Trailer brake control

Abstract: A brake control system/method for preventing or arresting and minimizing trailer brake induced trailer-swing in an articulated vehicle (10) is provided. The control system/method senses or calculates values indicative of articulation angle (AA) and/or time derivatives thereof (dAA/dt,) and indicative of vehicle dynamic turning radius of curvature (DTRC), or of steer angle (SA), and/or a time derivative thereof, and processes same to sense conditions indicative of an incipient or initial trailer brake induced trailer-swing event.

Description: Field of the Invention The present invention relates to a control system/method for controlling the braking force applied to the brakes of a towed subvehicle in an articulated vehicle system, such as the semitrailer subvehicle in a tractor-semitrailer system, to prevent, arrest, minimize and/or quickly recover from, the condition known as trailer brake induced trailer swing. Description of the Prior Art Brake control systems for all types of vehicles, including heavy duty tractor-semitrailer trucks, to improve the stopping and vehicle stability thereof are, of course, well known in the prior art. Brake systems of the anti-lock type, for all types of vehicles, are well known in the prior art. Briefly, these systems operate to maintain vehicle stability (i.e. acceptable transverse coefficient of friction of braked wheels) by maintaining the longitudinal slip of the braked wheels within predetermined limits. This usually requires modulating the braking forces on an individual wheel and/or individual axle basis to maintain at least some wheel rotation. Examples of prior art anti-lock brake systems ("ABSs") may be seen by reference to U.S. Patent Nos. 3,767,270; 3,768,872; 3,854,556; 3,893,696; 3,929,383; 3,929,382; 3,966,267; 4,392,202 and 4,591,213, the disclosures of all of which are hereby incorporated by reference. Brake systems which control braking to achieve a driver demand, sense driver demand in a "brake-by-wire" manner, sense coefficient of friction and modify brake forces accordingly, sense load on a wheel and modify braking effort accordingly, sense wheel slip and/or use electronic signals to achieve trailer brake response are also disclosed in the prior art as may be seen by reference to U.S. Patent Nos. 4,140,352; 4,327,414; 4,494,199; 4,512,615; 4,545,240; 4,591,213; 4,606,586; 4,616,881; 4,648,663 and 4,768,840, the disclosures of which are hereby incorporated by reference. Brake systems for heavy duty articulated vehicles such as tractor-semitrailer trucks are difficult to design as the loading and maintenance will vary in a truck, such as the loading on the tractor of a tractor-trailer which may comprise a tractor only, a tractor with an empty or lightly loaded trailer or a tractor with a heavily loaded trailer. Further, tractor-semitrailers are, by their nature, capable of exhibiting certain unstable dynamic behaviors known as jackknife and trailer swing, each of which has its own characteristic cause, effect and appropriate sequence of corrective action. Jackknife is sometimes called "tractor brake caused jackknife" while trailer swing is sometimes called "trailer brake caused jackknife". The dynamics of undesirable trailer articulation events, such as a jackknife event, are discussed in SAE Paper No. 710045, the disclosure of which is hereby incorporated by reference. Various systems to prevent or minimize undesirable trailer articulation have been proposed. These include mechanical devices such as chains or variable pivot resistance devices and also wheel speed sensors and anti-lock controls on the trailer per se. Examples of these prior art devices may be seen by reference to U.S. Patent Nos. 3,618,983; 3,810,521; 3,894,773; 4,023,864, 4,254,998, 4,040,507, 4,196,936, 4,405,145 and 4,620,717 the disclosures of which are hereby incorporated by reference. The prior art mechanical type devices were not satisfactory as the mechanical devices were somewhat slow to react, hindered required articulation during normal operation, required specially equipped/configured trailers and/or did not allow for a recovery from the locked-in condition. The anti-lock (ABS) type systems were not totally satisfactory as most existing trailers do not have ABS equipment, tractors are often driven with a variety of trailers and thus even if a trailer is provided with ABS equipment, it may not be compatible with the tractor ABS, providing all existing and future trailers with ABS equipment is prohibitively expensive and, under certain conditions, undesirable trailer articulation may occur in the absence of the wheel lock conditions sensed and reacted to by existing ABSs. The prior art controls were not satisfactory as a system/method to detect unacceptable trailer articulation during a vehicle maneuver (such as changing lanes in a curve) was not provided. EP-A-0 433 858 (published 26.6.91) shows an anti trailer swing brake control system for articulated vehicles. The system includes sensors for sensing the articulation angle as well as the steer angle and providing corresponding signals. The signals are processed to obtain the second time derivative of the articulation angle and a threshold value which is a function of the steering angle signal. The relationship between these signals is evaluated and it is assumed that the trailer swing event is onset if the second time derivative of the articulation angle exceeds the calculated threshold value. SUMMARY OF THE INVENTION In accordance with the present invention, many of the drawbacks of the prior art have been overcome or minimized by the provision of a trailer anti-swing control system/method which is suitable for use with semitrailers equipped with standard (i.e., non-ABS) brake controls and which will sense the onset of an unacceptable trailer articulation event during vehicle maneuvering and will control the pilot or actuation pressure supplied to the trailer brake