are also useful. It is to be understood that in some embodiments the alternator 205 may be provided on an opposite side of the primary MOSFET module 231 to the arrangement of FIG. 2. In such embodiments the primary MOSFET module 231 is not required to allow current to flow therethrough in the reverse direction from node D1 to node S1 in order to charge the primary battery 21 1.

Furthermore in some embodiments such as embodiments for use with hybrid electric vehicles, the alternator 205 may be replaced by a DC/DC converter arranged to supply power to the loads 220 and to recharge the primary battery 21 1 from an alternative power source. In some embodiments for use with hybrid electric vehicles the secondary battery 212 may be replaced by the DC/DC converter whilst in some alternative embodiments for use with hybrid electric vehicles the secondary battery 212 may still be present. FIG. 3 shows power management apparatus 300 according to a further embodiment of the invention. Like features of the embodiment of FIG. 3 to the embodiment of FIG. 2 are shown with like reference signs prefixed numeral 3 instead of numeral 2.

The controller 300 of FIG. 3 is similar to that of the embodiment of FIG. 2 except that the secondary MOSFET module 332 of the power management module 330 is connected the opposite way around. That is, the drains of the MOSFET devices of the module 332 at node D2 are connected to sense resistor R2 whilst the sources of the MOSFET devices of the module 332 at node S2 are connected to the loads 320.

It is to be understood that in this arrangement the secondary MOSFET module 332 is arranged automatically to allow charge to flow from node S2 to node D2 when the potential across the secondary battery 312 is less than the potential across the loads 320. This has the effect that the secondary battery 312 is charged automatically by the power management module 330 when the SoC of the secondary battery 312 falls. A risk that the SoC of the battery 312 falls to a critical level below which the battery 312 is unable to power the loads 320 (for example during cranking) is therefore reduced. In use, when it is required to crank the engine the LIN processor 334 sets a control signal fet2 ext_req to logic HIGH. This signal corresponds to the batt2 chrg req signal of the embodiment of FIG. 2 except that because the secondary MOSFET module 332 is connected the opposite way around in the embodiment of FIG. 3, this signal line is not set high when it is required to charge the secondary battery 312. Rather, this signal line is set high when it is required to allow current to flow through the module 332 from the secondary battery 312 to power the loads 320.

As the engine is cranked and the potential across the primary battery 31 1 falls, the primary MOSFET module 331 is subject to a reverse bias condition as in the arrangement of FIG. 2 and current does not flow through the module 331 .

The potential across the loads 320 is maintained at substantially the same potential as that across the secondary battery 312 as the secondary MOSFET module 332 allows current to flow therethrough from node D2 to node S2.

Once cranking of the engine has ceased, the fet2_ext_req signal line is set to logical LOW. If the potential across the secondary battery 312 is less than that across the loads 320 by a sufficient amount, the secondary MOSFET module 332 automatically allows current to flow therethrough in order to recharge the battery 312.

If charging of the primary battery 31 1 is required, the LIN processor 334 sets the fet1_ext_req signal line to logical HIGH causing the primary MOSFET module 331 to assume the conducting condition, allowing current to flow from the alternator 305 to the primary battery 31 1.

As discussed above, it is to be understood that when it is required to crank the engine, the arrangement of FIG. 3 requires the fet2_ext_req signal line to be set to logic HIGH in order to prevent a drop in potential across the loads 320. However, the arrangement of FIG. 3 maintains automatically the SoC of the secondary battery 312 above a prescribed value thereby reducing a risk that the SoC falls below a critical level. This feature has the advantage that a service life of the battery 212 may be increased.

Similarly, when the vehicle is in the shutdown condition and the power management apparatus 300 is in the standby mode, quiescent current drain from the secondary battery 312 to the loads 320 through the secondary MOSFET module 332 is not permitted. This because body diodes of the MOSFET devices of the module 332 would be under a reverse bias if the potential across the loads 320 were less than that across the secondary battery 312.

This has the advantage that a risk that the secondary battery 312 suffers excessive loss of charge whilst the vehicle is in the shutdown condition is reduced.

