GB2060285A - An hydraulic power braking system for a tractor vehicle provided with a trailer - Google Patents

Abstract

An hydraulic power braking system (10) for a tractor vehicle (11) and trailer (12) has an automatic electro-hydraulic disengagement brake for the trailer. Brake lights (71), the magnet (35) of a valve (21) on the trailer (12), and a charging indicator light (63) are connected in current circuits which only pass through three contacts (45, 46, 47) of a multi-pole electrical plug-in coupling (43). All the circuits of the three loads (71, 35, 63) are associated, at least periodically, with the contact (47), whereas the remaining contact (46) not associated with the earth conductor can be connected to both poles (52, 49) of a battery (51) through a double switch (55) actuated by a brake pedal (13). Whereas the brake lights (71) illuminate with each actuation of the brake pedal (13), the charging indicator light (63) is only switched on during the various operating conditions when the hydraulic accumulator (25) is being relieved. The usual standard seven pole plug-in coupling used on tractors can be retained with the present disengagement brake. <IMAGE>

Description

SPECIFICATION An hydraulic power braking system for a tractor vehicle provided with a trailer The invention originates from an hydraulic power braking system for a tractor vehicle provided with a trailer and with an automatic electro-hydraulic disengagement brake for the trailer according to the type set forth in the main claim. Such a power braking system is already known from German OS 27 26 514 in which, however, there are no brake lights connected in the electrical circuit on the trailer associated with the disengagement brake. Although with this braking system, only one charge indicator light and the magnet of a changeover valve are connected in the current circuit as an electrical load, they require an electrical plug-in coupling provided with three plug-in contacts for three parallel current circuits as well as an additional plug-in contact for an earth conductor.With this system, not only is it a disadvantage that no brake lights are controlled but the usual seven pole standard plug-in coupling cannot be used in the electrical system. Since, in this instance, the conductors of the electrical device are not used repeatedly, its construction is relatively expensive.

ADVANTAGES OF THE INVENTION As opposed to this, the power braking system in accordance with the invention for a tractor vehicle provided with a trailer and with automatic electro-hydraulic disengagement brakes comprising the characterising features of the main claim, has the advantage that, by multiple use of electrical conductors, a plurality of electrical loads on the system can be controlled with one plug-in coupling having relatively few plug-in contacts. In particular, the functions of the brake lights, the magnets for the magnetic valve for the disengagement brake and the charging indicator light are controllable by three plug-in contacts of the plug-in coupling wherein one of these plug-in contacts is used for the earth conductor.In this manner, it is possible to use the usual seven pole standard plug-in coupling with hydraulic power braking systems of that kind for tractor vehicles and with electro-hydraulic disengagement brakes for the trailer. Thus, the system is produced with relatively small outlay having regard to the plurality of functions.

Advantageous further developments and improvements of the power braking system set forth in the main claim are made possible by the measures set forth in the sub-claims. The use of a double switch according to claim 3 is of special advantage by which illumination of the charging indicator light only in the required circumstance may be achieved.

DRAWING An embodiment of the invention is illustrated in the drawing and is described in more detail in the following specification. The single figure shows in a simplified representation, an hydraulic power braking system for a tractor vehicle provided with a trailer and with automatic electro-hydraulic disengagement braking for the trailer.

DESCRIPTION OF THE EMBODIMENT The figure shows an hydraulic power braking system 10 for a tractor vehicle 11 provided with a trailer 1 2 and with automatic electro-hydraulic disengagement braking for the trailer 12. A brake pedal 1 3 with an associated master cylinder 1 4, the hydraulic pressure from which is transmitted on the one hand to the tractor vehicle brake 1 5 and on the other hand for controlling a brake valved 16, is arranged on the tractor vehicle 11.

