Patent Publication Number: US-6220271-B1

Title: Checkvalve unit

Description:
The present application is a Continuation Application of Application Ser. No. 09/078,198, filed May 13, 1998, now U.S. Pat. No. 6,035,881. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a checkvalve unit which is generally used to connect an operating system, e.g. the braking force amplifier of a vehicle braking system or the servomotor of the power steering system, of a vehicle requiring negative pressure to a suction system which produces negative pressure, e.g. the suction pipe or aspiration channel of a combustion engine. The checkvalve unit is to ensure that a negative pressure produced in an operating system is maintained, even when the pressure in the suction system rises or when the negativepressure production in the suction system is completely interrupted. The latter is the case for example when the vehicle engine is stopped. 
     A checkvalve unit comprises an inlet and an outlet connected to each other via a main air channel. In the assembled state or in case of utilization, the inlet is connected to the operating system and the outlet to the suction system. A first checkvalve is located in the main air channel. This prevents the negative pressure from escaping once it has been produced in the operating system in case that pressure rises in the suction system. Furthermore, one single outlet channel which branches off from the main air channel downstream of the first checkvalve and lets out into the atmosphere is provided with the checkvalve unit in question. A venturi pipe or a narrowing of the cross-section is provided in this outer-air channel. This narrowing of the cross-section is connected via a channel, hereinafter the venturi channel, to the main air channel at a point located upstream of the first checkvalve. 
     Such a checkvalve unit, hereinafter the valve unit, is described in U.S. Pat. No. 5,291,916; DE 43 44 624 A1 and DE 43 10 761 C2. In the known valve units, it is a disadvantage that air is constantly sucked in through the outer-air channel. This is especially detrimental with combustion engines where the air mass flowing through the choke valve of the air suction pipe is used for engine control or to optimize the combustion process. In a valve unit described in U.S. Pat. No. 3,754,841 the outer-air channel containing the venturi pipe can be closed off by a sliding valve when the system pressure of the operating system has reached its target value. The sliding valve is controlled by differential pressure. In addition, a membrane holding a plunger which actuates the sliding valve is subjected on the one hand to the system pressure and on the other hand to a reference pressure. To produce the reference pressure, a venturi pipe is installed in a second outer-air channel letting out into the atmosphere and connected to the suction pipe of the engine. A connecting channel branches off from the narrowing point of the venturi pipe and influences the above-mentioned membrane from one side. The second outer-air channel is permanently open, so that a stream of wrong air is constantly aspired by the suction pipe. Furthermore this valve unit can only be produced at high manufacturing and assembly costs. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Based on this, it is a principal object of the present invention to propose a valve unit which is simple in design and with which constant suction of outside air is prevented. 
     According to the present invention, a cut-off valve is installed before or after the narrowing of the cross-section of the venturi pipe in the single outer-air channel, said cut-off valve being actuated as a function of the system pressure prevailing in the operating system in such a manner that the connection to the atmosphere is opened when a predetermined target pressure is exceeded and is interrupted when this pressure is not reached. The connection to the outer air is thus open only when the system pressure exceeds a predetermined target pressure. As soon as the system pressure has dropped back to its target pressure, the outer-air channel is again shut off. An adulteration of the air mass flowing through the checkvalve is thereby substantially prevented. As a seat valve, the checkvalve is made with two defined switching positions, i.e. one open and one closed position. Such a valve is easy to produce and is also less prone to failure than a sliding valve, in which a suitably sized valve bore must be precisely made. 
     In an example of an embodiment of the invention, the shutoff valve is an electromagnetically actuated 2-way valve which is actuated by a control device which senses the system pressure by means of a pressure sensor. In this embodiment, it is first of all advantageous that the duration of the outer air arrival or of the open state of the outer-air channel can be kept very short thanks to the electrical control. Generally speaking, opening the outer-air channel with a valve unit according to the invention is only rarely needed, e.g. with repeated braking, after a long stoppage or with rpm ranges of the engine which are rarely reached. An additional advantage of the electrical controls consists in the fact that analog electrical signals for other electrical or electromechanical control functions can be utilized for the actual negative pressure in the braking force amplifier. 
