GB2532092A

GB2532092A - A method for preventing malfunctioning of a combined valve and aspirator assembly

Info

Publication number: GB2532092A
Application number: GB1502884.8A
Authority: GB
Inventors: Leroy Tom; Robert Valentine Paul; Brett Kevin
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-02-20
Filing date: 2015-02-20
Publication date: 2016-05-11
Anticipated expiration: 2035-02-20
Also published as: DE102016102623A1; RU2016105736A3; RU2698615C2; MX2016002100A; RU2016105736A; CN105905089A; GB201502884D0; GB2532092B

Abstract

Malfunctioning of a combined valve and aspirator assembly 10 is prevented by opening an aspirator valve 11 forming part of the combined valve and aspirator assembly 10 when an engine 6 of a motor vehicle 1 is to be shut-down. Opening the valve 11 when the engine 6 is off allows fluid to drain and prevents risk of the valve sticking in the closed position due to icing up of the valve 11 in cold ambient conditions. In some embodiments the valve 11 is only opened for a predefined period of time following the shutdown of the engine 6 in order to prevent unnecessary power usage if the engine is off for an extended period of time. Opening of the valve may be dependent on the temperature. Additionally, heat may be provided to the valve when a key-on event occurs, i.e. the engine is started.

Description

A Method for Preventing Malfunctioning of a Combined Valve and Aspirator Assembly This invention relates to a combined valve and aspirator assembly forming part of a vacuum boosted brake system and, in particular, to a method for preventing the malfunctioning of the combined valve and aspirator assembly due to icing up of the valve.

It is known to provide a motor vehicle with a vacuum assisted braking system in which a brake booster/ vacuum servo is used to amplify the force input from a driver of the motor vehicle.

Some vacuum assisted braking system use the vacuum in an inlet manifold of the engine to provide a source of vacuum for the brake booster. It is a disadvantage of such an arrangement that the level of the vacuum in the inlet manifold of the engine varies considerably during use of the engine and there are times where there is little or no vacuum present in the inlet manifold. To overcome this problem it has been proposed to use an aspirator connected to an inlet flow passage to the engine in order to boost the amount of vacuum available to the brake booster at times when there is very little vacuum present in the inlet manifold for use by the brake booster.

In order to minimise the interference of the aspirator with engine throttle control it is usual to incorporate with such an aspirator a valve (an aspirator valve) to control the flow of air through the aspirator. The aspirator valve is normally operable to either permit flow through the aspirator when it is open or prevent the flow of air through the aspirator when it is closed. Such an arrangement of a valve with an aspirator is normally referred to as a combined valve and aspirator assembly. -2 -

It is a problem with such a combined valve and aspirator assembly that, at very low ambient temperatures such as below zero degrees Celsius, any moisture remaining in the aspirator after the engine is shut-down will tend to freeze. This icing up will produce a bond between a body part of the aspirator and a valve element of the aspirator valve thereby holding the valve element in a closed position and causing the aspirator valve to malfunction when the engine is restarted if the aspirator valve is required to open as is often the case.

It is an object of the invention to prevent malfunctioning of a combined valve and aspirator assembly due to icing.

According to a first aspect of the invention there is provided a method for preventing the malfunctioning of a combined valve and aspirator assembly of a motor vehicle having an engine due to icing up of a valve forming part of the combined valve and aspirator assembly wherein the method comprises when a key-off event occurs indicating that the engine of the motor vehicle is to be shutdown, opening the valve so as to permit liquid to drain from the aspirator.

The method may further comprise mounting the aspirator at an angle with respect to horizontal so as to improve draining of liquid from the aspirator.

The valve may be a normally closed valve that is urged into an open position by the action of an actuator and the method may further comprise activating the actuator when a key-off event occurs.

The method may further comprise only opening the valve if the ambient temperature is less than a first predefined temperature threshold.

The method may further comprise, when a key-off event occurs, opening the valve for a predefined period of time so as to permit liquid to drain from the aspirator and then, when the period of time has elapsed, closing the valve.

Alternatively, the valve may be a normally open valve that is urged into a closed position by the action of an actuator and the method may further comprise deactivating the actuator when a key-off event occurs.

