Hydraulic actuation apparatus for a motor vehicle clutch

A hydraulic actuation apparatus for a motor vehicle clutch includes a master cylinder, a slave cylinder, a hydraulic line forming a main fluid channel connecting the master cylinder to the slave cylinder to form a pressure space, and a damping member arranged in the pressure space for attenuating pressure pulses. The damping member includes a connection channel connected to the main fluid channel and a fluid guide directing fluid from the main fluid channel into the connection channel. The damping member or other hydraulic operating component is preferably formed integrally with the hydraulic line, and is preferably injection molded plastic.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hydraulic actuation apparatus for a motor vehicle clutch, wherein the apparatus includes a master cylinder, a slave cylinder, a hydraulic line connecting the master cylinder to the slave cylinder to form a pressure space, and a damping member for attenuating pressure pulses in the pressure space.

2. Description of the Related Art

Hydraulic clutch actuation systems in motor vehicles have the undesirable characteristic that axial vibrations triggered by the periodically firing internal combustion engine are transmitted by the friction clutch and its diaphragm spring to the clutch release bearing and the clutch release devices connected to the latter. These axial vibrations continue into a hydraulic pressure space defined by a master cylinder and a slave cylinder and to the hydraulic channel connecting the latter and can trigger an unpleasant tingling in the foot of the driver of the vehicle when contacting the clutch pedal.

The pressure pulsations can be damped, on the one hand, by using a pressure line of limited flexibility, e.g., formed of a steel-rubber composite. In applications where this step is insufficient by itself, additional hydraulic damping members constructed as so-called tickle filters can be integrated in the hydraulic actuation system in addition. Further, steel-rubber lines are increasingly being replaced by pressure lines made entirely of plastic which are simpler to manufacture and less expensive. When loaded by pressure due to clutch actuation, these pressure lines have less elasticity than the type of line mentioned above and therefore hold less volume. In these cases, the use of a hydraulic damping member is particularly desirable.

A damping member can be placed in various positions in the pressure space of a hydraulic actuation device. For example, DE 100 08 479, which corresponds to GB 2,386,934, discloses a plurality of different kinds of damping members which are either constructed, e.g., according to the schematic view in FIG. 16, as a structural composite with the master cylinder or slave cylinder or are arranged separately within the hydraulic line. In this variant, the damping member shown in this reference has an inlet opening and an outlet opening with fluid coupling elements which are provided for connecting to two portions of a hydraulic line which also has corresponding coupling elements. Therefore, a hydraulic actuation device according to the described construction has a total of four coupling areas with eight coupling elements.

Generally, fluid clutches present critical areas in a hydraulic high-pressure system because they are a source of system failures particularly as operating time progresses. The fluid located in the hydraulic actuation device can exit from the latter and severely jeopardize the operating reliability of the vehicle. The arrangement of a damping member in combination with two hydraulic pressure lines shown in DE 100 08 479 is extremely disadvantageous in this respect and also results in high manufacturing and assembly costs.

U.S. Pat. No. 6,430,928 also describes, in FIG. 11, a damping member connected to two hydraulic lines. However, the damping member itself, in contrast to that shown in DE 100 08 479, has only a single connection area for connecting to the hydraulic lines which is formed by a T-piece, the ends of the fluid lines connected to the master cylinder and slave cylinder being inserted and permanently connected in the oppositely located connection openings of this T-piece. The remaining, third connection area of the T-piece is screwed to a connection area of the damping member by means of a thread. In this way, the quantity of detachable fluid connections is reduced by two, that is, to six, so that operating reliability is increased. On the other hand, the screw-in thread is also a source of leakiness in the hydraulic system. The provision and mounting of a separate T-connection element also represent significant cost factors.

U.S. Pat. No. 6,742,643 discloses another damping member for a hydraulic clutch actuation device. The housing of the damping member has a hydraulic line with a main channel extending between two plug-in couplers and a fluid connection for a pressure chamber of a damping member constructed as a diaphragm vibration damper, which fluid connection branches off laterally from a central area of the hydraulic line and opens into a pressure chamber of the damping member, which is constructed as a diaphragm vibration damper. The damping member itself is already very compact; but in order to produce a fluid connection to a master cylinder and slave cylinder at least one hydraulic line must also be interposed therebetween.

In an actuation system constructed in the manner described above and a damping member connected to a branch channel, it has been shown that in spite of an improvement over a system without damping, a significant proportion of pressure pulsations is still transmitted to the master cylinder and perceived by the driver as annoying.

