DEVICE FOR REGULATING THE ENGINE BRAKING POWER OF AN INTERNAL COMBUSTION ENGINE

Abstract: Device for controlling the engine braking power of an internal combustion engine (1) in a motor vehicle, which is equipped with a compression braking device arranged in brake mode to open the exhaust valves at the end of the induction stroke, at the end of the compression stroke or only at the latter, and an exhaust-driven turbocompressor unit (3) with a turbine portion (30), which has variable geometry to vary the degree of charge of the compressor (8). Restrictor valve means (42) are arranged in the exhaust conduit (41) upstream of the turbine portion (30).

Description: Device for regulating the engine braking power of an internal comDustion engine The present invention relates to a device for controlling the engine braking effect in an internal combustion engine m a motor \ ehicle. which is equipped with a compression braking device, means for varying the degree of charge m brake mode. compπsing. firstly, an exhaust-dπven turbocompressor un t with a turbine portion and a compressor portion and. secondly, valve means disposed in d e engine exhaust conduit and means actuatable by the dπver of the vehicle for activating the com¬ pression braking device and the means for varying the degree of charge It is known that the engme braking power of a vehicle can be increased with the aid of a deuce of the above descnbed type, by means of which the eng e combustion chambers in brake mode during the latter portion of the compression stroke is con¬ nected to the exhaust system, for example by opening the regular exhaust valve The result w ill be that the air compressed duπng the compression stroke flows out of the cylmders and that the compression work canned out duπng the compression stroke will not be recovered duπng the expansion stroke, and this will result in an increase m the engme braking power An additional increase m the braking power can be achieλ eα in tins case m a known manner by connecting the exhaust stem to the cylmders during the latter portion of the induction stroke, so that gas from the exhaust _\ stem can flow into the cylmders This results in an increase m pressure in the lrnder and an inner charging so that the compression work after breaking off the commumcaπon between the cylmders and the exhaust system will be increased In a deuce known by SE-A-9401059 of the type descπbed by way of mtroduction, said vah e means are formed of an exhaust pressure regulator ( EP regulator), I e. a damper in the exhaust line downstream of the turbine portion of the turbocompressor unit. arying the degree of opening of the damper, d e dπver can control the degree of inner charging and thus mcrease or reduce the braking power The damper is controlled b> a control unit to which the dπver feeds a desired value of the vehicle retardation and mto which eneine data is fed v a sensors such as tne degree vehicle retardation and into which engine data is fed via sensors such as the degree of charge and the φm. and vehicle data such as vehicle speed, accelerator position and clutch pedal position. The purpose of the present invention is in general to achieve a device of the described by way of introduction which makes it possible to e higher braking power in the engine than what could be achieved with the described device. The paπicuiar purpose is to achieve a device in which the turbocompressor unit can be utilized in a better manner together with the valve means in the exhaust line to vary the braking pow er of the engine. This is achieved according to the invention by virtue of the fact that the valve means are restrictor valve means arranged in the engine exhaust conduit upstream of the turbine portion of the turbocompressor unit. By placing the valve means closer to the exhaust outlet from the cylinders, there is a reduction in the volume of the exhaust conduit between the exhaust valves and the valve means in the exhaust conduit, which means that the pistons will not need to exhaust as much gas as previously in order to create a certain counter-pressure. High counter-pressure can therefore be obtained more rapidly In a turbocharged engine with an exhaust pressure regulator downstream of the turbine, the pressure drop required over the mrbine. so that the mrbine w ill be able to drive the compressor, cannot be obtained in brake mode. By instead placing the restrictor valve means prior to the mrbine portion and adapting the restriction area to the turbine area, the turbocompressor unit can provide supercharging even in brake mode. It is true that the pistons are imparted energy from the gas during the induc¬ tion stroke, but the work which the pistons must earn' out against the gas during the compression stroke will be so much greater that the net effect will be a higher braking power. Another advantage of circulating large volumes of gas through the engine in brake mode is that a greater amount of heat will be removed through the j gas than in installations with exhaust pressure regulators in which the heat is Dπma- πly diverted by cooling water The turbine portion in a turbocompressor unit w hich is dimensioned to operate m απve mode within the normal rpm range of the engine, w ill be too large to be able to supercharge in brake mode The device according to the invention is therefore regularly suited to be used in turbocharged engines with turbines which have ■ an- able geometr or in so-called turbocompound engines which have a turbocompres¬ sor unit with a first turbine stage, which drives the compressor portion, and a second turbine stage, which is