Abstract:
A method for controlling the feed rate of a feed pump, including a drive part having a drive motor and a hydraulic part having an intake opening, a discharge opening and a feed mechanism situated in between, a setpoint feed rate being predefined and the feed pump being triggered based on the setpoint feed rate, the temperature of the fluid and a pressure difference between the intake opening and the discharge opening of the hydraulic part of the feed pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Application No. 10 2010 001 150.9, filed in the Federal Republic of Germany on Jan. 22, 2010, which is expressly incorporated herein in its entirety by reference thereto. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for controlling the feed rate, i.e., the feed volume per unit of time, of a feed pump. 
       BACKGROUND INFORMATION 
       [0003]    Feed pumps for fluids are widely used. In the automotive field, for example, feed pumps are used for feeding fuel to the engine. These feed pumps are usually designed as vane pumps or rotary vane pumps. In internal combustion engines in particular, it is important to accurately preselect the feed rate in order to obtain the desired injection pressure, the desired combustion performance and also low-emissions combustion. It is therefore conventional to regulate the feed rate, i.e., the setpoint feed rate is to be compared with the actual feed rate, and the feed pump is to be controlled according to a control deviation. This requires actual feed rate sensors, which makes regulation of feed rate relatively complex. 
         [0004]    German Published Patent Application No. 10 2008 043 127 describes the regulation of the pump pressure. It is unnecessary to provide a pressure sensor if the actual pressure is ascertained by a so-called control observer. The feed pressure is determined on the basis of the motor current and the motor speed. No feed rate is determined. 
         [0005]    It is therefore desirable to regulate the feed rate of a feed pump without measuring the actual feed rate. 
       SUMMARY 
       [0006]    Example embodiments of the present invention include the provision of not measuring the actual feed rate of a feed pump but instead determining it based on the temperature of the fluid and the pressure difference of the intake opening and the discharge opening of the pump part or hydraulic part of the feed pump. Complex additional cost-intensive sensors may be omitted in this manner. The determination may be performed in practice on the basis of a characteristic map, for example, which extends over the temperature and pressure difference. The pressure difference to be taken into account includes the counter-pressure minus the inlet pressure. 
         [0007]    For ascertaining the pressure difference, a drive torque of the drive motor, which is proportional to the pressure difference, may be used. A viscosity and temperature of the fluid are expediently also taken into account as these also have an influence on the pressure difference. 
         [0008]    A relationship between drive torque M ZP  and pressure difference Δ p  may be written, for example, as: 
         [0000]    
       
         
           
             
               M 
               ZP 
             
             = 
             
               
                 
                   
                     V 
                     theo 
                   
                   · 
                   Δ 
                 
                  
                 
                     
                 
                  
                 p 
               
               
                 
                   2 
                   · 
                   π 
                 
                  
                 
                     
                 
                  
                 
                   η 
                   ZP 
                 
               
             
           
         
       
     
