Abstract:
A gas compressor for vehicle braking systems controlled by compressed air can be operated under load or in idle operation. In idle operation, no compressed air is produced. In operation under load, the gas compressor produces compressed air as required by the pressure medium installation. During prolonged operation of the gas compressor at a relatively high operating speed, for example, during travel on super-highways, the power consumption can be decreased and thereby also the production amount of the gas compressor, without having to switch the gas compressor over into idle operation. A clearance volume of less volume than the nominal volume of the gas compressor is provided which can be connected via a valve to the compression chamber of the gas compressor, thereby making it possible to enlarge the compression volume. In addition, a process for the control of the auxiliary valve takes into account different operating magnitudes of the gas compressor and other elements of the vehicle.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a gas compressor which can be switched between operation under load and operation in idle, and more particularly, a gas compressor of the type in which a suction chamber can be connected via at least one suction valve to a compression chamber and an outlet chamber can be connected via at least one outlet valve to the compression chamber. 
     A gas compressor of this type is disclosed, for example, in German patent DE 43 21 013 (U.S. Pat. No. 5,503,537), incorporated herein by reference. 
     Gas compressors of known construction generally include a compression chamber in which a movable compression element, i.e. a striking piston, alternately draws in the gas to be compressed and then compresses it. In order to achieve efficient performance in the output of compressed gas, the best utilization of the volume of the compression chamber is generally desirable. For this reason, it is general practice to keep the volume of the compression chamber remaining in the compression phase and which cannot be utilized, which is also referred to as the “dead space,” to a minimum. 
     When a gas compressor which is optimized in this manner is operated under load, a sufficient amount of compressed gas may be produced by the gas compressor even at relatively low rotational speeds. However, when the gas compressor is operated at a variable operating speed, for example, when connected to the drive engine of a vehicle, the output quantity may be undesirably great during extended operation at high rotational drive speeds, for example, when traveling on a super-highway. In such instances, the gas compressor has a relatively high power consumption, which results, among other things, in an undesirable heating of both the gas compressor itself and the compressed gas produced thereby. To overcome this situation, it is often not practical to switch the gas compressor to idle operation, because compressed gas is no longer produced in this operating mode. 
     It is therefore the object of the present invention to make it possible to reduce the power consumption occurring under certain operating conditions in a gas compressor under load operated at variable operating speed, and thereby also to reduce the temperatures that are produced in this manner. 
     SUMMARY OF THE INVENTION 
     In accordance with these and other objects of the invention, there is provided a gas compressor switchable between operation under load and operation in idle. The gas compressor includes a compression chamber, a suction chamber, an outlet chamber. At least one suction valve is provided, via which the suction chamber can be selectively connected to the compression chamber. In addition, at least one outlet valve is also provided, via which the outlet chamber can be selectively connected to the compression chamber. The gas compressor in accordance with the invention includes an auxiliary clearance volume and at least one auxiliary valve via which the auxiliary clearance volume can be connected to the compression chamber. The auxiliary valve is actuatable in response to an actuating signal which is derived from at least one of the operating magnitudes of the gas compressor occurring in operation under load or from a device connected to the gas compressor. 
     The invention provides the advantage of permitting the power consumption to be adapted to the current need for compressed gas in a gas compressor of any design, independently of the applicable operating principle applied, with the exception of dynamic type compressors. In addition, a rise in temperature of the gas compressor and the compressed gas due to dissipated energy can thus be avoided. The invention provides further advantage by reducing the occurrence of pressure surges and pulsation noises. By virtue of reduced vibration, the service life of the compressor is effectively extended. 
     It is yet another advantage of the invention that the actuating signal for actuating the auxiliary valve, which serves to connect the compression chamber to the auxiliary clearance volume, can be derived from a plurality of different operating magnitudes of the gas compressor, or from a device associated therewith, for example, a pressure medium installation supplied by the gas compressor which is connected to the gas compressor. In a preferred manner, a link between different operating magnitudes or operating states can also be effected thereby. 
