MEE 503 - Unit V

Prof Abraham Sudharson PonrajAsst Prof SENSEVIT ChennaiMEE 503 - Unit VVehicle Motion ControlThe term vehicle motion refers to its translation along and rotation about all three axes (i.e., longitudinal, lateral, and vertical).

Vehicle Motion ControlRotations of the vehicle around these three axes correspond to angular displacement of the car body in roll, yaw, and pitch. Roll refers to angular displacement about the longitudinal axis.Yaw refers to angular displacement about the vertical axis. Pitch refers to angular displacement about the lateral axis.Vehicle Motion ControlElectronic controls have been recently developed with the capability to regulate the motion along and about all three axes. Individual car models employ various selected combinations of these controls.TYPICAL CRUISE CONTROL SYSTEMAutomotive cruise control is an excellent example of the type of electronic feedback control system.The components of a control system include the plant, or system being controlled, and a sensor for measuring the plant variable being regulated. It also includes an electronic control system that receives inputs in the form of the desired value of the regulate variable and the measured value of that variable from the sensor.CRUISE CONTROL SYSTEM

CRUISE CONTROL SYSTEMThe control system generates an error signal constituting the difference between the desired and actual values of this variable.It then generates an output from this error signal that drives an electromechanical actuator. The actuator controls the input to the plant in such a way that the regulated plant variable is moved toward the desired value.CRUISE CONTROL SYSTEMIn the case of a cruise control, the variable being regulated is the vehicle speed. The driver manually sets the car speed at the desired value via the accelerator pedal.Upon reaching the desired speed the driver activates a momentary contact switch that sets that speed as the command input to the control system. From that point on, the cruise control system maintains the desired speed automatically by operating the throttle via a throttle actuator.CRUISE CONTROL SYSTEMThe PI controller is representative of good design for such a control system since it can reduce speed errors due to disturbances (such as hills) to zero.In this strategy an error e is formed by subtracting (electronically) the actual speed Va from the desired speed Vd.

CRUISE CONTROL SYSTEMThe controller then electronically generates the actuator signal by combining a term proportional to the error (KPe) and a term proportional to the integral of the error:

The actuator signal u is a combination of these two terms:

The throttle opening is proportional to the value of this actuator signal.

Cruise Control Block Diagram

Cruise Control Speed Performance

CRUISE CONTROL SYSTEMThe response characteristics of a PI controller depend strongly on the choice of the gain parameters KP and KI. It is possible to select values for these parameters to increase the speed of the system response to disturbance. If the speed increases too rapidly, however, overshoot will occur and the actual speed will oscillate around the desired speed.CRUISE CONTROL SYSTEMThe amplitude of oscillations decreases by an amount determined by a parameter called the damping ratio.The damping ratio that produces the fastest response without overshoot is called critical damping. A damping ratio less than critically damped is said to be underdamped.One greater than critically damped is said to be overdamped.Digital Cruise ControlCruise control is now mostly implemented digitally using a microprocessor-based computer. For such a system, proportional and integral control computations are performed numerically in the computer.The vehicle speed sensor is digital. When the car reaches the desired speed, Sd, the driver activates the speed set switch. At this time, the output of the vehicle speed sensor is transferred to a storage register.Digital Cruise ControlThe computer continuously reads the actual vehicle speed, Sa, and generates an error, en, at the sample time, tn (n is an integer).

