Double acting two stage piston type vacuum pump and compressor

Abstract

A double acting two stage piston type pump, comprising a pump housing having a piston arrangement connected to a driving shaft which, when driven, sets the piston arrangement into movement, wherein the piston arrangement comprises at least two first primary stage pistons, the first primary stage pistons being slidably seated in respective first primary stage cylinders formed in the pump housing The piston arrangement also comprises at least two secondary stage pistons slidably seated in respective secondary stage cylinders formed in the primary stage pistons. The primary stage pistons and the second secondary stage pistons are mounted on, and directly driven by, eccentrics mounted on the driving shaft. The piston pump of the invention can provide the functions of both a vacuum pump and a compressor.

Description

[0001] Double acting two stage piston type vacuum pump and compressor

[0002] The invention relates to a pump comprising a pump housing having a piston arrangement connected to a drive shaft which, when driven, sets the piston arrangement into movement, wherein the piston arrangement comprises a first primary stage piston, the first primary stage piston being slidably seated in a first primary stage cylinder which is formed in the pump housing, and a second primary stage piston, the second primary stage piston being slidably seated in a second primary stage cylinder which is formed in the pump housing. The piston arrangement also comprises a first secondary stage piston which is slidably seated in a first secondary stage cylinder formed in the first primary stage piston, and a second secondary stage piston which is slidably seated in a second secondary stage cylinder formed in the second primary stage piston. Such a piston pump may be used to induce a vacuum at the pump inlet and, at same time, to provide pressurized fluid, e.g. air, at the pump outlet. In other words, the double acting two stage piston pump of the invention may function as a vacuum pump and, at the same time, as a compressor.

[0003] Vacuum pumps are for example known from WO 2017 / 137144 A1 or WO 2017 / 137141 A1 . Such vacuum pumps are generally referred to as piston type vacuum pumps in distinction from so-called rotary vane vacuum pumps. Pumps of the aforementioned types include at least one piston which reciprocatingly moves inside a cylinder. The pump inlet usually is connected with the working chamber formed by the cylinder such that when the piston moves inside the cylinder for increasing the working volume of the working chamber the vacuum is induced at the inlet. For even increasing this vacuum, such piston type vacuum pumps often comprise primary and secondary stages, wherein the secondary stage further increases the vacuum generated by the primary stage.

[0004] Pumps of this type are used in passenger vehicles or trucks as in particular vacuum pumps to supply specific modules of the vehicle with a vacuum. This vacuum, for example, is used for brake boost modules, or for pneumatic braking systems in trucks. For common gasoline or diesel engine vehicles the vacuum pump was typically mounted in the engine region and connected to the crank shaft of the engine to be driven. Modern vehicles, however, comprise improved electric systems such that also vacuum pumps of modern vehicles are more often driven by an electric motor. The present invention particularly relates to such vacuum pumps, which are driven by an electric motor inside a vehicle.

[0005] Known piston pumps can be used to either generate pressurized air, therefore acting as a compressor, or else generate vacuum, therefore acting as a vacuum pump.

[0006] In some vehicle brake applications, brake boost modules, also known as brake boosters, are used, wherein both vacuum and positive pressure are needed to provide the required master cylinder output. Such brake boost modules are also referred to as vacuum brake valves with dual assistance.

[0007] Such vacuum brake valves with dual assistance generally comprise a vacuum-side portion wherein vacuum is provided to drive a master cylinder. To improve the master cylinder output, such vacuum brake valves with dual assistance also generally comprise a pressure-side portion wherein positive pressure is provided, to reinforce the output of the master cylinder.

[0008] In prior art applications, vacuum and positive pressure are provided to the brake booster by two separate devices, namely a vacuum pump and a compressor.

[0009] The presence of these two separate devices, in addition to the brake booster, is often cumbersone in terms of size and may lead to overly complicated designs and structures.

[0010] Problems associated with piston type pumps in the field of vehicles are in particular noise and vibration generation. This in particular is true for single piston one stage piston type pumps. Two stage piston pumps are more balanced from a torque perspective, since the two stages can be driven alternatingly. However, such common two stage piston pumps often suffer a higher out of balance inertia loading which again translates to higher noise and vibration levels.

[0011] One piston type vacuum pump, which is balanced in an improved manner, is disclosed in US 2015 / 0078932 A1. However, this vacuum pump is rather complicated and involves multiple different parts. Moreover, the vacuum pump disclosed in US 2015 / 0078932 A1 is relatively large compared to common vane type vacuum pumps.

