TRACTOR/TRAILER BRAKING SYSTEMS WITH SPRING BRAKE EMERGENCY BRAKING AND PARKING

Abstract: A full power closed centre hydraulic braking system for vehicle trailer combinations having service (20) and emergen­ cy (22) lines, with associated return lines (24), supplying hy­ draulic fluid from the vehicle through a relay valve (26) on the trailer, to a trailer-mounted accumulator. When the service line (20) is activated by a control on the vehicle or tractor, the relay valve (26) delivers fluid from the accumulator (40) to the trailer service brakes (12). There are spring brake actuators (10) which are connected to the accumulator (40) via a second re­ lay valve (34) triggered by pressure on the emergency line (22), preferably via a park valve (38) which is normally open except when set to a «park» position. This second relay valve (34) may be a dual relay valve also triggered by a manoeuvring valve (36) to permit temporary re-energization of the spring brake actua­ tors (10) when the towing vehicle and trailer are uncoupled.

Description: TRACTOR/TRAILER BRAKING SYSTEMS WITH SPRING BRSE EMERGENCY BRAKING AND PARKING This invention relates to full power closed ceni:re hydraulic braking systems for automotive vehicle trailer combinations and especially tractor/semi-trailer combinations. One kind of system which has been proposed includes both service and emergency line connections between the tractor and the trail or, each with its associated return line, the emergency line providing a consTant surely of hydraulic fluid from the vehicle through a relay valve on the trailer te 2 trailer - mounted storage unit or accurr,ulator, and a service line which when activated by the foot or hand control o;= the tractor, actuates the relay valve to deliver pressure fluid from the accumulator to the trailer service brakes. Although full power hydraulic braking systems hve beew used for some corsiderabe time on rigid vehicles, both privote and commercial, the system has not been widely used for road articulated combinations. This is for severa reasons not least among which is the problem of connecting and disconnecting the two systems, the inclusion of return lines (which are not required on air systems) and tht ability of the system to take care of internal leaks without pressurising the return linus and thence the coupling interface on the trailer when it is disconnected from the tractor. The greatest inhibiting factor, however. which is fundamentai to all hydraulic systems that the reservoir fluid volunie is limited. Air systems on the other hand have unlimited atmosphere to draw on and for example a single energy source (compressor) can pump against multi system protection valves thus ensuring continual charging of an unfailed circuit. This "overflow" technique cannot be applied to hydraulics and a serious system leak on the trailer could empty the tractor fluid rese-±voir in a few minutes, leaving only limited stored energy for braking. However, 'in order to overcome this deficiency the tractor system could be fitted with a tripie element pump, that is one element for each of the tractor axles (or circuits) and the third element for the trailer. This intention arose during design rjf a trailer system which can be coupled to such a trailer system or to a conventional power system embodying a dual storage reservoir dual hydraulic pump, dual brake valve which applies the front and rear brakes of the tractor as separate circuits and a pressure storage circuit for the parking brake which may be energised via a nor.-return valve by the pump element supplying the front axle circuit whilst the rear axle brake circuit together with pressure storage for the relay valves controlling the trailer brakes can be energised by the second element of the pump. When the tractor brakes are applied, trigger lines from the two axle circuits are silnultaneously eressurised to operate a dual relay valve in a modulated mariner to operate the trailer brakes. In the case of an accidental parting of any tractor and trailer in service the trailer brakes must be applied automatically this being triggered by either the disruption of the emergency (supply) line between tractor and trailer or by a disconnection of the emergency coupling. It is also desirable for the tractor system to be arranged seh that a failure in the parking circuit energy source destroys pressure in the trailer emergency line thus applying the trailer brakes. It is an object of this invention to provide secondary or residual braking in full power hydraulic trailer braking systems. According to this iiivention we propose a full power blazing system for a vehicle trailer combination, of the kind referred te and which comprises spring brake actuators connected to the accumulator via a second relay valve which is triggered by fluid pressure on the eme'."gency line. P eferablv, the relay valve is triggered via a park valve which is open except when set to a 'park' position. In a preferred embodimene, the relay valve is c dual relet valve also triggered by a manoeuvre valve when temporary re-energisation of the spring brake actuators is requited to brake release for example, when the towing vthicle and trailer are uncoupled. In the event that the trailer accumulator is discharged, release of the spring brakes would only be possible by means of a wind-off mechanism. A preferred embodiment of this invention is shown in the accompanying drawing which is a diagram of a two line trailer full power hydraulic braking system supplying service brake actuators 12 on axles I and II of a trailer. Axle I is additionally fitted with spring brake actuators 10 which are held "off" by a dual relay valve triggered by the fluid pressure on the emergency line as described below. The system illustrated has a four line coupling with the trailer, including a service control line 20 and'an emergency line 22 each with their associated return l nes 24. The service brakes are controlled by a simple relay valve 26 triggered by the service line pressure in turn modulated by a load sensing valve 28 connected to the emergency line 22 via a non-return valve 30 at the inlet port. The spring brake actuators are cuntrolled by a second relay valve 34 responsive to a manoeuvre valve 36 arA the emergency line pressure via a normally open park value 38, and supplied with motive fluid by a trailer sçsteln accumulator 40. The first relay valve 26 exhausts via an expansion chamber 42 to the service control return line 24. This system differs fundamentally from the system with reserve spring braking and parking described in our copending British Applicr ion c; even date numbered 7813597 in c'lat the spring brakes are used for emergency braking and are thus held in the "off" position when the emergency line 22 is energised, the pressure on this line acting as a trigger via the normally open park valve 38 onto the dual relay valve 34 supplied by the trailer accumulator. The manoeuvre valve 36 is connected so as also to trigger the dual relay valve 34 when temporary re-energising of the spring brake actuators is required to release the brakes. Should it be necessary to move a trailer with a discharged accumulator, the spring brakes would have to be wound-off as a temporary measure. Although the trailer goes automatically into 'emergency' when disconnected from the tractor, the park valve should be set to the park position to ensure that the spring brakes remain applied when the trailer is recoupled. Parking the trailer when coupled to a tractor is executed simply by moving tlie lever to "Park" thus exhausting the spring brake chambers to the expansion chamber 42

Claims: CLAIMS: 1. A full power closed centre hydraulic braking system for a vehicle trailer combination, comprising service and emergency line connections between the vehicle and the trailer each with its associated return line, the emergency line providing a constant supply of hydraulic fluid -from the vehicle through a relay valve on the trailer, to a trailer mounted storage unit or accumulator, and a service line which when activated by a control on the tractor actuates the relay valve to deliver pressure fluid from the accumulaeor to the -trailer service brake actuators, wherein the system further comprises spring brake actuators connected to the accumulator so ab to be held off by pressure fluid from the accumulator, via a second relay valve which is triggered by fluid pressure on the emergency line. 2. A braking system according to claim 1 wherein the second relay valve is triggered via a park valve which is open except when set to a "park" position, wherein tne spring brake actuatcrs are exhausted to apply te brakes. A A braking system according to-claim 2 wherein the second relay valve is dual relay valve triggered by the emergency line pressure via the park valve an also by 2. manoeuvre valve when temporary re-eergisçtion of the brake actuators is required to release Lhe brakes.

Inventors: PAGE, WILBUR MILLS
Applicants: CLAYTON DEWANDRE COMPANY LIMITED
Application year: 1980
Main classification: B60T13
IPC codes: B60T13