fig1 thus shows engine 1 equipped with a turbocompressor 2 the turbine portion 2a of which is fed through the exhaust manifold 3 of the engine , while compressor portion 2b breathes in atmospheric air and feeds the usual butterfly valve 5 and venturi - equipped means 4 through delivery pipe 6 . the butterfly valve 5 thus controls the flow of air admitted into intake manifold 7 . in known fashion , the assembly comprises a dump valve 8 allowing a larger or smaller fraction of , exhaust gasses from exhaust manifold 3 to pass directly into exhaust pipe 9 via bypass passage 3 &# 39 ; without passing through turbine portion 2a . this valve 8 comprises a valve integral with a lever 10a connected to a rod 10 activated by pneumatic actuator 11 , generally of the type having a diaphragm . the actuator 11 comprises a return spring 12 , although in contrast to the usual arrangement , this spring acts to open valve 8 , and its calibration is relatively weak and not up to the supercharging pressure . its diaphragm divides the acuator into a closing chamber 13 , which when pressurized closes valve 8 against spring 12 , and an opening chamber 14 which produces the opposite effect . the pressure reigning in delivery pipe 6 upstream of venturi 4 is collected at point 15 and transmitted through a check valve 15a to a pressure reserve 16 which , through tube 17 and solenoid 19 , feeds a common tube 18 off of which leads a tube 20 connected to closing chamber 13 . another tube 21 simultaneously feeds opening chamber 14 , but through a throttling constriction 22 which causes a high pressure drop . this same opening chamber 14 communicates with the atmosphere through a tube 23 ending in a pressure or variable calibration valve 24 which consists essentially of a valve 25 activated by a diaphragm 26 to close the outlet to the atmosphere of tube 23 when the pressure under diaphragm 26 in control chamber 27 is sufficient to overcome the force of a return spring 28 tending to open the valve . the calibration of this spring is controlled through lever 29 activated through a cable 30 by gas pedal 31 so that its point of equilibrium will correspond to the supercharging pressure desired for stabilized operation . this control chamber 27 is actually connected to intake manifold 7 through tubes 32 and 33 and a delay valve 34 . the latter consists essentially of a severe pressure drop passage 35 set up in parallel with a check valve 36 so that the assembly imposes a high pressure drop only in the direction proceeding from tube 33 to tube 32 . solenoid 19 , preferentially controlled in the opening direction , is supplied through an electrical switch 37 connected to the gas pedal 31 through elastic compensating means 38 which closes the electrical circuit when butterfly valve 5 reaches a full open position and then activates cable 30 calibrating pressure valve 24 . also found in the electrical circuit proceeding from switch 37 to solenoid 19 are safety means 39 consisting of a pressure switch connected to intake manifold 7 downstream of the butterfly 5 , which breaks the electric circuit when the pressure in the manifold reaches a dangerous level . as long as butterfly value 5 is not fully open , switch 37 is open and the two chambers 13 and 14 of actuator 11 are exposed to the atmospheric pressure by solenoid 19 , which closes tube 17 and and places common tube 18 into communication with the atmosphere through outlet 40 . under the effect of spring 12 , flap valve 8 of the dump valve is open to a maximum degree , meaning that the back pressure at the exhaust of engine 1 is as low as possible in order to avoid any loss of efficiency . if the unit is equipped with an anti - pollution catalytic converter , it can be started quickly since the exhaust gasses are not cooled by passing through turbine stage 2a of turbocompressor 2 . on the other hand , when accelerator pedal 31 is sufficiently depressed to move butterfly valve 5 into a fully open position , switch 37 closes and energizes solenoid 19 , which blocks outlet 40 to the atmosphere and places tubes 17 and 18 in communication . the supercharging pressure in reserve 16 is then transmitted to branchings 20 and 21 . when the engine is operating at a stabilized speed , two operating speeds of the means for regulating the supercharging pressure must be distinguished . if the pressure at intake manifold 7 is lower than the specified limit and corresponds to the calibration of spring 28 of pressure valve 24 , the latter will maintain chamber 14 open to the atmosphere , with the pressure drop produced by throttling constriction 22 being much greater than that experienced in tube 23 and