FIG. 4 shows power management apparatus 400 according to a further embodiment of the invention. Like features to the embodiment of FIG. 3 are shown with like reference numerals prefixed numeral 4 instead of numeral 3. The embodiment of FIG. 4 is similar to the embodiment of FIG. 3 except that the alternator 405 is provided on the same side of the primary MOSFET module 431 as the starter motor 407 and battery 41 1 . Thus, powering by the alternator of the loads 420 and charging of the secondary battery 412 must be performed through the primary MOSFET module 431 .

It is to be understood that powering of the loads 420 and charging of the secondary battery 412 by the alternator 405 via the primary MOSFET module 431 is performed automatically by the power management module 430 without a requirement for the GWM 461 to provide specific external control signals to trigger charging of the secondary battery 412. This is because when the potential across the primary battery 41 1 is sufficiently higher than the potential across the loads 420 (such as is to be expected when the alternator 405 is being driven by the engine) the primary MOSFET module 431 automatically allows current to flow through the primary MOSFET module 431 to the loads 420.

Likewise, when the potential across the secondary battery 412 is below that across the loads 420 the secondary MOSFET module 432 is arranged automatically to allow current to flow therethrough to charge the secondary battery 412.

It is to be understood that the fet2_ext_req signal line may be set to logical HIGH when it is required to power the loads 420 by means of the secondary battery 412, for example during cranking of the engine as described above with respect to the embodiment of FIG. 3.

The fet1_ext_req signal line may be set to logical HIGH if it is required to provide power from the secondary battery 412 to a load on the opposite side of the primary MOSFET module 431 such as any non-sensitive loads 421 .

FIG. 5 shows power management apparatus 500 according to a further embodiment of the invention for use in HEV applications. Like features of the embodiment of FIG. 5 to those of the embodiment of FIG. 3 are shown with like reference signs prefixed numeral 5 instead of numeral 3.

The apparatus 500 differs from that of the embodiment of FIG. 3 in that the apparatus 500 is not configured to be connected directly to an engine-driven alternator 205. Rather, charging of primary battery 51 1 is performed by electrical current supplied by a DC/DC converter 513 which is in turn coupled to a propulsion battery of the vehicle (not shown). The propulsion battery is used primarily to power an electrical motor of the vehicle to provide motive force for propelling the vehicle.

When it is required to charge the primary battery 51 1 by means of the DC/DC converter 513, the fet1_ext_req signal line is set to logical HIGH in order to allow current to flow from the DC/DC converter 513 to the primary battery 51 1 . Likewise, in some embodiments when it is required to crank the engine by means of the starter motor 507, the fet2_ext_req signal line is set to logical HIGH in order to allow current to flow from the secondary battery 512 to the loads 520 during cranking. Alternatively or in addition, in some embodiments power to the loads 520 during cranking may be provided by the DC/DC converter 513.

The apparatus 500 is thus configured to be operated in a similar manner to the apparatus 300 of FIG. 3. In some alternative embodiments, the secondary battery 512 may be omitted. Thus powering of the loads 520 may be performed substantially exclusively by the DC/DC converter 513 when the engine is being cranked or the engine is running.

When the vehicle is in the standby mode power to the loads 520 may be supplied by the DC/DC converter 513. In some embodiments when the vehicle is in the standby mode power to the loads 520 is supplied by the primary battery 51 1 via the primary MOSFET module as described with respect to the embodiments of FIG. 2, FIG. 3 and FIG. 4.

It is to be understood that other arrangements are also useful.

The DC/DC converter 513 may also be employed to power electrical loads 520 of the vehicle under certain conditions. For example, if a state of charge (SoC) of the primary battery 51 1 falls below a prescribed value the apparatus 500 may be arranged to prevent any flow of current from the primary battery 51 1 to the loads 520.

Alternatively or in addition if the SoC of the primary battery 51 1 falls below a critical level the apparatus 500 may be arranged to recharge the primary battery 51 1 by means of the DC/DC converter 513 even when the vehicle is in the shutdown mode, for example after the vehicle has been parked for an extended period of time with the engine off.

Other arrangements are also useful.