         [0009]    where: 
         [0010]    V theo  represents the theoretical feed volume per revolution; 
         [0011]    η ZP  represents the overall efficiency of the pump. 
         [0012]    The drive torque may in turn be determined relatively easily based on known or easily determinable variables. The drive torque may be derived from the motor current, for example, if an engine characteristic map is known. This current measurement may be implemented inexpensively in the power electronics equipment. 
         [0013]    A highly accurate quantitative regulation may be achieved even without performing a flow measurement by taking into account the pump geometry, for example, by performing a single measurement and storing additional measured values to correct the characteristic map. 
         [0014]    Conventional feed pumps include a hydraulic part and a drive part flange-connected to the former. In addition, there are certain variants in which an internally or externally geared pump axially flange-connected to a motor shaft. The drive motors are arranged as DC variants as well as brushless DC variants. All these electric feed pumps are always arranged such that the feed part and the drive part are separate units. However, example embodiments of the present invention provide for the use of a pump of an integrated configuration, i.e., when the drive part and the hydraulic part form an inseparable unit. Examples of such a pump are described in U.S. Pat. No. 2,761,078 and European Published Patent Application No. 1 803 938. The use of such integrated pumps offers the advantage of a close spatial contact between the fluid and the electronics, so that a temperature sensor may be installed easily and without complex cabling, for example. If the control electronics or power electronics are connected directly to the feed medium, a temperature measurement cell may be accommodated here inexpensively and used for the regulation described herein. 
         [0015]    In determining the pressure difference, a temperature-dependent leakage is expediently taken into account. This may be accomplished in particular from the following standpoints: 
         [0016]    Based on a leakage cross section, such that positions  1  and  2  having pressures p 1  and p 2  are adjacent in the direction of the backpressure, and positions  3  and  4  having pressures p 3  and p 4  are adjacent in the intake pressure direction, it holds that: 
         [0017]    p 1 ≈p 2  pump backpressure 
         [0018]    p 4 ≈p 3  pump intake pressure 
         [0019]    Since fluids are usually incompressible media, density ρ 1  is the same in positions i=1 through 4: ρ 1 =ρ 2 =ρ 3 =ρ 4 =ρ 
         [0020]    Using a Bernoulli equation with a loss term, the influence of β p  on the leakage flow is estimated as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           v 
                           2 
                           2 
                         
                         2 
                       
                       + 
                       
                         
                           p 
                           1 
                         
                         ρ 
                       
                     
                     = 
                     
                       
                         
                           v 
                           3 
                           2 
                         
                         2 
                       
                       + 
                       
                         
                           p 
                           4 
                         
                         ρ 
                       
                       + 
                       
                         
                           Δ 
                            
                           
                               
                           
                            
                           
                             p 
                             v 
                           
                         
                         ρ 
                       
                       + 
                       
                         ρ 
                          
                         
                           
                             ∫ 
                             
                               s 
                                
                               
                                   
                               
                                
                               1 
                             
                             
                               s 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                            
                           
                             
                               
                                 ∂ 
                                 v 
                               
                               
                                 ∂ 
                                 t 
                               
                             
                              
                             
                                 
                             
                              
                             
                                
                               s 
                             
                           
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         assuming 
                          
                         
                             
                         
                          
                         
                           
                             ∂ 
                             v 
                           
                           
                             ∂ 
                             t 
                           
                         
                       
                       = 
                       
                         
                           0 
                            
                           
                               
                           
                            
                           and 
                            
                           
                               
                           
                            
                           
                             v 
                             2 
                           
                         
                         = 
                         
                           v 
                           3 
                         
                       
                     
                     , 
                     
                       it 
                        
                       
                           
                       
                        
                       follows 
                        
                       
                           
                       
                        
                       that 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         p 
                         1 
                       
                       ρ 
                     
                     = 
                     
                       
                         
                           p 
                           4 
                         
                         ρ 
                       
                       + 
                       
                         
                           Δ 
                            
                           
                               
                           
                            
                           
                             p 
                             v 
                           
                         
                         ρ 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   or 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         p 
                         v 
                       
                     
                     ρ 
                   
                   = 
                   
                     
                       
                         
                           p 
                           1 
                         
                         ρ 
                       
                       - 
                       
                         
                           
                             p 
                             4 
                           
                           ρ 
                         
                          
                         
                             
                         
                          
                         or 
                          
                         
                             
                         
                          
                         Δ 
                          
                         
                             
                         
                          
                         
                           p 
                           v 
                         
                       
                     
                     = 
                     
                       
                         p 
                         1 
                       
                       - 
                       
                         p 
                         4 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0021]    The loss term for a constant cross section is 
         [0000]    
       
         
           
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     
                       p 
                       v 
                     
                   
                   = 
                   
                     
                       
                         λ 
                         · 
                         l 
                       
                       d 
                     
                     · 
                     ρ 
                     · 
                     
                       
                         v 
                         2 
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0022]    It thus follows that: 
         [0000]    
       
         
           
             
               
                 
                   
                     v 
                     = 
                     
                       
                         
