Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
2000-05-02
2001-10-23
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
C188S273000, C137S630120
Reexamination Certificate
active
06305349
ABSTRACT:
This invention relates to a sliding gate exhaust brake assembly.
Exhaust brakes are known for location in the exhaust system of internal combustion engines of motor vehicles to provide additional braking of the vehicle. Exhaust brakes operate by obstructing an outflow of exhaust gases from the engine to build up pressure in the exhaust manifold so that back pressure acts on the pistons during their compression strokes to create a retardation effect, which is transferred through the vehicle's transmission system to the road wheels to act as a non-fade supplementary braking system. Known sliding gate exhaust brake assemblies comprise a housing having aligned inlet ports and outlet ports and a slidable gate within the housing for sliding between an open position in which exhaust gases flow through the exhaust brake assembly and a closed position in which the gate closes at least one of the ports to build up pressure in the exhaust manifold. In known devices the gate is moved from the open position, against a force exerted by a return spring, by a piston of a single-action pneumatic or hydraulic cylinder.
To avoid possible damage to the engine by excessive pressures created by the exhaust brake, it is known to incorporate pressure relief features into the exhaust brake, for example, by providing an aperture through the gate. This sets a maximum pressure that can be generated in the exhaust manifold by the exhaust valve, but has a disadvantage that the aperture has to be of such a size to prevent overpressure when the engine is working at maximum speed and is, therefore, larger than required when the engine is not working at maximum speed, resulting in less than optimum back pressure being generated by the exhaust brake except at maximum working speed.
U.S. Pat. No. 4,556,027 discloses an exhaust brake in which the opening of the exhaust valve is continuously variable to maintain a required pressure.
EP 0250310 and U.S. Pat. No. 4,669,585 disclose a slidable gate assembly having an exhaust gas relief passage within the gate with a closure device which is biased to the closed position and is forced open by overpressure of the exhaust gas in the exhaust manifold.
PCT/GB94/01300 discloses a slidable gate valve with an aperture having a control arrangement which is pre-selectably variable according to driving conditions, to prevent over-severe braking in poor driving conditions.
The manifold pressures generated by known exhaust brakes may be over 450 kPa (65 psi). At such a pressure it is found in a 100 mm diameter exhaust system that a force of at least 1,090 N (245 lbf) is required to operate the gate to overcome the pressure of exhaust gases on a closed gate or the reaction forces caused by increasing pressure of exhaust gases on a closing gate and the force of the return spring. This requires a return spring and a piston and cylinder of such a size that the overall size of the exhaust brake is too bulky to use in many modern commercial vehicles, because legal requirements of noise and pollution emission control result in the space in which to install an exhaust brake being extremely limited. As a result, in such situations it is necessary to use known less effective and less robust butterfly valve type exhaust brakes. This disadvantage of the present exhaust valves is particularly acute in the case of turbo charged engines. It is well known, as discussed below, that the optimum position for an exhaust brake in a turbo charged engine is upstream of the turbo charger between the exhaust manifold and turbo charger. Prior art slide valve exhaust brakes have been excluded from this application primarily owing to their size and weight. In addition, butterfly type exhaust brakes are not suitable for mounting upstream of a turbo charger because the high velocity, extremely hot, exhaust gases acting under high pressure have the effect of eroding edges of a closure disk of the butterfly brake and these eroded particles may pass into the vanes of the turbo charger. This can unbalance the vanes and, since the turbo charger vanes may be rotating at over 100,000 rpm, may result in the destruction of the turbo charger.
Furthermore, it is often required to use an exhaust brake in combination with an engine compression release brake, since such a combination gives an increased amount of retardation than is available from either type of brake individually. A known compression release brake operates by altering the valve timing of the engine to use what would normally be the compression stroke to brake the engine, releasing the high pressure which has been built up against the piston at close to top dead centre. This pressure is released into the exhaust system where it is maintained by the exhaust brake, increasing the back pressure on the pistons. The effect of this combination is limited if the exhaust brake is placed downstream of the turbo charger. In this position, the pressure generated by the exhaust brake has the effect of slowing the turbo charger, thereby reducing the amount of air being delivered by the turbo charge vanes to the engine which has a marked effect on the compression release brake, which is dependent on an adequate air supply to the cylinders for its retarding effect.
It will be understood that the exhaust system may be connected to the exhaust aperture in a known manner and the exhaust manifold may be connected to the input chamber by a gas-tight joint passing around the periphery of the input aperture and around the operating rod housing.
It is an object of this invention to provide a sliding gate exhaust brake assembly in which these disadvantages are substantially overcome and thereby to provide an exhaust brake assembly which can be used in applications in which known exhaust brake assemblies cannot be used.
According to one aspect of the present invention there is provided a sliding gate exhaust brake assembly for closing an exhaust outlet, the assembly comprising gate means located within a housing, the gate means being moveable between an open position and a closed position, the assembly further comprising a first pressure relief passage having first closure means openable for relieving exhaust gas pressure on the gate means during movement from the closed position to the open position thereof, and the assembly further comprising a second pressure relief passage having second closure means openable for reducing exhaust gas pressure on the gate means during movement from the open position to the closed position thereof.
Advantageously, the first pressure relief passage is a gate aperture through the gate means and the first closure means include a first closure plate, slideable on the gate means between a gate closing position and a gate opening position, for closing and opening the gate aperture.
Conveniently, the first closure plate is provided with a first closure plate aperture for alignment with the gate aperture in the gate opening position.
Advantageously, the assembly further comprises operating rod means and the first closure means include engagement means for engagement with the operating rod means for movement of the first closure means by the operating rod means between the gate opening position and the gate closing position.
Conveniently, the first closure means are adapted to open the first relief passage before opening the gate means.
Preferably, the housing is divided into an input chamber and an exhaust chamber by a partition wall therebetween.
Conveniently, the second relief passage is formed by a closeable passage in the partition wall.
Advantageously, the second closure means include a second closure plate, slideable on the partition wall between an open position and a closed position of the closeable passage.
Conveniently, the second closure means are provided with engagement means for engaging the gate to move the second closure means from the closed position to the open position of the closeable passage in the partition wall.
Conveniently, the second closure means includes operating pin means for passing through a wall of the housing and th
Dolinar Andrew M.
Hersham Valves LTD
Ladas and Parry
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