The method may further comprise applying heat to the aspirator when a key-on event occurs.

The method may further comprise only applying heat to 15 the aspirator if the ambient temperature is below a second predefined temperature threshold.

The method may further comprise applying heat to a valve element of the valve when a key-on event occurs.

The method may further comprise only applying heat to the valve element if the ambient temperature is below a second predefined temperature threshold.

According to a second aspect of the invention there is provided a motor vehicle having an engine, a human machine interface to switch on and switch off the engine and a vacuum boosted braking system including a combined valve and aspirator assembly and a controller for controlling the opening and closing of a valve of the combined valve and aspirator assembly wherein the controller is operable to open the valve so as to permit liquid to drain from the aspirator when operation of the human machine interface indicates that the engine of the motor vehicle is to be shutdown. -4 -

The aspirator may be mounted at an angle with respect to horizontal so as to improve draining of liquid from the aspirator.

The valve may comprise a valve element and an actuator to move the valve element between open and closed positions and the valve element may be in a closed position when the actuator is deactivated and may be urged into an open position by activation of the actuator and the controller may be operable to activate the actuator when the engine of the motor vehicle is to be shutdown.

The valve may only be opened if the ambient temperature is less than a first predefined threshold.

When the engine of the motor vehicle is to be shutdown, the controller may be operable to open the valve for a predefined period of time so as to permit liquid to drain from the aspirator and then, after expiry of the predefined period of time, may be further operable to close the valve.

The valve may alternatively comprise a valve element and an actuator to move the valve element between open and closed positions and the valve element may be in a open position when the actuator is deactivated and may be urged into a closed position by activation of the actuator and the controller may be operable to deactivate the actuator when the engine of the motor vehicle is to be shutdown.

The aspirator may include a heater and the controller may be operable to use the heater to apply heat to the aspirator when the engine is to be started.

A valve element heater may be provided for the valve 35 element of the valve and the controller may be operable to use the valve element heater to apply heat to the valve element when the engine is to be started. _ 5 _

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1 is a high level flow chart of a first embodiment of a method for preventing malfunctioning of a combined valve and aspirator assembly due to icing in accordance with a first aspect of the invention; io Fig.2 is a high level flow chart of a second embodiment of a method for preventing malfunctioning of a combined valve and aspirator assembly due to icing in accordance with the first aspect of the invention; Fig.3 is a cross-section through a combined valve and aspirator assembly of a vacuum boosted braking system according forming part of a motor vehicle according to a second aspect of the invention; and Fig.4 is a schematic diagram of a motor vehicle according to the second aspect of the invention.

Referring firstly to Fig.1 the method starts at box 110 which represents a key-on event. In older motor vehicles the electrical circuits of the motor vehicle and the starting of an engine of the motor vehicle were affected via a key operated switch often referred to as an 'ignition switch'. The moving of such a switch into an 'on' position in which all major electrical circuits of the motor vehicle are enabled and the engine of the motor vehicle has been started is conventionally referred to as a 'key-on' event and this designation is used to indicate that the same effect has been produced.

Similarly, the moving of such a switch into an 'off' position in which all major electrical circuits of the motor vehicle are deactivated and the engine of the motor vehicle -6 -is stopped is conventionally referred to as a 'key-off' event and this designation is used to indicate that the same effect has been produced.

However, it will be appreciated that on many modern motor vehicles a key switch is not used to effect 'key-on' and 'key-off' events but rather a different form of machine-human interface (HMI). This invention is not limited to any particular type of HMI and any type of HMI that can effect switching on of the major electrical circuits of the motor vehicle and starting of the engine (a 'key-on' event) and switching off and stopping of the engine (a 'key-off' event) of the major electrical circuits of the motor vehicle could be used.

Referring back to box 110 from this box when the engine has started the method moves to box 120 where the aspirator valve is controlled to provide the required vacuum for the brake booster. That is to say, generally speaking, if the vacuum available directly from the engine is high, the aspirator valve will be closed and conversely, if the vacuum available directly from the engine is below that required for the brake booster, the aspirator valve is opened.

