Abstract: A method for the braking of a vehicle train with pressure-actuated brakes and arrangements for performing this method are disclosed. The prior art shows that, because of a different rapid build-up of a braking pressure in the various rigid vehicles of a vehicle train, there occurs an overrun shock during adjustment transition shifting braking phases. According to one embodiment of the invention, there is furnished a lead and predominance by a predetermined value in the co-braking signal furnished from the one rigid vehicle to the second rigid vehicle of a vehicle train. According to a further embodiment, a predominance by a predetermined amount in the braking pressure in the second vehicle versus the co-braking signal is furnished, if during the preceding brake application actuation the overrun shock has surpassed a preset tolerance width. The invention can be applied in particular for vehicle trains made up of a motor vehicle and one or several trailers or semitrailers.

Abstract: A fluid pressure braking system for a tractor trailer vehicle includes a supply line connecting the tractor and trailer braking systems. A low pressure responsive switch responds to the pressure level in the supply line for actuating a warning device when the pressure level in the supply line drops below a predetermined pressure level to thereby warn the driver before a brake actuation is effected that a low pressure level exists in the trailer braking system. A normally open stoplight switch is connected in series with the low-pressure responsive switch so that the signal generated by the low-pressure responsive switch is prevented from actuating the warning device when the tractor is operated in the "bobtail" mode without a trailer.

Abstract: Two different types of converter boxes (38, 84) provide the required interface for transmitting service brake control signals from the tractor unit (12) of a tractor-trailer combination vehicle to the trailer unit (16) thereof in which the tractor unit (17) and trailer unit (16) are provided with dissimilar braking systems. One type of converter box (38) provides the interface between a tractor (12) equipped with an electropneumatic braking system in which service brake applications are controlled by electrical signals and a conventional trailer (16) in which service brakes are controlled by pneumatic signals. The other type of converter box (84) provides the required interface between a tractor (12) which has service brakes controlled by conventional pneumatic signals and a trailer unit (16) which is provided with and electropneumatic braking system in which service brake applications are controlled by electrical signals.

Abstract: An integrated gladhand and quick-release valve for tractor-trailer highway vehicles is mounted on the tractor, as opposed to the trailer, so the operator of a particular tractor will uniformly have quick-release capability for any trailer drawn by the truck. The integrated gladhand and quick-release valve provides an inlet port for fluid communication from the tractor brake system and an outlet port for fluid communication to the trailer brake system. The intermediate passageway that provides fluid communication between the inlet and outlet ports contains a valve element. The valve element may be apertured to allow limited, continuous fluid communication between the tractor and trailer brake lines. During the quick-release mode, the tractor side is substantially isolated and the trailer side is vented through an exhaust port. The present invention provides a uniform and safe braking system for tractor-trailer highway vehicles where the tractor operator does not own or maintain the trailers.

Abstract: A seal for use in fluid couplings, such as those utilized in compressed air braking systems for tractor trailers and the like, has a lower portion, an intermediate portion, and an upper portion. The outer diameter of the intermediate portion is less then the outer diameters of the lower and upper portions and the outer diameter of the upper portion is less then the outer diameter of the lower portion. A bore extends through the lower, intermediate, and upper portions for providing fluid communication through the seal. The outer diameter of the upper portion and the upper surface of the upper portion at the bore are formed to have bevels such that the propensity for swaging or folding over of the upper surface during the coupling process is reduced. The seal is molded of polyurethane and color coded to mitigate the potential for cross connecting of the normal and emergency compressed air lines of a truck's braking system.

Abstract: Within a single envelope or housing, this full-function valve integrates all of the emergency and service requirements of a tandem axle air brake system for heavy duty truck semi-trailers, thereby decreasing complexity and cost and enhancing safety, reliability and operating capability while also satisfying applicable Federal Regulations. The housing encloses a spring brake valve module, a relay valve module and a biased one-way pressure protection valve, all interconnected to meet operating requirements, while preventing non-intentional spring brake engagement, foreclosing trailer movement without adequate service brake capability and optionally providing anti-compounding protection.

Abstract: Surge brake systems are used so that the brakes of towed vehicles can be applied automatically during slowing and stopping of towing vehicles. However, the known surge brake systems automatically apply the brakes to the towed vehicle during backing of the towing vehicle. The subject brake system includes a solenoid actuated valve which is disposed in a brake line to communicate a surge brake coupler to the brakes in a towed vehicle. A relay receives an electrical signal from an outputting device which places the valve in a closed position which disables the surge brake coupler and prevents the application of the brakes on the towed vehicle during backing of a towing vehicle. The relay receives an electrical signal from a producing device which overrides the electrical signal from the outputting means placing the valve in an open position. The open position of the valve allows application of the brakes on the towed vehicle so that braking is possible during backing of the towing vehicle.