A control signal, d, is computed that has the following form:

Digital Cruise ControlThis control signal is actually the duty cycle of a square wave (Vc) that is applied to the throttle actuator (as explained later). The throttle opening increases or decreases as d increases or decreases due to the action of the throttle actuator.Digital Cruise Control

Collision Avoidance Radar Warning SystemAn on-board low-power radar system can be used as a sensor for an electronic collision avoidance system to provide warning of a potential collision with an object lying in the path of the vehicle.As early as 1976, at least one experimental system was developed that could accurately detect objects up to distances of about 100 yards. This system gave very few false alarms in actual highway tests.Collision Avoidance Radar Warning System

Collision Avoidance Radar Warning SystemFor an anti-collision warning application, the radar antenna should be mounted on the front of the car and should project a relatively narrow beam forward. Ideally, the antenna for such a system should be in as flat a package as possible.Should project a beam that has a width of about 2 to 3 horizontally and about 4 to 5 vertically.False AlarmLarge objects such as signs can reflect the radar beam, particularly on curves, and trigger a false alarm. If the beam is scanned horizontally for a few degrees, say 2.5 either side of center, false alarms from roadside objects can be reduced.Same Lane in Curve?In order to test whether a detected object is in the same lane as the radar equipped car traveling around a curve, The radius of the curve must be measured.This can be estimated closely from the front wheel steering angle for an unbanked curve. The scanning angle of the radar beam.Knowing both, a computer can quickly perform the calculations to determine whether or not a reflecting object is in the same lane as the protected car.COLLISION WARNING SYSTEMBetter results can be obtained if the radar transmitter is operated in a pulsed mode rather than in a continuous wave mode.In this mode, the transmitter is switched on for a very short time, then it is switched off. During the off time, the receiver is set to receive a reflected signal. If a reflecting object is in the path of the transmitted microwave pulse, a corresponding pulse will be reflected to the receiver.COLLISION WARNING SYSTEMThe round trip time, t, from transmitter to object and back to receiver is proportional to the range, R, to the object.

Where c is the speed of light (186,000 miles per second). The radar system has the capability of accurately measuring this time to determine the range to the object.

COLLISION WARNING SYSTEM

COLLISION AVOIDANCE SYSTEMA collision avoidance system compares the time needed for a microwave signal to be reflected from an object to the time needed for a signal to be reflected from the ground. By comparing these times with vehicle speed data, the computer can calculate a time to impact value and sound an alarm if necessary.

VEHICLE SPEEDIt is possible to measure the vehicle speed, V, by measuring the Doppler frequency shift of the pulsed signal reflected by the ground.The Doppler frequency shift is proportional to the speed of the moving object.This reflection can be discriminated from the object reflection because the ground reflection is at a low angle and a short, fixed range.REFLECTION FROM AN OBJECTThe reflection from an object will have a pulse shape that is very nearly identical to that of the transmitted pulse. The radar system can detect this object reflection and find R to determine the distance from the vehicle to the object. In addition, the relative speed of closure between the car and the object can be calculated by adding the vehicle speed, V, from the ground reflected pulses and the speed of the object, S, which can be determined from the change in range of the objects reflection pulses.

COLLISION AVOIDANCE SYSTEMThe computer can perform a number of calculations on these data. For example, the computer can calculate the time to collision, T. Whenever this time is less than a preset value, a visual and audible warning is generated. The system could also be programmed to release the throttle and apply the brakes, if automatic control were desired.COLLISION AVOIDANCE SYSTEMIf the object is traveling at the same speed as the radar-equipped car and in the same direction, S = -V, and T is infinite. That is, a collision would never occur. If the object is stationary, S = 0 and the time to collision is:

COLLISION AVOIDANCE SYSTEMIf the object is another moving car approaching the radar-equipped car head-on, the closing speed is the sum of the two car speeds.In this case, the time to closure is

Low Tire Pressure Warning System

Low Tire Pressure Warning SystemIn this scheme, a tire pressure sensor continually measures the tire pressure. The signal from the sensor mounted on the rolling tire is coupled by a link to the electronic signal processor.Whenever the pressure drops below a critical limit, a warning signal is sent to a display on the instrument panel to indicate which tire has the low pressure.Low Tire Pressure Warning SystemDesign Constraints:The link from the tire pressure sensor mounted on the rotating tire to the signal processor mounted on the body.Slip ring.Small radio transmitter mounted on the tire.Low Tire Pressure Warning System

