Generic Engine

Internal combustion engine with throttle and rotational inertia and time lag

Library:
Simscape / Driveline / Engines & Motors

Description

The Generic Engine block represents a general internal combustion engine. This block is a suitable generic engine for 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 the engine fuel consumption rate based on the fuel consumption model that you choose. Optional speed and redline controllers prevent engine stall and enable cruise control.

Engine Speed, Throttle, Power, and Torque

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

The block evaluates engine power demand as a function of engine speed, 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.

Engine Power Demand

The engine power is nonzero when the speed is limited to the operating range, Ω_min ≤ Ω ≤ Ω_max. The absolute maximum engine power P_max defines Ω₀ such that P_max = g(Ω₀). Define w ≡ Ω/Ω₀ and g(Ω) ≡ P_max·p(w). Then p(1) = 1 and dp(1)/dw = 0. The torque function is:

τ = (P_max/Ω₀)·[p(w)/w].

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

p(w) = p₁·w + p₂·w² – p₃·w³

that satisfies

p₁ + p₂ – p₃ = 1, p₁ + 2p₂ – 3p₃ = 0.

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:

$w_{\pm} = \frac{1}{2} (- p_{2} \pm \sqrt{p_{2}^{2} + 4 p_{1} p_{3}}) .$

For the engine power polynomial, there are restrictions on the polynomial coefficients p_i to achieve a valid power-speed curve. If you use tabulated power or torque data, the corresponding restrictions on P(Ω) apply.

Typical Engine Power Demand Curve

Determine the speed and power, w = Ω/Ω₀ and p = P(Ω)/P₀, and define the boundaries as w_min = Ω_min/Ω₀ and w_max = Ω_max/Ω₀. Then:

The block restricts the engine speed 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_min) ≥ 0. If you use the polynomial form, this condition is a restriction on the p_i:
p(w_min) = p₁·w_min + p₂·w²_min – p₃·w_min³ ≥ 0.
The engine power at maximum speed must be nonnegative: p(w_max) ≥ 0. If you use the polynomial form, this condition is a restriction on w_max: w_max ≤ w₊.

Engine Power Forms for Different Engine Types

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

Power Demand Coefficient	Engine Type
Power Demand Coefficient	Spark-Ignition	Diesel
p ₁	1	0.6526
p ₂	1	1.6948
p ₃	1	1.3474

Idle Speed Controller Model

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

$Π = \max (Π_{i}, Π_{c})$

and

$\frac{d (Π_{c})}{d t} = \frac{0.5 \cdot (1 - \tanh (4 \cdot \frac{ω - ω_{r}}{ω_{t}})) - Π_{c}}{τ}$

where:

Π is the engine throttle.
Π_i is the input throttle (port T).
Π_c is the controller throttle.
ω is the engine speed or crankshaft angular velocity.
ω_r is the idle speed reference.
ω_t is the controller speed threshold.
τ is the 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 part of the equation smooths the time derivative of the controlled throttle. The function limits the controlled throttle 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 it computes the lag.

Redline Controller Model

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_r is the redline speed reference.
ω_t is the redline speed threshold.
τ is the redline time constant.

Performance

To increase simulation speed, set Fuel consumption model to No fuel consumption.

If you select any other option for Fuel consumption model, the block must perform a nonlinear computation. 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.

Assumptions and Limitations

This block contains an engine time lag limitation.

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

Hardware-in-the-Loop Simulation

To improve simulation performance, set the Dynamics > Time Constant parameter to No time constant - Suitable for HIL simulation.

Ports

Input

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`T` — Normalized engine throttle level, unitless
physical signal

Engine torque demand as a fraction of maximum possible torque.

Output

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`P` — Instantaneous engine power, W
physical signal

Power produced by the engine, in W.

`FC` — Fuel consumption rate, kg/s
physical signal

Fuel consumed by the engine, in kg/s.

Conserving

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`B` — Engine block
mechanical rotational

Mechanical rotational conserving port associated with the engine block. This is the base port. The engine block is the physical body that contains the piston cylinders.

`F` — Engine crankshaft
mechanical rotational

Mechanical rotational conserving port associated with the engine crankshaft. This is the follower port of engine. The crankshaft transmits the power generated from the combustion process. Typically, you attach a clutch and transmission at this port.

Parameters

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Engine Torque

`Model parameterization` — Engine modeling parameter selection
`Normalized 3rd-order polynomial matched to peak power` (default) | `Tabulated torque date` | `Tabulated power data`

Engine modeling selection. Choose between these options based on the available data:

Normalized 3rd-order polynomial matched to peak power — Parametrize the engine with a power curve lookup table defined by power and speed characteristics.
Tabulated torque data — Engine is parametrized by a speed–torque table that you specify.
Tabulated power data — Engine is parametrized by a speed–power table that you specify.

`Engine type` — Combustion process to model
`Spark-ignition` (default) | `Diesel`

Internal combustion modeling choice. Either option will cause the block to use the coefficients for that option in the third-order polynomial.