     In an advantageous embodiment of the invention, the auxiliary valve is provided in the form of an elastic, deformable part of a seal installed in the gas compressor. The auxiliary valve can thus be produced with particular ease and economy. Furthermore, no additional labor is required for the assembly of the auxiliary valve. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a cross-sectional view of a gas compressor of piston-type design; 
     FIG. 2 is a detailed view of the gas compressor of FIG. 1; and 
     FIG. 3 is a schematic view of an embodiment of a pressure medium supply for a vehicle with a gas compressor according to FIG. 1, in which pressure medium lines are depicted as continuous lines and electrical lines are depicted as broken lines. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the figures, and in particular FIG. 1, a gas compressor of piston design is depicted in cross-section, generally designated by the reference numeral  1 . Gas compressor  1  includes a cylinder  20  and a piston  4  movable within the cylinder  20 . Movement of the piston  4  is effected by a rotatable drive shaft (not shown) via a connecting-rod drive (also not shown). A cylinder head comprising an upper part  3  and a lower part  2  is attached to the cylinder  20 . A seal  9  is provided between the cylinder head  2 ,  3  and the cylinder  20  to maintain air-tightness. An additional seal  23  is located between the upper part  3  and the lower part  2  of the cylinder head. 
     A suction chamber  5 , which can be connected directly via a suction connection  16 , or via a conduit, to the surrounding atmosphere or to a turbo-supercharger of a combustion engine, is located in the cylinder head  2 ,  3 . In this application, the gas used is air. The suction chamber  5  can be connected to a compression chamber  7  via a suction valve  10 , provided, as shown, in the form of a bending elastic check valve of lamellar design. The boundary of the compression chamber  7  is defined by the cylinder  20 , the piston  4 , and the cylinder head  2 ,  3  or the seal  9 . The volume of the compression chamber  7  can be changed by movement of the piston  4 , i.e. from a nominal volume which occurs when the piston  4  is at its lower dead center, and a design-based clearance volume which occurs when the piston  4  is at its upper dead center. 
     The compression chamber  7  can be connected via an outlet valve  18  to an outlet chamber  6  located in the cylinder head  2 ,  3 . The outlet chamber  6  can, in turn, be connected to a pressure medium installation of, for example, a vehicle, via a pressure medium line (not shown) connected to an outlet connection  17 . 
     The compression chamber  7  can furthermore be connected via an auxiliary valve  15  to an auxiliary clearance volume  12 . In accordance with an advantageous embodiment of the invention, the auxiliary valve is provided in the form of a bendable elastic part of the seal  9 . An auxiliary piston  13  with a piston rod  14 , acting mechanically upon the auxiliary valve  15 , is provided for actuation of the auxiliary valve  15 . The auxiliary piston  13  moves in a longitudinal direction within a piston guide  21 . The auxiliary piston  13  can be placed under pressure via a control connection  19 , and can thus actuate the auxiliary valve  15 , so that a connection is established between the compression chamber  7  and the auxiliary clearance volume  12 . When the auxiliary piston  13  is not subjected to pressure, it is moved back into its starting position by means of a spring  24  which biases the auxiliary piston with the additional assistance of the above-mentioned bending elastic effect of the auxiliary valve  15 , which is in the form of part of the seal  9 . This movement is restricted by a stop  26  located on the side of the auxiliary piston  13  away from the piston rod  14 . 
     Turning now to FIG. 2, a detailed view of the gas compressor  1  is depicted in an enlarged scale, highlighting, in particular, the action of the auxiliary valve  15 . In both Figs. 1 and 2, the auxiliary valve  15  is shown in an open state, having been actuated as a result of the auxiliary piston  13  being subjected to pressure. When the pressure on the auxiliary piston  13  is relieved, the auxiliary piston is moved back into its starting position in the direction of the stop  26  by the biasing force of the spring  24 , with the assistance of the bending elastic nature of the auxiliary valve  1 S. At the same time, the auxiliary valve  15  closes, due to its bending elastic nature. 