                           
                             2 
                             ρ 
                           
                         
                         · 
                         Δ 
                       
                        
                       
                           
                       
                        
                       
                         p 
                         · 
                         
                           d 
                           
                             λ 
                             · 
                             l 
                           
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   where 
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
             
               
                 
                   λ 
                   = 
                   
                     
                       
                         ρ 
                         · 
                         64 
                       
                       Re 
                     
                     = 
                     
                       
                         ρ 
                         · 
                         64 
                       
                       
                         
                           v 
                           · 
                           d 
                         
                         γ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0023]    A friction moment estimate M Reib  of a radial friction bearing is given, for example, as: 
         [0000]    
       
         
           
             
               M 
               Reib 
             
             = 
             
               μ 
               · 
               
                 F 
                 Lager 
               
             
           
         
       
       
         
           where 
         
       
       
         
           
             μ 
             = 
             
               
                 μ 
                 0 
               
               · 
               
                  
                 
                   ( 
                   
                     - 
                     
                       
                         a 
                         · 
                         
                           h 
                           min 
                         
                       
                       Rq 
                     
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where 
         [0024]    a represents a constant; and 
         [0025]    Rq represents a standard deviation of roughness Rq for contact pairing; 
         [0000]    where: 
         [0000]    
       
         
           
             
               h 
               min 
             
             ≈ 
             
               
                 
                   B 
                   
                     F 
                     Lager 
                   
                 
                 · 
                 
                   
                     η 
                     · 
                     
                       D 
                       3 
                     
                   
                   C 
                 
                 · 
                 
                   
                     π 
                     · 
                     n 
                   
                   60 
                 
               
                
               
                 
                   ( 
                   
                     1 
                     + 
                     
                       
                         
                           
                             2 
                           
                           · 
                           
                             ( 
                             
                               1 
                               - 
                               
                                 γ 
                                 2 
                               
                             
                             ) 
                           
                         
                          
                         F 
                       
                       
                         B 
                         · 
                         E 
                         · 
                         
                           h 
                           min 
                         
                       
                     
                   
                   ) 
                 
                 
                   2 
                   / 
                   3 
                 
               
             
           
         
       
     
         [0000]    where 
         [0026]    B represents a supporting width; 
         [0027]    η represents a dynamic viscosity; 
         [0028]    E represents a modulus of elasticity; 
         [0029]    γ represents a transverse contraction number; 
         [0030]    D represents a diameter; 
         [0031]    n represents a rotational speed [1/min] 
         [0032]    Thus a loss term which depends on rotational speed may be given. 
         [0033]    Frictional resistance M of the rotor is formulated in a manner similar to that of a rotating disk: 
         [0000]    
       
         
           
             
               
                 
                   M 
                   = 
                   
                     2 
                      
                     
                       ∫ 
                       
                         r 
                          
                         
                            
                           
                             F 
                             r 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     2 
                      
                     
                       ∫ 
                       
                         
                           rc 
                           F 
                         
                          
                         
                           
                             ρ 
                              
                             
                                 
                             
                              
                             
                               v 
                               2 
                             
                           
                           2 
                         
                          
                         
                            
                           A 
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     
                       ∫ 
                       0 
                       
                         d 
                         / 
                         2 
                       
                     
                      
                     
                       
                         
                           rc 
                           F 
                         
                         · 
                         ρ 
                         · 
                         
                           ω 
                           2 
                         
                       
                        
                       
                         
                           r 
                           2 
                         
                         · 
                         2 
                       
                        
                       π 
                        
                       
                           
                       
                        
                       r 
                        
                       
                           
                       
                        
                       
                          
                         r 
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     
                       
                         
                           4 
                           · 
                           π 
                           · 
                           
                             c 
                             F 
                           
                         
                         5 
                       
                       
                          
                         
                           C 
                           M 
                         
                       
                     
