Ambient air-pulsed valve control

[0002] The present invention relates to an apparatus for controlling a coasting air recirculation valve of the turbocharger of an internal combustion engine, the coasting air recirculation valve being arranged in a coasting air recirculation line that bypasses a compressor in the intake duct, and the coasting air recirculation valve being controllable by way of the intake duct pressure on the downstream side of the throttle valve.

[0003] A conventional apparatus is described in German Patent No. 28 23 067. In this German Patent, the coasting air recirculation valve is activated exclusively pneumatically by the intake duct pressure: the coasting air recirculation valve opens when a certain negative pressure, occurring while the vehicle is in coasting mode, is present in the intake duct on the outflow side of the throttle valve. The fact that the outlet of the compressor is connected to its inlet via the coasting air recirculation line causes a decrease in the boost pressure in the intake duct downstream from the compressor, which is expressed as better engine response to rapid closing of the throttle valve. The opening or closing behavior of the coasting air recirculation valve is not optimally defined in the case of activation exclusively by way of the intake duct pressure.

[0004] U.S. Pat. No. 5,083,543 describes a coasting air recirculation valve which has its control pressure delivered from a negative pressure vessel. This negative pressure vessel is fed from the intake duct pressure. The coasting air recirculation valve is thus controlled solely as a function of the intake duct pressure.

[0005] Japanese Patent Application No. 06 117 263 (provided in, e.g., Patent Abstracts of Japan, Vol. No. 408, Jul. 29, 1994) describes a coasting air recirculation valve which is controlled as a function of the negative pressure in the intake duct on the downstream side of the throttle valve, and which is located in a coasting air recirculation line. Inserted in a line between the intake duct downstream side and the coasting air recirculation valve is a vacuum vessel whose negative pressure depends solely on the negative pressure in the intake duct on the downstream side of the throttle valve. The purpose of the vacuum vessel is to damp air flow noises that occur when the coasting air recirculation valve is opened.

[0006] It is therefore the object of the present invention to describe an apparatus of the kind cited initially that allows highly defined opening and closing of the coasting air recirculation valve.

[0007] This object is achieved with an electrically controllable solenoid valve according to the present invention, which delivers to the coasting air recirculation valve (as a function of a control signal) either the intake duct pressure or a control pressure, independent thereof, from a negative pressure vessel. Thus, it is possible to prevent the coasting air recirculation valve from being prematurely closed by the negative intake duct pressure on the downstream side of the throttle valve in the event of rapid closure of the throttle valve due to pumping of the boost air column. The boost pressure is uniformly and continuously decreased. Boost pressure fluctuations, and jerking of the vehicle caused thereby, are prevented.

[0008] It is advantageous for a control signal activating the solenoid valve to be emitted if the load gradient of the engine exceeds a threshold that depends on reference boost pressure. The load gradient can have a predictive value superimposed on it if the current load gradient has risen as compared with the load gradient existing one timing cycle earlier.

[0009] It is advantageous for a control signal activating the solenoid valve to be made available if the absolute intake duct pressure lies below a pressure threshold at which the coasting air recirculation valve would open. A control signal activating the solenoid valve should then be made available if the absolute intake duct pressure exceeds the pressure threshold. The pressure threshold can be taken from a characteristics diagram that depends on the actual boost pressure and the ambient pressure.

[0010] FIG. 1 shows a schematic block diagram of an engine which includes an apparatus according to the present invention.

[0011] FIG. 2 shows a functional diagram of the apparatus according to the present invention.

[0012] FIG. 1 shows an internal combustion engine 1 having an intake duct 2 and an exhaust conduit 3. Located in intake duct 2 are a throttle valve 4 and a sensor 5 for sensing the opening angle α of throttle valve 4. Also arranged in intake duct 2, on the downstream side of throttle valve 4, is a pressure sensor 6 for sensing the actual boost pressure pvdk. An engine speed sensor 7, for sensing the engine speed nmot, is mounted on internal combustion engine 1. A control unit SG receives as input signals the opening angle α of throttle valve 4, the actual boost pressure pvdk, the engine speed nmot, and a measured ambient pressure pu.