It is to be understood that the primary and secondary MOSFET modules may alternatively be any other suitable solid state switch module. Thus, other types of transistor may also be used such as non-MOS field effect transistors, insulated-gate field effect transistors (IGFETs) and/or insulated-gate bipolar transistors (IGBTs). Other devices are also useful. The above described embodiments represent advantageous forms of the invention but are provided by way of example only and are not intended to be limiting. In this respect, it is envisaged that various modifications and/or improvements may be made to the invention within the scope of the appended claims.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS:

1 . An apparatus for a motor vehicle comprising:

a primary power storage device for powering an engine starter device;

a vehicle electrical load;

a secondary power storage device for powering the vehicle electrical load; and a solid state primary diode portion coupled between the primary power storage device and the vehicle electrical load,

the primary diode portion being operable to allow a flow of current in a forward direction therethrough from the primary power storage device to the vehicle electrical load when the starter device is not in use and to prevent a flow of current in a reverse direction therethrough from the secondary power storage device to the engine starter device when the starter is in use.

2. An apparatus as claimed in claim 1 wherein the primary diode portion comprises a primary transistor portion comprising at least one transistor device, the at least one transistor device having a first terminal, a second terminal and a third terminal coupled to respective first, second and third nodes of the primary transistor portion, the second and third nodes being coupled between the primary power storage device and the vehicle electrical load, the primary transistor portion being operable to control an amount of current flowing between the second and third nodes by means of the first node.

3. An apparatus as claimed in claim 2 wherein the primary transistor portion comprises a plurality of transistor devices having respective first, second and third terminals coupled to the first, second and third nodes respectively such that the devices are connected in parallel with one another.

4. An apparatus as claimed in any one of claims 2 or 3 arranged to control the primary transistor portion to function as a diode thereby to prevent the flow of current therethrough in the reverse direction when the starter is in use and to allow the flow of current therethrough in the forward direction when the starter device is not in use.

5. An apparatus as claimed in claim 4 arranged to control the primary transistor portion to function as a diode responsive to a potential difference between the second and third nodes of the primary transistor portion.

6. An apparatus as claimed in claim 4 or claim 5 comprising a primary diode controller arranged to control the primary transistor portion to function as a diode.

7. An apparatus as claimed in any preceding claim operable between an active mode and a standby mode, wherein in the standby mode power to the first node of the primary transistor portion is either reduced or terminated and an amount of power consumed by the apparatus is reduced.

8. An apparatus as claimed in claim 7 depending through claim 2 further comprising current detection means operable to detect a flow of current through the primary transistor portion in the forward direction, when the apparatus is in the standby mode the apparatus being operable to restore power to the first node responsive to the amount of current flowing through the primary transistor portion in the forward direction.

9. An apparatus as claimed in claim 7 or claim 8 wherein the current detection means comprises a sense resistor.

10. An apparatus as claimed in any one of claims 7 to 9 as depending through claim 6 arranged to place the primary diode controller in a standby mode when the apparatus is in the standby mode and to place the primary diode controller in an active mode thereby to restore power to the first node when the amount of current flowing through the primary transistor portion in the forward direction exceeds a prescribed value.

1 1. An apparatus as claimed in claim 2 or any one of claims 3 to 10 depending through claim 2 wherein the primary transistor portion is coupled between the primary power storage device and the vehicle load such that a body diode of the primary transistor portion is oriented to allow current to flow from the primary power storage device to the vehicle electrical load when power to the first node is terminated.

12. An apparatus as claimed in claim 2 or any one of claims 3 to 1 1 depending through claim 2 further operable to allow a flow of current through the primary transistor portion in the reverse direction.

13. An apparatus as claimed in any preceding claim comprising a battery charging device operable to supply charge to the primary power storage device to recharge the primary power storage device.

14. An apparatus as claimed in claim 13 wherein the battery charging device is arranged to be coupled to the primary power storage device through the primary diode portion.

15. An apparatus as claimed in claim 13 or claim 14 wherein the battery charging device is arranged to be coupled to the primary power storage device substantially directly and not through the primary diode portion.

16. An apparatus as claimed in any preceding claim further comprising a secondary diode portion coupled between the electrical load and the secondary power storage device, the secondary diode portion being operable to allow a flow of current therethrough from the secondary power storage device to the vehicle electrical load when the starter device is in use.

17. An apparatus as claimed in claim 16 wherein the secondary diode portion is operable to prevent discharge of the secondary power storage device when the starter is not in use.