                     · 
                     
                       
                         ρ 
                         · 
                         
                           ω 
                           2 
                         
                       
                       2 
                     
                     · 
                     
                       
                         ( 
                         
                           d 
                           2 
                         
                         ) 
                       
                       5 
                     
                   
                 
               
             
           
         
       
     
         [0000]    where for laminar flow and Re&lt;3·10 4  it holds that: 
         [0000]    
       
         
           
             
               C 
               M 
             
             = 
             
               
                 2 
                 · 
                 π 
                 · 
                 d 
               
               
                 s 
                 · 
                 Re 
               
             
           
         
       
     
         [0000]    where s represents an axial distance between the rotor and the housing; 
         [0034]    A loss term as a function of rotational speed may in turn be given using ω=2πn. 
         [0035]    The frictional resistance on the outer cylindrical surface is already taken into account in the bearing calculation. 
         [0036]    Thus to determine the feed rate, a characteristic map as a function of temperature and motor current may be used. This is particularly simple because these parameters may be determined relatively accurately but nevertheless inexpensively and with little effort. A preferred relationship is obtained as follows: 
         [0000]    
       
         
           
             
               V 
               . 
             
             = 
             
               
                 n 
                 · 
                 
                   ( 
                   
                     
                       V 
                       theo 
                     
                     · 
                     
                       K 
                       1 
                     
                   
                   ) 
                 
               
               - 
               
                 
                   V 
                   . 
                 
                 Temp 
               
               - 
               
                 
                   V 
                   . 
                 
                 
                   Δ 
                    
                   
                       
                   
                    
                   ρ 
                 
               
               + 
               
                 
                   
                     
                       n 
                       2 
                     
                     · 
                     
                       K 
                       10 
                     
                   
                   + 
                   
                     
                       n 
                       
                         1 
                         / 
                         2 
                       
                     
                     · 
                     
                       K 
                       11 
                     
                   
                   + 
                   
                     K 
                     12 
                   
                 
                 
                    
                   
                     drehzahlabh 
                      
                     
                         
                     
                      
                     
                       a 
                       .. 
                     
                      
                     
                         
                     
                      
                     ngige 
                      
                     
                         
                     
                      
                     Verluste 
                   
                 
               
             
           
         
       
     
         [0037]    where drehzahlabhängige Verluste refers to rpm-dependent losses; 
         [0000]    where 
         [0000]    
       
      
       {dot over (V)} 
       Temp 
       =T 
       2 
       −K 
       2 
       +T·K 
       3 
       +T 
       1/2 
       ·K 
       4 
       +K 
       5  
      
     
         [0000]      and 
         [0000]    
       
      
       {dot over (V)} 
       Δρ 
       =I 
       Motor 
       2 
       ·K 
       6 
       +I 
       Motor 
       ·K 
       7 
       +I 
       Motor 
       1/2 
       ·K 
       8 
       +K 
       9  
      
     
         [0000]    where V theo  denotes the theoretical feed volume per revolution of the pump. 
         [0038]    A computation unit, for example, a control unit of a motor vehicle, is equipped, in particular as far as programming is concerned, to perform a method described herein. 
         [0039]    It should be understood that the features mentioned above and those yet to be explained below may be used not only in the particular combination given but also in other combinations or alone. 
         [0040]    Example embodiments of the present invention are illustrated schematically in the Figures and are described below in more detail with reference to the Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]      FIG. 1  schematically shows a feed pump, which is suitable in particular for performing a method according to an example embodiment of the present invention. 
           [0042]      FIG. 2  shows in a diagram the relationship between feed rate and rotational speed as a function of the pressure difference at a constant fluid temperature. 
           [0043]      FIG. 3  shows in a diagram the relationship between feed rate and rotational speed as a function of the inlet pressure at a constant pressure difference and a constant fluid temperature. 
           [0044]      FIG. 4  shows in a diagram the relationship between feed rate and rotational speed as a function of the fluid temperature at a constant pressure difference. 
       