The brake valve 16 is one such as is known from German specification 20 55 801. From the valve, a trailer brake line 17 leads through an hydraulic coupling 1 8 to a valve connection 19 for a magnetic valve 21 arranged on the trailer 12. The brake valve 1 6 receives pressure medium from a pump 22 which normally supplies an hydraulic load 23, for example a power lift on a tractor vehicle, with oil. An accumulator connection 24 of the magnetic valve 21 is in communication with an hydraulic accumulator 25 the pressure of which is monitored by an electro-hydraulic pressure switch 26. A cylinder connection 27 of the magnetic valve 21 is in communication through a brake pressure regulator 28 with a trailer brake cylinder 29 which acts on a trailer brake 31.The magnetic valve 21 has a control slide 32 which is maintained in the illustrated central position 34 by a spring 33. The control slide 32 can be moved by a magnet 35 into a right-hand limit position 36 and can be moved by a manually actuated device 37 into a left-hand limit position 38.

The electro-hydraulic pressure switch 26 is par of an electrical switching device 41 the part 42 of which arranged on the tractor vehicle 11 is connected through an electrical plug-in coupling 43 to a part 44 arranged on the trailer. The plug-in coupling 43 is a usual standard seven pole plug-in coupling of which, in the present case, only a first plug-in contact 45, a second 46 and a third plugin contact 47 are used whilst the remaining plugin contacts remain available for operations which are not of particular interest in this case. The parts of the plug-in contacts 45, 46, 47 arranged on the tractor vehicle 11 are connected to further components arranged on the tractor vehicle as follows: from the first plug-in contact 45, a first conductor 48 leads to one side of an electrical energy source which, in this case, is the negative pole 49 of a battery 51.A second conductor leads from the positive pole 52 of the battery to the third plug-in contact 47. A third conductor 54 leads from the second plug-in contact 46 to an electro-mechanical double switch 55 which is actuated by the brake pedal 1 3. The double switch 55 has a normally closed contact 56 and a normally open contact 57. A first terminal 58 of the normally closed contact 56 and a first terminal 59 of the normally open contact 57 are connected to the third conductor 54. A fourth conductor 62 leads from a second terminal 61 of the normally closed contact 56 to the negative pole 49. A charging indicator light 63 is included in the said fourth conductor 62. A fifth conductor 65 leads from a second terminal 64 of the normally open contact 57 to the positive pole 52 of the battery 51.Moreover, a second electro-hydraulic pressure switch 66 which is so connected in the second conductor 53 that it is in parallel with the normally open contact 57, is arranged on the tractor vehicle 11. The pressure switch 66 is actuated in accordance with the pressure prevailing in the master cylinder 14. Furthermore, an electrical switch 67 is connected in the second conductor 53 in series with the pressure switch 66.

The part 44 of the electrical switching device arranged on the trailer 12 has a sixth conductor 68 which connects the first plug-in contact 45 to the magnet 35 on the magnetic valve 21.

Furthermore, a seventh conductor 69 leads from the magnet 35 to the third plug-in contact 47.

Two brake lights 71 on the trailer 12 are in communication on the one hand through an eighth conductor 72 with the second plug-in contact 46 and on the other hand through a ninth conductor 73 with the sixth conductor 68 and thus with the first plug-in contact 45. The electrohydraulic pressure switch 26 is connected in a tenth conductor 74 which leads from the seventh conductor 69 to the eighth conductor 72.

The method of operation of the power braking system is as follows, wherein only that much of the system is described as is necessary for the understanding of the invention. Moreover, the operation of the brake valve 1 6 is assumed to be known from the previously referred to German patent specification. Of the numerous possible operating conditions with such braking systems, only one is considered in detail in the following.

As a first operating condition will be considered that in which the trailer 1 2 is coupled to the tractor vehicle 11 which is in operation. Thus, it is assumed that the brake pedal 1 3 is not actuated.

