Reservoir piston device

Abstract

The present invention relates to a reservoir piston arrangement (10) according to the features of claim 1. A reservoir piston arrangement (10) is a pressure medium reservoir of an electronically slip-controllable vehicle brake system, which is used for intermediate storage of pressure medium released from wheel brakes within the context of brake pressure control. In particular in electrically powered vehicles, such a pressure medium reservoir is used for each braking process. In this case, a reaction pressure as low as possible of this pressure medium reservoir is particularly important, since this promotes the efficiency of the recuperation of braking energy, reduces friction between the reservoir piston arrangement (10) and the associated receiving parts, and minimizes wear on the guides and / or seals of the reservoir piston. For this purpose, a reservoir piston arrangement (10) is proposed which has a reservoir piston (12) with a first guide ring (14a) on a first circumference of a first skirt section (18a), which surrounds the piston skirt (18) and projects radially above a second skirt section (18b) of the piston skirt (18) which is larger in terms of its outer dimensions.

Description

Technical Field

[0001] The present invention relates to a reservoir piston device having the constituent elements of the preamble of claim 1. Such a type of reservoir piston device is already known, for example, from Patent Document 1.

Background Art

[0002] The reservoir piston device is used particularly as a pressure medium reservoir of a hydraulic unit for electronically controlling the pressure in the braking equipment of a motor vehicle. For this purpose, the reservoir piston device is movably guided and accommodated in a reservoir cylinder, separating a reservoir chamber that can be filled with a hydraulic pressure medium from an air chamber in which at least one piston spring for biasing the reservoir piston device is arranged. The pressure medium discharged from at least one wheel brake attached to the vehicle braking equipment within the framework of brake pressure control flows into the reservoir chamber against the force of the piston spring.

[0003] In a conventional vehicle, i.e., a vehicle driven by an internal combustion engine, such a type of brake pressure control is usually carried out depending on the current slip situation of the wheel attached to the wheel brake. The purpose at that time is to deal with the locking of the wheel and maintain the lateral stability of the wheel and, as a consequence, the stable driving state of the vehicle. Since such critical driving states occur relatively rarely, the pressure medium reservoir is subjected to a relatively low load.

[0004] A vehicle braking equipment that can be electronically slip-controlled or pressure-controlled is well known under the name of ABS / ESP braking equipment.

[0005] In recent years, vehicles equipped with electric drive in addition to internal combustion engines, and vehicles driven solely by electric motors, have become increasingly common in the market. Electric drive has the advantage of being able to switch from locally emission-free operation to generator operation, during which the vehicle's kinetic energy is converted into electrical energy, which can then be used to brake the vehicle. The energy obtained can then be used to propel the vehicle at a later time, which ultimately improves the efficiency of the drivetrain of such vehicles.

[0006] By simply switching the vehicle's electric drive to generator operation, many of the driver's braking requests can be realized without using the vehicle's conventional hydraulic brake system. Only when the generator's braking torque alone is insufficient for the desired deceleration of the vehicle is the hydraulic brake system activated to provide supplemental braking torque.

[0007] However, the generator brake torque decreases with vehicle speed and, consequently, with the rotational speed of the driven rotor. Accordingly, in order to provide the desired brake torque set by the driver or the corresponding overall brake torque, the proportion of hydraulic brake torque increases as the proportion of generator brake torque decreases. To ensure that the driver is as unaware as possible of this so-called torque blend, electric vehicles require continuous adjustment of the hydraulic brake pressure during the braking process. Such adjustment is performed through the hydraulic unit of the hydraulic non-manual brake system or through the operation of the pressure medium reservoir.

[0008] Therefore, unlike conventionally driven automobiles, in the braking process of electric-powered vehicles, the hydraulic unit's pressure medium reservoir is involved in almost the entire braking process and is consequently subjected to a much greater load. Furthermore, in electric-powered vehicles, the efficiency of energy recovery during the braking process is as high as possible. To achieve this, it is essential that the pressure medium reservoir has a low reaction pressure, that is, that only a small pressure difference is required to operate the reservoir piston device.

[0009] Well-known pressure medium reservoirs are problematic in this respect. This is because their reservoir piston device is guided along the wall of the reservoir cylinder with a relatively high radial clamping force for effective guidance and sealing within the reservoir cylinder. The reason such a high clamping force is necessary is that reservoir piston devices are often made of plastic, and consequently, they are demolded radially from the mold. In this process, burrs are generated in the area of ​​the reservoir piston device where the sealing material is later installed, which can negatively affect the sealing condition, and this must be taken into account by increasing the clamping force.

