GB2328294A

GB2328294A - Controlling exhaust gas return rate in an internal combustion engine

Info

Publication number: GB2328294A
Application number: GB9814058A
Authority: GB
Inventors: Max Engl; Hong Zhang
Original assignee: Siemens AG; Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 1997-06-30
Filing date: 1998-06-29
Publication date: 1999-02-17
Anticipated expiration: 2018-06-29
Also published as: GB2328294B; DE19727866A1; DE19727866C2; FR2765271A1; FR2765271B1; GB9814058D0

Abstract

EGR rate is controlled not only by signal EGRV_SP acting on an exhaust gas return valve but also by signal THR_SP acting on the throttle valve in the air intake which affects the inlet gas partial pressure downstream of both valves. Torque requirement TQI_REQ is based at least on accelerator pedal value PV and engine speed N at block B1 and a desired EGR return rate EGRR_SP is established therefrom at block B2. Controllers 6 and 62 use this desired rate to determine EGR and throttle valve reductions ARED_EGRV and ARED_THR. These are regulated by regulators 63, 64 based on actual value of the EGR rate EGRR_AV derived by observer B3 from sensed engine conditions N to TEG and block B4 and finally signals EGRV_SP and THR_SP are generated via blocks B8, B9. Blocks B1, B2, B8, B9 can comprise engine maps and block B3 a model of the EGR and intake sections.

Description

X is li 1 1:" 1 2328294 Device for controlling an internal combustion

engine The invention relates to a device for controlling an internal combustion engine, in particular an internal combustion engine with direct injection of the fuel and/or a load control which is to a large extent throttle- free.

There is known from DE 43 32 171 A1 an internal combustion engine having an intake section, in which there is arranged a throttle valve, and having an exhaust-gas return device, which comprises an exhaustgas return valve. There is provided for each cylinder of the internal combustion engine an injection valve, which meters out the fuel directly into the combustion chamber. There is provided a control device, which controls the throttle valve and the exhaust-gas return valve. In operating ranges of the internal combustion engine with exhaustgas return, the throttle valve is brought into a substantially constant partially open position. There additionally takes place either a regulation of the air ratio to the desired value Lambda = 1, in which case the exhaust-gas return valve is provided as a final controlling element, or a control of the returned exhaust gas as a function of the injected amount of fuel or the position of the accelerator pedal or the-amount of intake air.

In this connection, however, the adjustment of the exhaust-gas return rate always takes place only by means of an activation of the exhaust-gas return valve. High exhaust-gas return rates in particular can, however, be established only slowly with the known control device. -The peak combustion temperature during the combustion of the air-fuel mixture in the combustion chamber is reduced by the returned exhaust gas. The higher the proportion of returned exhaust gas, the more the emission of nitrogen oxides is is reduced. The efficiency of the internal combustion engine 1 rises with the quantity of returned exhaust gas as well, because less heat is given off at the cylinder walls and pumping losses are reduced.

There is known from DE 196 31 112 a control device for an internalcombustion engine. In one arrangement described a throttle valve is actuated in a controlled manner by way of a pneumatic valve. A controller is provided, the controlled variable of which is the travel of an exhaustgas return valve (its final controlling element). In another arrangement the controller and a further controller are provided, the controlled variable of which is the degree of opening of the final controlling element, the throttle valve.

According to the invention there is provided a control device for controlling an internal combustion engine having a throttle valve and an exhaust-gas return valve, the control device including a first controller for controlling the exhaust-gas return valve and having the exhaust-gas return rate as the control variable, a second controller for controlling the throttle valve and having the exhaust-gas return rate as the control variable, and a regulator for controlling the throttle valve or the exhaust-gas return valve and having the exhaust-gas return rate as the control variable.

The control device thus controls the exhaust gas return rate using both the throttle valve and the exhaust gas return valve, in contrast to the prior art where only one controlling element is used. Thus, even during an unsteady operation of the internal combustion engine, the respective exhaust-gas return rate can quickly be established. The invention allows the throttle valve to be activated in order to adjust the exhaust-gas return rate. Thus, by appropriate adjustment of an inlet gas partial pressure downstream is of the throttle valve, a very quick alteration of the exhaust-gas return rate can be achieved.