system to minimize or halt sensed trailer swing initiation and allow the trailer to safely recover therefrom. The above is accomplished by providing, preferably entirely on the tractor, an ABS type valve located on the tractor upstream from the glad hand connection, sensors for sensing and/or providing signals allowing the calculation of tractor/trailer articulation angle ("AA") and a time derivative thereof such as, rate of change of articulation angle ("dAA/dt") and rate of change of rate of change of articulation angle ("d 2 AA/dt 2 "), sensors for providing signals indicative of the dynamic turning radius of curvature of the vehicle or of the steer angle of the vehicle front steering wheels, and time derivatives thereof, and a control device, preferably microprocessor based, for receiving input signals, processing same in accordance with predetermined logic rules and issuing command output signals to control the trailer brake ABS type valve. Preferably, a value indicative of the vehicle dynamic turning radius of curvature and a time derivative thereof is determined and compared to the current articulation angle and a time derivative thereof, respectively, to determine if an unacceptable trailer articulation event is occurring. Preferably, the level of confidence in the calculated value of dynamic turning radius of curvature is calculated and a determination of a trailer swing event and initiation of corrective action will occur only if the calculated level of confidence exceeds a predetermined value. The "ABS type valve" should have the functions of lowering pressure to release the trailer brakes, holding the pressure at a low value to maintain brakes released, then reapplying the brakes in a controlled manner to a desired reapply pressure, all independent of the degree of braking effort demanded by the vehicle driver. Accordingly, it is an object of the present invention to provide an improved trailer brake control system/method for the trailer type subvehicle of an articulated vehicle system, such as the trailer of a tractor-semitrailer truck system, which is operative to detect the onset of and prevent, or to minimize and allow recovery from, a trailer swing condition. Preferably, all of the control components, at least the active control components, will be mounted on the tractor subvehicle and will allow use of the control system with any standardly equipped trailer subvehicle. This and other objects and advantages of the present invention will become apparent from a reading of the detailed disclosure of the preferred embodiments taken in connection with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a conventional heavy duty tractor-semitrailer truck articulated vehicle. Figure 2 is a schematic illustration of a tractor mounted brake control system including an anti-lock brake system, and also incorporating the trailer anti-swing control system of the present invention. Figure 3 is a schematic illustration of a standard trailer brake system which may be utilized with the trailer anti-swing brake control system of the present invention. Figure 4 is an enlarged, fragmentary, schematic illustration of the king pin/fifth wheel pivotal connection between a tractor and a semitrailer illustrating the angular relationship defined by the articulation angle. Figure 5 is a graph illustrating the trailer brake applied pressure versus time curve(s) for the trailer anti-swing control system/method of the present invention. Figure 6 is a schematic illustration of the occurrence of an uncontrolled trailer swing event. Figure 7 is an illustration of a floating rotor potentiometer type of articulation angle sensor for the control system/method of the present invention. Figure 8 is a schematic illustration, in the form of a flow chart, of the trailer anti-swing control system/method of the present invention. Figure 9 is a schematic illustrating the control method of the present invention. Figure 10 is a schematic illustrating the calculation of an equilibrium turning radius of curvature. DESCRIPTION OF THE PREFERRED EMBODIMENT The trailer anti-swing control system/method of the present invention is applicable to articulated multiple vehicle systems such as the tractor-semitrailer system 10 illustrated in Figure 1. Briefly, as is well known to the prior art, the tractor-semitrailer system 10 comprises a tractor 12 and a semitrailer 14 attached thereto by a connecting means 16 which comprises the well known fifth wheel 34 fixed to the tractor for selective engagement with a king pin fixed to the trailer. The tractor typically comprises a pair or tandem set of rear drive axles 36 and 38 and a front steer axle 40. The trailer 14 typically comprises a tandem pair of non-steerable, non-driven trailer axles 42 and 44. Typically, but not necessarily, the front axle 40 will have non-driven steerable wheels. The tractor and/or the trailer may be equipped with single or three or more drive and/or trailer axles. The term "trailer" as used herein is intended to apply to various trailed subvehicles including semitrailers. The ability to utilize fifth wheel/king pin connections to relatively quickly and easily couple or connect standardly equipped tractors to standardly equipped semitrailers in an articulated or pivoted manner provides the well appreciated advantages of commercial and operational flexibility as well as increasing the maneuverability of the vehicles. However, under certain conditions, often associated with braking while negotiating a curve or a turn, one or both of the tractor-semitrailer subvehicles may lose transverse stability resulting in a condition of uncontrolled excessive articulation, i.e. jackknife or trailer swing. Tractor-semitrailer uncontrolled excessive articulation is generally considered to consist of two distinct types of events, namely "jackknife" and "trailer swing", both of which may lead to catastrophic results. Jackknifing, which is considered to be the most