METHOD FOR CALIBRATING A TURBOCHARGER

5

The present invention relates a method for calibrating a turbocharger comprising a turbine and a compressor to set a calibration flow position of a variable no/zle of the turbo charger.

0 In order to enhance the thermal efficiency of combustion engines to decrease the fuel consumption thereof, turbocharger systems comprising a variable nozzle (VNT) are widely used. Such a variable nozzle is adjustable such that the passage area and/or the geometry of the nozzle can be set between a minimum flow position and a maximum flow position 5

According to the known technology, the variable nozzle is operated by an actuating mechanism which is provided with stop positions for the maximum flow position arid the minimum flow position, ϊn such systems it is assumed that the mechanical and the flow related structure of each single turbocharger is in ^* a certain ffcnge. Howe\er, C recent requirements regarding exhaust measurements of internal combustion engines equipped with such turbocharger systems became stricter. Therefore, deviations between individual turbocharger products are no ionger negligible.

It is the object of the present invention to provide a method for calibrating a 5 turbocharger which can decrease the deviation of characteristics between individual turbocharger products, in particular, in the minimum flow position thereof.

The object rs solved by a method for calibrating a iurbocharger having the features of the independent claims. Further advantageous de\elopments are defined in the 0 dependent claims

According to a first aspect of the present invention, the method for calibrating a turbocharger, comprising a turbine and a compressor, to ^* set a calibration flow position of έ variable nozzle of said turbocharger comprises the steps of dri\ ing the 5 turbocharger by a predetermined fluid supply, changing the flow position of said

variable nozzle while monitoring the speed of the turbocharger. setting the fl op ^¬ position of the variable nozzle as calibration flow position when the monitored speed of the turbocharger reaches a predetermined speed

5 According to the first aspect of the present invention, the turbocharger is calibrated based on the speed of the turbocharger Thereby, differences among individual products which affect the characteristic of the turbocharger system can be adjusted considering the speed of the turbocharger as being a necessarily constant \alue.

0 According to a second aspect of the present invention, the method for calibrating a turbocharger, comprising a turbine and a compressor, to set a calibration flow position of a variable nozzle of said turbocharger comprises the steps of driving the turbocharger by a predetermined fluid supply, changing the flow position of said variable nozzle while monitoring the outlet pressure of said compressor, setting the 5 flow position of the \ arlable nozzle as calibration flow position when the monitored outlet pressure of said compressor reaches a predetermined pressure

According to the second aspect of the present invention, the compressor outlet pressure is employed as value which is to be kept constant among indh idual C products in order to compensate for any deviations which -are caused by the manufacture of the turbocharger s> stem.

It is noted that the solutions according to the first aspect and according to the second aspect of the present invention can be appropriately combined with each other. In 5 particular, both the speed of the turbocharger and the outlet pressure of the compressor can be used for calibrating the minimum flowposition of the tiirbocharger system.

According to a preferable form of the present .m ention, the calibration flow position 0 is the minimum flow position of said variable nozzle. In particular, the minimum flow position is a delicate part of the range of the nozzle at which changes are caused by the manufacture of the turbocharger s>stem. Therefore, calibrating the flow position at the minimum Dow position is most advantageous.

According Io a preferable form of the present indention, the flow position of the variable nozzle is changed from an open position towards a dosed position in the step of changing the flow position Changing the flow position of the variable nozzle from an open position towards a closed position corresponds to one of the actual operations of the iiirbocharger system Therefore, the calibration accuracy can be enhanced

According to a preferable form of the present im ention, for driving the tiirbocharger by the predetermined fluid supply, air is supplied Io an inlet of the turbine of the turbocharger through said variable nozzle Air can be handled in a simple manner and provided at any lest bench.

According to a preferable form of the preseni invention, the pressure and/or temperature of the air supply are monitored. The knowledge of the pressure and/or the temperature of the air supply is an option io improve the repeatability of the calibration method

According to a preferable form of 4he present invention, the pressure and/or temperature of the air supply are controlled so as to be substantially constant. As stated above, the repeatability of the calibration method can be irhpro\ed Therefore, the thermodynamics of the air supply should be the same among all turbochargers calibrated by the method according to the present invention.

According to a preferable form of the present invention, an outlet of the turbine is unrestricted Keeping the outlet of the turbine unrestricted, that is, without arranging any orifice at the outlet, further enhances the repeatability of the ^" calibration

According to a preferable form of the present invention, lubricant is supplied to and discharged from portions of the tarbocharger to be lubricated. The.lubrication of the turbocharger system is necessary in order Io provide an operation state of the turbocharger system which is comparable to Ae actual operation. This further enhances the accuracy of the calibration.

According to a preferable form of the present invention, pressures and/or temperatures of the lubricant supplied io and discharged from ^' the turbocharger are „

morutored. Further, the pressures and/or temperatures of the lubricant supplied to and discharged from the turbocharger are controlled so as to be within predetermined ranges. Keeping the pressures and/or temperatures of the lubricant within predetermined ranges further irhpππes the repeatability of the calibration and provides a defined operation state.

