Maximum engine torque, general
The maximum engine torque allowed for the engine is stored as a table in memory. The table specifies the highest torque the engine is allowed to generate at various speeds.
Scheme 1
Torque request from pedal exceeding maximum engine torque
In conditions close to wide open throttle when the driver (pedal) requests e.g. 300 Nm at an engine speed of 3000 rpm, while the table for maximum engine torque allows 265 Nm.
In these cases, the maximum engine torque function will limit the driver's request to 265 Nm unless another function, e.g. knock control, is limiting it further.
Torque request from pedal less than maximum engine torque
When the driver presses the accelerator pedal only lightly, a relatively low engine torque will be requested. Suppose the driver (pedal) requests 150 Nm, while the maximum engine torque function allows 235 Nm at the current speed.
In this case, the maximum engine torque function has no effect and the driver's (pedal) request will be fulfilled provided another function does not affect it.
Note. The graph illustrates the maximum torque allowed for the B207L engine variant. Other graphs apply to other engines.
Operating principle, torque limitation
ECM affects throttle area and ignition timing to reduce engine torque during TCS/ESP regulation.
Note. ECM can increase engine torque on request from TCS/ESP but this is covered at another point in the function chain.
Torque limitation, automatic transmission
Engine torque must occasionally be limited for the sake of comfort in gear changing and in certain cases also for reasons of durability.
Scheme 2
Engine torque limitation, bus from TCM
TCM determines the maximum engine torque to be allowed. During gear changing, engine torque is often reduced somewhat for comfort. Torque can also be reduced for reasons of durability.
Engine torque limitation, stalling
Engine torque for a stalling gearbox is limited to 200 Nm to protect the gearbox.
Scheme 3
TCS/ESP torque increase, general
When the drive wheels are rotating too slowly, TCS can request an increase in engine torque so that the wheels can regain their grip and thereby also course stability.
Scheme 4
Likewise, ESP can increase engine torque when the car is skidding in order to counter the skid.
Operating principle, torque increase
ECM affects throttle area and ignition timing to increase engine torque during TCS/ESP regulation.
Note. ECM can reduce engine torque on request from TCS/ESP but this is covered at another point in the function chain.
Knock control engine torque limitation, general
Knock control can limit engine torque in order to protect the engine.
Scheme 5
Maximum engine torque can be limited in case of a fault in the throttle control. Depending on the type of fault, the limit can be set to 170 Nm or 140 Nm.
Scheme 6
The pedal position sensors consist of two potentiometers supplied 5 V from control module pins 29 (A) and 44 (A). The sensors are grounded from control module pins 34(A) and 50(A).
The voltage from sensor 1 is connected to control module pin 12(A) and increases when the pedal is depressed, approx. 0.5-4.5 V.
The voltage from sensor 2 is connected to control module pin 13(A) and increases when the pedal is depressed, approx. 0.3-2 V.
The control module uses the value from sensor 1 as an indicator of the driver's torque request. The value is converted into requested air mass/consumption and constitutes the most important input signal for air mass control.
The value from potentiometer 2 is used to check potentiometer 1. If the values are not in agreement then a fault code will be generated and the pedal sensor will go into limp-home mode.
When the pedal is fully released, the control module adapts the voltage from sensor 1. When the accelerator is fully released, the requested air mass/consumption = 0 and if the car speed = 0 also, the idle speed control will be activated.
Scheme 7
The engine torque must be increased in case of A/C activation or increased electrical load to compensate for the increase in load on the engine.
See also ENGINE TORQUE CONTROL for more information.
Scheme 8
- Throttle motor
The throttle disc is turned by a DC motor via a reduction gear. The motor is supplied from ECM with a PWM signal from pins 46(B), 63(B) and 47(B), 64(B). ECM can turn the throttle disc in both directions, i.e. open and close. A spring strives to keep the throttle slightly open.
Scheme 9
When the throttle control goes into limp-home mode then it is this position that determines the throttle area and thereby controls the air mass/combustion that can enter the engine. Fuel shut-off and ignition timing are used as control instruments in order to control the engine torque. The idling speed is around 900 rpm. The engine will run erratically with low loads due to fuel shut-off. The car can still be driven but performance will be impaired.