severe and least correctable type of uncontrolled excessive trailer articulation event, usually results from the tractor subvehicle, usually the tractor subvehicle drivewheels, losing transverse stability, often while cornering, which lack of stability is quickly compounded by the often relatively many times greater inertia imposed by the trailer. The other type of uncontrolled excessive trailer articulation event, trailer swing, is generally the result of the trailer wheels, 42 and 44, losing transverse stability usually cornering, resulting in the trailer swinging radially outwardly relative to the center of the curve being negotiated which may result in the trailer swinging into adjacent traffic lanes with the obvious potential for catastrophic results therefrom. Trailer swing events often occur less rapidly than jackknife events, and, upon sensing conditions indicative of the advent of a trailer swing condition, corrective action may be taken of the trailer brakes to minimize the extent of trailer swing and to cause the trailer to resume its tracking condition. As is very well known, decreasing the slip of a tire will increase the transverse coefficient of friction thereof. Accordingly, trailer swing events induced by locked or almost locked trailer brakes, if sensed at the onset or initiation thereof, may be arrested or reduced by increasing the transverse stability of the trailer wheels by releasing the brakes thereof and allowing the wheels to roll up to or towards vehicle speed. The schematic illustration of an extreme trailer swing event may be seen by reference to Figure 6 wherein the trailer at the right-hand portion of the illustrated curve has swung totally out of its lane. The purpose of the control system/method of the present invention is to prevent the occurrence of, or to minimize the extent of, trailer brake induced trailer swing events. The trailer brake control system/method of the present invention is preferably utilized with a tractor 12 fully equipped with an ABS system and a trailer 14 equipped with a standard, i.e. non-ABS, brake system. However, the control of the present invention would also provide benefits if utilized with a vehicle having both tractor and trailer ABS as, under certain conditions, undesirable trailer articulation may occur even though the vehicle wheels have not locked up to the extent that is necessary to cause corrective action by currently existing ABS systems. Additionally, although not preferred, the trailer anti-swing control system/method of the present invention will provide a degree of improved vehicle stability when utilized on a tractor trailer system wherein neither the tractor nor the trailer was provided with an ABS logic control. As stated above, the purpose of the present invention is to prevent or minimize trailer brake induced trailer swing events while the occurrence of jackknife events is minimized by the provision of the tractor ABS control logic and devices. A braking system for the tractor 12 of an articulated tractor-semitrailer system 10 which utilizes the trailer brake control system/method of the present invention may be seen by reference to Figure 2. It is noted that while the braking system for tractor 12 illustrated in Figure 2 is of the "brake by wire" type, the present invention is equally applicable to other types of brake controls and ABS systems. Briefly, as is well known in the prior art, tractor 12 includes a front steer axle 40, which is usually not driven, and a tandem pair of rear drive axles comprising front-rear drive axle 36 and rear-rear drive axle 38. Wheels 140 and 142 are associated with the rear-rear drive axle 38, wheels 144 and 146 are associated with the front-rear drive axle 36 and wheels 148 and 150 are associated with the front steer axle 40. The rear drive axles, 36 and 38, are driven by engine 46 through transmission 48 and driveline 50. Air actuated brake chambers 60, 62, 152, and 154 are provided for retarding the rotation of wheels 144, 146, 140 and 142, respectively. The rear brakes 60, 62, 152 and 154 are, as is well known in the prior art, of the same size and type as likewise are the front brakes 64 and 66 which are provided for selectively braking the rotation of front steer drive axle wheels 148 and 150, respectively. In the system illustrated, the brakes are air actuated brakes of one of the well known types, such as the "S" cam actuated brake type or the air disc brake type, the details of which are well known in the prior art and may be seen in greater detail by reference to U.S. Patent Nos. 4,476,968 and 4,457,407, the disclosures of both of which are hereby incorporated by reference. While all of the front brakes and all of the rear brakes should be of the same size and type, it is not necessary, and is not preferable, that the front and rear brakes be of the same size. Compressed air for actuating the brakes is supplied from a plurality of supply tanks 68, only one of which is shown, which supply tanks are provided with compressed air from the vehicle onboard compressor (not shown) or the like. The braking system includes a control unit 70, which for purpose of flexibility and responsiveness is preferably an electronic microprocessor based control unit having means 72 for receiving a plurality of input signals, means for processing input signals in accordance with predetermined logic rules, and means 74 for issuing command output signals to various system operators. Control units of this type are well known in the prior art as may be seen by reference to U.S. Patent No. 4,595,986, the disclosure of which is incorporated by reference. A sensor 76 senses the operator's displacement of a brake pedal 78 to provide an input signal indicative of the driver's demand or vehicle stopping effort. Sensors of this type are known in the prior art and may be seen by reference to above-mentioned U.S. Patent Nos. 4,140,352; 4,327,414 and 4,512,615. Typically, such transducers