[0012] WO 2019 / 114923 A1 shows a piston type pump, comprising a pump housing having at least one pump inlet and one pump outlet and a piston arrangement connected to a driving shaft which, when driven, sets the piston arrangement into movement, wherein the piston arrangement comprises a first primary stage piston, the first primary stage piston being slidably seated in a first primary stage cylinder formed in the pump housing; a first secondary stage piston; whereas the first secondary stage piston is slidably seated in a first secondary stage cylinder formed in the first primary stage piston. Such a piston type pump is formed as a so-called twin piston type pump and therefore also comprises a second primary stage piston and a second secondary stage piston, wherein the second primary stage piston is slidably seated in a second primary stage cylinder formed in the pump housing, and the second secondary stage piston is slidably seated in a second secondary stage cylinder formed in the second primary stage piston In the piston type pump of WO 2019 / 114923 A1 , the piston arrangement is set into movement thanks to sliding block guides that connect the pistons to respective eccentrics mounted on the driving shaft. In other words, a so-called “Scotch yoke” mechanism is used to convert the rotational movement of the driving shaft into the sliding movement of the block guides and then into the linear movement of the pistons.

[0013] However, in the context of piston type pumps, the “Scotch yoke” mechanism carries several problems. In particular, it does not represent a robust solution and leads to wear and noise issues. Also, such an arrangement leads to high power consumption. Furthermore, the “Scotch yoke” design features the crank as part of the piston pack: the diameter operating bore therefore tends to become a constraint, preventing the use of adequately sized bearings.

[0014] An object of the present invention is therefore to provide a more robust piston type pump which allows to achieve better durability. Another object of the present invention is to provide a piston type pump which features lower noise and power consumption. Another abject of the present invention is to provide a piston type pump which avoids the issue of linear sliding motion at the bearings and permits the use of larger rolling element bearings.

[0015] A further object of the present invention is to provide a piston type pump that can easily integrate the functions of a vacuum pump and of a compressor within a single device. Another object of the present invention is to provide a piston type pump which allows a more compact design and that is easier to assemble and manufacture.

[0016] Another object of the present invention is to provide a piston type pump that can improve the efficiency of a brake booster connected to such pump. These and other objects are achieved by a piston type pump comprising a pump housing having a piston arrangement connected to a driving shaft which, when driven, sets the piston arrangement into movement. Such a piston arrangement comprises: a first primary stage piston, the first primary stage piston being slidably seated in a first primary stage cylinder formed in the pump housing; a first secondary stage piston, the first secondary stage piston being slidably seated in a first secondary stage cylinder formed in the first primary stage piston; a second primary stage piston, the second primary stage piston being slidably seated in a second primary stage cylinder formed in the pump housing; a second secondary stage piston, the second secondary stage piston being slidably seated in a second secondary stage cylinder formed in the second primary stage piston.

[0017] The driving shaft of the piston type pump of the invention comprises a first eccentric and a second eccentric, which are phase shifted by 180°; furthermore, the first secondary stage piston comprises a first seconday stage piston rod and the second secondary stage piston comprises a second seconday stage piston rod.

[0018] The piston type pump of the invention is characterized in that the first primary stage piston and the second secondary stage piston rod are mounted on, and directly driven by, the second eccentric and in that the first seconday stage piston rod and the second primary stage piston are mounted on, and directly driven by, the first eccentric.

[0019] The piston type pump of the invention is also characterized by the fact that the first primary stage piston and the first secondary stage piston are configured to generate pressurized air, and the second primary stage piston and the second secondary stage piston are configured to generate vacuum.

[0020] The direct driving of the primary and of the secondary stage pistons by the eccentrics permits the direct conversion of the rotary motion of the driving shaft into the linear, reciprocating motion of the pistons, thus disposing of any intermediate sliding mechanism. The pump of the invention is based on the idea that a single, compact device, can provide the functions of both a vacuum pump and a compressor, dependent on how consumers are connected to the pump inlet and / or pump outlet.

[0021] The pump of the invention is also based on the idea that the space within the primary stage pistons, which usually have a larger piston face than the secondary stage pistons, is used for forming the secondary stage cylinders, in which the secondary stage pistons can reciprocatingly move. Due to this arrangement, the overall size of the pump can be reduced. The second stage is formed inside the first stage and not adjacent to it or at any other position. While the primary stage pistons move relative to the pump housing inside respective primary stage cylinders formed inside the pump housing, the secondary stage pistons move inside the primary stage pistons. For inducing a vacuum of the second stage it is thus necessary that the secondary stage pistons move relative to the primary stage pistons and preferably also relative to the pump housing.

[0022] Preferably, when the invention relates to a vacuum pump, the secondary stage cylinders have a bigger volume than the primary stage cyllinders.

[0023] Even more preferably, the secondary stage cylinders of the vacuum pump of the invention have a volume that is approximately 10% larger than the volume of their respective primary stage cylinders.

[0024] According to one aspect, when the invention relates to a vacuum pump, the secondary stage cylinders have a bigger volume than the primary stage cyllinders due to the fact that the stroke of the secondary stage pistons is approximately twice as long as that of the primary stage pistons.

[0025] Preferably, when the invention relates to a compressor, the secondary stage cylinders have a smaller volume than the primary stage cylinders.

[0026] According to one aspect, the stroke of the primary and secondary stage pistons associated to the compressor can be reduced when compared to the stroke of the primary and secondary pistons associated to the vacuum pump.

