ACTUATOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of US Patent application number 62/694,158, filed on July 5, 2018, the contents of which are incorporated herein by reference in their entirety.

FIELD

[0002] The specification relates generally to pneumatic actuators and systems. In particular, the following relates to a vacuum actuator for a vacuum pump. BACKGROUND OF THE DISCLOSURE

[0003] It is known in the automotive industry to provide vacuum systems for various uses, such as providing power for a brake booster, the operation of a turbo waste gate, and other functions. In some applications, a vacuum actuator is used to mechanically initiate operation of a vacuum pump when the vacuum level in the vacuum system is too low (i.e. when the pressure in the vacuum system is too high such that there is not enough vacuum to generate the force needed for operation of the intended device). The vacuum actuator typically includes a diaphragm in a housing, wherein a spring urges the diaphragm in one direction. An actuator arm is connected to the diaphragm. The amount of vacuum present on one side of the diaphragm dictates whether the diaphragm overcomes the spring and moves the actuator to a new position. A problem with typical vacuum actuators is that they tend to dither when the pressure is very close to the pressure that triggers their actuation, causing them to repeatedly activate and deactivate the vacuum pump. To solve the dithering problem, some vacuum pumps have been fitted with solenoids that are operated by an ECU that reads pressure in the vacuum system via a pressure sensor. However, such solutions can be expensive and add to the complexity of the vehicle’s vacuum system. It would be desirable to provide a vacuum actuator that is relatively simple, and inexpensive, that avoids the use of electronics, but which solves the dithering problem incurred by typical vacuum actuators.

SUMMARY OF THE DISCLOSURE [0004] Broadly, in some aspects, the present disclosure relates to a pneumatic actuator and a pneumatic system. In some aspects, the pneumatic actuator is a vacuum actuator, and the pneumatic system is a vacuum system.

[0005] In one aspect, there is provided a vacuum actuator for use in a vehicular vacuum system, which includes an actuator housing, an actuator output member, an inter-chamber valve member, a first membrane, a second membrane, a first membrane biasing member, and a second membrane biasing member. The actuator housing includes a first chamber and a second chamber. The first chamber is fluidically connectable to a first vacuum source to provide the first chamber with a first chamber pressure. The second chamber is fluidically connectable to the first vacuum source through a second chamber feed conduit. The second chamber has a second chamber pressure. The actuator output member is movable relative to the actuator housing between a first output member position and a second output member position. The inter-chamber valve member is movable between a closed position in which the inter-chamber valve member prevents fluid communication between the first and second chambers, and an open position in which the inter-chamber valve member permits fluid communication between the first and second chambers. The first membrane acts as a wall of the first chamber, such that a first side of the first membrane is exposed to the first chamber pressure, and a second side of the first membrane is exposed to a first membrane exterior pressure. The first membrane is connected to the inter-chamber valve member. The second membrane acts as a wall of the second chamber, such that a first side of the second membrane is exposed to the second chamber pressure, and a second side of the second membrane is exposed to a second membrane exterior pressure. The second membrane is connected to the actuator output member. The first membrane biasing member is positioned to apply a first biasing force to urge the inter-chamber valve member towards the closed position. The first membrane is movable by differential pressure thereacross against the first biasing force when the first chamber pressure is less than a first selected pressure to move the inter-chamber valve member from the closed position to the open position. The second membrane biasing member is positioned to apply a second biasing force to urge the actuator output member towards the second output member position. The second membrane is movable by differential pressure thereacross against the second biasing force when the second chamber pressure is less than a second selected pressure to move the actuator output member from the second position to the first position. The first selected pressure is less than the second selected pressure. The first vacuum source has a first volume and the second chamber has a second volume, wherein the first volume and second volume are sized relative to one another such that, reduction of the first chamber pressure to less than the first selected pressure causes movement of the first membrane to move the inter-chamber valve member from the closed position to the open position, which exposes the second chamber to the first chamber, thereby reducing the second chamber pressure to below the second selected pressure.

