Abstract:
A drive for a vehicle includes an internal combustion engine having a combustion chamber delimited by a cylinder and a piston, a compressed gas storage connectable with the combustion chamber for storing a gas compressed in the combustion chamber, a separate expansion machine for expanding compressed gas from the combustion chamber or from the compressed gas storage by performing mechanical work, and devices for supplying gas from the expansion machine into the combustion chamber or into an intake passage of the internal combustion engine. The drive may, alternatively or in addition, also include devices for heating the compressed gas from the combustion chamber or from the compressed gas storage before the compressed gas enters into the expansion machine.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application, Serial No. 10 2010 056 238.6, filed Dec. 24, 2010, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a drive for a vehicle, in particular a motor vehicle, with an internal combustion engine and to a method for operating a drive for a vehicle, in particular a drive for a motor vehicle, with an internal combustion engine. 
     The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
     A hybrid engine for a motor vehicle with a compressed air energy store, wherein air is compressed in the combustion chambers of the internal combustion engine when the motor vehicle brakes and this compressed air is temporarily stored in a compressed air energy store, is known in the art. The compressed air can again be supplied from the compressed air energy store into the combustion chambers of the internal combustion engine as needed, for example when the internal combustion engine is started. In conjunction with the compressed air, a larger quantity of the fuel can also be supplied into the cylinders for boosting the internal combustion engine during compression. 
     It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved drive for a vehicle with an internal combustion engine and an improved method for operating a drive for a vehicle with an internal combustion engine, in particular a drive for a motor vehicle such that the energy contained in the compressed gas can be optimally utilized. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the concept to utilize the residual energy and/or the residual pressure of the gas, which passes through the expansion machine but is not completely expanded, for improving the charging of the internal combustion engine in certain operating states. Whereas in a conventional open system the gas is discharged into the environment after passing through the expansion machine, it can be supplied to a further use by employing the feature combinations according to the invention. 
     According to one aspect of the present invention, a drive for a vehicle includes an internal combustion engine having at least one combustion chamber delimited by a cylinder and a piston, at least one compressed gas store connectable with the at least one combustion chamber for storing a gas storage compressed in the at least one combustion chamber, a separate expansion machine for expanding compressed gas storage from the at least one combustion chamber or from the compressed gas store by performing mechanical work, and devices for supplying gas from the expansion machine into the at least one combustion chamber or into an intake passage of the internal combustion engine. 
     According to another aspect of the invention, a drive for a vehicle includes an internal combustion engine having at least one combustion chamber delimited by a cylinder and a piston, at least one compressed gas store connectable with the at least one combustion chamber for storing a gas compressed in the at least one combustion chamber, a separate expansion machine for expanding compressed gas from the at least one combustion chamber or from the compressed gas store by performing mechanical work, and devices for heating the compressed gas from the at least one combustion chamber or from the compressed gas store before the compressed gas enters into the expansion machine. 
     According to yet another aspect of the invention, a method for operating a drive for a vehicle, in particular a motor vehicle, with an internal combustion engine, a compressed gas store storage connectable with at least one combustion chamber of the internal combustion engine, and a separate expansion machine, includes the steps of expanding a gas compressed in the at least one combustion chamber in the expansion machine by performing work, and supplying at least a portion of the gas from the expansion machine into the at least one combustion chamber or into an intake passage of the internal combustion engine. 
     According to still another aspect of the invention, a method for operating a drive for a vehicle, in particular a motor vehicle, with an internal combustion engine, a compressed gas storage connectable with at least one combustion chamber of the internal combustion engine, and a separate expansion machine, includes the steps of expanding a gas compressed in the at least one combustion chamber in the expansion machine by performing work, and heating the compressed gas from the at least one combustion chamber or from the compressed gas storage before the compressed gas enters into the expansion machine. 
     According to an advantageous feature of the present invention, the internal combustion engine may have several cylinders or combustion chambers into which the gas from the expansion machine is alternatingly supplied. 
     According to an advantageous feature of the present invention, the devices for heating the compressed gas may be embodied as a heat exchanger, for example an exhaust gas heat exchanger, in which the compressed gas is further heated through heat transfer from the exhaust of the internal combustion engine beyond the heating that occurs during compression. In this way, on one hand, the energy content of the compressed gas and hence the amount of energy recoverable in the expansion machine is increased and, on the other hand, at least a portion of the energy contained in the exhaust gas of the internal combustion engine is supplied to a beneficial use. 