will sense the displacement of and/or force applied to the brake pedal 78 and will provide an output signal proportional thereto. As indicated above, the present invention is equally applicable to more conventional brake systems wherein the amount of braking effort is controlled by a well known treadle valve. To provide tractor ABS operation, wheel speed sensors 160, 162, 98, 100, 102, 104 are provided for providing input signals indicative of the rotational speed of wheels 140, 142, 144, 146, 148 and 150, respectively. A sensor 101 may be provided to providing input signals indicative of the steer angle of the front steer wheels 148 and 150. See U.S. Patents Nos. 4,219,208, 4,728,923 and 4,800,976, the disclosures of which are incorporated herein by reference. The central processing unit 70 will, as is well known in the ABS prior art, process the input signals in accordance with predetermined logic rules to generate command output signals to the front control valve 108 and the rear control valve 168. Briefly, control valve 108 is connected to the supply tank 68 through supply line 110, and, in accordance with the command output signals from CPU 70, independently pressurizes the conduits 116 and 118 leading to air brakes 64 and 66, respectively. Rear control valve 168 is also connected to supply tank 68 through supply line 110 and, in accordance with command output signals from CPU 70, individually provides pressurized fluid via branch conduits to the rear axle brakes 60, 62, 152 and 154. Accordingly, it may be seen that the braking efforts of each of the tractor wheels may be individually controlled for ABS purposes in a closed loop manner in response to command output signals generated by the CPU 70 in response to the input signals received and processed thereby, as is known ABS technology. To provide the trailer brake anti-swing control system/method of the present invention, the tractor braking system is also provided with one or more sensors 170 and 172, preferably mounted on the tractor such as at the fifth wheel 34, for providing input signals to CPU 70 indicative of and/or allowing the calculation of the current articulation angle (AA), and of time derivatives thereof such as the rate of change of articulation angle (dAA/dt) and the rate of change of the rate of change of articulation angle (d 2 AA/dt 2 ). Of course, sensors may be provided for directly sensing one or more of the time derivatives of articulation angle. In addition, a control valve 174, controlled by command outputs from CPU 70, will provide pilot controls to the standard trailer brake system control valves. Preferably, the control valve 174 is located on the tractor just upstream of one of the gladhand connectors 206. Valves 108, 168 and 174 may be replaced by a standard treadle valve having an output proportional to the displacement of brake pedal 78 and an ABS type valve connected in series downstream therefrom. Applicant's convention for the measurement of articulation angle, and the first and second derivatives thereof with respect to time, and various sensing means for sensing same will be described in greater detail below. Referring now to Figure 3, a prior art standard trailer brake system (i.e, non-ABS) is illustrated. Briefly, the trailer includes a king pin 176 for selective engagement and disengagement to the tractor fifth wheel 34 as is well known in the prior art. The trailer includes a supply tank 178 connected to the tractor air system by means of a fluid connection 180. Trailer axles 42 and 44 support trailer wheels 182, 184, 186 and 188, each of which is provided with an air brake actuators or chambers 190, 192, 194 and 196, respectively. Typically, all of the trailer brakes are controlled at the same pressure by means of a relay valve 198 which has an inlet 200 connected to the trailer supply tank 178 and a pilot valve portion 202 for receiving a pilot air signal from the tractor air system by means of connector 204. Each of the trailer brakes is actuated at approximately the same pressure from a single output 208 from a pilot controlled relay valve 198. Connector 204 is designed for connection with connector 206 on the tractor. Briefly, the connectors 204 and 206 and likewise connector 180 and its associated connection with a vehicle air system (not shown) form the fluid connection commonly known as the "gladhand". Applicant's convention, which will be used throughout this application, for the measure of the articulation angle (AA) may be best understood by reference to Figure 4 wherein the pivot axis between the tractor 12 and trailer 14 defined by the fifth wheel 34 and king pin 176 connection is viewed from the top of the vehicle, i.e. with the trailer extending rearwardly from left to right as shown in Figure 4. The articulation angle between the tractor and trailer, AA, is defined as the included angle between the longitudinal axis 200 of the tractor 12 passing through the king pin/fifth wheel pivot axis and the longitudinal axis 202 of the trailer 14 passing through the fifth wheel/king pin pivot axis. The articulation angle AA is measured from the tractor longitudinal axis 200 to the trailer longitudinal axis 202 and is assigned a positive value in the counterclockwise direction and a negative value in the clockwise direction. In the example shown in Figure 4, accordingly, the articulation angle AA would have a positive value under applicant's herein defined convention. The loss of transverse stability of the trailer wheels sufficient to result in a trailer swing event as illustrated in Figure 6, is typically associated with an application of the trailer brakes as the vehicle 10 is maneuvered in a curve resulting in wheel slip exceeding a desirable value and/or total wheel lock. To prevent the occurrence of a trailer brake induced trailer swing event, or to arrest and minimize the extent thereof and to allow quick recovery therefrom, it is desirable that conditions indicative of