Patent Application
20070046098
This invention relates in general to diagnostic systems for antilock/stability braking systems used with commercial vehicles such as tractors, trucks and buses, and in particular to a system and method for providing the operator of a vehicle with information as to whether or not certain components or subsystems associated with an antilock/stability brake system are functioning properly.
Antilock braking systems are electronic systems that monitor and control wheel slip during vehicle braking. Antilock braking systems can improve vehicle control during braking, and reduce stopping distances on slippery (split or low coefficient of friction) road surfaces by limiting wheel slip and minimizing lockup. Rolling wheels typically have much more traction than locked wheels. Reducing wheel slip improves vehicle stability and control during braking, since stability increases as wheel slip decreases. Antilock braking systems can be used with nearly all types of vehicles and can be successfully integrated into hydraulic and air brake systems. The National Highway Traffic Safety Administration (NHTSA) defines an antilock braking system as a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by: (i) sensing the rate of angular wheel rotation; (ii) transmitting signals regarding the rate of wheel rotation to one or more devices, which interpret these signals and generate responsive controlling output signals; and (iii) transmitting those signals to one or more devices that adjust braking forces in response to the signals.
A typical antilock braking system consists of several basic components: an electronic control unit (ECU), wheel speed sensors, modulator valves, and exciter rings. The wheel speed sensors constantly monitor the wheel speed and send electrical pulses to the ECU at a rate proportional to the wheel speed. When the pulse rates indicate impending wheel lockup, the ECU signals the modulator valves to reduce and/or hold the brake application pressure to the wheel(s) in question. The ECU then adjusts pressure to provide maximum braking without risking wheel lockup. The ECU checks itself for proper operation, and if it detects a malfunction or failure in the electrical/electronic system, it may shut down that part of the antilock braking system affected by the problem, or the entire antilock braking system, depending upon the system and the problem. A malfunction indicator lamp may light when the system has been partially or completely shut down.
In addition to a basic antilock braking system, some vehicles include additional systems or subsystems that work in combination with the antilock braking system. These additional systems may provide traction control, vehicle stability, or other benefits and they typically share certain components such as the ECU, modulator valves, pneumatic lines and electrical lines with the antilock brake system. Just as with the antilock brake system, the vehicle's operator should at all times be aware of the operability of these systems when the vehicle is in use. Because the possibility exists that various system components may have been improperly installed or incorrectly connected to one another, a need exists for a means for making the operator aware of problems with the antilock brake system and any associated systems. Some antilock brake systems utilize a so-called “chuff” test to detect incorrectly wired modulator valves. This test is based on the difference in the exhaust sound generated by a correctly wired modulator versus an incorrectly wired modulator. While basically effective for detecting problems with the antilock brakes, this test is not capable of detecting problems with other systems or subsystems associated with the antilock braking system. Thus, a need exists for a system and method for diagnosing the operability of a secondary system, such as a stability system, that works in combination with a vehicle's primary antilock brake system.
Deficiencies in and of the prior art are overcome by the present invention, the exemplary embodiment of which provides an air brake system for use with a vehicle. An exemplary embodiment of this system includes an antilock system component, a stability system component, and a means for determining the operability of stability system component. The antilock braking component further includes: (i) an electronic control unit; (ii) at least one antilock modulator in communication with the electronic control unit; and (iii) at least one brake in communication with the at least one antilock modulator, wherein the at least one antilock modulator controls the at least one brake in response to commands received from the electronic control. The stability system component further includes: (i) a first stability system modulator in communication with the electronic control unit and the at least one antilock modulator; (ii) a second stability system modulator in communication with the electronic control unit and the first stability system modulator; and (iii) an electronic indicator in communication with the electronic control unit. The means for determining the operability of stability system component further includes (i) introducing pressurized air into stability system component; (ii) generating feedback within stability system component by selectively energizing and de-energizing the at least one antilock modulator, the first stability system modulator, and the second stability system modulator in a predetermined sequence; (iii) analyzing the feedback with the electronic control unit to determine the operability of stability system component; and (iv) using the electronic indicator to the display the results of the feedback analysis.
Additional features and aspects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the exemplary embodiments. As will be appreciated, further embodiments of the invention are possible without departing from the scope and spirit of the invention. Accordingly, the drawings and associated descriptions are to be regarded as illustrative and not restrictive in nature.