The regulator has a controlled variable which is the exhaust-gas return rate and controls the exhaustgas return valve or the throttle valve. This permits very precise adjustment of the exhaust-gas return rate If the final controlling element of the controller is the throttle valve, a very simple and therefore cheap exhaust-gas return valve can be provided. The exhaustgas return valve can then be provided as a simple on/off valve, without position feedback.

In an advantageous development of the invention, the second controller controls the throttle valve as a function of the engine's rotational speed and the ambient pressure. This has the advantage that the exhaust- gas return rate can be adjusted very quickly, but also precisely. The operating variables rotational speed and ambient pressure are in this case the key influencing variables, with the aid of which an actuating signal for controlling the throttle valve can be established in order to adjust the desired exhaustgas return rate.

Specific embodiments of the invention will now be explained, purely by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows an internal-combustion engine having a control device in accordance with the invention; and Figure 2 shows a block-circuit diagram of the control device.

Elements having the same construction and function are provided with the same reference numerals throughout the Figures.

An internal combustion engine (Figure 1) comprises an intake section 1 having a throttle valve 10, and an 1 4- engine block 2, which has a cylinder 20 and a crankshaft 23. A piston 21 and a connecting rod 22 are allocated to the cylinder 20. The connecting rod 22 is connected to the piston 21 and the crankshaft 23.

There is furthermore provided a cylinder head 3, in which there is arranged a valve drive having at least one intake valve 30, at least one outlet valve 31 and a valve driving mechanism 32a allocated to the or each intake valve 30 and a valve driving mechanism 32b allocated to the or each outlet valve 31. The valve driving mechanisms 32a, 32b comprise in each case a camshaft (not shown) having a transmission device, which transmits the cam travel to the intake valve 30 and the outlet valve 31 respectively. Devices for adjusting the valve travel times and the valve travel path can also be provided. Alternatively, there can also be provided a respective electromagnetic actuator, which controls the valve travel path of the intake valve 30 and outlet valve 31 respectively.

There is furthermore inserted into the cylinder head 3 an injection valve 33 and a spark plug 34. The injection valve 33 is arranged in such a way that the fuel is metered out directly into the inner space of the cylinder 20. The injection valve 33 can, however, also be arranged in such a way that the metering out of the fuel takes place in the intake section 1. The internal combustion engine can also be constructed as a self-igniting internal combustion engine. A spark plug 34 is then not provided and instead of the injection valve 33, an injection pump and an injection nozzle are provided if appropriate. In Figure 1, the internal combustion engine is shown having one cylinder 20. it can, however, also comprise a plurality of cylinders, as usual.

The internal combustion engine further comprises an exhaust section 4, in which there is arranged a catalytic converter 40. The internal combustion engine has an exhaust-gas return device 5 having an exhaustgas return pipe 50, which is led from the exhaust section 4 to the intake section 1. Arranged in the exhaust- gas return pipe 50 is an exhaust-gas return valve 51. The exhaust-gas return valve 51 is constructed as a lifting valve. It can, however, also be constructed as a butterfly valve, for example.

There is provided a control device 6 for the internal combustion engine, to which there are allocated sensors which establish measured values of different measured variables. As a function of at least one measured variable, the control device 6 establishes one or more actuating signals, each of which controls a controlling element.

The sensors are a pedal position sensor 71, which detects a pedal position PV of the accelerator pedal 7, a throttle valve position sensor 11, which detects a degree of opening THR of the throttle valve 10, an air mass meter 12, which detects an air mass flow MAF, and/or an induction pipe pressure sensor 13, which detects an induction pipe pressure MAP, a temperature sensor 14, which detects an intake air temperature TAL, a rotational-speed sensor 24, which detects a rotational speed N of the crankshaft 23, an oxygen probe 41, which detects the residual oxygen content of the exhaust gas and allocates an air ratio LAM thereto, and a position sensor 52, which detects the degree of opening EGRV - AV of the exhaust-gas return valve 51. Depending on the embodiment of the invention, there can be any subset of the above-mentioned sensors, or even additional sensors.

The measured variables include operating variables as well as variables derived therefrom, such as an exhaust-gas temperature TEG, which are established by way of an ignition map interrelationship or by an observer, which calculates estimated values of the operating variables.