Two throttle position sensors are connected to the shaft. The sensors comprise potentiometers supplied with 5V from ECM pins 30(B) and 31(B) and are grounded to ECM pins 34(B) and 35(B).
The voltage from potentiometer 1 is connected to ECM pin 28(B) and increases as the throttle opens (increased area). The voltage from potentiometer 2 is connected to ECM pin 25(B) and drops as the throttle opens (increased area). The sum of the two voltages is therefore always 5V.
The value from potentiometer 1 is used by ECM to detect the current throttle opening (area).
The result of torque control is converted to air mass/combustion. Throttle control converts it to a certain requested value for throttle position sensor 1 and compares this requested value with the current value of the sensor. The difference (deviation) will give rise to a throttle motor PWM of a magnitude and polarity that will turn the throttle until the desired value (area) is obtained. If a major fault arises in the throttle control then it will be shut down and the throttle will go to a position of rest that is determined by a spring. Engine torque can now only be regulated using fuel shut-off and ignition timing.
Scheme 10
When the system's total requested air mass/combustion (engine torque) has been calculated then firstly the throttle and secondly, if necessary (high engine load), turbo control will have to realize it.
Requested air mass/combustion is corrected with the density of the charge air (air before throttle). Thinner air (lower density) gives a greater throttle opening angle (larger area) so that the same air mass/combustion is obtained as with normal air density.
Air density is calculated using the charge air absolute pressure and the temperature.
This value is converted to a certain requested value for throttle position sensor 1 and compares this requested value with the current value of the sensor. The difference (deviation) gives rise to a throttle motor PWM of a magnitude and polarity that will turn the throttle until the desired value (area) is obtained.
The PWM value is finely adjusted if necessary so that the requested position agrees with the current one, i.e. zero deviation.
If the requested air mass/combustion is too high to be treated (attained) only by throttle control then the excess (difference) will be handled by turbo control.
If a safety-related fault should arise in the throttle control then it will go into limp-home mode. The Check Engine symbol will come on immediately and a message will be displayed on SID informing that the engine is running with limited performance.
Note. It is normal that the throttle is not fully open even though the accelerator pedal is fully depressed.
Scheme 11
The airflow from the turbocharger is regulated by a solenoid valve, which controls the exhaust turbine wastegate pneumatically.
The solenoid valve is supplied with current from the main relay and is grounded from control module pin 56 (B) with a 32Hz PWM. The compressor flow increases as the pulse ratio increases.
When the requested air mass/combustion is too great to be regulated by the throttle alone, the turbo control must supply the excess requirement. The excess is converted to a PWM that controls the charge air control valve.
The value of the atmospheric absolute air pressure and the temperature of the intake air are used to correct the conversion. At low atmospheric pressures or when the intake air temperature is high, a greater PWM ratio is required to obtain the same air mass/combustion.
Scheme 12
The control module therefore makes sure that the current air mass/combustion corresponds with the requested. If necessary, the PWM ratio is finely adjusted by multiplying it with a correction factor.
The correction factor (adaptation) is stored in the control module memory and is always included in the calculation of the PWM ratio.
This is to ensure that the current air mass/combustion will correspond with the requested as soon as possible after a change in load. The limit for adaptation is 100%.
Scheme 13
Scheme 14
- Basic calculation of fuel mass/combustion The current air mass/combustion is divided by 14.7 and moved to section 2. The unit is now mg fuel/combustion.
- Compensation In cases of cold engine, short time after start, fast load changes, knocking or high load, the current value is multiplied by a compensation factor.
- Lambda control The lambda control value is multiplied in. The value is moved to section 4.
- Correction for purge Multiply by the value for purge adaptation. The value is moved to section 5.
- Multiplicative adaptation The value from the multiplicative adaptation is multiplied in and the new value moved to section 6.
- Additative adaptation The value from the additative adaptation is multiplied in and the new value moved to section 7.
- Start fuel mass If the engine has not yet started, the start fuel mass is determined.
- Fuel mass/combustion The fuel mass/combustion is the mass of petrol to be added to the engine on each combustion.
- Injector opening time Converts the fuel mass to injector opening time in ms.
- On injection twice/combustion Before the engine is synchronized, i.e. the camshaft position found by means of the ignition system, injection occurs twice per combustion. The injection time calculated in block 12 is divided by two.
