Internal combustion engine with throttle and rotational inertia and time lag

Simscape / Driveline / Engines

The Generic Engine block represents a general internal combustion engine. Engine types include spark-ignition and diesel. Speed-power and speed-torque parameterizations are provided. A throttle physical signal input specifies the normalized engine torque. Optional dynamic parameters include crankshaft inertia and response time lag. A physical signal port outputs engine fuel consumption rate based on choice of fuel consumption model. Optional speed and redline controllers prevent engine stall and enable cruise control.

By default, the Generic Engine model uses a programmed relationship between torque and speed, modulated by the throttle signal.

The engine model is specified by an *engine power demand*
function *g*(Ω). The function provides the maximum power available
for a given engine speed Ω. The block parameters (maximum power, speed at maximum
power, and maximum speed) normalize this function to physical maximum torque and
speed values.

The normalized throttle input signal *T* specifies the actual
engine power. The power is delivered as a fraction of the maximum power possible in
a steady state at a fixed engine speed. It modulates the actual power delivered,
*P*, from the engine:
*P*(*Ω*,*T*) =
*T*·*g*(*Ω*). The engine
torque is *τ* =
*P*/*Ω*.

The engine power is nonzero when the speed is limited to the operating range, *Ω _{min}* ≤

*τ* =
(*P _{max}*/

You can derive forms for *p*(*w*) from engine
data and models. Generic Engine uses a third-order polynomial form:

*p*(*w*) =
*p _{1}*·

satisfying

*p _{1}* +

In typical engines, the *p*_{i} are positive.
This polynomial has three zeros, one at *w* = 0, and a conjugate pair. One of the pair is positive and physical;
the other is negative and unphysical:

**Typical Engine Power Demand Function**

For the engine power polynomial, there are restrictions, as shown, on the polynomial coefficients

*p*_{i}, to achieve a valid power-speed curve.If you use tabulated power or torque data, corresponding restrictions on

*P*(Ω) remain.

Specify the speed and power as *w* =
*Ω*/*Ω _{0}* and

The engine speed is restricted to a positive range above the minimum speed and below the maximum speed: 0 ≤

*w*≤_{min}*w*≤*w*._{max}The engine power at minimum speed must be nonnegative:

*p*(*w*) ≥ 0. If you use the polynomial form, this condition is a restriction on the_{min}*p*_{i}:*p*(*w*) =_{min}*p*·_{1}*w*+_{min}*p*_{2}·*w*^{2}_{min}–*p*·_{3}*w*_{min}^{3}≥ 0.The engine power at maximum speed must be nonnegative:

*p*(*w*) ≥ 0. If you use the polynomial form, this condition is a restriction on_{max}*w*:_{max}*w*≤_{max}*w*._{+}

For the default parameterization, Generic Engine provides two choices of internal combustion engine types, each with different engine power demand parameters.

Power Demand Coefficient | Engine Type: | |
---|---|---|

Spark-Ignition | Diesel | |

p_{1} | 1 | 0.6526 |

p_{2} | 1 | 1.6948 |

p_{3} | 1 | 1.3474 |

The idle speed controller adjusts the throttle signal to increase engine rotation below a reference speed according to the following expressions:

$$\Pi =\mathrm{max}({\Pi}_{i},{\Pi}_{c})$$

and

$$\frac{d({\Pi}_{c})}{dt}=\frac{0.5\cdot \left(1-\mathrm{tanh}\left(4\cdot \frac{\omega -{\omega}_{r}}{{\omega}_{t}}\right)\right)-{\Pi}_{c}}{\tau}$$

where:

*Π*— Engine throttle*Π*— Input throttle (port T)_{i}*Π*— Controller throttle_{c}*ω*— Engine speed*ω*— Idle speed reference_{r}*ω*— Controller speed threshold_{t}*τ*— Controller time constant

The controlled throttle increases with a first-order lag from zero to one when
engine speed falls below the reference speed. When the engine speed rises above the
reference speed, the controlled throttle decreases from one to zero. When the
difference between engine velocity and reference speed is smaller than the
controller speed threshold, the *tanh* function smooths the time
derivative of the controlled throttle. The controlled throttle is limited to the
range 0–1. The engine uses the larger of the input and controlled throttle values.
If engine time lag is included, the controller changes the input
*before* the lag is computed.