From box 120 the method advances to box 130 to check whether a 'key-off' event has occurred indicating that the engine of the motor vehicle is to be stopped. If a 'key-off' event has not occurred the method returns to box 120 and the boxes 120 and 130 will continue to be executed until a key-off event occurs. That is to say, when the engine is running, the aspirator valve is controlled in a conventional manner to provide the desired vacuum for a brake booster.

However, if when checked in box 130, a key-off event 35 has occurred, the method advances from box 130 to box 140 where the aspirator valve is opened. At the time an engine shutdown occurs any entrapped moisture in the aspirator will -7 -always be in the liquid state because, irrespective of the ambient temperature in which the motor vehicle is operating, the temperature of the aspirator will always be significantly above zero degrees Celsius due to its location in the engine compartment in close proximity to the engine.

As the combined valve and aspirator assembly cools during a long shutdown period the temperature within the engine compartment will fall until eventually it reaches substantially the same temperature as the ambient air in which the motor vehicle is located. Therefore, if the ambient temperature is well below the freezing point of the moisture located in the aspirator, ice will form in the aspirator. However, because the aspirator valve was opened when the engine was shutdown, any ice that forms in the aspirator will not stick the aspirator valve to the body of the aspirator because the aspirator valve is not in contact with the aspirator body because it is in the open position.

Therefore, malfunctioning of the combined valve and aspirator assembly is avoided and the aspirator valve can function correctly as soon as the engine is restarted.

Referring back to box 140, from box 140 the method advances to box 150 to check whether the engine has been restarted that is to say, a key-on event has occurred. If a key-on event has not occurred the method will cycle through boxes 140 and 150 and the aspirator valve will be kept open.

Such an embodiment it particularly advantageous if the apparatus used to move the aspirator valve between its open and closed positions such as an actuator is arranged such that, when there is no input to the aspirator valve, it remains open and the actuator has to apply a force to the aspirator valve in order to close it. Such an aspirator valve is referred to as being a 'normally open valve'. -8 -

This type of valve is advantageous because no power or energy has to be used to keep the aspirator valve open when the engine is shutdown. It is usual in the case of a normally open valve' to use a spring to bias the valve open and use an actuator to power the valve against the action of the spring closed.

Another type of valve is known as a 'normally closed valve' in which the actuator has to provide a force to the aspirator valve to open it and when there is no input to the aspirator valve from the actuator the aspirator valve will be closed by a spring. It will be appreciated that with such a 'normally closed valve' energy is required to keep the valve open.

Therefore, if a method as shown in Fig.1 is to be used with a normally closed type of valve, it is desirable to provide a latch to hold the valve open when it is required to do so thereby obviating the need to keep the valve powered open when there is a risk of icing occurring.

Referring now to Fig.2 there is shown a second embodiment of a method for preventing malfunctioning of a combined valve and aspirator assembly due to icing that is particularly suitable for use with a normally closed type of valve. The terms 'key-on' and key-off' have the same meaning as previously discussed and any suitable type of HMI could be used.

The method starts at box 210 which represents a check to see whether a 'key-on' event has occurred. If a 'key-on' event has not occurred the motor vehicle is in an off state and the method effectively remains in box 210 as indicated by the 'No' arrow from box 210 back to box 210.

However, if when checked in box 210, there has been a key-on' event indicating that the engine has started then _ 9 _ the method moves from box 210 to box 220. In box 220 the aspirator valve is controlled to provide the required vacuum for the brake booster. That is to say, generally speaking, if the vacuum available directly from the engine is high, the aspirator valve will be closed and conversely, if the vacuum available directly from the engine is below that required for the brake booster, the aspirator valve is opened.

From box 220 the method advances to box 230 to check whether a 'key-off' event has occurred indicating that the engine of the motor vehicle is to be stopped. If a 'key-off' event has not occurred the method returns to box 220 and the boxes 220 and 230 will continue to be executed until a 'key-off' event occurs. That is to say, when the engine is running the aspirator valve is controlled in a conventional manner to provide the desired vacuum for the brake booster.

