Survey of Advanced Suspension Developments and Related Optimal Control Applications1,2
Section snippets
INTRODUCTION
As is well known, conventional vehicle suspensions achieve the road-induced vibration isolation through passive means such as springs and dampers or shock absorbers. On the other hand, the active suspensions are characterized by a requirement that at least a portion of suspension force generation is provided through active power sources such as compressors, hydraulic pumps, etc. Practical applications of active suspensions have been facilitated by maturing of microprocessors and associated
BACKGROUND
This section summarizes background material needed to formulate the optimal suspension design problem. This includes a brief introduction of an appropriate road input disturbance description, ride performance measure, and an appropriate definition of passive and active suspension actuators. A more detailed account of each of these important background topics is given in recent surveys (Hrovat (1993), Hrovat (1994)); the present section summarizes only the main related aspects from these
OPTIMAL SUSPENSIONS FOR QUARTER-CAR MODELS
Armed with the background information from the previous sections we will now review some of the many findings based on simple, quarter-car or “Unicycle”, 1D vehicle models. These have been the subject of many investigations during the past 30 years. Here, it is the most appropriate to start with the simplest possible, 1 DOF models, which, while neglecting the unsprung masses, still yield some very useful results, forming the bounds for limiting optimal performance of more complex, higher
OPTIMAL SUSPENSIONS FOR HALF-CAR MODELS
There are a number of publications (e.g. Thompson, 1979; Hac, 1986) investigating optimal and suboptimal ride characteristics of half-car, 2D vehicle models, which include both sprung mass heave and pitch modes as shown in Fig. 14. Most of the past work was based on numerical analysis which was used to evaluate optimal active suspension performance at a (usually) single operational point. This was extended by Krtolica and Hrovat (1992), who developed a global analytical solution for the optimal
OPTIMAL SUSPENSIONS FOR FULL-CAR MODELS
In this section we will briefly survey some past and recent full-car, 3D results, and place them in a proper perspective with respect to previously discussed half-car and quarter-car counterparts. Some of the earlier investigations of the optimal 3D suspensions can be found in Barak (1985), Barak and Hrovat (1988), and Chalasani (1986b), where numerical solutions of the corresponding LQ problem were obtained for a few specific operational road/speed conditions. On the other hand, recent
RELATED TOPICS
The objective of this section is to briefly discuss developments in important areas which are directly or indirectly related to the main theme of the present paper. A full survey of the related topics would typically require a separate paper for each, something that is obviously beyond the scope here. However, it is hoped that, while not complete, the following sections will help put the subject of optimal suspension controls in a proper perspective with respect to these related developments,
CONCLUDING REMARKS
Based on the two or three decades of analytical developments, it can be concluded that each of the above discussed vehicle models with increasing complexity had a useful evolutionary role and contributed to subsequent advancements. For example, the analysis based on a simple 1 DOF, quarter-car model established that active suspensions have a potential to substantially improve ride and handling when compared with their conventional, passive counterparts. The resulting optimal structure gave
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- 1
This paper was not presented at any IFAC meeting. This paper was recommended for publication in revised form by Editor Karl Johan Åström.
- 2
Simple, mostly LQ-based optimal control concepts gave useful insight about performance potentials, bandwidth requirements, and optimal structure of advanced vehicle suspensions. The present paper reviews these optimal control applications and related practical developments.