[0013] The internal combustion engine is equipped with a turbocharger, an exhaust gas turbine 8 being arranged in exhaust conduit 3, and a compressor 9 in intake duct 2. Compressor 9 is driven by exhaust gas turbine 8 via a shaft 10. Exhaust gas turbine 8 is bypassed in a conventional manner by a bypass line 10 in which a bypass valve 11 is arranged. The control signal ldtv for bypass valve 11 is generated in control device SG. The manner in which bypass valve 11 is controlled is not described here in further detail.

[0014] Compressor 9 in intake duct 2 is bypassed by a coasting air recirculation line 12 through which air can be returned from intake duct 2 on the delivery side of compressor 9 into intake duct 2 on the suction side of compressor 9. Inserted into coasting air recirculation line 12 is a pneumatic coasting air recirculation valve 13 that is connected to a control line 14. The pressure on control line 14 governs whether coasting air recirculation valve 13 opens or closes.

[0015] An electrically controllable solenoid valve 15 is located in the control line. If this solenoid valve 15 is closed, control line 14 is connected to a line 16 that opens into intake duct 2 on the downstream side of throttle valve 4. In this situation the pressure existing on the downstream side of throttle valve 4 is applied to coasting air recirculation valve 13. When throttle valve 4 closes, for example when the vehicle is coasting, a negative pressure is created on the downstream side of throttle valve 4. Once this negative pressure acting on coasting air recirculation valve 13 has fallen below a certain threshold, valve 13 opens, so that a pressure decrease occurs, via the coasting air recirculation valve, on the delivery side of compressor 9 in intake duct 2. The boost pressure on the upstream side of throttle valve 4 thus decreases. This prevents any oscillation in the boost pressure.

[0016] Control of coasting air recirculation valve 13 solely by way of the pressure on the downstream side of throttle valve 4 does not result in optimally defined opening or closing behavior of coasting air recirculation valve 13. This shortcoming can be eliminated by the fact that coasting air recirculation valve 13 is controllable independently of the pressure in intake duct 2 on the downstream side of throttle valve 4. For this purpose, a negative pressure vessel 17 is connected to electrically controllable solenoid valve 15. When solenoid valve 15 is opened, negative pressure is delivered to coasting air recirculation valve 13 from negative pressure vessel 17 via control line 14, resulting in immediate opening of coasting air recirculation valve 13. A control signal B_ldsua present at solenoid valve 15 determines whether solenoid valve 15 is open or closed. This control signal B_ldsua is generated by control unit SG. The conditions under which the control signal B_ldsua is made available to activate solenoid valve 15 will be described below with reference to FIG. 2.

[0017] As shown in the functional diagram in FIG. 2, the control signal B_ldsua is set to a logical “1” at the output of an OR gate OR, and thus activates solenoid valve 15, when either a signal pdpd or a signal pdps is present at the inputs of OR gate OR.

[0018] The signal pdpd is intended to ensure very fast activation of solenoid valve 15 during dynamic operation of the internal combustion engine. The signal pdpd for dynamic operation is set (logical “1”) if the load gradient of the engine satisfies the condition described below. The load gradient dp is the difference, determined at node V1, between the actual boost pressure pvdk that is measured on the downstream side of throttle valve 4 in intake duct 2, and a reference boost pressure plsol. The reference boost pressure plsol can be read out, in known fashion, from a characteristics diagram KFLDPS that depends on the engine speed nmot and the opening angle α of the throttle valve.

