Patent Publication Number: US-6698711-B2

Title: Valve for controlling fluids

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 01/0534 filed on Feb. 13, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to valves for controlling fluids, in which a valve closing member divides a low-pressure region in the valve from a high-pressure region. Such valves are known in the industry in various embodiments, for example in fuel injectors, especially common rail injectors, or in pumps of motor vehicles. 
     2. Description of the Prior Art 
     Such a valve is also known from European Patent Disclosure EP 0 477 400 A1; the valve described in this reference is actuatable via a piezoelectric actuator and has an arrangement for a travel converter, acting in the stroke direction, of the piezoelectric actuator. The deflection of the actuator is transmitted via a hydraulic chamber, which serves as a hydraulic booster and as a tolerance compensation element. The hydraulic chamber encloses a common work volume between two pistons defining the hydraulic chamber, of which one piston is embodied with a smaller diameter and is connected to a valve closing member to be triggered, and the other piston is embodied with a greater diameter and is connected to the piezoelectric actuator. The hydraulic chamber is fastened between the pistons in such a way that the actuating piston executes a stroke that is lengthened by the boosting ratio of the piston diameter, when the larger piston is moved by a certain travel distance by means of the piezoelectric actuator. In addition, via the work volume of the hydraulic chamber, tolerances, resulting for instance from different temperature expansion coefficients of the materials used and possible settling effects, can be compensated for without the valve closing member&#39;s experiencing any change in its position. 
     To assure the function of such valves, the hydraulic system in the low-pressure region, in particular the hydraulic coupler, requires a system pressure. The system pressure drops because of leakage, unless hydraulic fluid is adequately replenished. 
     In common rail injectors known in the industry, for instance, in which the system pressure is expediently generated in the valve itself and is also kept as constant as possible upon a system start, the filling of the system pressure region is accomplished by the delivery of hydraulic fluid from the high-pressure region of the fuel to be controlled into the low-pressure region where the system pressure is to prevail. Often, the filling is done with the aid of leakage gaps, which are represented by leakage or filling pins. The system pressure is as a rule adjusted by means of a valve, and the system pressure can also be kept constant for a plurality of common rail valves, for example, as well. 
     However, if the system pressure in the hydraulic chamber is substantially constant, and is at least largely independent of the prevailing high pressure in the high-pressure region, this is problematic, since at high pressure values, great actuator force is required to open the valve closing member counter to the high-pressure direction; this dictates a correspondingly large, cost-intensive dimensioning of the actuator unit. Furthermore, at high pressure in the high-pressure region, the positive displacement of hydraulic volume out of the hydraulic chamber via the gaps surrounding the adjacent pistons is reinforced accordingly, meaning that under some circumstances, the refilling time for building up and maintaining the counterpressure on the low-pressure region is prolonged, so that for lack of complete refilling, in the event of a re-actuation of the valve soon thereafter, a shorter valve stroke will be executed, which can adversely affect the opening behavior of the entire valve. 
     SUMMARY OF THE INVENTION 
     The valve of the present invention for controlling fluids has the advantage that for refilling the hydraulic chamber, a system pressure dependent on the pressure level in the high-pressure region is furnished, and this system pressure assures the reliable function of the hydraulic chamber as a hydraulic booster. In a valve according to the invention, an increase in the system pressure is possible at a high pressure level in the high-pressure region in the hydraulic chamber, and as a result, the opening of the valve closing member counter to the high pressure applied is reinforced. In this way, compared to a valve with constant system pressure, a reduced triggering voltage of the actuator unit, preferably embodied as a piezoelectric unit, is sufficient. The valve according to the invention can therefore be equipped with a smaller and less-expensive actuator unit. 
     In addition, the invention makes a defined refilling of the low-pressure region, in particular the hydraulic chamber, possible. A very precise setting of the system pressure can be effected by flow changes at the throttle body, which are performed in an especially preferred way by hydroerosive rounding during assembly. The valve of the invention is thus distinguished not only by reliable furnishing of the requisite system pressure over the entire engine performance graph, but also by low costs for production and assembly. This is due above all to the structurally simple design of the valve, which makes it possible to define the variable system pressure in the hydraulic chamber by means of easily adjustable geometrical variables, such as the throttle flow and the dimensions of the body along which the system pressure is reduced to the low pressure. 
     Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Several exemplary embodiments of the valve of the invention for controlling fluids are shown in the drawing and will be explained in further detail in the ensuing description. Shown are: 
     FIG. 1 is a schematic, fragmentary view of a first exemplary embodiment of the invention for a fuel injection valve for internal combustion engines, in longitudinal section; 
     FIG. 2 is a view similar to FIG. 1 showing exemplary embodiment of the invention, in longitudinal section; and 
     FIG. 3 is a simplified basic sketch of an addition to the embodiments shown in FIGS.  1  and  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The exemplary embodiment shown in FIG. 1 illustrates a use of the valve of the invention in a fuel injection valve  1  for internal combustion engines of motor vehicles. In the present embodiment, the fuel injection valve  1  is embodied as a common rail injector for injecting preferably Diesel fuel; the fuel injection is controlled via the pressure level in a valve control chamber  2 , which communicates with a supply of high pressure. For adjusting the injection onset, a duration of injection, and an injection quantity via force ratios in the fuel injection valve  1 , a valve member  3  is triggered via an actuator unit embodied as a piezoelectric actuator  4 , which is disposed on the side of the valve member  3  remote from the valve control chamber and from the combustion chamber. The piezoelectric actuator  4  is constructed in the usual way in a plurality of layers, and on its side toward the valve member  3 , it has an actuator head  5 , while on its side remote from the valve member  3  it has an actuator foot  6 , which is braced against a wall of a valve body  7 . Via a support  8 , a first piston  9  of the valve member  3 , which will be called a control piston, rests on the actuator head  5 . The valve member  3  is disposed axially displaceably in a longitudinal bore of the valve body  7  and in addition to the first piston  9  it includes a further, second piston  11 , which actuates a valve closing member  12  and will therefore also be called an actuating piston. 
     The pistons  9  and  11  are coupled to one another by means of a hydraulic booster, which is embodied as a hydraulic chamber  13  and transmits the deflection of the piezoelectric actuator  4 . The hydraulic chamber  13 , between the two pistons  9  and  11  defining it, where the diameter A 1  of the second piston  11  is less than the diameter A 0  of the first piston  9 , encloses a common compensation volume, in which a system pressure p_sys prevails. The valve member  3 , its pistons  9  and  11 , and the piezoelectric actuator  4  are located one after the other on a common axis, and the second piston  11  executes a stroke that is lengthened by the boosting ratio of the piston diameter when the larger, first piston  9  is moved a certain travel distance by means of the piezoelectric actuator  4 . 
     The compensation volume of the hydraulic chamber  13  makes it possible to compensate for tolerances resulting from temperature gradients in the component or different temperature expansion coefficients of the materials used and possible settling effects, without affecting the position of the valve closing member  12  to be triggered. 
     The ball-like valve closing member  12  cooperates, on the end of the valve member  3  toward the valve control chamber  2 , with valve seats  14 ,  15  embodied on the valve body  7 ; the valve closing member  12  divides a low-pressure region  16  that is at the system pressure p_sys from a high-pressure region  17  that is at a high pressure or rail pressure p_R. The valve seats  14 ,  15  are embodied in a valve chamber  18 , formed by the valve body  7 , from which a leakage outlet conduit  19  leads away on the side of the valve seat  14  toward the piezoelectric actuator  4 . On the high-pressure side, the valve chamber  18  can be made to communicate with the valve control chamber  2  of the high-pressure region  17 , via the second valve seat  15  and an outlet throttle  20 . The valve control chamber  2  is merely suggested in FIG.  1 . In it there is a movable valve control piston, not identified by reference numeral. By the axial motions of this piston, the injection behavior of the fuel injection valve  1  is controlled in a manner known per se; typically, the valve control chamber  2  communicates with an injection line, which communicates with a high-pressure reservoir (common rail) that is common to a plurality of fuel injection valves. 
     On the end of the bore toward the piezoelectric actuator is a further valve chamber  21 , which is defined by the valve body  7 , the first piston  9 , and a sealing element  22  that is connected to both the first piston and the valve body  7 . The sealing element  22 , embodied here as a bellowslike diaphragm, prevents the piezoelectric actuator  4  from coming into contact with the fuel contained in the low-pressure region  16 . For removal of leakage fluid, a leakage line  23  branches off from the valve chamber  21 . 
