This paper compares several strategies for air-fuel ratio tran-sient control. The strategies are: A factory-standard look-up table based system (a SAAB Trionic 5), a feedback PI controller with and without feed-forward throttle correction, a linear feed-forward control algorithm, and two nonlinear feed- forward algorithms based on artificial neural networks. The control strategies have been implemented and evaluated in a SAAB 9000 car during a transient driving test, consisting of an acceleration in the second gear from an engine speed of 1500 rpm to 3000 rpm. The best strategies are found to be the neural network based ones, followed by the table based factory system. The two feedback PI controllers offer the poorest performance.

Two virtual sensors are proposed that use the spark-plug based ion current sensor for combustion engine control. The first sensor estimates combustion variability for the purpose of controlling exhaust gas recirculation (EGR) and the second sensor estimates the pressure peak position for control of ignition timing. Use of EGR in engines is important because the technique can reduce fuel consumption and NOx emissions, but recirculating too much can have the adverse effect with e.g. increased fuel consumption and poor driveability of the vehicle. Since EGR also affects the phasing of the combustion (because of the diluted gas mixture with slower combustion) it is also necessary to control ignition timing otherwise efficiency will be lost. The combustion variability sensor is demonstrated in a closed-loop control experiment of EGR on the highway and the pressure peak sensor is shown to handle both normal and an EGR condition.

It is desirable for an engine control system to maintain a stable combustion. A high combustion variability (typically measured by the relative variations in produced work, COV(IMEP)) can indicate the use of too much EGR or a too lean air-fuel mixture, which results in less engine efficiency(in terms of fuel and emissions) and reduced driveability. The coefficient of variation (COV) of the ion current integral has previously been shown in several papers to be correlated to the coefficient of variation of IMEP for various disturbances (e.g. AFR, EGR and fuel timing). This paper presents a cycle-to-cycle ion current based method of estimating the approximate category of IMEP (either normal burn, slow burn, partial burn or misfire) for the case of lean air-fuel ratio. The rate of appearance of the partial burn and misfire categories is then shown to be well correlated with the onset of high combustion variability(high COV(IMEP)). It is demonstrated that the detection of these categories can result in faster determination(prediction) of high variability compared to only using the COV(Ion integral). Copyright © 2004 SAE International.

Estimation of combustion variability can be performed by using ion currents measured at the spark plug. A scheme is here proposed that exploits the potential of using measurements from multiple cylinders to improve the estimation accuracy of combustion variability (measured by the coefficient of variation of IMEP). This is realised by dividing combustion variability into categories and having one classifier running for each cylinder with the ion current as input signal. The final estimate of combustion variability is then formed by a majority vote among the classifiers. This scheme is shown to improve estimation accuracy by up to 15% on measurements taken from highway driving in a production vehicle.

The integration of microcontrollers within mechanical systems is a current trend. However, decreasing the size of the system and satisfying higher precision requirements make it necessary to reevaluate the common signal processing techniques for controller implementations, because limited controller size, computation speed, and power consumption become major topics. In this paper, we demonstrate that serial computations with the most significant digits first, that is, on-line arithmetic, offer an important potential for real-time control. They enable a combination of traditional functions, such as analog-to-digital converters and control data computations. This leads to very efficient controller implementations with small size, high speed, and low power consumption. After a brief description of the requirements and challenges of microsystem controller design, the use of on-line arithmetic for real-time control is proposed. A short introduction to on-line arithmetic is given and control-specific implementation guidelines are presented and finally applied to a simple test system.

Combustion timing control of SI engines can be improved by feedback of the peak pressure position (PPP). However, pressure sensors are costly, and therefore, nonintrusive and cheap ion-current ’soft sensors’ have been suggested. Three different algorithms have been proposed that extract information about PPP from the ion current signal. In this paper, these approaches are compared with respect to accuracy, operational range, implementation aspects, as well as sensitivity to engine load and inlet air humidity. Copyright © 2001 Society of Automotive Engineers, Inc.

In this paper a novel ion current based estimation scheme for the in-cylinder pressure peak position (PPP) is proposed. A reliable estimate is constructed by appropriate signal processing based on local curvatures of the post flame phase of the ion current. The peak-finding algorithm is simple and easy to implement in an engine control unit for feedback control of the combustion phasing. Results on real data, sampled onboard a commercial car are presented. Further, the performance of the algorithm is compared to two state of the art algorithms for PPP estimation from the ion current. The comparison shows that the algorithm presented in this paper outperforms its competitors. Copyright © 2000 Society of Automotive Engineers, Inc.