However, if when checked in box 230, a 'key-off' event has occurred then the method advances from box 230 to box 240 where it is checked whether the current ambient temperature (T) is below a first predefined temperature threshold (Tlim) . The value set for the first predefined temperature threshold (Tilm) is a temperature close to the temperature at which freezing of any moisture in the aspirator could be expected to occur. So, for example and without limitation, the value of Inn, could fall within the range of one to ten degrees Celsius. This temperature threshold is provided to prevent the aspirator valve being held open if there is no risk of icing from occurring in the case where a 'normally closed valve' is used.

Referring back to box 240, if when checked in box 240, 35 the current ambient temperature T is greater than the predefined temperature threshold Mint, the method advances from box 240 to box 245 where the aspirator valve is closed -10 -and then returns to box 210 to wait for the next 'key-on' event to occur.

However, if when checked in box 240, the current ambient temperature T is less than the predefined temperature threshold Tt,, the method advances from box 240 to box 250.

In box 250 the aspirator valve is opened and a timer is started. The timer is set such that by the time it expires any ice that is likely to form in the aspirator will have already done so. That is to say, at the end of the period set by the timer, the temperature of the aspirator is likely to be substantially equal to the ambient temperature of the air in which the motor vehicle is located.

Once any ice likely to form in the aspirator has already done so then the aspirator valve can be closed and then the aspirator valve if then closed will simply sit upon any ice that has formed rather than be stuck to the aspirator body by the ice.

Referring back to box 250, the method advances to box 260 to check whether the timer has elapsed or expired and, if the timer has not expired, it returns to box 250 via box 265 with the aspirator valve held open.

However, if when checked in box 260, the timer has lapsed or expired, the method advances to box 270 where the aspirator valve is closed and then returns to box 210 to wait for the next key-on event to occur.

As before, because the aspirator valve is opened at the time an engine shutdown occurs any entrapped moisture in the aspirator will always be in the liquid state because the temperature of the aspirator will always be significantly above zero degrees Celsius and so the aspirator valve cannot become stuck to the body of the aspirator.

By keeping the aspirator valve open during a period of time following the engine shutdown allows ice to form in the aspirator without producing a bridge between the aspirator valve and the body of the aspirator. Therefore the aspirator valve will not become stuck to the aspirator body causing a malfunction when the engine is eventually restarted.

It will be appreciated that the temperature check in box 240 need not be used and in such a case the method would advance directly from box 230 to box 250 and would then continue as described above.

Referring now to Figs.3 and 4 there is shown a motor vehicle 1 having an engine 6 and a vacuum assisted braking system.

Ambient air is admitted to an induction system 3 for the engine 6 via an inlet 2 as indicated by the arrow 'A'. The inlet 2 may included an air filter to remove particulate matter from the air entering the induction system 3.

The induction system 3 comprises a first part 3u located upstream from a throttle valve 4 and a second part 3d located downstream from the throttle valve 4.

A combined valve and aspirator assembly 10 comprises an aspirator valve 11 and an aspirator 12.

-12 -The aspirator 12 has an inlet end 12i connected to the first part 3u of the induction system 3 at a position upstream from the throttle valve 4 via a first conduit 7 and an outlet end 12o connected via second conduit 8 to the second part 3d of the induction system 3 at a position downstream from the throttle valve 4 and upstream from an inlet manifold 5 of the engine 6.

The aspirator 12 has a vacuum inlet 12s connected via a first one way valve 13 to a low pressure side 15LP of a vacuum brake booster 15. The vacuum brake booster 15 also includes a diaphragm 15d separating the low pressure side 15LP from a high pressure side 15HP of the brake booster 15. Air at atmospheric pressure is admitted to the high pressure side 15HP of the brake booster 15 as indicated by the arrow a'.

A mechanical input is provided to the brake booster 15 from a brake pedal 16 when the brake pedal is depressed by a driver of the motor vehicle 1. When the brake pedal 16 is depressed hydraulic fluid at pressure is supplied from a master cylinder (not shown) forming part the brake booster 15 to a number of brake callipers 18 to effect braking of the vehicle 1.