The control devices each comprise an actuator and a controlling element. The actuator is an electromotive drive, an electromagnetic drive, a mechanical drive or a further drive known to the specialist. The controlling elements are constructed as throttle valve 10, as exhaust-gas return valve 51, as injection valve 33, as spark plug 34 or as adjusting device for adjusting the valve travel of the intake or outlet valves 30, 31. In the following, the actuators are referred to with the associated controlling element in each case.

The control device 6 is preferably constructed as an electronic engine control. It can, however, also comprise a plurality of control devices, which are electrically conductively connected to each other, for example by way of a bus system.

Figure 2 shows a block-circuit diagram of the preferred embodiment of the control device 6. In a block B1, a desired indicated torque TQI - REQ is established as a function of the accelerator pedal value PV and the rotational speed N. The establishing of the desired indicated torque TQI_REQ preferably takes place by way of a first ignition map, which is dependent on the pedal value PV and the rotational speed N. In an embodiment that provides greater driving comfort, the establishing of the desired indicated torque TQI - REQ takes place additionally as a function of further operating variables, such as the intake air temperature TAL or a cooling water temperature or an oil temperature.

In a block B2, a desired value EGRR SP of the exhaust-gas return rate is established from a second ignition map as a function of the desired indicated torque TQI-REQ and the rotational speed N. The is ignition map values are optimised with regard to the efficiency of the internal combustion engine and with regard to the NOx emissions. An internal combustion engine having direct petrol injection is, in specified operating ranges, thus, for example, in the partial load range, operated with an air-fuel mixture which is inhomogenously very lean and high exhaust-gas return rates (up to 50%). In order to ensure the conversion of the NOx emissions by the catalytic converter 4, the internal combustion engine is, at specified time intervals (for example 1 minute), operated with a homogenous air-fuel mixture and a low exhaust- gas return rate (for example < 10%). The ignition map values in the second ignition map are therefore plotted additionally as a function of a manner of operation of the internal combustion engine - i.e. homogenous or inhomogeneous.

A block B3 comprises an observer which, by forming a physical model of the intake section 1 and the exhaust-gas return device 5, calculates an estimated value EGRMF - MOD of the returned exhaust-gas mass flow through the exhaust-gas return pipe 50, an estimated value EGBP - MOD of an exhaust-gas back-pressure in the exhaust section 4, an estimated value AMP MOD of the ambient pressure and, if appropriate, an estimated value MAP MOD of the induction pipe pressure. Such a model of the intake section 1 is described in WO 96/32579, the contents of which relating to this are herewith included. Such a model of the intake section 1 and the exhaust-gas return device 5 is described in the patent application (not a prior publication) by the same applicant (official file number: PCT/DE97/00529, our reference GR 96 P 1259 P), the contents of which relating to this are included. For this purpose, the model is established from the state equation of ideal gases, the through- flow equation of ideal gases through 8- throttles and a linear association between the. induction pipe pressure and a mass flow in the cylinder 20. The rotational speed N, the air mass flow MAF, the induction pipe pressure MAP, the actual value THR - AV of the degree of opening of the throttle valve 10, the actual value EGRV - AV of the degree of opening of the exhaustgas return valve 51, the intake temperature TAL and the exhaust-gas temperature TEG are input variables of the block B3. If there is no sensor for establishing the exhaust-gas temperature TEG, the exhaust-gas return temperature can also be established from an ignition map as a function of the rotational speed N and a load equivalent variable - for example an injected fuel mass per working cycle of the internal combustion engine or the air mass flow MAF.

In a block B4, an actual value EGRR AV of the exhaust-gas return rate is established as a function of the estimated value EGRMF-MOD of the returned exhaust gas mass flow and the air mass flow MAF. The actual value EGRR AV of the exhaust-gas return rate is preferably calculated with the equation EGRR-AV = EGRAIF-MOD EGRMF-MOD + MAF As a function of the desired value EGRR SP of the exhaust-gas return rate, the estimated value EGBP - MOD of the exhaust- gas back-pressure and the induction pipe pressure MAP in the intake section 1, a first controller 61 establishes a reduced flow cross-section ARED-EGRV at the exhaust-gas return valve 51. There is provided a first regulator 63, the controlled variable of which is the exhaust-gas return rate and the error signal of which is the difference between the desired value EGRR - P and the actual value EGRR-AV of the exhaust-gas return rate.

