GB2582001A - Method to determine the torque of a spark ignition engine - Google Patents

Abstract

Disclosed is a method of determining the torque output of a vehicle’s engine based on an equation which has the following variables: a fuel lower heat value, LHV; he engine volumetric efficiency, effvol; the manifold pressure, MAP; the manifold temperature, MAT; the air fuel ratio at stoichiometric conditions, AFR_Stoich; the optimum Lambda value that maximises torque, λopti; the engine capacity, Displ; a constant, r; and the engine thermal efficiency, eff_therm. The equation is: The spark efficiency of the engine may be determined from the parameter of engine speed which may be derived from the engine torque output. The method can be used to detect unwanted vehicle acceleration even in the event of sensor failure.

Description

METHOD TO DETERMINE THE TORQUE OF A SPARK INGNITION

ENGINE

TECHNICAL FIELD

This relates to a method of determining the torque generated in a spark ignition combustion engine.

BACKGROUND OF THE INVENTION

There are various prior art methods of monitoring and determining torque in spark ignition vehicles. Patent DE19916725A1 describes a method for torque monitoring in the case of Otto engines in motor vehicles. Patent US7289899B2 describes a method and system for calculating brake torque produced by a turbocharged engine. 1JS6704639B2 describes a method of calculating engine torque. US8050841B2 describes security for engine torque input air-per-cylinder calculations The two main problems with the prior art are: that some methods only use one or two sensors to estimate torque which make it inaccurate and proves difficult to detect small torque deviations. Alternatively, prior are systems uses more sensors but does not include fail safe mechanisms for the torque estimator to continue to provide sufficient accuracy in the event of a failure on one of the used sensor is detected.

So in other words prior art using only one or two sensors has got a limited accuracy. That is solved by setting higher limit before detecting unwanted torque production thus compensating for accuracy loss by lowering accuracy requirement. However, this is preventing the system to detect small torque deviation. Prior art is also using desired set points for the actuators to evaluate estimated torque but this is a speculative approach on what will be the engine actual torque and this assumes the actuators deliver the desired set points.

Prior art uses plausibilisation mechanism on intake manifold pressure sensor or air flow sensor through the throttle position but these are the only sensor having fail safe mechanism for the torque estimator to continue to provide sufficient accuracy despite failure of that sensor.

Prior art also captures injected fuel quantity to estimate the air flow then finally estimate the torque based on that. This method is based on the assumption the engine control achieves a stoichiometric combustion which is not the case for example during engine warm-up. As a consequence, that method cannot estimate the torque in all engine conditions.

SUMMARY OF THE INVENTION

In one aspect is provided a method of determining the torque (Tq) output of a vehicle engine using the following equation: MAP ottispl LHV * (enrol r tMAT AFR stoich Aopti) Tq - * eff therm 44Th where LHV is the fuel lower heat value; effvoi is the engine volumetric efficiency; MAP is the manifold pressure; MAT is the manifold temperature; AFR Stoich is the air fuel ratio at stocihiometric conditions Aopti is the optimum Lambda value that maximizes torque; Displ is the engine capacity; -287 J/kg/K; mmolgas eff therm is the engine thermal efficiency.

The torque (Tq) output may be determined from the following equation: MAP tDispl (ef f vat r tMAT LHV * AFR Match* Aping) - * eff therm * eff spark Tq 1 *Pi where eff spark is the spark efficiency.

Thermal efficiency (eff therm) may be determined from the parameters of manifold or engine temperature, and engine speed.

Aopt may be assumed to be stoichiometric.

Spark efficiency may be determined from the parameter of engine speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 shows a simplified block diagram of a method of determining torque.

DESCRIPTION OF THE PREFERRED END3ODEVIENTS

The problem of inaccuracy impeding the detection of small torque deviation of an internal combustion engine is solved by multi-sensor torque estimation according

to examples below.

The problem of providing an accurate torque estimation in case of a malfunctioning sensor is solved by cross-check plausiblisation of sensors and arbitration between sensors and/or recovery sensor models in order to continue to provide an accurate torque estimation.

