Abstract:
The invention relates to a multicylinder internal combustion engine ( 1 ) comprising intake valves and exhaust valves that are provided with at least one additional valve ( 10 ) for each cylinder (C 1 , C 2 , C 3 , C 4 , C 5 , C 6 ), a preferably tubular pressure container ( 9 ) with a gas chamber ( 90 ) into which extend ducts ( 11 ) originating from the valves ( 10 ) such that gas can be exchanged between individual cylinders (C 1 , C 2 , C 3 , C 4 , C 5 , C 6 ) when the valves ( 10 ) are actuated. The pressure container ( 9 ) is provided with a device ( 17 ) for cooling the quantities of gas exchanged between individual cylinders (C 1 , C 2 , C 3 , C 4 , C 5 , C 6 ). In order to increase the cooling capacity, the cooling device ( 17 ) encompasses at least one cooling pipe ( 17 ) which is axially inserted into the pressure container ( 9 ) and is penetrated by coolant. The outer jacket ( 171 ) of the cooling pipe ( 170 ) borders the gas chamber ( 90 ), the gas that is exchanged between individual cylinders (C 1 , C 2 , C 3 , C 4 , C 5 , C 6 ) flowing around said outer jacket ( 171 ).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a multicylinder internal combustion engine comprising intake valves and exhaust valves which are provided with at least one additional valve for each cylinder, a preferably tubular pressure container with a gas chamber into which extend ducts originating from the valves, so that gas can be exchanged between individual cylinders when the valves are actuated. The pressure container comprises a device for cooling the quantities of gas exchanged between individual cylinders. 
   2. The Prior Art 
   Brake systems integrated in vehicle engines, especially in utility vehicles, are gaining increasingly in importance because these systems concern additional brake systems that are cost-effective and compact. The increase in the specific output of modern utility vehicles, however, also requires an increase in the braking power to be achieved. 
   A four-stroke internal combustion engine with two groups of cylinders with four cylinders each is known from DE 34 28 626 A. Each cylinder comprises gas exchange valves and an additional exhaust valve. The additional exhaust valves are opened during the entire braking process in braking operations. Moreover, a throttle valve which is torsionally rigidly held on a shaft is arranged in the common exhaust port of the two cylinder groups. Its position can be influenced by a control rod by an actuating device. The disadvantageous aspect in this known system is the dependence on the speed, especially a relatively low braking output in the lower speed range. 
   DE 25 02 650 A further shows a valve-controlled reciprocating internal combustion engine in which compressed air is conveyed into a feed boiler via a compressed-air valve and is guided back during the starting via the same compressed-air valve for work output. 
   A decompression valve motor brake system is known in this connection from EP 0 898 059 A with which a compressed-air generator can be realized for all operating states of the internal combustion engine. A compressed-air tank of a compressed-air system is filled with compressed gas from the combustion chamber of the cylinders via a bypass line. One or more cylinders can be used for supplying the compressed-air system. 
   A motor brake system is known from EP 0 828 061 A in which a gas exchange is enabled between the individual cylinders via the common exhaust manifold. The gas exchange occurs via the exhaust valves of the six-cylinder internal combustion engine. The disadvantageous aspect in this motor brake system is, among other things, the relatively low achievable brake pressure. 
   GB 603 499 A describes a device for heat recovery from exhaust gas for internal combustion engines. A heat exchanger which is flowed through by a fluid is arranged in an exhaust manifold. 
   A multicylinder internal combustion engine of the kind mentioned above is known from AT 4.963 U1. It comprises a tubular pressure container with a pressure-control valve into which brake ports open which originate from brake valves, so that a gas exchange is enabled between the individual cylinders when the brake valves are actuated. In order to increase the braking power, the pressure container comprises a device for cooling the gas quantities exchanged between the individual cylinders, which device is integrated in the coolant circulation of the internal combustion engine. The cooling device comprises a cooling jacket which is flowed through by the coolant, which cooing jacket encloses the tubular pressure container. Although the braking power can be increased considerably by the cooling device, a further increase in the braking power would be desirable. 
   It is the object of the present invention to avoid such disadvantages and to further improve the cooling of the gas in the pressure container in an internal combustion engine. 
   SUMMARY OF THE INVENTION 
   This is achieved in accordance with the invention in such a way that the cooling device comprises at least one cooling pipe which is axially inserted into the pressure container and is penetrated by coolant, with the outside jacket of the cooling pipe being adjacent to the gas chamber and being circulated by gas exchanged between the individual cylinders. The cooling capacity and thus the braking power of the motor brake device can be increased by the cooling pipe penetrated by the coolant. A further increase of the cooling capacity is enabled in such a way that the cooling device comprises a bundle of coolant-penetrated cooling pipes which is inserted axially into the pressure container. The outsides of the cooling pipes border the gas chamber of the pressure container and are circulated by gas exchanged between the individual cylinders. 
   For the purpose of increasing the heat-dissipating surfaces it is especially advantageous when in the gas chamber of the pressure container there is arranged at least one cooling fin which is connected with a cooling pipe in a thermally conductive way. As an alternative or in addition it may be provided that at least one cooling fin which is connected in a thermally conductive manner with the cooling pipe is arranged within at least one cooling pipe. 
