GB2131509A - Failsafe means in tractor and trailer braking systems - Google Patents

Abstract

To ensure that the braking systems of vehicles forming a vehicle train mutually coact, and that if such is not the case they trigger measures for emergency braking, the tractor braking system includes an electrically controlled emergency venting valve (51) in a supply line (53) to a coupling part (20) for the trailer, said emergency venting valve (51) being connected to a pressure transducer (50) adapted for sensing the operating pressure in a service supply line (35) to a second coupling part (36). When the pressure has failed or is too low in the supply line (35) between the vehicles, and when simultaneously there is an indication from driver's valve (11) that the vehicle brakes are in use, control unit (40) activates the emergency venting valve (51) to interrupt the pressure transfer to the trailer, which responds by applying the trailer brakes. <IMAGE>

Description

SPECIFICATION An arrangement in a braking system for heavy road vehicles The present invention relates to an arrangement in a braking system for heavy road vehicles, including at least one electrical operating circuit for controlling at least one pneumatic supply circuit for regulated pressure supply to a plurality of brake cylinders for the vehicle wheels, braking systems for trailers being connectible to this system via coupleable coupling parts.

In heavy road vehicles and combined such vehicles, e.g. a truck with one or more trailers, the use of pneumatically operating braking systems is dominant. In such a braking system there often is a comparatively large time difference between events taking place at the front and at the rear axles of a vehicle train when engaging or disengaging the brakes. With the object of eliminating this disadvantage it is known to utilize an electrical system for operating the brakes, which system enables rapid and simultaneous braking of the wheel axles supplied with brakes in the vehicle train. The transmission of electrical operation signals has involved many practical problems, however, as a result of poor contact formation and difficulties in easily detecting whether triggered signals are correct or not.

The present invention relates to an arrangement which wiil ensure that the braking systems of the vehicles included in a vehicle train mutually coact and trigger measures for emergency braking should they not do so. The invention is essentially distinguished in that the braking system includes an electrically controlled emergency venting valve in a supply line to a coupling part for the trailer, said emergency venting valve being connected to a pressure transducer adapted for sensing operating pressure in a supply line to a second coupling part for the trailer and adapted for sending, in response to a failed or too low operating pressure in the supply line, a signal for activating the emergency venting valve so as to interrupt pressure transfer to the trailer.

Secure detection of the operating signals transferred to the trailer during a braking sequence are obtained by the inventive arrangement. The operating signals are transmitted to the trailer braking system solely with the aid of compressed air, and such signals can easily be detected.

Should pressure fail or become too low during braking, there is an immediate triggering of the electrically controlled emergency venting valve.

This puts a supply circuit in the trailer into communication with the atmosphere, and an emergency braking valve in the braking system of the trailer triggers braking of the trailer.

The pneumatic signal transmission does indeed have a certain time loss compared with an electrical operating signal transmission, but this is negligible in this connection. On the other hand, there is avoided the function and reliability problems which have been found in practical use to be difficult to put right in electrical signal transmission between the vehicles. Furthermore, the standardized pneumatic coupling systems of today can be utilized in the inventive solution.

Other characterizing features distinguishing the invention are apparaent from the accompanying claims and the description hereinafter of an embodiment exemplifying the invention. The description is made with reference to the accompanying drawings, where Fig. 1 schematically illustrates an inventive braking system for a traction vehicle, and Fig. 2 schematically illustrates a braking system for a trailer connectible to the traction vehicle.

The braking system illustrated in Fig. 1 for a traction vehicle, e.g. a heavy truck, includes a compressor 1 which supplies compressed air to the traction vehicle via a pressure regulator 2, a wet tank 3 for dehumidifying the compressed air, and a four-way safety valve 4. In this case there are supplied a front wheel circuit 5, a rear wheel circuit 7, a supply circuit 9 to a trailer and an auxiliary circuit 10.There is a pressure tank 6 in the front brake circuit 5 for supplying pressure to a travel brake valve 11 and to two electrically controlled solenoid valves 1 2, 13, each of which is assigned to a respective front wheel brake cylinder 14, 1 5. There is a pressure tank 8 included in the rear brake circuit 7 for supplying pressure to two electrically controlled solenoid valves 1 6, 1 7, each of which is assigned to a respective rear wheel brake cylinder 18, 1 9. The supply circuit 9 supplies pressure to a coupling head 20 intended to be connected to a corresponding coupling head 21 on a trailer (see Fig. 2), for maintaining a prescribed pressure in the supply circuit 70 of the trailer.

An electrically controlled parking brake valve 22 is also connected to the supply circuit 9, and is controlled by an electrical switch 23 actuable by the driver. With its aid, the driver can regulate the compressed-air supply to two spring brake cylinders 24, 25 which function in a manner known per se and are to be found one at each rear wheel of the traction vehicle. The supply circuit 9 further supplies pressure to an electrically controlled solenoid valve 26 regulating the operating pressure to the trailer in a manner which will be more clear from the description below.