coupled, v la a transmission, to the engine crankshaft In such turbo units, the first turbine stage is a small high-pressure turbine, hile the second turbine stage is a larger low-pressure turbine It has been lound that the corrected mass flow to the compressor turbine in brake mode is approximated equal to that for turbocompound engine mode In a conventional turbocharged engme the compres- sor mrbme is substantially larger, which means that the corrected massflows in brake mode and drive mode will approximately equal first at engine rpm:s above the normal operating rpm The invention will be described in more detail below with reference to examples shown in the accompan ing draw ings, where Figure 1 shows schematically a turbo¬ compound engine with a device according to the invention. Figure 2 a simplified schematic representation of the engine in Fig 1. Figure 3 a simplified schematic representation of a turbocharged engine with a mrbine with variable geometry and with a device according to the invention. Figure 4 a schematic representation of a turbocompound engine with a device according to the invention in a third embodi¬ ment, Figure 5 a simplified schematic representation of the engine in Fig 4, Figure 6 a longitudinal section through an exhaust restnctor valve according to the invention, and Figure 7 a longitudinal section through a combined restnctor and venting valve on the intake side In Fig 1, 1 designates a six cvhnder engine with a gearbox 2 attached thereto A turbocompressor unit, generally designated 3. has a first turbine stage 4 and a second turbine stage 5 connected to the engine exhaust manifold 6. The first turbine stage 4 is a small high-pressure stage, which drives a compressor 8 connected to the engine intake conduit 7. while the second turbine stage 5 is a larger low-pressure stage, which is coupled via a transmission 9 to the engine crankshaft 10. The trans¬ mission 9 comprises a gear 1 1 on the output shaft 12 of the mrbine stage 5. said shaft 12 driving, via a pair of gears 13.14 on an intermediate shaft 15 a gear 16 on the crankshaft 10 see Fig 2). Via a first continuously adjustable waste-gate valve 17. a larger or smaller amount of exhaust can be shunted past the high-pressure turbine 4 in order to vary the degree of charge. Via a second shunt valve 18. the exhaust can be shunted past the low-pressure turbine 5. The engine 1 has a schematically indi¬ cated compression braking device 19. which can be of the type which is shown and described in SE-466 320. and by means of which the engine cylinders during the latter portion of induction stroke, as well as during the latter portion of the compres- sion stroke, can be connected to the engine exhaust manifold to increase the engine braking power. For a more detailed description of the construction and function of a possible embodiment of the compression braking device 19. reference to made to SE-466 320. Fig 2 shows schematically a few details which are not apparent from Fig 1. viz. an air filter 20. a charged air cooler 21. an intake manifold 22. intake valves 23. cylinders 24, exhaust valves 25 and a muffler 27. Fig 3 shows an engine installation differing from that described above by virtue of the fact that the mrbocompound unit has been replaced by a mrbocompressor unit with a turbine portion 30, which has continuously variable geometry. Details corre¬ sponding to those in Fig 2 have been given the same reference numerals in Fig 3 as in Fig 2. Figs 4 and 5 show an engine installation differing from that in Figs 1 and 2 by virtue of the fact that the waste-gate valve 17 on the exhaust side has been eliminated and been replaced bv a combined restrictor and v enting valve 80 in me induction conduit 7 on the pressure side ot the compressor 8 The valve 80 is _.no n in more detail in Fig " Parts coπesponding to those in Figs 1 and 2 have been g en the same refer¬ ence numerals in Figs 4 and 5 as in Figs 1 and 2 The van e 80 has a housing 81 made in one piece with the engme induction conduit 7 with a Under 82. in w hich a piston 83 is axially displaceable The piston has a througn-bore 84 and is biased by a spring 85 towards the oσen position shown in Fig 7. in w hich air m the induction conduit can flow through the bore 84 to the engine cy linders When the degree of charge of the compressor 8 is to be reduced, pressure medium is introduced to the cy linder chamber 85 to the left ot the piston $3. and the piston is thus displaced to the right in Fig " so that the piston portion 8 " to the left of the bore 84 is displaced into the induction conduit 7 and reduces its flow-through area. At the same time, the piston portion 88 to the right of the bore 84 reveals the inlet 89 to the venting conduit 90 for releasing induction air from the induction con¬ duit w hen the valve piston is in the restriction position. A valve 80 on the induction side operates in a cleaner environment than a waste-gate valve on the exhaust side and is also sub j ected to substantially lower thermal load than the latter The valve 80 is of paπicularh simple construction by virtue ot the fact that it onK has a single moving part, l e the piston 83, which functions both as a restnctor in the induction conduit and as a valve element for the venting opening 89 The manifold 6, as is most clearly illustrated in Figs 2 and 3. is divided into two sub- manifoids 40. the output exhaust conduits 41 of which meet in a confluence before the miet to the mrbocompressor unit 3 resp 30 In each exhaust conduit 41 a restnc¬ tor valve 42 is disposed in accordance with the invention, each valve having a com¬ pletely open