10 15 20

Prior Art

It is known in prior art system to estimate fast indicated torque using the equation 1 below.

fvol MArPrihDA'TsPr LT-IV( APR starch Ad" carbcontlem5-4cara scav any) Tq indicated fast - * eff comb * eff therm * eff spark with: LHV Fuel lower heat value eff©i Engine volumetric efficiency MAP Manifold pressure MAT Manifold temperature Ades Lambda that is injected, part of it will be condensated on walls or will go away if scavenging.

Displ Engine displacement mmulgas Qtarbcond Amount of fueling that condensate on walls during cold ens start and that may not participate to combustion (2 Ca rbscaveng eff comb Correction factor for combustion efficiency when lambda is not at a stochiometric value eff therm Thermal losses eff spark Spark efficiency This equation can provide very accurate estimation of actual torque, up to only few Newton meters error. Achieving that accuracy level demands high complexity of modelling, development and tuning This complexity adds for malfunctions 4 *Tr -287 J/kg/K Amount of fuel in g that will go out of cylinder in scavenging situation sources of the final torque estimator because it would be based on a too large number of inputs.

Invention In one aspect is a method of determining torque which has a reduced number of inputs while keeping sufficient accuracy for torque monitoring.

In one aspect is provided torque estimator equation simplified enough to ensure resilience to one sensor malfunction. In one example the troque of an engine is determined according to the following simplified equation 2: MAP Wisp' LHV (e f fra I r MAT AFR_stoichs Aupti) Tq (indicated slow) fast - * eff therm 4 -Pi LHV Fuel lower heat value. This may be assumed. In advanced systems there may be on board systems to determine this from the fuel (e.g. detection systems for ethanol mix/cetane or octane numbers) ef fvot Engine volumetric efficiency. This may be determined from calibration. For volumetric efficiency e.g. 4 dimension mapping may be used with the inputs of i)engine speed ii) -Pressure ratio of Inlet Manifold Pressure/Atmospheric pressure; iii) -position Cam exhaust iv) position Cam intake. Of course this is only applicable to engines fitted with cam phasers. Also if they are fitted on an engine then it is mandatory to consider them in the volumetric efficiency maps. Where cam phaser information is not available the engine vol. efficiency may be estimated form just i) and ii) MAP Manifold pressure MAT Manifold temperature 1-opti This is the Lambda value that produces the most torque It is generally to stoichiometric.

lisp! Engine capacity / (e.g. 1.0L) -287 J/kg/K Mmolgas eff therm Thermal efficiency. This may be determined from estimated thermal losses and e.g. from calibration e.g. from a calibration curve map with e.g. manifold/engine temperature and engine speed e.g as inputs.

AFR Stoic!: Air fuel ratio at stocihiometric conditions Further Refinement In a refined embodient, the torque may be determined from the following equation: MAP *Dispi LHV: (et, vol r *MAT AFR stoich * Ao ' * eff therm * eff spark dq (indicated fast) -4 * Pi P eff spark Spark efficiency This may be determined from calibration e.g. from a calibration curve map.

A) One or more sensor inputs may be used to determine this e.g. 1) Slow Indicated mean effective pressure; -2) Operating mode 3) position Cam exhaust; 4) -position Cam intake 5) engine speed 6) -lambda 7)-coolant temperature; 8) -Manifold temperature; 9)-injection pulse data including split injection pulses data; 10)-injection angle B) The operating mode can be assumed. They can be considered for accuracy reasons without securing them because they will have little influence on torque estimator if they get corrupted. So in one example one can assume normal mode so torque estimator. In one example preferably only the following parameters are used to determine spark efficiency: i) Slow Indicated mean effective pressure; ii) Operating mode; iii) position Cam exhaust; iv) position Cam intake; v) engine speed; vi) coolant temperature; vii) -Manifold temperature C) preferably in a further simplified example only the following parameters are used to determine Spark efficiency: a) Slow (LMEP) Indicated mean effective pressure; b) Operating mode; c) position Cam exhaust; d) position Cam intake; e) engine speed; D) Again c) and d) do not have to be used if not available and operating mode may be assumed thus in a further simplified example only the slow IMEP and the engine speed are used as parameters are used to determine Spark efficiency In addition optionally the parameter of actual spark angle may be used in the above cases A, B, C, D above.