     According to another advantageous feature of the present invention, the expansion machine may be a single-stage expansion machine with a single pressure stage, but may also have several consecutive pressure stages. According to an advantageous feature of the present invention, the expansion machine may include at least one turbine because a turbine requires a relatively small installation space and is also capable of converting the energy stored in the compressed gas directly into a rotary motion. 
     According to yet another advantageous feature of the present invention, the expansion machine may be coupled with a generator for generating electrical energy, because a rotor of the generator can thus be powered by the rotation of a turbine wheel of the turbine while experiencing only a small energy loss. 
     According to an advantageous feature of the present invention, the generator may be controlled by a control device, which may simultaneously also control the supply of the gases which exit from the expansion machine and are supplied into the combustion chambers and/or the intake passage of the internal combustion engine. In this way, the electrical power supplied by the generator can be increased and, if not needed by the onboard network of the vehicle, stored in a vehicle battery if no additional compressed gas or only a small quantity of compressed gas is required for charging the internal combustion engine. Conversely, the electrical power supplied by the generator can be reduced when, for example, a higher charge pressure should be provided in certain operating states of the internal combustion engine, for example in the lower RPM range for overcoming the so-called turbo lag or in transient operation of the internal combustion engine, which would typically require a greater quantity of compressed gas to be supplied into the combustion chambers or into the intake passage from the compressed gas storage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
         FIG. 1  is a schematic diagram of a drive according to the invention for a motor vehicle, wherein a completely or partially expanded gas from a separate expansion machine is supplied into an intake passage of an internal combustion engine downstream of a compressor of the exhaust gas turbocharger; 
         FIG. 2  is a diagram similar to  FIG. 1 , wherein however the gas from the expansion machine is supplied into the intake passage upstream of the compressor of the exhaust gas turbocharger; 
         FIG. 3  is a diagram similar to  FIGS. 1 and 2 , wherein however the gas from the expansion machine is supplied into the intake passage downstream of an air filter; 
         FIG. 4  is a diagram similar to  FIG. 1 , wherein however the gas from the expansion machine is directly supplied into the combustion chambers of the internal combustion engine; 
         FIG. 5  is a schematic diagram of another drive according to the invention for a motor vehicle; 
         FIG. 6  is a diagram similar to  FIG. 5 , wherein however compressed gas can be supplied from the combustion chambers of the internal combustion engine directly into the expansion machine; and 
         FIG. 7  is a diagram similar to  FIG. 6 , wherein however the compressed gas from the combustion chambers of the internal combustion engine can be heated again before being supplied into the expansion machine. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
     Turning now to the drawing, and in particular to  FIG. 1 , there is shown in form of a schematic diagram a drive  1  for a motor vehicle which includes an internal combustion engine  2  with an exhaust gas turbocharger  3 . For sake of simplification, only three cylinders  4  of the internal combustion engine  2  are shown, wherein each cylinder delimits in the conventional manner together with a cylinder head and a piston (not shown) a combustion chamber into which a fuel can be supplied. Above each cylinder, the cylinder head has two intake ports  5 ,  6  provided with intake valves and three exhaust ports  7 ,  8 ,  9  provided with exhaust valves. The intake ports  5  and  6  of each cylinder  4  are connected with an intake passage  10  of the internal combustion engine  2 , which includes an air filter  11 , a compressor  12  of the exhaust gas turbocharger  3  and a charge air cooler  13 . The exhaust ports  7  and  8  of each cylinder  4  are connected with an exhaust gas passage  14  of the internal combustion engine  2  which includes a turbine  15  of the exhaust gas turbocharger  3 . The exhaust port  9  of each cylinder  4  is not connected with the exhaust gas passage  14 , but instead with a storage vessel  17  of compressed gas storage  18  by way of a manifold  16 . The exhaust ports  9  of the cylinders  4  and the manifold  16  are used to supply in a braking or overrun phase of the internal combustion engine  2  compressed, gas which is supplied into the cylinders  4  while the fuel supply is interrupted and compressed in the cylinders  4  during the compression, from the cylinders  4  while the fuel supply is interrupted and compressed in the cylinders  4  during the compression, from the cylinders  4  into the compressed gas storage  18  for temporary storage, wherein the stored compressed gas can be withdrawn again as needed. 