[0027] In a preferred embodiment of the pump, the drive shaft of the pump comprises a first eccentric and a second eccentric, which are phase-shifted by 180°, wherein a first primary stage piston and a second secondary stage piston are driven by the second eccentric, and wherein a first secondary stage piston and a second primary stage piston are driven by the first eccentric. It shall be understood that since the secondary stage pistons move inside the primary stage pistons, they are connected to the eccentrics by means of rods, which move together with their respective secondary stage pistons. Furthermore, it shall be understood that also other phase shiftings can be preferred, dependent on the overall design of the pump. For example, pumps are known which use a 90 degree phase shift or a 120 degree phase shift. A 180° phase shift however has shown to be most efficient and a very well balanced pump can be achieved. In a preferred further development the first eccentric comprises a first eccentricity with respect to a rotational axis of the drive shaft and the second eccentric comprises a second eccentricity with respect to the rotational axis. The first eccentricity preferably is identical to the second eccentricity, so that respective piston strokes can be identical. However, when different piston strokes are desired, the first and second eccentricities may vary from each other.

[0028] According to one aspect, the first and second eccentrics are integrally formed with the drive shaft. Thus, the drive shaft, the first eccentric and the second eccentric are formed in a one-piece construction which makes it possible to reduce parts for the piston type pump.

[0029] According to one preferred aspect, the first and the second eccentrics are separate components, which allow for a simple manufacturing and mounting. According to one preferred aspect, the pistons and / or the piston rods are mounted on the eccentrics via respective bearings, for instance needle bearings.

[0030] In a preferred embodiment, the driving shaft comprises a stud, and the first and the second eccentrics are mounted on the stud. According to one aspect, the driving shaft and / or the stud, the first eccentric and the second eccentric are separate components. According to one aspect, the driving shaft and / or the stud, the first eccentric and the second eccentric are formed into a single component.

[0031] According to one aspect, at least the first eccentric and / or at least the second eccentric is fixedly mounted on the stud. According to one aspect, at least the first eccentric and / or at least the second eccentric is in threaded engagement with the stud.

[0032] In a further preferred embodiment, the first eccentric is provided with first torque-transmitting and aligning means configured to engage, in a predetermined angular way, with respective second torque-transmitting and aligning means provided on the second eccentric. Preferably, the first torque-transmitting and aligning means comprise a first form locking element, and the second torque-transmitting and aligning means comprise a second form locking element, engaging the first form locking element. According to a preferred aspect, the first torque-transmitting and aligning means provided on the first eccentric comprises at least a first and preferably a second protrusion. The second torque-transmitting and aligning means provided on the second eccentric preferably comprises at least one third protrusion configured to fit with the at least first and preferably second protrusions provided on the first eccentric. According to one aspect, such first and second torque-transmitting and aligning means allows the first and second eccentrics to be rotationally positioned at a predetermined angle, for instance at 180°.

[0033] According to one aspect, such first and second torque-transmitting and aligning means allow the first and second eccentrics to transmit torque and jointly rotate together with the driving shaft and / or the stud. Moreover, they allow for a simple manufacturing and mounting. According to one preferred aspect, the first torque-transmitting and aligning means provided on the first eccentric and the second torque-transmitting and aligning means provided on the second eccentric are located in proximity to the stud, so that to minimize inertia forces. According to one aspect, a nut is threadedly engaged to the stud and in contact force transmitting engagement with the second eccentric.

[0034] According to a second, alternative embodiment, the driving shaft comprises a cap screw and the first and second eccentrics are mounted on such cap screw. According to one aspect, at least the first eccentric and / or at least the second eccentric is fixedly mounted on the cap screw. According to one aspect, at least the first eccentric and / or at least the second eccentric is in threaded engagement with the cap screw. According to one aspect, the second eccentric is provided with a flange configured to fit with a recess provided on the first eccentric.

[0035] According to one aspect, the piston type pump of the invention according to the second, alternative embodiment, also comprises a pin configured to fixedly secure the flange provided on the second eccentric with the recess provided on the first eccentric. Preferably, the pin is interference mounted in respective bores provided in both the flange and the recess.

[0036] According to an aspect of the invention the above stated objects are solved by a method for mountig a piston type pump preferably according to the first embodiment, comprising the steps of: mounting the first seconday stage piston rod and the second primary stage piston on the first eccentric; interference mounting the driving shaft into the first eccentric; inserting the first seconday stage piston rod, the second primary stage piston, the first eccentric and the driving shaft into the piston housing; mounting the second eccentric on the driving shaft and aligning it with the first eccentric; mounting the first primary stage piston and the second seconday stage piston rod on the second eccentric.

[0037] According to one aspect, the first eccentric is interference mounted on the stud. According to another aspect, the first secondary stage piston rod, the second primary stage piston, the first eccentric, the driving shaft and / or the stud represent a „piston pack" or at least an intermediate „piston pack" and, as such, are conveniently slid down and / or inserted together into the pump housing.

[0038] According to one option, the first secondary stage piston is mounted on the first secondary stage piston rod before the “piston pack” is inserted into the pump housing: in other words, the first secondary stage piston belongs to the “piston pack”.