18. An apparatus as claimed in claim 16 or claim 17 as depending through claim 13 wherein the secondary diode portion is operable to couple the secondary power storage device to the battery charging device.

19. An apparatus as claimed in any one of claims 16 to 18 as depending through claim 13 wherein the secondary diode portion is operable to decouple the secondary power storage device from the battery charging device.

20. An apparatus as claimed in any one of claims 16 to 19 wherein the secondary diode portion comprises a secondary transistor portion, the secondary transistor portion comprising at least one transistor device, the at least one transistor device having a first terminal, a second terminal and a third terminal coupled to respective first, second and third nodes of the secondary transistor portion, the second and third nodes being coupled between the secondary power storage device and the vehicle electrical load.

21. An apparatus as claimed in claim 20 operable to control the secondary transistor portion to function as a diode responsive to a potential difference between the second and third nodes of the secondary transistor portion.

22. An apparatus as claimed in claim 21 further comprising a secondary diode controller operable to control the secondary transistor portion to function as a diode whereby current may flow only in a forward direction through the secondary transistor portion, the apparatus being further operable to override the secondary diode controller thereby to allow a flow of current in a reverse direction through the secondary transistor portion opposite the forward direction when required.

23. An apparatus as claimed in any one of claims 20 to 22 further comprising current detection means operable to detect a flow of current through the secondary transistor portion.

24. An apparatus as claimed in claim 23 wherein the current detection means comprises a sense resistor in series with the secondary transistor portion.

25. An apparatus as claimed in any one of claims 20 to 24 arranged to place the secondary diode controller in a standby mode wherein power to the first node is terminated when the apparatus is in the standby mode and to place the secondary diode controller in an active mode wherein power to the first node is restored when the amount of current flowing through the secondary transistor portion in the forward direction exceeds a prescribed value.

26. An apparatus as claimed in any one of claims 21 to 25 wherein the forward direction corresponds to a direction from the secondary power storage device to the load.

27. An apparatus as claimed in any one of claims 21 to 25 wherein the forward direction corresponds to a direction from the load to the secondary power storage device.

28. An apparatus as claimed in claim 2 or any one or claims 3 to 27 depending through claim 2 wherein the at least one transistor device of the primary transistor portion comprises a metal oxide semiconductor field effect transistor (MOSFET) device.

29. An apparatus as claimed in claim 2 or any one of claims 3 to 28 depending through claim 2 wherein the first terminal of the at least one transistor device of the primary transistor portion corresponds to a gate terminal and the first node of the primary transistor portion corresponds to a gate node, the second terminal of the at least one transistor device of the primary transistor portion corresponds to a source terminal and the second node of the primary transistor portion corresponds to a source node, and the third terminal of the at least one transistor device of the primary transistor portion corresponds to a drain terminal and the third node of the primary transistor portion corresponds to a drain node.

30. An apparatus as claimed in claim 20 or any one of claims 21 to 29 depending through claim 20 wherein the secondary transistor portion comprises at least one transistor device.

31. An apparatus as claimed in claim 30 wherein the first terminal of the at least one transistor device of the secondary transistor portion corresponds to a gate terminal and the first node of the secondary transistor portion corresponds to a gate node, the second terminal of the at least one transistor device of the secondary transistor portion corresponds to a source terminal and the second node of the secondary transistor portion corresponds to a source node, the third terminal of the at least one transistor device of the secondary transistor portion corresponds to a drain terminal and the third node of the secondary transistor portion corresponds to a drain node.

32. An apparatus as claimed in claim 30 or claim 31 wherein the at least one transistor device of the secondary transistor portion comprises a metal oxide semiconductor field effect transistor (MOSFET) device.

33. A method of controlling a motor vehicle comprising:

allowing by means of a primary diode portion a flow of current in a forward direction from a primary power storage device to a vehicle electrical load when an engine starter device is not in use and preventing by means of the primary diode portion a flow of current in a reverse direction from a secondary power storage device to the engine starter device when the starter is in use.

34. A method as claimed in claim 33 comprising the step of allowing current to flow through the primary diode portion responsive to a potential difference between a pair of nodes of the primary diode portion connected between the primary power storage device and the vehicle electrical load.