In the above paper, an example is given, showing that the LQ controller gives an arbitrary small gain margin with respect to variations of the open-loop plant. As a remedy, a dynamic-state feedback is proposed which is claimed to give an arbitrary large gain margin. This is incorrect. In fact, the proposed dynamic state feedback controller does not even stabilize the nominal system.

A pole-projection approach is proposed as a useful tool for multi-objective robust control design. Different load conditions or nonlinearities are considered in the design by simultaneously stabilizing a set of linear models. The idea is to repeatedly project the poles for each model (one at a time) to a generalized stability region until all models are stabilized. Similarly, pole projections are also performed for an auxiliary set of models. Stability of the latter gives guaranteed bounds on different sensitivity functions for the former. The method solves a benchmark problem for which a controller of lower complexity than has been reported before is obtained. © 1999 EUCA.

Proposes a low-complexity virtual sensor for the pressure peak position of the crank angle in a spark-ignited car motor. Establishment of the relationship between pressure peak position (PPP) and produced work; Introduction of ion-current signal and related to the PPP; Description of previously proposed virtual sensors; Presentation of the low-complexity virtual sensor algorithm; Demonstration of the closed-loop control using the virtual sensor.

A pneumatic loudspeaker for intensive sounds is presented. It operates by modulation of air from over- and underpressure reservoirs, as opposed to siren-like loudspeakers that use compressed air only. The symmetric construction makes the behavior more linear both with respect to aperture amplitudes and frequency bandwidth. Therefore, it may be used as secondary source in industrial active noise control problems where generation of large volume velocities are necessary. It is also shown that a Hammerstein model can model the loudspeaker over a wide frequency band. © 2001 EUCA.

A data-driven controller design procedure is proposed in this paper. The controller is based on both an estimated plant model and its estimated uncertainty described by an ellipsoid in parameter space. Desired performance is specified by the speed and the damping of the modeled response. The unmodeled response is rejected by requiring robust performance with respect to a generalized stability region. Moreover, estimation of a disturbance model enables further rejection of the unmodeled response. The methodology is applied to a nonlinear and unstable magnetic suspension system. High performance is achieved for various specifications over a large operational range.

This paper describes the Halmstad University entry in the Grand Cooperative Driving Challenge, which is a competition in vehicle platooning. Cooperative platooning has the potential to improve traffic flow by mitigating shock wave effects, which otherwise may occur in dense traffic. A longitudinal controller that uses information exchanged via wireless communication with other cooperative vehicles to achieve string-stable platooning is developed. The controller is integrated into a production vehicle, together with a positioning system, communication system, and human–machine interface (HMI). A highly modular system architecture enabled rapid development and testing of the various subsystems. In the competition, which took place in May 2011 on a closed-off highway in The Netherlands, the Halmstad University team finished second among nine competing teams.

A power assisted wheelchair combines human power, which is delivered by the arms through the pushrims, with electrical motors, which are powered by a battery. Todays electric power assisted wheelchairs use force sensors to measure the torque exerted on the pushrims by the user. This leads to rather expensive and clumsy constructions. A new design, which only relies on velocity feedback, thus avoiding the use of expensive force sensors in the pushrims, is proposed in this paper. The control design is based on a simple PD-structure with only two design parameters easily tuned to fit a certain user; one parameter is used to adjust the amplification of the user’s force and the other one is used to change the lasting time of the propulsion influence. Since the new assisting control system only relies on the velocity, the torque sensor free power assisted wheelchair will besides giving the user assisting power also give an assistant, which pushes the wheelchair, additional power. This is a big advantage compared to the pushrim activated one, where this benefit for the assistant is not possible.

A minimax approach for multi-objective controller design is proposed, in which structured uncertainty is characterized by multiple discrete-time SISO models. Typical engineering objectives are optimized for all models, such as bounds on different sensitivity functions and time-domain responses. The approach is illustrated by improving the best performing controller of a flexible arm benchmark example.

When walking on inclined ground the biological foot adjusts the ankle angle accordingly. Prosthetic foot users have often a limited range of motion in their ankle which makes walking on hills uncomfortable. This paper describes a system which can autonomously correct the ankle angle to the inclination. The ground angle is estimated using an accelerometer. The angle foot blade to heel is then adjusted with a DC-motor. Since the controller only activates the motor when the foot is lifted and thus not loaded, a small powered system can be used.

A control procedure is proposed for an ankle-footorthosis (AFO) for different gait situations, such as inclinations and stairs. This paper presents a novel AFO control of the ankle angle. A magneto-rheological damper was used to achieve ankle damping during foot down and locking at swing, thereby avoiding foot slap as well as foot drop.