     The shut-off valve may be a pneumatic shut-off valve which is actuated by the difference in pressure between the system pressure and the atmospheric pressure. Such a checkvalve unit is simple in design if for no other reason than that the pressure difference is not between the system pressure and a separately produced reference pressure, but that the reference pressure used is the atmospheric pressure. Advantageous embodiments of the valve unit are characterized in particular by simple and compact construction. 
    
    
     The invention is described in greater detail below through the examples of embodiments described in the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 . is a functional diagram showing the utilization of a checkvalve unit with electromagnetic shut-off valve in a motor vehicle braking system, 
     FIG. 2 shows the checkvalve unit of FIG. 1, but without the electromagnetically actuated shut-off valve, 
     FIG. 3 is a schematic sectional representation of an embodiment with pneumatically controlled shut-off valve in a first operating state, 
     FIG. 4 shows the checkvalve unit of FIG. 3 in a second operating state,. 
     FIG. 5 shows the auxiliary braking system of a vehicle with a checkvalve unit as in FIGS. 3 and 4, 
     FIG. 6 shows a braking system according to FIG. 5, but with the checkvalve unit connected in a different manner, 
     FIG. 7 shows a cut section of another embodiment of a checkvalve unit, 
     FIG. 8 shows a schematic cross-sectional view of another embodiment of a valve unit in a first operating state, 
     FIG. 9 shows the valve unit of FIG. 8 in a second operating state and 
     FIG. 10 is a diagram showing the dependence of the air mass flowing through the outside-air channel on the pressure in the suction pipe. 
     FIG. 11 is a diagram of volume flow Q through the outside air channel particularly illustrating the volume flow when P SOLL  has been reached. 
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the presently preferred embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. It is intended that the present application include such modifications and variations. 
     As can be seen in FIGS. 1 and 2, a checkvalve unit according to the invention (hereinafter valve unit  1  for short) comprises an inlet  2 , an outlet  3 , a main air channel  4 , an outside-air channel  5 , a venturi pipe  6  located in the outside-air channel with a cross-sectional narrowing  7  which is normally found in a venturi pipe, a venturi channel  8  connecting the cross-sectional narrowing  7  to the main air channel  4  as well as a first checkvalve  9  and a second checkvalve  10 . The first checkvalve  9  is located in the main air channel  4 . Downstream of the first checkvalve  9 , the outside-air channel  5  letting out into the atmosphere branches off from the main air channel. The venturi channel  8  lets out upstream of the first checkvalve  9  into the main air channel and contains a second valve  10 . The checkvalves  9 , 10  are plate valves and each comprises accordingly a ring-shaped valve seat  12  and a valve plate  13  interacting with it. A pneumatically actuated 2-way valve is intercalated in the outside-air channel. The outside-air channel in the application shown in FIG. 1 is connected to the air filter  14  of the air suction system of a vehicle via a circuit  15 . The inlet  2  of the valve unit  1  is connected via a circuit  16  to the braking force amplifier  17  of the auxiliary braking system of the vehicle. A pressure sensor  18  is connected to the circuit  16  and is connected via a control circuit  19  to an electrical or electronic control device  20 . The control device produces a setting signal which is retransmitted via a control circuit  22  to the solenoids  23  of the 2-way valve  21 . The outlet  3  of the valve unit  1  is connected via a circuit  24  downstream of the throttle valve  25  to the suction channel  27  leading to the combustion chamber of an engine  26 . The throttle valve  25  is thus subjected to air flow from the circuit  15 , the outside-air channel  5 , the main air channel  4  and the circuit  24 , in the manner of a bypass. A constant air flow through this bypass is however prevented by the shut-off valve  21 . 