Hydraulic coupling elements in the form of plug-in connectors or bushings at the ends of a hydraulic line serve to connect the master cylinder and slave cylinder directly or at least indirectly with the intermediary of additional hydraulic operating components.

The hydraulic actuation devices in question usually comprise an air-bleed element for removing air from the hydraulic actuation device, such as is described in DE 195 16 389, U.S. Pat. No. 5,960,922, DE 197 18 332 and DE 199 54 919, which is arranged at the housing of a slave cylinder or master cylinder. Further, it is known from practice to construct an air-bleed element as a separate T-piece that is arranged so as to be connectable between the hydraulic line and a hydraulic actuating member constructed as a concentric slave cylinder.

Further, the hydraulic actuation device can also comprise a throttle member for limiting the rate of flow of a hydraulic fluid which is arranged at the housing of a master cylinder or slave cylinder in the connection area for the hydraulic line, e.g., according to U.S. Pat. No. 6,250,201.

Further, a separate damping member can be provided in the actuation device for attenuating pressure pulsations. The pressure pulsations are caused principally by axial vibrations which are triggered by a periodically firing internal combustion engine in a vehicle and are transmitted by the friction clutch and its diaphragm spring to the clutch release bearing and the clutch release devices connected therewith. These axial vibrations continue into a hydraulic pressure space defined by a master cylinder and a slave cylinder and to the hydraulic channel connecting the latter and can trigger an unpleasant tingling in the foot of the driver of the vehicle when contacting the clutch pedal.

SUMMARY OF THE INVENTION

Based on the prior art cited above, it is the object of the present invention to further reduce the amount of structural component parts of a hydraulic actuation device for a motor vehicle clutch and, in so doing, to increase its operating reliability. It is a further object to improve the action of a damping member that is connected to a main fluid channel by a branch channel.

According to the invention, the damping member is connected to the main fluid channel by a connection channel having a fluid guide which directs fluid to a pressure chamber.

The inventor has recognized that pressure pulsations propagating in direction of the master cylinder from the slave cylinder communicating with the drivetrain of the vehicle are divided in the connection area of the damping member into a first pulsation which becomes weaker inside the damping member and a second pulsation which excites an oscillation of the piston in the master cylinder. Proceeding from this understanding, fluid is diverted in the area where the connection channel is connected to the main channel in order to generate a fluid flow that is directed substantially to the damping member so that a direct flow connection between the master cylinder and slave cylinder is eliminated to a great extent. In this way, a pressure pulsation propagating in the system is initially deflected almost completely into the damping member and can be attenuated therein. Accordingly, this functionality corresponds to that of a damping member arranged in series with an inlet fluid connection and an outlet fluid connection to the main channel.

The quantity of coupling areas in the hydraulic actuation device can be reduced even further by constructing the damping member integral with the hydraulic line so that only two coupling areas for connecting a master cylinder and slave cylinder need to be provided at the damping line element provided by the invention.

It is particularly advantageous when the damping member, the hydraulic line and the hydraulic coupling elements are made from plastic. In this case, the housing of the damping member can be injection-molded on a pre-manufactured hydraulic line in a reliable manner in terms of process technique.

Where an additional operating component, for example, an air-bleed element, provided in the hydraulic actuation device is formed integrally with the hydraulic line, this component can be exchanged more easily in the event of an operating malfunction or failure. The hydraulic line is usually connected to a master cylinder and a slave cylinder by plug-in couplings so as to enable a simple manual assembly in the normally extremely cramped installation space in a time-saving manner without the use of special tools.

When a plurality of operating components are formed integrally with the hydraulic line, there is the additional advantage that all of these operating components can be installed in the hydraulic system simultaneously in one step or can be removed or exchanged, e.g., for inspection purposes, so that the time required for inspection or repair can be reduced.

When a damping member, for example, is formed integral with the hydraulic line, the quantity of coupling areas in the hydraulic actuation device can be even further reduced so that only two coupling areas for connecting a master cylinder and slave cylinder need to be provided at the damping line element.

Where the damping member is arranged at an end area of the hydraulic line, a hydraulic coupling element, i.e., a connector or a receiving area, can be constructed simultaneously with the damping member.