Abstract: A combination including an electric brake control, ammeter and multiple brackets are disclosed for installation at the driver's station of a trailer towing vehicle. The brackets permit optional mounting of the ammeter on the control. A slotted opening in one of the brackets permits adjustment of the bracket about a horizontal axis for optimum viewing the bracket supported ammeter by the towing vehicle driver and also vertical positioning of the ammeter relative the brake control.

Abstract: A towed motor vehicle brake integrated between a towing and a towed vehicle, capable of applying the brakes of the towed vehicle. The structure of a towing hitch linkage deflects somewhat when it experiences tension or compression. A sensing device, preferably consisting of a hydraulic cylinder and an attached activating rod, grounded to a rotating lever connecting to the towed vehicle, senses compression of the deflecting portion of the linkage and activates the brakes of the towed vehicle to reduce the compressive forces. The tow brake requires no modification of the towed vehicle except allowing an interface with the towed vehicle's braking system. This provides flexibility of use with a variety of towed vehicles and ease of attachment and detachment.

Abstract: A multi-axle vehicle equipped with an antilock braking system which provides regulated braking operations to prevent locking of the wheels when the vehicle is braked and spinning of the wheels when the vehicle is started up, comprises a front axle, first and second rear axles, the first rear axle being a drive axle and the second rear axle being a liftable following axle, wheels mounted on each of the axles, rotational speed sensors producing signals indicative of the rotational speeds of the wheels associated with each of the wheels mounted on the front axle, on the drive axle, and on the following axle, brake cylinders associated with each of the wheels, a circuit supplying a pressure medium to the brake cylinders so that a braking pressure is applied to the wheels, and at least one electronic control unit which controls the braking pressure applied to each of the wheels.

Abstract: An analog service brake response enhancing circuit including an intelligent filter circuit for removing voltage transients appearing on input feedback signals, a friction brake request circuit for receiving input brake command request signals, a force motor calculating circuit for calculating the degree of service brake which is to be applied on a railway vehicle, and service brake control apparatus for controlling whether an application or a release mode of braking should be instituted on the vehicle and for accelerating the operation of an analog valve device to produce a full service brake condition for a predetermined time period.

Abstract: The preferred embodiment of the invention is a brake system comprised of a primary source of air under pressure, and independent secondary source of air under pressure, a primary relay, a secondary relay valve, a device for actuating the service brakes, a device for actuating the park brakes and a control device, and a plurality of brake assemblies. The primary relay receives air under pressure only from the primary source and the secondary relay receives air under pressure only from the secondary source, but the other components are so arranges as to achieve complete system redundancy in operation at the source level, the brake level, the hose level, and at the actuation level.

Abstract: An AND-type control valve useful in a vehicle braking system to prevent application of the vehicle brakes when only the right-hand or left-hand vehicle brakes are applied for the purpose of steering the vehicle. The control valve has two input flowpaths corresponding to the hydraulic braking circuit on different sides of the vehicle and a control output port for connection to the vehicle brake valve. Each input flowpath contains a non-return valve having associated therewith a flow sensitive device to provide a restricted flowpath which gives rise to a pressure drop which will tend to close or assist in closure of the non-return valve. A device is provided to prevent simultaneous closure of both non-return valves.

Abstract: A method operating a braking system to prevent or overcome glazing of the brake linings. The brake system has a friction-affected service brake and a wear-free auxiliary brake. A brake value, for instance vehicle deceleration, can be specified to the brakes by a brake value transducer. On the specification of the brake value transducer signals, a control unit triggers the brakes; it detects and evaluates signals characterizing the braking action. Upon a request for braking, the control unit preferentially triggers the auxiliary brake. If the brake value transducer signal level is high, it additionally switches on the service brake. The control unit detects the number of braking events of the service brake and their intensity (duration, action, etc.). As a function of these data, the control unit detects a threatening danger of glazing or glazing that has already begun and triggers the service brake exclusively.

Abstract: An air brake control system for use in truck trailers, including tandem trailers, having at each axle compressed-air spring brakes and service brakes with each trailer being coupled to receive compressed air through an emergency (supply) gladhand and to receive service brake signals through a service (control) gladhand and which includes an integrated brake valve system for each trailer within a common valve housing.