     In addition, the compression chamber  7  can be connected via an additional valve  11  to an additional chamber  8 , which surrounds the suction chamber  5  in the depicted example of FIG.  1 . The auxiliary clearance volume  12  is integrated by design into the additional chamber  8 , but is separated in a pressure-fast manner from the additional chamber  8  by a wall. The additional valve  11  can be moved by means of a horizontal switching piston (not shown) from the closed position shown in FIG. 1, into an open position. This switching piston can be subjected to pressure via another control connection (not shown in FIG.  1 ). The switching piston thus opens the additional valve  11  when subjected to pressure. The functioning of the additional valve  11  and the switching piston are described in detail, for example, in German patent DE 39 04 172 A1, which is incorporated herein by reference. 
     A temperature sensor  60  is provided in the upper part  3  of the cylinder head in proximity to the outlet chamber  6 . A measuring tip of the temperature sensor  60  extends into the outlet chamber  6  for the purpose of determining the temperature of the compressed air therein, and the temperature sensor  60  emits an electrical signal. In accordance with an advantageous embodiment of the invention, described in further detail below, the actuation of the auxiliary valve  15  is controlled by means of this signal. 
     The gas compressor described above operates in the following manner under load. For purposes of description, it is assumed that the piston  4  is initially at its upper dead center, whereby the compression chamber  7  exhibits its smallest volume. By drive the gas compressor via the drive shaft, as well as the connecting-rod drive, the piston  4  is moved in the direction of its lower dead center, which, at first results in creation of a negative pressure in the compression chamber  7 , i.e. a pressure difference is formed between the compression chamber  7  and the suction chamber  5 . This pressure difference causes the bending elastic suction valve  10  to open, thereby initiating air flow from the suction chamber  5  into the compression chamber  7 . Upon reaching the lower dead center, the piston  4  moves in the opposite direction, until it reaches its upper dead center. At the same time, the air accumulated thus far in the compression chamber  7  is compressed, thereby creating a higher pressure in the compression chamber  7  than in the suction chamber  5 . This causes the suction valve  10  to close. The pressure increases in the compression chamber  7 , ultimately reaching and exceeding the pressure in the outlet chamber  6 , which, until then, has held the outlet valve  18  in a closed state. As the pressure in the outlet chamber  6  is exceeded, the outlet valve  18  opens as a result of the pressure in the compression chamber  7 , and compressed air flows from the compression chamber  7  into the outlet chamber  6 . 
     The above-described process is repeated several times until sufficient pressure, also referred to as “nominal pressure,” prevails in the pressure medium installation connected to the gas compressor  1 . When the nominal pressure is reached, the gas compressor, which was running until then under load, is switched to idle run. 
     To set the operating mode of the gas compressor at a given time, a distinction is made in automotive technology between “pressure regulator control” and “governor control.” If pressure regulator control is applied, in idle the outlet connection  17  is connected to a relief space which is free of over-pressure, i.e. the atmosphere. If governor control is applied in idle, the compression chamber  7  is customarily connected to the suction chamber  5 , for example, by holding the suction valve  10  in an open state by means of a pressure-medium-actuated switching piston. 
     In accordance with the particular embodiment of a governor control used in the present example, the compressed-air production of the gas compressor is suppressed in idle operation by a considerable enlargement of the effective clearance volume of the gas compressor, such that even during a compression stroke, no pressure exceeding the pressure in the outlet chamber  6  can be produced in the compression chamber  7 . In order to switch over to idle and concomitantly reduce the power consumption of the gas compressor  1 , the additional valve  11  is therefore actuated, connecting the compression chamber  7  to the additional chamber  8 . The effective clearance volume is thereby enlarged to a considerable degree, i.e. by the size of the additional chamber  8 . The additional chamber  8  advantageously has a volume of approximately 10 percent to 100 percent of the nominal volume of the compression chamber  7 , so that only a relatively minor rise in pressure occurs in the compression chamber in idle operation, and the outlet valve  18  remains permanently closed. Reference is made to the state of the art (DE 43 21 013 A1 mentioned above) with respect to the action of the additional chamber in idle operation. 