However, it is also possible in principle to start with a separate damping member and a separate hydraulic line and to produce only the connecting area by means of an injection molding process or vulcanizing process, for example.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

A hydraulic actuation device10for actuating a motor vehicle clutch12is shown schematically inFIG. 1. The hydraulic actuation device10is arranged at a chassis14of a motor vehicle. A master cylinder16with a piston18and a slave cylinder20with a piston22are connected with one another by plug-in couplings or hydraulic coupling elements24to a hydraulic line26filled with a fluid25and form a common pressure space28. The piston18of the master cylinder16can be actuated by a pedal30, whereupon the piston22of the slave cylinder20is displaced and controls a clutch fork32for releasing the clutch12in a driving unit constructed as a combustion engine34. The clutch12is connected on the input side to the driven shaft of the combustion engine34and on the output side to a shift transmission36. A damping member29is provided inside the hydraulic line26for damping pressure pulsations and is connected by a connection channel31that branches off from a main fluid channel27. The damping member29can be constructed in one piece with, i.e., integral with, the hydraulic line or, alternatively, can be connected to it by hydraulic coupling elements24.

FIGS. 2A and 2Bshow a damping member29that is constructed as a diaphragm oscillator and comprises a cylindrical housing38with a circular steel-plate diaphragm40which is arranged therein at the face and which can oscillate during pressure pulsations of the hydraulic fluid. When there is a sudden increase in pressure, the diaphragm can deflect outward briefly and so provide additional volume so that a pressure pulsation can be reduced. The diaphragm40is pressed against an annular web43by a housing cover42and seals off a fluid pressure chamber48from the atmosphere by an O-ring seal46located in a groove44. The cover42is held on its seat by a bead50. The inner surface52of the cover42is concave so that, when a maximum permissible fluid pressure is reached, the diaphragm40can adapt to this so as to prevent overstretching of the diaphragm40and a possible bursting of the damping member29.

In order to produce a fluid connection between the hydraulic line26and the damping member29, a free end of a hydraulic line26, which is preferably made of PA12plastic, is provided with a housing38that is injection-molded at this end and accordingly connected therewith so as to be tight against fluid. The housing38likewise comprises PA12, but is additionally structurally reinforced by a fiber material, preferably glass fiber. It is important that a suitable, injectable plastics combination is used for the hydraulic line26and the housing38. The other end, not shown, of the hydraulic line26is provided with a first hydraulic coupling element24for connecting to the slave cylinder20. The housing38of the damping member29is formed integral with a second coupling element24for connecting to the master cylinder16. The combination of the housing38with the coupling element24proves advantageous in technical respects with regard to manufacture because these parts can preferably be based on the same material and can accordingly be produced in one work cycle.

As can be seen inFIG. 2B, the main fluid channel27, starting from the left-hand side, initially extends within the hydraulic line26and then passes into the housing38so as to exit by way of the coupling connector24. A connection channel31branches off from the main channel27within the housing38and has a fluid connection to the pressure chamber48and can introduce pressure pulsations into the latter. The connection channel31is arranged in such a way that it opens into the peripheral area of the pressure chamber48so that when the damping member29is installed vertically, i.e., when the main channel27is oriented vertically and the coupling element24is directed upward, air bubbles located in the damping member29can easily escape from the latter in this way and the actuation system10can be completely bled.

As an alternative to the embodiment example inFIG. 2a, the connection channel27can also open out inside the hydraulic line26laterally into its jacket area54or into the coupling element24.

According toFIG. 2C, the damping member29can also be arranged in any predeterminable position at a hydraulic line26that has already been outfitted at both sides with coupling elements24. For this purpose, the jacket54of the hydraulic line26is provided at this position with an opening55and the housing38of the damping member29is injection molded on the hydraulic line29, wherein the fluid connection, i.e., the connection channel31to the pressure chamber48, is produced by the jacket opening. In this construction, therefore, the hydraulic line26is formed continuously in the area of the damping member29.

A damping member29integrated in a hydraulic line26can also be realized by producing a hydraulic line26and a separate damping member29in a first step and connecting the two parts26,29with one another in a fluid-tight manner in a second step in that the seal locations can be produced, for example, by injecting plastic or by vulcanizing a rubber material or similar sealing substance.

The function of the damping member29can be considerably improved by a fluid guide element56arranged at least in the area where the connection channel31is connected to the main channel27, wherein this fluid guide element56influences the flow in the main fluid channel27and generates a fluid flow which is directed substantially to the damping member29. The fluid guide element56which is shown at the damping member29inFIG. 2Bextends chiefly inside the connection channel31and continues on both sides into the main channel27and into the pressure chamber48.

According toFIG. 3, two or more diaphragms40a,40bwith identical or different stiffness which are spaced apart by spacers41can also be placed in the pressure chamber48instead of only one diaphragm40in order to adapt the damping behavior specifically to different drivetrain configurations and/or pressure ranges in an optimal manner. Further, as is shown inFIG. 4, a spring device, e.g., in the form of a disk spring45, can also be arranged on the side remote of the pressure chamber48, i.e., between the diaphragm40and the cover42, to generate a counterforce depending on the extent of pressure pulsations and/or to limit the deflection of the diaphragm oscillator29. The disk spring45is snapped onto a connection element47arranged at the diaphragm40and has intervening space for play with respect to the latter and/or with respect to the cover42to accommodate a deformation of the disk spring45.