   It is provided for in a further embodiment of the invention that the at least one cooling fin is twisted in a screw-like manner in the direction of the longitudinal axis of the pressure container. The screw-like twisting of the cooling fin further increases the thermally conductive surface and improves the heat transmission to the coolant. The twisting further increases the swirling in the gas chamber or the coolant chamber. In comparison with a cooling jacket which encloses the tubular pressure container, a considerable increase of the cooling capacity can be effected. 
   It can further be provided for within the scope of the invention that the cooling device additionally comprises a cooling jacket penetrated by the coolant, which jacket encloses the tubular pressure container. The cooling capacity and thus the braking power can be increased in an especially high way. 
   The cooling pipe or the bundle of cooling pipes is preferably sealed on the coolant side with O-rings. On the gas side, the piston rings protect the O-rings from being directly subjected to the hot braking or exhaust gas. 
   In order to secure the cooling pipes against oscillations it is provided that the cooling pipe is connected with at least one fixing device (preferably formed by a screw) with the pressure container. The fixing device is preferably arranged in the region of half the length of the cooling pipe. As a result of the central arrangement of the fixing device, thermal expansions of the cooling pipe are divided to both sides of the fixing device. 
   In the case of a bundle of cooling pipes it is advantageous when several cooling pipes are joined with a flange and this entire pipe package is axially inserted into the pressure container. The inserted cooling pipe or the inserted bundle of cooling pipes is only included in the cooling circulation at the ends. 
   In order to keep production costs as low as possible it is advantageous when the cooling pipe is an extruded profile. It can be provided for alternatively that the cooling pipe is a hydroformed thin-walled sheet metal pipe. It is further possible that the cooling fins are soldered onto the cooling pipes. 
   The cooling fins can be provided integrally with the heat pipe or in several parts. 
   The invention is explained below in closer detail by reference to the enclosed drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic illustration of an internal combustion engine in accordance with the invention; 
       FIG. 2  shows a pressure container of the internal combustion engine in a first embodiment in a side view; 
       FIG. 3  shows the pressure container in a top view; 
       FIG. 4  shows the pressure container in a front view; 
       FIG. 5  shows the pressure container in a sectional view according to line V-V in  FIG. 3 ; 
       FIG. 6  shows the pressure container in a sectional view according to line VI-VI in  FIG. 3 ; 
       FIG. 7  shows the pressure container in a sectional view according to line VII-VII in  FIG. 3 ; 
       FIG. 8  shows the pressure container in a sectional view according to line VIII-VIII in  FIG. 3 ; 
       FIG. 9  shows the pressure container in a sectional view according to line IX-IX in  FIG. 3 ; 
       FIG. 10  shows the pressure container in a sectional view according to line X-X in  FIG. 4 ; 
       FIG. 11  shows the pressure container in a sectional view according to line XI-XI of  FIG. 4 ; 
       FIG. 12  shows a pressure container in a second embodiment in a side view, and 
       FIG. 13  shows said pressure container in a sectional view along line XIII-XIII in  FIG. 12 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention is explained in detail by reference to  FIG. 1  based on the example of a six-cylinder turbocharger engine. Notice must be taken that the function of the engine brake device in accordance with the invention is independent both of the number of cylinders as well as the charging system and can also be used in an aspirating engine. 
   The six cylinders C 1  to C 6  of internal combustion engine  1  are in connection with an intake manifold  2  via intake ports (not shown in closer detail), which intake manifold is supplied with charge air starting from the air filter  3  via the compressor part C of the turbocharger  4  and via the charge air cooler  5 . The exhaust valves of the internal combustion engine  1  open into the exhaust system  6 , with the exhaust gases being guided in a conventional manner via the turbine part T of the turbocharger  4  and exit via a muffler  7 . 
   The engine brake device comprises a tubular pressure container  9  (brake rail). Ports  11  originating from the valve  10  lead to said pressure container, so that a gas exchange is enabled between the individual cylinders C 1  to C 6  at a relatively high pressure level. In braking operations of the internal combustion engine  1 , the valves  10  are actuated several times per working cycle of the engine, e.g. two braking strokes per working cycle, with the first braking stroke occurring close to the upper dead center of the high-pressure stroke. During this braking stroke, highly compressed air exits from one of the cylinders C 1 , C 2 , C 3 , C 4 , C 5  or C 6  into the brake rail  6 . As a result, the brake rail  6  is filled with compressed air on the one hand (up to approx. 20 bars of working pressure), and the expansion work of the cylinder is reduced on the other hand, thus leading to braking power. Shortly after the closure of the intake valve, the valve  10  opens again, as a result of which compressed air flows from the brake rail  9  into the combustion chamber. As a result of the second braking stroke, the cylinder pressure rises at the beginning of the compression phase of the high-pressure cycle to the pressure level of the brake rail  9 . This increases the compression work to be applied and thus the braking power of the engine. 