As far as slow [MEP is concerned this is an internally computed parameter and may be provided directly by the torque estimator itself, so in the above the value of IMEP may be considered not to be an (external) parameter which is required. Thus in sub-examples A, B, C, D, the value of IMEP can be disregarded so in example D) only external input is engine speed in a simple example.

Torque and IMEP are equivalent so slow Torque/IMEP is just an intermediary step in the fast torque/LMEP calculation MAP,Displ LHV (effvol* r.MAT APR stoich,Aopti ' 4 *Pi Tq_indicated_slow * eff therm eff spark = f(Tq indicated slow, Engine speed) then Tqindicated_fast = Tq_indicated_slow eff spark MAP t Dispi LI1V* ("mil r *VAT) AFR_stoich Aopti 4 *Pi In combustion engine, assuming it has stoichiometric ratio, the produced torque mainly (and this is really simplistic) depends on the air trapped inside cylinder and spark angle applied. Changing air inside a cylinder is slow. It takes up to few seconds. Torque achievable by air inside cylinder is called slow torque. If a particular spark angle is the best one for torque (this is called maximum best torque spark angle or MBT) then engine torque = slow torque because spark efficiency =1 because spark angle is best one for torque. Changing spark angle is a faster command. It can be changed at each cylinder revolution. Torque achieved according to actual spark angle is called fast torque. In some conditions if the spark angle used is not the best one for torque so engine torque = slow torque(achievable by air) * spark efficiency(actually achieved by spark) with spark efficiency<1.

In one example a map (2D calibration) map is used to evaluate spark efficiency.

Spark efficiency is defined as spark efficiency = f(spark angle at mbt -actual spark angle) . Having a secured torque is then all about determining the spark at mbt and actual spark. Spark mbt can be mapped (2D calibration) in e.g. a safe memory area. These calibrations may depend on a lot of variables as described above.

In an example spark mbt = f( engine speed, slow IMEP/torque). The actual spark angle may be read back or computed from hardware.

In one aspect a plausibility test may be provided which comprises comparing spark feedback reading of coil command with demanded spark. In another test it is checked whether the spark angle is inside the expected range i.e between minimum spark for not stalling the engine and maximum brake torque spark.

* eff therm * eff spark.

These tests are important to have a fully secured FAST indicated torque.

To secure that hardware feedback we need a plausibilisation that is as follows: It is assumed that the engine operates at stoichiometric conditions and so the elf comb has disappeared from equation 1.

In examples, torque estimation determination is based on the following inputs/parameters which may be derived from actual sensors or models.

i) Engine speed; ii) Atmospheric pressure; This is optional. The atmospheric pressure may be fixed or assumed e.g. at average or a general sea level value. Alternatively in refined embodiments a pressure sensor may be used or the pressure determined from GPS (with optionally GPS plus weather data maps including pressure at the location) . It is preferable to use estimates of pressure at altitudes or use GPS and other data we have no choice than use this. Typical example: sea level: Patmo = 1013 hPa, High altitude (4700m) 20: Patmo = 580 hPa.

iii) Intake manifold pressure (MAP); iv) Intake manifold temperature (MAT) . v) Intake and exhaust cam position angle (if applicable i.e. this is optional) Cam phaser are not fitted on every engines (even this is becoming quite rare not to have both intake + exhaust phasers). Examples are applicable to all type of engines (no cam phasers or one cam phasers or both cam phasers if fitted==applicable here) vi) Engine temperature vii) Slow (IMEP) -this may derived from a model. 30 Other In providing the above parameters for such simplified torque estimation; in refined embodiments for improved robustness (e.g, resilient to a sensor failure) there is for one or more sensors a cross-check plausiblisation and arbitration and/or recovery method or model.