incipient or actual onset of trailer swing be quickly sensed and that the vehicle brake system react thereto by releasing the trailer brakes allowing the trailer wheels to roll back up towards vehicle speed to minimize the slip and increase the transverse coefficient of friction, and thus increase the centripetal force of the trailer wheels. The trailer anti-swing control method and system of the present invention is operable to sense conditions indicative of incipient, or the onset of, a trailer brake induced trailer swing event by the sensing and/or calculating if the vehicle brakes are applied therefor at least one or more of the articulated vehicles' articulation angle, and a time derivative of articulation angle, such as the first derivative of articulation angle with respect to time, and to compare these values with the range of expected values at current vehicle steer angle/dynamic turning radius of curvature conditions. It is important to sense trailer swing at the initiation or onset, i.e. prior to the trailer swinging towards an almost zero articulation angle position, to have sufficient time to arrest and/or minimize the condition. It is also important to distinguish trailer swing from jackknife as different corrective responses are required. Upon sensing conditions indicative of the onset of a trailer swing event, the control logic of the present invention will declare the existence of conditions indicative of an incipient trailer swing event and will release the trailer brakes for a given period of time (T) selected to allow the trailer wheels to roll back up towards vehicle speed to increase the transverse stability thereof and preferably minimize or eliminate the trailer swing and allow the trailer wheels to again track on the curve. After the predetermined period of time, trailer brakes will be reapplied at a rate (R) which may be fixed or may vary with measured system variables to a reapplication pressure (P) which is preferably a function of the value of the first and/or second derivative of articulation angle with respect to time at the onset of the trailer swing event. The brakes will be maintained at this pressure peak until such time as the braking event is terminated, i.e., the operator removes his foot from the brake pedal, at which point trailer brakes will again be controlled by the treadle valve until such time as incipient trailer swing is again sensed. The application of pressure to the trailer brakes is controlled by trailer anti-swing control valve 174, an ABS type valve, which varies the pressure applied to the pilot portion 202 of the trailer relay valve 198. A graphic illustration of the pressure applied to the trailer brakes to minimize and recover from a sensed incipient trailer swing event may be seen by reference to Figure 5. Referring to Figure 5, at point 204 to point 206 the vehicle brakes are not applied. At point 206, the vehicle operator has fully depressed the treadle valve or brake pedal 78 causing the relay valve 198 in the trailer, under the control of trailer brake control valve 174, to apply the trailer brakes with a high pressure as seen in point 208. If the operator continues to request a relatively high braking effort, trailer brakes will remain applied at a relatively high level from point 208 to point 210. For purposes of this example, at point 210 it will be assumed that the input signals processed by the CPU controller 70 indicate the existence of an incipient trailer swing event. The CPU 70 will then issue command output signals to the trailer brake control valve 174 causing the trailer brakes to be released as may be seen at point 212. The trailer brakes will be maintained in the released position for a period of time T which is selected as a time sufficient to allow the trailer wheels to roll back up to near vehicle speed. Time T may be predetermined or may vary with the value of sensed inputs to the CPU. Typically, as the trailer wheels are not provided with speed sensors, this is an empirically predetermined value. Applicant has discovered that a period of time from 0.25 to 1.25, preferably from 0.50 to 0.75, seconds is sufficient to allow the trailer wheels to roll back up to approximately vehicle speed and allow the trailer brakes to be reapplied to minimize the stopping distance of the total vehicle 10. Accordingly, at the end of the predetermined period of time T, i.e., at point 214, the trailer brakes are reapplied at a rate R until a pressure P is achieved at point 216, which pressure P is preferably a function of the sensed or calculated first and/or second derivative of the articulation angle at the onset of the trailer swing event. Vehicle brakes will then be maintained at pressure P until termination of the braking event. Applicants have discovered that a rate of reapply R equal to about 10 PSI per second is an effective rate to achieve the pressure P as rapidly as possible without resulting in a repeat trailer wheel transverse loss of stability. To sense an incipient or occurring trailer swing event, the CPU 70 will determine a current value of articulation angle (AA) and preferably of a time derivative thereof (dAA/dt) based upon signals from the articulation angle sensors 170 and 172. The CPU 70 will also determine an articulation angle reference value (REF 1 ) and preferably an articulation angle time derivative reference value (REF 2 ) as functions of sensed and/or calculated current dynamic turning radius of curvature (DTRC) or steer angle (SA), and a time derivative thereof, respectively. The references REF 1 and REF 2 may be single values or ranges of values and may be determined from a look up table provided in CPU memory. If the vehicle is not equipped with a steer angle sensor 101, the related values of vehicle dynamic turning radius of curvature (DTRC) and of time derivatives thereof (dDTRC/dt) may be calculated from the wheel speed sensors, preferably at least the steer axle wheel speed sensors, 