The travel brake valve 11 has a pneumatic valve portion 28 and an electrical current regulator 29, which are activated simultaneously on the driver's actuation of the valve 11. The valve portion 28 passes pressure from the pressure tank 6 to a pneumatic supply circuit 30 which transfers pressure to one input on each of two-way valves 31, 32 each of which is assigned to a respective front wheel brake cylinder 14, 1 5. The other input on each of the two-way valves 31, 32 receives pressure from the solenoid valves 12, 1 3 which are assigned to the respective brake cylinders 14, 1 5. The two-way valves 31, 32 thus pass pressure to the brake cylinders 14, 1 5 from either of the mentioned inputs.

The pneumatic supply circuit 30 is also connected to a supply circuit 33 passing operating pressure to one input of a third two-way valve 34.

The other input on this valve 34 is supplied with pressure from the solenoid valve 26 which is connected to the supply circuit 9. The outlet of the two-way valve 34 is connected by a short line 35 to a coupling head 36 intended for transmitting operating pressure between the vehicles when it is coupled together with a corresponding coupling head 37 on a trailer coupleable to the traction vehicle.

The current regulator 29 of the travel brake valve 11 transmits, via a line 38, a regulated electrical operating signal to an electronic control unit 40. Said signal represents the criterion value for the braking operation, and the control unit 40 is disposed for reforming it to a modified operating signal which, via a forward circuit 41, a rear circuit 42 and a so-called trailer circuit 43 is applied to the respective solenoid valves 12, 1 3, 1 6, 1 7, 26 for activating then.The modified operating signal is also affected by other means connected with the control unit 40, e.g. by axle pressure sensor 44 and by possible regulating means for anti-lock braking (not shown), so that the operating signals supplied to the respective circuits 41 13 provide varied pressure application to the brake cylinders 14, 1 5, 1 8, 19 for optimum braking of the vehicle.

The control unit 40 is furthermore connected via a line 47 to a pressure transducer 50 which senses prevailing pressure between the two-way valve 34 and the coupling head 36 and sends electrical signals corresponding hereto back to the control unit 40. Furthermore, the control unit 40 is connected by a line 48 to an electrically controlled emergency venting valve 51 which is disposed in the supply circuit 53 to the trailer, immediately in front of the coupling head 20 on the traction vehicle.

The emergency venting valve 51 is activated by an electric output signal in the line 48, a communication then being opened between the supply line 53 connected to the coupling head 20 and the atmosphere. As described in more detail below in conjunction with Fig. 2, this means that the trailer is caused to brake automatically.

Activation of the emergency venting valve 51 takes place when the control unit 40 via the line 38 receives a signal indicating that the travel brake valve 11 is activated for braking simultaneously as the transducer 50 via the line 47 sends a signal representing the existence of no pressure in the line 35 or at least a pressure which is too low in said line. This means that a fault has occurred which prevents operating pressure from being transferred to the trailer. The fault can have occurred either in the traction vehicle operating system 30, 33, 34 or in the operating pressure transfer between the respective coupling heads 36, 37.For pressure failure to occur at the transducer 50 as a result of a faulty traction vehicle operating system 30, 33, 43, it is required that a fault simultaneously occurs in the electrical trailer circuit 43 and in the pneumatic supply circuit 30, 33 to the trailer.

The braking system has the following function during normal operation. When the internal combustion engine (not shown) of the traction vehicle drives the compressor 1, there is created and maintained a predetermined supply pressure, about 8 bar, in the outgoing supply circuits 5, 7, 9, 10 of the braking system, while the pneumatic supply circuits 30, 33 transmitting the operating signals are without pressure. The electrical operating circuits 41, 42, 43 are inactive at the same time, e.g. no current passes through them.In activating the travel brake valve 11, the current regulator 29 supplies an operating signal to the electronic control unit 40 which then passes on reformed operating signals to the solenoid valves 12, 13, 16, 17, 26 in the electrical operating system 41, 42, 43. The pneumatic valve portion 28 in the travel brake valve 11 simultaneously allows compressed air to be fed to the pneumatic supply circuits 30, 33. The electrical operation of the solenoid valves 12, 13, 16, 17, 26 results in that compressed air may be more rapidly supplied to the brake cylinders 14, 1 5, 18, 1 9 than if a purely pneumatic operating system were to cater for the compressed-air supply.In the normal case, the pneumatic supply circuits 30, 33 do not participate in the braking operation, and participation first takes place when the electrical operating system 41, 42, 43 is entirely or partially out of operation. In such a fault situation, the twoway valves 31, 32, 34 allow compressed air from the pneumatic supply circuits 30, 33 to be supplied to the brake cylinders 14, 15, 18, 19 and to the coupling head 36 for operating pressure transfer to the trailer. The pneumatic supply circuits 30, 33 thus constitute a safety braking system which comes into action for faults in the ordinary electrical operating system 41, 42, 43.