The accompanying drawings, which are incorporated into and form a part of the specification, schematically illustrate one or more exemplary embodiments of the invention and, together with the general description given above and detailed description of the embodiments given below, serve to explain the principles of the invention.
The present invention relates to a system and method for providing the operator of a vehicle that includes an antilock braking system (ABS), such as the ABS-6 (Bendix Commercial Vehicle Systems LLC; Elyria, Ohio) and a supplemental vehicle stability system (known by such terms as “ESP” or “RSP”), with an audible and/or electronic indicator of the operability of the stability system. By providing a consistent audible “cue” to the operator each time the vehicle is started, the operator learns the “sound” of a properly operating stability system. In addition to the audible indicator, the system and method of this invention utilizes electrical feedback by way of the vehicles brake lights so that the integrity of the stability system can be self-ascertained. Thus, the exemplary embodiment is capable of detecting missing stability system valves, as well as malfunctioning valves, and/or valves that have been incorrectly wired. The exemplary embodiment of this invention includes an ABS component, a stability system component that works in combination with the ABS component, and a diagnostic test method for automatically determining the integrity and operability of the stability system component.
The ABS component of the present invention prevents wheel lock up during braking to maintain the steering and stability of the vehicle and to minimize stopping distance. In general terms, the first basic component of the exemplary ABS are the speed sensors (SS), which are located at the wheels to sense the instantaneous movement of individual wheels and to send an electrical signal directly proportional to the rotational velocity of the sensed wheel to the electronic control unit. The second basic component of the exemplary ABS is the electronic control unit (ECU), which monitors the speed sensor signals and determines when ABS intervention is required and actuates the appropriate pressure modulation valves to optimize the brake pressure. The ECU continually monitors the system to detect and warn the driver of any malfunctions. Failure specific codes are stored in the ECU and can be recalled to diagnose a failure. The third basic component of the exemplary ABS are the pressure modulation valves (PMV), which are located near the brake chambers and are controlled by the ECU to decrease, hold or allow the full applied brake pressure into the brake chamber to control the braking torque at the wheels. The ABS intervenes during braking whenever the available friction between the road and the tire of a monitored wheel is less than the braking force applied to the wheel causing the wheel to decelerate quickly (impending wheel lock).
Regarding the supplemental stability system, during stability interventions, the ECU applies the vehicle's brakes without action on the part of the driver or operator. An exemplary method for accomplishing this function utilizes an ATC valve in the front and rear brake circuits (or axle group(s)) which, when energized, supplies a reference pressure to the corresponding axle. The wheel end modulators are then used to control air pressure flow to each wheel end using the reference pressure supplied by the ATC valve. For the front and rear axle of a truck, bus, or tractor, these modulators are typically pressure modulator valves that are also used for ABS/ATC purposes. In situations where the powered unit may tow other non-powered units (e.g., tractors and trucks that can haul trailers), the stability system may apply the brakes of the towed unit as well. For this application, a PMV valve is attached to the ATC valve (which provides reference pressure to the front (or rear) axle) and modulates and controls pressure delivered to the trailer during stability interventions. A brake light switch is typically included downstream of the output of this PMV. During power-up, the stability portion of the diagnostics energizes the ATC valve to provide the reference (input) air, control the operation of the PMV, and monitor brake light status to validate the integrity of the system. For example, when the ATC is energized, if the PMV is holding, the brake lights are not expected to light. When pressure builds, the brake lights are expected to come on, and when pressure is exhausted, the brake lights are expected to go off. The status of the brake lights is available as an electrical input to the ECU, and the operator does not need to monitor the system. If the vehicle does not include a towed unit (e.g., a bus), the PMV would typically not be included. In this case, an audible signal is available and is derived from energizing and de-energizing the ATC valve.