     In certain operating states when the gas compressor  1  operates under load, for example, in the event of considerable heating up of the gas compressor or when the engine drive the gas compressor  1  is under great load, it may be necessary to adapt the power consumption and thereby also the delivery of pressure medium to these operating conditions, i.e. to decrease them slightly without switching over to the idle operating state in which no pressure medium is supplied. For this purpose, the auxiliary valve  15  is then actuated by means of the auxiliary piston  13  via the piston rod  14 , and the compression chamber  7  is thereby connected to the auxiliary clearance volume  12 . The auxiliary clearance volume  12  has a relatively smaller volume in comparison with the compression chamber  7 , preferably about 5% to about 20% of the volume of the compression chamber  7 . 
     Referring now to FIG. 3, a pressure medium installation employing the gas compressor  1  of the type presented in FIG. 1 is schematically depicted, and which includes the suction connection  16  connected to the surrounding atmosphere, the outlet connection  17  for the compressed air, the control connection  19  which can be subjected to the pressure medium for actuation of the auxiliary valve  15 . The gas compressor  1  of FIG. 3 further includes an additional control connection  22  which can be subjected to a pressure medium for the actuation of the additional valve  11 . The gas compressor  1  is driven via a drive shaft  55  by an engine  54 . The engine  54  is preferably the drive engine of a vehicle in which the pressure medium installation functions. 
     The engine  54  is connected permanently and tightly via the drive shaft  55  to the gas compressor  1 . The gas compressor  1  is therefore always driven at the rotational speed of the engine. This rotational speed is subject to great variations, particularly in a vehicle. 
     The gas compressor  1  supplies different pressure medium circuits with compressed air via a check valve  50  connected to the outlet connection  17 , and a multi-circuit safety valve  51  connected thereto. Of these pressure medium circuits, FIG. 3 shows a compressed-air reservoir  52  as an example. Compressed-air consumers, and which are not shown in FIG. 3, are furthermore connected to the compressed-air reservoir  52 . 
     The gas compressor  1  can be operated under load when pressure medium is required in one of the pressure medium circuits. In such event, the gas compressor supplies additional compressed air. When no additional compressed air is temporarily needed in the pressure medium circuit because sufficient pressure is present, the gas compressor can be operated in idle. In this operating state, it does not supply compressed air into the pressure medium circuits. 
     The governor control for the setting of the operating modes of load and idle is applied in FIG.  3 . For this purpose, a governor  53  is provided, and which is connected on an input side thereof to the compressed-air reservoir  52 . The governor  53  emits a pressure signal on an output side thereof, which is transmitted via a line to the control connection  22  of the gas compressor  1  when a predetermined shut-off pressure, for example, 8.5 bar is reached. In the presence of a corresponding pressure signal at the control connection  22 , the compression chamber  7  is connected via the additional valve  11  to the additional chamber  8 . As a result, the gas compressor  1  is then in idle state operation. The governor  53  permits the pressure signal after exceeding the shut-off pressure, and continues to emit the pressure signal until the pressure drops below a switching pressure, for example, 7.5 bar in the compressed-air reservoir  52 . By virtue of the hysteresis between the shut-off pressure and the switching pressure, a constant alternation between the operating conditions of load and idle is effectively avoided. 
     The pressure medium installation according to FIG. 3 additionally includes a series of sensors which serve to transform certain operating magnitudes of the pressure medium installation into electrical signals, and thus make it possible to determine these operating magnitudes of the pressure medium installation. The sensors consist of a pressure sensor  58  for sensing an over-pressure produced by a turbo-charger which is assigned to the engine  54 , a pressure sensor  59  for sensing a negative pressure representing the stress imposed on the engine  54 , the aforementioned temperature sensor  60  which determines the temperature of the compressed air, a pressure sensor  62  for sensing the pressure in the compressed-air reservoir  52 , and a rotational-speed sensor  63  for sensing the operating speed of the gas compressor  1 . 