While the idle speed controller determines the minimum throttle value for maintaining engine speed, the redline controller prevents excessive speed based on a maximum throttle input. To determine the maximum throttle value, the redline controller uses the idle speed controller model equation. However, for the redline controller:

*ω*is the redline speed reference._{r}*ω*is the redline speed threshold._{t}*τ*is the redline time constant.

To increase simulation speed, use the default option, ```
No fuel
consumption
```

, for the **Fuel consumption model**
parameter.

If you select any other option for the **Fuel consumption
model**, the block solves a nonlinear equation that is required for
calculating fuel consumption. The block solves the equation even if the
**FC** port, which reports the fuel consumption rate, is not
connected to another block.

When the parameter is set to `No fuel consumption`

, the
block does not calculate fuel consumption, even if the **FC** port
is connected to another block.

This block contains an engine time lag limitation.

Engines lag in their response to changing speed and throttle. The Generic Engine block optionally supports lag due to a changing throttle only. Time lag simulation increases model fidelity but reduces simulation performance.

Port | Description |
---|---|

B | Rotational conserving port representing the engine block |

F | Rotational Conserving port representing the engine crankshaft |

T | Physical signal input port specifying the normalized engine throttle level |

P | Physical signal output port reporting the instantaneous engine power |

FC | Physical signal output port reporting the fuel consumption rate |

Port **T** accepts a signal with values in the range 0–1. The signal
specifies the engine torque as a fraction of the maximum torque possible in steady state
at fixed engine speed. The signal saturates at zero and one. Values below zero are
interpreted as zero. Values above one are interpreted as one.

Port **FC** does not output data when the **Fuel consumption
model** parameter is set to ```
No fuel
consumption
```

.

The table shows how the visibility of some parameters depends on the option that you choose for other parameters. To learn how to read the table, see Parameter Dependencies.

**Engine Torque Parameter Dependencies**

Engine
Torque | ||
---|---|---|

Model parameterization —
Choose | ||

Normalized 3rd-order polynomial matched
to peak power | Tabulated torque
data | Tabulated power data |

Engine type — Choose
| Speed vector | |

Maximum power | Torque vector | |

Speed at maximum power | Interpolation
method — Choose | |

Maximum speed | ||

Stall speed |

**Model parameterization**Select how to model the engine. Choose between these options, each of which enable other parameters:

`Normalized 3rd-order polynomial matched to peak power`

— Parametrize the engine with a power function controlled by power and speed characteristics. This is the default option.`Tabulated torque data`

— Engine is parametrized by speed–torque table that you specify.`Tabulated power data`

— Engine is parametrized by speed–power table that you specify.

**Engine type**Choose type of internal combustion engine. Choose between

`Spark-ignition`

, the default option, and`Diesel`

.Selecting

`Normalized 3rd-order polynomial matched to peak power`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Maximum power**Maximum power

*P*that the engine can output. The default is_{max}`150`

`kW`

.Selecting

`Normalized 3rd-order polynomial matched to peak power`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Speed at maximum power**Engine speed

*Ω*at which the engine is running at maximum power. The default is_{0}`4500`

`rpm`

.Selecting

`Normalized 3rd-order polynomial matched to peak power`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Maximum speed**Maximum speed

*Ω*at which the engine can generate torque. The default is_{max}`6000`

`rpm`

.During simulation, if

*Ω*exceeds this maximum, the simulation stops with an error. The engine maximum speed*Ω*cannot exceed the engine speed at which the engine power becomes negative._{max}`Normalized 3rd-order polynomial matched to peak power`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Stall speed**Minimum speed

*Ω*at which the engine can generate torque. The default is_{min}`500`

`rpm`

.During simulation, if

*Ω*falls below this minimum, the engine torque is blended to zero.`Normalized 3rd-order polynomial matched to peak power`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Speed vector**Vector of values of the engine function's independent variable, the speed Ω. The default is

`[500, 1000, 2000, 3000, 4000, 5000, 6000, 7000]`

`rpm`

.The first and last speeds in the vector are interpreted as the stall speed and the maximum speed, respectively. If the speed falls below the stall speed, engine torque is blended to zero. If the speed exceeds the maximum speed, the simulation stops with an error.