According to a preferable form of the present indention, an inlet of said compressor is connected to ambient air and an outlet thereof is provided with a restricted orifice. Providing a restricted orifice at the outlet of the compressor improves the accuracy of the calibration since the detection of the pressure at the outlet of the restricted orifice is facilitated In particular, the thermodynamics of the compressor comprising a restricted oπfice at its outlet is adapted for the calibration method according to the present invention

According to a preferable form of the present in\ entioa temperatures and/or pressures of air al the inlet and/or outlet of the compressor are monitored. In order to provide defined operational states ΌF the turbocharger system, the thermodynamic quantities of the compressor system should be available This further increases the repeatability of the calibration.

According to a preferable form of the present invention, an actuating speed for changing the flow position of the variable nozzle is set such that the speed of the turbocharger is at least close to a steady-state speed. ^• Furthermore, it is preferable to sex the actuating speed for changing the flow position of the variable nozzle such that the outlet pressure of the compressor is at ieasi close to a steady-state pressure. Employing the steady-state speed and/or the steady-state pressure of the turbocharger increases the accuracy of the calibration, since any deviations due Io control variations of the quantities in question are eliminated.

According to a preferable form of the present indention, the determined calibration flow position is set as a stop at an actuation mechanism of the turbo charger. " Preferably, said stop is formed as adjustable and fixable element for defining the determined calibration flow position. Thereby, the determined calibration flow position can be capped and fixedly adjusted such that the turbocharger system can be provided with this calibrated flow position which is unchangeable ^' '

Further advantages and effects of the present invention become apparent from the following description based on the enclosed drawings

Fig. 1 is a schematic new of the turbocliargβr system which is prepared for the calibration on a bench

Fig. 2 shows a flow chart of the calibration method according to a first embodiment of lhe present invention

Fig. 3 shows a flow chart of a second embodiment of the calibration method of the present invention.

In the following, preferable embodiments of the present invention are explained in more detail based on the drawings.

First embodiment

Fig. 1 shows the turbocharger system which is prepared for the calibration method according to the present invention It is noted that the view of Fig. I merely shows essential parts of the turbocharger and further details which are necessary for the explanation of a calibration method according to the present invention.

The turbocharger according to FIg. 1 comprises a compressor 1 and a turbine 2 which are connected by a shaft 3 In the drawing, the compressor 1 is represented by a compressor wheel and the turbine 2 is represented by έ turbine ^' wheel ^" . The shaft 3 is rotatably supported by a bearing assembh 4 which is formed by a fluid bearing operated b\ oil supply.

The compressor 1 comprises an inlet and an outlet. At the outlet of the compressor, an orifice 5 is provided. This orifice 5 comprises a fixed throttle effect.

The turbine 2 of the turbocharger comprises an inlet and an outlet.. At the inlet, a variable nozzle 6 with a known structure is prouded. This ^' \ariabie riό/zle can be formed by an insert which is dispSaceabie along the axial' direction of the

turbocharger. by an arrangement including vanes which are provided in an annular passage for passing the fluid for driving the turbine or by a combination thereof. In the following, the structure of the variable nozzle is not limited as long as the nozzle can be adjusted between a minimum flow position and a maximum flow position.

For performing the calibration method according to the present invention, the turbocharger is mounted on a xest bench (not shovm). Next the bearing arrangement 4 is connected to an oil supply. The outlet of the bearing arrangement 4 is connected to an oil discharge.

The iniet of the compressor is connected to the atmosphere. The pressure at the outlet of the orifice 5 is monitored as compressor outlet pressure Pic-

The inlet of the turbine is connected to an air supph . The temperature and the pressure of the air supply is monitored. In particular, the value of the turbine' inlet temperature Trr and the value of the turbine inlet pressure Pn- are detected. Furthermore, the outlet of the turbine is connected to a test bench exhaust system. The turbine outlet pressure ? ₂ τ is monitored.

The turbocharger system which is mounted on the test bench is pro\ ided with a speed sensor for detecting the speed N of the shaft 3 Moreover, the pressure and the temperature of the atmosphere Po and To are detected

The detected values PIOIL, TIODL- P201L, Pic, Tic. Vic, TIT, Pn- P ₂ T, N. P ₀ . To are supplied to a control unit which is not shown. The control unit -can be any computer like system which is capable of recehing, displaying and processing the abo\e- mentioned detection values.

In order to prepare the turbocharger for the calibration method, in the turbocharger mounted on the test bench, the inlet of the turbine 2 is connected to the air supply, the inlet of the bearing assembly 4 and the outlet thereof are connected to the oil supply and the oil discharge, respectively, and the detection of the above-mentioned quantities is started.