The regulator is constructed as a PI-controller.

-g- The output signal of the regulator is a correction value.DARED EGRV of the reduced flow cross-section at the exhaust-gas return valve 51.

A block B8 comprises a further ignition map, from which a desired value EGRV - SP of the degree of opening of the exhaust-gas return valve is established as a function of the sum of the correction value DARED and the reduced flow cross-section ARED EGRV. The desired value EGRV - SP of the degree of opening of the exhaust gas return valve 51 is supplied to a position controller (not shown) of the exhaust-gas return valve 51, which generates an actuating signal for the exhaust-gas return valve 51.

There is provided a second controller 62, the controlled variable of which is the desired value EGRR-SP of the exhaust-gas return rate and the input signal of which is a reduced flow cross-section ARED-THR of the throttle valve 10. A very quick adjustment even of high exhaust-gas return rates is achieved by the second controller 62. This is an important advantage if the internal combustion engine in the case of a constant load is operated alternately with inhomogeneous air-fuel mixture and high exhaustgas return rate, and homogenous air-fuel mixture and low exhaust-gas return rate.

In the following, a calculation standard for establishing the reduced flow cross-section ARED - THR at the throttle valve 10 is described. The desired value EGRR - SP of the exhaust-gas return rate can alternatively be calculated according to the equation EGRR-SP = EGRMF EGRMF+AMF where EGRMF is the returned exhaust-gas mass flow.

It is furthermore true that the partial pressures in the induction pipe, i.e. in the intake section 1 (1) downstream of the throttle valve 10, behave in the stati,onary operation in an identical manner to the mass flows. Accordingly:

EGRR-SP PRG PRG PAMB-PFG PFG + PRG MAP MAP (2) applies, where P,,G is a residual gas partial pressure in the intake section 1 and PFG is an inlet gas partial pressure in.the intake section 1. The returned exhaust gases are residual gases.

In a substantially throttle-free operation, a slight pressure drop takes place at the throttle valve 10. The pressure drop at the throttle valve 10 can be established with sufficient accuracy as a function of the rotational speed N. According, the following relation applies:

Kp = MAP =AN) AMP where Kp is a first factor, which is preferably established from an ignition map as a function of the rotational speed N. The equation 3, solved according to the induction pipe pressure MAP, gives the equation MAP = Kp. AMP PFG = AMP. (1 -EGRR-SP. Kp) (1), (2) and (4).

The equation (3) (4) (5) results from the equations In a good approximation, a linear interrelationship between the air mass flow MAF and the inlet gas partial pressure P, in the intake section 1 can be assumed. The following equation thus applies:

1 -11 MA F = KO + KS. PFG (6) where KO is a zero offset and Ks is a gradient. In this connection, the zero of f set KO and the gradient K. are dependent on the rotational speed N, the induction pipe geometry and the travel path of the intake and outlet valves 30, 31.

In order to adjust the air mass flow MAF, an appropriate degree of opening of the throttle valve 10 is to be set. The through-flow through the throttle position in the intake section 1 in the case of the throttle valve 10 is modelled for the subcritical operation by the equation MA P = A PM TTJP 2 X. 1 - A LTP X-1 (MAP) 21x MAP X+1 AMP - (AMP) X R - T with and X adiabatic exponent, R specific gas constant, in which case equation (3) inserted into (8) results in:

X+1 = Kp 21x - Kp x (7) (8) (9) Equation (7) is solved according to the reduced cross-section ARED THR at the throttle valve 10 and the equations (6), (5) and (9) are inserted. In this way, the following equation results for the reduced flow cross- section ARED-THR:

ARED-THR = KO +KS - [AMP(1 -EGRR-SP - Kp)l 2X 1 X-1 R - TAL X + AMP. k. F 21x - Kp x reduced flow cross-section ARED-THR at the throttle The (10) valve 10 is calculated in the second controller 62 in accordance with equation (10). The estimated value AMP-MOD of the ambient pressure is used for the ambient pressure AMP.