- Needle lift compensation The voltage-dependent needle lift time is added to the injection time. This compensates for the delay between activation of the current in the injector coil and supply of the fuel.
- Fuel shut-off Under certain conditions, e.g. on engine braking, car immobilized, the fuel shut-off can apply. The injection time is then zero.
- Selection of fuel shut-off function
- Activation of injector The ECM controls the injector which is currently supplying fuel, and the sequence is controlled by the ignition sequence. The camshaft angle at which injection takes place depends on the prevailing operating conditions.
Scheme 15
The mass air flow sensor grounds the control module input with a frequency that is dependent on the mass air flow. When the mass air flow increases, the frequency will also increase. The control module converts the frequency to grams air/second (g/s).
Most interesting, however, is the air mass that is drawn into each cylinder, as it is to this air the petrol is to be added. The control module registers the air mass drawn in during one engine revolution. As the engine is 4-cylinder 4-stroke, two cylinders must have drawn in air simultaneously during this engine revolution. The air mass passing the mass air flow sensor is divided by two so that the control module will be aware how much each cylinder has drawn in. The unit has now changed to milligrams air/combustion (mg/c).
To achieve lambda = 1, there must be a specific fuel/air ratio, namely 1 kg fuel to 14.7 kg air. As we know how much air has been drawn into each cylinder per combustion, the control module can easily calculate how much fuel is to be injected into the cylinders each time. The milligrams air/combustion is divided by 14.7 and the result is the number of mg fuel/combustion to be injected into the cylinder.
The following text is an account of why the basic fuel quantity must sometimes be adjusted to a leaner, or most often, a slightly richer mixture so that the engine will run smoothly and emissions will be kept within required limits.
Scheme 16
The calculated basic quantity of fuel will enable the engine to run perfectly under normal conditions, i.e. as long as it is warm and the load or rpm does not change. However, the fuel/air mixture must sometimes be corrected for the engine to function well and emissions to remain low under all conditions.
The basic fuel quantity is multiplied by a correction factor which is normally 1.00. If the correction factor is changed, for example to 1.01, the fuel quantity will be increased by 1%. If instead the correction factor is changed to 0.98, the fuel quantity will be reduced by 2%. The closed loop control system is usually disabled if the correction has a value other than 1.00, otherwise the compensation would be corrected by the closed loop system and be ineffective.
Scheme 17
Immediately after starting the engine, the correction factor is slightly over 1 and then falls gradually to 1.00. The extent to which the correction factor exceeds 1 and the time it takes to reach 1.00 again depend on the coolant temperature. On cars with carburetor engines, this function is the choke. The closed loop starting criteria are such that it starts just when fuel enrichment after starting has dropped to 1.00.
Scheme 18
Scheme 19
A sudden load increase causes the mg air/combustion to increase rapidly and it is well known that petrol engines then require a richer mixture. This is because fuel is deposited on the walls of the intake manifold due to the increase in pressure there, and the wet-film thickness increases. The fuel quantity used here must be replaced by a slightly larger quantity of injected fuel, which is achieved by increasing the correction factor by a few percentage points. For example, the correction factor can be increased from 1.00 to 1.03, which gives 3% more fuel.
As soon as the load increase stops, the correction factor returns to its original value.
In the case of a load reduction, the function is reversed. The wet-film deposited on the walls of the inlet manifold thins quickly as the pressure drops. The quantity of injected fuel must then be reduced to avoid a negative effect on emissions and fuel consumption, so the correction factor is reduced by a few percentage points. For example, the correction factor can be reduced from 1.00 to 0.96, giving a 4% reduction in fuel quantity.
When the engine coolant temperature is below 40°C, the closed loop will be disabled during load changes (if it was active). The reason for this is that the closed loop would otherwise compensate. When the engine coolant temperature exceeds 70°C, the closed loop will be active during load changes, as the fuel correction is then so small that the compensation would not affect the running of the engine. The amount that the correction factor is moved from 1.00 in connection with load changes depends on how fast the air mass/combustion changes and on the engine coolant temperature.
On a car with a carburetor engine, the function described above corresponds to the accelerator pump or damper piston.