The calibration method according io the first embodiment of the present invention is explained based on Fig. 2

In step SlOO, the ^anable nozzle 6 are set to an open position. In- particular, lhe \ariable nozzle 6 is actuated such that the position thereof is substantially different from the dosed position.

In step Sl Ol, the oil supply is turned on. Furthermore, in step S 102. Pioi _t and Tiorju Paoϊi. are monitored such that the values thereof are within a certain predetermined range.

In step Sl 03. air is supplied to the turbine inlet In particular, the flow rate of the supplied air is slowly increased from zero m order to start the operation of the turbocharger. The flow rate is increased slowly in order to increase the speed of the turbocharger and, thus, the compressor outlet pressure P _2C at the outlet of the compressor 1.

In step S 104. the values P _1T , T _n , N are monitored. In particular, the turbine inlet pressure PIT and the turbine inlet temperature Tn are monitored such thai the same are within a predetermined range This process can be automated by an> known control system which provides a closed loop control.

After the turbocharger system reaches and maintains the defined operation state, which means, that P IOIL. ϊIOIL, P201L- Pi r, TIT are within predetermined ranges, the \ ariable nozzle 6 is closed at a predetermined actuating speed. This actuating speed is determined such that the change of the rotational speed N of the turbocharger and/or the compressor outlet pressure ?2c of the compressor of the turbocharger changes that slowly such that an operation state is established ftϋich is at least close to the steady-state operation.

In step S 106, a turbocharger speed N Is compared with a predetermined target speed NTARGET- If the turbocharger speed has not reached the target speed N _TλRGEI . ^" the \aπab!e nozzle 6 is further closed at the predetermined actuating speed as defined in step Sl 05 Once the turbocharger speed N has reached the- target- speed N _f ^a- _T -. the vane position is fixed.

As an option, the position of the variable nozzle 6 can be kept unchanged for a predetermined period after the predetermined target speed NT _A R _G EI of the turbocharger is reached in order to make sure thai the operation is in a steady-state

In particular, the ~% ane position is fixed by adjusting a set screw forming a slop of the actuating mechanism of the variable nozzle 6 However, any other means for fixing the vane position can be used as long the minimum flow position of the nozzle is defined while the nozzle can be opened.

After fixing the position of the variable nozzle 6, the calibration is complete. Therefore, any lines and supplies are removed and the turbocharger system is removed from the test bench.

After the removal of the turbocharger. the next turbocharger can be calibrated by the same method. The above mentioned ranges and quantities musi be constant for each individual product of a respective line of turbo chargers of a specific type

According to the basic -concept of -the present invention, the minimum flow position of the variable noz/le 6 is calibrated by employing the rotational speed N of the turbocharger. as calibration quantity. This means, that each individual turbocharger product of certain product line will reach the target speed N _IARGET at the minimum flow position of the -variable nozzle 6 under the condition that the remaining quantities are constant

Second embodiment

A second embodiment of the present invention is explained based on Fig. 3. The arrangement of the turbocharger system on the test bench is the same-as in the first embodiment.

In the following, merely the differences between the first embodiment and the second embodiment are explained. In the second embodiment, the calibration method is performed for the mrbo charger which is mounted on the test bench According to this method, the variable nozzle 6 is set to an open position (S200),, the oil supply is

turned on (S201 J, P _I O _IL - T _1OIL are monitored (S202), and air is supplied to the turbine inlet (S203). as in the first embodiment.

In step S204, the turbine inlet pressure P _IT , the turbine inlet temperature T _IT and the compressor outlet pressure VJC are πioniiored

Then ₅ in step S205, the variable nozzle is closed at the predetermined actuating speed corresponding to step S 105 of the first embodiment.

The mam difference between the first embodiment and the second embodiment is that in step S206, the monitored compressor outlet pressure Pac is compared with a predetermined target pressure PICTARGE'F- This means, that the calibration of the turbocharger system is based on the fact that the minimum flow position of the vane of the variable nozzle 6 should provide a constant compressor outlet pressure P ₂ c among each individual turbo charger product of a certain product line,

Once the compressor outlet pressure P ₂ c has reached the target pressure P ₂ CT _A R _GLI - the vane position of the variable nozzle 6 is fixed in step S207 which corresponds to step S 107 of the first embodiment. Thereafter, calibration process for ^* this turbocharger is complete and is repeated for further iurbo chargers of this product line while keeping the above mentioned ranges and quantities constant for the respective product line.

The present invention has been explained based on preferred embodiments ^• However, the present invention is not limited to the above explained specific embodiments.

Io particular, the calibration method is not limited to the tiirbocharger system disclosed in -Fig. I Rather, any turbocharger system is .applicable for the present invention which includes a compressor and a turbine.

The bearing arrangement 4 is not limited to an oil bearing; It is possible to provide any bearing arrangement, such as ball- bearings, roller bearings, or a combination thereof