[0006] In another aspect, a vehicular vacuum system is provided and includes a first vacuum source that is at less than ambient air pressure outside the vehicular vacuum system, a vacuum load that is operated using the first vacuum source, thereby increasing pressure in the first vacuum source, a vacuum pump that is fluidically connected to the first vacuum source and which is operable to decrease pressure in the first vacuum source, and a vacuum actuator. The vacuum actuator includes an actuator housing including a first chamber and a second chamber, an actuator output member, an inter-chamber valve member. The first chamber is fluidically connectable to a first vacuum source to provide the first chamber with a first chamber pressure, wherein the second chamber is fluidically connectable to the first vacuum source through a second chamber feed conduit, and wherein the second chamber has a second chamber pressure, a first membrane, a second membrane, a first membrane biasing member and a second membrane biasing member. The actuator output member is movable relative to the actuator housing between a first output member position and a second output member position. The actuator output member is connected to a clutch that controls a connection between a rotor of the vacuum pump and a rotor drive source for driving operation of the rotor, such that movement of the actuator output member to the second output member position connects the rotor drive source to the rotor through the clutch so as to drive the rotor to reduce pressure in the first vacuum source, and such that movement of the actuator output member to the first output member position disconnects the rotor drive source from the rotor to stop driving the rotor. The inter-chamber valve member is movable between a closed position in which the inter-chamber valve member prevents fluid communication between the first and second chambers, and an open position in which the inter-chamber valve member permits fluid communication between the first and second chambers. The first membrane that acts as a wall of the first chamber, such that a first side of the first membrane is exposed to the first chamber pressure, and a second side of the first membrane is exposed to a first membrane exterior pressure, wherein the first membrane is connected to the inter-chamber valve member. The second membrane acts as a wall of the second chamber, such that a first side of the second membrane is exposed to the second chamber pressure, and a second side of the second membrane is exposed to a second membrane exterior pressure. The second membrane is connected to the actuator output member. The first membrane biasing member is positioned to apply a first biasing force to urge the inter-chamber valve member towards the closed position. The first membrane is movable by differential pressure thereacross against the first biasing force when the first chamber pressure is less than a first selected pressure to move the inter- chamber valve member from the closed position to the open position. The second membrane biasing member is positioned to apply a second biasing force to urge the actuator output member towards the second output member position. The second membrane is movable by differential pressure thereacross against the second biasing force when the second chamber pressure is less than a second selected pressure to move the actuator output member from the second position to the first position. The first selected pressure is less than the second selected pressure. The first vacuum source has a first volume and the second chamber has a second volume, wherein the first volume and second volume are sized relative to one another such that, reduction of the first chamber pressure to less than the first selected pressure causes movement of the first membrane to move the inter- chamber valve member from the closed position to the open position, which exposes the second chamber to the first chamber, thereby reducing the second chamber pressure to below the second selected pressure. [0007] In yet another aspect, a vacuum actuator is provided, for use in a vehicular vacuum system, and includes an actuator housing, an actuator output member, a first membrane, a second membrane, a first membrane biasing member, and a second membrane biasing member. The actuator housing includes a first chamber and a second chamber, wherein the first chamber is at a first chamber pressure. The second chamber has a second chamber pressure. The actuator output member is movable relative to the actuator housing between a first output member position and a second output member position. The first membrane acts as a wall of the first chamber, such that a first side of the first membrane is exposed to the first chamber pressure, and a second side of the first membrane is exposed to a first membrane exterior pressure. The first membrane is operatively connected to the actuator member for movement of the actuator output member to the first output member position. The second membrane acts as a wall of the second chamber, such that a first side of the second membrane is exposed to the second chamber pressure, and a second side of the second membrane is exposed to a second membrane exterior pressure. The second membrane is operatively connected to the actuator output member for movement of the actuator output member to the second output member position. The first membrane biasing member is positioned to apply a first biasing force to the first membrane. The first membrane is movable by differential pressure thereacross against the first biasing force when the first chamber pressure is less than a first selected pressure to cause movement of the actuator output member from the second output member position to the first output member position. The second membrane biasing member that is positioned to apply a second biasing force to the second membrane and the actuator output member to urge the output member towards the second output member position. The second membrane is movable by differential pressure thereacross against the second biasing force when the second chamber pressure is less than a second selected pressure to move the actuator output member from the second position to the first position. The first selected pressure is less than the second selected pressure. The first biasing member has a first spring rate that is determinative of the first selected pressure, and the second biasing member has a second spring rate that is determinative of the second selected pressure. [0008] Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0009] For a better understanding of the embodiment(s) described herein and to show more clearly how the embodiment(s) may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

[0010] Figure 1 is a schematic view of a vehicular engine that includes a vacuum pump in accordance with v embodiment of the present disclosure;