     The valve unit shown in FIGS. 1 and 2 functions as follows: Only two defined operating states are provided with the proposed valve unit. In one operating state, the 2-way valve  21  is closed, in the other operating state it is open. In FIG. 2 a situation is shown in which the 2-way valve  21  is closed. Starting from a situation where the pressure is balanced, e.g. after a long stoppage of the vehicle, air is sucked from the braking force amplifier  17  in direction of flow, mainly via the checkvalve  9  as the engine is switched on. The 2-way valve is open as shown in FIG.  1 . Thereby outside air is sucked in through the venturi pipe  6 . The air flowing through the outside-air channel is accelerated with the increased narrowing of the venturi pipe  6 , and this causes pressure to drop. At the narrowest point of the venturi pipe, the cross-sectional narrowing  7 , the speed of flow is the greatest and therefor the pressure of the air sucked in is correspondingly lowest. After the cross-sectional narrowing  7 , the speed of flow is again reduced and the pressure rises accordingly. In the segment  29  located upstream before the checkvalve  9 , the system pressure which is equal to the system pressure p s  is lower -than the suction pipe pressure P SR  in the segment  30  of the main air channel  4  extending away from the venturi pipe  6 . Due to these pressure relations, the valve plate  13  of the checkvalve  9  is pressed against its valve seat  12  as the air flow lets up. The main air channel is thus closed off, and the air sucked from the braking force amplifier  17  is thereby sucked away via the venturi channel  8 , at least towards the end of the evacuation process. When the system pressure p s  has dropped to a target value P soll , the control unit  20  actuates the solenoid  23  of the two-way valve  21  and moves it into its second valve position, in which it closes off the outside-air channel  5 . If the system pressure P S  rises, e.g. because of multiple braking, the power flow to the solenoid  23  of the two-way valve is interrupted and the valve  21  is moved by a spring  32  into its open switch position. Outside air is then again sucked in through the venturi pipe  6 , causing its negative pressure amplification to become active. 
     The pressure and flow conditions are shown in form of two diagrams in FIGS. 10 and 11 for clarification. In the diagram of FIG. 10, the system pressure P S  is shown over the suction pipe pressure P SR  It can be seen that a continuous drop of P S  takes place up to the pre-set target pressure P soll . The drop in the system pressure P S  is however greater than the drop of the pressure P SR  because of the negative-pressure amplification through the venturi pipe. When P soll  has been reached, the outside-air channel is closed off, the two checkvalves  9 , 10  are closed, because the pressure in segment  30  of the main air channel  4  is greater than P S . Only when the pressure P SR  becomes greater than P Soll , does further evacuation of the braking force amplifier  17  take place. FIG. 11 shows how the volume flow Q through the outside-air channel  5  stops suddenly when P Soll  has been reached. 
     In the valve unit shown in FIG. 3, the outside-air channel  5  is closed off by a directional seat valve  32  actuated by a pressure difference between the system pressure P S  and the atmospheric pressure. This directional seat valve  32  comprises a valve chamber  51  which is subdivided by a membrane  33  into an atmosphere chamber  34  and a negative-pressure chamber  35 . The atmosphere chamber is connected on the one side to the atmosphere through an inlet opening  36 , and on the other side to the outside-air channel  5  through an outlet opening  37 . The negative-pressure chamber  35  has a connection opening  41  through which it is connected to the main air channel at a point upstream of the checkvalve  10 . The negative-pressure chamber  35  contains a helical spring  38  which bears on the one side against the housing wall of the negative-pressure chamber and on the other side on the membrane  33 . The membrane  33  has a central reinforced area  39  supporting a valve plunger  40  which protrudes essentially at a right angle to the plane surface of the reinforced area and reaches through the connection opening. The free end of the valve plunger  40  widens radially and is made in form of a valve plate  42 . This valve plate  42  interacts with a valve seat  43  surrounding the connection opening  37  outside the atmosphere chamber  34  in form of a ring. 
     A system pressure P S  prevails in the negative-pressure chamber  35 , while the atmospheric pressure prevails on the other side of the membrane, in the atmosphere chamber  34 . The helical spring  38  is designed so that it exerts a force upon the membrane  39 , said force being slightly less than the force exerted in closing direction  44  due to the pressure difference over the membrane. When the braking force amplifier reaches the target system pressure P Soll , the valve plunger  40  is pushed in closing direction and the valve plate  42  is accordingly pressed against the valve seat  43 . The connection to the outside air is then closed off. When, e.g. due to braking occurrences succeeding each other in rapid sequence, the pressure P S  in the braking force amplifier rises to such an extent that the pressure difference at the membrane  33  is equal to or smaller than the force exerted by the helical spring  38 , the membrane, and accordingly the valve plunger  40 , moves in opening direction  45 . The state shown in FIG. 4 is then reached. The valve plate  42  is lifted from the valve seat  43  and atmospheric air can be sucked in through the inlet opening  36  and the outlet opening  37  via the venturi pipe  6  in flow direction  28 . In the cross-sectional narrowing  7  of the venturi pipe or in the venturi channel  8  following it, a pressure drop occurs. Upstream of the venturi pipe  6  on the other hand, the suction pipe pressure P SR  substantially prevails again. Due to this pressure difference, the checkvalve  9  closes. The air sucked from the braking force amplifier goes therefore through the venturi channel  8 . When the target system pressure P S  has again been reached, the pressure conditions over the membrane  33  are again such that the valve plunger  40  moves in closing direction  44  and the outlet opening  37  is closed. 