[0039] According to an alternative option, the first secondary stage piston is mounted on the first secondary stage piston rod only after the “piston pack” has been inserted into the pump housing.

[0040] According to yet another aspect, the first secondary stage piston rod, the second primary stage piston, the first eccentric, the driving shaft and / or the stud, the second eccentric, the second secondary stage piston rod and the first primary stage piston represent a “piston pack” and, as such, are slid down and / or inserted into the pump housing. The first secondary stage piston and / or the second secondary stage piston may or may not belong to the “piston pack”: in other words, thay may be mounted on their respective secondary stage piston rods before the “piston pack” is inserted into the pump housing or after the “piston pack” in inserted into the pump housing.

[0041] Optionally, the "piston pack" also comprises a nut mounted on the stud, said nut being in contact force transmitting engagement with the second eccentric.

[0042] According to yet another alternative option, the nut is mounted on the “piston pack” only after the “piston pack” has been inserted into the pump housing, Preferably, the nut is threadedly engaged to the stud.

[0043] According to one aspect, the first primary stage piston and the first secondary stage piston are configured to generate pressurized air; in other words, they are configured to function as a compressor.

[0044] According to one aspect, the second primary stage piston and the second secondary stage piston are configured to generate vacuum; in other words, they are configured to function as a vacuum pump. According to one aspect, the first primary stage cylinder comprises a first outlet valve and the first secondary stage cylinder comprises a second outlet valve, the first outlet valve and the second outlet valve being in fluid communication with a pump outlet. According to one aspect, the pump outlet comprises a pump outlet valve, the pump outlet valve being in fluid communication with an outlet conduit for providing pressurized air to a pressure-side portion of a vacuum brake valve with dual assistance.

[0045] According to one aspect, the second primary stage cylinder comprises a first inlet valve and the second secondary stage cylinder comprises a second inlet valve, the first inlet valve and the second inlet valve being in fluid communication with a pump inlet.

[0046] According to one aspect, the pump inlet comprises a pump inlet valve, the pump inlet valve being in fluid communication with an inlet conduit for providing vacuum to a vacuum-side portion of a vacuum brake valve with dual assistance.

[0047] According to one aspect, the first outlet valve, the second outlet valve and the pump outlet valve are preferably formed as one-way valves and more preferably as an umbrella valve. In case the piston pump is used to induce a positive pressure at the pump outlet, the first outlet valve, the second outlet valve and the pump outlet valve preferably open from the direction of both the primary and secondary stage cylinders and into the direction of the pump oulet, and block flow of fluid, e.g. air, out of the oulet conduit into the direction of the cylinders.

[0048] According to one aspect, the first inlet valve, the second inlet valve and the pump inlet valve are preferably formed as one-way valves and more preferably as an umbrella valve. In case the piston pump is used to induce a vacuum at the pump inlet, the first inlet valve, the second inlet valve and the pump outlet valve preferably open from the direction of the pump inlet and into the direction of both the primary and secondary cylinders, and block flow of fluid, e.g. air, out of the cylinders into the direction of the inlet conduit.

[0049] According to an aspect of the invention, the above stated objects are solved by a vehicle, in particular a passenger car, comprising a piston type pump according to any of the aforementioned preferred embodiments of a piston type pump. It shall, however, also be understood that the pump according to the present invention may also be used in applications other than vehicles, and in particular other than braking systems. Other uses of pumps for generating a vacuum and a positive pressure on a vehicle can include engine mounts, compressor waste-gate and bypass valves actuation. This type of pump could also feasibly be used to evacuate a housing for a KERS (Kinetic Energy Recovery System) for example.

[0050] For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawings. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and as claimed hereinafter. Further, the features described in the description, the drawings and the claims disclosing the invention may be essential for the invention considered alone or in combination. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording “comprising” does not exclude other elements or steps. The word “a” or “an” does not exclude the plurality. The wording “a number of” items comprising also the number 1 , i.e. a single item, and further numbers like 2, 3, 4 and so forth. In the accompanying drawings:

[0051] Figure 1 shows a perspective view of a piston type pump of the invention;

[0052] Figure 2 shows a schematic diagram of the piston type pump of the invention operatively coupled with a vacuum brake valve with dual assistance;

[0053] Figure 3 shows a cut view, along a first plane, of a piston arrangement of the piston type pump of the invention;

[0054] Figure 4 shows a cut view, along a second plane that is perpendicular to the first plane of Figure 3, of the piston type pump of the invention;

[0055] Figure 5 shows a simplified cut view of the crank mechanism of a first embodiment of the piston type pump of the invention;

[0056] Figure 6 shows a perspective view of the crank mechanism of Figure 5; Figure 7 shows a perspective view of a first eccentric and of second eccentric making part of the crank mechanism of Figures 5 and 6;

[0057] Figure 8 shows a simplified cut view of the crank mechanism of a second embodiment of the piston type pump of the invention;

[0058] Figure 9 shows a perspective view of the crank mechanism of Figure 8;

[0059] Figure 10 shows a perspective view of a first eccentric and of second eccentric making part of the crank mechanism of Figures 8 and 9; and

[0060] Figure 11 shows a schematic view of a vehicle.