A bypass conduit 9 bypasses the first one way valve 13 and includes a second one-way valve 14. The non-return valves 13, 14 prevent vacuum from being drawn back from the inlet manifold 5 when the pressure in the low pressure side 15LP of the brake booster 15 is below the pressure in the inlet manifold 5. That is to say, flow from the inlet manifold 5 to the low pressure side 15LP is prevented when the vacuum in the low pressure side 15LP is greater than the vacuum in the inlet manifold 5.

The bypass conduit 9 is connected at one end at a position between the first one way valve 13 and the low -13 -pressure side 15LP and is at an opposite end to the second part 3d of the induction system 3 at a position between the throttle valve 4 and the inlet manifold 5.

Opening and closing of the aspirator valve 11 is controlled by a controller 20. The controller 20 can be a single unit such as a powertrain control module or could be two or more interconnected units or modules operable in combination to effect control of the aspirator valve 11.

The controller 20 receives, in the case of this example, an input from a pressure sensor 17 used to sense the magnitude of the vacuum subsisting in the low pressure side 15LP of the brake booster 15. Opening and closing of the aspirator valve 11 during normal running of the engine 6 is based at least in part on the magnitude of the pressure sensed to be present in the low pressure side 15LP of the brake booster 15 by the pressure sensor 17. It will be appreciated that in other examples the vacuum subsisting in the low pressure side 15LP of the brake booster 15 could be modelled and not directly sensed.

The controller 20 may directly control the aspirator valve 11 or may provide a signal to a separate unit (not shown) to control the medium used to control the opening and closing of the aspirator valve 11. For example and without limitation, the controller 20 may control a valve used to control the flow of pneumatic pressure or hydraulic pressure to the aspirator valve 11 or supply a control signal to an electrical power supply or electric power amplifier.

A human machine interface 19 is provided to switch 'on' and switch 'off' the major electric circuits of the motor vehicle 1 and to control starting and stopping of the engine 6.

-14 -With particular reference to Fig.3, the combined valve and aspirator assembly 10 comprises the aspirator valve 11 and the aspirator 12 that are coupled together to form the combined valve and aspirator assembly 10.

The aspirator valve 11 comprises a body lib in which is mounted an actuator lla used to move a valve element in the form of a pintle valve 11p. It will be appreciated that the invention is not limited to aspirator valves using a pintle valve. In the case of this example the aspirator valve 11 is a normally closed valve and is opened by the application of pneumatic pressure via an inlet port 11c. However, it will be appreciated that the invention is not limited to the use of a normally closed aspirator valve or to the type of actuator used for the aspirator valve 11. For example, the actuator could be an electrical actuator such as a solenoid valve or a hydraulic actuator.

The aspirator 12 has a body 12b defining a venturi 12v through which in use air flows in the direction indicated by the arrow 'f'. The venturi 12v extends along a longitudinal axis X-X that is shown horizontally disposed in Fig.3. It will be appreciated that, if the longitudinal axis X-X were to be inclined relative to horizontal, then this would assist with the draining of moisture from the venturi 12v of the aspirator 12 after a key-off event has occurred.

An aperture 12a in the aspirator body 12b provides a connection between the venturi 12v and a vacuum inlet 12s.

The aspirator 12 is conventional in construction and operation. The flow of air through the venturi 12v causes the pressure in the region of smallest diameter to drop thereby drawing air out from the low pressure side 15LP of the brake booster 15 via the first one way valve 13 and into the aspirator 12 through the vacuum inlet 12s, as indicated -15 -by the arrow 's'. The air is then drawn via the aperture 12a into the venturi 12v.

During normal operation of the engine 6, the controller 20 controls the aspirator valve 11 so as to move the pintle valve lip between a position in which it is engaged with the aperture 12a in the body 12b of the aspirator 12, as shown in figure 2 that is referred to as an aspirator valve closed' position to a position in which the pintle valve llp does not obstruct the flow of air through the aperture 12a into the venturi 12v referred to as an aspirator valve open' position. As is well known in the art, generally speaking, the aspirator valve 11 is moved to the open position when the magnitude of the vacuum in the inlet manifold 5 is less than that required for the low pressure side 15LP of the brake booster 15 and is moved to the closed position when the magnitude of the vacuum in the inlet manifold 5 is sufficient for the low pressure side 15LP of the brake booster 15.