Abstract: A vehicle brake controller includes a variable pulse-width modulator operating at a constant frequency and with a variable pulse width to provide control pulses to a MOSFET element which actuates vehicle braking. The controller further includes a visual indicator which displays different colors to representatively indicate the amount of current applied to the brakes, and also to indicate whether an operable connection exists between the electronic controller and the vehicle brakes.

Abstract: In a vehicle combination consisting of a haulage truck (1) and a semitrailer (2) the brake system of the haulage truck (1) comprises a control valve (8) which allows the brake pressure imparted to the brakes (4) of the semitrailer (2) to be adapted to the brake pressure imparted to the brakes (3) of the haulage truck (1). The adaptation is carried out with the use of an electrical control unit (16), in which the actual deceleration of the vehicle during a braking sequence is compared to an expected deceleration. In the event of a discrepancy between these, a control member (15) on the control valve (8) is actuated automatically so that the semitrailer (2) is supplied with a higher or lower brake pressure relative to the haulage vehicle (1) depending on whether the actual deceleration was lower or higher than the expected deceleration. As a result of the adaptation, the brakes of the haulage truck (1) and of the semitrailer (2) can be used better under various operating conditons.

Abstract: The present invention provides a method of and an apparatus for regulating an electrically regulated brake circuit of a multi-circuit brake mechanism with pressure medium activated brakes. To decrease the expense of such multi-circuit brake mechanism, the invention transforms the pressure, modulated by the brake actuating mechanism, to an electrical signal and regulates or co-regulates the electrically regulated brake circuit (II) by this electrical signal.

Abstract: A brake system including an anti-skid apparatus with an electronic control unit for monitoring the grip of the vehicle tires on the road. It is also equipped with a yawing moment attenuator, controlled by the control unit, that in the event of highly varying coefficients of friction prevents an excessively great difference in brake pressure on the two sides of the vehicle. Tractor or towing vehicles driven without the trailer, especially semitrailer trucks, are difficult to control on road surfaces with variable grip, because of the major yawing and steering moments. The tractor or towing vehicle is therefore equipped according to the invention with a trailer detection unit, the signal of which is evaluatable in the control unit and can be fed as a control variable to the yawing moment attenuator. If the truck is driven without a trailer, the yawing moment attenuator can be controlled on the basis of this signal in such a way as to lessen the difference in brake pressure.

Abstract: A pneumatic braking system for a tractor and trailer which delivers air to the trailer substantially first and in a greater amount than to the tractor but which continues to deliver to the tractor until the pressure at the tractor approaches the pressure at the trailer. This gives better control and substantially avoids jack-knifing. A valve is also provided to lessen the time factor of air to the tractor when a greater braking pressure is applied. Also when "bob-tailing" only substantially 50% of air is delivered to the tractor to prevent over-braking.

Abstract: For engaging and disengaging a permanent-magnet slipper brake for a rail vehicle there are required relatively high forces which are generated either by a hydraulic motor or an electric motor. Therefore, in rail vehicles without external electric or external hydraulic connections and comprising a pneumatic brake line or brake-pressure lead, there is incorporated a pneumatically driven hydraulic power pump by means of which a hydraulic motor can be driven. This hydraulic motor is then capable of applying the forces required for engaging and disengaging the permanent-magnet slipper brake. The engaging and disengaging process is preferably controlled by a main air line.

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.

Abstract: A method for calculating a value indicative of tractor dynamic turning radius of curvature (DTRC), and of the level of confidence in the determined value, is provided. Wheel speeds from a front-steer axle (40) and a rear axle (36, 38) are sensed to determine the value indicative of DTRC and the speed variance between the wheels on each side of the vehicle (VAR-L, VAR-R). The speed variance values are used to calculate a filtered value of DTRC (FDTRC) and to determine a level of confidence in the DTRC and/or FDTRC values.

Abstract: A technique for acoustically communicating through existing air brake lines between a tractor and a trailer. The diagnostic status of the trailer antilock system is communicated via acoustic signals from the trailer antilock system through the air brake lines of the trailer and into the tractor air brake line. A piezo crystal located in the tractor air brake line converts the acoustic signal into an electrical signal which may be used to illuminate a lamp providing a display on the tractor dashboard.

