Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Patent
1995-12-14
1997-05-20
Nelli, Raymond A.
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
F02D 906
Patent
active
056303920
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an exhaust brake particularly of the type which is generally referred to as sliding gate type exhaust brake.
Exhaust brakes are devices which obstruct the outflow of exhaust gases of an engine and builds up a back pressure in the exhaust manifold of the engine as far back as the engine pistons. On the travel of the piston to its top dead centre position the piston will act against this pressure and this has a marked retardation effect on a vehicle which is driven by its forward momentum only and acts as a non-fade supplementary braking system.
Such devices are well known and have been in use for many years. A large number of such devices incorporate a fixed orifice through the slidable gate or closure plate to comply with engine manufacturers criteria, that the exhaust manifold pressure will not exceed a given pressure at engine overspeed, in some cases plus ten percent of rated engine speed. The main reason for this is to limit exhaust valve lift.
An exhaust brake which builds excessive pressure in the manifold system will cause the exhaust valve to lift from its seat, this pressure then drops rapidly when passing into the cylinder bore or, on valve overlap through to the atmosphere via the air intake, and the exhaust valve then returns to its seat at high speed. This is known as the "Hammer Effect" and has a long term detrimental effect on both valve and seating.
JP-A-58 158333 discloses a variable aperture control dependent upon engine revolutions and has improved the previously known defects on the valve and seating. The engine revolutions are however monitored separately electrically and the signal representing the number of revolutions processed to control the amount of opening of a rotary bar valve to variably vent exhaust gases past the exhaust gate valve.
Recent innovations such as that disclosed in our co-pending European Patent 0,205,310 have improved the performance of exhaust brakes, notably those which have the ability to control manifold pressure without fixed orifices, these devices use a manifold pressure to open an orifice in the face of the closure member and bleed excessive pressure therethrough into the exhaust system. This pressure is sensed by a closure plate of a known size which is balanced against a remotely mounted spring of known rate and thus the manifold pressure is used to open and the spring to close the orifice.
Like most retarding devices exhaust brakes act on the drive axle of the vehicle and with the enhanced performance of these devices, up to four hundred brake horse power has been recorded. Great care must be taken therefore when applying the exhaust brake especially when the vehicle is empty or on wet greasy roads, in these conditions an articulated vehicle could be prone to jackknife blocking the road to oncoming traffic.
With all known exhaust brakes in use at the present time, both the fixed orifice and the spring balanced brake types, the exhaust brake is operated to be either on or off. Therefore, the driver in adverse conditions has only two choices. Either he applied his exhaust brake and risks the "jackknife" or deprives himself of the use of the exhaust brake.
Some attempts have been made to allow the driver of a vehicle to vary the amount of retardation obtained from the exhaust brake. The most successful of these comprises a switch under control of the driver acting on the operation of a cylinder mechanism which allows the exhaust brake to partially close. However, this method is erratic because the force generated by the operating cylinder is counteracted by the manifold pressure acting on the closure member because the manifold pressure is a sum of the size of the opening through the exhaust brake valve and the amount of air produced by the engine. It follows therefore that engine revolutions control the position of the closure valve. It is also a fact that from the position first selected, the manifold pressure cannot be lowered unless the exhaust brake is first deactivated because once the operating cylinder closure member equ
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Hersham Valves Limited
Nelli Raymond A.
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