J.C. Gerdes

Integrating INS sensors with GPS velocity measurements for continuous estimation of vehicle sideslip and tire cornering stiffness

This paper details a unique method for measuring key vehicle states-body sideslip angle, and tire sideslip angle-using GPS velocity information in conjunction with other sensors. A method for integrating inertial navigation system (INS) sensors with GPS measurements to provide higher update rate estimates of the vehicle states is presented. Additionally, it is shown that the tire sideslip estimates can be used to estimate the tire cornering stiffnesses. The experimental results for the GPS velocity-based sideslip angle measurement and cornering stiffness estimates compare favorably to theoretical predictions, suggesting that this technique has merit for future implementation in vehicle safety systems.

Residual-effected homogeneous charge compression ignition at a low compression ratio using exhaust reinduction

Abstract Studies have been conducted to assess the performance of homogeneous charge compression ignition (HCCI) combustion initiated by exhaust reinduction from the previous engine cycle. Reinduction is achieved using a fully flexible electrohydraulic variable-valve actuation system. In this way, HCCI is implemented at low compression ratio without throttling the intake or exhaust, and without preheating the intake charge. By using late exhaust valve closing and late intake valve opening strategies, steady HCCI combustion was achieved over a range of engine conditions. By varying the timing of both valve events, control can be exerted over both work output (load) and combustion phasing. In comparison with throttled spark ignition (SI) operation on the same engine, HCCI achieved 25–55 per cent of the peak SI indicated work, and did so at uniformly higher thermal efficiency. This was accompanied by a two order of magnitude reduction in NO emissions. In fact, single-digit (ppm) NO emissions were realized under many load conditions. In contrast, hydrocarbon emissions proved to be significantly higher in HCCI combustion under almost all conditions. Varying the equivalence ratio showed a wider equivalence ratio tolerance at low loads for HCCI.

Calculating longitudinal wheel slip and tire parameters using GPS velocity

While tire parameters are quite important to both current vehicle control systems and proposed future systems, these parameters are subject to considerable variability and are difficult to estimate while driving due to the unavailability of absolute vehicle velocity. This paper details a method of generating longitudinal tire force-slip curves using absolute velocity information from the Global Positioning System (GPS). By combining GPS measurements with measured wheel speeds, the effective tire radius and longitudinal stiffness of the tires can be identified using a simple least-squares regression technique. Preliminary results demonstrate the feasibility of the technique, show that the effective radius can be identified with considerable precision and suggest that the identified longitudinal stiffness exhibits noticeable sensitivity to changes in inflation pressure.

Modeling for control of HCCI engines

The goal of this work is to accurately predict the phasing of homogeneous charge compression ignition (HCCI) combustion for a single cylinder research engine using variable valve actuation (VVA) at Stanford University. Three simple single-zone models were developed and compared with experiment. The difference between the three modeling approaches centered around the combustion chemistry mechanism used in each case. The first modeling approach, which utilized a temperature threshold to model the onset of the combustion reaction, did not work well. However, an integrated reaction rate threshold accounting for both the temperature and concentration did correlate well with experiment. Additionally, another model utilizing a simple two-step kinetic mechanism also showed good correlation with experimental combustion phasing.

Modification of vehicle handling characteristics via steer-by-wire

This paper presents a physically intuitive method for altering a vehicle handling characteristics through active steering intervention. A full state feedback controller augments the driver steering command via steer-by-wire to achieve desired handling behavior. Accurate estimates of vehicle states are available from a combination of the Global Positioning System (GPS) and inertial navigation system (INS) sensor measurements. By canceling the effects of steering system dynamics and tyre disturbance forces, the steer-by-wire system is able to track commanded steer angle with minimal error. Experimental results verify that with precise steering control and accurate state information, a vehicle handling characteristics can be modified to match driver preference or to compensate for changes in operating conditions.

A probabilistic approach to residual processing for vehicle fault detection

This paper presents a probabilistic method for processing and analyzing residuals for the purpose of fault detection. The method incorporates residuals from multiple models using a hybrid dynamic Bayesian network in order to yield a low-cost, complete, diagnostic system. Continuous residuals are used as evidence directly in the network, and this paper discusses options for representing their probability distributions. The Bayesian network is used to model the temporal behavior of the faults, and the assumptions necessary to do this are analyzed. The diagnostic method is demonstrated on a cars handling system and experimental results are presented.

Decoupled control of combustion timing and work output in residual-affected HCCI engines

Homogeneous charge compression ignition (HCCI) is a promising low temperature combustion strategy for internal combustion engines. However, when HCCI is achieved with variable valve actuation (VVA) the lack of a direct combustion initiator and cycle-to-cycle dynamics complicate control of the process. This work outlines a strategy for the simultaneous control of both in-cylinder pressure and combustion timing through the use of an approximately decoupled timing/pressure controller. The decoupling is achieved by controlling peak pressure and combustion timing on separate time scales with different VVA-induced control inputs, inducted gas composition and effective compression ratio, respectively. The paper also details how the strategy can be extended to handle decoupled timing/work output control. Experimental results show that in-cylinder pressure or work output can be controlled on a cycle-to-cycle basis, while combustion timing is slowly varied.

A two-input two-output control model of HCCI engines

This paper outlines a 2-input, 2-state control-oriented system model of the residual-affected homogeneous charge compression ignition (HCCI) process. The combustion timing and peak pressure are the model states, while the inducted gas composition and effective compression ratio are the model inputs. In previous work the authors utilized the self-stabilizing characteristic of residual-affected HCCI to neglect the combustion timing dynamics to arrive at a single-input, single-output dynamic model. In this paper the combustion timing dynamics are explicitly included for two reasons: the resulting model is more accurate and allows the simultaneous, coordinated control of both in-cylinder pressure and combustion timing. Following the model development, the experimental results of an H2 controller are given, demonstrating the utility of the control model outlined

Nonlinear estimation of longitudinal tire slip under several driving conditions

This paper presents an effectively unbiased nonlinear estimation scheme which identifies tire longitudinal stiffness and effective radius using GPS and ABS wheelspeed sensors. This estimation strategy is then used to experimentally identify the longitudinal stiffness and effective radius of a summer tire and a winter tire under several different test conditions. The data clearly shows that there are several important parameters which govern tire longitudinal stiffness behavior in the low slip region. At a minimum, inflation pressure, tread depth, normal loading and temperature have a strong influence on longitudinal stiffness estimates; the change from dry to wet asphalt had the smallest effect on longitudinal stiffness estimates.

A gentle nudge towards safety: experimental validation of the potential field driver assistance system

This paper presents experimental validation of a driver assistance lanekeeping system based on a potential field framework. This system is implemented on a 1997 Corvette modified for steer-by-wire capability. This testbed has no mechanical connection between the hand wheel and road wheels, allowing the lanekeeping system to add control inputs independently from the driver. The potential field framework provides an intuitive approach for combining commands from the controller and driver. The state estimation and lane position errors are obtained using the Global Position System (GPS) and precision road maps. Preliminary experimental data shows that this control scheme performs extremely well for driver assistance and closely matches simulation results, verifying previous theoretical guarantees for safety.