[0010] To avoid these inconveniences, it is possible to use reservoir piston devices that are preferably manufactured as turned parts from aluminum; however, such manufacturing methods are costly and expensive, leading to an increase in the total weight of the hydraulic unit.

[0011] Another drawback is that conventional pressure medium reservoirs are equipped with molded packings that have a solid sealing cross-section, either based on the increased clamping force or for wear prevention. These types of molded packings have drawbacks in terms of sealing and / or frictional properties when the ambient temperature drops, due to their reduced elasticity. Consequently, well-known pressure medium reservoirs have a reactive behavior that puts a strain on the efficiency of energy regeneration, ultimately slowing down the depletion of the pressure medium reservoir and, consequently, slowing down the reduction of brake pressure at the end of the braking process. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] German Patent Application Publication No. 102012219054A1 Specification [Overview of the Initiative]

[0013] In contrast, the invention based on the constituent elements of claim 1 has the advantage that the proposed reservoir piston device provides a pressure medium reservoir with extremely good reaction behavior. This good reaction behavior is particularly due to the fact that only low radial pressing forces are required for guiding and sealing the reservoir piston device within the reservoir cylinder. This means that the guide ring is pressed against the wall of the reservoir cylinder with relatively low force, and consequently experiences only low friction, and therefore has improved wear behavior.

[0014] This is achieved by a reservoir piston device configuration that allows the reservoir piston to be removed axially from the mold along the direction of the piston's long axis. Consequently, burrs can be avoided, at least in the area of ​​the reservoir piston device where the sealing material is placed. Furthermore, the reservoir piston device or its reservoir piston can be manufactured from plastic at low cost and with low weight. For this reason, it is preferable to apply conventional injection molding methods.

[0015] In addition, the good responsive behavior of the pressure medium reservoir results in the reservoir volume of the pressure medium reservoir being rapidly emptied at the end of the braking process, and consequently, a rapid reduction in brake pressure.

[0016] Other advantages and preferred developments of the present invention will become apparent from the dependent claims or the following description.

[0017] Based on the low radial clamping force, lip seal rings can be used as sealing materials. Due to their elasticity, lip seal rings have the advantage of having good sealing characteristics over a wide temperature range, especially with low friction and correspondingly less wear at the reservoir cylinder wall. Furthermore, in terms of material selection, lip seal rings can be adapted to a given sealing situation more easily than well-known molded packings.

[0018] The guide ring serves two functions in the reservoir piston device according to the present invention. On the one hand, it guides the reservoir piston within the reservoir cylinder, and on the other hand, it supports the sealing material of the reservoir piston device in the direction of the piston's long axis. The latter simplifies the design configuration of the reservoir piston.

[0019] In a particularly favorable development of the present invention in terms of mold costs, the guide ring may be integrally molded with the piston skirt of the reservoir piston by a material bonding method, which can be done, for example, using a conventional two-component injection molding method.

[0020] Embodiments of the present invention are shown in the drawings and will be described in detail below. For this purpose, the drawings include several figures in which corresponding components are denoted by a unified reference numeral.

[0021] Each drawing shows an embodiment in cross-sectional view. [Brief explanation of the drawing]

[0022] [Figure 1]It is a perspective view showing a first embodiment of a reservoir piston device according to the present invention. [Figure 2] It is a reservoir piston of a reservoir piston device manufactured by a molding die. [Figure 3] It is a second embodiment of the present invention.

Modes for Carrying Out the Invention

[0023] A first embodiment of a reservoir piston device (10) shown in FIG. 1 includes a reservoir piston (12), two guide rings (14a, 14b) respectively attached to opposite ends on the outer circumference of the reservoir piston (12), and a seal ring (16) disposed between the guide rings (14a, 14b).

[0024] The reservoir piston (12) is configured as a hollow piston by itself and includes a sleeve-shaped piston skirt (18) and a piston bottom surface (20) that closes an end portion located above in FIG. 1 of the piston skirt (18). The end face facing outward of the piston bottom surface (20) can be arbitrarily configured, and in the illustrated embodiment, it is structured in a star shape as an example.

