Abstract:
A method of controlling a trailer brake system using a trailer brake controller positioned within a passenger vehicle is provided. The method includes obtaining intended braking inputs and developing an effective baseline trailer brake controller output profile based thereon. The method scales the effective baseline trailer brake controller output profile in response to an adjustable gain setting set by an operator. A vehicle velocity is obtained and used to calculate a correction factor to the effective baseline trailer brake controller output profile. The effective baseline trailer brake controller output profile is then adjusted using the correction factor to generate a corrected trailer brake controller output signal.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to a passenger vehicle brake controller and more particularly to a passenger vehicle trailer brake controller.  
       BACKGROUND OF THE INVENTION  
       [0002]     Passenger vehicle transport capacity is an important design aspect of modern vehicles. The ability to haul objects and equipment is often as important as the vehicle&#39;s ability to transport additional passengers. Solutions aimed at increasing a vehicle&#39;s hauling capabilities must not only be directed at improving the vehicle&#39;s utility but must also be directed towards improving a vehicle&#39;s safety and performance while accomplishing this task. One traditional approach towards improving a vehicle&#39;s transport capabilities has been through the addition of a trailer attached to the vehicle. Trailers allow for a wide range of items to be transported by a vehicle, often without impacting transport capabilities of the vehicle&#39;s passenger compartment.  
         [0003]     Passenger vehicles commonly control trailer braking through the use of a trailer brake controller located within the vehicle. The trailer is commonly equipped with electrically actuated trailer brakes. An operator sets the gain on the controller, where the gain dictates how much electrical output is generated by the controller for a given set of vehicle inputs. The controller utilizes a brake input signal in combination with the user set gain to generate a brake control signal. It is known that this signal can take different forms, such as a duty cycle output or DC voltage output. This control signal is sent to the electrically actuated brakes which are thereby utilized to effectuate braking within the trailer. Systems such as described translate vehicle input, such as brake pedal force or position, brake pressure or vehicle acceleration, into a brake control signal which is adjustable according to the operator set gain. The brake control output signal, in turn, energizes the trailer brakes, which subsequently generates a braking torque on the trailer wheels.  
         [0004]     Although the aforementioned systems may benefit from a lack of complexity, they fail to address the real world principles of mechanics that electrically actuated dual-servo drum brake assemblies are subject to. At increased velocities, it is known that the effectiveness of dual-servo brake torque is reduced and therefore a given brake control signal generates less effective brake torque at higher vehicle speeds than it did at lower vehicle speeds. As such, trailer brake performance degenerates at higher vehicle speeds. It would be highly desirable to have a trailer brake control apparatus and method that compensated for the loss of effective brake torque at increased vehicle speeds such that a consistent brake torque could be generated over the entire range of expected vehicle speeds.  
         [0005]     It is further known, that a brake torque desirable over a broad range of vehicle speeds may be undesirable at low vehicle speeds. At low vehicle speeds, electric dual-servo drum braking systems are subject to significant increases in effectiveness wherein an applied brake torque may result in the brakes locking up (also known as “grabbiness”) rather than incrementally applying braking friction. Existing electric trailer braking systems commonly fail to address this known phenomenon and thereby produce undesirable vehicle low-speed results. It would, therefore, be highly desirable to have a trailer braking system that improved low-speed performance by reducing brake-grab.  
         [0006]     Finally, if one is to consider vehicle speed in the development of a brake control signal, it is important to consider the issues involved with accurate velocity calculation. Measurement of vehicle velocity based on wheel speed is subject to a host of errant readings due to automotive performance conditions. During rapid deceleration, it is known that a wheel may generate excessive slip relative to the road surface. In such circumstances, if vehicle speed was estimated based solely on this wheel in deep slip, the estimate would be lower than the actual vehicle speed. Similarly in rapid acceleration if a wheel breaks away from the road surface it may result in a velocity value abnormally high. In other circumstances, such as vehicle turns, outer wheels may experience a velocity increase while inner wheels a decrease. Thus it would be further beneficial to develop an improved method of calculating vehicle speed prior to its utilization in effecting the trailer brake control signal.  
