Abstract:
A turbocompound internal combustion engine having a turbocharger with a variable-geometry turbine; and an auxiliary turbine, which is located downstream from the turbine of the turbocharger, provides for recovering energy from the exhaust gas, and is connected mechanically to the drive shaft of the engine via a transmission; a control device compares the rotation speed of the auxiliary turbine, detected by means of a sensor, with a range of permissible speeds calculated on the basis of the speed of the drive shaft, and controls fuel supply to the engine and the geometry of the variable-geometry turbine to maintain the speed of the auxiliary turbine within predetermined limits in the event of a fault on the transmission.

Description:
The present invention relates to a so-called “turbocompound” internal combustion engine, in particular for an industrial vehicle. 
     BACKGROUND OF THE INVENTION 
     “Turbocompound” internal combustion engines are known, which comprise an auxiliary turbine downstream from the turbocharger turbine and connected mechanically to the drive shaft to recover and convert part of the residual energy of the exhaust gas into mechanical power for the drive shaft. 
     The auxiliary turbine and drive shaft are normally connected mechanically (here intended in the broader sense of the ability to transfer mechanical power, as opposed to a “rigid connection”) by a transmission comprising a gear reducer and a hydraulic joint permitting a certain amount of “slippage”. In the event of a breakdown of the hydraulic joint or relative hydraulic supply circuit, the auxiliary turbine may become mechanically disconnected from the drive shaft, and so unaffected by the braking torque produced by rotation of the drive shaft, so that the speed of the turbine, driven exclusively by the exhaust gas, may exceed the safety limit, thus resulting in breakdown of the turbine. 
     By way of a solution to the problem, turbocompound engines have been devised featuring a safety control device for detecting the oil pressure of the hydraulic joint, and which intervenes when the pressure falls below a predetermined limit. This type of device, however, is only effective and only intervenes in the case of hydraulic faults, whereas faults in the torque transmission of the hydraulic joint have been found to occur, for example, even when the system circuitry is sound but the oil particularly dirty. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a turbocompound internal combustion engine featuring an auxiliary turbine speed control device designed to eliminate the aforementioned drawbacks typically associated with known devices. 
     According to the present invention, there is provided a turbocompound internal combustion engine comprising a drive shaft; a turbocharger comprising a turbine and a compressor; an auxiliary turbine located along the path of the exhaust gas, downstream from said turbine of said turbocharger; and transmission means between said auxiliary turbine and said drive shaft; characterized by comprising a first angular speed sensor for detecting the rotation speed of said auxiliary turbine; and a control device for controlling the rotation speed of said auxiliary turbine, and which is connected to said first sensor and in turn comprises calculating means for calculating a range of permissible values of said rotation speed of said auxiliary turbine, comparing means for comparing the rotation speed of said auxiliary turbine measured by said first sensor with said range of permissible values, and control means for controlling operating parameters of the engine in response to an enabling signal generated by said comparing means, so as to maintain said speed of said auxiliary turbine within said range of permissible values. 
     The present invention also relates to a method of controlling a turbocompound internal combustion engine comprising a drive shaft; a turbocharger comprising a turbine and a compressor; an auxiliary turbine located along the path of the exhaust gas, downstream from said turbine of said turbocharger; and transmission means between said auxiliary turbine and said drive shaft; said method being characterized by comprising the steps of measuring the rotation speed of said auxiliary turbine by means of a sensor; calculating a range of permissible values of said rotation speed of said auxiliary turbine; comparing the rotation speed of said auxiliary turbine measured by said sensor with said range of permissible values; and controlling operating parameters of the engine in response to the outcome of said comparing step, so as to maintain said speed of said auxiliary turbine within said range of permissible values. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a diagram of a turbocompound engine in accordance with the present invention; 
     FIG. 2 shows a block diagram of a control device of the FIG. 1 engine. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 1 indicates as a whole an internal combustion engine for an industrial vehicle. 