As long as there is no control pressure at the brake valve 1 6, it conducts the pressure medium delivered by the pump 22 through the hydraulic load 23 back to the tank. In the electrical part 42 on the tractor vehicle 11 the normally closed contact 56 of the double switch 55 is closed and the normally open contact 57 is open. The electrical switch 67 coupled to a hand brake on the tractor vehicle 11 is closed with the hand brake not actuated. Likewise, the second pressure switch 66 is closed when there is no braking pressure in the master cylinder 14. Moreover, it is assumed that when the trailer 12 is not yet coupled, the hydraulic accumulator 25 is completely relieved. The pressure prevailing in the accumulator 25 is lower than the value set at the first pressure switch 26, or is completely relieved, so that the pressure switch 26 is closed.

Moreover, the magnet 35 on the magnetic valve 21 is not energised; thus, the control slide 32 is retained by the spring 33 in its central position 34.

If, by coupling the trailer 12 to the tractor vehicle 11, the hydraulic coupling 18 and the electrical plug-in coupling 43 are now closed, then a current flows from the positive pole 52 through the second conductor 53 including the switches 66, 67, through the third plug-in contact 47, the seventh conductor 69 to the magnet 35 and back through the sixth conductor 68, the first plug-in contact 45 and the first conductor 48 to the negative pole 49. The magnet 35 is energised and pushes the control slide 32 in the magnetic valve 21 into its right-hand limit position 36. In so doing, it connects the valve connection 1 9 to the cylinder connection 27, whereas the accumulator connection 24 is blocked by the non-return valve.

As a result of the accumulator 25 not being charged, the first pressure switch 26 is closed. For that very reason, a second current circuit proceeding from the positive pole 52 leads parallel to the first current circuit through the magnet 35 to the negative pole 49 through the second conductor 53, the third plug-in contact 47, a portion of the seventh conductor 69, the tenth conductor 74 including the pressure switch 26, a portion of the eighth conductor 72, the brake lights 71, the ninth conductor 73, a portion of the sixth conductor 68, the first plug-in contact 45 and the first conductor 48.Furthermore, a third current circuit proceeding from the positive pole 52 leads back to the negative pole 49, likewise parallel to the first current circuit, through the second conductor 53, the third plug-in contact 47, the tenth conductor 74, a portion of the eight conductor 72, the second plug-in contact 46, the third conductor 54, the normally open contact 56, the fourth conductor 62, the charging indicator light 63 and a portion of the first conductor 48.

Thus, when the accumulator 25 is not charged, both the brake lights 71 and the charging indicator light 63 light up whereby an indication is given to the driver that the disengagement brake is not prepared for operation. In so doing, the three parallel current circuits through the magnet 35, the brake lights 71 and the charging indicator light 63, pass through the plug-in contact 47.

The charging of the hydraulic accumulator 25 in order to prepare the disengagement brake for operation is considered as the next operating condition. For this purpose, the service brake of the tractor vehicle 11 and of the trailer 12 is actuated with the aid of the brake pedal 13. The pressure generated in the master brake cylinder 14 controls the brake valve 1 6 so that the circulation flowing from the pump 22 through the load 23 is throttled and the brake valve 1 6 controls pressure medium in the trailer brake line 17 the pressure of which behaves proportionally to the control pressure. Thus, pressure medium flows from the brake valve 16 through the trailer brake line 17, the hydraulic coupling 18 and the control slide 32 located in its right-hand limit position 36 to the hydraulic accumulator 25 which is charged thereby. On charging the accumulator 25, pressure medium flows in addition through the brake pressure regulator 28 into the trailer brake cylinder 29 and actuates the brake 31. In addition, on actuating the brake pedal 13, the double switch 35 is actuated. Thus, its normally closed contact 56 acts so that the current circuit through the charging indicator lamp 63 is interrupted and the latter is extinguished.

