SE457897B - Turbocharged automobile engine with antiknock control - Google Patents

Abstract

The engine has a knock detector (22) attached to the engine block coupled to a microprocessor controlling the charging press and the ignition timing angle. When engine knock of a given intensity is detected the charging press is reduced via a control valve (13) while at the same time the ignition timing angle is increased, so that the knock is eliminated. The reduction in the charging press is balanced by the increase in the ignition timing angle to maintain the engine exhaust temp. at a constant value below a given max. when the engine is switched from one fuel to another with a different octane rating. The anti-knock control allows the engine to operate at its optimum point just below the knock threshold.

Description

457 897 This is achieved according to the invention in a method of the type stated in the introduction by using the signals indicating knocking to lower the engine ignition in parallel with the reduction of the boost pressure and that the ignition reduction is weighed against the pressure reduction, so that the engine exhaust temperature is kept at a substantially constant level below a predetermined maximum level when switching between different fuel qualities.

By selecting the exhaust temperature as the controlling parameter and balancing the ignition reduction against the pressure reduction, so that the exhaust temperature is kept at a substantially constant level, a significant reduction in performance losses is achieved compared to pressure reduction alone, eliminating the risk of thermal overloading of the engine exhaust side.

Because the ignition can be regulated to follow the knock limit over the entire pressure range, a lower spec is achieved. fuel consumption than with pressure control alone.

A device of the type indicated in the introduction for carrying out the method is characterized in that the signal processing means, preferably comprising a microprocessor, are arranged to output signals to the engine ignition setting regulating means in order to lower the engine ignition in parallel with the reduction of the boost pressure.

The invention is described in more detail with reference to exemplary embodiments shown in the accompanying drawings, in which Fig. 1 schematically shows a turbocharged internal combustion engine with a system for preventing knocking combustion, Figs. 2 and 3 are diagrams of exhaust temperature and specific fuel consumption at different fuel qualities and control methods, Fig. 4 a diagram illustrating torque reduction at different fuel qualities and control methods, Fig. 5 a diagram illustrating the ignition position in relation to the position for best fuel economy at different control methods and Fig. 6 diagram illustrations ignition reduction as a function of time at the same knock intensity in the control procedure according to the invention.

BO H0 3 457 897 The engine 1 shown in Fig. 1 is a four-cylinder otto engine with a per se known turbocharger assembly 2, comprising a turbine part 3 in communicating connection with the engine exhaust manifold U and a compressor part 5 in communicating connection with the engine intake manifold 6 via an charge-air cooler 7 of air-air type and a damper housing 8, containing the engine throttle 9. The gas flow through the turbine 3 is regulated in a known manner by means of a shunt valve 11 connected in a shunt line, whose damper is operated by a pneumatic actuator 12 and in closed position leads the entire gas flow through the turbine. The pressure in the actuator 12 and thus the setting of the shunt valve is determined by an electromagnetic frequency valve 15 in a line 1ü, which via a calibrated choke 15 connects the suction and pressure side of the compressor to each other and from which a line 16 to the actuator 12 branches. During operation, the frequency valve alternates periodically between open and closed position and by varying the period length, the pressure in the line 16 can be varied and thus also the pressure in the actuator 12.

The frequency valve 13 is controlled by a signal processing unit in the form of a microprocessor 17, in which signals representing engine speed, damper setting, charge air pressure and charge air temperature are input and in which a setpoint of the charge pressure as a function of the speed is stored.

The inputs to the microprocessor are obtained from various sensors 18, 19, 20 and 21, of which the sensor 18 located in the tube between the compressor 5 and the charge air cooler 7 can be a piezoresistive transducer, which registers the charge pressure, the sensor 19 a fast NTC resistor , which registers the charge air temperature and the sensor 20 a potentiometer 20 connected to the damper 9, which registers the damper setting. Signals representing speeds can be obtained from an existing Hall effect sensor 21 in the current distributor.

On the basis of the input signals from the sensors 19, 20, 21, the processor 17 determines the setpoint of the charge air pressure at each operating state. The signal from the boost pressure sensor 18 thereby provides information about any deviation between the setpoint and the actual value of the boost pressure. Signal indicating UO 457 897 'L' for low actual charge air pressure leads to the processor 17 extending the opening time of the valve 13, which in turn means a pressure drop in the line 16 to the actuator 12, which then regulates the shunt valve 11 towards the closed position.