[0011] Figure 2 is a schematic diagram showing various components of a vacuum system that includes the vacuum pump and a vacuum actuator for the vacuum pump with a clutch in a disengaged state;

[0012] Figure 2A is a schematic diagram showing the vacuum pump and the actuator for the vacuum pump with a clutch in an engaged state;

[0013] Figure 3 is a sectional perspective view of the actuator shown in Figure 2; [0014] Figure 4 is a sectional side view of part of the vacuum system including the actuator shown in Figure 2 in a first state;

[0015] Figure 5 is a sectional side view of part of the vacuum system including the actuator shown in Figure 2 in a second state;

[0016] Figure 6 is a sectional side view of part of the vacuum system including the actuator shown in Figure 2 in a third state;

[0017] Figure 7 is a sectional side view of part of the vacuum system including the actuator shown in Figure 2 in a fourth state; and

[0018] Figure 8 is a sectional side view of part of the vacuum system including the actuator shown in Figure 2 in a fifth state. [0019] Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0020] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiment or embodiments described herein. Flowever, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0021] Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise:“or” as used throughout is inclusive, as though written“and/or”; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns so that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender;“exemplary” should be understood as“illustrative” or“exemplifying” and not necessarily as“preferred” over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description.

[0022] Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document,“each” refers to each member of a set or each member of a subset of a set.

[0023] The present disclosure related, in one aspect, to a vacuum actuator 36 that can be connected, for example to a clutch for a vacuum pump or to some other device. In some embodiments, the vacuum actuator 36 operates more stably between one actuation state and another, does not suffer from dithering the way that other, typical vacuum actuators of the prior art do. Additionally, the vacuum actuator 36 achieves this stability without the need for electronic solenoids, which have been used in the past on traditional prior art vacuum actuators in order to address the dithering problem. Furthermore, in some embodiments, the vacuum actuator 36 is capable of having a selectable pressure at which it moves to one actuation state and another selectable pressure at which it moves to another actuation state by means of selecting two springs that are determinative of the pressures needed to move it between its actuation states.

[0024] Reference is made to Figure 1 , which is a schematic view of a vehicular engine 10. The engine 10 includes a crankshaft 12 that drives one or more camshafts 14 via an endless drive member 16, which may be, for example, a timing belt or a timing chain. The camshaft 14 is shown with two cams 18 thereon, for illustrative purposes only. It will be understood that the actual number of cams 18 on the camshaft 14 will depend on the number of cylinders the engine has, the number of valves per cylinder and the total number of camshafts being employed to control the opening and closing of the valves, as well as other possible factors. The engine 10 is shown in a simplified format for the purposes of avoiding extraneous detail.

[0025] Figures 1 and 2 show (in schematic form) a vacuum pump 22. The vacuum pump 22 may be any suitable type of vacuum pump such as a rotary vane vacuum pump. An example of a vacuum pump that would be suitable for the vacuum pump 22 is shown and described in PCT publication WO2018137045, the contents of which are incorporated herein by reference in their entirety. The vacuum pump 22 is part of a vacuum system 24 that may be used to for a number of purposes within the vehicle. For example, the vacuum system 24 may be used for providing power to a vacuum-powered device 25 such as a brake booster, or for the operation of a turbo wastegate (in vehicles equipped with a turbo), or for any other suitable purpose. The vacuum-powered device 25 may be referred to as a vacuum load 25.

[0026] Figure 2 further shows a clutch 26 that controls a connection between a rotor 28 of the vacuum pump 22 and a rotor drive source for driving operation of the rotor 28. In the present example, the rotor drive source is the aforementioned one of the one or more camshafts 14, however the rotor drive source could alternatively be any other suitable source of power for the rotor 28.

[0027] The clutch 26 may be any suitable type of clutch. For example, the clutch 26 shown schematically in the present figures is a friction plate clutch. Alternatively (and preferably) the clutch 26 may be a wrap spring clutch as is disclosed in WO2018137045.

[0028] The vacuum system 24 further includes a first vacuum source 30 that is at a pressure P1 , which may initially be equal to or less than ambient air pressure outside the vehicular vacuum system 24. The ambient air pressure is shown at P3. The first vacuum source 30 may include a vacuum reservoir 32 and one or more vacuum conduits 34 (or portions thereof) that make up part of the vacuum system 24 and that are in fluid communication with the vacuum reservoir 32. For example, in the present embodiment, the first vacuum source 30 includes at least portions of the vacuum conduits shown individually at 34a, 34b, 34c and 34d.