pressure valv 24 . because of the low calibration of spring 12 , actuator 11 then closes dump valve 8 , thereby placing turbocompressor 2 into operation . when , following this commencement of operation , the engine passes over the threshold of the atmospheric phase and into the supercharged phase , as soon as the supercharging pressure exceeds the value set by the calibration of spring 28 , which depends on the extent to which the accelerator pedal is depressed beyond the point corresponding to the fully open position of the butterfly valve , pressure valve 24 disconnects the outlet to the atmosphere via tube 23 , causing the pressure in opening chamber 14 to gradually reach ( through throttling constriction 22 ) the same value as the pressure in closing chamber 13 , so that dump valve 8 is opened by spring 12 . in stabilized operation , dump valve 8 thus tends to assume an equilibrium position depending on the extent of depression of the accelerator pedal . by contrast , during a phase of rapid acceleration , delay valve 34 only transmits the pressure at control chamber 27 after a certain delay , which improves the dynamic response of the assembly by delaying opening of dump valve 8 and by forcing engine 1 to operate temporarily at a supercharging speed greater than the regulating limit . nevertheless , the real pressure in intake manifold 7 must not exceed the danger point during this period . this is controlled by safety means 39 which may come into play to cut off the power supply to solenoid 19 and thus open dump valve 8 . all of the functions desired are thus obtained with relatively simple , automatic , and low - maintenance means . the alternate embodiment represented in fig2 is analogous to that of fig1 but from which it is distinguished by the replacement of pressure or variable calibration valve 24 with a constant calibration valve 24a and by the replacement of simple switch 37 of fig1 ( the opening and closing points of which coincide with the full open position of the butterfly valve 5 ) with a switch 37a having two stable positions , which is closed when the butterfly valve is fully open and opened only after a delay , e . g ., when the butterfly valve 5 returns to an intermediate position . in this example , the travel of the accelerator pedal 31 is limited to the position corresponding to full opening of the butterfly valve 5 . in the embodiment of fig2 it is preferable to connect tube 33 not to manifold 7 but to pipe 6 so as to take as the reference pressure for control of pressure valve 24a the pressure delivery pipe 6 above the butterfly valve . spring 28 of valve 24a is precisely calibrated so that its point of equilibrium will correspond to the desired supercharging pressure in stabilized operation without being modified by the gas pedal 31 . electrical switch 37a with two stable positions is linked to gas pedal 31 by elastic compensating means 38a which close the electric circuit when the butterfly valve 5 reaches a fully open position and then opens it only around the middle of the travel of the gas pedal . safety means 39 are identical to the first case . when accelerator pedal 31 is depressed enough fpr butterfly valve 5 to be in fully open position , switch 37a closes and energizes solenoid 19 , which blocks outlet 40 to the atmosphere and places tubes 18 and 18 in communication . the supercharging pressure in reserve 16 is then transmitted to the two branchings 20 and 21 . when the engine is at stabilized operating speed , the device has the same two operating speeds as in the first case , except that the opening of the butterfly valve 5 may be only partial , while in the accelerating phase , the same operation and the same delay are obtained . the embodiment of fig3 is distinguished from that of fig2 by the absence of reserve 16 and check valve 15a , which means that collection pipe 15 plays the role of inlet 17 to solenoid 19 , although it would also be possible to provide reserve 16 and check valve 15a in this case and by the direct connection of tube 33 to common tube 18 downstream of valve 19 . in addition , switch 37b and its elastic compensator 38b are of a simpler type than in the preceding examples and bring the supercharger into play by closing the circuit before butterfly valve 5 is fully open . with these exceptions , the operation is analogous to that in the preceding example . obviously , numerous modifications and variations of the present invention are possible in light of the above teachings . it is therefore to be understood that within the scope of the appended claims , the invention may be practiced otherwise than as specifically described herein .