[0025] The piston skirt (18) is divided in the direction of the piston major axis (L) into two cylindrical skirt regions (18a, 18b) in total as an example, and these are different from each other in terms of outer dimensions. The first skirt region (18a) where the piston bottom surface (20) is disposed has an outer diameter smaller than that of the second skirt region (18b) having an end portion of the reservoir piston (12) that opens downward so as to face the piston bottom surface (20) following this. The transition portion between the first and second skirt regions is manufactured as a right-angled step portion as an example. This step portion forms a stopper shoulder (22) for the sealing material (16) of the reservoir piston device (10) disposed on the circumference of the first skirt region (18a).

[0026] The sealing material (16) is configured as a lip seal ring having two seal lips extending in the direction of the piston's long axis (L). The seal ring (16) is closed at the edge facing the stopper shoulder (22) and open at the opposite edge. Thus, the seal lips surround a wedge-shaped circumferential groove that opens toward the first guide ring (14a) between them.

[0027] The lip seal ring is positioned in the first skirt area (18a) of the reservoir piston device (10) between the first guide ring (14a) and the stopper shoulder (22). The first guide ring (14a) is manufactured as a closed ring, and its overall cross-section is divided into a first cross-sectional area that defines the inner diameter of the guide ring and a second cross-sectional area that defines the outer diameter of the guide ring (14a). The first cross-sectional area of ​​the guide ring (14a) is inserted into an annular groove (24a) formed in the first skirt area (18a) of the reservoir piston (12), while the second cross-sectional area protrudes radially from this annular groove (24a) and extends radially onto the second skirt area (18b) of the piston skirt (18). This second cross-sectional area of ​​the guide ring (14a) is exposed toward the piston bottom surface (20), meaning that its lateral edges projecting radially from the piston bottom surface (20) are not covered by the reservoir piston (12).

[0028] The second guide ring (14b) of the reservoir piston device (10) is located in the second skirt area (18b), that is, the skirt area having the larger outer dimension of the reservoir piston (12), and is also located in the annular groove (24b). The outer diameters of both guide rings (14a, 14b) are approximately equal.

[0029] Figure 2 shows a mold (30) for manufacturing the reservoir piston (12) shown in Figure 1 from plastic using injection molding technology. The mold (30) consists of a cup-shaped mold (32), a molding die (34) inserted into the mold (32), and two pairs of lateral sliders (36a, 36b) that can be inserted from opposite directions at different heights into an attached horizontal gap of the mold (32). Both pairs of sliders (36a, 36b) are used to form annular grooves (24a, 24b) on the outer circumference of the first and second skirt sections (18a, 18b) of the piston skirt (18), which are intended to accommodate both guide rings (14a, 14b). The inner wall of the mold (32) shapes the outer contour of the reservoir piston (12), that is, the different outer dimensions of both skirt areas (18a, 18b), as well as the stopper shoulder (22) at the transition between these two skirt areas (18a, 18b). The bottom surface of the mold (32) is configured to form the star-shaped texture described above on the outward-facing end face of the piston bottom surface (20).

[0030] The molding die (34) closes the opening of the mold (32) outward by the die plate (38). A die (40) is mounted on this die plate (38), and when closed, this die protrudes into the interior of the mold (32), enclosing a hollow space between the outer wall of the die (40) and the inner wall of the mold (32). This hollow space houses a reservoir piston (12), which is produced when plastic fills the hollow space during the injection process. After the injected plastic material has cooled, the slider pair (36a, 36b) has been retracted, and the molding die has been removed, the reservoir piston (12) can be axially demolded from the mold (32) in the direction of the piston's long axis (L). The axial demolding possibility of the reservoir piston (12) is indicated by the directional arrows R1 and R2 in Figure 2.

[0031] Based on the axial release capability of the reservoir piston (12) from such a mold (32), at least one region (42) of the reservoir piston (12), which is formed between the annular groove (24a) in the first skirt region (18a) and the stopper shoulder (22) and where the seal material (16) of the reservoir piston device (10) will later be placed, can be manufactured with particularly high surface quality and without particularly problematic burrs. The absence of burrs allows for the use of a seal material (16) that is pressed against the housing for the reservoir piston device (10) with a relatively low initial radial stress, and consequently allows for the use of a lip seal material instead of a seal material (16) having a solid seal material cross-section.