     To compensate for leakage losses on the low-pressure region  16  upon an actuation of the fuel injection valve  1 , a filling device  24  which communicates with the high-pressure region  17  is provided. The filling device  24  is embodied with a channel-like hollow chamber  25 , in which a pinlike throttle body  26  with a continuous throttle bore  27  is press-fitted into place. On the high-pressure end of the throttle body  26 , a line  33  leading to the high-pressure region  17  discharges into the hollow chamber  25 , while on the opposite end of the throttle body  26 , a system pressure line  28  leading to the hydraulic chamber  13  branches off from the hollow chamber  25 . a line  27  leading to the high-pressure region  17  discharges into the hollow chamber  25 , while on the opposite end of the throttle body  26 , a system pressure line  28  leading to the hydraulic chamber  13  branches off from the hollow chamber  25 . 
     In the preferred embodiments shown in the drawing, the system pressure line  28  in each case discharges into a gap  29 , surrounding the first piston  9 , by way of which gap the system pressure is reduced toward the valve chamber  21  and the leakage line  23 . However, it can also be provided that as an alternative or in addition, the system pressure line  28  discharges into a gap  30 , surrounding the second piston  11 , as indicated by dot-dashed lines for the line  28 ′ in the drawings. In each case, the indirect filling of the hydraulic chamber  13  serves to improve the pressure holding capacity in the hydraulic chamber  13  during the triggering, but it is understood that it is also possible for the hydraulic chamber  13  to be filled directly via the system pressure line  28 . 
     The system pressure p_sys, in the fuel injection valve  1  of the invention shown in FIG. 1, is built up as a function of the prevailing pressure p_R in the high-pressure region  17  by geometric definition of the throttle bore  27  in the throttle body  26  and of the dimensions, that is, the length and the diameter A 0 , of the first piston  9  along which the system pressure p_sys is reduced toward the low-pressure region  16 . 
     By a change in the flow cross section of the throttle bore  27 , for instance effected by hydroerosive rounding, the coupler pressure or system pressure p_sys can be adjusted during assembly such that it varies as a function of the pressure p_R prevailing in the high-pressure region  17 . The system pressure p_sys that is attained after an injection following a certain refilling time must not exceed a maximum allowable static system pressure or coupler pressure that would lead to automatic valve opening without triggering of the piezoelectric unit  4 . The gap sizes at the pistons  9  and  11  are also dimensioned accordingly. The diameter A 0  of the first piston  9  and the diameter A 1  of the second piston  11  are thus parameters for the geometric definition of the throttle body  26  and the first piston  9 . Other parameters for their geometric definition are, besides the diameter ratio of the pistons  9  and  11 , a seat diameter A 2  of the first valve seat  14  and a spring force F_F of a spring  31 , which in the present case is disposed between the valve closing member  12  and the second valve seat  15  and keeps the valve closing member  12  in the closing position on the first valve seat  14  upon relief of the high-pressure region  17 . 
     Referring now to FIG. 2, a detail of a further exemplary embodiment of the fuel injection valve is shown, which in principle functions like the fuel injection valve shown in FIG.  1 . For the sake of simplicity, functionally identical components are identified by the same reference numerals as in FIG.  1 . 
     Compared to the version of FIG. 1, in which the high pressure p_R toward the low-pressure region  16  is reduced via an in-line connection of the throttle body  26  and the first piston  9 , in this version the function of the pressure reduction along the piston  9  is alternatively achieved by means of a further throttle body  32 . This throttle body  32 , likewise embodied in sleevelike fashion with a throttle bore  34 , is press-fitted into the hollow chamber  25 , which also receives the first throttle body  26 , and it precedes a leakage line  35  that branches off directly from the hollow chamber  25 . Between the throttle bodies  26  and  32 , the system pressure p_sys builds up in the hollow chamber  25  as well as in the system pressure line  28  and the hydraulic chamber  13  as a function of the prevailing pressure p_R in the high-pressure region  17 . The system pressure p_sys is reduced here along the second throttle body  32  to the low-pressure region  16 . In the version shown in FIG. 2 as well, the possibility exists of adjusting the system pressure in the hydraulic chamber  13  in a simple way by purposeful adaptation of the throttle bores  27  and  34 , which is accomplished for instance by hydroerosive rounding. As soon as the first throttle body  26  becomes cavitated, the system pressure p_sys and the incident leakage are limited to a maximum value. 