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In the exemplary embodiments of the present invention, the ABS system continuously monitors a variety of vehicle parameters and sensors to determine if the vehicle is reaching a critical stability threshold. If this threshold is reached, the stability system component, referred to in the Figures as “ESP”, quickly and automatically intervenes to stabilize the vehicle. During operation, the ECU 70 compares performance models to the vehicle's actual movement using the wheel speed sensors of the ABS system, as well as lateral, yaw, and steering angle sensors. If the vehicle shows a tendency to leave an appropriate travel path, or if critical threshold values are approached, the system will intervene to assist the driver. In the case of a potential roll event, the system will override the throttle and quickly apply brake pressure at selected wheel ends to slow the vehicle below a critical threshold. In the case of vehicle slide, i.e., over-steer or under-steer situations, the system will reduce the throttle and then brake one or more of the “four corners” of the vehicle, in addition to potentially applying trailer brakes, thus applying a counter-force to better align the vehicle with an appropriate path of travel. For example, in an “over-steer” situation, the system applies the “outside” front brake; while in an under-steer condition, the inside rear brake is applied.
Because the stability system, i.e., ESP or RSP, provides important safety features to the vehicle and to the operator, it is highly desirable to ascertain the integrity of the system prior to operating the vehicle. The present invention provides a diagnostic test method for making this determination and providing the vehicle's operator with one or more indicators of system operability. The stability system diagnostic usually begins immediately after the ABS (regular) chuff test and is a stability system specific extension of the ABS chuff test previously discussed (see U.S. Pat. No. 6,237,401, which is hereby incorporated by reference in its entirety). By introducing just enough air pressure into the brake system to create detectable feedback, the energy introduced into the system and any motion of brake components is minimized. Advantageously, the operator does not need to apply the brakes to hear an audible signal. Without the operator's foot on the brake pedal, the brake lamp switch can be used to monitor the system. The ECU uses the switch feedback to monitor and record errors. However, if the driver leaves his foot on the brake, there is still an audible difference as the stability system test cycles through the additional steer axle and trailer stability system modulators.
If operating conditions are such that the ABS chuff test is not run, then the stability system diagnostic will also not run. In the exemplary embodiment, the stability system diagnostic differs from the ABS chuff test in regards to what the system can self-diagnose. While the ABS chuff test does not typically detect cross-wired ABS modulators, the stability system diagnostic is capable of detecting cross-wired stability system valves due to the fact that the stability system diagnostic utilizes the air pressure activated brake light switch as closed-loop feedback to make sure that the system is operating properly. The ABS chuff test relies on the operator to detect an audible difference between a correctly wired modulator and a cross-wired modulator. The stability system diagnostic also provides a distinctive audible difference between a correctly wired stability system valve and a cross-wired valve. However, the system does not depend completely on the operator's ability to hear a problem. The stability system diagnostic also has the ability to identify a “diagnostic trouble code” associated with the stability system, and can shut down the stability portion of the system if and when necessary. The stability portion of the chuff test does not run if there are active diagnostic trouble codes associated with the stability portion of the control system. The disappearance of a previously existing audible feedback is also an indicator for the operator that the stability system is no longer fully operational. A dash diagnostic trouble code indicator (not shown) in communication with ECU 70 will also be lighted in this situation.
As previously discussed, the stability system diagnostic utilizes the brake lamp pressure switch for feedback. Therefore, to prevent false test results, the ECU must monitor for driver interventions (i.e., brake applications) throughout the testing portion of the stability system diagnostic. Throughout the stability system diagnostic, pressure sensors in the driver control lines are monitored. If the ECU detects a driver intervention, then the results of the current stability system diagnostic are not used as indication of system status (good or bad). In this case, the audible ESP diagnostic results may still be valid. Additionally, once the stability system portion of the chuff tests starts, the end portion of the stability system diagnostic cannot typically be terminated (e.g., if the vehicle starts moving). The end portion of the stability system chuff exhausts any air in the system that the ESP chuff may have introduced.
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Each time the stability system diagnostic determines an incorrect result a stored internal counter is incremented by 5 counts. Each time the stability system diagnostic determines correct results, the same internal counter is decremented by 1 count. If the count reaches or exceeds 50, then the stability system is faulted requiring repair. Once repaired, clearing faults results in the counter being set back to 49. If the repair was not performed properly, the stability system will fault again on the very next usable stability system diagnostic. If the repair was done correctly, then the counter will slowly decrease to zero with each of the next 49 successful diagnostic tests.
While the present invention has been illustrated by the description of exemplary embodiments thereof, and while the embodiments have been described in certain detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to any of the specific details, representative devices and methods, and/or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.