Abstract: An electronic braking system in a motor vehicle capable of towing a standard trailer not having its own EBS system has a separate pressure control channel for the generation of a trailer service brake pressure signal in the event that a driver's braking demand is sensed at any axle of the towing vehicle. The pressure signal level is set in the towing vehicle so as to be a function of the driver's electrical demand signal modified in dependence upon the load exerted by the trailer on the towing vehicle as measured at a towing link therebetween.

Abstract: The railborne bogie vehicle with electrohydraulic brakes and hydropneumatic leveling suspension has in each of its bogies a hydraulic pressure supply unit (9) from which pressure control valves (15, 16) parallel to each other provide pressure to both the hydraulic brakes (19) and the hydropneumatic suspension (20) of that bogie. The back pressure lines (26 and 32) of the electrohydraulic brakes (19) or of the hydropneumatic suspension (20) lead to a hydraulic tank or sump (10) associated with the pressure supply unit (9).

Abstract: An electropneumatic subsystem of a vehicle compressed air braking system controls communication within the trailer control line, the trailer supply line, and the tractor spring brake delivery line. A valve operated by pilot pressure is installed in the trailer control line, and responds to the pressure level in the trailer supply line to open or close the trailer control line in accordance therewith, thereby providing a tractor protection function. A solenoid valve in the trailer supply line is actuated by an electronic control unit to open and close the trailer supply line to thereby perform a trailer spring brake control function and tractor protection function.

Abstract: A freely-flexing cantilever-type inertial sensor is suspended from one end so that its other end may move in response to inertial forces, for example, as a result of braking in a towing vehicle. The pendulum blade is secured to a rigid support structure in a manner whereby the opposite sides of the pendulum, which is preferably of multiple-layer construction and is elastically-deformable, may freely shift longitudinally with respect to one another upon lateral flexure of the pendulum in response to inertial forces. Preferably, this is accomplished by utilizing an adhesive connection directly between the rigid support and the adjacent side of the pendulum, whereby only that layer closest to the support is directly secured to it. The support for the pendulum preferably includes a self-hinge by which the position of the pendulum-supporting portion may be changed with respect to that of a base portion, in order to current for non-verticality in the actual operating environment.

Abstract: An electronic braking system (EBS) for a towing vehicle which provides for trailer service brake pressure supply via an additional EBS sub-system, and wherein, in order to speed up the application of trailer braking, the electrical signal representing the driver's braking demand is processed to generate an additional pressure pre-pulse of predetermined amplitude to pressurise the trailer braking circuit in advance of the proportional pressure setting determined by the driver. The pre-pulse is made up of two parts, a preset fixed duration pulse followed without break by a variable duration continuation pulse. The variable duration of the variable duration pulse is determined primarily by the rate of increase of the driver's demand signal.

Abstract: The specification relates to electronic controllers for braking systems, such as those used to actuate the brakes on towed vehicles in response to commands from the towing vehicle. The controller is responsive to an inertial sensor and/or manual control, and is completely independent of the towing vehicle brake light circuit. The controller includes a constant frequency variable pulse-width modulator which interacts with the towed vehicle braking system through a power MOSFET switch, which is preferably of N-channel configuration, that comprises the control element for the braking current supplied to the electromagnets that actuate the towed vehicle brakes. The controller advantageously includes a dual-slope integrator which provides a comparatively slow and gradually increasing control voltage to the variable pulse-width modulator, but discharges comparatively quickly to insure fast brake disengagement, in response to the inertial sensor or manual control.

Abstract: A pressurized fluid control module is provided for a tractor-trailer brake system to effect the appropriate braking function.

Abstract: A trailer braking system for a towing vehicle has a trailer braking valve (26) is fed with a pressurized air supply which is modulated by the opening of the valve, as controlled by a first control pressure regulated by a trailer braking controller (24) in accordance with braking demand signals, to produce a trailer braking pressure. In order that a trailer braking pressure may be generated even if the above trailer braking valve control fails, the valve is supplied with a second control pressure independently of the first, and which is also capable of operating the trailer braking valve (26). In a preferred embodiment, the second control pressure is supplied from a braking line of the towing vehicle, such that the "back up" control pressure is a function of the towing vehicle braking.