The flow through the shunt line 10 decreases and the turbine speed and thus the charging pressure increases.

If the boost pressure is too high, the regulation is reversed.

Through this feedback of the charging pressure, it is possible to continuously keep the charging pressure at a predetermined value. The principle allows great flexibility in determining the boost pressure characteristic and makes the system independent of mechanical tolerances such as variations in the characteristics of the actuator spring return mechanism.

The microprocessor control makes it possible to set the level of the maximum charging pressure just below the knock limit at full load in order to obtain optimal performance for a given fuel quality. The result, however, is that the margins for harmful knocking are very small. To primarily compensate for the increased sensitivity of the engine to variations in fuel quality, the system described above includes a knock detector 22 mounted on the engine block, which may be a piezoelectric accelerometer, which is connected to the processor 17 and provides this continuous information on the knock intensity, wherein the processor is programmed to trigger corrective measures when recording a predetermined knock intensity by according to the invention giving a signal to the valve 13 to effect reduction of the actual charge pressure below the setpoint pressure and giving a signal to the engine ignition system 24 to effect lowering, ie deceleration. engine ignition setting.

The diagram in Fig. 2 illustrates how pressure reduction and ignition lowering, represented by a dashed and solid curve, respectively, each affected the exhaust temperature during tests performed on a 2.1 liter four-cylinder engine with a maximum power of 11H kW DIN. The tests were performed with a maximum load at the knock limit (DBL) at 3000 rpm and with 97, 9U and 91 RON of fuel respectively. As can be seen from diagram HO 457 897, a sharp increase in the exhaust gas temperature was obtained with only ignition reduction when switching to a lower quality fuel, while only pressure reduction resulted in lowering the temperature but instead a sharp deterioration of engine performance as shown in the table below. In the diagram in Fig. 3, the solid line illustrates the effect of ignition reduction and the dashed line of the pressure reduction on the specific fuel consumption of the engine.

In the method according to the invention, the exhaust gas temperature was chosen as the controlling parameter in the programming of the processor 17, whereby the pressure reduction and the ignition lowering were weighed against each other to keep the exhaust gas temperature constant, as illustrated by the dashed curve in Fig. 2. Resulting changes in the specific fuel consumption the curve in Fig. 5.

With the specified test engine, the optimal balance between pressure reduction and ignition reduction was found to be approximately 0.03 bar per crankshaft degree.

The table below shows the impact of the various measures on the engine's performance, fuel economy and exhaust gas temperature.> - - "~“ temperature. Action Change Change Change On- Load- of spec of of lowering presses fuel-. Turn- exhaust- reduce- burn torque šemp crankshaft_ ring%% C degrees bar I Ignition +5.1 -5.7 +30 -5 0 only II Pressure reduction- + Q .8 -9.1 -19 0 -0.13 ring only III Combined + 2, H -6.3 0. -3 Q, 075 ignition reduction 'and pressure reduction HO 457 897' 6 As shown in the table, measure I leads to a sharply elevated exhaust gas temperature with unacceptably high thermal load on the components on the exhaust side, while measure II leads to performance losses that are more than ü3% greater than in measure III.

The diagram in Fig. H shows absolute values of torque and exhaust temperature in the same engine test and 97 and 91 RON fuel, respectively, but here at 2700 rpm. Solid, dashed and dotted arrows represent the change in torque in measures I, II and III respectively. As can be seen from the diagram, pressure reduction alone leads to a reduction of the torque from 250 Nm to 214 Nm, while combined pressure and ignition reduction only results in a torque reduction from 250 Nm to 233 Nm while maintaining the exhaust gas temperature of ce 9o5 ° c. Ignition reduction alone leads to an increase in the exhaust gas temperature of about 10 ° C.