Simultaneously, the normally open contact 57 provides a connection between its terminals 64 and 59. Thus, a current can flow from the positive pole 52 through a portion of the second conductor 53, the fifth conductor 65, the normally open contact 59, the third conductor 54, the second plug-in contact 46, the eighth conductor 72, the brake lamps 71, the ninth conductor 73, the sixth conductor 68, the first plug-in contact 45 and the first conductor 48 to the negative pole 49. Thus, the double switch 55 acts so that on actuation of the brake pedal 13 the brake lights 71 are also illuminated. Furthermore, on actuation of the brake pedal 13, the second pressure switch 66 is still not opened due to the control pressure acting in the master cylinder 1 4 so that the current circuit to the magnet 35 still exists through the said pressure switch 66.The second pressure switch 66 is set to such a high value that it still does not open at pressures generated in the master cylinder 14 by normal braking. Only when the brake pedal 13 is fully depressed, as is the case in emergency situations, does the pressure in the master cylinder 14 rise to a value lying thereabove at which the pressure switch 66 opens. Even such an opening of the pressure switch 66 and with it a cutting out of the magnet 35, the charging operation of the accumulator 25 would not be upset since this operation could still take place in the central position 34 of the control slide 32. Normally, during charging of the accumulator 25, the magnet 35 remains energised and retains the control slide in its righthand limit position 36.Finally, if, when charging the accumulator 25, the pressure in it exceeds the pressure set at the pressure switch 26, then the latter is opened. However, chiefly due to the open pressure switch 26, the charging indicator light 63 also remains without current when the brake pedal 13 is released once again or even is actuated afresh. This charging operation occurs relatively rapidly during a brief actuation of the brake pedal 13. If the driver actuates the brake pedal 13 too briefly or too weakly so that the accumulator 25 cannot be charged sufficiently, then the first pressure switch 26 remains closed and after the release of the brake pedal 1 3 the charging indicator light 63 lights up once again which induces the driver to perform a fresh braking operation for the purpose of charging.

As the next operating condition, the case is considered where the service brake on the tractor vehicle 11 and trailer 12 is actuated. Moreover, it is assumed that the accumulator 25 is charged and the pressure switch 26 is thus open. On actuation of the service brake, the brake pedal 1 3 is depressed which, in so doing, changes over the double switch 55 once again. As previously described during the operating condition for charging, the magnet 35 is energised and retains the control slide 32 in its right-hand limit position 36. Furthermore, the actuated double switch 55 causes a current to flow through the brake lights 71 and illuminate them whilst the charging indicator light 63 is switched off.The pressure generated in the master cylinder 1 4 acts in the tractor vehicle brake 1 5 and in addition in the brake valve 1 6. The brake valve 1 6 controls the pressure in the trailer brake line 17 and thus also in the trailer cylinder 29 proportionally to the brake pressure in the master brake cylinder 14 whereupon the trailer brake 31 is braked proportionally with respect to the tractor vehicle brake 1 5. Moreover, the non-return valve in the control slide 32 prevents charging of the accumulator 25.

The operation of the automatic disengagement brake is considered as the next operating condition. If the trailer 1 2 brakes away from the tractor vehicle 11, then apart from the hydraulic coupling 1 8 the plug-in contacts 45, 46, 47 in the plug-in coupling 43 are also separated from one another. In so doing, the current circuit to the magnet 35 is interrupted and the control slide 32 of the magnetic valve 21 is pushed into its central position 34 by the spring 33. Whilst the valve connection 1 9 is blocked by the non-return valve located in the controi slide 32, oil can flow from the hydraulic accumlator 25 through the accumulator connection 24 to the cylinder connection 27 and further to the trailer brake cylinder 29.Thus, the trailer brake 31 is actuated and the trailer 12 is braked.

The disconnection of the trailer 1 2 is described in the following as a further operating condition.

For this purpose, the control slide 32 is brought into its left-hand limit position 38 by the manual actuating device 37. The non-return valve incorporated in the control slide is then ineffective and the hydraulic accumulator 25 as well as the trailer brake cylinder 29 is relieved through the trailer brake lines 17 and the hydraulic coupling 1 8 to the brake valve 1 6 and then to the tank.

Finally, the trailer brake 31 is actuated through a mechanical parking brake (not shown in detail).