The braking system illustrated in Fig. 2 for a trailer includes an electrical operating circuit 60, a pneumatic supply circuit 70 and a pneumatic emergency braking circuit 80. A pressure transducer 61 is included in the electrical operating circuit 60, the transducer sensing the pneumatic pressure transferred to the coupling head 21 on the trailer when it is coupled together with the corresponding coupling head 20 on the traction vehicle. The transducer 61 sends an electrical signal in response to the supply pressure level transferred to the trailer, and this signal is applied via a line 63 to an electronic control unit 65 arranged on the trailer. The signal is reformed in the control unit 65, and the reformed operating signal is passed on via lines 66, 67 to electrically controlled solenoid valves 68, 69 disposed in the supply circuit 70 for regulating the supply of compressed air to the brake cylinder 73, 74 of the respective wheel, from a pressure tank 77 included in a the supply circuit 70.

Braked wheels on further trailer axles may of course be controlled for braking via further electrical operating circuits, solenoid valves, supply circuits and brake cylinders coupled in a similar manner. It is also suitable here to have the trailer equipped with an axle pressure transducer 78 which senses the load on at least one of the trailer axles. A signal corresponding to the axle pressure is applied to the control unit 65 and influences the electrical output signal to the operating circuit 65, 67 of the axle for giving differentiated braking on the axle in response to the output signal of the axle pressure transducer 78.

The regulated supply of compressed air during braking, from the solenoid valves 68, 69 to the brake cylinders 73, 74, takes place, as at the front axle of the traction vehicle, via two two-way valves 75, 76, one for each brake cylinder 73, 74.

On the respective two-way valves 75, 76 the outlet is connected to the brake cylinder in question, while one inlet is connected to the corresponding solenoid valve 68, 69 and the other inlet is connected to the emergency braking circuit 80.

The emergency braking circuit 80 is controlled by an emergency brake valve 82 in the supply circuit 70 of the trailer, between the pressure tank 77 and the coupling head 21, for transferring supply pressure from the tractiori vehicle. The emergency braking valve 82 has the task of preventing venting the pressure tank 77 should there be a failure in the supply pressure transfer, e.g. due to the emergency venting valve 51 on the traction vehicle being activated because of a fault in its operating system 30, 33, 43, and instead establish communication between the pressure tank 77 and the emergency braking circuit 80.

Pressure supply to the brake cylinders 73, 74 then takes place via the two-way valves 75, 76 for emergency braking of the trailer.

The emergency braking valve 82 furthermore coacts with a so-called shunt valve 84 in the emergency braking circuit 80 for enabling movement of a trailer disconnected from the traction vehicle during the time when the supply circuit 70, via the emergency brake valve 82, is still capable of maintaining pressure for braking the trailer in the brake cylinders 73, 74, in spite of a continuous supply pressure drop due to leakage in the supply ciruit 70. The shunt valve 84 is manually operable, and in the shunt position it connects the brake cylinders 73, 74 to atmosphere simultaneously as communication between the pressure tank 77 and the brake cylinders 73, 74 is interrupted. Venting the brake cylinders 73, 74 thus provides the desired shunting facility.

The inventive solution also allows the emergency braking of a trailer connected to a traction vehicle for failed operating signal transmission between the vehicles in the cases where the traction vehicle is equipped with an electropneumatic braking system. There is thus eliminated the need for being able to detect the operating signal transmission, and neither is there required an electrical connection between the vehicles, such a connection being sensitive from the operational and reliability aspects. To the traction vehicles equipped with an inventive braking system there can be coupled trailers equipped with a conventional pneumatic braking system with an emergency braking function, or trailers equipped with a braking system as described in Fig. 2. Failed operating signal transmission is detected in both cases, and in activation of the travel brake the emergency venting valve is controlled such as to trigger the emergency braking function of the trailer.

The embodiment described above is not to be regarded as restricting the invention, and the latter can be modified in alternative embodiments within the scope of the following claims.

Claims (4)

1. An arrangement in a braking system for heavy road vehicles, including at least one electrical operating circuit for controlling at least one pneumatic supply circuit for regulated pressure supply to a plurality of brake cylinders for the vehicle wheels, braking systems for trailers being connectible to this system via coupleable coupling parts, characterized in that the braking system includes an electrically controlled emergency venting valve in a supply line to a coupling part for the trailer, said emergency venting valve being connected to a pressure transducer adapted for sensing operating pressure in a supply line to a second coupling part for the trailer and adapted for sending, in response to a failed or too low operating pressure in the supply line, a signal for activating the emergency venting valve so as to interrupt pressure transfer to the trailer.

2. An arrangement as claimed in Claim 1, characterized in that the pressure transducer is connected to the emergency venting valve via a control unit included in the electrical operating system of the braking system, said control unit also being connected to a sensing means sensing the position of the vehicle brake and sending a signal in response hereto to the control unit, and in that the control unit controls the emergency venting valve in response to input signals from said units.

3. An arrangement as claimed in Claim 2, characterized in that the emergency venting valve on activation is disposed for opening an outlet for the supply line to the atmosphere.

4. An arrangement substantially as hereinbefore described with reference to and as shown in the accompanying drawings.