As stated in the introduction, an engine with a knock control system, which applies only charge pressure reduction, has poorer fuel economy than an engine equipped with the system according to the invention when driving on a fuel with a low knock tendency, eg 97 RON fuel. This is because the ignition system of the first-mentioned engine must be adapted so that ignition - at the lowest pressure the system can regulate down to - takes place below the knock limit for the most knock-prone fuel engine is specified for, eg 91 RON fuel. This is illustrated in the diagram in Fig. 5, where P1-PH denotes different constant pressure levels and the MBT ignition position for best fuel economy, which as shown in the diagram and which applies to most engines - is higher than the knock limit even for 97 RON fuel at these loads. To the left of the line DBL 91 RON are the ignition points a, b and c for the three discussed control methods when driving on 91 RON fuel and full load. With AM1, AM2, AM; is called the torque reduction at transition from 97 to 91 RON fuel. At partial load (pressure level Ph) and 97 RON fuel, in the control method according to the invention the ignition can be applied at point d, while the ignition, when only pressure change is applied, must remain at point 7 457 897 point b even when driving on 97 RON fuel. The difference Au in ignition performance leads to a fuel consumption at partial load which is H-5% higher with the latter control method.

A denotes the range of constant exhaust gas temperature in the control method according to the invention.

In the described embodiment, the microprocessor 17 was programmed to reduce the charging pressure and to rapidly lower the ignition a number of absolute steps of 0.075 bar and 3 crankshaft degrees, respectively. The system was set to operate when detecting knocking combustion during five or more of twenty consecutive recorded cycles and to reset charge pressure and ignition setting to the original values at a rate of 0.075 bar and 5 crankshaft degrees per 5 s upon cessation of knocking. Fig. 6 illustrates this change in charge pressure and ignition setting as a function of time at different knock intensities.

The invention thus achieves an efficient method of reducing the performance losses of a high-power engine when switching to a fuel of lower quality than the fuel specified for the engine. Because the exhaust temperature «is not affected, permanently high power consumption can be allowed without shortening the service life of the engine. The control system shown in Fig. 1 also includes a safety device in the form of a pressure switch 23 mounted on the intake pipe. This switches off the engine's fuel supply in the event of a fault, which results in the charging pressure rising above the permissible level.

Claims (8)

10 15 _20 25 30 35 457 897 Patent claim A method of preventing knocking combustion in a turbocharged otton engine. in which a knock detector is used to detect knocking, wherein signals emitted by the detector indicating knocking down a certain intensity are used to reduce the engine charge air pressure, characterized in that the signals indicating knocking are used to lower the reduction of the charge air pressure in parallel. It is true that the reduction in ignition is balanced by the pressure reduction, so that the exhaust gas temperature of the notary is kept at a substantially constant level below a predetermined nox level when switching between different fuel qualities. Method according to Claim 1, characterized in that the charge pressure and the ignition are reduced when the knock is indicated, resp. sank rapidly step by step and upon cessation of tapping increase resp. satisfied with lower speed note the original values. 3. A method according to claim 2, characterized in that the charge pressure is reduced by about 0.03 bar per crankshaft degree of ignition. Device for preventing knocking combustion in a turbocharged ottonotor for carrying out the method according to any one of claims 1-4. comprising a true signal processing means mounted on the notary block of the notary block. son are arranged to take note of signals emitted from the detector and output of these dependent control signals to charge pressure controlling means. wherein the signal processing means are arranged to, when taking signals indicating knocking down a certain intensity, give a signal to the charge pressure controlling means to reduce the charge pressure, characterized in that the signal processing means (17) are arranged to emit signals to the ignition setting of the notary regulating means (24) for simultaneously lowering the reduction of the charge pressure and lowering the ignition of the notary. m. 10 15 20 25 457 897 5. Device according to claim 4, characterized in that the signal processing means (17) are arranged so as to balance the reduction of the ignition against the pressure reduction. that the engine exhaust temperature is kept substantially constant independent of the fuel quality within a predetermined quality range. Device according to claim 4 or 5, characterized in that the signal processing means (17) comprise a microprocessor, which is programmed to reduce the pressure and lower the ignition rapidly in absolute steps when recording a predetermined knock intensity, and that in cessation of knocking increase the pressure resp. increase the ignition lower speed to the original values. Device according to claim 5 or 6, characterized in that the microprocessor (17) is programmed to reduce the pressure by about 0.03 bar per crankshaft degree of ignition. Device according to one of Claims 4 to 7, characterized in that the crack detector (22) is connected: in Signal processing means (17), in which a setpoint value of the charging pressure as a function of the notary speed is stored, and in that the signal processing means are arranged to, when taking a signal indicating knocking down a certain intensity, give a signal to the charge pressure controlling means (13) to lower the actual charge pressure to a level below the setpoint pressure.