[0061] A piston type pump 1 according to the present disclosure is suitable to be mounted within a vehicle 100 (see Figure 11 ) and used to provide vacuum and positive pressure for a braking system or any other consumer in this vehicle. The piston type pump 1 in particular is suitable to be driven by an electric motor 4.

[0062] The following embodiments show the piston type pump 1 prepared to be used as both a vacuum pump and as a compressor to induce, respectively, a vacuum at a pump inlet 7 and a positive pressure at a pump outlet 9.

[0063] With reference to Figure 1 , the piston type pump 1 comprises a pump housing 2 which is substantially cylindrical. The pump housing 2 has a pump inlet 7 and a pump outlet 9 which can be connected to a consumer. Fluid, in particular air, which is drawn away from the pump inlet 7, when not used can be discharged to the environment instead of being provided to any consumer, for instance via a discharge conduit (not shown).

[0064] The pump housing 2 comprises a silencer 29, that may be preferably shaped for acting as a Helmholtz resonator.

[0065] The piston type pump 1 of the invention generally comprises two portions, a first portion 5 configured to generate vacuum, in other words configured to function as a vacuum pump, and a second portion 6 configured to generate compressed air, in other words configured to function as a compressor.

[0066] With reference to Figure 2, the piston type pump 1 is operatively connected to a consumer 99, for instance to a brake booster or vacuum brake valve with dual assistance. More in detail, the pump outlet 9 provides positive pressure to a pressure-side portion 991 of the brake booster 99 via outlet conduit 404, whereas the pump inlet 7 provides vacuum to a vacuum-side portion 992 of the brake booster 99 via inlet conduit 504. Thanks to the combined effect of vacuum and positive pressure, the output of master cylinder 993 of the brake booster 99 can be considerably improved.

[0067] The pump of the invention is preferably capable of generating vacuum at approximately 980 mbar and a positive pressure of approximately 10 bar.

[0068] Within the pump housing 2 a piston arrangement 8 is provided, which will be described in more detail below. The piston arrangement 8 is connected to a drive shaft 10 which, when driven, sets the piston arrangement 8 into movement for inducing a vacuum at the pump inlet and a positive pressure at the pump outlet. The drive shaft 10 is rotatable about a rotational axis A and may be connected to an electric motor 4.

[0069] The piston arrangement 8 according to the embodiment shown in Figure 3 and in Figure 4 comprises a first primary stage piston 12 which is slidably seated in a first primary stage cylinder 14 formed in the pump housing 2.

[0070] The piston type pump 1 according to the shown embodiment is formed as a twin type two-stage piston pump and therefore also comprises a first secondary stage piston 16, which is provided within a first secondary stage cylinder 18, which is formed within the first primary stage piston 12. The first primary stage piston 12, therefore, is formed in a hollow manner, to form the first secondary stage cylinder 18. The first primary stage piston 12 comprises a first primary stage piston wall 13 which defines the first secondary stage cylinder 18. The first secondary stage cylinder 18 in particular is formed by an inner circumferential surface of the first primary stage piston wall 13 within the first primary stage piston 12.

[0071] For movement of the first primary stage piston 12 and the first secondary stage piston 16, the first primary stage piston 12 is driven by a second eccentric 22 of the drive shaft 10 and the first secondary stage piston 16 is driven by a first eccentric 20 of the drive shaft 10. Both the first and the second eccentric 20, 22 are mounted on a stud 21 . The first and second eccentrics 20, 22 are phase-shifted by 180°. In a similar fashion the piston arrangement 8 according to this embodiment also comprises a second primary stage piston 40, which is slidably seated in a second primary stage cylinder 42, which again is formed inside the pump housing 2. The complete interior 3 of the pump housing 2 can be formed as a cylindrical hollow portion to form both, the first primary stage cylinder 14 and the second primary stage cylinder 42.

[0072] Also a second secondary stage piston 44 is provided which is slidably seated in a second secondary stage cylinder 46 formed within the second primary stage piston 40. Again the second primary stage piston 40 comprises a second primary stage piston wall 41 which defines the second secondary stage cylinder 46 by its inner circumferential surface restricting a second hollow space 47.

[0073] For driving the second primary stage piston 40 and the second secondary stage piston 44, the second primary stage piston 40 is connected to the first eccentric 20 and the second secondary stage piston 44 is connected to the second eccentric 22. Thus, the first eccentric 20 drives the second primary stage piston 40 as well as the first secondary stage piston 16 and in turn the second eccentric 22 drives the first primary stage piston 12 and the second secondary stage piston 44. Therefore, the movement of the pistons is identical, however, phase- shifted by 180°.