FIGS. 5A and 5Bshow a separate fluid guide element56which is manufactured as a plastic injection molded article and is based on an L-shaped dividing wall58which divides the connection channel31into an inlet channel60and an outlet channel62depending on the direction of flow. Two webs64,66project from the two sides of the dividing wall58and serve as spacers for fixing the fluid guide element56. One of the webs64,66is constructed as a resilient catch hook66to produce a snap connection with the connection channel31and main channel27. An end portion68of the dividing wall58projecting into the main channel27is formed as a semicircular disk and contacts the inner wall of the main channel27so that the otherwise continuous and direct main fluid channel27between the master cylinder16and the slave cylinder20is substantially interrupted in this area. The dividing wall58projects partially into the pressure chamber48and has, as its upper termination, a bend70which is oriented approximately parallel to the diaphragm40and by means of which the fluid flowing in is guided preferably laterally into the pressure chamber48so as to be swirled. In order to increase the dwell period of the fluid in the pressure chamber48, the fluid guide element56can have additional dividing wall arrangements or guide arrangements, e.g., a web, or the like, which projects perpendicularly from the spacer64.

The described fluid guide element56deflects the fluid flow entering, e.g., from the slave cylinder20into the main channel27so as to generate a fluid flow directed into the damping member29. This flow is kept away from a flow exiting the damping member29in the direction of the master cylinder16by the dividing wall58that is arranged in the connection channel31and is finally forced by the area arranged in the pressure chamber48onto a flow path whose length is greater by a multiple than the mutual distance of the inlet channel60and outlet channel62so as to exit the pressure chamber48again via the outlet channel62.

Alternatively, the above-described guiding and dividing means influencing the flow can also be carried out individually, i.e., separately, at the hydraulic line, the connection channel and the pressure chamber.

Finally, it should be mentioned that the damping member29, shown by way of example inFIGS. 2A–2Ccan be formed with two or more pressure chambers48, each of which is arranged with a connection channel31at the main channel27. The individual pressure chambers48can be arranged in parallel in the main channel, which means that a propagating pressure pulsation impinges on all of the pressure chambers48without preference and simultaneously. On the other hand, it is also conceivable to arrange the pressure chambers48in series which can be realized, for example, by connection channels31that are arranged at the main channel so as to be offset in the direction of flow. In this case, a pressure pulsation passes through the individual pressure chambers48successively and becomes increasingly weaker along its flow path.

FIGS. 6A and 6Bshow a hydraulic line26having, at one end, a damping member29according toFIGS. 2A,3or4whose housing38is constructed jointly with a fluid coupling element24aconstructed as a plug-in connector. The fluid coupling element24bformed at the other end of the hydraulic line26as a receiving part has a housing in common with an air-bleed element29band a throttle member29c. In order to compensate for variations in spacing between the master cylinder16arranged at the chassis and the slave cylinder20mounted at the drivetrain that occur as a result of vehicle vibrations in running combustion engines, the hydraulic line26, which is made of plastic, is provided with an expansion loop71. This improves its elasticity appreciably. The letters A-L designate points of contraflexure along the course of the line or fitting dimensions for adapting to specific installation conditions depending on the type of vehicle.

FIGS. 7A and 7Bshow a detail of the fluid coupling element24bshown inFIG. 6with a throttle member29carranged inside the main fluid channel27. Adjacent to the end portion of the jacket area54, the fluid coupling element24bhas a recess72with a stepped down diameter relative to the latter. A stop ring74for a valve body78that is axially displaceable in a movement space76is arranged in this recess72. The transition to a continuing center portion79of the main channel27is carried out with a step80of another stepped down diameter which forms another stop for the valve body78. Depending on the direction of flow, the valve body78can move against the stop ring74at one time and against the step80at another time. The valve body78has a central, funnel-shaped bore hole82and, at the circumference, at least one through-channel84through which the fluid can flow.

A connection channel86opens laterally into the central portion79and produces a fluid connection to the air-bleed element29which is screwed into a housing portion88of the fluid coupling element24bwith a multiple-stepped internal bore hole, this housing portion88projecting laterally from the main body.

In other respects, the construction and design of the air-bleed element29band throttle member29ccorrespond to the elements known from the prior art so that detailed descriptions are not necessary.