       SUMMARY OF THE INVENTION  
       [0007]     It is, therefore, an object of the present invention to provide a passenger vehicle braking system with an integrated trailer brake controller. It is a further object of the present invention to provide a passenger vehicle braking system with velocity sensitive performance.  
         [0008]     In accordance with the objects of the present invention, a method of controlling a trailer brake system using a trailer brake controller positioned within a passenger vehicle is provided. The method includes obtaining intended braking inputs and developing an effective baseline trailer brake controller output profile based thereon. The method scales the effective baseline trailer brake controller output profile in response to an adjustable gain setting set by an operator. A vehicle velocity is obtained and used to calculate a correction factor to the effective baseline trailer brake controller output profile. The effective baseline trailer brake controller output profile is then adjusted using the correction factor to generate a corrected trailer brake controller output signal.  
         [0009]     Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a block diagram of an embodiment of a trailer brake controller in accordance with the present invention.  
         [0011]      FIG. 2  is an illustration of an automotive dash assembly illustrating an embodiment of communication elements intended for use with the present invention.  
         [0012]      FIG. 3  is a detail of the communication elements illustrated in  FIG. 2 , the communication elements are intended for use with a trailer brake controller in accordance with the present invention.  
         [0013]      FIG. 4  is a block diagram of an embodiment of the trailer brake controller in accordance with the present invention.  
         [0014]      FIG. 5  is a flow diagram of an acceleration sensitive vehicle velocity algorithm for use in the present invention.  
         [0015]      FIG. 6  is a graph of gain adjusted effective baseline trailer brake controller output profiles for use with the present invention.  
         [0016]      FIG. 7  is a detail of an effective brake torque curve as illustrated in  FIG. 6 , the detail showing an embodiment wherein brake torque is increased with increased vehicle velocity. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring now to FIGS.  1  to  4 , which are illustrations of a trailer brake controller  10  in accordance with the present invention. The trailer brake controller  10  is intended for integration into a passenger vehicle braking system. It is further intended that the trailer brake controller  10  be designed, assembled, and sold with the passenger vehicle such that its control characteristics can be properly set by the vehicle manufacturer for a specific passenger vehicle. Additionally, by integrating the trailer brake controller  10  into the passenger vehicle through manufacture, assembly and distribution, control and display features for the trailer brake controller  10  may be professionally integrated into the passenger vehicle  12  design. Thus, appearance, performance, safety, and customer convenience may be improved.  
         [0018]     The trailer brake controller  10  utilizes control element  11  having an intended braking input  14  (such as a brake pressure input) and a vehicle speed input  16  in order to adjust the trailer brake output  18 . It is contemplated that the intended braking  14  and vehicle velocity  16  inputs may be utilized to adjust trailer brake output  18  in a variety of fashions. One advantage of the present invention is that the relationship of the trailer brake output  18  to the brake pressure input  14  may be adjusted for the particular vehicle  12  in which the trailer brake controller  10  is mounted.  
         [0019]     It is contemplated that the intended braking input  14  and the vehicle speed input  16  may be supplied by a variety of sources within the vehicle  12 . In one embodiment, however, it is contemplated that the intended braking input  14  and the vehicle speed input  16  are supplied through a communication between the vehicle brake control system  22  (such as the antilock braking system or electronic stability control system) and control element  11 . It is known that modern tow vehicle brake control systems  22  (such as ABS) contain sensors that can be used to estimate vehicle speed. By placing the vehicle brake control system  22  in communication with the control element  11 , the vehicle speed input  16  may be easily estimated. Finally, the vehicle brake control system  22  may be utilized to communicate to the control element  11  when the system  22  has been activated. This can allow the trailer brake controller  10  to tailor its output  18  such that the trailer brakes works more efficiently with the vehicle brake control system  22 . It should be understood that although the vehicle brake control system  22  may be utilized to supply both the intended braking input  14  and the vehicle speed input  16 , in alternate embodiments, the intended braking input  14  may be supplied through a variety of known devices or sensors such as vehicle brake pressure  24 , brake pedal force  66 , brake pedal travel, or vehicle accelerometer. Again, although specific embodiments have been described that provide a brake pressure input  14  and a vehicle speed input  16 , a variety of methods of obtaining these inputs would be obvious to one skilled in the art in light of this application.  
