Abstract:
A hydraulic actuation system, especially for actuating the clutch of a vehicle, containing a master cylinder unit, a slave cylinder unit, a hydraulic medium line connecting the two cylinder units and a throttle valve which is used to alter the flow resistance between the cylinders of the master cylinder unit and the slave cylinder unit.

Description:
The present invention relates to a hydraulic clutch system, in particular for actuating a vehicle clutch. Furthermore, the present invention relates to a device for connecting a pipe-shaped hydraulic medium line to a connector on a housing, in particular in a hydraulic system according to the present invention. 
     BACKGROUND 
     Hydraulic actuation systems having a master cylinder unit, which is, for example, operated by a pedal using the foot, and which is connected via a pressure medium line to a slave cylinder unit, which actuates an assembly such as a vehicle clutch, transmission, or brake, have many applications. Actuation systems of this kind, in particular actuation systems for actuating a vehicle clutch, are designed to ensure that the assembly in question can be actuated safely and comfortably. 
     One problem encountered when vehicle clutches are actuated hydraulically is that the engine stalls if a clutch pedal is actuated too quickly to engage the clutch. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a hydraulic actuation system, in particular for actuating a vehicle clutch, which allows actuation to be carried out in a carefully measured manner. 
     The present invention provides a hydraulic actuation system, in particular for actuating a vehicle clutch that includes a master cylinder unit, a slave cylinder unit, a pressure medium line connecting the two cylinder units, and a throttle valve for adjusting the flow resistance between the cylinders of the master cylinder unit and the slave cylinder unit. With the actuation system according to the present invention, the through-flow resistance between the cylinder units and thus the behavior of the hydraulic transfer section is adjustable based on the requirements in question by designing or controlling the throttle valve appropriately. 
     It is advantageous that the throttle valve is actuated by an actuator controlled by a control unit that is connected to a sensor which detects the engine speed and if necessary adjusts the through-flow cross section between the master cylinder unit and the slave cylinder unit during the starting-off procedure as a function of the engine speed curve. In this way, the through-flow cross section between the master cylinder unit and the slave cylinder unit may be adjusted as a function of the movement of the piston in question. The signals for controlling the device may of course also be generated using sensors already present in the vehicle, e.g., engine sensors, transmission input sensors, transmission output sensors and/or wheel speed sensors. 
     If the actuation system according to the present invention is used to actuate a vehicle starting clutch, it is advantageous that the sensor detects the engine speed and, if the engine speed curve exceeds predefined limiting values as the clutch engages, the control unit triggers the actuator in the direction of a reduction of the through-flow cross section. This means that the engine&#39;s required increase in torque as the clutch engages does not have to increase abruptly, and hence stalling of the engine is avoided. 
     It is advantageous that, if the engine speed curve exceeds predefined limiting values as the clutch engages, the control unit of the aforementioned actuation system triggers an actuator for adjusting the output of an internal combustion engine of the vehicle in the direction of an output increase. This further reduces the risk of stalling the engine, i.e., the internal combustion engine. 
     It is advantageous that the control unit is connected to further sensors for detecting the rotational speed of a vehicle wheel and/or a transmission ratio so that the through-flow cross section of the hydraulic section of the actuation system is adjustable optimally based on the prevailing operating conditions and in accordance with the requirements in question. 
     In a modified embodiment of an actuation system according to the present invention, a valve element of the throttle valve is movably mounted in a bore hole that extends roughly at right angles to a connector bore hole leading into the working chamber of one of the cylinder units and is designed and works in conjunction with walls of the bore hole in such a way that it is moved in one or another direction into contact with a stop edge by a hydraulic medium flow between the two cylinder units, and as a result a flow cross section made available by the valve element is reduced when it rests against the stop edge. With the aforementioned embodiment of the throttle valve, the axial space occupied by the corresponding cylinder unit is only minimally increased by the throttle valve, and furthermore the design is straightforward and very reliable. 
     It is advantageous that the valve as a whole is pipe-shaped, has an axial through-channel and is movably mounted so that hydraulic medium flowing out of the corresponding working chamber flows through the through-channel, and hydraulic medium flowing into the corresponding working chamber moves the valve element so that its end face rests against a wall that encloses the bore hole, so that the through-channel is at least partially closed and the hydraulic medium flows through a radial opening in the wall of the through-channel. 