Abstract: The brake system having an electrically controllable brake apparatus of a trailer, the brake apparatus includes a control unit which is connected via electrical lines to an electrical energy source of a tractor. In braking, electrical currents are brought about of such a magnitude as to cause severe voltage drops in long lines that the functional safety of the brake apparatus may be threatened. The brake apparatus therefore has an electrical energy storage device disposed on the trailer, which can be charged by an energy source of the tractor and can be discharged upon triggering of the brake apparatus of the trailer. Voltage drops in the relatively short lines between the energy storage device and the control unit are therefore minimum. The lines between the electrical energy source of the tractor and the energy storage device of the trailer are charged by only low charging currents. The voltage drop is therefore low despite the long line length.

Abstract: A brake control system/method for preventing or minimizing trailer-swing (FIG. 6) in an articulated vehicle (10) is provided. The control system/method senses or calculates values indicative of articulation angle (AA) and time derivatives thereof (dAA/dt,d.sup.2 AA/dt.sup.2) and processes same to sense conditions indicative of an incipient or initial trailer brake induced trailer-swing event. An incipient or initial trailer brake induced trailer swing is sensed when the vehicle brakes are applied, the absolute value of articulation angle exceeds the absolute value of a reference value, the time derivative of articulation angle is in an opposite direction from articulation angle and/or the absolute value of one of the time derivatives of articulation angle exceeds the absolute value of a reference.

Abstract: The fifth wheel of an articulated vehicle comprising the coupling between a semi-trailer and a tractor is provided with measuring apparatus for measuring forces imparted from the semi-trailer. The apparatus comprises a sensing device for measuring horizontal loads, and a sensing device for measuring vertical loads. The signals from the sensing devices and are fed into an electronic controller, in turn to cause the brakes on the trailer to be applied to achieve balanced braking, anti-lock control, and traction control of the wheels. A tractor fitted with a braking system of the brake-by-wire type with a conventional semi-trailer, without modifications to semi-trailer or to the braking components of the semi-trailer can therefore be used.

Abstract: A brake control system/method for preventing or arresting and minimizing trailer-swing in an articulated vehicle (10) is provided. The control system/method senses or calculates values indicative of articulation angle (AA) and time derivatives thereof (dAA/dt, d.sup.2 AA/dt.sup.2) and processes same to sense conditions indicative of an incipient or initial trailer brake induced trailer-swing event.

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 a second order or higher time derivative thereof (d.sup.2 AA/dt.sup.2) and processes same to sense conditions indicative of a trailer brake induced trailer-swing event.

Abstract: A brake control system/method for preventing or arresting and minimizing trailer-swing (FIG. 6) in an articulated vehicle (10) is provided. The control system/method senses or calculates values indicative of least one time derivative of trailer transverse movement and processes same to sense conditions indicative of an incipient or initial trailer brake induced trailer-swing event.

Abstract: The invention provides a system for selective extension and retraction of a support leg of equipment such as a trailer or dock leveller, comprising a fluid motor which is adapted to be mechanically connected with an actuating member of the leg whereby on operation of the motor the leg can be extended or retracted, and apparatus for mounting the system onthe equipment so that a drive line from the motor to the acutating member is non-linear.

Abstract: An electronic braking system for a towing vehicle for towing a standard semi-trailer without such a braking system has a separate pressure control channel for the generation of trailer brake pressure whenever the towing vehicle is braked or if the parking brake of the towing vehicle is applied. The pressure signal level set in the towing vehicle is a function of the driver's electrical demand signal, compensated for trailer load and operating gradient. The compensation for trailer load is evaluated by assessing the total trailer mass from measurements of towing load during acceleration and substracting from this value the portion of the trailer load being supported by the towing vehicle as sensed by vertical force protection means on the towing means.

Abstract: Emergency brake control system for towed vehicles comprising brake regulation device and a plurality of switches whereby a discrete braking force may be selected and applied to the towed vehicle brakes upon actuation by the user of one of the switches and whereby the braking force is maintained without any intervention by the user.

Abstract: A brake control system/method for preventing or arresting and minimizing trailer-swing and jackknife in an articulated vehicle (10) is provided. The control system/method senses or calculates values indicative of articulation angle (AA) and time derivatives thereof (dAA/dt, d.sup.2 AA/dt.sup.2) and processes same to sense conditions indicative of the onset of a trailer brake induced trailer swing event or of a tractor brake induced jackknife event.

Abstract: A tractor-(28) trailer (30) vehicle (24) brake system control for distributing the brake effort to obtain inter-tractor-trailer proportional braking (H.sub.1 /V.sub.1 =H.sub.2 /V.sub.2) by use of sensors (80, 170, 172) mounted to the trailer only is provided. The control system senses (80) acceleration (a) and the ratio of vertical to horizontal forces (H.sub.F /V.sub.F) at the fifth wheel/king pin connection (34/176) by means of sensors (170, 172) mounted to the trailer (30) only and modulates the trailer sub-vehicle brakes only to cause the ratio H.sub.F /V.sub.F to equal a function of acceleration.