     The above-mentioned sensors are connected via an electrical line to an evaluating device, provided in the form of an electronic control unit  57 . The electronic control unit  57  processes the signals of these sensors in accordance with a process, in the form of a control program which will be explained in further detail below. As a result of the processing of the sensor signals, the electronic control unit  57  produces an electrical output signal which is transmitted via an electrical line to a solenoid valve  61  connected to the electronic control unit  57 . The solenoid valve  61  is provided in the form of a 3/2 way valve and therefore has two switched positions. The solenoid valve  61  can also be integrated into the gas compressor  1 . 
     The solenoid valve  61  is connected to the compressed-air reservoir  52  and the control input  19  of the gas compressor  1  on the side towards the compressed-air reservoir  52 . In the first switching position of the solenoid valve  61 , as shown in FIG. 3, the magnetically operated valve is not actuated as a consequence of an output signal to that effect coming from the electronic control unit  57 . In this case, the solenoid valve  61  connects the control input  19  to the atmosphere, so that the auxiliary valve  15  is also not actuated. When the magnet of the solenoid valve  61  receives an actuating signal from the electronic control unit  57 , the solenoid valve  61  overcomes a biasing force and assumes its second switched position. The solenoid valve  61  thereby connects the outlet connection  17  to the control input  19 , causing the auxiliary valve  15  to be opened, such that the compression chamber  7  is connected to the auxiliary clearance volume  12 . As a result, the power consumption of the gas compressor  1  is reduced, and furthermore, pressure peaks are decreased in the pressure chamber  6 . 
     The following is a description of the process for the evaluation of the signals of the sensors  58 ,  59 ,  60 ,  62 ,  63  used to obtain the actuating signal for the solenoid valve  61 . 
     For purposes of the description, it is assumed that the solenoid valve  61  is initially non-actuated. When at least one of the following conditions is met, the solenoid valve  61  is actuated by the electronic control unit  57  through emission of an actuating signal: 
     The temperature value determined by the sensor  60  exceeds a first temperature limit value. 
     The turbo-charger pressure value exceeds a pressure limit value. 
     The engine negative pressure value drops below a predetermined negative-pressure limit value for a minimum time period. 
     The rotational speed value sensed by the sensor  63  exceeds a limit rotational speed value for a given time period. 
     The above-mentioned actuating signal for the solenoid valve  61  is, however, not produced, or is immediately switched off, under the above-mentioned conditions if it is detected in the electronic control unit  57  that the pressure value, i.e. the supply pressure sensed by the pressure sensor  62  falls below a minimum pressure value. This condition is thus given priority over the conditions mentioned above. 
     Another condition superseding the conditions mentioned above occurs when the temperature value sensed by the sensor  60  exceeds a second temperature limit value which is greater than the first temperature limit value. In such event, production of an actuating signal for the solenoid valve  61  is consistently maintained. In this manner, a failure of the gas compressor due to continued overload and the excessive heat caused thereby is effectively avoided. In the operating state when the solenoid valve  61  is actuated, i.e. with the addition of the auxiliary clearance volume  12 , the gas compressor can be operated for greatly extended periods of time without danger of failure, whereby at least a sufficient pressure supply is maintained in the compressed-air reservoir  52  in order to brake the vehicle. 
     It is intended that the above-mentioned limit values for temperature, pressure or negative pressure and rotational speed are to be empirically determined through tests as a function of the gas compressor and drive engine of the particular vehicle used. Periods of one to ten minutes are especially well suited as minimum periods for the failure to reach the negative pressure limit value and for the excess of the rotational speed limit value. 
     Having described preferred embodiments of the invention with reference to the accompanying drawing, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.