The present invenϋon relates to a valve device, compnsmg a housmg w ith an mlet and an outlet to be connected to an exhaust conduit in an internal combustion engine, an exhaust passage disposed between said mlet and outiet, a vah e bod\ which can be set m vaπous positions to vary the throughflow area of the exhaust passage, and operating means for setting the valve body

It is known that it is possible by merely mcreasmg the exhaust counterpressure in the exhaust conduit of an internal combustion engme with the aid of a \ alve deuce of the above mentioned type to achieve a certain mciease m the engme bi aking effect of the vehicle A. further mcrease in the engme braking effect can be achieved if communicaπon is established m a known manner between the exhaust svstem and the engme cylinders duπng the latter portion of the intake stroke, so that gas from the exhaust system can flow mto the cylmders This results in a pressure mcrease m the cylinder and an inner charging which mcreases the compression w ork after cuttmg off the communication between the cylmders and the exhaust stem

A known type of valve device for varying the exhaust counterpressure is an exhaust pressure regulator compnsmg a damper m the exhaust conduit Great demands are placed on the design of damper valves which must be able to function w ith high reliability and long life m the exhaust conduit environment They must be able to withstand high mechanical and thermal stresses, m the open position they must not provide any flow impediment or create turbulence in the exhaust conduit and they must not stick so that they do not reach their defmed positions, something which often happens after a relatively short operating penod due to deposits of soot

The purpose of the present mvention is m general to achieve a valve device of the type descnbed by way of introduction which can withstand higher thermal and mechanical stresses than a damper valve and which has a simple design and high reliability The particular purpose is to achieve a valve device hich makes it

mechanical stresses than a damper valve and which has a simple design and high reliability. The particular purpose is to achieve a valve device which makes it possible in a turbocharged engine to utilize the turbo unit in a better manner than previously to vary the braking power ofthe engine.

This is achieved according to the invention by virtue of the fact that the housing has a cylinder communicating with the exhaust passage, said cylinder housing with radial play having a valve body in the form of a piston displaceable into the passage under the effect of a pressure medium, said piston having at its distal and proximal end surfaces valve discs, the proximal disc in an extended position of the piston abutting against a proximal seat formed in the cylinder and the distal disc in a re¬ tracted position of the piston abutting against a distal seat formed in the cylinder.

In such a valve device the piston is the only moving part. The piston does not require any return spπngs or particular operating means, since it functions in itself as both the valve body in a valve housing and the operating piston in an operating cylinder.

It has been shown that a valve device according to the invention, in contrast to a damper valve, can function as a throttle valve in the extremely aggressive environ¬ ment prevailing in engine exhaust pipes. In a turbocharged engine it can be ananged as a throttle valve upstream of the turbine pottion of the turbocompressor unit, which provides a number of advantages.

By placing a valve device closer to the extiaust outlet ofthe cylinders, the volume of the exhaust conduits is reduced between the exhaust vaives and the valve device in the exhaust conduit, which means that the pistons need not force out as much gas as previously to create a certain level of counterpressure. High counterpressure can therefore be obtained more rapidly.

In a turbocharged engine with the exhaust pressure regulator dow nstream of the turbine, the pressure drop required over the turbine to enable the turbine to drive the compressor, is not obtained in braking mode. By arranging instead a throttle valve device prior to the turbine portion and adapting the throttle area to the turbine area. the turbocompressor unit can provide supercharging even in braking mode. It is true that the pistons are imparted energy from the gas during the intake stroke, but the work which the pistons must perform during the compression stroke against the gas is so much greater that the net result will be higher braking pow er. Another advantage of circulating large volumes of gas through the engine in braking mode is that a greater amount of heat is removed with the gas than in installations with exhaust pressure regulators, in which the heat is primarily dissipated by the coolant.

The turbine portion of a turbocompressor unit, which is dimensioned to work within the normal engine speed range when in driving mode, will be too large to be able to supercharge in braking mode. The valve device according to the invention can therefore be used with advantage in turboengines with turbines which have variable geometry or in so-called turbocompound engines which have a turbocompressor unit with a first turbine step driving the compressor unit and a second turbine step which is coupled via a transmission to the engine crankshaft. In such turbo units, the first turbine step is a small high-pressure turbine, while the second turbine step is a larger low pressure turbine. It has been found that the conected mass flow to the compressor turbine in braking mode is approximately equal to that in turbo compound driving mode. In a conventional turbo engine, however, the compressor turbine is significantly larger, which means that the corrected mass flows during braking mode and driving mode will be approximately equal first at engine speeds above normal driving mode rpms.

The invention will be described in more detail below with reference to examples shown in the accompanying drawings, where Fig. 1 shows schematically a turbo

compound engine with a valve device according to the invention and Fig. 2 show s a longitudinal section through one embodiment of a valve device according to the invention.

In Fig. 1, the numeral 1 designates a six-cylinder engine with gearbox 2. A turbo compressor unit, generally designated 3, has a first turbine step 4 and a second turbine step 5 coupled to the engine exhaust manifold 6. The first turbine step 4 is a small high-pressure step, which drives a compressor 8 coupled to the engine intake conduit 7, while the second turbine step 5 is a larger low-pressure step, which is coupled, via a transmission 9 to the engine crankshaft 10. Via a first continuously variable waste-gate valve 17. a greater or smaller portion of the exhaust can be shunted past the high-pressure turbine for the purpose of varying the degree of charge 4. Via a second waste-gate valve 18. the exhaust can be shunted past the low-pressure turbine 5. The engine 1 has a schematically indicated compression braking device 19.