102 and 104, on opposite sides of the vehicles. The reference values, REF 1 and REF 2 may be determined as functions of dynamic turning radius of curvature and time derivatives thereof, respectively. Referring to Figure 10, the equilibrium turning radius of curvature for a single axle vehicle in circular motion is TRC E = 1 R = 1 TW W 1 W 2 - 1 where: A = center of circle, R = turn radius, W 1 = speed of the outside wheel, W 2 = speed of the inside wheel, and TW = track width = center to center spacing of the two wheels. The above equation can be approximated as a dynamic equation by means of a series expansion: DTRC = TRC E + Δt dTRC dW 1 dW 1 dt + dTRC dW 2 dW 2 dt + HIGHER ORDER TERM = 1 TW W 1 W 2 - 1 + Δt 1 W 2 W 1 - W 1 W 2 2 W 2 + HIGHER + ORDER TERMS where: W ˙ 1 = first time derivative of W 1 W ˙ 2 = first time derivative of W 2 The higher order terms may be dropped as being less significant to the approximation of the dynamic value. Assuming the vehicle is in motion, the dynamic turning radius of curvature of the steer axle of a vehicle may be approximated as of function of the expression: K W 1 W 2 - 1 + t W 1 W 2 - W 1 W 2 W 2 K = a constant depending upon vehicle geometry; W 1 = speed of the outside wheel; W 2 = speed of the inside wheel; W ˙ 1 = first time derivative of W 1 ; W ˙ 2 = first time derivative of W 2 ; and t = change in time. Referring to Figure 9, based upon a sensed or calculated current steer angle SA (or sensed or calculated dynamic turning radius of curvature) for tractor 12, an expected reference articulation angle (REF 1 ) may be determined. Assuming REF 1 equals the minimum expected articulation angle at current dynamic turning radius of curvature or current steer angle, then a current sensed articulation angle in the area represented by arrow 230 represents a non-trailer swing event (but possibly a jackknife event) while current articulation angle in the area represented by arrow 232 represents an incipient or occurring trailer swing event. Accordingly, unless the sensed articulation angle (AA) is in the same direction of rotation (of the same sign) as the first reference (REF 1 ) and the absolute value of the sensed articulation angle is equal to or greater than the absolute value of the first reference, a trailer swing event (i.e. trailer wheels transverse stability unable to overcome centrifugal forces on trailer) is incipient and/or occurring and the trailer brakes should be released to allow the trailer wheels to roll up to or towards vehicle speed thereby increasing the transverse stability thereof. Similarly, for a sensed/calculated rate of change of dynamic turning radius of curvature (dDTRC/dt) or steer angle (dSA/dt), an expected rate of change of articulation angle (REF 2 ) may be determined. Referring to Figure 9, if the steer angle increases over time, the absolute value of articulation angle should increase at a given rate while a decrease in steer angle over time should result in the absolute value of articulation angle decreasing at a given rate. Therefore, a trailer swing event will be indicated in the following conditions: (i) if the expected rate of change of articulation angle (REF 2 ) is in the same direction as REF 1 (i.e. a sharper cornering maneuver), if sensed rate of articulation angle (dAA/dt) is not in same direction of rotation as REF 2 or if the absolute value of dAA/dt does not equal or exceed the absolute value of REF 2 ; (ii) if the expected rate of change of articulation angle (REF 2 ) is in the opposite direction as REF 1 (i.e. a straightening out maneuver), if dAA/dt is in the same direction as REF 2 and the absolute value of dAA/dt is greater than the absolute value of REF 2 ; or (iii) if the absolute value of REF 2 equals about zero (i.e. a steady turn) and the absolute value of sensed dAA/dt exceeds the absolute value of REF 2 . Preferably, prior art to taking any corrective action, to assure that such action will correct and not exacerbate an existing situation, the level of confidence in the calculated/approximated value of DTRC is determined and corrective action is not undertaken until the level of confidence exceeds a predetermined value. The control system/method of the present invention is schematically illustrated, in flow chart format, in Figure 8. As is known, the use of higher order time derivatives of sensed steer angle or dynamic turning radius of curvature and articulation angle will provide the possibility of earlier sensing of an incipient trailer swing condition, especially for more lightly loaded trailers and/or lower coefficient of friction road surfaces, while the use of lower order time derivatives responds somewhat later in time but will allow a less sensitive, somewhat more reliable, determination of incipient trailer swing especially for more heavily loaded trailers and/or higher coefficient of friction road surfaces. Accordingly, the various logical methods described herein for testing for trailer swing conditions are not considered to be mutually exclusive but may be used in combination with one another. Various sensing devices for sensing the articulated vehicle articulation angle, first derivative of articulation angle with respect to time, and/or higher derivatives of articulation angle with respect to time may be utilized. By way of an example, referring to Figure 7, a fifth wheel assembly 34 is modified by the provision of two rollers, preferably spring loaded floating rollers 220 and 222 which are associated with potentiometers or the like and which will be caused to rotate by pivotal movement of the tractor relative to the trailer to provide input signals indicative of articulation angle and/or the first or second derivatives thereof with respect to time. As may be seen, applicant has provided an improved trailer brake control system/method for controlling the trailer brake application forces to prevent, arrest or minimize and provide rapid recovery from trailer swing events.