[0019] From the signal dp for the load gradient, a predictive value pdw is created by first taking, at a node V2, the difference between the current load gradient dp and a load gradient dp(i−1) existing one timing cycle earlier (i−1). A delay element VZ makes the previous load gradient dp(i−1) available at its output. The difference signal is then sent through a limiter BG1 that sets it to zero if the current load gradient dp is less than or equal to the previous load gradient dp(i−1). In a multiplier MU, the predictive value pdw is multiplied by an applicable time interval PIDLDSUA. In node V3, this predictive value, existing only for the specific time interval, is superimposed on the signal dp for the load gradient. A signal value pdpld that is elevated with respect to the current load gradient is therefore present, for the aforesaid time interval, at the output of node V3.

[0020] The predictive value pdw thus has a positive value deviating from zero only if the current load gradient dp is greater than the load gradient dp(i−1) existing one timing cycle earlier. In other words, the reference boost pressure plsol has decreased with respect to the actual boost pressure pvdk because of an increasing decrease in the opening angle of the throttle valve. Coasting air recirculation valve 13 would now need to be opened immediately if the load gradient exceeds a specific threshold. Superimposition of the predictive value pdw causes the load gradient to reach this predefined threshold more quickly, thus resulting in earlier or quicker opening of solenoid valve 15, and consequently in timely opening of coasting air recirculation valve 13.

[0021] The summed signal pdpld made up of the signal dp for the load gradient and the predictive value pdw is sent, prior to the threshold value decision, through a limiter BG2 that allows only positive values of the signal pdpld to pass. A threshold value decider SE performs the aforesaid comparison between the signal pdpld and the predefinable threshold sdsua. The threshold sdsua is taken from a characteristic curve SDLDSUA that is a function of the reference boost pressure plsol. In the range close to full load, the threshold sdsua is much greater than when the internal combustion is operating close to idle. If the signal pdpld has exceeded the threshold sdsua, the signal pdpd is present with a logical “1” at the output of threshold value decider SE. Threshold value decider SE possesses a hysteretic characteristic curve according to which the output signal pdpd is reset to zero after a predefinable hysteresis HDLDSUA. The hysteresis describes the difference between the lower and upper switching point, and must be adapted to the particular engine so as to prevent the signal pdpd from switching back and forth in undefined fashion.

[0022] The second signal pdps present at the input of OR gate OR is to be set (logical “1”) if the following pressure conditions exist:

[0023] A divider DV forms, from the actual boost pressure pvdk and the ambient pressure pu, a quotient dpp that corresponds approximately to the compressor pressure ratio.

[0024] This quotient dpp is compared by a comparator K1 to a threshold svuvs. The threshold svuvs is taken from a characteristic curve SVDLDUVS that is a function of the engine speed nmot. If the quotient dpp falls below the threshold svuvs, the output signal of comparator K1 then sets an RS flip-flop FF. The output signal pdps of RS flip-flop is thus set if the compressor pressure ratio reaches a value at which coasting air recirculation valve 13 could open. RS flip-flop FF—and thus signal pdps, i.e. the control signal B_ldsua for coasting air recirculation valve 13—is reset if the reference boost pressure plsol exceeds the ambient pressure pu. A threshold value decider SES compares the reference boost pressure plsol to the ambient pressure pu. A hysteresis HSLDSUA is taken into account in this threshold value decision in order to prevent the signal pdps from switching back and forth in undefined fashion.

[0025] Because the signal pdps, and thus the control signal B_ldsua for solenoid valve 15, are set and reset in the manner described, coasting air recirculation valve 13 is indeed opened when the intake duct pressure on the downstream side of throttle valve 4 has dropped below a certain threshold. Subsequent closure of coasting air recirculation valve 13 is accomplished, however, not in undefined fashion by way of the intake duct pressure, but rather in quite defined fashion by way of the control signal B_ldsua for solenoid valve 15, which disconnects the negative pressure out of negative pressure vessel 17 from control line 14 only when the reference boost pressure plsol exceeds the ambient pressure pu, taking into account a hysteresis HSLDSUA.