Scheme 20
Scheme 21
If the engine is knocking, it is corrected by retarding the ignition for the cylinder in question. If knocking persists despite the retardation, the correction factor will be increased. Closed loop will then be deactivated (if it was active) as it would otherwise counter-compensate.
Scheme 22
Scheme 23
When the engine load and speed has reached a certain limit, the correction factor will gradually increase as the load or engine speed increases further. At the same time, the closed loop will be de-activated (if it was active) as it would otherwise counter-compensate. This is to ensure that all the air is consumed during combustion and to keep the combustion temperature under control. The result is increased engine torque and decreased thermal load.
Scheme 24
Scheme 25
The basic fuel quantity has been calculated to give an air/fuel ratio of 14.7:1. The calculation is based on the reading obtained from the mass air flow sensor. Air leaks and tolerances in the mass air flow sensor can affect this calculation. When the fuel quantity is subsequently converted into injection duration, the control module assumes the flow through the injectors to be functioning faultlessly. Tolerances in the injectors and variations in the fuel pressure can affect this calculation.
For optimum operation, the catalytic converters require an air/fuel ratio of exactly 14.7:1. Therefore, the system is fitted with oxygen sensors before and after the front catalytic converter, the front one called oxygen sensor 1 or O2S 1. The oxygen sensor is connected to control module pin 5(B) and is grounded from control module pin 6(B).
In order to supply a voltage quickly after starting, the oxygen sensor must be preheated. The preheating is supplied with B+ from the fuel pump relay via fuse 3 and is grounded via control module pins 40(B) and 57 (B)9. The preheating circuit ground is PWM so that the preheating effect can be regulated.
The control module estimates the exhaust temperature based on load and engine speed. At high exhaust temperatures, preheating is disengaged so that the oxygen sensor is not damaged.
When the exhaust gases pass the oxygen sensor, their oxygen content is measured by a chemical reaction. The oxygen sensor output voltage is proportional to the current oxygen content. The oxygen content describes the composition of the fuel/air mixture. If the engine has a richer mixture than normal (lambda less than 1), the oxygen sensor output voltage will be about 0.9 V. If the fuel mixture is leaner than normal (lambda over 1), the sensor output voltage will be about 0.1 V.
The sensor voltage changes very quickly when lambda passes 1.
The closed loop correction factor is 1.00 when the system is not active. As soon as the closed loop system is activated, the oxygen sensor voltage is allowed to influence its correction factor. If the oxygen sensor produces a voltage of less than 0.50 V, the correction factor will be slowly increased. Conversely, the correction factor will be slowly decreased if the oxygen sensor output voltage exceeds 0.50 V.
The correction factor limits are 0.75 and 1.25 respectively.
The diagnostic tool always shows 0% when closed loop is not active, 25% when the correction factor is 1.25 and -25% when the correction factor is 0.75.
The following conditions must be fulfilled for closed loop to be engaged
Scheme 26
- Engine speed above 500 rpm.
- The engine must have performed 25-200 revolutions since starting. The value is dependent on coolant temperature.
- The oxygen sensor voltage must have passed below 0.3 V or above 0.6 V at some time since starting.
- At idling speed, the engine coolant temperature must have exceeded approx. -10 - +30°C, depending on the starting temperature.
- Under conditions of partial load, the engine coolant temperature must have exceeded approx. -10 - +30°C, depending on the starting temperature.
- Fuel compensation for knocking or high load must not take place at the same time.
- Engine load above 50 mg/c.
- No fuel compensation for load changes when the engine coolant temperature is below 40°C.
Scheme 27
Scheme 28
To be able to diagnose the front catalytic converter, there is an oxygen sensor mounted after it in the exhaust system. This sensor is called oxygen sensor 2 or O2S 2 and is connected to control module pin 7(B) and grounded from control module pin 19(B).
In order to supply a voltage quickly after starting, the oxygen sensor must be preheated. The preheating is supplied with B+ from the fuel pump relay via fuse 3 and is grounded via control module pins 61(B) and 62 (B). The preheating circuit ground is PWM so that the preheating effect can be regulated.
Preheating is activated as soon as the engine coolant temperature exceeds 50°C.
The control module estimates the exhaust temperature on the basis of engine load and speed. If the exhaust temperature is high, preheating will be disconnected to prevent damage to the sensor.