There is provided a second control device 64, the controlled variable of which is the exhaust-gas return rate and the error signal input to which is the difference between the desired value EGRR SP and the actual value EGRR - AV of the exhaust-gas return rate. The second control device 64 is preferably constructed as a PI controller. The adjusting input signal of the second control device is a correction value DARED THR of the reduced flow crosssection at the throttle valve 10. The gain of the PI controller is preferably low so that an oscillation of the actuating signal is avoided; at the same time, however, the exhaust-gas return rate is quickly adjusted by the second controller. Thus, a high driving comfort of the motor vehicle in which the internal combustion engine is arranged is achieved.

In a block B9, there is established from an ignition map, as a function of the sum of the correction value DARED-THR and the reduced flow crosssection ARED-THR at the throttle valve 10, a desired value THR-SP of the degree of opening of the throttle valve 10. The desired value THR-SP is supplied to a position controller (generally known and not shown) of the throttle valve 10.

A block B10 comprises a sequencing control, which coordinates the manner of operation of the first and second controller 61, 62 and the first and second control device as a function of the desired value EGRR-SP of the exhaust-gas return rate. The sequencing control occupies logic variables LV - S - I, LV S-II, LV-R-I, LV-R-II with specified values. As a function of the respective value of the logic variable which is allocated to the respective controller or control is device, the respective controller or control device is activated or deactivated, or there is a specified output signal at the output thereof.

In the preferred exemplary embodiment, the sequencing control establishes the values for the logic variables as a function of an actual value EGRR AV of the degree of opening of the exhaustgas return valve 51. So long as the actual value EGRV - AV of the degree of opening of the exhaust-gas return valve 41 is lower than a specified threshold value, only the control device 63 and the first controller 61 are activated. The throttle valve has a substantially maximum degree of opening. The adjustment of the exhaust-gas return rate accordingly takes place in this range by way of the final controlling element, the exhaust-gas return valve 51.

If the actual value EGRV - AV of the degree of opening of the exhaust-gas return valve 51 exceeds the specified threshold value, the second control device 64 and the second controller 62 are additionally activated. A quick adjustment of the inlet gas partial pressure PFO thus takes place, something which leads to an increase in the returned exhaust-gas mass flow through the exhaust-gas return pipe 50.

Ignition maps are established by stationary measurements on an engine test bed or in driving tests.

The invention is not restricted to the exemplary embodiment which is described. It is, for example, unimportant whether the control device is realised as a hard-wired circuit arrangement or, in the form of a program, is processed by a microprocessor in an engine control.

Claims

1. A control device for controlling an internal combustion engine having a throttle valve and an exhaust-gas return valve, the control device including a first controller for controlling the exhaust-gas return valve and having the exhaust-gas return rate as the control variable, a second controller for controlling the throttle valve and having the exhaust-gas return rate as the control variable, and a regulator for controlling the throttle valve or the exhaust-gas return valve and having the exhaust-gas return rate as the control variable.

2. A control device according to claim 1 wherein the regulator controls the exhaust-gas control valve.

3. A control device according to claim 1 wherein the regulator controls the throttle valve.

4. A control device according to any preceding claim wherein the control device further includes a sequencing controller for activating or deactivating the first controller and/or the second controller as a function of at least one operating variable of the internal combustion engine.

5. A control device according to claim 4 wherein the sequencing controller is also for activating or deactivating the regulator as a function of at least one operating variable of the internal combustion engine.

6. A control device according to any preceding claim and further including a rotational speed sensor and a means for monitoring ambient pressure, wherein -is- the second controller activates the throttle valve as a function of the rotational speed and ambient pressure.

is

7. A control device according to any preceding claim, further including an observer for calculating an estimated value of the returned exhaustgas mass flow as a function of at least one operating variable of the internal combustion engine, an air mass meter connected to the observer for detecting an air mass flow and establishing an actual value of the air mass flow, and a means for calculating an actual value of the exhaust- gas return rate as a function of the estimated value of the returned exhaust-gas mass flow and the actual value of the air mass flow.

A control device according to any preceding claim wherein a desi--ed value of an indicated torque at an output shaft of the engine is derived from an accelerator pedal value and in that a desired value of the exhaust-gas return rate is established as a function of the desired value of the indicated torque and the accelerator pedal value.

9. A control device for controlling an internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.

10. An internal combustion engine including a throttle valve an exhaustgas return valve, and a control device according to any preceding claim.