The manifold 6 is divided into two submanifolds 40. the outlet conduits 41 of which converge prior to the inlet into the turbo compressor unit 3. In each exhaust conduit 41 there is a throttle valve 42 according to the invention, which has a completely open position and a throttle position in which the exhaust passage 41a of the conduit

41 , between the inlet 41b and the outlet 4 i c. is reduced to create an exhaust counter¬ pressure in the exhaust manifold 6 during engine braking.

A valve, which is to function in the environment prevailing in an exhaust manifold, must be able to withstand high mechanical and thermal stresses. In its open position it must not constitute a flow hindrance or create turbulence in the exhaust conduit. The valve 42 fulfils these requirements and is shown in more detail in Fig. 2, where 50 designates a cylindrical valve housing which is preferably cast in one piece with the exhaust manifold 6. The cylinder space 51 in the housing 50 opens into the

interior of he exhaust conduit 41. The opening 52 itself is surrounded by a conical seat 53. against which a corresponding seat 54 at one end of a sleeve of stainless steel abuts. The sleeve 55 is held in place by a cover 56 screwed securely to the housing portion 50. The cover 56 presses with a conical surface 57 against a coπe- sponding conical surface at the opposite end of he sleeve 55. The sleeve 55 has a portion 58 of reduced diameter in order to form a cylindrical airgap 59. which communicates with the s rounding air via an annular gap 66 between the housing portion 50 and the cover 56.

Inside the sleeve 55 there is disposed a valve body in the form of a hollow piston 60. As can be seen in Fig. 2. there is a small play ^" s ^" between outer lateral surface of the piston 60 and the inner lateral surface of the sleeve 55. The cylindrical portion of the piston 60 consists of a tube 60a of hard chromium plated stainless steel. At the ends, the piston end pieces 61.62 are fixed to the tube 60a. These form valve discs with conical edge portions 60a.62a and are preferably sintered. The sleeve 55 is provided at its distal end with a seat 55a. against which the edge portion 61 a of the disc 61 abuts sealingly in the open position of he valve (as shown in Fig. 2). When air pressure exceeding ca 8 bars is supplied to the cylinder chamber 63 via an inlet 64, the piston 60 is displaced to the left in Fig. 2 at the same time as the leaking air in the gap ^" S ^" blows out any soot. The piston 60 is displaced perpendicularly to the exhaust conduit 4 land stops with its disc 61 a short distance from a surface 65 on the opposite wall portion of the conduit 41 , when the conical edge portion 62a of the disc 62 strikes a proximal conical seat 55b ofthe sleeve 55, so that exhaust gases cannot leak into the cylinder chamber. As long as there is pressure in the cylinder chamber, the piston 60 will be held in its throttle position. The diameter of the piston 60 and the cross-section of the conduit 41 are adapted to each other so that a throttled passage for exhaust is obtained between the interior wall of the conduit and the piston. When the piston 60 is to be returned to the starting position in Fig. 2. the cylinder chamber 63 is drained, and the exhaust pressure which is propagated

through the gap "S ^" and acts against the disc edge 62 a will displace the piston into the sleeve 55. No return springs are required and the only moving part of the valve is the piston 60, which results in high reliability.

The compression braking device 19 is electrically operated, while the waste-gate valves 17, 18 and the throttle valves 42 are pneumatically operated. They are con¬ trolled by a control valve unit 70 connected to a pressure source (not shown) and a control unit 71 , which is preferably a microprocessor, which provides output signals for turning the compression braking device on and off and for setting the valves 17.18 and 42 depending on a number of different engine and vehicle data fed into the control unit from sensors known per se and not shown in more detail here. As is indicated in Fig. 1. signals are fed into the control unit 71 representing charge pres¬ sure and engine speed, i.e. engine data, and signals representing ABS on/off, vehicle speed, clutch pedal position, accelerator position, cruise control on/off and retarda- tion level, i.e. vehicle data.

The device can function as follows:

The driver sets, by manual means (not shown), the retardation to a certain level and activates the cruise control, so that a signal representing selected retardation is fed into the control unit 71 , which compares the command value fed in for retardation with the computed actual value of retardation computed via the actual speed value. When the driver lets up on the accelerator, assuming the clutch pedal is not depres¬ sed, the control unit 71 will set. via the control valve unit 70, the throttle valves 42 in the throttle position, will open the waste-gate valve 18 to shunt past the second turbine step 5 and will, depending on the difference between the actual value and the command value, regulate via the waste-gate valve 17 the suitable degree of charge in the first turbine step 4 and activate the compression braking device 19. If the selected retardation level should be too high in view of the road conditions, so that the drive wheels slip, the ABS on/off will provide a signal to reduce the

engine braking power by tuming off the compression brake 19 and then tuming it on again at a lower retardation level or alternatively providing the driver with the possibility of selecting a lower retardation level. Tuming off the compression brake 19 also occurs if the driver should depress the clutch pedal, which is important in order to prevent engine shut off with accompanying loss of servo assisted steering and brakes.