     Engine  1  comprises a turbocharger  2  comprising a turbine  3  and a compressor  4  fitted to a common shaft. Turbine  3  has an inlet  5  connected to an exhaust manifold  6  of engine  1 , and an outlet  7 . Compressor  4  has an inlet connected to an air intake circuit  8 , and an outlet  9  connected to an intake manifold (not shown) of the engine via an intercooler  10 . 
     Engine  1  also comprises an auxiliary or power turbine  13  having an inlet  14  connected to outlet  7  of turbine  3 , and an outlet  15  connected to an exhaust system  16 . 
     Auxiliary turbine  13  is fitted to a shaft  18 , which is connected mechanically to a drive shaft  19  of engine  1  by a transmission indicated as a whole by 20. 
     More specifically, transmission  20  comprises a first gear reducer  24 ; a hydraulic joint  25 ; and a second gear reducer  26  connected at the output to drive shaft  19 . 
     According to the present invention, an angular speed sensor  28 —e.g. comprising a pulse generating wheel  29  associated with shaft  18  or any other member rotating at fixed speed with respect to it—detects the rotation speed of auxiliary turbine  13 , is connected to a first input  30  of a device  31  for controlling fuel supply and the geometry of turbine  3 , and supplies input  30  with a signal I 1  related to the speed of auxiliary turbine  13 . A second sensor  34 , of conventional type (not shown) and associated, for example, with the input shaft of the vehicle transmission to detect the angular speed of the drive shaft (hereinafter referred to simply as “engine speed”, is connected to and supplies a second input  35  of device  31  with a signal I 2 . 
     FIG. 2 shows a block diagram of device  31 . 
     Device  31  substantially comprises a first block  36  for calculating the theoretical speed nTCteor of auxiliary turbine  13  on the basis of signal I 2 . Block  36  is connected to second input  35 , substantially comprises a multiplier for multiplying the engine speed value by a constant taking into account the transmission ratio of transmission  20 , and is connected at the output to a block  37 , which compares the actual speed of the auxiliary turbine with a range of permissible values defined on the basis of the theoretical speed calculated above. More specifically, block  37  comprises a first adder  40 , which calculates a theoretical maximum speed nTCmax of auxiliary turbine  13  by adding a constant (e.g. 10,000 rpm) to nTCteor; and a second adder  41 , which calculates a theoretical minimum speed nTCmin of auxiliary turbine  13  by subtracting a constant (e.g. 20,000 rpm) from nTCteor. 
     The two values nTCmax and nTCmin are supplied to a first threshold comparator  42  defining a range of permissible values of the speed nTC of auxiliary turbine  13 . Speed nTC is calculated in known manner, on the basis of signal I 1  from sensor  28 , in an interface block  43  connected to first input  30  of device  31 , and which also generates in known manner a diagnostic signal  44  indicating the operating state of sensor  28 , and having, for example, a 0 logic value when sensor  28  is operating correctly, and a 1 logic value in the event signal I 1  of sensor  28  is implausible, e.g. absent or inevaluable. 
     Threshold comparator  42  receives signal nTC from interface block  43 , and compares it with threshold values nTCmax and nTCmin. More specifically, threshold comparator  42  generates a digital signal  45  of value 1 if nTC is between nTCmax and nTCmin, and of value 0 if nTC is outside the range defined by nTCmax and nTCmin. 
     Signal  45  is supplied to one input of a first AND gate  46 , the other input of which is supplied with a signal  47  equal to diagnostic signal  44  inverted by a NOT gate  48 . The output of AND gate  46  is connected to a time filtering block  50 , which generates a signal  53  of the same logic value as the input signal when the input signal remains stable for a predetermined time interval. Signal  53  is supplied to a reset input  54  of a flip-flop  55 . 
     The nTCmax value calculated by first adding block  40  is used to set the switching threshold of a second threshold comparator  54 , which receives signal nTC generated by interface block  43 , and generates a signal  56  of logic value 1 if nTC is greater than nTCmax, thus indicating a malfunction of auxiliary turbine  13 , and of logic value 0 if nTC is less than nTCmax. 
     Output signal  56  from comparator  54  and output signal  47  from NOT gate  48  are supplied to the inputs of a second AND gate  57 . 