     FIG. 5 is an installation example for the valve unit described above. The main air channel  4  of the valve unit  1  is connected via a circuit  46  to the braking force amplifier  17 . The inlet opening  36  is connected via a circuit  47  to the air filter  14 . And to outlet  3  finally, a circuit  47   a  is connected which lets out into the suction channel  27  downstream of the throttle valve  25 . The arrangement of FIG. 6 differs from that of FIG. 5 in that the outside-air channel  5  is not connected to the air filter but to the crank housing  48  of the engine. 
     In the embodiment shown in FIG. 7, a valve chamber  51  is also present, and is subdivided by a membrane  33   a  into an atmosphere chamber  34   a  and into a negative-pressure chamber  35   a . The membrane  33   a  has a central, reinforced area  39   a . The outside-air channel  5  lets out via a first inlet opening  49  into the atmosphere chamber and emerges again via a first outlet opening  50 . A valve plunger  40   a  protrudes essentially at a right angle from the flat side of the membrane  33   a  or the reinforced area  39   a  towards the atmosphere chamber  34   a  and reaches through the first outlet opening  50  while its free end radially widens into a valve plate  42   a . The valve plate  42   a  interacts with a valve seat  43   a  which surrounds the first outlet opening in form of a ring. A helical spring  38   a  is installed in the negative-pressure chamber  35   a  and presses the membrane  33   a  in the opening direction  45 . The main air channel  4  lets out into the negative-pressure chamber  35   a  via a second inlet opening  52  and emerges again via a second outlet opening  53 . Finally the venturi channel  8  lets out via a third outlet opening  54  into the negative-pressure chamber  35   a.    
     From the flat side of the reinforced area  39   a  towards the negative-pressure chamber  35   a , a second valve plunger  40   b  extends essentially at a right angle, its free end widening radially and forming a valve plate  42   b . This valve plate interacts with a valve seat  43   b  surrounding the third outlet opening  54  in form of a ring on the inside of the negative-pressure chamber  35   a . The valve plate  42   b  and the valve seat  43   b  constitute the second checkvalve  10   a  which is also present in the previously described examples of embodiments and which serves to shut off the venturi channel  8  against the main air channel  4 . The second outlet opening  53  of the negative-pressure chamber  35   a  is surrounded on the outside by a valve seat  55  in the form of a ring which interacts with a valve plate  55   a  located outside the negative-pressure chamber  35   a . The valve plate  55   a  and the valve seat  55  together constitute the first checkvalve  9   a  which is also present in the previous examples of embodiments and is intercalated in the main air channel  4 . As seen in flow direction  28 , the outside-air channel  5  lets out into the main air channel  4  before this valve. In the segment of the main air channel  4  following the second inlet opening  52  against the flow direction  28 , another checkvalve  56  is installed which comprises a valve seat  56   a  and a valve plate  56   b  interacting with same. 
     The valve unit  1  according to FIG. 7 operates as follows: With the vehicle engine shut off, extensive pressure equalization takes place in the course of the stoppage phase inside the valve unit. Only in the braking force amplifier itself some negative pressure locked in by the checkvalve  56  may still be present. Since the pressure conditions over the membrane  33   a  are balanced out, the membrane is moved by the helical screw  38   a  into opening position, i.e. the first outlet opening  50  and the third outlet opening  54  are open. If the engine is then started, a negative pressure pSR builds up in the suction channel  27 . Because of the cross-sectional narrowing  7  in the venturi pipe  6  and the flow resistance connected with this, the main air mass is sucked away through the main air channel  4 . The checkvalves  56  and  9   a  located therein are open. A partial air stream is however also sucked in through the outside-air channel  5 . As the system pressure pS decreases, the force exerted upon the membrane  33   a  increases due to the pressure difference between the system pressure and the atmospheric pressure. The spring, as described earlier, is designed so that the membrane is moved in closing direction  44  at a predetermined target system pressure pSoll. When the target system pressure has been reached, the outside-air channel  5  is closed. This also applies to the venturi channel. An air flow in the main air channel only takes place under such conditions if the suction pipe pressure pSR drops below the target system pressure. 