     In a further refinement of the aforementioned throttle valve, the bore hole which bears the valve element is positioned in the housing of the corresponding cylinder unit and the pressure medium line is connected to the bore hole. 
     It is advantageous that the throttle valve is assigned to the master cylinder of a vehicle hydraulic clutch actuation system and reduces the flow cross section of a flow of hydraulic medium into the master cylinder. 
     A particularly straightforward design of a device for connecting a pipe-shaped hydraulic medium line to a connector on a housing, which in particular may be used in a hydraulic system of the type described above, includes an insertion channel in a cylindrical attachment part of the housing for insertion of a pipe, an annular space being formed between the outside of the pipe and the inside of the insertion channel, this being delimited axially inward by a radial annular surface, a locking element which is cylindrical as a whole and which is insertable into the insertion channel and which in its inserted state protrudes with its front end-section into the annular space and with its rear end-section lies outside the cylindrical attachment part, at least one sealing ring which may be positioned in the annular space between an end face of the locking element and the radial annular surface, and a locking sleeve which is rotatable relative to the locking element and is rotatable from an unlock position, in which the pipe is insertable through the locking sleeve and locking element beyond the annular surface of the attachment part and into the insertion channel, to a lock position in which the pipe is held axially against the attachment part by the locking element and/or locking sleeve. 
     The aforementioned device has a straightforward and cost-effective design and has the additional advantage that even when the pipe has not been installed, the sealing ring is held against the pre-assembled assembly that includes the housing and the locking element and, if applicable, the locking sleeve, and is thus protected against dirt and damage. 
     It is advantageous that the front end-section of the locking element in its inserted state extends back through the annular space of the cylindrical attachment part so that the locking element cannot be moved outward because it rests against the cylindrical attachment part in a form-locking manner. 
     It is advantageous that the annular space has in the outward direction a radial holding surface against which a counter-surface on the end-section of the locking element rests. This ensures that the locking element may be positioned against the attachment part without any problem. 
     If the rear end side of the locking element has radially inward a radial stop surface against which a projection on the pipe rests, the pipe may be positioned easily and reliably. 
     It is advantageous that the radial stop surface of the locking element delimits an annular space which overlaps the projection on the pipe. This ensures that the pipe cannot be shifted outward. 
     The projection is formed in a particularly straightforward manner by an annular bulge. 
     It is advantageous that the locking element has at least two fingers located diametrically opposite one another which rest against the outside of the cylindrical attachment part and work in conjunction with fingers on the locking sleeve so that in the locking sleeve&#39;s lock position they are pressed into engagement with the outside of the cylindrical attachment part in a form-locking manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention, which may generally be used for all kinds of hydraulic actuation systems, in particular those for actuating a vehicle clutch, is described in greater detail below by way of examples and with the help of schematic drawings. 
         FIG. 1  shows a schematic drawing of a hydraulic actuation system of a vehicle clutch; 
         FIGS. 2 and 3  show side views of a throttle valve with the valve element in two different positions; 
         FIGS. 4 and 5  show side views of a further embodiment of a throttle valve with the valve element in two different positions; 
         FIG. 6  shows an axial section through a connector device; 
         FIG. 7  shows a perspective view of the device shown in  FIG. 6 ; and 
         FIG. 8  shows a longitudinal section through a pipe having a projection formed by a bulge. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a hydraulic actuation system for a clutch includes a master cylinder unit  10 , which is connected to a slave cylinder unit  12  via a hydraulic medium line  14 . A clutch  16  is actuated hydraulically when master cylinder unit  10  is acted upon by an actuating element  18 , which may be a foot pedal, an actuator, for example an electrical actuator or similar. When actuating element  18  is actuated, a movable piston  24  in cylinder  22  of master cylinder unit  10  is moved by a piston rod  20  to the left as shown in  FIG. 1  so that pressure builds up in cylinder  22  and is conveyed via hydraulic medium line  14  through a throttle valve  26  into slave cylinder unit  12 . It is advantageous that slave cylinder  12  is, as shown, positioned concentrically around a transmission input shaft  28  and rests axially on a transmission housing (not shown) so that the necessary release force may be exerted via a release bearing of clutch  16 , i.e., on its release elements, e.g., disk springs, in a manner known heretofore. 