   A pressure control valve  12  which is controlled electronically for example limits the maximum pressure in the brake rail  9  in order to prevent any damage to the engine. This control valve  12  further allows the driver to reduce the pressure in the brake rail  9  by means of a brake switch  14  in the driver&#39;s cabin for example, such that the compressed air is bled from the brake rail  9  via the connecting line  13  to the exhaust system and thus the braking power can be adjusted to the respective driving situation. 
   An exhaust gas vane  15  is shown as an alternative with the broken line. It can be combined with the brake device in accordance with the invention. 
   The pressure container  9  advantageously comprises a cooling device  17  integrated in the coolant circulation  16 ,  16 ′ of the internal combustion engine for cooling the gas quantities exchanged between the individual cylinders C 1  to C 6 . As indicated with arrow  16 , the coolant reaches the cooling device  17  via a coolant connection  19  at one end of the pressure container and is recycled back to the coolant circulation again via a further connection  19 ′ on the cooling device  17  at the other end of the pressure container  9  (see arrow  16 ′). As an alternative to a single coolant circulation  19 , one coolant connection  19   a  can be provided per cylinder for supplying the coolant. The motor brake device can also be used in engine operation as an exhaust gas recirculation system. The cooling device  17  is used in this case as a cooler for the recirculated exhaust gas. 
   The pressure container  9  with the cooling device  17  which is shown only in a schematic way in  FIG. 1  is shown in detail in  FIGS. 2  to  FIG. 11 . The cooling device  17  comprises a cooling pipe  170  which is inserted from a face side axially into the tubular pressure container  9 . The outside diameter d of the cooling pipe  170  is substantially smaller than the inside diameter D of the pressure container  9 , so that an annular pressure chamber  90  is formed between the cooling pipe  170  and the pressure container  9 . The cooling pipe  170  is penetrated by coolant between the coolant connections  19 ,  19 ′ and is penetrated by braking or exhaust gas in the pressure chamber  90 . The pressure chamber  90  is connected via port connections  20  with the ports  11  originating from the cylinders C 1 , C 2 , C 3 , C 4 , C 5 , C 6 . The connection  27  on the output side leads to the connecting line  13  with the exhaust gas system  6 . 
   In order to increase the heat transmission between the pressure chamber  90  and the cooling pipe  170 , the cooling pipe  170  comprises cooling fins  172  on its outside jacket  171 , which fins are twisted in a screw-like manner, increase the surface touched by the hot gas and also increase the turbulence. Cooling fins can also be arranged on the coolant side within the cooling pipe  170  as a alternative to this or in addition to the same. 
   The cooling pipe  170  is held by flanges  175 ,  176  in the pressure container  9  in a longitudinally displaceable manner in the region of the two ends  173 ,  174 , so that thermal expansions can be compensated. The cooling pipe  170  is sealed on the coolant side by O-ring seals  177 . On the gas side, piston rings  178  protect the O-ring seals from direct contact with the hot braking or exhaust gases. In the region of half the length of the cooling pipe  170 , the same is connected with the pressure container  9  by a fixing device  179  formed by a screw. It is thus secured against oscillations. Thermal expansions of the cooling pipe  170  are divided to both sides. 
   Instead of a single cooling pipe  170  it is also possible to insert an entire package of cooling pipes into the pressure container  9 . Several cooling pipes are joined with the end flanges and this entire pipe package is inserted into the pressure container  9 . 
   The cooling device  17  can further comprise an outside cooling jacket  18  which is connected with the cooling pipe  170  in the region of the ends  173 ,  174 . 
   As is indicated by the arrows  16 ,  16 ′, the coolant reaches the cooling device  17  via the coolant connection  19 , flows through the cooling pipe  170  and the outside cooling jacket  18  and leaves the cooling device  17  via the coolant connection  19 ′. As an alternative to this, a coolant transfer  19   a  to the outside cooling jacket  18  can be provided for each cylinder, through which the coolant reaches the cooling jacket  18 . The inserted cooling pipe  170  is only included in the cooling circulation at the ends  173 ,  174 . 
   Moreover, the cooling device  17  may comprise a thermostatically controlled coolant control element  26  ( FIG. 1 ) which is preferably arranged in the coolant circulation of the internal combustion engine. It is also possible to provide a separate coolant circulation for the brake rail  9  (e.g. as a bypass to the coolant circulation) and to arrange a coolant control element there. 
     FIGS. 12 and 13  show an embodiment of a pressure container with a bundle  180  of cooling pipes  170 . The cooling pipes  170  are fixed parallel with respect to each other in flanges  175 ,  176  and are arranged in a longitudinally displaceable way in the pressure container  9  with these flanges  175 ,  176 . The outside jackets  171  can be provided with a smooth configuration or comprise cooling fins  172  for enlarging the surface touched by the hot gas. 
   Since the engine brake system in accordance with the invention works independent of any conventional intake and exhaust systems of the engine, the function of the engine brake is independent of the respective charging system (aspirating engine/conventional turbocharger/VTG). The engine output in fuelled operation is advantageously not reduced.