[0032] Figure 3 shows a cross-sectional view of a second embodiment of a reservoir piston (12) equipped with guide rings (14a, 14b). This reservoir piston (12) corresponds to the reservoir piston (12) described in relation to the description in Figure 1 or Figure 2 in terms of its internal and external shape. However, it differs from the reservoir piston (12) described above in that both guide rings (14a, 14b) are not placed in an annular groove, but rather are directly integrally molded or injection-molded onto the circumferential surface of the reservoir piston (12) using a two-component injection molding method. By integrally molding the guide rings (14a, 14b), i.e., attaching them to the reservoir piston (12) in a material-bonding manner, it is possible to omit the pair of mold sliders used to create the annular groove for housing the guide rings during the manufacturing of the reservoir piston. Consequently, burrs that would inevitably occur on the separation surface between each pair of sliders are also avoided. Furthermore, the mold for manufacturing the reservoir piston (12), and the associated labor, are simplified.

[0033] Naturally, modifications or additions to the reservoir piston device (10) beyond the scope described above are also conceivable, provided that such modifications do not deviate from the scope of protection of one of the claims of claim 1 or its dependent claims. [Explanation of symbols]

[0034] 10 Reservoir Piston Device 12 Reservoir Piston 14a First guide ring 14b Second guide ring 16. Sealant 18 Piston Skirt 18a, 18b Skirt area 20 Piston bottom 22 Stopper shoulder area 24a Annular groove 30 Molding molds

Claims

1. A reservoir piston device (10), The reservoir piston (12) has a sleeve-shaped piston skirt (18) and a piston bottom surface (20) that closes the sleeve-shaped piston skirt (18) at one end thereof. The piston skirt (18) is divided into continuous skirt regions (18a, 18b) with different outer diameters in the direction of the piston's long axis (L). The outer diameter of the skirt regions (18a, 18b) increases in stages starting from the first skirt region (18a) where the piston bottom surface (20) is positioned directly or via an inclined portion, and the first skirt region (18a) defines the first outer diameter, which is the smallest outer diameter of the skirt regions (18a, 18b). In a reservoir piston device, the first stepped portion between the first skirt area (18a) and the subsequent skirt area (18b) along the piston's long axis (L) constitutes a stopper shoulder portion (22) for the seal material (16) of the reservoir piston device (10), which is located in the first skirt area (18a). The reservoir piston (12) includes a first guide ring (14a) in the first skirt region (18a), the first guide ring (14a) is formed to surround the piston skirt (18) and protrudes radially onto the subsequent skirt region (18b) of the piston skirt (18), A reservoir piston device characterized in that the maximum diameter of the piston bottom surface is less than or equal to the first outer diameter of the first skirt area (18a).

2. The reservoir piston device (10) according to claim 1, characterized in that the sealing material (16) is positioned on the circumference of the first skirt area (18a) between the first guide ring (14a) and the stopper shoulder (22).

3. The reservoir piston device according to claim 2, characterized in that the sealing material (16) is a lip seal ring supported on the stopper shoulder (22) with an edge that is closed in the direction of the piston's long axis (L).

4. The reservoir piston device according to any one of claims 1 to 3, characterized in that the first guide ring (14a) is partially housed in an annular groove (24a) in the first skirt area (18a) of the reservoir piston (12) and partially protrudes radially from the annular groove (24a).

5. The reservoir piston device according to any one of claims 1 to 4, characterized in that the reservoir piston (12) is an injection-molded product made of plastic that can be released from the molding die (30) in the direction of the piston's long axis (L).

6. The reservoir piston device according to any one of claims 1 to 5, characterized in that the sealing material (16) abuts against the outer wall of the first skirt area (18a) of the reservoir piston (12), which is manufactured by injection molding technology without cutting post-processing.

7. The reservoir piston (12) is equipped with a second guide ring (14b) in the skirt area (18b) which has the largest outer dimension of the reservoir piston (12), The reservoir piston device according to any one of claims 1 to 6, characterized in that the outer dimensions of the first guide ring (14a) and the second guide ring (14b) correspond to each other at least approximately.

8. The reservoir piston device according to any one of claims 1 to 3, characterized in that at least the first guide ring (14a) of the reservoir piston device (10) is integrally molded in a material-bonding manner to the first skirt area (18a) of the piston skirt (18).

9. A reservoir piston device according to any one of claims 1 to 8, characterized in that the lateral edge of the first guide ring (14a) facing toward the piston bottom surface (20) in the direction of the piston's long axis (L) is not covered by the reservoir piston (12).

10. The reservoir piston device according to any one of claims 1 to 9, characterized in that the reservoir piston (12) has the first skirt area (18a) and exactly one second skirt area (18b).

11. The reservoir piston device according to any one of claims 1 to 10, wherein the reservoir piston device is for a pressure medium reservoir of a hydraulic unit for brake pressure control in an electronically pressure-controllable non-human-powered brake system of an electrically driven automobile.

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