Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Patent
1995-10-18
1997-03-11
Lo, Weilun
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
123 9016, 123 9046, F01L 124, F01L 1306
Patent
active
056091338
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an exhaust valve mechanism in an internal combustion engine, comprising at least one exhaust valve in each cylinder, a rocker arm, mounted on a rocker arm shaft, for each cylinder for operating the exhaust valve, a cam shaft with a cam lobe for each rocker arm, said cam lobe cooperating with a first follower at one end of the rocker arm, a valve play absorbing device arranged between an opposite end of the rocker arm and the exhaust valve, said valve play absorbing device comprising a piston element which is housed in a first cylinder chamber disposed in said opposite rocker arm end, and a hydraulic circuit for supplying or draining hydraulic oil to or from said cylinder chamber.
BACKGROUND OF THE INVENTION
SE-A-468132 reveals an exhaust valve mechanism of the above type which, together with a special type of cam shaft with an extra small cam lobe, can be used to increase the braking power of the engine. The extra cam lobe is dimensioned so that its lift approximately corresponds to the normal valve play in the valve mechanism. By reducing, by means of the valve play absorbing mechanism, the valve play to zero, an extra lift can be achieved of the exhaust valve corresponding to the normal valve play, during a suitable time interval. For example, the extra cam lobe can be placed relative to the ordinary cam lobe, so that an extra exhaust valve lift is obtained during a latter portion of the compression stroke, resulting in loss, during the compression stroke, of a portion of the compression work, which cannot be recovered during the expansion stroke. The result is an increase in the engine braking power.
An engine with such an arrangement for increasing-the braking power has, however, a somewhat lower efficiency than a corresponding conventional engine. This is due to the fact that the maximum lift of the exhaust valves at zero valve play is utilized for brake mode and not for engine mode, which means that engine mode must be compensated by lower lift when the valve play absorbing device is not activated, which also means that the exhaust valves close earlier than if a maximum lift can be used for engine mode. An additional disadvantage of the known arrangement is that it requires a special cam shaft.
SUMMARY OF THE INVENTION
The purpose of the present invention is to achieve an exhaust valve mechanism of the type described by way of introduction, which can be used together with a conventional cam shaft to achieve an engine where so-called compression braking is possible without a reduction in efficiency in comparison with the same engine without this braking capacity.
This is achieved according to the invention by virtue of the fact that the hydraulic circuit contains a hydraulic pump housed in the rocker arm and driven by the cam lobe, said hydraulic pump having a second cam follower arranged at a predetermined cam angle distance from the first cam follower and communicating via a channel with the first cylinder chamber.
According to the invention, the known arrangement with a rigid mechanical drive device in the form of an extra cam lobe on the cam shaft is replaced with a hydraulic drive device actuated by the ordinary cam lobe and which can be made in such a manner that the exhaust valve closing sequence in engine mode will be the same as in brake mode.
In a preferred embodiment of the valve mechanism according to the invention, the pump is a piston pump, which via the channel in the rocker arm, communicates with a pressure accumulator, in which an equalizing volume of hydraulic oil is introduced during the initial piston stroke, so that the volume fed into the first cylinder chamber will be less than the stroke volume of the piston pump. By also coordinating the piston element of the valve play absorbing device with an abutment which limits the piston stroke and arranging a relief valve through which the hydraulic oil can be drained when the pressure in the hydraulic circuit rises after the piston element has reached its end position, a ra
REFERENCES:
patent: 4261307 (1981-04-01), Oldberg
patent: 4711210 (1987-12-01), Reichenbach
patent: 5036810 (1991-08-01), Meneely
patent: 5107803 (1992-04-01), Furnivall
AB Volvo
Lo Weilun
LandOfFree
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