Patent Publication Number: US-2009229547-A1

Title: Electromotive device for operating gas exchange valves

Description:
The invention relates to an electromotive device for operating gas exchange valves in combustion engines. 
     For controlling the aforementioned valves, a number of technical solutions exist which have in common that they have arrangements whose movable parts move the valve shafts of the gas exchanged valves into the desired positions during gas intake or exhaust. A number of requirements are placed on these arrangements, which relate to the precision of the movements, their soft termination at the endpoints (soft landing problem) and the greatest possible positioning speed. This arrangement should also take up the least possible space for operating the valves, assure operation with low energy consumption, guarantee high reliability and a simple construction. The known arrangements satisfy several, but not all, of these requirements in different ways. DE 197 35 375 C1 and DE 197 44 714 C1 propose electromagnetic actuators for operating a gas exchange valve with rotors (armatures) which exert a force on the gas exchange valve, which is held in the end positions of the stroke by electromagnets and moved from one end position to the other by springs. These arrangements have the disadvantage that the force characteristic curve of an electromagnet depends on the rotor position and exhibits strong nonlinearities, which causes problems, in particular during a “soft landing”, due to the strong increase in the force. In addition, the proposed arrangements are not capable at all or only a limited way to perform partial strokes and to compensate for valve play changing during the operation. 
     DE 101 42 670 C1 proposes an electromechanical actuator for a valve drive which is intended to solve the “soft landing problem” with a structure having an increased distance between armature and pole face of the electromagnets. Aside from the suitability of the solution, the solution makes uses the existing installation space ineffectively due to its rotationally symmetric structure. In addition, zero-current holding in the end positions is not possible, which increases the dissipated power. 
     Another solution is proposed in DE 101 26 211 A1. This solution should improve the reliability by reducing structural friction and wear. However, the rotationally symmetric structure again uses the existing installation space poorly, which is exacerbated by the large number of superpositioned magnets. 
     DE 101 25 767 C1 also discloses a solution for improving the reliability of a drive for a gas exchange valve. The proposed structure has an arrangement with ring-shaped magnets, which does, on one hand, not save much space and is, on the other hand, complex to manufacture. 
     In addition to the solutions for linear-motion-based electric valve controllers, valve controllers exist where valve motion is produced by electrically generated rotation. 
     For example, U.S. Pat. No. 5,331,931 C and U.S. Pat. No. 5,873,335 C disclose electromotive valve controllers for an internal combustion engine, wherein rotation of a motor drives a valve lifter or a cylindrical cam that moves the valve stem. However, the proposed solution disadvantageously requires electrically generated holding forces at the endpoints of the valve stem motion in order to hold the valve open and closed, respectively. This prevents an energy-efficient operation of the valve control. In addition, at least the solution employing the cylindrical cam suffers from particularly severe wear. 
     EP 1 144 813 B1 also proposes a valve motion electrically generated by a segment motor. This approach also represents a complex structure requiring a large installation space. Disadvantageously, a fixed stop is also required for stably holding the valve in its end position. This prevents compensation of the valve play by implicit means of valve control, so that additional components are required for compensation. 
     Based on the disadvantages of the known solutions, it is an object of the invention to develop an electromotive device for actuating gas exchange valves, which have a simple, wear-resistant structure that does not require a large installation space and wherein valve motion can be predefined and the actuation path can be precisely controlled. In addition, the electromotive device to be developed for operating gas exchange valves should be designed for energy-saving operation. 
     The object is solved by configuring the electromotive device for operating gas exchange valves with the features of the independent claim. Advantageous embodiments of the devices are recited in the corresponding dependent claims. 
     The core concept of the invention include configuring the actuation device with a reluctance motor having a very low ratio of dissipated power to attainable acceleration of the controlled valve shafts. A design of the reluctance motor as a motor with a rotor having a particularly small diameter keeps not only the installation space small, but the motor also has a very small moment of inertia, enabling the aforementioned high acceleration. The low-mass construction of the reluctance motor as a core component of the electromotive device for operating gas exchange valves results in very low energy consumption. 
     According to another aspect of the invention, with the aforementioned design of the reluctance motor, the device of the invention can be arranged perpendicular to the longitudinal axis of the motor, so that several devices for operating several gas exchange valves can be arranged next to one another, without running out of space. It is also possible with the invention to operate several gas exchange valves with a single electromotive device for operating gas exchange valves, either on the same cylinder or on an adjacent cylinder, which reduces, or cuts almost in half, the hardware requirements for controlling the gas exchange valves of an internal combustion engine. 
     Is also important for the invention that the claimed electromotive device for operating gas exchange valves does not require additional holding devices for maintaining the end positions, because with the reluctance motor and associated spring elements the end positions are maintained without requiring much energy. This can produce significant energy savings during the operation of the electromotive device for operating gas exchange valves. 
     A positive valve control may be implemented if only a single gas exchange valve is to be controlled. 
     The conventional valve overlap is not affected during operation according to the invention. 
     Advantageously, with the inventive arrangement concept, temperature- and wear-related valve play can be compensated by adapting the control current of the reluctance motor. 
     With the electromotive device for operating gas exchange valves, the valve lift curves can be freely adjusted and partial strokes can be implemented. This is particularly advantageous for “soft landing” and mixture conditioning, because fuel and combustion air can be very efficiently mixed with a small valve opening which produces particularly high inflow speeds. Potential implementation of partial strokes reduces the work required for gas exchange, which significantly improves the efficiency of the internal combustion engine. 
     Finally, with the slim design of the rotationally symmetric components of the electromotive device for operating gas exchange valves, a very small installation height can be attained compared to conventional valve drive components. 
    