Thereafter, the hydraulic coupling 1 8 and the electrical plug-incoupling 43 can be disengaged.

Thus, with the present power braking system provided with an electro-hydraulic disengagement brake for the trailer, the seven pole standard plugin coupling used in large quantities with tractors is sufficient in an advantageous manner although a series of operations for the automatic disengagement brake need to be controlled.

Above all, the expenditure is decreased by the double utilisation of conductors for controlling the brake lights and the charging indicator light. The arrangement and design of the double switch 55 is extremely preferable with the aid of which the charging indicator light 63 is not illuminated when the service brakes are actuated and the disengagement brake is ready for operation.

Moreover, the present disengagement brake is of extremely economic construction and may be easily incorporated in existing hydraulic power braking systems.

Claims (10)

1. A hydraulic power braking system for a tractor vehicle provided with a trailer and with an automatic electro-hydraulic disengagement brake for the trailer, on which an hydraulic accumulator can be connected to a trailer brake cylinder through a magnetic valve and provided with current circuits in which there are connected, through an electrical plug-in coupling, the magnet of the magnetic valve on the trailer and a pressure switching actuated by the accumulator pressure and a switch influenced by the brake pedal on the tractor vehicle and a charging indicator light, characterised in that, the plug-in coupling has a plug-in contact through which pass, at least periodically, three current circuits for the charging indicator light, for the magnet of the magnetic valve and for the brake lights arranged on the trailer.

2. A braking system according to claim 1 characterised in that the current circuits for the three current loads, charging indicator light, brake lights and magnet pass through three plug-in contacts of the plug-in coupling wherein one of the said plug-in contacts is associated with an earth conductor.

3. A braking system according to claim 1 or 2 characterised in that the switch actuated by the brake pedal is a double switch with a noramlly open contact and a normally closed contact, one of the plug-in contacts connects alternately with one side or the other side of an electrical energy source.

4. A braking system according to claim 3 characterised in that the plug-in coupling 43 has a first plug-in contact, a second plug-in contact and a third plug-in contact of which, on the tractor vehicle, the first is connected through a first conductor to the other side of the energy source from one side of which a second conductor leads to the third plug-in contact and that, on the tractor vehicle, a third conductor leads from the second plug-in contact to the first terminals of the normally open contact and of the normally closed contact and that a fourth conductor leads from the second terminal of the normally closed contact to the other side and a fifth conductor leads from the second terminal of the normally open contact to one side of the energy source wherein the charging indicator light is connected in the fourth conductor.

5. A braking system according to claim 4 characterised in that, on the trailer, a sixth conductor leads from the first plug-in contact to the magnet which connects a seventh conductor to the third plug-in contact and an eighth conductor leads from the second plug-in contact to the brake lights from which a ninth conductor leads to the first plug-in contact and that the pressure switch controlled by the pressure in the hydraulic accumulator is connected between the seventh and the eighth conductor.

6. A braking system according to claim 4 characterised in that a second pressure switch actuated by the pressure in the master cylinder on the tractor and arranged in parallel with the normally open contact is connected in the second conductor.

7. A braking system according to claim 6 characterised in that an electrical switch is arranged in series with the second pressure switch.

8. A braking system according to one of claims 1 to 7 characterised in that the magnetic valve has a control slide which, with the magnet not energised, is held by a spring in a central position in which it connects an accumulator connection to a cylinder connection and both connections are in communication with a valve connection through a non-return valve safeguarding the connections and that with the magnet energised, the control slide takes up a right-hand limit position in which the valve connection and the cylinder connection are connected to one another and the connections are connected to the accumulator connection through the non-return valve which safeguards the connection.

9. A braking system according to claim 8 characterised in that the control slide can be set by a manually actuated device in a left-hand limit position in which all the connections are in free communication with one another.

10. An hydraulic power braking system for a tractor vehicle provided with a trailer substantially as herein described with reference to the accompanying drawing.