Selecting

`Tabulated torque data`

or`Tabulated power data`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Torque vector**Vector of values of the engine function's dependent variable, the torque

*τ*. The default is`[380, 380, 380, 380, 350, 280, 200, 80]`

`N*m`

.Selecting

`Tabulated torque data`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Power vector**Vector of values of the engine function's dependent variable, the power

*P*. The default is`[20, 40, 78, 120, 145, 148, 125, 60]`

`kW`

.Selecting

`Tabulated power data`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

**Interpolation method**Method to interpolate the engine speed–torque or speed–power function between discrete relative velocity values within the range of definition. Choose between

`Linear`

, the default choice, and`Smooth`

.Selecting

`Tabulated torque data`

or`Tabulated power data`

for the**Model parameterization**parameter exposes this parameter.For more information, see the Engine Torque Parameter Dependencies table.

The table shows how the visibility of some parameters depends on the option that you choose for other parameters. To learn how to read the table, see Parameter Dependencies.

**Dynamics Parameter Dependencies**

Dynamics | |
---|---|

Inertia — Choose
| |

No
inertia | Specify inertia and initial
velocity |

Engine inertia | |

Initial velocity | |

Time constant — Choose
| |

No lag - Suitable for HIL
simulation | Specify time constant and initial
value |

Engine time constant | |

Initial normalized throttle |

**Inertia**Select how to model the rotational inertia of the engine block. Choose between these options, each of which exposes other parameters:

`No inertia`

— Engine crankshaft is modeled with no inertia. This option is the default.`Specify inertia and initial velocity`

— Engine crankshaft is modeled with rotational inertia and initial angular velocity.

**Engine Inertia**Rotational inertia of the engine crankshaft. The default is

`1`

`kg*m^2`

.Selecting

`Specify inertia and initial velocity`

for the**Inertia**parameter exposes this parameter.For more information, see the Dynamics Parameter Dependencies table.

**Initial velocity**Initial angular velocity

*Ω*(0) of the engine crankshaft. The default is`800`

`rpm`

.Selecting

`Specify inertia and initial velocity`

for the**Inertia**parameter exposes this parameter.For more information, see the Dynamics Parameter Dependencies table.

**Time constant**Select how to model the time lag of the engine response. Choose between these options, each of which exposes other options:

`No lag — Suitable for HIL simulation`

— Engine reacts with no time lag. This option is the default.`Specify time constant and initial value`

— Engine reacts with a time lag.Selecting

`Specify time constant and initial value`

exposes other parameters.For more information, see the Dynamics Parameter Dependencies table.

**Engine time constant**Engine time lag. The default is

`0.2`

`s`

.Selecting

`Specify time constant and initial value`

for the**Time constant**parameter exposes this parameter.For more information, see the Dynamics Parameter Dependencies table.

**Initial normalized throttle**Initial normalized engine throttle

*T*(0), ranging between zero and one. The default is`0`

.Selecting

`Specify time constant and initial value`

for the**Time constant**parameter exposes this parameter.For more information, see the Dynamics Parameter Dependencies table.

**Speed threshold**Width of the speed range over which the engine torque is blended to zero as Ω approaches the stall speed. The default is

`100`

`rpm`

.

The table shows how the visibility of some parameters depends on the option that you choose for other parameters. To learn how to read the table, see Parameter Dependencies.