Claims: A trailer anti-swing brake control method for articulated vehicles (10) of the type comprising a tractor (12) and a trailer (14) connected at an articulating connection (34/176) defining a pivot axis (176) about which the trailer is pivotable relative to the tractor, an articulation angle (AA) of said vehicle defined by the included angle defined by a longitudinally extending axis of the trailer passing through said pivot axis (202) relative to a longitudinally extending axis of the tractor passing through said pivot axis (200), said tractor (12) including a pair of steerable wheels (148, 150) and a steer angle (SA) defined by the included angle between a line (234) perpendicular to the axis of rotation of said steerable wheels and a line (236) parallel to said tractor longitudinally extending axis (200), a tractor brake system, a trailer brake system, a driver operated brake effort demand device (76/78) for providing a demand input signal indicative of the magnitude of operators demand for vehicle braking, trailer brake control means (174) responsive in at least one operating mode for causing the trailer brake system to be applied with an operating force generally proportional to the magnitude of said demand input signal, said control method comprising: determining (170/172) a value indicative of at least one of articulation angle (AA), and a time derivative of articulation angle (dAA/dt) and providing at least one articulation input signal indicative thereof; determining a value indicative of at least one of tractor turning radius of curvature and a time derivative of tractor turning radius of curvature; determining at least one reference value (REF 1 , REF 2 ) as a function of at least one of the values indicative of tractor turning radius of curvature and a time derivative of tractor turning radius of curvature; comparing the value indicative of at least one of articulation angle, and a time derivative of articulation angle to at least one of a first reference value (REF 1 ) determined as a function of a value indicative of tractor turning radius of curvature, and a second reference value (REF 2 ) determined as a function of a value indicative of a time derivative of tractor turning radius of curvature, to detect the existence of conditions indicative of at least one of incipient and initial trailer brake induced trailer swing events. The method of Claim 1 further comprising: generating command output signals in response to detection of the existence of said conditions, and responding (174) by said control means to said command output signals by causing the trailer brake system brakes to be applied with a substantially reduced force (210-212) regardless of the magnitude of said demand input signal. The method of Claim 1 wherein said vehicle is provided with a sensor (101) providing input signals indicative of vehicle steer angle, said signals being indicative of tractor turning radius of curvature. The method of Claim 1 wherein said vehicle includes wheel speed sensors (102, 104) for providing input signals indicative of the rotational speeds of the wheels on at least one axle of said vehicle (148, 150) and said processing further comprises processing said input signals from said wheel speed sensors to determine a value (DTRC) indicative of the tractor turning radius of curvature. The method of Claim 1 wherein said vehicle is provided with a sensor (101) providing input signals indicative of vehicle steer angle, said signals being further indicative of tractor turning radius of curvature. The method of Claim 1 wherein said vehicle includes wheel speed sensors (102, 104) for providing input signals indicative of the rotational speeds of the wheels on at least one axle of said vehicle (148, 150) and said processing further comprises processing said input signals from said wheel speed sensors to determine a value (DTRC) indicative of tractor turning radius of curvature. The control method of Claim 1 wherein said control means responds to said command output signals by first causing said trailer brake system brakes to be substantially released (212-214) for a period of time (T) and then causing said trailer brake system brakes to be reapplied (214-216). The control method of Claim 7 wherein subsequent to releasing said trailer system trailer brakes said trailer brake system brakes are reapplied at a selected rate (R) to a selected maximum reapplication force (P), said selected maximum reapplication force having a magnitude considerably smaller than the maximum trailer brake system brake application force (208, 210). The control method of Claim 1 wherein the absolute value of said first reference value (REF 1 ) corresponds to a minimum absolute value of articulation angle at the current determined value indicative of tractor turning radius of curvature in the absence of the occurrence of one of incipient and initial trailer brake induced trailer swing. The control method of Claim 1 wherein said processing said input signals and determined values to determine the existence of said conditions further comprises initially (i) sensing that the vehicle operator has demanded at least partial braking and (ii) sensing that the value indicative of tractor turning radius of curvature is indicating a greater than zero absolute value of steer angle. The control method of Claim 4 wherein said processing said input signals and determined values to determine the existence of said conditions further comprises initially (i) sensing that the vehicle operator has demanded at least partial braking and (ii) sensing that the value indicative of tractor turning radius of curvature is indicating a greater than zero absolute value of steer angle. The control method of Claim 9 wherein said processing said input signals and determined values to determine the existence of said conditions further comprises initially (i) sensing that the vehicle operator has demanded at least partial braking and (ii) sensing that the value indicative of tractor turning radius of curvature is indicating a greater than zero absolute value of steer angle. The method of claim 4 wherein said value (DTRC) indicative of the tractor turning radius of curvature is determined as a function of the expression K W 1 W 2 - 1 + t W 1 W 2 - W 1 W 2 W 2 where: K = a constant depending upon vehicle geometry. W 1 = speed of the outside wheel W 2 = speed of the inside wheel; W ˙ 1 = first