35. A method as claimed in claim 34 wherein the step of allowing current to flow through the primary diode portion responsive to a potential difference between the pair of nodes of the primary diode portion is performed by means of a primary diode portion controller.

36. A method as claimed in claim 35 comprising the step of controlling the primary diode portion controller to assume a standby mode, the step of controlling the primary diode portion controller to assume the standby mode comprising the step of terminating a supply of power to a control node of the primary diode portion not being one of said pair of nodes of the primary diode portion.

37. A method as claimed in claim 36 comprising the step of detecting a flow of current through the primary diode portion, when the primary diode portion is in the standby mode the method comprising restoring power to the control node of the primary diode portion responsive to the amount of current flowing in the forward direction therethrough.

38. A method as claimed in any one of claims 36 or 37 comprising the step of allowing a quiescent current to flow from the primary power storage device to the vehicle electrical load through the primary diode portion when a supply of power is terminated to the control node.

39. A method as claimed in any one of claims 33 to 38 comprising the step of allowing a flow of current through the primary diode portion in the reverse direction.

40. A method in any one of claims 33 to 39 comprising the step of supplying charge by means of a battery charging device to the primary power storage device to recharge the primary power storage device.

41. A method as claimed in claim 40 comprising the step of supply charge by means of the battery charging device to the primary power storage device through the primary diode portion.

42. A method as claimed in claim 40 comprising the step of supply charge by means of the battery charging device to the primary power storage device substantially directly and not through the primary diode portion.

43. A method as claimed in any one of claims 33 to 42 comprising the step of providing a flow of current from the secondary power storage device to the vehicle electrical load when the starter device is in use through a secondary diode portion.

44. A method as claimed in claim 43 comprising the step of preventing discharge of the secondary power storage device when the starter is not in use by means of the secondary diode portion.

45. A method as claimed in claim 43 or claim 44 as depending through claim 40 comprising the step of providing charge to the secondary power storage device from the battery charging device by means of the secondary diode portion.

46. A method as claimed in any one of claims 43 to 45 as depending through claim 40 comprising the step of decoupling the battery charging device from the secondary power storage device by means of the secondary diode portion.

47. A method as claimed in any one of claims 43 to 46 comprising the step of allowing current to flow through the secondary diode portion in a forward direction responsive to a potential difference between a pair of nodes of the secondary diode portion connected between the secondary power storage device and the vehicle electrical load.

48. A method as claimed in claim 47 wherein the step of allowing current to flow through the secondary diode portion responsive to a potential difference between the pair of nodes of the secondary diode portion is performed by means of a secondary diode portion controller.

49. A method as claimed in claim 48 comprising the step of controlling the secondary diode portion controller to assume a standby mode, the step of controlling the secondary diode portion controller to assume the standby mode comprising the step of terminating a supply of power to a control node of the secondary diode portion not being one of said pair of nodes of the secondary diode portion.

50. A method as claimed claim 50 comprising the step of allowing a quiescent current to flow through the secondary diode portion in the forward direction when a supply of power is terminated to the control node thereof.

51. A method as claimed in any one of claims 49 or 50 comprising the step of detecting a flow of current through the secondary diode portion, when the secondary diode portion is in the standby mode the method comprising restoring power to the control node of t e secondary diode portion responsive to the amount of current flowing therethrough in the forward direction.

52. A method as claimed in any one of claims 47 to 51 comprising the step of allowing a flow of current through the secondary diode portion in a reverse direction opposite the forward direction.

53. A method as claimed in any one of claims 47 to 52 wherein the forward direction corresponds to a direction from the secondary power storage device to the load.

54. A method as claimed in any one of claims 47 to 52 wherein the forward direction corresponds to a direction from the load to the secondary power storage device.

55. A method as claimed in any one of claims 33 to 54 wherein the primary diode portion comprises at least one transistor device.

56. A method as claimed in claim 43 or any one of claims 44 to 55 depending through claim 43 wherein the secondary diode portion comprises at least one transistor device.

57. An apparatus substantially as hereinbefore described with reference to the accompanying drawings.

58. A method substantially as hereinbefore described with reference to the accompanying drawings.