[0029] The vacuum load 25 is fluidically connectable to the first vacuum source 30 via the vacuum conduit 34d, and is operated using the first vacuum source 30, which consumes vacuum, thereby increasing pressure in the first vacuum source 30. As can be seen, the vacuum pump 22 is in fluid communication with the first vacuum source 30 and is operable to decrease pressure in the first vacuum source 30 (i.e. to draw vacuum in the first vacuum source 30). [0030] A vacuum actuator 36 is provided and includes an actuator housing 38 including a first chamber 40 and a second chamber 42, shown more clearly in Figure 3. The vacuum actuator 36 further includes an actuator output member 44, an inter-chamber valve member 46, a first membrane 48, a second membrane 50, a first membrane biasing member 52, and a second membrane biasing member 54. [0031] The first chamber 40 is fluidically connected to the first vacuum source 30 (via the vacuum conduit 34a) to provide the first chamber 40 with a first chamber pressure, which is the pressure P1. The first chamber 40 is defined between an interior dividing wall 56 of the actuator housing 38, an exterior wall 58 of the actuator housing 38 (which in the present example is the first portion 38a of the actuator housing 38), and the first membrane 48.

[0032] The second chamber 42 is fluidically connectable to the first vacuum source 30 through a second chamber feed conduit, which is the vacuum conduit 34c. The second chamber 42 is defined between the interior dividing wall 56, the exterior wall 58, and the second membrane 50. The second chamber 42 has a second chamber pressure P2. [0033] The first membrane 48 may be sealingly connected to the actuator housing 38 in any suitable way. For example, the first membrane 48 may be clamped between a first portion 38a of the actuator housing 38 and a second portion 38b of the actuator housing 38. The second membrane 50 may also be sealingly connected to the actuator housing 38 in any suitable way. For example, the second membrane 50 may be clamped between the first portion 38a of the actuator housing 38 and a third portion 38c of the actuator housing 38. The first and second membranes 48 and 50 may be made out of any suitable material that is known to one skilled in the art for use in vacuum actuators.

[0034] The actuator output member 44 is movable relative to the actuator housing 38 between a first output member position (shown in Figure 2) and a second output member position (shown in Figure 2A). The actuator output member 44 is connected to the clutch 26, such that movement of the actuator output member 44 to the second output member position connects the rotor drive source (e.g. the camshaft 14) to the rotor 28 through the clutch 26 so as to drive the rotor 28 to reduce pressure in the first vacuum source 30, and such that movement of the actuator output member 44 to the first output member position disconnects the rotor drive source 44 from the rotor 28 to stop driving the rotor 28.

[0035] The actuator output member 44 may have any suitable structure. In the figures, the actuator output member 44 is an actuator arm, and the first output member position is a retracted position of the actuator arm relative to the actuator housing and the second output member position is an extended position of the actuator arm relative to the actuator housing, in which the actuator arm extends further out from the actuator housing than in the retracted position.

[0036] The first membrane 48 acts as a wall of the first chamber 40, such that a first side 60 of the first membrane 48 is exposed to the first chamber pressure P1 , and a second side 62 of the first membrane 48 is exposed to a first membrane exterior pressure. In the example embodiment shown, the first membrane exterior pressure is the ambient air pressure P3, however, in an alternative embodiment that is not shown it could be any other suitable pressure such as a pressure in an additional portion of the actuator housing 38 that is isolated from the ambient environment outside the vacuum actuator 36. [0037] The first membrane 48 is connected to the inter-chamber valve member 46.

Thus, movement of the first membrane 48 drives movement of the inter-chamber valve member 46. The inter-chamber valve member 46 is movable between a closed position in which the inter-chamber valve member 46 prevents fluid communication between the first and second chambers 40 and 42, and an open position in which the inter-chamber valve member 46 permits fluid communication between the first and second chambers 40 and 42.

[0038] In the example embodiment shown in the figures, the inter-chamber valve member 46 includes a piston 46a in the second chamber 42, and a connecting arm 46b that extends through an aperture in the interior dividing wall 56 from the piston 46a to the first membrane 48 in the first chamber 40. Prevention of air flow past the inter-chamber valve member 46 when it is in the closed position may be achieved in any suitable way, such as by an o-ring 57 on a trailing surface of the piston 46a, which seals against the interior dividing wall 56. When the piston is moved away from the interior dividing wall 56, air can flow around the piston 46a and through the aperture in the interior dividing wall 56 around the connecting arm 46b, so as to provide fluid communication between the second chamber 42 and the first chamber 40.

