Prior Art
Brake proportioning systems for vehicles are generally well-known devices for regulating the rear-to-front brake effort applied to vehicle brakes in response to operator input braking force or motion to prevent premature lock-up of rear wheels of the vehicle during rapid deceleration of the vehicle.
Virtually all multi-axle passenger vehicles in production use some form of brake proportioning valve to regulate the ratio of rear-to-front brake effort to prevent rear wheel lock-up, but these are usually fixed systems that provide a compromise proportioning of brake effort on the basis of an assumed loading of the vehicle.
It is generally recognized that it would be desirable to provide variable brake proportioning ratios in response to vehicle loading to overcome brake proportioning problems encountered with modern passenger vehicles, particularly front-wheel drive vehicles. However, variable load responsive brake proportioning systems that are commercially available or described in prior art literature tend to be complex and costly, which limits their applications in high volume production passenger vehicles. Prior art brake proportioning systems generally involve the use of sophisticated electro-mechanical or electro-hydraulic components specifically designed for heavy-duty trucks, rail vehicles, buses and the like, and are regarded as being too complex and expensive to be cost-effective for use in automobiles or light trucks.
Examples of such prior art designs are described in U.S. Pat. Nos. 3,685,868; 4,093,316 and 4,050,743. In such typical systems, vehicle load distribution is usually detected by an electro-mechanical sensor that generates an analog or digital electric load distribution signal that is processed by a signal processor, including logic circuitry, to vary the ratio of rear-to-front brake effort that will result from operator input application of braking force. These typical systems attempt to constantly monitor vehicle loading and constantly adjust the ratio of rear-to-front braking effort in accordance with proprietary algorithms so as to constantly fine tune the proportioning of brake effort that will be produced when the operator applies input braking force or motion. The proportioning control usually is without regard to vehicle motion or speed, although some brake systems do incorporate anti-skid features that are speed or motion sensitive.
While such prior art systems may be desirable in certain environments, they leave much to be desired from the standpoints of simplicity, cost-effectiveness, reliability and adaptation for high-volume mass production.