The controller used feedback from the ankle angle only. Still it was capable of not only adjusting damping within a gait step but also changing control behavior depending on level walking, ascending and descending stairs. As a consequence, toe strike was possible in stair gait as opposed to heel strike in level walking.

Tests verified the expected behavior in stair gait and in level walking where gait speed and ground inclinations varied. The self-adjusted AFO is believed to improve gait comfort in slopes and stairs.

An embedded measurement system for foot orthosis during gait is proposed. Strain gauge sensors were mounted on a foot orthosis to give information about strain in the sagittal plane. The ankle angle of the orthosis was fixed and strain characteristics were therefore changed when walking on slopes. With a Fourier series representation of the strain during a gait cycle, ground angle at different walking speeds and inclinations could be estimated with similar accuracy as previous studies using kinematically based estimators. Furthermore, if the angle of the mechanical foot ankle was changed, the sensing technique still could estimate ground angle without need for recalibration as opposed to kinematical sensors. This indicates that embedded strain sensors can be used for online control of future orthoses with inclination adaptation. Also, there would be no need to recalibrate the sensing system when changing shoes with different heel heights.

A portable gait measurement system for foot dynamic analysis is proposed. Portable cheap sensors are suitable in active control rehabilitation equipments such as prostheses and orthoses. A system of one gyroscope and two accelerometers was used to measure the foot movement in the sagital plane. Both ground inclination during stance and foot angle relative to ground during swing are estimated. This enables fast detection of changing environments such as hills and stairs.

A ground angle estimation technique for use on ankle-foot-orthosis AFO, during gait is proposed. Strain gauge sensors were mounted on a foot orthosis in order to give information about strain in the sagittal plane. The ankle angle of the orthosis was fixed. Strain characteristics were therefore changed when walking on slopes. It was investigated if strain information could be used for detection of inclination and estimation of inclination angle. With a Fourier series representation of the strain during a gait cycle, ground angle at different walking speeds and inclinations could be estimated with similar accuracy as previous studies using kinematically based estimators. This indicates that embedded strain sensors can be used for online control of future orthoses with inclination adaptation.

Gait measurement is of interest for both orthopedists and biomechanical engineers. It is useful for analysis of gait disorders and in design of orthotic and prosthetic devices.

In this chapter an algorithm is presented to suit estimation of one foot angle in the sagital plane, independent on gait conditions. Only one gyro is used during swing and two accelerometers are needed for calibration during stance. Also, the sensor placement at the front foot avoids the need for heel strike for stance transition. Stair walking can therefore be studied. From the estimated swing trajectory three different gait conditions: up stair, horizontal and down stair are classified.

An embedded measurement system for foot orthosis during gait is proposed. In this paper strain gauge sensors are mounted on a foot orthosis in order to give information about strain in the sagital plane. The ankle angle of the orthosis is fixed. Strain characteristics are therefore changed when walking on slopes. It is investigated if strain information can be used for detection of inclination and estimation of inclination angle. Also walking speed influence is studied. It is shown that strain sensing only gives significant information about up hill walking. At a known walking speed ground angle can be estimated for up hill walking.

The maximization of biomass productivity in the fed-batch fermentation of Saccharomyces cerevisiae is analyzed. Due to metabolic bottleneck, often attributed to limited oxygen capacity, ethanol is formed when the substrate concentration is above a critical value, which results in a decrease in biomass productivity. Thus, to maximize the production of biomass, the substrate concentration should be kept at the critical value. However, this value is unknown a priori and may change from experiment to experiment. A way to overcome this lack of knowledge is to allow the cells to produce a very small amount of ethanol. This way, the problem of maximizing the production of biomass is converted into that of regulating the concentration of ethanol, for which cell growth can be viewed as a perturbation. A novel adaptive control methodology based on the internal model principle is used to maintain the desired ethanol setpoint and reject the perturbation. Only a single parameter needs to be estimated on-line. Experimental results demonstrate the effectiveness of the proposed control methodology.

A method for robust tuning of individual cylinders air-fuel ratio is proposed. The fuel injection is adjusted so that each cylinder has the same air-fuel ratio in inner control loops, and the resulting air-fuel ratio in the exhaust pipe is controlled with an exhaust gas oxygen sensor (EGO) in an outer control loop to achieve stoichiometric air-fuel ratio. Correction factors to provide cylinder individual fuel injection timing are calculated based on measurements of the ion currents for the individual cylinders. An implementation in a production vehicle is shown with results from driving on the highway. © 2005 SAE International.