[0039] The second membrane 50 acts as a wall of the second chamber 42, such that a first side 64 of the second membrane 50 is exposed to the second chamber pressure P2, and a second side 66 of the second membrane 50 is exposed to a second membrane exterior pressure. In the example embodiment shown, the second membrane exterior pressure is the ambient air pressure P3, however, in an alternative embodiment that is not shown it could be any other suitable pressure such as a pressure in an additional portion of the actuator housing 38 that is isolated from the ambient environment outside the vacuum actuator 36. [0040] The second membrane 50 is connected to the actuator output member 44. Thus, movement of the second membrane 50 drives movement of the actuator output member 44 between the first and second output member positions.

[0041] The first membrane biasing member 52 is positioned to apply a first biasing force to urge the inter-chamber valve member 46 towards the closed position . The first membrane is movable by differential pressure thereacross against the first biasing force when the first chamber pressure P1 is less than a first selected pressure to move the inter-chamber valve member 46 from the closed position to the open position.

[0042] The second membrane biasing member 54 is positioned to apply a second biasing force F2 to urge the actuator output member 44 towards the second output member position. The second membrane 50 is movable by differential pressure thereacross against the second biasing force when the second chamber pressure P2 is less than a second selected pressure to move the actuator output member 44 from the second position to the first position. In some embodiments, the first selected pressure is less than the second selected pressure. [0043] The first vacuum source 30 has a first volume and the second chamber has a second volume. The first volume and second volume are sized relative to one another such that, reduction of the first chamber pressure P1 to less than the first selected pressure causes movement of the first membrane 48 to move the inter-chamber valve member 46 from the closed position to the open position, which exposes the second chamber 42 fluidically to the first chamber 40, thereby reducing the second chamber pressure P2 to below the second selected pressure.

[0044] A check valve 68 is present in the second chamber feed conduit 34c which prevents air flow from the second chamber 42 to the first vacuum source 40 through the second chamber feed conduit 34c in instances when the second chamber pressure P2 is higher than the first chamber pressure P1 , but permits air flow from the first chamber 40 to the second chamber 42 through the second chamber feed conduit 34c in instances when the first chamber pressure P1 is higher than the second chamber pressure P2. The check valve 68 may be any suitable kind of check valve.

[0045] Operation of the vacuum system 24 will now be described with reference to Figures 4-8, and with reference back to Figures 2 and 2A. Figure 4 shows the vacuum actuator 36 in an initial state when the vehicle is off and all the pressures, namely P1 , P2 and the first and second membrane external pressures are equal to one another. As a result of the equality of these pressures, the first and second membrane biasing members 52 and 54 keep the inter-chamber valve member 46 in the closed position and the actuator output member 44 in the second position, which engages the clutch 26 as shown in Figure 2A, thereby operatively connecting the rotor drive source (the camshaft 14) with the rotor 28 of the vacuum pump 22. As a result of the operative connection, the vacuum pump 22 operates to reduce the pressure P1. During this reduction in the first chamber pressure P1 , the inter-chamber valve member 46 remains in the closed position and the check valve 68 prevents air flow from the second chamber 42 through the second chamber feed conduit 34c, thereby preventing the second chamber pressure P2 from equalizing with the first chamber pressure P1.

[0046] After a period of time of operation, the first chamber pressure P1 drops to below the first selected pressure and the first membrane external pressure (e.g. pressure P3) overcomes the first chamber pressure P1 plus the first biasing force of the first membrane biasing member 52, and the first membrane 48 moves to drive the inter-chamber valve member 36 to the open position as shown in Figure 5.

[0047] Once the inter-chamber valve member 36 is in the open position the second chamber 42 is in fluid communication with the first chamber 40 and so the second chamber pressure P2 drops towards the first chamber pressure P1 until the first and second chamber pressures P1 and P2 reach an equilibrium that is based on the size of the first volume V1 as compared to the second volume V2. As noted above, the drop in the second chamber pressure P2 is sufficient to bring the second chamber pressure P2 to significantly below the second selected pressure. As a result, the second membrane external pressure (e.g. pressure P3) overcomes the second chamber pressure P2 plus the second biasing force of the second membrane biasing member 54, and the second membrane 50 moves to drive the actuator output member 44 to the first output member position as shown in Figure 6, thereby disengaging the clutch 26 (Figure 2) and operatively disconnecting the rotor drive source from the rotor 28.