When the aspirator valve 11 is open, approximately 40% of the air entering the inlet manifold 5 has passed through the aspirator 12 and so controlling the opening and closing of the aspirator valve 11 by the controller 20 has to be managed so as to prevent it adversely affecting engine throttle control by, for example, producing an unrequested increase in torque generation. It will be appreciated that in other examples the amount of air flowing through the aspirator could be more than or less than 40% of the air entering the inlet manifold 5.

During normal running of the engine 6 the operation of the combined valve and aspirator assembly 10 therefore follows conventional practice.

However, when the engine 6 is to be shutdown in a situation where the motor vehicle 1 is operating in a very -16 -low ambient temperature likely to produce icing in the venturi 12v of the aspirator 12 after engine shut-off, the controller 20 is programmed to open the aspirator valve 11 so as to prevent ice forming around the pintle valve lip between it and the aspirator body 12b where it might collect in the venturi 12v. In the aspirator valve open position there is no contact between the tip of the pintle valve llp and the aspirator body 12b because it is disengaged from the aperture 12a in the aspirator body 12b.

Therefore, when the engine 6 is restarted, there is no risk of the aspirator valve 11 malfunctioning due to ice sticking or bonding the pintle valve lip to the aspirator body 12b. This is important because it is often the case that following an engine start-up (a 'key-on' event) there is a need for replenishing of the vacuum in the low pressure side 15LP of the brake booster 15 but the magnitude of vacuum available from the engine 6 is insufficient to achieve this. Therefore, immediately following start-up of the engine 6, the aspirator valve 11 is often required to be open. However, if the pintle valve lip is stuck to the aspirator body 12b in the closed position by a build up of ice, it cannot be opened and so malfunctioning of the aspirator valve 11 will occur. Such malfunctioning of the aspirator valve may result in the driver experiencing a heavy brake pedal if there is a need to apply the brakes shortly after a 'key-on' event has occurred.

In the case where a normally closed aspirator valve is used, the controller 20 may be arranged to only hold the aspirator valve 11 open for a period of time after the engine is shut-down. That is to say, after a 'key-off' event has occurred, the aspirator valve 11 is held open for a sufficient period of time to ensure that any ice that is likely to form in the venturi 12v of the aspirator 12 has already done so. Therefore, when the pintle valve lip is then closed it will simply sit on the ice and will not -17 -become embedded in the ice causing it to stick to the body 12b of the aspirator 12.

By using such a time delay will reduce the amount of power that is consumed compared to a situation where the valve remains open for the entire period of time that the engine is shut-off, which could be a period of several weeks.

In addition, the opening of the aspirator valve 11 may only be permitted if the ambient temperature is low enough that icing could be reasonably expected to occur. For example, if the ambient temperature is below five degrees Celsius when the engine 6 is shut-down then there is a risk that icing may occur. Therefore, whenever the ambient temperature is below approximately 10 degrees Celsius when a key-off' event occurs, the aspirator valve 11 is opened by the controller 20 but, if the temperature is above 10 degrees Celsius, the aspirator valve 11 is not opened as there is only a low risk of icing from occurring. Once again, by using such a temperature limit, reduces the risk of unnecessarily using power to keep the aspirator valve 11 open in circumstances when icing is not likely to occur.

Although not shown in Figs.3 and 4 a heating device may be incorporated as part of the combined valve and aspirator assembly 10.

The heater could comprise a positive temperature coefficient device attached to the aspirator body 12b to warm the aspirator body 12b and/or a heater element either attached to or formed as part of the aspirator valve 11 such, for example, a resistive or positive temperature device formed in or included as part of the pintle valve 11p.

-18 -The use of a heating device is particularly useful in very low temperatures such as, for example, below minus 10°C where there is a risk of icing even after the engine has started if the aspirator valve is kept closed due to the time it takes for the aspirator to warm up. In such a case the heater is switched on when a 'key-on event' occurs and is kept on until the risk of icing has abated.

