Method for speed control of an internal combustion engine

Abstract

A method for speed control of an engine in a motor vehicle, wherein the engine is connected to a drivetrain via a clutch, wherein an actual speed value and a target speed value are compared, wherein the actual speed value in the drivetrain is detected downstream of the clutch according to the power flow, characterized in that a control variable switching takes place, wherein the coupling of the engine in the drivetrain is used as the criterion for the control variable switching, wherein a distinction is made between decoupling and coupling, wherein the engine in the drivetrain is coupled when a driving gear is engaged and the clutch is closed.

Description

Technical field

[0001] The present invention relates to a method for controlling the speed of an internal combustion engine when used in a motor vehicle. State of the art

[0002] In modern engine control systems for combustion engines used in conventional vehicles, speed control is implemented in the lower load and speed range. At idle, the engine speed is precisely controlled to reduce emissions, minimize fuel consumption, and, most importantly, maintain a constant engine speed despite varying power demands from components such as the air conditioning or alternator. Therefore, functions have been developed to regulate the idle speed of the combustion engine at a constant target speed. The speed controller also operates the combustion engine near idle speed even when the drivetrain is closed, for example, when a manual transmission is in gear. This generates positive drive torque, allowing the vehicle to move at low speeds.This driving condition is frequently used when driving slowly in a traffic jam or in stop-and-go traffic. For modern vehicles, whose combustion engines already exhibit high torque at idle speed, such as diesel engines or turbocharged gasoline engines with corresponding transmission ratios, this driving condition is becoming increasingly important in the so-called driving cycle for evaluating exhaust emissions and fuel consumption, and of course also in real-world driving. However, this driving condition causes the vehicle to jerk, resulting in an uncomfortable ride.

[0003] In other words, when operating a motor vehicle with a closed drivetrain—that is, with the clutch engaged and a gear selected—at low vehicle speeds, the engine often transitions to idle speed. At this point, the idle speed control of the internal combustion engine is activated. This maintains the vehicle speed at a specific level with the drivetrain closed, as long as the necessary actuators for maintaining that speed are not exhausted. However, at higher load or engine speeds, pressing the accelerator pedal does not activate the idle speed control.

[0004] In the automotive industry, the term "powertrain" encompasses all components of a motor vehicle that, through their interaction, contribute to its propulsion. These include, for example, the internal combustion engine, clutches, transmissions, drive shafts, and propeller shafts. However, electric motors, or electric motors in combination with internal combustion engines in so-called hybrid drive systems, can also propel the vehicle.

[0005] German patent application DE 34 37 324 A1 describes a method and a device for controlling the idle speed of internal combustion engines, which includes an anti-jerk circuit. The idle speed control, which is based on comparing a target and actual speed and the resulting control deviation, is supplemented by an analysis of the speed signal. For this purpose, the speed signal is subjected to frequency and amplitude evaluation, and an inference is drawn about engine jerking. The engine speed is then regulated via a control intervention, thus counteracting the jerking. This is intended to prevent engine oscillations, for example, due to cyclic fluctuations in combustion, so that the vehicle can quickly settle down.

[0006] Furthermore, control systems for the longitudinal dynamics of motor vehicles, so-called cruise control systems, are known in the prior art, in which a predetermined vehicle speed is regulated via a speed controller.

[0007] From the patent application DE 10 2007 050 114 A1, a method for controlling the speed of an engine in a motor vehicle with a hybrid powertrain is known, wherein the engine is connected to a powertrain via a clutch and an actual speed value in the powertrain is recorded after the clutch in accordance with the power flow.

[0008] However, a disadvantage of the state of the art is that the control systems lead to unsatisfactory results at lower vehicle speeds.

[0009] Conventional idle speed control systems operate as closed-loop systems. The current engine speed (actual speed) is compared to a target speed, and the difference between these two values ​​is used to generate a control signal. This signal is then used by a controller to actuate an actuator that controls the engine speed. The controller is specifically designed for the control loop, including its controlled system, potential disturbances, and measuring devices. A toothed crankshaft sensor wheel is used to detect the engine speed. Actuators used to control the internal combustion engine's speed can include, for example, a throttle valve, ignition timing, or injection parameters such as injection quantity and timing. Object of the invention

[0010] The present invention is based on the objective of providing an improved method for adjusting the engine speed in the idle range. Solution to the task

[0011] The problem is solved by a method with the features of claim 1; advantageous further developments of the invention are the subject of the dependent claims. Description of the invention

[0012] The invention provides an improved method for enabling convenient engine speed control. In connection with the method according to the invention, the term "engine" can refer to internal combustion engines, electric motors, and electric motors in combination with internal combustion engines, as so-called hybrid drives. The method is described below using the example of an internal combustion engine, without excluding other drive options. For convenient engine speed adjustment, as with conventional speed control systems, an actual value is determined and compared with a target value. Based on the determined difference between the actual and target values, the corresponding parameters of the controller are then determined, and a manipulated variable for controlling an actuator is calculated. The aim is to minimize the difference between the actual and target values ​​or even reduce it to zero. If the internal combustion engine is decoupled from the drivetrain, i.e.,If no gear is engaged in the transmission or the clutch is disengaged, idle speed control is achieved by measuring the actual engine speed via a crankshaft position sensor and comparing it to a target engine speed. Thus, the engine speed is used as the reference variable.