[0048] With the rotor 28 not operating, the first chamber pressure P1 climbs as the vacuum load 25 is operated using vacuum from the first vacuum source 30. With the inter- chamber valve member 46 in the open position, however, the second chamber pressure P2 remains equalized with the first chamber pressure P1.

[0049] After a period of time, the first chamber pressure P1 climbs sufficiently that the first membrane external pressure can no longer overcome the first biasing force and the first chamber pressure P1 , and as a result, the first membrane 48 moves to drive the inter- chamber valve member 46 to the closed position as shown in Figure 7. As the first chamber pressure P1 continues to climb, the check valve 68 opens as needed to permit continued equalization of the second chamber pressure P2 with the first chamber pressure P1. Thus, the second chamber pressure P2 also continues to climb. After a further period sufficient vacuum use by the vacuum load 25 causes the first chamber pressure P1 and correspondingly the second chamber pressure P2 climb sufficiently that the second chamber external pressure is can no longer overcome the second biasing force plus the second chamber pressure P2. As a result, the second membrane 50 is moved to drive the actuator output member 44 to the second output member position as shown in Figure 8, which drives engagement of the clutch 26, thereby operatively connecting the rotor drive source with the rotor 28 (Figure 2A) to cause operation of the vacuum pump 22 in order to reduce the pressure in the first vacuum source 30. At this point the second chamber pressure P2 will be higher than the first chamber pressure P1 and so the check valve 68 will be closed.

[0050] An advantage of the vacuum system 24 and of the vacuum actuator 36 is that, as noted above, it is not prone to dithering. This occurs as a result of several features. As can be seen, as soon as the inter-chamber valve member 36 opens, the second chamber 42 evacuates to equalize its pressure P2 with the first chamber pressure P1. Selection of the relative volumes V1 and V2 and the spring rates of the first and second membrane biasing members 52 and 54 can be made so that, once the pressure P2 of the second chamber 42 equalizes with the first chamber pressure P1 , (which occurs quickly), it takes some longer period of time for the second chamber pressure P2 to reach the second selected pressure in order for the actuator output member 44 to be driven to the second output member position. As can be seen in Figure 7, even when the inter-chamber valve member 46 has moved to its closed position, the actuator output member 44 remains in the first output member position. Thus, even if there is dithering by the first membrane 48 and the inter- chamber valve member 46 if the first chamber pressure P1 winds up for a period of time very close to the pressure needed to move the membrane one way or the other, there is no dithering by the actuator output member 44, since as soon as the inter-chamber valve member 46 opens the second chamber pressure P2 drops very quickly (e.g. within less than 0.5 seconds) to well below the second selected pressure and it takes some period of time before the second chamber pressure P2 climbs to the second selected pressure as vacuum is consumed by the vacuum load 25.

[0051] The volumes V1 and V2 can be selected such that the second chamber pressure P2 drops to essentially the same pressure as the first chamber pressure P1 that was present before the inter-chamber valve member 46 opens. For example, if the first volume V1 is about 20 times the size of the second volume V2, then the second chamber pressure P2 and the first chamber pressure P1 will equalize to a pressure that is very close of the first chamber pressure P1 before the inter-chamber valve member 46 opened. In an example, the second volume V2 may be about 200 ml, while the first volume V1 may be in the range of 4-5 I. It will be understood that the larger the ratio of the first volume V1 to the second volume V2, would be better, at least for a certain first and second selected pressures, as it would potentially result in a faster drop in pressure in the second chamber 42 and would result in a greater drop in pressure in the second chamber 42. If, alternatively, the first and second volumes V1 and V2 were equal, then the second chamber pressure P2 would drop by 50% of the difference between the first and second chamber pressures P1 and P2, once the inter-chamber valve member 46 opens. Thus, selection of the first and second volumes V1 and V2 can be made to control the length of time that it takes for the second chamber pressure P2 to build back up to the point where the actuator output member 44 moves to the second output member position, based on the average rate of consumption of vacuum that occurs by the vacuum load 25.