[0074] Moreover, in Figure 3 it can be seen that the first primary stage cylinder 14 comprises a first central axis B1 and the second primary stage cylinder 42 comprises a second central axis B2, which are coaxial. Thus, the first and the second central axes B1 , B2 form a single axis on which the first primary stage piston 12 and the second primary stage piston 40 move. When the first secondary stage cylinder 18 and the second secondary stage cylinder 46 are formed concentrically within the respective first primary stage piston 12 and the second primary stage piston 40, also the first secondary stage piston 16 and the second secondary stage piston 44 move coaxially with the first and second central axes B1 , B2. Thus, the overall design of the piston type pump 1 is a boxer type piston type pump in which the single pistons move in opposing directions. This may lead to a well-balanced design.

[0075] The first secondary stage piston 16 comprises a first piston rod 54 which extends through a first assembly opening 60 (not shown) in the first primary stage piston wall 13. The portion of the first hollow space 19 which is on the opposite side of the piston rod 54 with respect to the first secondary piston face 30 can be named the first secondary stage working chamber. In the same manner the second secondary stage piston 44 comprises a second piston rod 56 which extends through a second assembly opening 58 (not shown) formed in the second primary stage piston wall 41 of the second primary stage piston 40.

[0076] The first primary stage piston 12 and the second secondary stage piston rod 56 are mounted on, and directly driven by, the second eccentric 22. In turn, the first seconday stage piston rod 54 and the second primary stage piston 40 are mounted on, and directly driven by, the first eccentric 20.

[0077] The mounting of the first primary stage piston 12 and of the second secondary stage piston rod 56 on the second eccentric 22 may comprise a needle bearing 229. In turn, the mounting of the first seconday stage piston rod 54 and of the second primary stage piston 40 on the frst eccentric 20 may also include a needle bearing 209.

[0078] With reference to Figure 3 and Figure 4, the flow of fluid, e.g. air, within the piston type pump of the invention will be now briefly described.

[0079] The first primary stage cylinder 14 comprises a first outlet valve 401 and the first secondary stage cylinder 18 comprises a second outlet valve 402. The first outlet valve 401 and the second outlet valve 402 are in fluid communication with the pump outlet 9. The pump outlet 9 comprises a pump outlet valve 403 which is in fluid communication with an outlet conduit 404 for providing pressurized air to the pressure-side portion 991 of the brake booster 99.

[0080] The first outlet valve 401 , the second outlet valve 402 and the pump outlet valve 403 are one-way valves, and they open from the direction of the primary and secondary stage cylinders towards the direction of the pump oulet 9, thus preventing any flow of fliud from the oulet conduit 404 into the direction of the cylinders.

[0081] The second primary stage cylinder 42 comprises a first inlet valve 501 and the second secondary stage cylinder 46 comprises a second inlet valve 502. The first inlet valve 501 and the second inlet valve 502 are in fluid communication with the pump inlet 7. The pump inlet 7 comprises a pump inlet valve 503 which is in fluid communication with an inlet conduit 504 for providing vacuum to a vacuum-side portion 992 of the brake booster 99. The first inlet valve 501 , the second inlet valve 502 and the pump inlet valve 503 are one-way valves, and they open from the direction of the pump inlet 7 towards the direction of the primary and secondary cylinders, thus preventing any flow of fluid, e.g. air, from the cylinders into the direction of the inlet conduit 504.

[0082] The crank mechanism of Figure 3, which is shown in detail in Figure 5, Figure 6 and Figure 7, relates to a first embodiment of the present invention and comprises a stud 21 fixedly mounted on the driving shaft 10. The first eccentric 20 is fixedly mounted on the driving shaft 10 and / or on the stud 21 , for instance by screws or other form-locking mechanisms. Preferably, the first eccentric 20 is fixedly mounted on the driving shaft 10 and / or on the stud 21 , through interference mounting. The first eccentric 10 comprises a bore 213 to allow the insertion and the mounting on the stud 21 and / or on the driving shaft 10.

[0083] In proximity to the bore 213, a first protrusion 211 and a second protrusion 212 are provided, each having at least a flat coupling surface. The second eccentric 22 also comprises a bore 223 to allow the insertion and the mounting on the stud 21 . In correspondence to, preferebly coaxial to, the bore 223, a third protrusion 222 is also provided, the third protrusion 222 having at least two flat coupling surfaces configured to engage, in a predetermined angular way, with the respective flat coupling surfaces of the first and second protrusions 211 , 212 provided on the first eccentric 20. This way, it is possible to align the first and the second eccentrics in a predetermined angular fashion. The protrusions 211 , 212, 222 are designed to transmit torque between the first and the second eccentrics 20, 22 so that they can jointly rotate around rotational axis A of the driving shaft 10 and of the stud 21 . It shall be understood, that in other embodiments, the first and second protrusions 211 , 212 are provided on the second eccentric 22, while the third protrusion is provided on the first eccentric 20. Also any other means for at least a partial form-locking torque transmission are envisaged. It also shall be understood that in exchange of the first and second protrusions 211 , 212 a groove may be provided on one of the eccentrics 20, 22 in which the third protrusion 222 may engage.