     The compressed gas from each cylinder  4  is always supplied into the compressed gas storage  18  during a compression stroke by opening the exhaust valve in the exhaust port  9  of the cylinder  4  in the vicinity of the top dead center of the piston. The opening times of the exhaust valves of the exhaust ports  9  are controlled by an engine controller  19  of the internal combustion engine  2 . Possible approaches for controlling the exhaust valves of the exhaust ports are described in the aforementioned publications and will therefore not be discussed here in detail. 
     Because compressed gas is withdrawn from a cylinder  4 , a greater drag work is performed in the cylinder  4  during the expansion stroke of the cylinder  4  following the compression stroke due to the deficiency in air mass and the reduced pressure level. The internal combustion engine  2  then operates as a cooling machine while in the braking or overrun phase compressed gas is supplied from the cylinders  4  into the compressed gas store storage  18  where it is temporarily stored. This in turn causes an increased braking action of the internal combustion engine  2  operating as an engine brake. 
     To maximize the quantity of the compressed gas stored in the storage vessel  17  commensurate with a maximum compressive strength defined in the design of the compressed gas storage  18 , the manifold  16  arranged upstream of the compressed gas storage  18  includes a heat exchanger for cooling the compressed gas, which is preferably the charge air cooler  13 . 
     If the internal combustion engine  2  includes an (unillustrated) exhaust gas return, then exhaust gases or an exhaust gas/air mixture may be compressed in the cylinders  4  instead of the compressed gas and supplied into the compressed gas storage  18 . 
     The compressed gas temporarily stored in the compressed gas storage  18  can be used with the drive  1  according to the invention for two different purposes: on one hand, the compressed gas may be completely or partially expanded by performing mechanical work. On the other hand, the compressed gas may be supplied in a partially expanded state as charge air into the intake passage  10  of the internal combustion engine  2 , for example for briefly increasing the charge pressure in transient operating states. 
     For the first purpose mentioned above, an outlet  20  of the compressed gas storage  18  is connected via a valve  21  with adjustable flow cross-section to an inlet  22  of an expansion machine  23 , wherein for the last-mentioned purpose the outlet  24  of the expansion machine  23  is connected with the intake passage  10 . The expansion machine  23  is formed by a turbine  34  having a turbine wheel which is set in rotation by the compressed gas exiting the compressed gas storage  18  when the valve  21  is open. The shaft of the turbine wheel is coupled with the rotor of a generator  25 , so that the generated  25  can generate electrical energy and supply the generated electrical energy to a vehicle battery  26  and/or the (unillustrated) onboard network of the motor vehicle, when the gas from the compressed gas storage  18  flows through the expansion machine  23 . 
     The controllable valve  21  arranged downstream of the outlet  20  of the compressed gas storage  18  and the generator  25  are controlled by the engine controller  19  of the internal combustion engine  2 , namely on one hand depending on the desired quantity and the desired pressure of the compressed gas to be supplied into the intake passage  10  and, on the other hand, depending on the quantity of the electrical energy to be generated by the generator. For example, the valve  21  can be wide open and the turbine  34  and the generator  25  can be operated in idle when a large quantity of compressed air at high pressure is to be supplied into the intake passage  10 . To reduce the quantity of the air supplied into the intake passage  10 , the flow cross-section of the valve  21  can be reduced. To reduce both the pressure and the quantity of the air supplied into the intake passage  10 , the load of the generated  25  and thus the flow resistance of the turbine can be increased, whereby the fraction of the compressed air energy converted into electrical energy in the generator  25  increases. When the flow cross-section of the valve  21  is increased, the pressure of the air supplied into the intake passage  10  can be reduced without reducing the quantity of air. If only electrical energy is to be produced, then the pressure can be reduced essentially down to atmospheric pressure through a commensurate increase of the load. The energy content of the stored compressed air can thereby be optimally used for both purposes. 
     Optionally, a bypass line (not shown) may be disposed between the inlet  22  and the outlet  24  of the expansion machine  23 , through which the compressed gas can be supplied from the compressed gas storage into the intake passage  10 , bypassing the expansion machine  23 , for eliminating a loss of efficiency when electrical energy is not demanded from the onboard network or for charging the vehicle battery  26 . 
     The drive  1  in  FIG. 2  differs from the drive  1  in  FIG. 1  in that the expanded compressed pas exiting from the expansion machine  23  is supplied into the intake passage  10  upstream of the compressor  12  of the exhaust gases turbocharger  3 , whereas the compressed gas from the expansion machine  23  in the drive of  FIG. 3  is supplied into the intake passage  10  downstream of the air filter  11 . 