**Fuel Consumption Parameter Dependencies**

Fuel
Consumption | ||||
---|---|---|---|---|

Fuel consumption model — Choose
`No fuel consumption` ,
`Constant per revolution` ,
```
Fuel consumption by speed and
torque
``` , ```
Brake specific fuel
consumption by speed and torque
``` , or
```
Brake specific fuel consumption by speed and
brake mean effective pressure
``` | ||||

No fuel
consumption | Constant per
revolution | Fuel consumption by speed
and torque | Brake specific fuel
consumption by speed and torque | Brake specific fuel consumption by
speed and brake mean effective pressure |

Fuel consumption per revolution | Displaced volume | |||

Revolutions per cycle | ||||

Speed vector | ||||

Torque vector | Brake mean effective pressure vector | |||

Fuel consumption table | Brake specific fuel consumption table | |||

Interpolation method —
Choose |

**Fuel consumption model**Select a model for calculating engine-fuel consumption. Model parameterizations are compatible with standard industrial data. Choose between these options:

`No fuel consumption`

— The default option`Constant per revolution`

`Fuel consumption by speed and torque`

`Brake specific fuel consumption by speed and torque`

`Brake specific fuel consumption by speed and brake mean effective pressure`

Some options expose other parameters. For more information, see the Fuel Consumption Parameter Dependencies table.

**No fuel consumption**The block does not calculate fuel consumption even when the

**FC**port, which reports the fuel consumption rate, is connected to another block. Selecting this option increases simulation speed.**Fuel consumption per revolution**Enter the volume of fuel consumed in one crankshaft revolution. The default is

`25`

`mg/rev`

.Selecting

`Constant per revolution`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Displaced volume**Enter the volume displaced by a piston stroke. The default is

`400`

`cm^3`

.Selecting

`Brake specific fuel consumption by speed and brake mean effective pressure`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Revolutions per cycle**Enter the number of crankshaft revolutions in one combustion cycle — e.g.

`2`

for a four-stroke engine, or`1`

for a two-stroke engine. The default is`2`

.Selecting

`Brake specific fuel consumption by speed and brake mean effective pressure`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Speed vector**Enter vector of engine speeds used in lookup table parameterizations. Vector size must match

**Torque vector size**. The default is`[1000, 2000, 3000, 4000, 5000, 6000]`

`rpm`

. Selecting`Fuel consumption by speed and torque`

,`Brake specific fuel consumption by speed and torque`

, or`Brake specific fuel consumption by speed and brake mean effective pressure`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Torque vector**Enter vector of engine torques used in the lookup table parameterizations. Vector size must match

**Speed vector**size. The default is`[0, 80, 160, 200, 240, 320, 360, 400]`

`N*m`

. Selecting`Fuel consumption by speed and torque`

or`Brake specific fuel consumption by speed and torque`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Fuel consumption table**Enter matrix with fuel consumption rates corresponding to engine speed and torque vectors. The number of rows must equal the number of elements in the

**Speed vector**. The number of columns must equal the number of elements in the**Torque vector**. The default is`[.5, .9, 1.4, 1.6, 1.9, 2.7, 3.4, 4.4; 1, 1.7, 2.7, 3.1, 3.6, 5, 6, 7.4; 1.4, 2.7, 4, 4.8, 5.6, 7.5, 8.5, 10.5; 2, 3.6, 5.8, 6.7, 8, 10.4, 11.7, 13.3; 2.5, 4.8, 7.9, 9.4, 10.8, 14, 16.2, 18.6; 3.1, 6, 10.3, 11.9, 13.8, 18.4, 22, 26.5]`

`g/s`

.Selecting

`Fuel consumption by speed and torque`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Brake mean effective pressure vector**Enter vector of brake mean effective pressure (BMEP) values. The default is

`[0, 250, 500, 625, 750, 1000, 1150, 1250]`

`kPa`

. The BMEP satisfies the expression:$$BMEP=T\cdot \left(\frac{2\pi \cdot {n}_{c}}{{V}_{d}}\right)$$

where:

*T*— Output torque*n*— Number of cycles per revolution_{c}*V*— Cylinder displaced volume_{d}

Selecting

`Brake specific fuel consumption by speed and brake mean effective pressure`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Brake specific fuel consumption table**Selecting

`Brake specific fuel consumption by speed and torque`

or`Brake specific fuel consumption by speed and brake mean effective pressure`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

For the

`Brake specific fuel consumption by speed and torque`

fuel model, enter the matrix with brake specific fuel consumption (BSFC) rates corresponding to engine speed and torque vectors. BSFC is the ratio of the fuel consumption rate to the output power. The number of rows must equal the number of elements in the**Speed vector**. The number of columns must equal the number of elements in the**Torque vector**.For the

