Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Patent
1991-07-25
1993-11-23
Cross, E. Rollins
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
123 9016, F01L 902, F01L 112, F02D 1302
Patent
active
052634418
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is based on a hydraulic valve control apparatus for an internal combustion engine as set forth herein after.
In a known hydraulic valve control apparatus of this type (German Offenlegungsschrift 3 511 820), the pressure line is controlled via a 3/2-way valve; in a special exemplary embodiment (FIGS. 8 and 9), the multi-position valve, in one switching position, connects the pressure line to the pressure chamber of a valve tappet, and in the other switching position connects it to the pressure chamber of a different valve tappet, using only a single liquid reservoir for both pressure chambers. Accordingly, for two engine inlet valves, one control position each of the magnet valve is used, and only one reservoir is used for both inlet valves. Especially at high rpm, the precision of control, or in other words how accurately the opening time cross section of the engine valve sought is attainable, depends on how large the total oil volume is that has to be shifted back and forth in control, and how many control conduits, with corresponding control cross sections, must be traversed. The magnet valve, especially, bears considerable responsibility for the expense and vulnerability to malfunction of this kind of hydraulic valve control apparatus; in engines having a typical maximum rpm, far from full utilization of the possible switching frequency of these magnet valves is made. A further factor is the burden due to the cost of every extra magnet valve.
In a hydraulic valve control apparatus of this type, it has also already been proposed (German Patent 38 15 668.7; U.S. Pat. No. 4,889,084) to embody the reservoir as a movable valve member; the end edge of the piston cooperates with a valve seat, so that the connection between the pressure line and reservoir chamber can be controlled. The reservoir piston simultaneously acts as an armature for a magnet valve that is open when without current, so that when the magnet is excited the pressure line is separated from the reservoir chamber. Although a combination of fluid reservoir and magnet valve, in which the same part serves as both the movable valve element of the magnet valve and as a reservoir piston, is attained by this provision, nevertheless one such "magnet valve reservoir unit" must be available for each valve control unit.
ADVANTAGES OF THE INVENTION
The valve control apparatus according to the invention has the advantage over the prior art that even a low determined control pressure from the control lines suffices to lift the reservoir piston from its valve seat. Since the control line is controlled by the magnet valve, opening of the magnet valve acts, in the feed line that is at low pilot pressure, as a pressure thrust of the control oil on the reservoir piston.
In an advantageous feature of the invention, a pressure face acting counter to the force of the reservoir spring and always acted upon by the pressure of the control oil present in the pressure conduit is provided on the reservoir piston; the force of the reservoir spring is greater than the control force plus the pilot pressure force effected by this pressure face. This reinforcing actuation force that engages the pressure face of the reservoir piston from the pressure chamber is then correspondingly strong if the associated valve tappet is just then being actuated by the drive cam, which as a result produces the high working pressure in the pressure chamber necessary for the actuation of the inlet valve. When a plurality of reservoir pistons are acted upon simultaneously by the control pressure, in this embodiment of the invention, the pressure thrust thus remains ineffective for all the reservoir pistons at which the drive cam of the engine valve is inoperative at that time as well. The control pressure, even with the pressure thrust, is not sufficient by itself to lift the reservoir piston from the valve seat. It is thus made possible in a very simple way for a plurality of control units to be acted upon by the control pressure simultaneously, yet
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Linder Ernst
Rembold Helmut
Cross E. Rollins
Greigg Edwin E.
Greigg Ronald E.
Lo Weilun
Robert & Bosch GmbH
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