         [0020]     It is intended that the trailer brake output  18  be capable of controlling a plurality of embodiments of trailer brakes. Although a variety of trailer brake outputs  18  are contemplated by the present invention, one embodiment contemplates the trailer brake output  18  taking the form of an electrical output. In addition, the trailer brake controller  10  may include a variety of additional components to increase its functionality and performance. A brake indicator lamp output  26  may be used in conjunction with the trailer brake output  18  to improve the safety and performance of the trailer brake controller  10 . Similarly, a diagnostic input/output  28  may be included such that the trailer brake controller  10  may provide self diagnostic information concerning the trailer  30  and controller  10  to a service technician. This trailer brake electrical output  18  not only provides power to the trailer brakes, but by monitoring the electrical characteristics of this signal, the trailer brake controller  10  can inform a vehicle operator of improper electrical connection with the trailer or of damage to the trailer brake&#39;s electrical system  70 . Power supplies  34 , ignition run/start inputs  36 , and other known elements may be utilized in conjunction with the present design to provide basic functionality, concepts well known in the art.  
         [0021]     It is further contemplated that the trailer brake controller  10  may provide communication between the control element  11  and the owner/operator. Although this communication can take on a variety of forms, in one embodiment it is contemplated to take the form of a display  42 , a user control input  44  (such as a gain input control) and an override switch  46 . These communication elements  48  can be adapted and complimented to provide a range of communication and control to the owner/operator. Similarly, although these communication elements  48  may be positioned in numerous locations, one embodiment mounts them to the vehicle dash  50  (see  FIGS. 2 and 3 ). By equipping the vehicle with such a control system during design and manufacture, the appearance of the communication elements  48  can be significantly improved and thereby increase customer satisfaction. The display  42  can include a gain display  52  and a signal strength display  54 . The signal strength display  54  allows the owner operator to visualize the trailer brake output  18  signal and adjust the gain input control  44  to suit individual preferences. The override switch  46  can be operated by the owner/operator to apply the trailer brakes independently of the vehicle without braking. It is further contemplated that the display  42  may be utilized to communicate to the owner any improper connections or diagnostic faults determined by the control element  11 . This can serve to increase the safety and awareness of the owner by properly apprising them of the status of their trailer&#39;s operation.  
         [0022]     A novel feature of the present invention is derived from the methodology it invokes to develop a velocity tailored trailer brake output signal  18 . A key innovation which enables velocity-sensitive trailer brake control is development of a generic trailer brake torque vs. speed vs. voltage mapping  19  preferably developed using laboratory testing of trailer brakes on a chassis dynamometer. By sweeping trailer wheel rotational speed and electric brake input voltage, while measuring brake torque output, the data shown in  FIG. 6  can be collected for a single trailer brake or across the range of available electric trailer braking systems, considering critical noise factors, such as piece-to-piece brake system variability, brake lining wear, brake magnet wear and brake temperature. While the magnitude of the individual torque curves vary across trailer brake types, the characteristic decrease in torque as speed increases at higher voltages is adequately similar to create a generic relationship which can be used in open loop trailer brake control, as described earlier in this patent. The fact that the operator is required to set TBC gain for given trailer conditions provides adequate adjustment of the torque/speed/voltage mapping for a given trailer brake system.  