     When clutch  16 , which is positioned concentrically with a crankshaft  30  of an internal combustion engine  32 , is engaged, transmission input shaft  28  transfers the torque of internal combustion engine  32  to a transmission (not shown) and from that to the drive wheels of a vehicle. 
     A pressure medium reservoir  34  supplies pressure medium in a manner that is known heretofore, and is connected to master cylinder  10  when the latter is in the inoperative position, i.e., no pressure is being exerted on slave cylinder  12 . In this position, pressure medium is able to flow back into master cylinder unit  10 . When master cylinder unit  10  is actuated, pressure medium reservoir  34  is separated from master cylinder unit  10  by a valve (e.g., a covered snifter hole) which is not shown. 
     Throttle valve  26  includes a valve element  40  which is pushed into the open position by a spring  42  and which has a shaft that functions as an armature for an electromagnet  44 . Electromagnet  44  is triggered by a control unit  46 , the inputs of which are connected to a sensor  48  for detecting the speed of piston rod  20  and actuating element  18 , a sensor  50  for detecting the rotational speed of a vehicle wheel (not shown), and a sensor  52  for detecting the gear, i.e., gear ratio, of a transmission (not shown). A further output of control unit  46  is connected to an actuator  54  for actuating a power control element of internal combustion engine  32 , e.g., a throttle. 
     Electronically actuated throttle valve  26  functions as follows: 
     During the clutch&#39;s engaging procedure, the engine speed is detected. If the engine speed falls below an rpm limiting value which is dependent on the drop rate of the engine speed, current is applied to electromagnet  44  so that valve element  40  moves into a flow cross section formed by a housing of throttle valve  26  and reduces it. 
     The flow of hydraulic medium through line  14  is thus reduced so that clutch  16  engages more slowly, thus reducing the danger of stalling internal combustion engine  32 . 
     Actuator  54  is optional. If it is present, it is advantageous that simultaneously with the increasing closure of throttle valve  26  the power control element is opened so that the engine speed is increased. This provides additional help in preventing stalling. The speed of opening of the power control element is, for example, proportional to the speed of closure, i.e., speed of engagement of the clutch. 
     Sensors  50  and  52  are also optional. If the wheel rotational speed and the gear position are detected, the throttle valve may be actuated in a manner appropriate to the operating situation, for example, the through-flow cross section of line  14  may be limited over a longer period if the vehicle is starting off in first gear than is the case when shifting between other gears, it also being possible for the degree of throttling, i.e., reduction of cross section, to also be dependent on the vehicle speed. 
     Various control strategies are feasible for the throttle valve, for example path control as a proportional valve, or pulses of the electromagnet having different frequencies, or 2-point control with open/closed only. Furthermore, various strategies are feasible for path measurement for master cylinder unit  10 , for example, continuous path measurement, which may at the same time replace a currently customary brake light switch, and moreover the signals may be used in conjunction with an engine control system for improving driving comfort. In a straightforward form, 2- or 3-point measurement is sufficient, as found currently with pedal switches or at the master cylinder unit. 
     Active throttle valve  26  as described, which may be designed and actuated in a variety of ways (globe valve, turning valve etc.), is advantageous when starting off, i.e., for preventing stalling of the engine, and furthermore may also advantageously be used when shifting between higher gears. 
     A further advantageous application of the active throttle valve is that it may be used to suppress back-engagement between the engine and the clutch pedal, e.g., as caused by engine vibration. Excessively high pressure in hydraulic medium line  14 , which in  FIG. 1  is shown to the left of throttle valve  26 , as may be induced by vibration, may be detected by a pressure sensor.(not shown) and converted into a throttling of the through-flow cross section. 
       FIGS. 2 and 3  show cross sections through a passive throttle valve  60 , the valve element of which is in two different positions. An axial cross section through a part of master cylinder  22  is shown. From working chamber  62  of a master cylinder  22 , connector bore hole.  64  leads into a further bore hole  66  which is roughly at right angles to connector bore hole  64  in the housing of cylinder  22  and which, as shown in  FIG. 2 , is closed off from above by a stopper  68  so that a fluid-tight seal is ensured. Stopper  68 , which may be, for example, screwed into bore hole  66 , has an end face  70  which is roughly flush with the upper side of connector bore hole  64 . A pipe- or sleeve-shaped valve element  72  is movable in bore hole  66  via a collar  74 . 