[0084] A nut 23 is threadedly fixed on the stud 21 and further secures the second eccentric 22 in both its axial position along the rotational axis A of the stud 21 and in its rotational position in respect of the first eccentric 20. The assembly of the piston type pump 1 according to the first embodiment of the invention may conveniently envisage that at least part of the pistons are assembled together before being slid down the pump housing 2. As a first assembly step, the first seconday stage piston rod 54, together with the first seconday stage piston 16, and the second primary stage piston 40 are mounted on the first eccentric 20. Subsequently, the first eccentric 20 is fixedly mounted on the driving shaft 10 and / or the stud 21 , for instance by interference mounting. This way, an intermediate „piston pack1' comprising the driving shaft 10 and / or the stud 21 , the first eccentric 20, the seconday stage piston 16 and its first seconday stage piston rod 54, as well as the second primary stage piston 40, is created. Such an intermediate „piston pack" is then inserted into the pump housing 2. Thereafter, the second eccentric 22 is mounted on the driving shaft 10 and aligned with the first eccentric 20 thanks to the torque-transmitting and aligning means, namely the protrusions, which are provided on both the first and second eccentrics. Finally, the first primary stage piston 12 and the second seconday stage piston rod 56 together with its respective second seconday stage piston 44, are mounted on the second eccentric 22.

[0085] Figure 8, Figure 9 and Figure 10 show a crank mechanism according to a second, alternative embodiment of the present invention. According to such alternative embodiment, the driving shaft 10, the first eccentric 20 and the second eccentric 22 are held together with a cap screw 300. The first eccentric 20 comprises a recess 302 and a bore 213 to allow the insertion and the mounting on the cap screw 300. The first eccentric 20 also comprises a second bore 304, to allow the insertion and the mounting of a pin 303.

[0086] The second eccentric 22 comprises a bore 223 to allow the insertion and the mounting on the cap screw 300, and a flange 301 . The flange 301 is designed to fit into the recess 302 of the first eccentric 20 and comprises a second bore 305 to allow the insertion and the mounting of the pin 303. In other words, the pin 303 secures the fixed coupling of the flange 301 of the second eccentric 22 with the recess 302 of the first eccentric 20 and as a result, the first and second eccentrics 20, 22 are aligned at a predetermined rotational angle, and they are capable of jointly rotate. Preferably, the pin 303 is inserted into the second bore 304 on the first eccentric 20 and into the second bore 305 on the flange 301 through interference mounting.

[0087] Figure 11 now depicts a schematic drawing of a vehicle 100. Vehicle 100 preferably is formed as a passenger car, or a light truck and comprises a pneumatic braking system 102. The braking system 102 is shown by lines 104 leading to wheels 106a, 106b, 106c, 106d for providing the wheels 106a, 106b, 106c,106d with the respective braking pressure. Lines 104 are connected to a central module 108. The vehicle 100 moreover comprises an engine 110 and a piston type pump 1 according to the invention, which is herein used as a vacuum pump and as a compressor. The piston type pump 1 provides the braking system 102 with vacuum and pressurized air, which e.g. could be used by a brake booster of the braking system 102, which could be implemented in the central module 108.

[0088] List of reference signs (Part of the description)

[0089] 1 piston type pump

[0090] 2 pump housing

[0091] 3 interior of the pump housing

[0092] 4 electric motor

[0093] 5 first portion configured to generate vacuum

[0094] 6 second portion configured to generate compressed air

[0095] 7 pump inlet

[0096] 8 piston arrangement

[0097] 9 pump outlet

[0098] 10 driving shaft

[0099] 12 first primary stage piston

[0100] 13 first primary stage piston wall

[0101] 14 first primary stage cylinder

[0102] 16 first secondary stage piston

[0103] 18 first secondary stage cylinder

[0104] 19 first hollow space

[0105] 20 first eccentric

[0106] 21 stud

[0107] 22 second eccentric

[0108] 23 nut

[0109] 29 silencer

[0110] 30 first secondary piston face

[0111] 40 second primary stage piston

[0112] 41 second primary stage piston wall

[0113] 42 second primary stage cylinder

[0114] 44 second secondary stage piston

[0115] 46 second secondary stage cylinder

[0116] 47 second hollow space

[0117] 54 first seconday stage piston rod

[0118] 56 second seconday stage piston rod

[0119] 58 second assembly opening

[0120] 60 first assembly opening

[0121] 99 consumer vehicle pneumatic braking system lines leading to wheels a wheel (front right) b wheel (rear right) c wheel (front left) d wheel (rear left) central module engine first torque-transmitting and aligning means needle bearing (first eccentric)

[0122] (first) protrusion on the first eccentric (second) protrusion on the first eccentric bore on the first eccentric second torque-transmitting and aligning means (third) protrusion on the second eccentric bore on the second eccentric needle bearing (second eccentric) cap screw flange recess pin second bore on first eccentric second bore on second eccentric first outlet valve second outlet valve pump outlet valve outlet conduit first inlet valve second inlet valve pump inlet valve inlet conduit pressure-side portion vacuum-side portion master cylinder A rotational axis of drive shaft