     Conversely, with the drive of  FIG. 4 , expanded compressed gas the from the expansion machine  23  is supplied directly into the combustion chambers of the internal combustion engine  2  without being detoured via the intake passage  10 . For this purpose, the manifold  16  is provided with a three-way valve  27  which is connected via a line  28  with the outlet  24  of the expansion machine  23 , so that the compressed gas after flowing through the expansion machine  23 , can be conveyed into the combustion chambers through the manifold  16  and the exhaust ports  9 . 
     The compressed gas directly supplied from the compressed gas storage  18  into the combustion chambers can be used to a start the internal combustion engine  2  without a starter in a direct start mode with the help of the compressed air or to implement a pure compressed air operation of the internal combustion engine  2  without supplying fuel into the combustion chambers. In both situations, the compressed air is supplied into the combustion chambers under high pressure from the compressed gas storage  18  preferably without significant expansion in the expansion machine  23  or through the bypass line disposed between the inlet  22  and the outlet  24  of the expansion machine  23 , whereby the supply is controlled with the engine controller  19  by opening and closing the exhaust valves in the exhaust ports  9 . The direct supply of the compressed gas into the combustion chambers can also be used to accelerate the motor vehicle by not only supplying compressed air into the combustion chambers when operating the internal combustion engine  2  as a motor, but by simultaneously increasing also the quantity of the fuel supplied into the combustion chambers, in order to increase the drive power of the internal combustion engine  2  through “boosting.” 
     The drive  1  in  FIG. 5  differs from the afore described drives  1  in that, on one hand, a two-stage compressed gas storage  18  with two storage vessels  29 ,  30  is provided instead of a single-stage compressed gas storage  18 . Both storage vessels  29 ,  30  are connected to the manifold  16  via corresponding separate supply lines equipped with controllable shutoff valves  31 ,  32 , so that a higher pressure can be applied to one of the two storage vessels  29 ,  30  through suitable control of the shutoff valves  31 ,  32  and the exhaust valves in the exhaust ports  9 , whereas a lower pressure is applied to the second storage vessel. The two storage vessels  29 ,  30  are connected to the expansion machine  23  by a single line  33  having a controllable valve  21 , wherein the expansion machine  23  in the drive of  FIG. 5  is constructed as a two-stage expansion machine  23  with two turbines connected in series. 
     In the drive of  FIG. 6 , the manifold  16  may be selectively connected via a three-way valve  35  either with the compressed gas storage  18  or directly with the inlet  22  of the expansion machine  23  for applying compressed air from the combustion chambers of the cylinders  4  through the exhaust ports  9  and the manifold  16  to the expansion machine  23  directly, i.e., without temporary storage in the compressed gas storage  18 , for generating electrical energy. The two storage vessels  29 ,  30  of the compressed gas storage  18  are here furthermore connected to the expansion machine  23  via two separate lines  36 ,  37  equipped with controllable valves  21 , so that compressed gas under higher pressure or under lower pressure can be selectively applied to the expansion machine  23 , depending on the demand for electrical energy from the onboard network or for charging the vehicle battery  26 . 
     With the drive in  FIG. 7 , the manifold  16  can also be selectively connected via a three-way valve  35  with the compressed gas storage  18  or directly with the expansion machine  23 , wherein however additionally an exhaust gases heat exchanger  38 , through which exhaust gases and compressed air flows, is arranged between the three-way valve  35  and the expansion machine  23  for increasing the temperature of the compressed gas before supplying the compressed gas into the expansion machine  23 , thereby significantly increasing the performance of the expansion machine  23 . A portion of the otherwise unusable exhaust gas energy of the internal combustion engine  2  can then be used in an open process cycle. This approach has a significant advantage over a closed steam process cycle because the compressed gas heated in the exhaust gases heat exchanger  38  can be used as combustion air for the combustion in the internal combustion engine  2  after expansion in the expansion machine  23 . In contrast to a closed steam process cycle, no condenser is required, which not only reduces the number of components, but also the installation space. 
     An exhaust gases heat exchanger (not illustrated) through which exhaust gases and compressed gas flow can also be arranged between the compressed gas storage  18  and the expansion machine  23  for increasing the temperature of the compressed air gas from the compressed gas storage  18  before the compressed air is supplied into the expansion machine  23 , which also increases the performance of the expansion machine  23 . 
     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.