       FIG. 2  shows the fully opened position of throttle valve  60  assumed by valve element  72  when hydraulic medium flows from working chamber  62  into bore hole  66 , to which as shown in  FIG. 2  hydraulic medium line  14  ( FIG. 1 ) is connected at the lower end. In the fully open position, collar  74  rests against a step  76  of bore hole  66  so that the opening movement of valve element  72  is limited. Of course valve element  72  is ribbed on its outside beneath collar  74  and/or bore hole  66  is ribbed below step  76  so that hydraulic medium between the collar and the step is able to escape. As can be seen, when valve element  72  is in the open position the entire cross section of a through-channel  78  through valve element  72  is available. 
     When the flow direction of medium is reversed, i.e., it flows out of bore hole  66  into working chamber  62 , valve element  72  moves out of the position shown in  FIG. 2  into the position shown in  FIG. 3  in which its upper annular end face  80  rests against end face  70  of stopper  68 . In this case there is only a small flow cross section available for the medium to flow through through-channel  78 , this being formed by one or a plurality of recesses  82  on the upper edge of valve element  72 . Of course recess or recesses  82  do not have to be located directly on the upper edge of valve element  72 , but rather may be in the form of one or a plurality of radial bore holes above collar  74 . 
     The functioning of throttle valve  60  as shown in  FIGS. 2 and 3  is as a whole similar to that of throttle valve  26  shown in  FIG. 1 , with the difference that throttle valve  60  functions passively. When medium flows rapidly into working chamber  62 , for example when the clutch is engaged, valve element  72  moves into its upper resting position and reduces the through-flow cross section to a minimum defined by recess  82 . In this way, the dynamic torque that the engine has to provide, in particular when the vehicle starts off with the clutch pedal having been released very rapidly, is limited. 
     Of course various embodiments of valve element  72 , which is moved by the pressure medium flow, i.e., by the pressure of the pressure medium, and of throttle valve  60  are feasible. For example, valve element  72  may have a plurality of axial through-flow channels which in the position shown in  FIG. 2  are all open and at least a few of which are closed in the position shown in  FIG. 3 . In addition, a spring may be provided to pre-tension the valve element in one of its end positions. 
     The design of throttle valve  60  which is integrated into the housing of cylinder  22  is extremely compact and straightforward and only minimally lengthens cylinder  22  in its axial direction by the diameter of bore hole  66 . 
       FIGS. 4 and 5 , which largely correspond to  FIGS. 2 and 3 , show a modified embodiment of a valve element. Collar  74  of valve element  72  is axially longer than in the embodiment shown in  FIGS. 2 and 3  and includes, near its upper edge, one or a plurality of radial holes  84 . In the closed position of valve element  72  shown in  FIG. 4 , radial holes  84  are covered by the wall of bore hole  66 , and the entirety of through-channel  78  of valve element  72  is available for through-flow, whereas in the closed position shown in  FIG. 5 , hole or holes  84  are open to connector bore hole  64  and through-channel  78  is closed off in the upward direction because end faces  70  and  80  are resting against one another. 
     Hydraulic actuation systems of the type described are produced in large volumes and it is important that there be an inexpensive and functionally reliable connection between hydraulic medium line  14  and cylinder units  10  and  12 . 
       FIGS. 6 and 7  show an axial section through and a perspective view of a connector of this kind. 
     Cylinder  22 , i.e., its housing, ends in a cylindrical attachment part  86 , in which an insertion channel  88  for the insertion of hydraulic medium line  14  ( FIG. 1 ) which ends as pipe  90 , is provided. The insertion channel, which is connected to working chamber  62  of cylinder  22 , enlarges its diameter at a first step  92  and then again at a second step  94  which is axially at a distance therefrom, and then ends after a third step  96  at which the diameter is reduced. The section between first step  92  and second step  94  has an inner diameter which roughly matches the outer diameter of pipe  90 . As shown in  FIGS. 6 and 7 , locking element  98 , which is as a whole cylindrical, is inserted from the left into insertion channel  88 , has an inner diameter which matches the outer diameter of the pipe, protrudes with front end-section  100  into an annular space between second step  94  and third step  96 , and extends back against third step  96 . Locking element  98 , which is made of, for example, plastic, has on its outside fingers  102 , which are positioned at a distance from one another around the circumference, for example offset by 180° from one another, may be pushed onto the slightly conical outer surface of attachment part  86  subject to elastic expansion, and extend back against annular rib  104  of attachment part  86  in a form-locking manner. Before locking element  98  is pushed onto attachment part  86 , at least one sealing ring  106  is placed in the annular space between steps  94  and  96 . 