position and a restnctor position in which the flo -through area of the conduit 41 is reduced to create an exhaust counter-pressure in the exhaust manifold 6 dunng engme braking. Λ vah e 42. which is to function in the environment or an exhaust manifold must be able to withstand high mechanical and thermal stresses In the open position it must not present any flow obstacles or create turbulence in the evnaust conduit \ alve 42 which fulfills these conditions is shown in Fig 6. where 50 designates a _v lindπ- cai valve housing, which is preterablv cast in one piece w ith the exhaust manifold 6 The inner cylinder chamber 51 of the housing portion 50 opens into the interior of the exhaust conduit 41 The opening 52 itself is suπounded by a conical seat 53. against which there abuts a coπesponding seat 54 at an end of a sleeve 55 of stain¬ less steel. The sleeve 55 is kept in place by a cover 56 held secureh in place on the housing portion 50 by means of screws The cover 56 has a conical surface 5 " which presses against a facing conical surface at the end of the sleeve 55 The sleev e 55 has a portion 58 of reduced diameter so that a cylindrical air gap 59 is tormed w hich communicates with the suπounding air via an annular gap 66 between the housing portion 50 and the cover 56 Inside the sleeve 55 there is a valve element in the form of a hollow piston 60. As can be seen in Fig 6. there is a small play ' " S" between the exterior lateral surface of the piston 60 and the interior lateral surface of the sleeve 55 The cy lindrical portion of the piston 60 consists of a tube 60a ol hard-chromium plated stainless steel End plates 6 1 62 are fixed to the ends of the tube 60a These form valv e discs w ith conical edge portions 61a, 62a and are preferably sintered The sleeve 55 is provided at its distal end with a seat 55a. against which the edge portion 61a of the disc 61 is m sealing contact when the valve is in its open position fas is shown in Fig 4) When compressed air with a pressure on the order of 8 bar is supplied to the cy linder chamber 63 via an inlet 64. the piston 60 is displaced to the left in Fig 4 at the same time as leaking air into the gap "S" blows it free of any soot there The piston 60 is displaced perpendicular to the exhaust conduit 41 and stops with its disc 61 at a small distance from a surface 65 of the opposite wall portion of the conduit 41. when the conical edge portion 62a of the disc 62 stπkes an inner conical seat 55b of the sleeve 55 so that exhaust cannot leak into the cylinder chamber As long as there is pressure in the cylinder chamber, the piston 60 is held in its restncting position The diameter of the piston 60 and the cross-section of the conduit 41 are adapted to each other so that a restricted passage for exhaust is obtained between the inner wall of the conduit and the piston. When the piston oύ is to be returned to its starting posi¬ tion in Fig 6. the cylinder chamber 63 is drained, and the exhaust pressure, which is propagated through the gap "S " and acting against the disc edge 62a. causes the piston to be displaced into the sleeve 55. No return spring is required and the only moving part of the valve is the piston 60. and this results in high operational reli¬ ability. The compression braking device 19 is electrically operated while the valves 17. 18. 42 and 70 are operated by compressed air. They are controlled 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 compres¬ sion braking device on and off and for adjusting the valves 17. 18 and 42 depending on a number of different engine and vehicle variables fed into the control unit from sensors which are known per se and are not shown in more detail here. As is indi¬ cated in Fig I. signals are fed into the control unit 71 representing induction air pressure (charge pressure) and engine φm. i.e. engine data, and signals representing ABS on/off. vehicle speed, clutch pedal position, accelerator position, cruise control on/off and retardation level, i.e. vehicle data. The device can function in the following manner: The driver adjusts, with a hand control (not shown) the retardation to a certain level and activates the cruise control, so that a signal representing the selected retardation is fed into the control unit 71. which compares the set desired value of the retarda¬ tion with the actual value of the retardation computed via the acmal value of the speed. When the driver lets up on the accelerator, providing the clutch pedal is not depressed, the control unit 71 will set. via the control valve unit 70. the restrictor valves 42 in restrictor position, open the shunt valve 18 to bypass the second mrbine stage 5 and, depending on the difference between the acmal value and the desired value, adjust the waste-gate valve 17 to provide a suitable degree of charge in the first turbine stage 4. and activate the compression braking device 19 In the embodi¬ ment shown in Fig 3. the degree of charge is instead prov ided by vary ing the turbine geometry in the mrbine portion 30 If the selected level of retardation should be too high in view of the road surface, so that the dπv e wheels lose their gnp. the ABS system reduces the engine braking power by sending a signal to turn off the com¬ pression brake 19 and then engage it again at a lower retardation level or. alterna¬ tively, to provide the driver with the possibility of selecting a lower retardation level. Disengagement of the compression brake 19 also occurs if the driver should depress the clutch pedal, which is important to prevent killing the engine and thereby losing power steering and power brakes.