     FIG. 3, in a basic illustration, shows an addition to the embodiments of FIGS. 1 and 2, in which the hollow chamber  25  receiving at least the first throttle body  26  is preceded on the high-pressure side by a further hollow chamber  36  with a solid body  37  disposed in it. This solid body  37 , which in the advantageous embodiment shown is embodied in pistonlike fashion, is disposed in the hollow chamber  36  axially movably and with a play by means of which it acts at least primarily as a filter for the throttling of the downstream first throttle body  26 . Especially for a small throttle diameter of the first throttle body  26 , which is often necessary in passenger cars, filtration of the high-pressure flow to the first throttle body  26  is advantageous. To prevent dirt particles from plugging up the throttle bore  27  of the throttle body  26 , these particles that are larger than a predefined gap size are trapped by the piston  37 . Because of the preferably large gap size around the piston  37 , only a very slight throttling occurs as a result of this piston. The pressure divider function for adjusting the system pressure p_sys is thus effected only via the first throttle body  26  and the first piston  9  or the second throttle body  32 . 
     At the same time, the axial mobility of the piston  37  acting as a filter assures that its gap size, which for instance can amount to from 10 μm to 15 μm, is such that the gap will not become plugged up with dirt particles. To assure at least an axial motion of the piston  37  in the event of pressure fluctuations, a spring device  39  is provided between the solid body or piston  37  and a stop  38  on the throttle side; by means of this spring device, if the high pressure p_R in the high-pressure region  17  drops, the piston  37  is displaceable against a stop  40  on the high-pressure side. Thus the piston  37  is moved in every turn-on and turn-off phase, and a result the piston gap is automatically created. To adjust the system pressure p_sys, the piston  37  is geometrically defined as a function of the parameters already discussed with regard to the throttle body dimensioning. 
     The fuel injection valve of FIGS. 1,  2  or  3  functions as described below. 
     In the closed state of the fuel injection valve  1 , that is, when voltage is not applied to the piezoelectric actuator  4 , the valve closing member  12  is seated on the upper valve seat  14  assigned to it and is pressed against the first valve seat  14 , among other elements, by the spring  31  having the spring force F_F, and primarily by the rail pressure p_R. 
     In the case of a slow actuation, for instance as a consequence of temperature-dictated changes in length of the piezoelectric actuator  4  or other valve components, the first piston  9  acting as a control piston penetrates the compensation volume of the hydraulic chamber  13  in the event of temperature increases, and upon a temperature drop withdraws from it again, without affecting the closing and opening position of the valve closing member  2  and of the fuel injection valve  1  overall. 
     If the valve is to be opened and an injection is to take place through the fuel injection valve  1 , then the piezoelectric actuator  4  is subjected to voltage, which causes it to suddenly expand axially. The piezoelectric actuator  4  is braced against the valve body  7  at this time and builds up an opening pressure in the hydraulic chamber  13 . Not until the valve  1  is in equilibrium, as a result of the system pressure p_sys in the hydraulic chamber  13 , does the second piston  11  force the valve closing member  12  out of its upper valve seat  14  into a middle position between the two valve seats  14  and  15 . At a high rail pressure p_R, a greater force on the piezoelectric actuator side is required in order to reach the pressure of equilibrium in the hydraulic chamber  13 . In the filling device  24  of the invention, however, if the rail pressure p_R is high, then the pressure in the hydraulic chamber  13  is also elevated accordingly. In this way, for the same voltage applied to the piezoelectric actuator  4 , the force on the piezoelectric actuator side exerted on the valve closing member  12  is increased. This force increase is equivalent to a substantially higher voltage that would have to be applied to the piezoelectric actuator  4 . The force reserve thus gained can be utilized in the design of the valve, for instance in order to reduce the size of the piezoelectric actuator. 
     To move the valve closing member  12  backward again into a middle position counter to the rail pressure p_R after it has reached its second, lower valve seat  15  and to attain a fuel injection again, the supply of electrical current to the piezoelectric actuator  4  is interrupted. Simultaneously with the return motion of the valve closing member  12 , refilling of the hydraulic chamber  13  to the system pressure p_sys is effected via the filling device  24 . 
     The versions described each pertain to a so-called double-seat valve, but the invention is understood to be applicable to single-switching valves having only one valve seat as well. 
     Nor is it obligatory that the line  33 , leading to the high-pressure region  17 , of the filling device  24  communicate, as it does in the preferred embodiments shown, with the valve chamber  18  in which the valve closing member  12  is movable between the valve seats  14  and  15 . In alternative versions it can also be provided that the line  33  communicates fluidically with a high-pressure inlet from a high-pressure pump, for instance to the valve control chamber  2  in the high-pressure region  17 , or with the outlet throttle  20 . 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.