If the catalytic converter is damaged, its ability to absorb oxygen will deteriorate. The normal fluctuations of the closed loop will then be detected by the voltage from oxygen sensor 2 and a diagnostic trouble code will be generated. The diagnosis is performed once per driving cycle.
In addition to the catalytic converter diagnosis, the oxygen sensor value is also used to correct the closed loop for minor faults in oxygen sensor 1.
Optimum emission values are obtained when the voltage from oxygen sensor 2 is 0.6V.
If the voltage is 0.3V, for example, the engine is running slightly lean. The closed loop correction factor will then be held in the rich setting for a certain number of combustions before oxygen sensor 1 is allowed to affect the value again.
Scheme 29
The (Scheme 29) shows the system with vapor recovery (ORVR) and tank leak diagnosis.
The fuel which evaporates in the tank is passed through a pipe to the evaporative emission canister. The active charcoal in the canister absorbs the hydrocarbon vapors. When the engine starts, ambient air is drawn through the canister via the purge valve and a check valve into the intake manifold. The petrol vapors follow and are burned in the engine.
In currentless state, the purge valve is closed. It is supplied from the main relay and controlled with a 16 Hz PWM from control module pin 17(B). For tank leak diagnosis however the frequency is 8 Hz.
Scheme 30
The flow is regulated by the pulse conditions so that is always constitutes a particular proportion of the total flow consumed by the engine.
If the air/fuel ratio of the flow differs from 14.7:1, the closed loop system is affected. However it is not the task of the closed loop system to correct for purge surplus and therefore the purge has a correction factor which is influenced by the closed loop system as soon as the purge begins. The entire lambda control deviation from 1.00 is moved to the purge correction factor, which means that the lambda control fluctuates around 1.00 (0%) even if the purge contains large quantities of hydrocarbon or consists of pure air.
When the purge is not active, a factor of 1.00 is used and the entire fuel error corrected by the closed loop system and the multiplicative and additative adaptation.
The limit value for purge adaptation is 0.75 or 1.25.
The following conditions should be fulfilled for the purge to be engaged
- Lambda control active
- No fuel adaptation in progress, this takes place for 30 seconds every 5 minutes.
- Coolant temperature exceeds 40°C.
- If the charge air temperature is below 15°C, the car speed must exceed 6 km/h. The function is active throughout the drive cycle and reduces the risk of valve noise. The valve leaks more when cold.
- Battery voltage below 16 V.
- No tank leak diagnosis active.
- Engine speed not below nominal idle speed but above 150 rpm.
Diagnosis tool shows 25% when the correction factor is 1.25 and -25% when the correction factor is 0.75.
Scheme 31
Scheme 32
The on-board diagnosis must find a leak in the purge system corresponding to a hole of 0.5 mm diameter.
For this reason, a differential pressure sensor is mounted on the fuel pump cover and a shut-off valve for the atmospheric connection of the evaporative emission canister. When the shut-off valve is closed, a reduced pressure is created and maintained in the tank using the purge valve. Otherwise the system leaks, and a trouble code is set. Diagnosis is performed once per drive cycle.
The pressure sensor is supplied with 5V from the control unit pin 43(A), and grounded through control unit pin 32(A). Depending on the pressure difference between the tank and atmosphere, the pressure sensor gives a proportional voltage to control unit pin 11(A).
The shut-off valve is open in currentless state. It is supplied from the main relay and controlled by control unit pin 2(B).
Engine torque requirement
The control module calculates the necessary engine torque in order to drive the engine and other loads such as the A/C compressor and the generator.
This calculation is the basis for the idling speed ignition timing so that the correct torque is obtained.
Scheme 33
In order to heat the catalytic converter as fast as possible after starting, the ignition will be retarded.
Ignition timing together with a high idling speed means that the exhaust temperature will rise, which, in turn, heats the catalytic converter much faster. The function is active when starting and the coolant temperature is between -8°C and 35°C.
The function is active for up to 2000 combustions at low coolant temperatures and for a shorter period at higher coolant temperatures.
The ignition retardation is dependent on load and engine speed, a typical ignition timing is around 10° after top dead center (ATDC).
Scheme 34
Specifications
Weicon Anti-Seize - 2801120. 120 g jar.
See also:
• INTERIOR LIGHTING AND READING LAMPS, 4D/5D