     The inward movement of locking element  98  relative to attachment part  86  (to the right as shown in the figures) is limited because the front end of attachment part  86  rests against locking element  98  within fingers  102 , which ensures that sealing ring  106  is not forcibly misshapen when locking element  98  is inserted. 
     At its left-hand end-section  109 , as shown in the figures, the locking element has an annular space  108  formed by the stepped design, which at the right-hand side as shown in the figures forms a stop surface  110  for a projection  112  on pipe  90 . At its left-hand end, annular space  108  surrounds projection  112  in a form-locking manner. From the left, a locking sleeve  114  is placed onto locking element  98  and has fingers  116  which, when locking sleeve  114  is in the appropriate rotated position, overlap fingers  102  of locking element  98  and hold them against the outer surface of attachment part  86 . Locking sleeve  114  functions as a bayonet in conjunction with locking element  98  via corresponding diagonal surfaces. 
     The described system is assembled as follows: 
     Sealing element  106  is inserted into insertion channel  88 . Next, locking element  98  is inserted, and locking sleeve  114  is pushed onto locking element  98 , its being feasible to push it on in a rotated position, locking between locking sleeve  114  and locking element  98  then occurring after locking sleeve  114  has been rotated by 90°. Thus the assembly of sealing element  106 , locking element  98 , and locking sleeve  114  may be pre-mounted on cylinder  22 . To create a connection with the hydraulic medium line, pipe  90  is inserted from the left through locking sleeve  114  and locking element  98  into insertion channel  88  until projection  112 , which forms a single component along with pipe  90 , comes to rest against stop surface  110  after end-section  109  of locking element  98  has been gently elastically expanded. The end face of pipe  90 , which is shown on the right in the figures, is then at a distance from step  92 , and sealing element  106  creates a reliable seal between pipe  90  and attachment part  86 . Next, locking sleeve  114  is rotated so that it presses end-section  109  of locking element  98  so that there is form-locking contact with projection  112  and so that its fingers  116  press fingers  102  so that they rest in a form-locking manner against the outer surfaces of attachment part  86 . In this way, pipe  90  is attached reliably to attachment part  86  so that there is a seal. 
     Of course the described system may be modified in many ways. For example, projection  112  of pipe  90  is not needed if pipe  90  is only to be held in place by friction. Nevertheless, with the described undercuts a particularly reliable positive lock between the individual components, which hold pipe  90  axially in place on cylinder  22 , may be achieved. 
       FIG. 8  shows a particularly straightforward embodiment of projection  112  of pipe  90 . As shown in  FIG. 8 , projection  112  may be created in a straightforward manner by compressing pipe  90  axially so that a radial bulge is created. This means inexpensive pipe produced by the meter may be used for the hydraulic medium line, i.e., pipe  90 . 
     The patent claims filed with the application are formulation proposals without prejudice of the achievement of broader patent protection. The applicant reserves the right to claim additional feature combinations previously only disclosed in the description and/or the drawing. The back-references used in the dependent claims indicate further refinements of the object of the independent claim by the features of the particular dependent claim. They are not to be understood as a waiver of obtaining independent objective protection for the combinations of features of the back-referenced dependent claims. Because the objects of the dependent claims may form separate independent inventions with respect to the related art on the priority date, the applicant reserves the right to make them the object of independent claims or division clarifications. They may furthermore also contain independent inventions having a design that is independent of the objects of the aforementioned dependent claims. 
     The exemplary embodiments are not to be understood as limitations of the present invention. Rather, numerous modifications and variants are possible within the present disclosure, in particular variants, elements, and combinations and/or materials that are obvious to those skilled in the art regarding the achievement of the object or the achievement of advantages, for example, by combination or modification of individual features or elements or method steps described in conjunction with those in the general description and embodiments as well as in the claims and contained in the drawing, resulting in a new object or new method steps or method step sequences via combinable features, including those concerning manufacturing, testing, and work methods.