[0013] However, as soon as a gear is engaged and the drivetrain is closed via the clutch, i.e., a connection exists between the internal combustion engine and the drive wheels, the vehicle speed is used as the control variable according to the invention. In contrast to the prior art, the speed control of the internal combustion engine is then not achieved by determining the crankshaft speed, but by determining the wheel speed from the wheel sensors or via the speed sensors arranged in the vehicle transmission. An ABS control unit, for example, can be used for this purpose. This has the advantage that the torsional vibrations of the internal combustion engine caused by the inertia of the vehicle and the drivetrain, as well as by the clutch slippage of the internal combustion engine, are not detected by the wheel sensors or are reduced to a minimum.For controlling the engine speed, a filtered signal in the form of wheel speed or vehicle speed calculated from the wheel speed is available. This eliminates the need for complicated and time-consuming correction methods known from the prior art. As a result, smooth, jerk-free speed control can be achieved in the idle speed range of the combustion engine.

[0014] The inventive method for speed control of an internal combustion engine involves switching the reference and controlled variables. When the internal combustion engine is idling and decoupled from the drivetrain, the idle speed of the internal combustion engine is controlled based on the reference variable engine speed. As soon as a gear is engaged in a vehicle transmission and the internal combustion engine is coupled to the drivetrain via a clutch, the reference variable of the speed controller is switched. The vehicle speed is then used as both the reference and controlled variable, with one or more wheel speed signals being evaluated. In a further embodiment of the invention, speed signals determined at other points in the drivetrain can also be used. However, the speed must be measured downstream of the clutch, corresponding to the power flow. Example of speed control using wheel sensors

[0015] An exemplary embodiment of the method according to the invention is presented here. The accompanying figures show: Fig. 1: a schematic representation of the speed control and Fig. 2: a schematic representation of the control variable switching of the speed control.

[0016] The block diagram, shown in Fig. Figure 1 shows a standard closed-loop control system. The control loop comprises a control unit consisting of a controller and an actuator, a controlled system, and feedback of the controlled variable via a measuring device. The controlled variable is compared to the reference input, the setpoint, within the control unit. The control error, also known as the control deviation, is fed to the controller, which generates a control input for the actuator according to the desired dynamics. The actuator acts as an interface between the controller and the controlled system, influencing the controlled variable. A measuring device measures the actual value of the controlled variable. This measured value is then compared to the reference input via feedback, thus creating a closed-loop control system. Because the system being controlled is dynamic, the controller is subject to special requirements and is typically implemented as a PID controller for conventional speed controllers.For the method according to the invention, depending on the control variable of the speed control, an engine speed of the internal combustion engine is used as the control variable n. SOLL as in Fig. 1 shown, or a vehicle speed is used as the reference variable. The switching of the reference variable from the engine speed n SOLL-MOT to wheel speed n SOLL-RAD This occurs when the condition of a closed clutch and an engaged gear is met, i.e., the internal combustion engine is coupled in the drivetrain, as in Fig. 2 shown. Depending on the reference variable, the measuring device determines a motor speed n. IST-MOT a wheel speed is determined or measured via the wheel sensors. IST-RAD determined. Alternatively, vehicle speeds can also be calculated and used from the rotational speeds as a reference and control variable.

[0017] The in Fig.The block diagram shown in Figure 2 illustrates a switching position as a result of a change in the reference variable n. SOLL-MOT to n SOLL-RAD and the controlled variable n IST-MOT to n IST-RAD under the conditions of a closed clutch and an engaged gear in the transmission.

Claims

[1] Method for speed control of an engine in a motor vehicle, wherein the engine is connected to a drive train via a clutch, wherein an actual speed value and a target speed value are compared, wherein the actual speed value in the drive train is detected downstream of the clutch according to the power flow, characterized by , that a control variable switching takes place, wherein the coupling of the motor in the drive train is used as a criterion for the control variable switching, distinguishing between decoupling and coupling, wherein the motor in the drive train is coupled when a driving gear is engaged and the clutch is closed. [2] Method for speed control according to claim 1, characterized by , that a rotational speed or vehicle speed is used as the reference variable and the measured rotational speed or a vehicle speed calculated from it is used as the controlled variable. [3] Method for speed control according to claim 1, characterized by , that in the case of a motor decoupled in the drive train, a motor speed is used as a reference and control variable. [4] Method for speed control according to claim 1, characterized by , that in the case of a motor coupled in the drivetrain, a speed in the drivetrain corresponding to the power flow after the clutch or a vehicle speed calculated from it is used as a control variable. [5] Method for speed control according to any one of the preceding claims, characterized by , that the rotational speed in the drivetrain, corresponding to the power flow after the clutch, is a gearbox, drive shaft or wheel speed.

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