    
    
     DETAILED DESCRIPTION 
       [0045]      FIG. 1  shows an electric feed pump of an integrated configuration, in which the drive part and the hydraulic part or feed part form an inseparable unit  120 , which is diagramed schematically and labeled as  100  as a whole. In the present example, the integrated configuration is achievable by the fact that the rotor of the drive motor at the same time also forms the moving pump element of the hydraulic part, as described in European Published Patent Application No. 1 803 938, for example, which is expressly incorporated herein in its entirety by reference thereto. Hydraulic part  120  thus includes drive motor  121 , which also acts as feed mechanism  121 , drawing in a fluid, fuel in particular, through an intake opening  122  and discharging it through a discharge opening  123 . There is therefore a pressure difference Δ p  between intake opening  122  and discharge opening  123 . 
         [0046]    The pump also includes an electronic part  110 . A regulating module  111  and a power module  112  are provided in electronic part  110 . Regulating module  111  receives a setpoint feed rate {dot over (V)} setpoint  from a motor control unit  150  and determines therefrom a setpoint rotational speed n setpoint  for the drive motor, which is transmitted to power module  112 . Power module  112  may have, for example, an inverter for operation of the drive motor. Motor current I motor  is determined in power module  112  and transmitted to regulating module  111 . 
         [0047]    Based on the integrated configuration of pump  100 , there is a close spatial contact between electronic part  110  and drive and hydraulic part  120 , so that fluid temperature T actual-fluid  is easily measurable by a measurement performed by a sensor  113  provided within electronic part  110 . 
         [0048]    The feed rate of feed pump  110  may be controlled on the basis of measured motor current I motor  and measured fluid temperature T actual-fluid . A characteristic map as a function of temperature T actual-fluid  and motor current I motor  is used in regulating module  111  according to the equation: 
         [0000]    
       
         
           
             
               
                 V 
                 . 
               
               Soll 
             
             = 
             
               
                 
                   
                     n 
                     Soll 
                   
                   · 
                   
                     
                       ( 
                       
                         
                           V 
                           theo 
                         
                         · 
                         
                           K 
                           1 
                         
                       
                       ) 
                     
                     -- 
                   
                 
                  
                 
                   
                     ( 
                     
                       
                         
                           T 
                           
                             
                               1 
                                
                               st 
                             
                             - 
                             Fluid 
                           
                           2 
                         
                         · 
                         
                           K 
                           2 
                         
                       
                       + 
                       
                         
                           T 
                           
                             
                               1 
                                
                               st 
                             
                             - 
                             Fluid 
                           
                         
                         · 
                         
                           K 
                           3 
                         
                       
                       + 
                       
                         
                           T 
                           
                             
                               1 
                                
                               st 
                             
                             - 
                             Fluid 
                           
                           
                             1 
                             2 
                           
                         
                         · 
                         
                           K 
                           4 
                         
                       
                       + 
                       
                         K 
                         5 
                       
                     
                     ) 
                   
                   -- 
                 
                  
                 
                   
                     ( 
                     
                       
                         
                           I 
                           Motor 
                           2 
                         
                         · 
                         
                           K 
                           6 
                         
                       
                       + 
                       
                         
                           I 
                           Motor 
                         
                         · 
                         
                           K 
                           7 
                         
                       
                       + 
                       
                         
                           I 
                           Motor 
                           
                             1 
                             2 
                           
                         
                         · 
                         
                           K 
                           8 
                         
                       
                       + 
                       
                         K 
                         9 
                       
                     
                     ) 
                   
                   ++ 
                 
                  
                 
                   
                     n 
                     Soll 
                     2 
                   
                   · 
                   
                     K 
                     10 
                   
                 
               
               + 
               
                 
                   n 
                   Soll 
                   
                     1 
                     2 
                   
                 
                 · 
                 
                   K 
                   11 
                 
               
               + 
               
                 K 
                 12 
               
             
           
         
       