Abstract: A braking system for an aircraft towing vehicle which supports the nose wheel of an aircraft in a raised position and firmly clamps it to the vehicle. The braking force generated by the front wheels of the towing vehicle is greater by about 2:1 to 8:1 than the braking force at the rear wheels. The braking system has two hydraulic circuits employing identical braking cylinders at all four wheels of the vehicle. The number of cylinders per wheel are varied and different effective lever arms are used to generate like braking forces at each side of the vehicle, and the relatively greater braking force at the front wheels, even if one of the hydraulic circuits fails. The system limits the braking force at the front and rear wheels to maximum values to prevent excessive forces from damaging the nose gear of relatively smaller aircraft.

Abstract: In a brake valve for the operation of the service brake and spring-loaded brake installation of a utility vehicle trailer, a service brake valve (3) and a spring-loaded valve (1) are provided in a common housing (5) in mirror image arrangement. The two valves, operating in a manner known per se, are constructed of identical components and a common ventilation in the form of a ventilation insert (47) in the center of the housing (5). The two valves are fed either from a common reservoir (55) or from separate reservoirs (77, 79) provided for each of the valves, which reservoirs can be refilled through overflow valves (81, 83) without reflux from the line of the trailer holding reserve air.

Abstract: The spring-operated parking brakes of a tractor-trailer are controlled by a novel electro-pneumatic system. Pneumatic valving through which compressed air is conducted is mounted on the tractor chassis and coupled via an electronic circuit to two hand-operated control devices on the dash of the tractor cab, one for the trailer parking brakes only and the other for the tractor parking brakes. The latter device inherently operates the trailer parking brakes via the circuit if they are not already applied, and the circuit incorporates a sequencing function for operating the trailer brakes slightly before the tractor brakes when the tractor parking brake control is operated. Compressed air for the system is obtained via an engine-driven compressor which charges a tank. A pressure transducer monitors tank pressure for the circuit with the circuit maintaining tank pressure through selective loading and unloading of the compressor. Purging of the dryer is coordinated with compressor unloading.

Abstract: In an anti-lock brake control system for a vehicle (1) equipped with tandem axles (3), incipient or actual lockup is sensed on the forward or more lightly loaded axle (10) of the tandem axle pair, which sensing gives early warning of incipient lockup of the rear or more heavily loaded axle (12) of the pair.

Abstract: The relay valve employs a body preferably of metal defining a central exhaust port and a pair of delivery ports on the bottom of the valve body as well as a supply port on the side thereof. The body defines a cylinder in which a spool or shuttle moves toward and away from the exhaust port. A cover seals the upper open end of the body and defines a second cylinder in which a large piston moves from an upward, non operative position to a lower, operated position in engagement with the spool. The cover includes a control line port through which control pressure is applied to the valve. Service brake delivery pressure for the brake system is available at the supply port of the relay valve and sealed from the two or more delivery ports by a pair of O rings sealing the spool to shuttle in the body.

Abstract: A proportioning control valve for heavy duty fluid pressure braking system includes a proportioning piston which is normally held in engagement with an abutment by control pressure. A tare pressure spring urges a caging member into engagement with a stop which is spaced a predetermined distance from the end of the proportioning piston, which is less than the distance between the valve engaging member carried by the proportioning piston in the proportioning valve member. Upon loss of pressure at the control pressure port, the proportioning piston is urged toward the caging member. The proportioning piston moves between the gap defined between the end of the proportioning piston and the caging member without opposition from the tare pressure spring, thereby permitting the full force of fluid pressure to break seal friction between the seals carried by the proportioning piston and the wall of the housing.

Abstract: A tractor-(28) trailer (30) vehicle (24) brake system control for distributing the brake effort to obtain inter-tractor-trailer proportional braking (H.sub.1 /V.sub.1 =H.sub.2 /V.sub.2) by use of sensors (170, 172) mounted to the trailer only is provided. The control system senses (80) acceleration (a) and the ratio of vertical to horizontal forces (H.sub.F /V.sub.F) at the fifth wheel (34) by sensors (170, 172) mounted to the tractor (28) only and modulates the brakes to cause the ratio H.sub.F /V.sub.F to equal acceleration.