The heating device is preferably only switched on if the ambient temperature is below a second predefined temperature threshold such as, for example, minus 10°C where there is a risk of aspirator icing after the engine has been started.

The second predefined temperature threshold is lower than the first predefined temperature threshold used to determine whether to open the aspirator valve.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

-19 -Claims 1. A method for preventing the malfunctioning of a combined valve and aspirator assembly of a motor vehicle having an engine due to icing up of a valve forming part of the combined valve and aspirator assembly wherein the method comprises when a key-off event occurs indicating that the engine of the motor vehicle is to be shutdown, opening the valve so as to permit liquid to drain from the aspirator.
2. A method as claimed in claim 1 wherein the method further comprises mounting the aspirator at an angle with respect to horizontal so as to improve draining of liquid from the aspirator.
3. A method as claimed in claim 1 or in claim 2 wherein the valve is a normally closed valve that is urged into an open position by the action of an actuator and the method further comprises activating the actuator when a key-off event occurs.
4. A method as claimed in claim 3 wherein the method further comprises only opening the valve if the ambient temperature is less than a first predefined temperature 25 threshold.
5. A method as claimed in any of claims 1 to 4 wherein the method further comprises, when a key-off event occurs, opening the valve for a predefined period of time so as to permit liquid to drain from the aspirator and then, when the period of time has elapsed, closing the valve.
6. A method as claimed in claim 1 or in claim 2 wherein the valve is a normally open valve that is urged into a closed position by the action of an actuator and the method further comprises deactivating the actuator when a key-off event occurs.

-20 -
7. A method as claimed in any of claims 1 to 6 wherein the method further comprises applying heat to the aspirator when a key-on event occurs.
8. A method as claimed in claim 7 wherein the method further comprises only applying heat to the aspirator if the ambient temperature is below a second predefined temperature threshold.
9. A method as claimed in any of claims 1 to 8 wherein the method further comprises applying heat to a valve element of the valve when a key-on event occurs.
10. A method as claimed in claim 9 wherein the method further comprises only applying heat to the valve element if the ambient temperature is below a second predefined temperature threshold.
11. A motor vehicle having an engine, a human machine interface to switch on and switch off the engine and a vacuum boosted braking system including a combined valve and aspirator assembly and a controller for controlling the opening and closing of a valve of the combined valve and aspirator assembly wherein the controller is operable to open the valve so as to permit liquid to drain from the aspirator when operation of the human machine interface indicates that the engine of the motor vehicle is to be shutdown.
12. A motor vehicle as claimed in claim 11 wherein the aspirator is mounted at an angle with respect to horizontal so as to improve draining of liquid from the aspirator.
13. A motor vehicle as claimed in claim 11 or in claim 12 wherein the valve comprises a valve element and an actuator to move the valve element between open and closed -21 -positions and the valve element is in a closed position when the actuator is deactivated and is urged into an open position by activation of the actuator and the controller is operable to activate the actuator when the engine of the motor vehicle is to be shutdown.
14. A motor vehicle as claimed in claim 13 wherein the valve is only opened if the ambient temperature is less than a first predefined threshold.
15. A motor vehicle as claimed in any of claims 11 to 14 wherein, when the engine of the motor vehicle is to be shutdown, the controller is operable to open the valve for a predefined period of time so as to permit liquid to drain from the aspirator and then, after expiry of the predefined period of time, is further operable to close the valve.
16. A motor vehicle as claimed in claim 12 or in claim 13 wherein the valve comprises a valve element and an actuator to move the valve element between open and closed positions and the valve element is in a open position when the actuator is deactivated and is urged into a closed position by activation of the actuator and the controller is operable to deactivate the actuator when the engine of the motor vehicle is to be shutdown.
17. A motor vehicle as claimed in any of claims 11 to 16 wherein the aspirator includes a heater and the controller is operable to use the heater to apply heat to the aspirator when the engine is to be started.
18. A motor vehicle as claimed in claim 13 or in claim 16 wherein a valve element heater is provided for the valve element of the valve and the controller is operable to use the valve element heater to apply heat to the valve element when the engine is to be started.