         [0023]     The mapping curves  19  illustrated in  FIG. 6  are contemplated to be multivariate curves dependent on intended braking inputs  14  and vehicle speed input  16  and therefore are in actuality three-dimensional plots. The curves  19 , however, are represented as two-dimensional plots for simplification and clarity of discussion. The curves are representative of an effective baseline trailer brake controller output profile  60  utilized by the present invention. The customer set gain  62  can then be utilized to scale this effective baseline trailer brake controller output profile  60 . It should be understood that a variety of scaling techniques and generic mapping techniques may be utilized in order to improve performance. Furthermore, although a single modified and scaled effective baseline trailer brake controller output profile  60  has been described, it should be understood that a plurality of differing or individually tailored profiles  60  may be utilized. The intended braking input  14  is intended to include any existing measurement of vehicle braking such as brake pedal force  66 , brake fluid pressure  24 , or similar methodology (see  FIG. 4 ). It should be further understood that the determination of the effective baseline trailer brake controller output profile  60  need not constitute a specific calculation step but may remain defined simply by the intended braking inputs  14  and vehicle speed input  16 . The effective baseline trailer brake controller output profile  60  is indicative of the brake torque applied by the trailer brakes if the trailer brake output was produced under existing operational conditions and a constant supply voltage. As supply voltage is changed this profile changes, but the same downward trend shape exists over a range of supply voltages. A flaw of electric dual-servo drum brakes  70 , as shown in  FIG. 6 , is that as vehicle speed  16  increases, a given trailer brake controller output  18  will produce reduced brake torque. Each of the effective baseline trailer brake controller output profiles  60  corresponds to a trailer brake controller output voltage scaled according to a plurality of available operator gain settings  62  (gain settings are effectively what determine the supply voltage). As can be seen, however, from the effective baseline trailer brake controller output profiles  60 , as vehicle speed  16  increases, the effective brake torque begins to drop. This generates different braking performance as well as different braking feel as speeds increase.  
         [0024]     The present invention, however, includes logic within the trailer brake controller  10  adapted to adjust the trailer brake output  18  such that this drop off in effective brake torque is neutralized. The present invention obtains the vehicle velocity  16  (or trailer velocity) and uses this in conjunction with the effective baseline trailer brake controller output profile  60  to determine an unadjusted output  71  and an estimate of effective brake torque loss  73 . The unadjusted output  71  is simply a value representative of a particular location along the effective baseline trailer brake controller output profile  60 . The logic is then adapted to calculate a correction factor  74  that compensates for the effective brake torque loss  73  such that a constant brake torque  76  is achieved throughout the velocity range of the trailer. Although these calculations or steps are presently described in terms indicative of individual steps by the logic, it is equally contemplated that linear regression may be performed on the mapping values  19  such that the correction factor  74  may be directly computed from the intended braking input  14  and velocity input  16 . The unadjusted output  71  is adjusted by the correction factor  74  to generate a corrected trailer brake output signal  75  that compensates for lost torque. The correction factor  74  can automatically make any range of partial corrections within the range of available supply voltage to provide a constant brake torque  76 . In an alternate embodiment, the correction factor  74  may be utilized to increase the effective brake torque  72  as velocity increases (see  FIG. 7 ). This allows a gradual ramp up in torque as speed increases.  
         [0025]     The preceding discussion involved compensating for effective brake torque losses at increased vehicle velocities. It is known, however, that trailer brake performance suffers at low vehicle velocities as well. The low velocity performance issues arise from the physics of electrically actuated dual-servo drum brakes. At very low vehicle speeds, namely less than ten miles per hour, application of the unadjusted output  71  can result in brake grabbing or temporary seizing. This provides undesirable feel to the operator. The present invention, therefore, further includes logic adapted to utilize the correction factor  74  to reduce brake grabbing. This is accomplished by decreasing the trailer brake output  18  at low vehicle speeds  16  to the point where brake grabbing is alleviated. Although a simple reduction in controller output may be implemented, the present invention contemplates the development and use of a brake torque reduction curve  78  specifically adapted to minimize brake grab while maintaining optimal braking performance.  