time derivative of W 1 ; W ˙ 2 = first time derivative of W 2 ; and t = change in time. The method of claim 13 further comprising determining a confidence level for the value (DTRC) indicative of the tractor turning radius of curvature and comparing said confidence level to a predetermined minimum confidence level reference value. The method of claim 6 wherein said value (DTRC) indicative of the tractor turning radius of curvature is determined as a function of the expression K W 1 W 2 - 1 + t W 1 W 2 - W 1 W 2 W 2 where: K = a constant depending upon vehicle geometry. W 1 = speed of the outside wheel W 2 = speed of the inside wheel; W ˙ 1 = first time derivative of W 1 ; W ˙ 2 = first time derivative of W 2 ; and t = change in time. The method of claim 15 further comprising determining a confidence level for the value (DTRC) indicative of the tractor turning radius of curvature and comparing said confidence level to a predetermined minimum confidence level reference value. A trailer anti-swing brake control system for articulated vehicles (10) of the type comprising a tractor (12) and a trailer (14) connected at an articulating connection (34/176) defining a pivot axis (176 about which the trailer is pivotable relative to the tractor, an articulation angle (AA) of said vehicle defined by the included angle defined by a longitudinally extending axis of the trailer passing through said pivot axis (202) relative to a longitudinally extending axis of the tractor passing through said pivot axis (200), said tractor (12) including a pair of steerable wheels (148, 150) and a steer angle (SA) defined by the included angle between a line (234) perpendicular to the axis of rotation of said steerable wheels and a line (236) parallel to said tractor longitudinally extending axis (200), a tractor brake system, a trailer brake system, a driver operated brake effort demand device (76(78) for providing a demand input signal indicative of the magnitude of operators demand for vehicle braking, and trailer brake control means (174) responsive in at least one operating mode for causing the trailer brake system to be applied with an operating force generally proportional to the magnitude of said demand input signal, said control system comprising: means for determining (170/172) a value indicative of at least one of articulation angle (AA), and a time derivative of articulation angle (dAA/dt) and providing at least one articulation input signal indicative thereof; means for determining a value indicative of at least one of tractor turning radius of curvature and a time derivative of tractor turning radius of curvature; means for determining at least one reference value (REF 1 , REF 2) as a function of at least one of the values indicative of tractor turning radius of curvature and a time derivative of tractor turning radius of curvature; and means for comparing the value indicative of at least one of articulation angle, and a time derivative of articulation angle to at least one of a first reference value (REF 1 ) determined as a function of a value indicative of tractor turning radius of curvature, and a second reference value (REF 2 ) determined as a function of a value indicative of a time derivative of tractor turning radius of curvature, to detect the existence of conditions indicative of at least one of incipient and initial trailer brake induced trailer swing events. The system of Claim 17 further comprising: means for generating command output signals in response to detection of the existence of said conditions, and means for responding (174) by said control means to said command output signals by causing the trailer brake system brakes to be applied with a substantially reduced force (210-212) regardless of the magnitude of said demand input signal. The system of Claim 17 wherein said vehicle is provided with a sensor (101) providing input signals indicative of vehicle steer angle, said signals being indicative of tractor turning radius of curvature. The system of Claim 19 wherein said vehicle includes wheel speed sensors (102, 104) for providing input signals indicative of the rotational speeds of the wheels on at least one axle of said vehicle (148, 150) and said processing further comprises processing said input signals from said wheel speed sensors to determine a value (DTRC) indicative of the tractor turning radius of curvature. The control system of Claim 17 wherein said processing said input signals and determined values to determine the existence of said conditions further comprises initially (i) sensing that the vehicle operator has demanded at least partial braking and (ii) sensing that the value indicative of tractor turning radius of curvature is indicating a greater than zero absolute value of steer angle. The control system of Claim 20 wherein said processing said input signals and determined values to determine the existence of said conditions further comprises initially (i) sensing that the vehicle operator has demanded at least partial braking and (ii) sensing that the value indicative of tractor turning radius of curvature is indicating a greater than zero absolute value of steer angle. The control system of Claim 17 wherein said processing said input signals and determined values to determine the existence of said conditions further comprises initially (i) sensing that the vehicle operator has demanded at least partial braking and (ii) sensing that the value indicative of tractor turning radius of curvature is indicating a greater than zero absolute value of steer angle. The control system of claim 20 wherein such value (DTRC) indicative of the tractor turning radius of curvature is determined as a function of the expression K W 1 W 2 - 1 + t W 1 W 2 - W 1 W 2 W 2 where: K = a constant depending upon vehicle geometry. W 1 = speed of the outside wheel W 2 = speed of the inside wheel; W ˙ 1 = first time derivative of W 1 ; W ˙ 2 = first time derivative of W 2 ; and t = change in time. The control system of claim 24 further comprising means for determining a confidence level for the value (DTRC) indicative of the tractor turning radius of curvature and means for comparing said confidence level to a predetermined minimum confidence level reference value.

Inventors: BREEN MICHAEL THOMAS, BREEN, MICHAEL THOMAS
Applicants: EATON CORP, EATON CORPORATION
Application year: 1991
Main classification: B60T8
IPC codes: B60T13, B60T8