TPMS tire pressure monitoring systems

Movement detectionIn order to optimize the management of this very low power consumption, which is essential to these applications, we must avoid any kind of wastage. The first idea that comes to mind will no doubt be to switch on the TPMS only when the wheel is rotating.Movement detection or not movement detection??TPMS without movement detectionFor simple financial reasons (the cost of movement detection circuits), some TPMS systems do not detect whether or not the vehicle is moving. Thus, these systems are woken up cyclically by watchdog circuits and periodically read the pressure and temperature even when the vehicle is stationary and transmit their values, even when the vehicle is parked. This considerably reduces the life of the battery fitted in a TPMS.TPMS with movement detectionThe TPMS has a battery fitted in it. To extend the battery life, it is really preferable not to switch on the system unless the vehicle is moving. For this purpose, we need movement detection systems, based on either mechanical designs or electronic solutions.TPMS with movement detectionMechanical:Using a metal ball associated with a contact which switches on the TPMS when a certain centrifugal force is reached along the radial axis of the wheel. In other words, when a certain linear velocity, and therefore an angular velocity, is reached.Limitation:These systems have (lower) limits which are directly dependent on the minimum angular velocities required to make this contact And are consequently dependent on the rim diameters, the reliability of the contacts, etc.

TPMS with movement detectionElectronic:Electronic movement detection device to achieve a longer life for the battery and therefore for the whole system.The rotation of the wheel is detected by detecting the synchronous magnetic flux of the movement of the wheel.An accelerometer is placed inside the TPMS, to measure the acceleration at the position of the valve.Locating the wheelsIf the information is to be of any practical use for the driver, he must able to locate the wheel that it comes from (right-hand front, left-hand back, etc.), and this must be done :

Dynamically (the vehicle must move for a minimum period to enable the system to correctly initialize the location of the wheels with respect to the vehicle).(OR) Statically, in other words, without any need to move the vehicle in order to carry out this wheel location survey.Locating the wheelsNo location:In order to avoid the complexity and cost of this electronic wheel location system, some companies make the economic choice to initialize the vehicle and its wheels in the factory, on the production line. This is done during a special learning phase, by creating an absolute one to-one mapping between a wheel and its location on the vehicle.Everything being based on the fact that each integrated circuit in the TPMS has a unique serial number.Locating the wheelsWith Location:The above problems must be resolved if we wish to allow for the fact that a user can swap the wheels or carry out any of the other operations mentioned above on his vehicle, at his own home, at the weekend. Locating the wheelsSeen from the valve, the directions of rotation of the front right-hand and front left-hand wheels are different (the same applies to the rear wheels):Movement takes place in the trigonometric direction or in the opposite direction with respect to a fixed reference point. A second inductance L2 can be positioned on the X-axis (axis of the tread), in quadrature with the inductance L1 mentioned previouslyLocating the wheels

Locating the wheelsWhen the wheels rotate, the two inductances L1 and L2 deliver voltages which, because of their relative position (90), are in quadrature.With L1 leading L2 for one wheel and L2 leading L1 for the other wheel. Thus, by making a relative measurement of the phases of the signals from L1 and L2, with the inductances kept in the same position in the TPMS, Using the sequence of movement of the voltages from L1 and L2, it is easy to determine which is the right-hand wheel and which is the left-hand one.Locating the wheelsAnother system can be considered, for example the one detecting the different degrees of fading of the propagation of the UHF signals obtained from the wheels, due to the mechanical shape of the vehicle.Given that each integrated circuit has a unique number (identifier), it becomes easier to mark the messages sent by each wheelIn static mode (when the vehicle is stationary).In this case, the TPMS must be operated without movement detection.After contact is made, the TPMS is woken up via an external signal, for example by sending a special message via one of the aforesaid inductances but at a higher frequency.A three-dimensional (3D) system is available, in order to make it possible to communicate with the TPMS at all times, even if the wheel has been taken completely out of its housing nd the valve on the rim is at the opposite end from the base station controlling the communication.