Cruise control | EPFL Graph Search

Cruise control (also known as speed control, cruise command, autocruise, or tempomat) is a system that automatically controls the speed of an automobile. The system is a servomechanism that takes over the throttle of the car to maintain a steady speed as set by the driver. Speed control existed in early automobiles such as the Wilson-Pilcher in the early 1900s. They had a lever on the steering column that could be used to set the speed to be maintained by the engine. In 1908, the Peerless included a governor to maintain the speed of the engine through an extra throttle lever on the steering wheel. Peerless successfully used a flyball governor. They advertised their system as being able to "maintain speed whether uphill or down". A governor was used by James Watt and Matthew Boulton in 1788 to control steam engines, but the use of governors dates at least back to the 17th century. On an engine, the governor uses centrifugal force to adjust throttle position to adapt the speed of the engine to different loads (e.g. when going up a hill). Modern cruise control (also known as a speedostat or tempomat) was invented in 1948 by the blind inventor and mechanical engineer Ralph Teetor. He came up with the idea due to being frustrated by his driver's habit of speeding up and slowing down as he talked. A more significant factor in the developing of cruise control was the speed limit imposed in the US during World War II to reduce gasoline use and tire wear. A mechanism controlled by the driver provided resistance to further pressure on the accelerator pedal when the vehicle reached the desired speed. Teetor's idea of a dashboard speed selector with a mechanism connected to the driveshaft and a device able to push against the gas pedal was patented in 1950. He added a speed lock capability that maintained the car's speed until the driver tapped the brake pedal or turned off the system. A 1955 U.S. patent for a "constant speed regulator" was filed in 1950 by M-Sgt Frank J. Riley.

Control of velocity for a linear actuator

Silas Kull

This project was done in the laboratory of integrated actuators (LAI) during the first master semester. It is part of a PhD-work with linear actuators, also called relays, where these actuators are optimized in design and equipped with a speed control during closure and aperture. The aim of this semester project was to find an optimal control algorithm for the closure of a relay. The relay has to follow a specific speed profile in function of position, so that a certain speed can be guaranteed near the contact closure position. To follow this speed profile, which has been developed by the corresponding company, will decrease electrical and mechanical wearout during closure. In this report, different approaches of control are shown and compared. It is also a report that should help as a guide to develop an optimal control for a specific relay. A final conclusion will give some advices on how to design an optimal control.

2010

Modélisation et réglage d'un entraînement à haute performance par un moteur réluctant

Michel Girardin

Usually, each phase of the direct reluctance motor is fed separately by its own inverter producing a squarewave phase current depending on the rotor position. In the present work, a star-connection of the three stator phases is used and the direct reluctance motor is fed by a three-phase switched inverter. The space phasor theory shows that three-phase sinewave currents can produce a constant electromagnetic torque. In this case, the rotating reference frame rotates at half of the rotor speed and in the opposite direction. This command strategy allows to reduce the stator deformation due to the electromagnetic radial force which is very high in this type of motor and which is mainly responsible for the acoustic noise. The electromagnetic torque control is realised by a sliding mode control of the three phase currents. In the rotating reference frame, it is possible to show that the eight commutation states of the switched inverter are placed around an ellipse in the complex plane of the derivatives of the space phasor of the phase current. A study of this ellipse has allowed to determine the maximal torque as a function of the speed for a given continuous voltage. It is important to insure that the torque reference will never exceed this limitation in order to avoid a pullout phenomenon, highly unwanted in the speed control. Despite the fact that the resolver inside the casing of the direct reluctance motor produces a small periodic error, it is accurate enough for the position measurement and to produce the three current references. However, the derivative of the position measurement provides a speed evaluation with such a ripple that the speed control cannot be outstanding. So, for the speed measurement, an additional laser rotary encoder is used. The experimental study in the steady-state mode of the speed control shows the presence of an electromagnetic torque ripple. This is a residual ripple caused by the dissimilarity between the stator poles teeth-shapes and the magnetic saturation effect. Although this torque ripple is rather low compared with the usual command strategy, two methods are proposed in order to compensate it. The first method is based on the use of a correction factor depending on the tooth angle. First, in steady-state conditions, the correction factor is stored off-line in a table. Then it is used in-line as a feedforward disturbance compensation. The second method of reducing the residual torque ripple consists in implementing an observer of variable disturbance. This is a disturbance observer able to determine the frequency content of the torque ripple. For instance, in order to observe the continuous component, the fundamental wave as well as the harmonics 2, 3, and 6, the observer must have ten poles. The main difficulty to deal with such an observer is the fact that each pole moves quickly as a function of the motor speed. So, in order to guarantee the observer stability over a large range of speed, the poles are located dynamically regarding to the motor speed by the way of a discontinuous adaptation of the feedforward coefficients. The theoretical study and the numerical simulation have allowed to formulate some criteria about the way of locating the poles. Experimental results confirm the efficiency of the observer of variable disturbance in order to reduce the electromagnetic torque ripple.

EPFL2000

Modélisation et réglage d'un entraînement à haute performance par un moteur réluctant

Michel Girardin

EPFL2000