Abstract: An exhaust gas pressure modulation valve for a diesel engine vehicle combines the functions of an exhaust brake and a warm-up valve and has a single butterfly valve (12) to close the exhaust passage. The butterfly is reactive and opens automatically at a predetermined back pressure to prevent engine damage. The butterfly includes a small bypass passage or aperture (29) to permit a low throughput of exhaust gas when closed.

Abstract: An exhaust modulator in or to be fitted in the exhaust system of an engine, having a body defining a flowpath therethrough for engine exhaust gases, a gate in the exhaust flowpath movable between an open and a closed position, one or more bleed flowpaths communicating between opposite sides of the gate, and a flow control mechanism. The mechanism is responsive to one or more operating parameters to control the flow of exhaust gases along the one or more bleed flowpaths so as to limit the back pressure applied to the engine to different predetermined levels as required for operation of the modulator in selected modes.

Abstract: A branched exhaust system having a particular filter in at least one branch thereof has valves in each branch operable by control means to route exhaust gases along any selected branch. Thus when the filter in one branch requires regeneration that branch can be closed. The control means is also operable in response to an exhaust braking demand signal to maintain all valves closed so as to at least restrict the flow of exhaust gas and so apply back pressure to the engine; to apply exhaust braking.