[0052] It will be noted that the effective surface area of the first membrane is larger than the effective area of the piston 46a on which the air in the second chamber 42 exerts pressure. Thus, the inter-chamber valve member 46 will move from the closed position if the pressure differential across the first membrane 48 is sufficiently large even if the second chamber pressure P2 is higher than the first chamber pressure P1. Effectively, it is beneficial that the second chamber pressure P2 has relatively little effect on the first selected pressure in the first chamber 40 at which the first membrane 48 is moved to drive the the inter- chamber valve member 46

[0053] It will be noted that the vacuum load 25 is shown as a single device, such as a brake booster, but it will be understood by one skilled in the art that it can be several devices, and that each of the several devices may connected independently or via one or more headers to the first vacuum source 30.

[0054] It will also be noted that, in an alternative embodiment, the actuator output member 44 could instead be a rotary device that is caused to rotate by the movement of the second membrane 50 instead of translating between its first and second output member positions. [0055] It will also be noted that the vacuum system 24 shown herein is simplified in the sense that there may be other control valves and the like that make up part of the vacuum system 24 that are not shown or described but which would be understood to be present for certain purposes, such as the inclusion of a check valve to permit air flow into the vacuum pump 22 but to prevent air flow from the vacuum pump 22 out to the first vacuum source 30.

[0056] It will further be noted that selection of the spring rates of the first and second membrane biasing members 52 and 54 can control the first and second selected pressures, which are the pressures that cause the actuator output member 44 to move between its first and second output member positions. Put in other words, the first membrane biasing member 52 has a first spring rate that is determinative of the first selected pressure, and the second membrane biasing member 54 has a second spring rate that is determinative of the second selected pressure. Thus, by selection of different springs with different spring rates, the vacuum actuator 36 can be tailored to different vehicles with different ranges of operation for their vacuum systems 24. This advantage is present regardless if the vacuum actuator 36 incorporates membranes or not. For example, it is possible for the vacuum actuator 36 to operate using first and second chamber pistons instead of first and second membranes. Thus, the first and second membrane biasing members 52 and 54 may, more broadly, be referred to simply as first and second biasing members.

[0057] As noted above, the first and second membranes 52 and 54 are examples of pressure-differential responsive members. Any other pressure-differential responsive members could alternatively be used, such as a first chamber piston and a second chamber piston instead of the first membrane 52 and the second membrane 54, respectively.

[0058] The vacuum pump 22 is an example of a pneumatic pump. Similarly, the vacuum system 24 is an example of a pneumatic system. Accordingly, the vacuum conduits 34 may more broadly be referred to as pneumatic conduits 34. Similarly, the vacuum actuator 36 may more broadly be referred to as a pneumatic actuator 36 and the first vacuum source 30 may be referred to as the first pneumatic source 30. In an example, the pneumatic actuator 36 could be used to control the operation of the pneumatic pump 22. In a case where the pneumatic pump 22 is present to increase the pressure in the first pneumatic source 30, the pneumatic actuator 36 may be configured to operate in reverse from how it is shown in the figures, in the sense that the actuator output member 44 may be driven to the second position to cause operation of the pneumatic pump 22 if the pressure in the second chamber 42 (i.e. the second chamber pressure P2) drops (instead of increases) beyond a second selected pressure. Similarly, the inter-chamber valve member 46 may be configured such that if the pressure P1 in the first chamber 40 is high enough that it overcomes the first membrane external pressure (e.g. pressure P3) and the first biasing force of the first membrane biasing member 52 moves the first membrane 48 to move the inter-chamber valve member 46 to the open position, which in turn causes fluid communication between the first and second chambers 40 and 42, which increases the pressure P2 in the second chamber 42, thereby causing the second membrane 50 to move to drive the actuator output member to the first output member position, thereby disengaging the clutch and stopping operation of the pneumatic pump 22. It is possible that the inter-chamber valve member 46 may be oriented to have its piston 46a inside the first chamber 40 for this embodiment, instead of being in the second chamber 42 as shown in the figures.

[0059] Thus in the present disclosure, the term‘pneumatic’ refers to the use of air (or other gas) and is not intended to be limited to positive pressures (i.e. pressure that are greater than atmospheric) but is intended to broadly cover both vacuum systems and positive pressure systems. [0060] Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages.

[0061] Persons skilled in the art will appreciate that there are yet more alternative implementations and modifications possible, and that the above examples are only illustrations of one or more implementations. The scope, therefore, is only to be limited by the claims appended hereto and any amendments made thereto.