     The valve unit  1  shown in FIG. 8 has a particularly compact design. All components are placed in a common housing  60  which encloses a valve chamber  51   a.  The valve chamber is subdivided by two separating partitions into an atmosphere chamber  34   b,  a negative-pressure chamber  35   b  and a suction chamber  57 . The atmosphere chamber  34   b  is connected via an atmosphere opening  58  to the outside air. The separating partition located between the atmosphere chamber  34   b  and the negative-pressure chamber  35   b  is a membrane  33   b  with a central reinforced area  39   b.  The separating partition  62  between the negative-pressure chamber  35   b  and the suction chamber  57  has a passage opening  63 . A valve plunger  59  in the form of a venturi pipe  6  extends essentially at a right angle from the side of the reinforced membrane area  39   b  away from the negative-pressure chamber  35   b . The valve plunger  59  reaches through the passage opening  63 . A movable sealing membrane  64  is provided between the outside circumference and the opening edge of the passage opening  63 . This membrane hermetically seals off the negative-pressure chamber  35   b  from the suction chamber  57 . A helical spring  38   b  is located in the negative-pressure chamber  35   b  and bears on the one side upon the separating partition  62  and on the other side on the reinforced membrane area  39   b  and surrounds the valve plunger  59  at a radial distance. The venturi channel  8  extends essentially radially to the valve plunger  59  and lets out on the one side into the cross-sectional narrowing  7  and on the other side into the negative-pressure chamber  35   b . The second check valve  10   b  is located in the venturi channel. It is fixed on the circumferential surface of the valve plunger  59  together with a valve housing  65 . 
     The free end of the valve plunger  59  is radially widened and formed into a valve plate  66 . The valve plate  66  interacts with a valve seat  69  located on the housing wall  67  across from the separating partition  62 . In addition to the passage opening  63 , a connecting opening  68  is also present in the separating partition  62  and is surrounded in the form of a ring by a valve seat  69  located on the suction chamber side of the separating partition  62 . A valve plate  70  interacts with the valve seat  69 . The valve seat  70  and the valve seat  69  constitute the first checkvalve  9   b  located in the main air channel  4 . The main channel  4  is constituted in the present case by the negative-pressure chamber  35   b  and the suction chamber  57 . An inlet  2  is located at the beginning of the main air channel  4 , and the outlet  3  forms its end. The outside-air channel  5  on the other hand is constituted by the atmosphere chamber  34   b  and the interior space of the valve plunger  59 , i.e. by the venturi pipe  6 . The shut-off valve closing the outside-air channel  5  is formed by the valve plate  66  and the valve seat  69 . 
     The manner in which the valve unit according to FIG. 8 operates, starting from a pressure-balanced state, such as with a long engine stoppage, is described as follows: At first the valve plunger  59 .is in its open position as shown in FIG.  9 . Following the starting of the engine, the suction pipe pressure pSR builds up in the suction chamber  57 , producing a main air stream through the first checkvalve  9   b  in the main air channel  4  and an accessory air stream through the venturi pipe  6 . Based on the venturi principle, a pressure drop then occurs between the cross-sectional narrowing  7  of the venturi pipe  6  and the negative-pressure chamber  35   b , causing a pressure drop going beyond the pressure produced by the suction channel of the engine. Accordingly the first checkvalve  9   b  closes, so that an evacuation takes place exclusively through the second checkvalve  10   b,  the venturi channel  8  and the suction chamber  57 . With increasing evacuation, the pressure difference at the membrane  33   b  increases until finally a state is reached in which the force exerted in closing direction  44  upon the membrane  33   b  is greater than the spring force of the helicoidal spring  38   b . As a result the valve plunger  59  is moved into its closed position shown in FIG. 8. A volume flow can then only take place when the pressure pSR in the suction chamber becomes greater than the target pressure pS. 
     It should be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit of the invention. It is intended that the present invention includes such modifications and variations as come within the scope of the appended claims and their equivalents.