Claims: Claims I . Dev ice for controlling the engme braking effect m an internal coiτiDustion engine in a motor \ ehicle. which is equipped with a compression braking device, means for varying the degree of charge in brake mode, compπsing. firsth an exhaust-dπven turbocompressor unit with a mrbine portion and a compressor portion and. secondly. valve means disposed in the engine exhaust conduit, and means actuatable by the driver of the vehicle for activating the compression braking ice and the means for varying the degree of charge, characterized in that the valve means are restnctor alve means (42), which are arranged in the engine exhaust conduit ( 41 ) upstream of the turbine portion (4: 30) of the turbocompressor unit (3) 2. Device according to Claim 1, characterized in that the turbocompressor unit (3) is coordinated with a first shunt valve ( 17) which can be set for v arious charge pres- sure levels. 3. Device according to Claim 2. characterized in that the mrbocompressor unit (3) comprises a first mrbine stage (4), which drives the compressor portion (8) and is co¬ ordinated w ith the first shunt valve ( 17), and a second turbine stage \ 5) which is coupled, v ιa a transmission (9), to the engine crankshaft ( 10) and is coordinated with a second shunt valve ( 18), which in one position conducts the exhaust past the second mrbine stage. 4. Device according to Claim 1, characterized in that the mrbocompressor unit (3) has a mrbine portion (30) with vanable geometry. 5. Device according to Claim 1, characterized in that a combined restnctor and venting \ alve ( 80) is arranged in the engine induction conduit on the pressure side of the compressor portion. 6. Device according to one of Claims 1 - 5. characterized in that the vaive means (42) are of two-position type with a restrictor position and a completely opened posi¬ tion. 7. Device according to one of Claims 1 - 6. characterized in that the valve means (42) are arranged in the engine exhaust manifold (41 ). 8. Device according to one of Claims 1 - 7. characterized in that the vaive means (42) comprise at least one vaive. which has a cylinder (55) communicating with an exhaust conduit (41 ) and arranged peφendicuiar to the said exhaust conduit, said cylinder receiving with radial play (S) a valve element (60) in the form of a piston displaceable into the exhaust conduit under the influence of a pressure medium, said piston at its distal and proximal end surfaces having valve discs (61. 62). of which the proximal disc, in an extended position of the piston, abuts against a proximal seat (55b) in the cylinder to form a restricted exhaust passage past the the piston and of which the distal disc in a retracted position of the piston is in contact with a distal seat (55a) in the cylinder. 9. Device according to Claim 8. characterized in that the cylinder is a sleeve of stainless steel (55) which is received with play in a cylindrical space ( 59) in a valve housing (50) cast in one piece with the manifold. 10. Device according to Claim 8 or 9. characterized in that the valve piston (60) consists of a tube (60a) of hard chromium-plated stainless steel and a sintered valve disc (61. 62) with a conical edge surface (61a, 62a) fixed at either end of the tube. 1 1. Device according to one of Claims 8 - 10 in a six-cylinder engine with two exhaust manifolds for each t ree cylinders, characterized in that a restrictor valve (42) is arranged in each manifold (40).

Inventors: PERSSON PER, PERSSON, PER
Applicants: PERSSON PER, VOLVO AB, AB VOLVO, PERSSON, PER
Application year: 1996
Main classification: F02D13
IPC codes: F02B37, F02B41, F02D9, F02D13, F02D23