     The output of AND gate  57  is connected to a second time filtering block  58 , which generates a signal  59  of the same logic value as the input signal when the input signal remains stable for a predetermined time interval. Signal  59  is supplied to the set input  60  of flip-flop  55 . 
     Flip-flop  55  generates an output signal O 1 , which is supplied to a block  38  for controlling the geometry of turbine  3 , and to a block  39  for controlling fuel supply by the injectors. Block  39 , operation of which is described in detail later on, also receives signal nTC relative to the speed of auxiliary turbine  13 . 
     Operation of device  31 , partly obvious from the foregoing description, is as follows. 
     To begin with, sensor  28  is assumed to be operating correctly, so that signal  44  is of value 1 and has no effect on the outputs of AND gates  46 ,  57 , which depend exclusively on the value of nTC. 
     If the speed nTC of turbine  13  falls within the range of permissible values, and sensor  28  is operating correctly, the output of first AND gate  46  is 1; and, if this value remains stable over time, the reset input of flip-flop  55  also equals 1. 
     If nTC falls within the range of permissible values, the condition nTC&lt;nTCmax is also definitely confirmed, so that the output of second threshold comparator  54  is 0, the output of second AND gate  57  is 0, and, if this value remains stable over time, the set input of flip-flop  55  is also 0. 
     The output signal O 1  of flip-flop  55  is zero, so there is no intervention on the part of blocks  38 ,  39 . 
     The upper branch of the FIG. 2 block diagram—indicated as a whole by  31   a —therefore acts as a recognition circuit for determining correct operation. 
     If the speed nTC of turbine  13  does not fall within the range of permissible values, and sensor  28  is operating correctly, the output of first AND gate  46  is 0; and, if this value remains stable over time, the reset input of flip-flop  55  also equals 0. 
     If nTC is greater than nTCmax, the output of second threshold comparator  54  is 1, the output of second AND gate  57  is 1, and, if this value remains stable over time, the set input of flip-flop  55  is also 1. 
     In this case, signal O 1  equals 1 and a correction of the geometry of turbine  3  and fuel supply is enabled. 
     The lower branch  31   b  of the block diagram therefore acts as a recognition circuit for determining a malfunction. 
     Conversely, if nTC is less than nTCmin, the output of second threshold comparator  54  is 0, the output of second AND gate  57  is 0, and, if this value remains stable over time, the set input of flip-flop  55  is also 0. Both the inputs of flip-flop  55  are 0, and the pre-existing situation is maintained. 
     The same applies in any case (i.e. regardless of the detected nTC value) in the event a fault is detected on sensor  28  (i.e. a 1 value of diagnostic signal  44 ); in which case, signal  47  is 0, so that the outputs of both AND gates  46 ,  57  are 0. 
     In the presence of a logic 1 value of signal O 1 , block  38  sets the geometry of turbine  3  to the full-open condition, thus reducing supercharging; and, at the same time, block  39  immediately reduces fuel supply by the injectors to a predetermined start value, and then modulates the full supply value to keep the speed of auxiliary turbine  13  constant and equal to an acceptable value, e.g. nTCmax. 
     The advantages of engine  1 , and particularly control device  31 , according to the present invention will be clear from the foregoing description. 
     In particular, by device  31  determining the rotation speed of auxiliary turbine  13 , any malfunction affecting the mechanical performance of the turbine is detected. 
     The control logic of device  31  only provides for correcting the operating parameters of the engine (geometry of turbine  3  and fuel supply) when the integrity of auxiliary turbine  13  is definitely at risk. That is, it does not intervene when the fault may possibly depend on a malfunction of sensor  28 , or when the fault does not threaten the integrity of turbine  13  (nTC&lt;nTCmin). 
     Moreover, intervention is designed to still allow albeit emergency operation of the vehicle, by supply to the engine being controlled to prevent overacceleration of auxiliary turbine  13 . 
     Clearly, changes may be made to engine  1 , and in particular to device  31 , without, however, departing from the scope of the accompanying claims.