`Brake specific fuel consumption by speed and brake mean effective pressure`

fuel model, enter the matrix with brake specific fuel consumption (BSFC) rates corresponding to engine speed and brake mean effective pressure (BMEP) vectors. BSFC is the ratio of the fuel consumption rate to the output power. The number of rows must equal the number of elements in the**Speed vector**. The number of columns must equal the number of elements in the**Brake mean effective pressure vector**.For both fuel-consumption models, the default is

`[410, 380, 300, 280, 270, 290, 320, 380; 410, 370, 290, 270, 260, 270, 285, 320; 415, 380, 290, 275, 265, 270, 270, 300; 420, 390, 310, 290, 285, 280, 280, 285; 430, 410, 340, 320, 310, 300, 310, 320; 450, 430, 370, 340, 330, 330, 350, 380]`

`g/hr/kW`

.**Interpolation method**Select the interpolation method used to calculate fuel consumption at intermediate speed-torque values. Methods are

`Linear`

and`Smooth`

. Outside the data range, fuel consumption is held constant at the last value given in the lookup table. Selecting`Fuel consumption by speed and torque`

,`Brake specific fuel consumption by speed and torque`

, or`Brake specific fuel consumption by speed and brake mean effective pressure`

for the**Fuel consumption model**parameter exposes this parameter.For more information, see the Fuel Consumption Parameter Dependencies table.

**Speed Control Parameter Dependencies**

Speed
Control | |
---|---|

Idle speed control — Choose
| |

Off | On |

Idle speed reference | |

Controller time constant | |

Redline control | |

Redline control — Choose
| |

Off | On |

Redline speed | |

Redline time constant | |

Redline threshold speed |

**Idle speed control**Select speed control model. The options are:

`Off`

— Omit idle speed controller. Throttle input is used directly. This option is the default.`On`

— Include idle speed controller to prevent engine stalling. This option exposes other parameters. For more information, see Idle Speed Controller Model.

**Idle speed reference**Enter the value of the speed reference below which speed increases, and above which speed decreases. The default is

`1000`

`rpm`

.Selecting

`On`

for the**Idle speed control**parameter exposes this parameter.For more information, see the Speed Control Parameter Dependencies table.

**Controller time constant**Enter the value of the time constant associated with an increase or decrease of the controlled throttle. The constant value must be positive. The default is

`1`

`s`

.Selecting

`On`

for the**Idle speed control**parameter exposes this parameter.For more information, see the Speed Control Parameter Dependencies table.

**Controller threshold speed**Parameter used to smooth the controlled throttle value when the engine’s rotational speed crosses the idle speed reference. For more information, see Idle Speed Controller Model. Large values decrease controller responsiveness. Small values increase computational cost. This parameter must be positive. The default is

`1`

`rpm`

.Selecting

`On`

for the**Idle speed control**parameter exposes this parameter.For more information, see the Speed Control Parameter Dependencies table.

**Redline control**Select redline control model. Options include

`Off`

and`On`

.`Off`

— Omit redline controller. Throttle depends only on the idle speed controller. This option is the default.`On`

— Include redline controller to prevent excessive speed. This option exposes other parameters.For more information, see the Speed Control Parameter Dependencies table.

**Redline speed**Enter the value of the speed reference above which the redline control activates. The default is

`5000`

`rpm`

.Selecting

`On`

for the**Redline control**parameter exposes this parameter.For more information, see the Speed Control Parameter Dependencies table.

**Redline time constant**Enter the value of the time constant associated with an increase or decrease of the controlled throttle. The constant value must be positive. The default is

`1`

`s`

.Selecting

`On`

for the**Redline control**parameter exposes this parameter.For more information, see the Speed Control Parameter Dependencies table.

**Redline threshold speed**Specify the width of the region around the redline speed where the controller goes from fully enabled to not enabled. The block uses this parameter for smoothing the controlled throttle value when the engine’s rotational speed crosses the redline speed reference. Large values decrease controller responsiveness. Small values increase computational cost. This parameter must be positive. The default is

`1`

`rpm`

.Selecting

`On`

for the**Redline control**parameter exposes this parameter.For more information, see the Speed Control Parameter Dependencies table.

For optimal simulation performance, set the **Dynamics** > **Time Constant** parameter to ```
No time constant - Suitable for HIL
simulation
```

.

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