     
         [0000]    where 
         [0049]    Soll denotes a setpoint, Ist denotes actual; and 
         [0050]    V theo  denotes the theoretical feed volume per revolution of the pump and is usually given on the data sheet. Characteristic map constants K 1 -K 12  are ascertained empirically. To do so, a sufficient number of measured points [{dot over (V)}, n, T, I] is preferably measured and evaluated using known fitting methods (e.g., least squares fitting). 
         [0051]    Based on the characteristic map, setpoint rotational speed n setpoint  is determined and transmitted to power module  112 . To regulate the feed rate, actual rotational speed n actual  of drive motor  121  is regulated at setpoint rotational speed n setpoint . A known rotational speed regulation may be used to do so. 
         [0052]    Alternatively it is possible to use actual rotational speed n actual  together with measured motor current I motor  and measured fluid temperature T actual-fluid  to determine the actual feed rate via the characteristic map and to regulate the actual feed rate at the setpoint feed rate, again with the setpoint rotational speed being regulated. 
         [0053]    Various relationships are explained purely qualitatively below with reference to  FIGS. 2 to 4  merely for the purpose of illustration. 
         [0054]      FIG. 2  shows a diagram  200 , illustrating the relationship between feed rate {dot over (V)} on the ordinate as a function of rotational speed n on the abscissa at a constant temperature. Three feed rate curves  210 ,  220  and  230  are shown in diagram  200 , each curve being characterized by a different pressure difference Δp between the intake opening and the discharge opening. Thus a first pressure difference Δp 1  is assigned to feed rate curve  210 , a second pressure difference Δp 2  is assigned to feed rate curve  200 , and a third pressure difference Δp 3  is assigned to feed rate curve  230 , the pressure difference increasing, so that it holds that: Δp 1 &lt;Δp 2 &lt;Δp 3 . The feed volume/rotational speed characteristic curve is shifted to the right with an increase in pressure difference Δp because internal leakage increases. In other words, a higher rotational speed is also necessary to supply a certain feed rate at a higher pressure difference. 
         [0055]    Each of the three feed rate curves includes a first essentially linearly increasing range A and a following curved range B. The slope in range A is constant and depends essentially only on the geometric displacement volume of the pump. The feed volume curve flattens out in range B due in particular to partial cavitation phenomena on the intake end, caused in particular by high local flow velocities. 
         [0056]      FIG. 3  shows in a diagram  300  the influence of pressure at the intake opening, i.e., inlet pressure p inlet  on the feed volume/rotational speed characteristic curve. Diagram  300  shows three characteristic curves  310 ,  320  and  330  at a constant pressure difference Δp, these characteristics differing in their inlet pressure. Characteristic curve  310  is defined by inlet pressure p inlet1  characteristic curve  320  is defined by inlet pressure p inlet2  and characteristic curve  330  is defined by p inlet3  where the following holds: p inlet1 &gt;p inlet2 &gt;p inlet3 . 
         [0057]    A variation in the inlet pressure produces a shift in ranges A and B such that the stable, i.e., linear operating range A becomes smaller with a drop in inlet pressure. In other words, the stable range is smaller the higher the inlet pressure p inlet . It is thus advisable to provide a limit in the pump specification to avoid operating in range B. 
         [0058]      FIG. 4  shows the influence of the fluid temperature on the feed volume/rotational speed characteristic curve in a diagram  400 . Three characteristic curves  410 ,  420  and  430  are shown in diagram  400 , a different fluid temperature T 1 , T 2  and T 3  being assigned to each diagram, where it holds that T 1 &lt;T 2 &lt;T 3 . The characteristic curves are shifted to the right with an increase in fluid temperature because the temperature influences the viscosity of the fluid and thus affects the leakage. Furthermore, the pump components expand, so that different materials are usually used for different components and thus there is different thermal expansion. For example, the housing is often made of aluminum, whereas the feed mechanism often has steel elements, which thus have a lower thermal expansion than the housing. As a result, the leakage increases with an increase in temperature. On the whole, it is apparent that a higher rotational speed is also needed at a higher fluid temperature to supply a certain feed rate.