[0123] B1 first central axis

[0124] B2 second central axis

Claims

Claims1. A piston type pump (1 ), comprising: a pump housing (2) having a piston arrangement (8) connected to a driving shaft (10) which, when driven, sets the piston arrangement (8) into movement, wherein the piston arrangement (8) comprises: a first primary stage piston (12), the first primary stage piston (12) being slidably seated in a first primary stage cylinder (14) formed in the pump housing (2); a first secondary stage piston (16), the first secondary stage piston (16) being slidably seated in a first secondary stage cylinder (18) formed in the first primary stage piston (12); a second primary stage piston (40), the second primary stage piston (40) being slidably seated in a second primary stage cylinder (42) formed in the pump housing (2); a second secondary stage piston (44), the second secondary stage piston (44) being slidably seated in a second secondary stage cylinder (46) formed in the second primary stage piston (40); wherein the driving shaft (10) comprises a first eccentric (20) and a second eccentric (22), which are phase shifted by 180°, and wherein the first secondary stage piston (16) comprises a first seconday stage piston rod (54) and the second secondary stage piston (44) comprises a second seconday stage piston rod (56), characterized in that the first primary stage piston (12) and the second secondary stage piston rod (56) are mounted on, and directly driven by, the second eccentric (22), and the first seconday stage piston rod (54) and the second primary stage piston (40) are mounted on, and directly driven by, the first eccentric (20), and in that the first primary stage piston (12) and the first secondary stage piston (16) are configured to generate pressurized air, and the second primary stage piston (40) and the second secondary stage piston (44) are configured to generate vacuum.

2. The piston type pump (1 ) according to claim 1 , wherein the driving shaft (10) comprises a stud (21 ), the first eccentric (20) and the second eccentric (22) being mounted on the stud (21 ).

3. The piston type pump (1 ) according to claim 2, wherein at least one of the first eccentric (20) and the second eccentric (22) is fixedly mounted on the stud (21 ).

4. The piston type pump (1 ) according to any of claims 2 or 3, wherein at least one of the first eccentric (20) and the second eccentric (22) is in threaded engagement with the stud (21 ).

5. The piston type pump (1 ) according to any of claims 2 to 4, wherein the first eccentric (20) is provided with first torque-transmitting and aligning means (201 ) configured to engage, in a predetermined angular way, with respective second torque-transmitting and aligning means (221 ) provided on the second eccentric (22).

6. The piston type pump (1 ) according to claim 1 , wherein the first primary stage cylinder (14) comprises a first outlet valve (401 ) and the first secondary stage cylinder (18) comprises a second outlet valve (402), the first outlet valve and the second outlet valve being in fluid communication with a pump outlet (9).

7. The piston type pump (1 ) according to claim 1 , wherein the second primary stage cylinder (42) comprises a first inlet valve (501 ) and the second secondary stage cylinder (46) comprises a second inlet valve (502), the first inlet valve and the second inlet valve being in fluid communication with a pump inlet (7).

8. The piston type pump (1 ) according to claim 6, wherein the pump outlet (9) comprises a pump outlet valve (403), the pump outlet valve (403) being in fluid communication with an outlet conduit (404) for providing pressurized air to a pressure-side portion (991 ) of a vacuum brake valve with dual assistance.

9. The piston type pump (1 ) according to claim 7, wherein the pump inlet (7) comprises a pump inlet valve (503), the pump inlet valve (503) being in fluid communication with an inlet conduit (504) for providing vacuum to a vacuum-side portion (992) of a vacuum brake valve with dual assistance.

10. The piston type pump (1 ) according to claim 1 , wherein the driving shaft (10) comprises a cap screw (300), the first eccentric (20) and the second eccentric (22) being mounted on the cap screw (300).11 . The piston type pump (1 ) according to claim 10, wherein at least one of the first eccentric (20) and the second eccentric (22) is fixedly mounted on the cap screw (300).

12. The piston type pump (1 ) according to any of claims 10 or 11 , wherein at least one of the first eccentric (20) and the second eccentric (22) is in threaded engagement with the cap screw (300).

13. The piston type pump (1 ) according to any of claims 10 to 12, wherein the second eccentric (22) is provided with a flange (301 ) configured to fit with a recess (302) provided on the first eccentric (20).

14. A method for mounting a piston type pump (1 ) according to any of claims 1 to 9, comprising the steps of:- mounting the first seconday stage piston rod (54) and the second primary stage piston (40) on the first eccentric (20);- interference mounting the driving shaft (10) into the first eccentric (20);- inserting the first secondary stage piston rod (54), the second primary stage piston (40), the first eccentric (20) and the driving shaft (10) into the pump housing (2);- mounting the second eccentric (22) on the driving shaft (10) and aligning it with the first eccentric (20);- mounting the first primary stage piston (12) and the second seconday stage piston rod (56) on the second eccentric (22).

15. A vehicle (100), in particular a passenger car or commercial vehicle, comprising a piston type pump (1 ) according to any of claims 1 to 13.

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