-22 -
19. A method for preventing the malfunctioning of a combined valve and aspirator assembly of a motor vehicle having an engine substantially as described herein with reference to the accompanying drawing.
20. A motor vehicle substantially as described herein with reference to the accompanying drawing.Amendments to the claims have been filed as follows: Claims 1. A method for preventing the malfunctioning of a combined valve and aspirator assembly of a motor vehicle having an engine due to icing up of a valve forming part of the combined valve and aspirator assembly wherein the method comprises mounting the aspirator at an angle with respect to horizontal so as to improve draining of liquid from the aspirator and, when a key-off event occurs indicating that the engine of the motor vehicle is to be shutdown, opening the valve so as to permit liquid to drain from the aspirator.2. A method as claimed in claim 1 wherein the valve is a normally closed valve that is urged into an open LC) position by the action of an actuator and the method further comprises activating the actuator when a key-off event a) occurs.O3. A method as claimed in claim 2 wherein the method further comprises only opening the valve if the ambient temperature is less than a first predefined temperature threshold.4. A method as claimed in any of claims 1 to 3 wherein the method further comprises, when a key-off event occurs, opening the valve for a predefined period of time so as to permit liquid to drain from the aspirator and then, when the period of time has elapsed, closing the valve.5. A method as claimed in claim 1 wherein the valve is a normally open valve that is urged into a closed position by the action of an actuator and the method further comprises deactivating the actuator when a key-off event 35 occurs.6. A method as claimed in any of claims 1 to 5 wherein the method further comprises applying heat to the aspirator when a key-on event occurs.7. A method as claimed in claim 6 wherein the method further comprises only applying heat to the aspirator if the ambient temperature is below a second predefined temperature threshold.8. A method as claimed in any of claims 1 to 7 wherein the method further comprises applying heat to a valve element of the valve when a key-on event occurs.9. A method as claimed in claim 8 wherein the method further comprises only applying heat to the valve element if LC) the ambient temperature is below a second predefined 1-- temperature threshold. C)CD 10. A motor vehicle having an engine, a human machine 1-- 20 interface to switch on and switch off the engine and a 1-- vacuum boosted braking system including a combined valve and aspirator assembly and a controller for controlling the opening and closing of a valve of the combined valve and aspirator assembly wherein the aspirator is mounted at an angle with respect to horizontal so as to improve draining of liquid from the aspirator and the controller is operable to open the valve so as to permit liquid to drain from the aspirator when operation of the human machine interface indicates that the engine of the motor vehicle is to be shutdown.11. A motor vehicle as claimed in claim 10 wherein the valve comprises a valve element and an actuator to move the valve element between open and closed positions and the valve element is in a closed position when the actuator is deactivated and is urged into an open position by activation of the actuator and the controller is operable to activate the actuator when the engine of the motor vehicle is to be shutdown.12. A motor vehicle as claimed in claim 11 wherein the 5 valve is only opened if the ambient temperature is less than a first predefined threshold.13. A motor vehicle as claimed in any of claims 10 to 12 wherein, when the engine of the motor vehicle is to be shutdown, the controller is operable to open the valve for a predefined period of time so as to permit liquid to drain from the aspirator and then, after expiry of the predefined period of time, is further operable to close the valve.14. A motor vehicle as claimed in claim 10 wherein the LC) valve comprises a valve element and an actuator to move the valve element between open and closed positions and the W valve element is in a open position when the actuator is deactivated and is urged into a closed position by activation of the actuator and the controller is operable to -- deactivate the actuator when the engine of the motor vehicle is to be shutdown.15. A motor vehicle as claimed in any of claims 10 to 14 wherein the aspirator includes a heater and the controller is operable to use the heater to apply heat to the aspirator when the engine is to be started.16. A motor vehicle as claimed in claim 11 or in claim 14 wherein a valve element heater is provided for the valve element of the valve and the controller is operable to use the valve element heater to apply heat to the valve element when the engine is to be started.17. A method for preventing the malfunctioning of a combined valve and aspirator assembly of a motor vehicle having an engine substantially as described herein with reference to the accompanying drawing.18. A motor vehicle substantially as described herein 5 with reference to the accompanying drawing.