Jerk pump provided for an internal combustion engine, with a dampened integral solenoid valve

A jerk pump provided for an internal combustion engine has an integral solenoid valve in which a pump plunger driven by a cam delivers fuel at high pressure through a channel that extends in the pump housing and through an injection line to an injection nozzle. An armature of the solenoid valve cooperates with a spring-loaded valve piston by which the channel-guiding high-pressure side can be connected with a low-pressure side. In order at least largely to avoid rebounding of the solenoid valve in such jerk pumps, provision is made such that the valve piston has an absorbent body held in its resting position by spring force, said absorbent body striking a stop body that holds the valve piston in its closed position when the valve piston is resting on its valve seat.

BACKGROUND AND SUMMARY OF THE INVENTION
 This application claims the priority of German application 198 39 522.1,
 filed in Germany on Aug. 29, 1999, the disclosure of which is expressly
 incorporated by reference herein.
 The invention relates to a jerk pump provided for an internal combustion
 engine, with an integral solenoid valve in which a pump plunger driven by
 a cam delivers fuel at high pressure through a channel that extends in the
 pump housing and through an injection line to an injection nozzle, and in
 which an armature of the solenoid valve cooperates with a spring-loaded
 valve piston by which the high-pressure side guiding the channel can be
 connected with a low-pressure side.
 Jerk pumps of this kind are known from MTZ Motortechnische Zeitschrift 57
 (1996) 4, FIGS. 2 and 3, from Neue Motoren "Thermodynamik OM 904 LA, FIGS.
 2 and 3, and from German Patent Document No. DE 196 41 952 A1 in which the
 valve piston permanently connected with the armature supports a spring
 plate that abuts a pressure shoulder of the valve piston by spring force.
 The valve piston is pressed against a valve stop by the spring force. As
 soon as the solenoid valve is activated, the valve piston strikes its
 valve seat against the spring force and interrupts the free connection
 between the high-pressure side and the low-pressure side. Injection begins
 and is terminated again only when the solenoid valve is deactivated and
 the pressure on the high-pressure side collapses.
 In designs of this kind, because of the high switching rate, rebounding of
 the valve piston or re-opening of the valve cannot be avoided.
 Hence, a goal of the invention is to provide simple means on the solenoid
 valve according to the species that minimize the rebounding of the valve
 piston or even prevent it entirely.
 This goal is achieved by preferred embodiments of the invention by
 providing a jerk pump for an internal combustion engine, comprising: an
 integral solenoid valve in which a pump plunger driven by a cam delivers
 fuel under high pressure through a channel that extends in a pump housing
 and through an injection line to an injection nozzle, an armature of the
 solenoid valve cooperating with a spring-loaded valve piston by which a
 channel-guiding high-pressure side can be connected with a low-pressure
 side, wherein the valve piston has an absorbent body held in a resting
 position by spring force, said body striking a stop body that is in an
 operating connection with valve piston when the valve piston is on its
 valve seat.
 Further advantageous features of preferred embodiments of the present
 invention are described below and in the claims.
 As a result of the special arrangement of an absorbent body, it is possible
 to suppress and/or eliminate the undesired re-opening of the valve and/or
 the multiple rebounding of the valve piston.
 In the resting state, the absorbent body is located at its stop or in its
 initial position. After the solenoid coil is energized, the valve piston
 is moved in the closing direction together with the absorbent body. As
 soon as the valve piston strikes its valve seat, the absorbent weight
 moves further in the closing direction under the influence of inertia. At
 the moment when the valve piston wants to rebound from its valve seat, the
 absorbent weight reaches its sleeve-shaped stop body. An opposite momentum
 is then generated that counteracts the rebounding of the valve piston.
 When the valve opens, the absorbent weight can follow the valve piston only
 after a delay because of its mass inertia. As a result, an opposite
 momentum is generated that counteracts the rebounding of the valve piston
 from the stop.
 In German Patent Document DE 197 08 104 A1, published subsequently, and in
 German Patent Document DE 40 20 951 A1, absorbent bodies for solenoid
 valves are mentioned, but an impact of the absorbent body against a stop
 body in an operating connection with the valve piston is not provided for
 closing movements.
 Other objects, advantages and novel features of the present invention will
 become apparent from the following detailed description of the invention
 when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS
 A jerk pump 1 according to FIG. 1 includes a roller tappet 3 guided
 displaceably lengthwise in a bushing 2 as well as a pump plunger 5
 delimiting a pump working chamber 4. From the pump working chamber 4, a
 channel 7 extends through a pump housing 6 and terminates at a connecting
 stub 8 at the head part 1a of jerk pump 1.
 Connecting stub 8 is provided for an injection line connected to an
 injection nozzle and not shown in greater detail.
 In the head part 1a of jerk pump 1, channel 7 intersects a transverse bore
 9 in which a valve piston 10 of a solenoid valve: 11 is mounted
 displaceably lengthwise. The valve piston 10 permanently connected with an
 armature 12 consists of a piston shaft 10a formed stepwise and a conical
 sealing part 10b that fits the conical seat surface 13 in the pump housing
 6.
 Piston shaft 10a has three sections a, b, and c, of which the middle
 section b has the largest diameter, while the section a on the valve seat
 side, like the section c that faces the armature 12, is made with a small
 diameter.
 The section a on the valve seat side delimits an annular intermediate
 chamber 14 in cross bore 9 which connects channel 7 on the high-pressure
 side with a low-pressure side 15 when the valve is open. In the open
 position, valve piston 10 abuts a valve stop 16 located in pump housing 6.
 The section c of the piston shaft on the armature side supports a spring
 plate 17 that abuts a pressure shoulder 18 and serves as a support for a
 compression spring 19 that operates in the opening direction of a valve
 piston 10, said spring also abutting a sealing part 20 fastened to pump
 housing 6.
 The section c on the armature side is surrounded by a stop body 21 that
 acts as a spacing bushing, between which said stop body 21 and the spring
 plate 17 an absorbent body 22 is guided displaceably lengthwise. This
 absorbent body 22 is pressed against spring plate 17 by a spring 23 that
 surrounds the spacing bushing and abuts the armature 12. Compression
 spring 19 and spring 23 are concentric with respect to one another.
 A distance defined to correspond to distance S is provided between the
 absorbent body 22 and the spacing bushing 21. With a specific design of
 the absorbent weight and distance S the rebound of the valve piston 10 is
 considerably reduced, as a comparison between the design according to the
 invention in the graph in FIG. 3 and the known design according to FIG. 4
 will show. In FIGS. 3 and 4, the respective closing stroke H.sub.s and
 opening stroke H.sub.o of the valve piston are shown, while in FIG. 3 the
 travel on the absorbent body 21 is plotted as well.
 In FIGS. 3 and 4, the travel S is expressed in millimeters (mm) and the
 time axis t is graduated in seconds (s).
 The foregoing disclosure has been set forth merely to illustrate the
 invention and is not intended to be limiting. Since modifications of the
 disclosed embodiments incorporating the spirit and substance of the
 invention may occur to persons skilled in the art, the invention should be
 construed to include everything within the scope of the appended claims
 and equivalents thereof.