    
     
       The invention will now be described with reference to exemplary embodiments. The appended drawings show in: 
         FIG. 1  a schematic diagram of a reluctance motor as a rotary actuator of the electromotive device for operating gas exchange valves according to the invention, 
         FIG. 2  a schematic diagram of the electromotive device for operating gas exchange valves according to the invention arranged on a cylinder of an internal combustion engine—in form of a top view and a cross-sectional view—, and 
         FIG. 3  a schematic diagram for operating gas exchange valves according to the invention arranged on two adjacent cylinders of an internal combustion engine—in form of a top view and a cross-sectional view. 
     
    
    
     As shown in  FIG. 1 , a reluctance motor  1  used according to the invention has a rotor consisting of a rotor shaft  2  and alternatingly magnetized permanent magnets  3 . A stator  4  of the reluctance motor  1  is composed of laminated magnetic sheet metal with poles  5 , between which windings  6  are arranged. Stator bores  7  are provided for attaching the reluctance motor  1 . 
       FIG. 2  shows the electromotive device for operating gas exchange valves according to the invention disposed on a cylinder  10  of an internal combustion engine. A lever  8  is arranged on the rotor shaft  2  of the reluctance motor  1  operating as a rotary actuator, with the end of the lever  8  facing away from the axle pressing against the valve stem end  9  of a gas exchange valve  12  associated with the cylinder  11  of an internal combustion engine. 
     Depending on the current supplied to the reluctance motor  1 , the gas exchange valves  12  is either controllably opened or controllably closed by releasing the valve shaft end  9 . The required closing force is supplied by a spring  13  operating on the valve shaft end  9 . 
     In a particularly advantageous embodiment, the electromotive device for operating gas exchange valves according to the invention may be optimized by arranging an additional spring, because the overall system can then be represented by a spring-mass-oscillator. 
     The reluctance motor  1 , which in a slim configuration is arranged perpendicular to the longitudinal axis of the motor as rotary actuator for actuating the gas exchange valve  12 , takes up very little space. Advantageously, because the valve operation is based on the reluctance principle, it is very energy-efficient. 
     The electromotive device for actuating gas exchange valves according to the invention operates particularly advantageous, if it is configured, according to another exemplary embodiment shown in  FIG. 3 , to operate adjacent valves of two cylinders of an internal combustion engine. 
     According to  FIG. 3 , a reluctance motor  1  for operating two gas exchange valves  12  and  18  is provided, which are located on two cylinders  10  and  16  with pistons  11  and  17 . A dual lever  14  is disposed on the rotor shaft  2  of the reluctance motor  1 , with the ends of the lever  14  configured to apply actuation forces to the valve shafts ends  9  and  15  of the two gas exchange valves  12  and  18 . The springs  9  and  19  supply the closing forces for the gas exchange valves  12  and  18 . 
     The arrangement of the second exemplary embodiment has the particular advantage that two gas exchange valves can be actuated by a single rotary actuator. This not only saves space and material, but also simplifies manufacture and installation. 
     The reluctance motors  1  of the electromotive device according to the invention for actuating gas exchange valves are controlled in single-phase. This advantageously simplifies the control: with the single-phase control, a valve stroke can be performed without reversing the current, whereby the current through the reluctance motor  1  can advantageously be decreased during the flight phase. This feature also contributes to driving the valve according to the invention with low dissipation losses. 
     LIST OF REFERENCE AND FORMULA SYMBOLS 
       
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 1 
                 reluctance motor 
               
               
                 2 
                 rotor shaft 
               
               
                 3 
                 permanent magnet 
               
               
                 4 
                 stator 
               
               
                 5 
                 pole 
               
               
                 6 
                 winding 
               
               
                 7 
                 stator bore 
               
               
                 8 
                 lever 
               
               
                 9 
                 valve shaft end 
               
               
                 10 
                 cylinder 
               
               
                 11 
                 piston 
               
               
                 12 
                 gas exchange valve 
               
               
                 13 
                 spring 
               
               
                 14 
                 dual lever 
               
               
                 15 
                 valve shaft end 
               
               
                 16 
                 cylinder 
               
               
                 17 
                 piston 
               
               
                 18 
                 gas exchange valve 
               
               
                 19 
                 spring