         [0026]     The present invention thereby contemplates the use of a correction factor  74  to improve the effective baseline trailer brake controller output profile  60  at both low and high vehicle speeds  16 . As the correction factor  74  is dependent on vehicle speed  16  input, the present invention contemplates an improvement in estimation of vehicle speed  16  through the use of vehicle dynamic status  80  (such as acceleration status) available from other vehicle systems (see  FIG. 5 ). The present invention includes logic adapted to calculate the wheel speed  82  at a plurality of wheel locations  84 . The wheel locations  84  are contemplated to encompass individual wheel locations such as Right Front  86 , Left Front  88 , Right Rear  90  and Left Rear  92 . The wheel locations  84  are also intended to encompass readings such as the use of a differential speed sensor  94  which may be substituted for the rear wheel readings  90 ,  92 . It is further contemplated that the wheel locations  84  may include trailer wheel locations  96  as opposed to the aforementioned towed vehicle locations. The present invention then determines if an acceleration event  98  is present. An acceleration event  98  is intended to encompass positive acceleration  100  (commonly just referred to as acceleration) in addition to negative acceleration  102  (commonly referred to as deceleration). The present invention uses the acceleration  98  to selectively choose one of the wheel speeds  82 . The vehicle velocity  16  is then set based on the selectively chosen wheel speed  82 .  
         [0027]     It is contemplated that both the selective choosing of a wheel speed  82  in addition to the use in setting vehicle velocity  16  may be achieved in a variety of fashions. In one embodiment, when a positive acceleration  100  event is recognized, the wheel speeds are simultaneously compared. The slowest  104  of these wheel speeds  82  is then chosen and the vehicle velocity  16  is set as this slowest wheel speed  104 . Similarly, during negative acceleration  102 , the wheel speeds are compared and the fastest wheel speed  106  is selectively chosen and set as the vehicle velocity  16 . Each of these chosen wheel speeds is then compared to physical limits of acceleration and if the change in this speed compared to the previously stored speed is outside of these limits, the newly stored speed is only advanced/decreased within the physical limit range.  
         [0028]     Although a single wheel speed  104 , 106  may be utilized using this logic, it is contemplated that multiple wheel speeds  82  may be alternately utilized. In this embodiment vehicle acceleration  98  is utilized to selectively remove at least one of the wheel speeds  108 . The logic is then adapted to calculate the vehicle velocity  16  and thereby the correction factor  74  based on the remaining wheel speeds  110 . In one example, during deceleration  102 , if a wheel speed indicates zero it is reasonable to assume that wheel is locked-up and therefore is removed from velocity calculations. In another example, during acceleration  100 , an unreasonably high value indicates wheel slippage and therefore is removed. These two methodologies are not exclusive. During deceleration  102 , if the fastest wheel speed  106  is selectively chosen, any wheel speeds  82  inconsistent with the fastest wheel speed  106  can be removed from the velocity calculation. The remaining velocities may be averaged or used in other algorithms to calculate a vehicle velocity  16 . Similarly during acceleration  100 , the slowest wheel speed  104  may be selected and any inconsistent values removed.  
         [0029]     The present invention contemplates that the logic adapted to translate individual wheel speed  82  into vehicle velocity  16  may be accomplished directly within the trailer brake controller  10  by way of measuring wheel speed  82  using a plurality of wheel speed sensors  112 , each of which located at one of the vehicle wheel locations  84 . The individual wheel speeds  82  may be communicated to the trailer brake controller  10  wherein the selective choosing or selective removing may be accomplished. In an alternate embodiment, however, it is contemplated that the vehicle velocity  16  maybe calculated using the aforementioned methodologies using logic within the anti-lock braking system  23 . In such an embodiment, it is contemplated that an output portal  114  be integrated into the anti-lock braking system  23  such that the trailer brake controller  10  may be placed in communication therewith during assembly through the use of a communication cable or similar data link. In this way, the anti-lock braking system  23  is adapted to port information to a host of vehicle systems.  
         [0030]     While particular embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.