The cross-check plausiblisation and arbitration and/or recovery models used in the application example are the following.

The engine speed may be computed through more than three available sources (these could be could be crank sensor, intake and exhaust cam sensors, combination between vehicle speed and transmission ratio). After correlation checks, an arbitration mechanism selects the most plausible and accurate inputs to be used as source of the engine speed information.

Figure 1 illustrates this and shows a simplified block diagram of a method of deteminging torque from e.g. sensor inputs. A main physical sensor is input A to a plausibility check block 1 along with optionally the inputs B from one or more other sensor/or indications of enviromental conditions. Block 1 checks whether the sensor input agrees with the expected sensors input computed or estimated from the one or more other sensors., and thus gives a plausibilty output D which may be an indication that the actual sensor output A is plausible or not. Optionally or alternatively or additionally a model 2 may be provided which models the parameter in respect of the sensor. Again this parameter provided by the model can be compared with the actual sensor input in block 3, and in embodiments depeding on the output D from plausibility block 1 various conclusion or indications are made. In one example, in block 4 a value of the parameter E which is a sensor failure resilient parameter value is determined. This may be the actual value A if the plausiblity check in 1, i.e. result D concludes the actual sensor value is plausible. Or if not plausible the value C from the model is used to provide E. E is then used to compute torque in block 5.

Atmospheric pressure sensor information may be correlated with the boost and exhaust pressures in non-boosted conditions. According to the result, an arbitration mechanism may be used to determine the value to use. The intake manifold pressure may be correlated with a modelization of the pressure based on the throttle position and boost pressure then compared to the sensor value. If the sensor value does not match the model, an environmental check is used to determine which information is correct and use it. If the environmental check fail, the highest pressure value of the two will be used. The intake manifold temperature is correlated with a modelization of the temperature based on boost temperature and then compared to the sensor value. Tithe sensor value does not match the model, an environmental check is used to determine which information is correct and use it. Tithe environmental check fail, the lowest temperature information will be used.

The intake and exhaust cam position is correlated with then current engine speed and the reference default mechanical cam position. If the signal is not plausible, the default mechanical position will be used instead as a recovery value.

The engine temperature information is correlated with oil and water temperature sensors. It the signal is not plausible, a warm-up engine temperature model will be used as a back up The initial value of the model is based on a average value of the engine-related temperature sensors used at start-up.

As an example of application of the torque estimator, we have secured our torque estimation from its inputs acquisition down to its output calculation, we can safely use it to detect undesired torque even in case of one sensor malfunction.

Used in the context of a safety monitoring and compared to prior art this torque estimator can detect any unwanted torque production leading to a vehicle unwanted acceleration even in case of one sensor malfunction.

The advantage of this invention is that smaller torque deviations are detected.

Furthermore, all sensors are covered against malfunctions which could cause the unwanted acceleration of being undetected

Claims (5)

1. CLAIMS1. A method of determining the torque (Tq) output of a vehicle engine using the following equation: LHV * (off vol MAri:MDAiTsPi APR stoich 'Topa) - * eff therm Tq 4 *Pi where LHV is the fuel lower heat value; effvoi is the engine volumetric efficiency; MAP is the manifold pressure; MAT is the manifold temperature; AFR Stoich is the air fuel ratio at stocihiometric conditions.Aopti is the optimum Lambda value that maximizes torque; Displ is the engine capacity; -287 J/kg/K; Mmolgas eff therm is the engine thermal efficiency.
2. 2. A method as claimed in claim 1 wherein the torque (Tq) output is determined from the following equation: AFR_stoich Appti * eft, therm MAP 4Dispi eff spark 1,HV * e f f vat mAT) where eff spark is the spark efficiency.
3. 3. A method as claimed in claims 1 or 2 where thermal efficiency (eff therm) is determined from the parameters of manifold or engine temperature, and engine speed.
4. 4 A method as claimed in claims 1 to 3 whereassumed to be Aopti stoichiometric.
5. 5. A method as claimed in claims 1 to 4 where spark efficiency is determined from the parameter of engine speed.